全文获取类型
收费全文 | 1357篇 |
免费 | 41篇 |
国内免费 | 4篇 |
专业分类
林业 | 75篇 |
农学 | 19篇 |
基础科学 | 8篇 |
220篇 | |
综合类 | 289篇 |
农作物 | 117篇 |
水产渔业 | 95篇 |
畜牧兽医 | 462篇 |
园艺 | 26篇 |
植物保护 | 91篇 |
出版年
2021年 | 10篇 |
2020年 | 18篇 |
2019年 | 19篇 |
2018年 | 12篇 |
2017年 | 15篇 |
2016年 | 18篇 |
2015年 | 12篇 |
2014年 | 20篇 |
2013年 | 60篇 |
2012年 | 45篇 |
2011年 | 51篇 |
2010年 | 33篇 |
2009年 | 23篇 |
2008年 | 73篇 |
2007年 | 85篇 |
2006年 | 79篇 |
2005年 | 81篇 |
2004年 | 95篇 |
2003年 | 80篇 |
2002年 | 99篇 |
2001年 | 18篇 |
2000年 | 24篇 |
1999年 | 20篇 |
1998年 | 27篇 |
1997年 | 12篇 |
1996年 | 18篇 |
1995年 | 21篇 |
1994年 | 16篇 |
1993年 | 16篇 |
1992年 | 13篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 15篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 13篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1955年 | 4篇 |
排序方式: 共有1402条查询结果,搜索用时 15 毫秒
31.
Mortality in longline fisheries is a critical global threat to most albatross and large petrel species. Here we identify key principles and approaches to identify and achieve broad use of effective seabird by‐catch avoidance methods. Despite the availability of highly effective and cost‐saving seabird avoidance methods, few longline fleets employ them. Given the political context and capacity of management authorities of the majority of longline fisheries, it is critical to identify seabird avoidance strategies that are not only highly effective, but are also economically viable and commercially practical. Adoption of an international performance standard for longline baited hook–sink rate, and prescribing minimum gear weighting designs that meet this standard that are achievable by all longline fisheries, would be an important step forward towards resolving low use of seabird avoidance methods by vessels, including those in illegal, unregulated and unreported fisheries. Due to differences between fleets, no single seabird avoidance measure is likely to be effective and practical in all longline fisheries. Therefore, testing of seabird avoidance methods in individual fleets is needed to determine efficacy and economic viability. Longline fishers should directly participate in these trials as they have a large repository of knowledge and skills to effectively develop and improve seabird by‐catch avoidance techniques, and this provides industry with a sense of ownership for uptake of effective by‐catch reduction methods. Establishing protected areas containing seabird colonies and adjacent waters within a nation's EEZ can be an expedient method to address seabird by‐catch. However, establishing high seas marine protected areas to restrict longline fishing in seabird foraging areas, which would require extensive and dynamic boundaries and large buffer zones, may not be a viable short‐term solution because of the extensive time anticipated to resolve legal complications with international treaties, to achieve international consensus and political will, and to acquire requisite extensive resources for surveillance and enforcement. Analysis of results of research on seabird avoidance methods reveals that the most reliable comparisons of the efficacy of alternative strategies are from comparing the effectiveness of methods tested in a single experiment. Benefits from standardizing the reporting of seabird by‐catch rates to account for seabird abundance are described. To provide the most precise inputs for seabird population models, estimates of seabird mortality in longline fisheries should account for seabird falloff from hooks before hauling, delayed mortality of seabirds caught but freed from gear, and mortality caused by hooks discarded in offal. 相似文献
32.
William S. Fisher Edgar H. Nilson J.Frank Steenbergen Donald V. Lightner 《Aquaculture (Amsterdam, Netherlands)》1978,14(2):115-140
Six microbial diseases of cultured American lobsters (Homarus americanus) determined to be of significant concern to commercial aquaculture are discussed in relation to present knowledge of characteristics of the causative microorganisms, lobster susceptibility, environmental influence, severity, gross and microscopic recognition, physiological changes, contagion and control. The diseases reviewed here include shell disease, Gaffkemia, microbial epibiont disease, Lagenidium disease, Haliphthoros disease, and Fusarium disease. 相似文献
33.
Effect of cultivated copepods (Acartia tonsa) in first‐feeding of Atlantic cod (Gadus morhua) and ballan wrasse (Labrus bergylta) larvae 下载免费PDF全文
G. Øie T. Galloway M. Sørøy M. Holmvaag Hansen I.A. Norheim C.K. Halseth M. Almli M. Berg M.R. Gagnat P.‐A. Wold K. Attramadal A. Hagemann J.O. Evjemo E. Kjørsvik 《Aquaculture Nutrition》2017,23(1):3-17
The aim of this study was to compare the nutritional composition and effects of short periods with cultivated copepod nauplii versus rotifers in first‐feeding. Atlantic cod (Gadus morhua) and ballan wrasse (Labrus bergylta) larvae were given four different dietary regimes in the earliest start‐feeding period. One group was fed the copepod Acartia tonsa nauplii (Cop), a second fed enriched rotifers (RotMG), a third fed unenriched rotifers (RotChl) and a fourth copepods for the seven first days of feeding and enriched rotifers the rest of the period (Cop7). Cod larvae were fed Artemia sp. between 20 and 40 dph (days posthatching), and ballan wrasse between 36 and 40 dph, with weaning to a formulated diet thereafter. In addition to assessing growth and survival, response to handling stress was measured. This study showed that even short periods of feeding with cultivated copepod nauplii (7 days) had positive long‐term effects on the growth and viability of the fish larvae. At the end of both studies (60 days posthatching), fish larvae fed copepods showed higher survival, better growth and viability than larvae fed rotifers. This underlines the importance of early larval nutrition. 相似文献
34.
