全文获取类型
收费全文 | 248篇 |
免费 | 6篇 |
专业分类
林业 | 10篇 |
农学 | 1篇 |
45篇 | |
综合类 | 18篇 |
农作物 | 6篇 |
水产渔业 | 25篇 |
畜牧兽医 | 135篇 |
园艺 | 4篇 |
植物保护 | 10篇 |
出版年
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 5篇 |
2013年 | 11篇 |
2012年 | 9篇 |
2011年 | 11篇 |
2010年 | 5篇 |
2009年 | 8篇 |
2008年 | 7篇 |
2007年 | 12篇 |
2006年 | 5篇 |
2005年 | 12篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 3篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有254条查询结果,搜索用时 15 毫秒
1.
Evaluation of an enzyme-linked immunosorbent assay for detection of antibodies to bovine virus diarrhoea virus in milk 总被引:3,自引:0,他引:3
R Niskanen S Alenius B Larsson N Juntti 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1989,36(2):113-118
The present study shows that milk is an appropriate source for detection of seroreactors to bovine virus diarrhoea virus (BVDV). There was close agreement between antibody titres in serum and in skim milk, as determined by an indirect enzyme-linked immunosorbent assay. The antibody titres were usually lower in skim milk than in serum, but all seropositive cows (n = 84) were also skim milk-positive and all but one seronegative cow (n = 55) proved negative in skim milk. During lactation, the level of antibodies to BVDV in milk showed an inverse relationship to the amount of milk produced. However, there was a sufficient level of antibodies in milk throughout lactation to permit an adequate determination of BVDV antibody status in dairy cows. There was a mutual good agreement between milk antibody titre in the four mammary quarters, irrespective of milk cell count. Milk can be used to detect seroreactors to BVDV. Milk is preferable to blood in large-scale epidemiological studies, since the sampling procedure is much simpler. 相似文献
2.
Torsten Larsson 《Biological conservation》1977,11(2):129-143
This paper briefly reviews some of the problems of nature conservation in Sweden and the legislative and other measures which have been recently taken in this field. The organisation and responsibility of different conservation bodies are described. An intensive debate about activities such as localisation of industries inimical to the environment, modern forestry and off-road driving has resulted in new guidelines or legislative measures in recent years. Site protection by means of the Nature Conservancy Act is believed to be the most effective way of safeguarding areas valuable to scientific conservation and outdoor recreation. Some examples of fauna preservation and habitat management are mentioned. 相似文献
3.
Johansson L Rytkonen A Bergman P Albiger B Källström H Hökfelt T Agerberth B Cattaneo R Jonsson AB 《Science (New York, N.Y.)》2003,301(5631):373-375
The human-specific bacterial pathogen Neisseria meningitidis is a major cause of sepsis and/or meningitis. The pili of N. meningitidis interact with CD46, a human cell-surface protein involved in regulation of complement activation. Transgenic mice expressing human CD46 were susceptible to meningococcal disease, because bacteria crossed the blood-brain barrier in these mice. Development of disease was more efficient with piliated bacteria after intranasal, but not intraperitoneal, challenge of CD46 transgenic mice, suggesting that human CD46 facilitates pilus-dependent interactions at the epithelial mucosa. Hence, the human CD46 transgenic mice model is a potentially useful tool for studying pathogenesis and for vaccine development against meningococcal disease. 相似文献
4.
C. Ekstrand C. Ingvast‐Larsson L. Olsén M. Hedeland U. Bondesson J. Gabrielsson 《Journal of veterinary pharmacology and therapeutics》2016,39(3):255-263
The cortisol response to glucocorticoid intervention has, in spite of several studies in horses, not been fully characterized with regard to the determinants of onset, intensity and duration of response. Therefore, dexamethasone and cortisol response data were collected in a study applying a constant rate infusion regimen of dexamethasone (0.17, 1.7 and 17 μg/kg) to six Standardbreds. Plasma was analysed for dexamethasone and cortisol concentrations using UHPLC‐MS/MS. Dexamethasone displayed linear kinetics within the concentration range studied. A turnover model of oscillatory behaviour accurately mimicked cortisol data. The mean baseline concentration range was 34–57 μg/L, the fractional turnover rate 0.47–1.5 1/h, the amplitude parameter 6.8–24 μg/L, the maximum inhibitory capacity 0.77–0.97, the drug potency 6–65 ng/L and the sigmoidicity factor 0.7–30. This analysis provided a better understanding of the time course of the cortisol response in horses. This includes baseline variability within and between horses and determinants of the equilibrium concentration–response relationship. The analysis also challenged a protocol for a dexamethasone suppression test design and indicated future improvement to increase the predictability of the test. 相似文献
5.
