全文获取类型
收费全文 | 1989篇 |
免费 | 98篇 |
专业分类
林业 | 52篇 |
农学 | 56篇 |
基础科学 | 3篇 |
336篇 | |
综合类 | 281篇 |
农作物 | 248篇 |
水产渔业 | 142篇 |
畜牧兽医 | 839篇 |
园艺 | 25篇 |
植物保护 | 105篇 |
出版年
2022年 | 18篇 |
2021年 | 37篇 |
2020年 | 22篇 |
2019年 | 26篇 |
2018年 | 48篇 |
2017年 | 44篇 |
2016年 | 47篇 |
2015年 | 43篇 |
2014年 | 56篇 |
2013年 | 100篇 |
2012年 | 101篇 |
2011年 | 135篇 |
2010年 | 62篇 |
2009年 | 52篇 |
2008年 | 96篇 |
2007年 | 107篇 |
2006年 | 64篇 |
2005年 | 80篇 |
2004年 | 71篇 |
2003年 | 72篇 |
2002年 | 51篇 |
2001年 | 33篇 |
2000年 | 43篇 |
1999年 | 37篇 |
1998年 | 12篇 |
1997年 | 18篇 |
1996年 | 16篇 |
1994年 | 14篇 |
1992年 | 23篇 |
1991年 | 34篇 |
1990年 | 32篇 |
1989年 | 30篇 |
1988年 | 20篇 |
1987年 | 28篇 |
1986年 | 27篇 |
1985年 | 28篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1979年 | 20篇 |
1978年 | 11篇 |
1977年 | 19篇 |
1976年 | 11篇 |
1974年 | 17篇 |
1973年 | 23篇 |
1972年 | 18篇 |
1971年 | 14篇 |
1970年 | 18篇 |
1969年 | 19篇 |
1968年 | 12篇 |
1966年 | 11篇 |
排序方式: 共有2087条查询结果,搜索用时 78 毫秒
41.
Indigenous populations of white clover (Trifolium repens L) collected from Europe, the Mediterranean area, as well as other parts of the world have been grown as spaced plants at Aberystwyth. Data were collected on various morphological characters, green weight and leaf marks.Leaflet length, width, area, plant height and green weight were all strongly correlated, but not the flowering date or leaflet shape (= ratio length/width).The mean leaflet size of Mediterranean populations (the supposed centre of origin) was very variable, and decreased northwards. All British populations were uniformly small leaved.Most of the populations were much less vigorous than the bred control varieties and only a few equalled them. Nevertheless some of the introductions exhibited seasonal growth patterns, especially growth into the autumn, and large leaves that could be usefully incorporated in improved varieties. Populations originating one step back towards the centre of origin will probably be the most useful when immediate adaptation is the aim. 相似文献
42.
43.
This study was conducted to evaluate the supplementation of glutamic acid(Glu)to reduced protein diets on the performance of weanling pigs.One hundred and eighty crossbred weanling pigs([YorkshireLandrace]Duroc,21 d old)having similar body weight(BW)of 6.45 kg were randomly allotted to 1 of 6 dietary treatments(5 pigs per pen[2 barrows and 3 gilts];6 pens per treatment)based on BW and sex during a 6-week trial.Dietary treatments consisted of positive control(PC)diet formulated to have 226.9,205.6,and 188.8 g crude protein(CP)during phases 1,2,and 3,respectively,and negative control(NC)diets with 20 g CP reduction from PC diets and addition of Glu with increasing levels,resulting in the calculated Lys-to-Glu ratios of 1:2.25,1:2.30.1:2.35,1:2.40,and 1:2.45,designated as NC,NC1,NC2,NC3,and NC4,respectively.The BW of pigs receiving PC diet was higher(P<0.05)than those receiving NC diet at d 7,21 and 42.A higher(P<0.05)average daily gain(ADG)from d 1 to 7,8 to 21,22 to 42 and during the overall experiment period was observed in pigs fed PC than NC diet.Pigs fed NC diets including the graded level of Glu linearly increased(P<0.05)BW at d 42,ADG and gain-to-feed ratio(G:F)during the overall experimental period.In addition,trends in linear increase in BW(P=0.056)at d 7 and ADG from d 1 to 7 and d 22 to 42(linear effect,P=0.081,P=0.058 respectively)were observed.A tendency in the linear increment of NH3(P=0.082)at d 21 and linear reduction in methyl mercaptans(P=0.054)emission at d 42 was observed in pigs fed NC diets supplemented with graded level of Glu.In conclusion,supplementing the reduced protein diet with Glu enhanced the growth performance in weanling pigs suggesting that supplementation of Glu can compensate the reduction of 2%CP in the basal diets. 相似文献
44.