Elena A. Mikhailova Donald Hagan Julia Sharp Brian Ritter Roxanne Stiglitz Veeander Mealing 《Communications in Soil Science and Plant Analysis》2017,48(9):1068-1077
Japanese stiltgrass (Microstegium vimineum), an exotic invasive plant, is native to Southeast Asia. This study was conducted to determine the chemical composition of Japanese stiltgrass as well as soil and landscape characteristics that correlate with invasion of Japanese stiltgrass around Lake Issaqueena in the upper Piedmont of South Carolina. Geographic Information Systems (GISs) and Light Detection and Ranging (LiDAR) were used to determine the spatial pattern of invasion with respect to the aspect, slope, canopy cover, soils, and distance to roads and trails. Japanese stiltgrass was distributed on both sides of Lake Issaqueena in Pacolet and Madison soil map units (Fine, kaolinitic, thermic Typic Kanhapludults) on the average slopes of 21%, but it was particularly common on the eastern shore of the lake in low-lying wet and shaded areas (mean canopy cover 51%). In addition, invasion by Japanese stiltgrass was correlated with the proximity to roads and trails. Plant tissue analysis revealed many differences in the distribution of macronutrients, macrominerals, and micronutrients in the leaves, stems, and roots of Japanese stiltgrass, although those differences were not always statistically significant. Concentrations of nitrogen (N), phosphorus (P), and calcium (Ca) were the highest in leaves while zinc (Zn) concentrations were the highest in stems and concentrations of magnesium (Mg), copper (Cu), manganese (Mn), iron (Fe), and sodium (Na) tended to be higher in roots. Carbon (C), sulfur (S), and potassium (K) concentrations were generally higher in above-ground tissues versus roots. Soil chemical analysis revealed no statistical differences between control and invaded plots. Our findings suggest that watershed areas surrounding lakes may be particularly susceptible to the invasion of Japanese stiltgrass due to their microclimates, low-lying wet pathways for seed distribution and recreational uses. 相似文献
35.
36.
37.
Harvey JW Stockham SL Scott MA Johnson PJ Donald JJ Chandler CJ 《Veterinary pathology》2003,40(6):632-642
This report describes erythrocyte biochemical findings in an adult Spanish mustang mare that exhibited persistent methemoglobinemia, eccentrocytosis, and pyknocytosis that were not related to the consumption or administration of an exogenous oxidant. The methemoglobinemia was attributed to a deficiency in cytochrome-b5 reductase (Cb5R) activity, and the eccentrocytes and pyknocytes were attributed to a marked deficiency in reduced nicotinamide adenine dinucleotide phosphate-dependent glutathione reductase (GR) activity that resulted in decreased reduced glutathione concentration within erythrocytes. The GR activity increased to a near-normal value after addition of flavin adenine dinucleotide (FAD) to the enzyme assay, indicating a deficiency of FAD in erythrocytes. The methemoglobinemia, eccentrocytosis, and pyknocytosis were attributed to deficiency of FAD in erythrocytes because the GR and Cb5R enzymes use FAD as a cofactor. This deficiency in FAD results from a defect in erythrocyte riboflavin metabolism, which has not been documented previously in animals. 相似文献
38.
In order to ensure adequate performance and warn of potential ground water contamination, land application systems must be monitored. The monitoring system for the Lake George Village Sewage Treatment Plant land application system is described, including suction lsyimeters, observation wells and tracer studies. 相似文献
39.
Muttucumaru N Halford NG Elmore JS Dodson AT Parry M Shewry PR Mottram DS 《Journal of agricultural and food chemistry》2006,54(23):8951-8955
When wheat was grown under conditions of severe sulfate depletion, dramatic increases in the concentration of free asparagine were found in the grain of up to 30 times as compared to samples receiving the normal levels of sulfate fertilizer. The effect was observed both in plants grown in pots, where the levels of nutrients were carefully controlled, and in plants grown in field trials on soil with poor levels of natural nutrients where sulfate fertilizer was applied at levels from 0 to 40 kg sulfur/Ha. Many of the other free amino acids were present at higher levels in the sulfate-deprived wheat, but the levels of free glutamine showed increases similar to those observed for asparagine. In baked cereal products, asparagine is the precursor of the suspect carcinogen acrylamide, and when flours from the sulfate-deprived wheat were heated at 160 degrees C for 20 min, levels of acrylamide between 2600 and 5200 microg/kg were found as compared to 600-900 microg/kg in wheat grown with normal levels of sulfate fertilization. 相似文献
40.
Prevention of vaginal SHIV transmission in rhesus macaques through inhibition of CCR5 总被引:1,自引:0,他引:1
Lederman MM Veazey RS Offord R Mosier DE Dufour J Mefford M Piatak M Lifson JD Salkowitz JR Rodriguez B Blauvelt A Hartley O 《Science (New York, N.Y.)》2004,306(5695):485-487
Topical agents, such as microbicides, that can protect against human immunodeficiency virus (HIV) transmission are urgently needed. Using a chimeric simian/human immunodeficiency virus (SHIV SF162), which is tropic for the chemokine receptor CCR5, we report that topical application of high doses of PSC-RANTES, an amino terminus-modified analog of the chemokine RANTES, provided potent protection against vaginal challenge in rhesus macaques. These experimental findings have potentially important implications for understanding vaginal transmission of HIV and the design of strategies for its prevention. 相似文献