全文获取类型
收费全文 | 658篇 |
免费 | 38篇 |
专业分类
林业 | 40篇 |
农学 | 18篇 |
基础科学 | 7篇 |
109篇 | |
综合类 | 99篇 |
农作物 | 40篇 |
水产渔业 | 43篇 |
畜牧兽医 | 290篇 |
园艺 | 21篇 |
植物保护 | 29篇 |
出版年
2021年 | 15篇 |
2020年 | 8篇 |
2019年 | 16篇 |
2018年 | 9篇 |
2017年 | 14篇 |
2016年 | 21篇 |
2015年 | 12篇 |
2014年 | 18篇 |
2013年 | 31篇 |
2012年 | 30篇 |
2011年 | 30篇 |
2010年 | 26篇 |
2009年 | 22篇 |
2008年 | 32篇 |
2007年 | 23篇 |
2006年 | 19篇 |
2005年 | 27篇 |
2004年 | 30篇 |
2003年 | 17篇 |
2002年 | 26篇 |
2001年 | 14篇 |
2000年 | 15篇 |
1999年 | 17篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 4篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1971年 | 7篇 |
1970年 | 3篇 |
1969年 | 4篇 |
1968年 | 8篇 |
1967年 | 4篇 |
1966年 | 6篇 |
1963年 | 3篇 |
1955年 | 3篇 |
排序方式: 共有696条查询结果,搜索用时 15 毫秒
41.
Olivera L Canul RR Pereira-Pacheco F Cockburn J Soldani F McKenzie NH Duncan M Olvera-Novoa MA Grant G 《Journal of agricultural and food chemistry》2003,51(1):319-325
The nutritional and physiological effects of raw cowpea (Vigna unguiculata (L) Walp.) seed meal, protein isolate (globulins), or starch on the metabolism of young growing rats have been evaluated in 14-day trials. Wet and dry weight gain, feed conversion efficiency, and lipid and protein accretion were significantly reduced as a result of inclusion of seed meal, globulins, or starch in the diet, with growth retardation being most marked with the seed meal. The proportional weights of the small intestine and pancreas were increased by meal diets, and serum cholesterol levels were slightly reduced. The globulins and raw starch also increased relative small intestine weights but had no effect on the pancreas or serum constituents. The effects of cowpeas on rats appeared to be due primarily to the combined actions of globulins, resistant starches, protease inhibitors, and possibly fiber and non-starch polysaccharides on intestinal and systemic metabolism. 相似文献
42.
The structural condition of swelling soils can be assessed from their shrinkage curves. We re‐evaluated data on six British swelling soils using modern methods to model the void ratio, e, as a function of the moisture ratio, ?. The points on the e–? curve were fitted with a constitutive shrinkage equation using an unbiased least‐squares, curve‐fitting program. The shrinkage curves were then differentiated to obtain their slopes, σ(?), which were used to calculate the overburden potentials, Ω. The slope functions were subsequently differentiated to obtain the curvatures, κ(?), from which the maximum curvature at the wet end was used to separate the structural shrinkage, Sc, from the proportional (unsaturated) shrinkage. At the point of maximum curvature, Sc and the volumetric air content, θac, were calculated and found to correspond closely to those reported previously. Water retention curves were constructed and fitted using the van Genuchten equation, from which the α coefficient appears an important structural parameter. The structural condition of a swelling soil appears to be well described by its air content at the point of maximum curvature, its van Genuchten α coefficient, and a parameter describing the effect of the overburden potential. 相似文献
43.
This paper offers projections of potential effects of climate change on rusts of wheat and how we should factor in a changing
climate when planning for the future management of these diseases. Even though the rusts of wheat have been extensively studied
internationally, there is a paucity of information on the likely effects of a changing climate on the rusts and their influence
on wheat production. Due to the lack of published empirical research we relied on the few published studies of other plant
diseases, our own unpublished work and relevant information from the vast literature on rusts of wheat to prepare this overview.