Inja Yeon Mi Young SongMyoung Ho Sohn Hak Jin HwangYang Jae Im Do Hoon KimHee Won Park Chang Ik Zhang 《Fisheries Research》2011,112(3):179-188
Landings in the blue crab, Portunus trituberculatus, fishery in Korean waters of the Yellow Sea have declined substantially from 11,000 t in the 1980s to 2,300 t in 2004. Blue crab habitat quality in the Yellow Sea has been degraded by anthropogenic activities including sand mining, land reclamation, and coastal pollution. Various traditional management measures have been implemented, including closed seasons during spawning and size limits, but these measures alone have been unsuccessful to conserve blue crab stocks. Consequently, a total allowable catch and a stock-rebuilding program using an ecosystem-based management approach were implemented in 2003 and 2006, respectively to rebuild blue crab stocks and restore habitats. This program involved assessment of both blue crab stock status and trammel-net fishery impacts at an ecosystem-level using an ecosystem-based fisheries assessment method (
[Zhang et al., 2009] and [Zhang et al., 2010]), which considered fishery data from catch and effort time-series, crab population biology, and ecosystem characteristics, including habitats and environmental conditions. Recent (2008) management status indices have shown significant positive change compared to conditions in 2000 with respect to sustainability of the stock and fishery and with regards to biodiversity and ecosystem habitat quality. 相似文献
45.
In the southern United States, corn production encounters moisture deficit coupled with high‐temperature stress, particularly during the reproductive stage of the plant. In evaluating plants for environmental stress tolerance, it is important to monitor changes in their physical environment under natural conditions, especially when there are multiple stress factors, and integrate this information with their physiological responses. A low‐cost microcontroller‐based monitoring system was developed to automate measurement of canopy, soil and air temperatures, and soil moisture status in field plots. The purpose of this study was to examine how this system, in combination with physiological measurements, could assist in detecting differences among corn genotypes in response to moisture deficit and heat stress. Three commercial hybrids and two inbred germplasm lines were grown in the field under irrigated and non‐irrigated conditions. Leaf water potential, photosynthetic pigments, cell membrane thermostability (CMT) and maximum quantum efficiency of photosystem II (Fv/Fm) were determined on these genotypes under field and greenhouse conditions. Variations observed in air and soil temperatures, and soil moisture in plots of the individual corn genotypes helped explain their differences in canopy temperature (CT), and these variations were reflected in the physiological responses. One of the commercial hybrids, having the lowest CT and the highest CMT, was the most tolerant among the genotypes under moisture deficit and heat stress conditions. These results demonstrated that the low‐cost microcontroller‐based monitoring system, in combination with physiological measurements, was effective in evaluating corn genotypes for drought and heat stress tolerance. 相似文献
46.
