全文获取类型
收费全文 | 2226篇 |
免费 | 34篇 |
国内免费 | 4篇 |
专业分类
林业 | 42篇 |
农学 | 1篇 |
210篇 | |
综合类 | 767篇 |
农作物 | 92篇 |
水产渔业 | 4篇 |
畜牧兽医 | 1064篇 |
园艺 | 16篇 |
植物保护 | 68篇 |
出版年
2012年 | 148篇 |
2011年 | 165篇 |
2010年 | 24篇 |
2009年 | 25篇 |
2008年 | 133篇 |
2007年 | 164篇 |
2006年 | 147篇 |
2005年 | 135篇 |
2004年 | 134篇 |
2003年 | 129篇 |
2002年 | 104篇 |
2001年 | 96篇 |
2000年 | 111篇 |
1999年 | 48篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 18篇 |
1993年 | 63篇 |
1992年 | 43篇 |
1991年 | 28篇 |
1990年 | 32篇 |
1989年 | 26篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 19篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1973年 | 10篇 |
1971年 | 10篇 |
1970年 | 9篇 |
1969年 | 13篇 |
1968年 | 9篇 |
1967年 | 15篇 |
1966年 | 15篇 |
1963年 | 17篇 |
1959年 | 7篇 |
1958年 | 9篇 |
1957年 | 7篇 |
1954年 | 9篇 |
1953年 | 11篇 |
1948年 | 12篇 |
1947年 | 12篇 |
排序方式: 共有2264条查询结果,搜索用时 46 毫秒
151.
Fleischer RL Price PB Walker RM Filz RC Fukui K Friedlander MW Holeman E Rajan RS Tamhane AS 《Science (New York, N.Y.)》1967,155(3759):187-189
Cosmic ray nuclei have been observed with the use of plastic trackdetecting solids in satellites and high-altitude balloon flights. Nuclear emulsions in the stacks of plastic sheets allowed the positive identification of cosmic raynuclei as light as nitrogen. The most striking new information was the failure to observe relativistic iron nuclei, a result which has led to an advance in the understanding of track registration criteria. 相似文献
152.
153.
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
154.
Among the ganglion cells in the rabbit's retina there is a class that responds to movement of a stimulus in one direction, and does not respond to movement in the opposite direction. The same directional selectivity holds over the whole receptive field of one such cell, but the selected direction differs in different cells. The discharge is almost uninfluenced by the intensity of the stimulus spot, and the response occurs for the same direction of movement when a black spot is substituted for a light spot. 相似文献
155.
Sea turtles (Lepidochelys kempi) are being artificially imprinted to Padre Island, Texas, in an effort to establish a new nesting population. These turtles spent more time per exposure in solutions made of Padre Island sand and seawater than in control solutions in a multiple-choice test. This is evidence that sea turtles may detect differences in natural water samples and remember olfactory cues to which they were exposed neonatally and that these differences may affect their orientation behavior. This suggests that imprinting could be used as a conservation technique for establishing new breeding populations of endangered sea turtles. 相似文献
156.
157.
The discovery of a new type of fossil nuclear track in mica is reported. This track is produced by the recoil nucleus accompanying the alpha-particle decay of uranium and thorium impurities. The tracks are very short and can be seen with phase contrast microscopy. Measurement of fossil alpha-recoil track densities, coupled with determinations of the thorium and uranium contents, provides a new dating technique analogous to the previously discovered "fission-track method." The primary advantage of the alpha-recoil method is a several-thousand-fold increase in sensitivity over the fission-track technique. The alpha-recoil method should also prove useful in studying the problem of extinct isotopes in meteorites. 相似文献
158.
Goldstein RM 《Science (New York, N.Y.)》1970,168(3930):467-468
Radar studies of Mercury have shown the presence of several large, rough surface features and of one smooth area. 相似文献
159.
160.
Shi C Huang Z Kilic S Xu J Enick RM Beckman EJ Carr AJ Melendez RE Hamilton AD 《Science (New York, N.Y.)》1999,286(5444):1540-1543
Compounds with strong thermodynamic affinity for carbon dioxide (CO(2)) have been designed and synthesized that dissolve in CO(2), then associate to form gels. Upon removal of the CO(2), these gels produced free-standing foams with cells with an average diameter smaller than 1 micrometer and a bulk density reduction of 97 percent relative to the parent material. 相似文献