PC Sereno AL Beck DB Dutheil B Gado HCE Larsson GH Lyon JD Marcot OWM Rauhut RW Sadleir CA Sidor DD Varricchio GP Wilson JA Wilson 《Science (New York, N.Y.)》1998,282(5392):1298-1302
Fossils discovered in Lower Cretaceous (Aptian) rocks in the Tenere Desert of central Niger provide new information about spinosaurids, a peculiar group of piscivorous theropod dinosaurs. The remains, which represent a new genus and species, reveal the extreme elongation and transverse compression of the spinosaurid snout. The postcranial bones include blade-shaped vertebral spines that form a low sail over the hips. Phylogenetic analysis suggests that the enlarged thumb claw and robust forelimb evolved during the Jurassic, before the elongated snout and other fish-eating adaptations in the skull. The close phylogenetic relationship between the new African spinosaurid and Baryonyx from Europe provides evidence of dispersal across the Tethys seaway during the Early Cretaceous. 相似文献
6.
Atle Foss Albert K. Imsland Erik Vikingstad Sigurd O. Stefansson Birgitta Norberg Skjalg Pedersen Trond Sandvik Bjrn Roth 《Aquaculture (Amsterdam, Netherlands)》2009,290(3-4):304-310
A group of juvenile Atlantic halibut (mean, SD, 199.5 g, 44.7) was split into two experimental groups: one group was fed in excess twice a day and later five days a week (i.e. Control group), and the other group was starved for 5 weeks and then subsequently re-fed for 10 weeks (i.e. 5/10 starvation/re-fed group). This treatment was repeated for three years until the fish were harvested (mean final weight, 4.4 kg). A size +specific compensatory response was seen; partial compensation was observed in halibut weighing less than 500 g whereas full recovery growth was seen in halibut over 2 kg. Food consumption and feed conversion efficiency was measured during two full 5/10 starvation/re-fed cycles. The Control group consumed 86% more food in the measurement period, whereas the FCE 40% higher in the 5/10 starvation/re-fed group (FCE = 0.95) compared to the Control group (FCE = 0.68). In males lower gonadosomatic index (2.2 vs. 3.0) and plasma 11-ketotestosterone (0.22 vs. 1.26 ng ml− 1) levels in the 5/10 starvation/re-fed group were observed during late winter and spring of 2006 (age 3 years) indicating higher age at 1st maturity. Starvation had a significant effect for improving the quality as starved fish had higher muscle pH (6.4 vs. 6.2), less gaping (0.1 vs. 0.3) and harder texture (61.4 vs. 57.6 N). Overall, the rearing on a repeated 5/10 starvation/re-fed regime for 3 years led to full growth compensation, higher feed conversion efficiency, lower male maturation and improved flesh quality. 相似文献
7.
8.