Three broad areas of potential risks from a changing climate were described: increased loss from wheat rusts, new rust pathotypes
evolving faster and the reduced effectiveness of rust resistances. Increased biomass of wheat crops grown in the presence
of elevated CO2 concentrations and higher temperatures will increase the leaf area available for attack by the pathogen leading to increased
inoculum production. If changed weather conditions were to accelerate the life cycle of a pathogen, the increased inoculum
can lead to severe rust epidemics in many environments. Likewise should the effects of climate change result in more conducive
conditions for rust development there will also be a corresponding increase in the rate of evolution of new pathotypes which
could increase the rate of appearance of new virulences. The effectiveness of some rust resistance genes is influenced by
temperature and crop development stage. Climate change may directly or indirectly influence the effectiveness of some resistance
genes but this can not be ascertained due to a complete lack of knowledge. Since disease resistance breeding is a long term
strategy it is important to determine if any of the important genes may become less effective due to climate change. Studies
must be made to acquire new information on the rust disease triangle to increase the adaptive capacity of wheat under climate
change. Leadership within the Borlaug Global Rust Initiative (BGRI) is needed to broker research on rust evolution and the
durability of resistance under climate change. 相似文献
44.
A copper-nitrosyl intermediate forms during the catalytic cycle of nitrite reductase, the enzyme that mediates the committed step in bacterial denitrification. The crystal structure of a type 2 copper-nitrosyl complex of nitrite reductase reveals an unprecedented side-on binding mode in which the nitrogen and oxygen atoms are nearly equidistant from the copper cofactor. Comparison of this structure with a refined nitrite-bound crystal structure explains how coordination can change between copper-oxygen and copper-nitrogen during catalysis. The side-on copper-nitrosyl in nitrite reductase expands the possibilities for nitric oxide interactions in copper proteins such as superoxide dismutase and prions. 相似文献
45.
Grant RM Hamer D Hope T Johnston R Lange J Lederman MM Lieberman J Miller CJ Moore JP Mosier DE Richman DD Schooley RT Springer MS Veazey RS Wainberg MA 《Science (New York, N.Y.)》2008,321(5888):532-534
After disappointing results from all efficacy trials conducted to date, the field of microbicides research now faces substantial challenges. Poor coordination among interested parties and the choice of nonvalidated scientific targets for phase III studies have hampered progress and created mistrust about the use of microbicides as a method to prevent HIV-1 sexual transmission. Although new promising strategies are available, there will need to be serious reappraisals of how decisions are made to advance the next generations of candidates into clinical trials, and the use of appropriate animal models in this process will be critical. 相似文献
46.
Distinct atmospheric conditions suggest that dark, ephemeral, filamentary lineations on the martian surface may be formed during the passage of intense atmospheric vortices. 相似文献
47.
Grant JA Arvidson R Bell JF Cabrol NA Carr MH Christensen P Crumpler L Des Marais DJ Ehlmann BL Farmer J Golombek M Grant FD Greeley R Herkenhoff K Li R McSween HY Ming DW Moersch J Rice JW Ruff S Richter L Squyres S Sullivan R Weitz C 《Science (New York, N.Y.)》2004,305(5685):807-810
The Mars Exploration Rover Spirit has traversed a fairly flat, rock-strewn terrain whose surface is shaped primarily by impact events, although some of the landscape has been altered by eolian processes. Impacts ejected basaltic rocks that probably were part of locally formed lava flows from at least 10 meters depth. Some rocks have been textured and/or partially buried by windblown sediments less than 2 millimeters in diameter that concentrate within shallow, partially filled, circular impact depressions referred to as hollows. The terrain traversed during the 90-sol (martian solar day) nominal mission shows no evidence for an ancient lake in Gusev crater. 相似文献
48.
Scanning electron microscopy and single unit recordings of male Trichoplusia ni antennae reveal at least two classes of pheromone-sensitive sensilla trichodea. The longer sensillum contains two receptor neurons each with small amounts of spontaneous activity. One neuron responds to large (10-microgram) doses of (Z)-7-dodecenyl acetate, a component of the female sex pheromone. The shorter sensillum contains two receptor neurons both with larger amounts of spontaneous activity and increased sensitivity to low (0.01-microgram) doses of pheromone. 相似文献
49.
The dynamics of a fluid surface filled with high-amplitude ripples were studied with a technique (diffusing light photography) that resolves the height at all locations instantaneously. Even when nonlinearities are strong enough to generate a (Kolmogorov) cascade from long wavelength (where energy is input) to shorter wavelength, the resulting turbulent state contains large coherent spatial structures. The appearance of these structures in a thermal equilibrium state (with the same average energy) would be highly improbable. 相似文献
50.