全文获取类型
收费全文 | 857篇 |
免费 | 55篇 |
专业分类
林业 | 25篇 |
农学 | 17篇 |
基础科学 | 2篇 |
81篇 | |
综合类 | 86篇 |
农作物 | 49篇 |
水产渔业 | 31篇 |
畜牧兽医 | 542篇 |
园艺 | 14篇 |
植物保护 | 65篇 |
出版年
2021年 | 12篇 |
2020年 | 21篇 |
2019年 | 12篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 20篇 |
2015年 | 13篇 |
2014年 | 15篇 |
2013年 | 39篇 |
2012年 | 22篇 |
2011年 | 26篇 |
2010年 | 15篇 |
2009年 | 14篇 |
2008年 | 46篇 |
2007年 | 23篇 |
2006年 | 39篇 |
2005年 | 27篇 |
2004年 | 31篇 |
2003年 | 30篇 |
2002年 | 21篇 |
2001年 | 23篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 11篇 |
1997年 | 12篇 |
1996年 | 15篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 11篇 |
1983年 | 9篇 |
1982年 | 7篇 |
1978年 | 7篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1974年 | 12篇 |
1973年 | 16篇 |
1972年 | 16篇 |
1971年 | 11篇 |
1970年 | 10篇 |
1967年 | 12篇 |
1966年 | 8篇 |
排序方式: 共有912条查询结果,搜索用时 101 毫秒
71.
Heald AH Sharma R Anderson SG Vyas A Siddals K Patel J Bhatnagar D Prabharkaran D Rudenski A Hughes E Durrington P Gibson JM Cruickshank JK 《Public health nutrition》2005,8(6):620-627
BACKGROUND: The insulin-like growth factor (IGF) system is implicated in the pathogenesis of diabetes and cardiovascular disease. OBJECTIVE: We report the effects of total energy intake on the IGF system in two populations with markedly different dietary macronutrient intake and cardiovascular event rate. DESIGN, SUBJECTS AND SETTING: Dietary macronutrient intake was measured in a specific Gujarati migrant community in Sandwell, UK (n=205) compared with people still resident in the same villages of origin in India (n=246). Fasting IGF-I, IGF-binding protein (IGFBP)-1 and IGFBP-3, insulin and glucose (0 and 2-hour) were measured. RESULTS: Total energy and total fat intake were higher in UK migrants, as were IGFBP-3 and IGF-I (mean (95% confidence interval): 145.9 (138.1-153.6) vs. 100.9 (94.6-107.3) ng ml(-1); F=76.6, P<0.001). IGFBP-1 was lower in UK migrants (29.5 (25.9-33.0) vs. 56.5 (50.6-62.5) microg l(-1); F=48.4, P<0.001). At both sites, IGF-I correlated positively with total energy (Spearman's rho=0.45, P<0.001) and total fat (rho=0.44, P<0.001) as did IGFBP-3 with total energy (rho=0.21, P<0.05) and fat (rho=0.26, P<0.001). Conversely, in Indian Gujaratis, IGFBP-1 fell with increasing total energy (rho=-0.27, P<0.001) and fat intake (rho=-0.26, P<0.01) but not in UK Gujaratis. Multiple linear regression modelling showed that increasing quartiles of fat intake were associated with higher IGF-I (beta=0.42, P=0.007) independent of age, body mass index, plasma insulin, fatty acids and 2-hour glucose. CONCLUSION: In these genetically similar groups, migration to the UK and adoption of a different diet is associated with marked changes in the IGF system, suggesting that environmental factors profoundly modulate serum concentrations and actions of IGFs. 相似文献
72.
Mitton-Fry RM Anderson EM Hughes TR Lundblad V Wuttke DS 《Science (New York, N.Y.)》2002,296(5565):145-147
The essential Cdc13 protein in the yeast Saccharomyces cerevisiae is a single-stranded telomeric DNA binding protein required for chromosome end protection and telomere replication. Here we report the solution structure of the Cdc13 DNA binding domain in complex with telomeric DNA. The structure reveals the use of a single OB (oligonucleotide/oligosaccharide binding) fold augmented by an unusually large loop for DNA recognition. This OB fold is structurally similar to OB folds found in the ciliated protozoan telomere end-binding protein, although no sequence similarity is apparent between them. The common usage of an OB fold for telomeric DNA interaction demonstrates conservation of end-protection mechanisms among eukaryotes. 相似文献
73.
74.
Krause O Rieke GH Birkmann SM Le Floc'h E Gordon KD Egami E Bieging J Hughes JP Young ET Hinz JL Quanz SP Hines DC 《Science (New York, N.Y.)》2005,308(5728):1604-1606
Two images of Cassiopeia A obtained at 24 micrometers with the Spitzer Space Telescope over a 1-year time interval show moving structures outside the shell of the supernova remnant to a distance of more than 20 arc minutes. Individual features exhibit apparent motions of 10 to 20 arc seconds per year, independently confirmed by near-infrared observations. The observed tangential velocities are at roughly the speed of light. It is likely that the moving structures are infrared echoes, in which interstellar dust is heated by the explosion and by flares from the compact object near the center of the remnant. 相似文献
75.
PM Lundquist R Wortmann C Geletneky RJ Twieg M Jurich VY Lee CR Moylan DM Burland 《Science (New York, N.Y.)》1996,274(5290):1182-1185
The performance of amorphous organic photorefractive (PR) materials in applications such as optical data storage is generally limited by the concentration of active molecules (chromophores) that can be incorporated into the host without forming a crystalline material with poor optical quality. In polymeric PR systems described previously, performance has been limited by the necessity of devoting a large fraction of the material to inert polymer and plasticizing components in order to ensure compositional stability. A new class of organic PR materials composed of multifunctional glass-forming organic chromophores is described that have long-term stability and greatly improved PR properties. 相似文献
76.
Astwood EB Hughes AM Lubin M Vanderlaan WP Adams RD 《Science (New York, N.Y.)》1945,102(2643):196-197
Page 148, 2d column, article by Dr. Gregory Shwartzman; the thirteenth line down on the right-hand column reads: "experiments which were all carried out in meat-inferior broth." This should have been "mneat infusion broth." 相似文献
77.
The evolution of worker behavior in the social insects is usually explained by kin selection: although workers do not produce offspring, they do reproduce their genes by aiding the reproduction of relatives. The most difficult case for kin selection theory would be species in which workers are fully capable of reproducing but instead opt to rear brood of low relatedness. These conditions are perhaps best fulfilled by the swarm-founding wasps because they have little caste differentiation and their colonies usually have multiple queens, which should lower relatedness. Estimates of within-colony relatedness for three species in this group confirm that it is sometimes (but not always) very low. Inbreeding is negligible in these species, so the hypothesis that inbreeding may raise relatedness is not supported. The maintenance of worker behavior in such species is a significant challenge for kin selection theory. 相似文献
78.
Models predict that food-web structure is regulated by both consumers and resources, and the strength of this control is dependent on trophic position and food-web length. To test these hypotheses, a meta-analysis was conducted of 11 fish (consumer)-by-nutrient (resource) factorial plankton community experiments. As predicted, zooplankton biomass was under strong consumer control but was weakly stimulated by nutrient additions; phytoplankton biomass was under strong resource control with moderate control by fish. However, the phytoplankton and zooplankton responses to nutrient additions did not follow theoretical predictions based on the number of trophic levels in the food web. 相似文献
79.
Hughes CE 《Science (New York, N.Y.)》1925,61(1567):24-26
80.