Mercury in the Swedish environment — Recent research on causes,consequences and corrective methods 总被引:3,自引:0,他引:3
Oliver Lindqvist Kjell Johansson Lage Bringmark Birgitta Timm Mats Aastrup Arne Andersson Gunnar Hovsenius Lars Håkanson Åke Iverfeldt Markus Meili 《Water, air, and soil pollution》1991,55(1-2):xi-261
During the last decade a new pattern of Hg pollution has been discerned, mostly in Scandinavia and North America. Fish from low productive lakes, even in remote areas, have been found to have a high Hg content. This pollution problem cannot be connected to single Hg discharges but is due to more widespread air pollution and long-range transport of pollutants. A large number of waters are affected and the problem is of a regional character. The national limits for Hg in fish are exceeded in a large number of lakes. In Sweden alone, it has been estimated that the total number of lakes exceeding the blacklisting limit of 1 mg Hg kg-1 in 1-kg pike is about 10 000. The content of Hg in fish has markedly increased in a large part of Sweden, exceeding the estimate background level by about a factor of 2 to 6. Only in the northernmost part of the country is the content in fish close to natural values. There is, however, a large variation of Hg content in fish within the same region, which is basically due to natural conditions such as the geological and hydrological properties of the drainage area. Higher concentrations in fish are mostly found in smaller lakes and in waters with a higher content of humic matter. Since only a small percentage of the total flow of Hg through a lake basin is transferred into the biological system, the bioavailability and the accumulation pattern of Hg in the food web is of importance for the Hg concentrations in top predators like pike. Especially, the transfer of Hg to low trophic levels seems to be a very important factor in determining the concentration in the food web. The fluxes of biomass through the fish community appear to be dominated by fluxes in the pelagic food web. The Hg in the lake water is therefore probably more important as a secondary source of Hg in pike than is the sediment via the benthic food chain. Different remedy actions to reduce Hg in fish have been tested. Improvements have been obtained by measures designed to reduce the transport of Hg to the lakes from the catchment area, eg. wetland liming and drainage area liming, to reduce the Hg flow via the pelagic nutrient chains, eg. intensive fishing, and to reduce the biologically available proportion of the total lake dose of Hg, eg. lake liming with different types of lime and additions of selenium. The length of time necessary before the remedy gives result is a central question, due to the long half-time of Hg in pike. In general it has been possible to reduce the Hg content in perch by 20 to 30% two years after treatments like lake liming, wetland liming, drainage area liming and intensive fishing. Selenium treatment is also effective, but before this method can be recommended, dosing problems and questions concerning the effects of selenium on other species must be evaluated. Regardless how essential these kind of remedial measures may be in a short-term perspective, the only satisfactory long-term alternative is to minimize the Hg contamination in air, soil and water. Internationally, the major sources of Hg emissions to the atmosphere are chlor-alkali factories, waste incineration plants, coal and peat combustion units and metal smelter industries. In the combustion processes without flue gas cleaning systems, probably about 20 to 60% of the Hg is emitted in divalent forms. In Sweden, large amounts of Hg were emitted to the atmosphere during the 50s and 60s, mainly from chlor-alkali plants and from metal production. In those years, the discharges from point sources were about 20 to 30 t yr 1. Since the end of the 60s, the emission of Hg has been reduced dramatically due to better emission control legislation, improved technology, and reduction of polluting industrial production. At present, the annual emissions of Hg to air are about 3.5 t from point sources in Sweden. In air, more than 95% of Hg is present as the elemental Hg form, HgO0. The remaining non-elemental (oxidized) form is partly associated to particles with a high wash-out ratio, and therefore more easily deposited to soils and surface waters by precipitation. The total Hg concentration in air is normally in the range 1 to 4 ng m-3. In oceanic regions in the southern hemisphere, the concentration is generally about 1 ng m?3, while the corresponding figure for the northern hemisphere is about 2 ng m-3. In remote continental regions, the concentrations are mainly about 2 to 4 ng m?3. In precipitation, Hg concentrations are generally found in the range 1 to 100 ng L?1. In the Nordic countries, yearly mean values in rural areas are about 20 to 40 ng L?1 in the southern and central parts, and about 10 ng L?1 in the northern part. Accordingly, wet deposition is about 20 (10 to 35) g km?2 yr?1 in southern Scandinavia and 5 (2 to 7) in the northern part. Calculations of Hg deposition based on forest moss mapping techniques give similar values. The general pattern of atmospheric deposition of Hg with decreasing values from the southwest part of the country towards the north, strongly suggests that the deposition over Sweden is dominated by sources in other European countries. This conclusion is supported by analyses of air parcel back trajectories and findings of significant covariations between Hg and other long range transported pollutants in the precipitation. Apart from the long range transport of anthropogenic Hg, the deposition over Sweden may also be affected by an oxidation of elemental Hg in the atmosphere. Atmospheric Hg deposited on podzolic soils, the most common