N. R. Atkinson S. D. Young A. M. Tye N. Breward E. H. Bailey 《Soil Use and Management》2012,28(4):559-570
Urban waste disposal occurred on fenland to the west of Manchester, England, between 1900 and 1964. The reclaimed fenland, Chat Moss, is now used for mixed arable farming. A total of 1.92 Mt of waste including privy midden, street sweepings, clinkers and slaughterhouse refuse was incorporated into the moss resulting in a modified topsoil with raised pH and reduced organic matter content compared with the subsoil. Elevated levels of potentially toxic elements (PTEs) are observed in the topsoil beyond the typical depth of atmospheric contamination; Cd and As concentrations exceed soil guideline values (SGVs) at 1.8 and 43 mg/kg, respectively. Sequential extraction indicates that waste‐derived Pb, Zn and Ni remain predominantly in the residual fraction, whereas Cu was mainly organically bound. Arsenic was predominately found in oxide and organic matter fractions with Cd in carbonate, oxide, organic matter and residual fractions. Pot trials indicated limited uptake of PTEs by vegetables grown on the waste‐amended soil, with the exception of Cd uptake by lettuce (0.22 mg/kg FW) and Pb uptake by radish (0.16 mg/kg FW), which exceeded current EU limits of 0.2 and 0.1 mg/kg FW, respectively. Hazard quotients (HQs) identified no risks to adults from consumption of vegetables grown in these soils with the exception of lettuce consumption with a HQ of 1.4. Risks to children were slightly greater with HQs >1 for Cd in lettuce, spinach, carrots and onion, As in lettuce, parsley and onion and for Zn in spinach. 相似文献
47.
48.
Young JM Bull CT De Boer SH Firrao G Gardan L Saddler GE Stead DE Takikawa Y 《Phytopathology》2001,91(7):617-620
ABSTRACT In a recent Letter to the Editor of Phytopathology, proposals were made for endorsement and for rejection of selected names of plant pathogenic Pseudomonas spp. and Xanthomonas spp. We believe that support for, and rejection of, several names was based on misconceptions concerning the Approved Lists of Bacterial Names and entails misinterpretations of several Rules of the International Code of Nomenclature of Bacteria. This letter aims to clarify those misconceptions and misinterpretations. 相似文献
49.
Rudy W Bauer Marjorie S Gill Rob P Poston Dae Young Kim 《Journal of veterinary diagnostic investigation》2005,17(3):281-285
Eastern equine encephalitis (EEE) was diagnosed (postmortem) in a sheep with clinical signs attributable to a central nervous system disease. The sheep was febrile and initially had front limb incoordination, which progressed to paralysis of both front and hind limbs during a course of 2 days. The sheep maintained an alert attitude with the ability to eat up to the time of euthanasia. The only clinical pathologic abnormalities were neutrophilia and lymphopenia without appreciable leukocytosis, a moderate hyperglycemia, and an elevated creatine kinase. Treatment included hydrotherapy for lowering body temperature, intravenous fluids, thiamine hydrochloride, tetanus antitoxin, antibiotics, and corticosteroids. The only gross lesion at the time of necropsy was a wet glistening surface of the brain (leptomeninges). Microscopically, there was severe nonsuppurative meningoencephalitis, poliomyelitis, and polyradiculoneuritis with mild multifocal neutrophilic infiltration. The EEE virus was isolated from the brain, and subsequent fluorescent antibody testing for EEE was positive on cell culture. 相似文献
50.
The insecticidal activities of materials derived from the fruit of fennel, Foeniculum vulgare, against adults of Sitophilus oryzae, Callosobruchus chinensis and Lasioderma serricorne were examined using direct contact application and fumigation methods. The biologically active constituents of the Foeniculum fruits were characterized as the phenylpropenes (E)‐anethole and estragole, and the monoterpene (+)‐fenchone, by spectroscopic analysis. Responses varied with insect species, compound, dose and exposure time. In a filter paper diffusion test, estragole at 0.168 mg cm?2 caused 91% mortality to S oryzae adults within 1 day after treatment (DAT), whereas (+)‐fenchone and (E)‐anethole gave over 90% mortality at 2 and 4 DAT, respectively. Against C chinensis adults, all test compounds revealed potent insecticidal activities at 0.021 mg cm?2 at 2 DAT. Against L serricorne adults at 0.105 mg cm?2, (E)‐anethole gave 100% mortality at 1 DAT, whereas 90 and 60% mortality at 4 DAT was achieved with estragole and (+)‐fenchone, respectively. In a fumigation test, the test compounds were much more effective against adults of S oryzae, C chinensis and L serricorne in closed cups than in open ones, indicating that the insecticidal activity of test compounds was largely attributable to fumigant action. As naturally occurring insect‐control agents, the F vulgare fruit‐derived materials described could be useful for managing field populations of S oryzae, C chinensis and L serricorne. © 2001 Society of Chemical Industry 相似文献