type of forest soil in Sweden, is effectively bound in the humus-rich upper parts of the forest soil. In the Tiveden area in southern Sweden, about 75 to 80% of the yearly deposition is retained in the humus layer, chemically bound to S or Se atoms in the humic structure. The amount of Hg found in the B horizon of the soils is probably only slightly influenced by anthropogenic emissions. In the deeper layers of the soil, hardly any accumulation of Hg takes place. The dominating horizontal flow in the soils takes place in the uppermost soil layers (0 to 20 cm) during periods of high precipitation and high groun water level in the soils. The yearly transport of Hg within the soils has been calculated to be about 5 to 6 g km?2. The specific transport of total Hg from the soil system to running waters and lakes in Sweden is about 1 to 6 g km?2 yr1. The transport of Hg is closely related to the transport of humic matter in the water. The main factors influencing the Hg content and the transport of Hg in run-off waters from soils are therefore the Hg content in soils, the transport of humic matter from the soils and the humus content of the water. Other factors, for example acidification of soils and waters, are of secondary importance. Large peatlands and major lake basins in the catchment area reduce the out-transport of Hg from such areas. About 25 to 75% of the total load of Hg of lakes in southern and central Sweden originates from run-off from the catchment area. In lakes where the total load is high, the transport from run-off is the dominating pathway. The total Hg concentrations in soil solution are usually in the range 1 to 50, in ground water 0.5 to 15 and in run-off and lake water 2 to 12 ng L?1, respectively. The variation is largely due to differences in the humus content of the waters. In deep ground water with a low content of humic substances, the Hg concentration is usually below 1 ng L?1. The present amount and concentrations of Hg in the mor layer of forest soils are affected by the total anthropogenic emissions of Hg to the atmosphere, mainly during this century. Especially in the southern part of Sweden and in the central part along the Bothnian coast, the concentrations in the mor layer are markedly high. In southern areas the anthropogenic part of the total Hg content is about 70 to 90%. Here, the increased content in these soils is mainly caused by long-range transport and emissions from other European countries, while high level areas in the central parts are markedly affected by local historical emissions, mainly from the chlor-alkali industry. When comparing the input/output fluxes to watersheds it is evident that the present atmospheric deposition is much higher than the output via run-off waters, on average about 3 to 10 times higher, with the highest ration in the southern parts of Sweden. Obviously, Hg is accumulating in forest soils in Sweden at the present atmospheric deposition rate and, accordingly, the concentrations in forest soils are still increasing despite the fact that the emissions of Hg have drastically been reduced in Sweden during the last decades. The increased content of Hg in forest soils may have an effect on the organisms and the biological processes in the soils. Hg is by far the most toxic metal to microorganisms. In some regions in Sweden, the content of Hg in soils is already today at a level that has been proposed as a critical concentration. To obtain a general decrease in the Hg content in fish and in forest soils, the atmospheric deposition of Hg has to be reduced. The critical atmospheric load of Hg can be defined as the load where the input to the forest soils is less than the output and, consequently, where the Hg content in the top soil layers and the transport of Hg to the surface waters start to decrease. A reduction by about 80% of the present atmospheric wet deposition has to be obtained to reach the critical load for Scandinavia. 相似文献
9.
PC Sereno DB Dutheil M Iarochene HCE Larsson GH Lyon PM Magwene CA Sidor DJ Varricchio JA Wilson 《Science (New York, N.Y.)》1996,272(5264):986-991
Late Cretaceous (Cenomanian) fossils discovered in the Kem Kem region of Morocco include large predatory dinosaurs that inhabited Africa as it drifted into geographic isolation. One, represented by a skull approximately 1.6 meters in length, is an advanced allosauroid referable to the African genus Carcharodontosaurus. Another, represented by a partial skeleton with slender proportions, is a new basal coelurosaur closely resembling the Egyptian genus Bahariasaurus. Comparisons with Cretaceous theropods from other continents reveal a previously unrecognized global radiation of carcharodontosaurid predators. Substantial geographic differentiation of dinosaurian faunas in response to continental drift appears to have arisen abruptly at the beginning of the Late Cretaceous. 相似文献
10.
T. Linares W. A. King K. Larsson I. Gustavsson A. Bane 《Veterinary research communications》1980,4(1):113-118
A total of 55 non-surgical collections, 7 days after spontaneous heat, was made in 19 heifers. Recovery rate was 57% (17/30) from 10 repeat breeder heifers and 72% (18/25) from 9 virgin heifers, this difference was not significant. Fertilization rate in both groups was 94%. The eggs were always recovered in the first 100 ml of flushing medium. Mean lengths of oestrous cycle after non-surgical collection were, respectively, 16.9 and 18.1 days in repeat breeder and virgin heifers. This difference was not significant. However, the cycle in which the first collection was made was significantly shorter (P<.005) than the cycle immediately before the collections. Only 61% of possible eggs were non-surgically collected from 4 superovulated repeat breeder cows and no further eggs were found after slaughter, one to two hours later. 相似文献