全文获取类型
收费全文 | 402篇 |
免费 | 23篇 |
专业分类
林业 | 13篇 |
农学 | 9篇 |
基础科学 | 4篇 |
42篇 | |
综合类 | 46篇 |
农作物 | 24篇 |
水产渔业 | 13篇 |
畜牧兽医 | 231篇 |
园艺 | 12篇 |
植物保护 | 31篇 |
出版年
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 12篇 |
2013年 | 23篇 |
2012年 | 16篇 |
2011年 | 16篇 |
2010年 | 11篇 |
2009年 | 8篇 |
2008年 | 19篇 |
2007年 | 14篇 |
2006年 | 10篇 |
2005年 | 14篇 |
2004年 | 20篇 |
2003年 | 16篇 |
2002年 | 13篇 |
2001年 | 15篇 |
2000年 | 17篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1968年 | 5篇 |
1967年 | 3篇 |
1966年 | 2篇 |
1902年 | 1篇 |
1896年 | 1篇 |
排序方式: 共有425条查询结果,搜索用时 437 毫秒
31.
Matthews R 《Science (New York, N.Y.)》1991,254(5037):1454-1455
32.
Structures of two thermolysin-inhibitor complexes that differ by a single hydrogen bond 总被引:3,自引:0,他引:3
The mode of binding to thermolysin of the ester analog Cbz-GlyP-(O)-Leu-Leu has been determined by x-ray crystallography and shown to be virtually identical (maximum difference 0.2 angstrom) with the corresponding peptide analog Cbz-GlyP-(NH)-Leu-Leu. The two inhibitors provide a matched pair of enzyme-inhibitor complexes that differ by 4.1 kilocalories per mole in intrinsic binding energy but are essentially identical except for the presence or absence of a specific hydrogen bond. 相似文献
33.
Matthews RG 《Science (New York, N.Y.)》1989,246(4933):1064-1065
34.
Bockelée-Morvan D Biver N Moreno R Colom P Crovisier J Gérard E Henry F Lis DC Matthews H Weaver HA Womack M Festou MC 《Science (New York, N.Y.)》2001,292(5520):1339-1343
The gas activity of comet C/1999 S4 (LINEAR) was monitored at radio wavelengths during its disruption. A runaway fragmentation of the nucleus may have begun around 18 July 2000 and proceeded until 23 July. The mass in small icy debris (=30-centimeter radius) was comparable to the mass in the large fragments seen in optical images. The mass budget after breakup suggests a small nucleus ( approximately 100- to 300-meter radius) that had been losing debris for weeks. The HNC, H2CO, H2S, and CS abundances relative to H2O measured during breakup are consistent with those obtained in other comets. However, a deficiency in CH3OH and CO is observed. 相似文献
35.
36.
Replacements of Pro86 in phage T4 lysozyme extend an alpha-helix but do not alter protein stability 总被引:10,自引:0,他引:10
T Alber J A Bell D P Sun H Nicholson J A Wozniak S Cook B W Matthews 《Science (New York, N.Y.)》1988,239(4840):631-635
To investigate the relation between protein stability and the predicted stabilities of individual secondary structural elements, residue Pro86 in an alpha-helix in phage T4 lysozyme was replaced by ten different amino acids. The x-ray crystal structures of seven of the mutant lysozymes were determined at high resolution. In each case, replacement of the proline resulted in the formation of an extended alpha-helix. This involves a large conformational change in residues 81 to 83 and smaller shifts that extend 20 angstroms across the protein surface. Unexpectedly, all ten amino acid substitutions marginally reduce protein thermostability. This insensitivity of stability to the amino acid at position 86 is not simply explained by statistical and thermodynamic criteria for helical propensity. The observed conformational changes illustrate a general mechanism by which proteins can tolerate mutations. 相似文献
37.
Creutzfeldt-Jakob disease (spongiform encephalopathy): transmission to the chimpanzee 总被引:48,自引:0,他引:48
C J Gibbs D C Gajdusek D M Asher M P Alpers E Beck P M Daniel W B Matthews 《Science (New York, N.Y.)》1968,161(839):388-389
Biopsy material taken from the brain of a patient with CreutzfeldtJakob disease with status spongiosus induced a similar fatal encephalopathy in a chimpanzee 13 months after inoculation. 相似文献
38.
Matthews KR 《Science (New York, N.Y.)》2011,331(6021):1149-1153
Vector-borne parasites cause major human diseases of the developing world, including malaria, human African trypanosomiasis, Chagas disease, leishmaniasis, filariasis, and schistosomiasis. Although the life cycles of these parasites were defined over 100 years ago, the strategies they use to optimize their successful transmission are only now being understood in molecular terms. Parasites are now known to monitor their environment in both their host and vector and in response to other parasites. This allows them to adapt their developmental cycles and to counteract any unfavorable conditions they encounter. Here, I review the interactions that parasites engage in with their hosts and vectors to maximize their survival and spread. 相似文献
39.
The large variation in the ratio of uranium-234 to uranium-238 (234U/238U) in rivers is not well understood, but may provide information about past weathering and rainfall and is important because it controls seawater (234U/238U). Here, we demonstrate the importance of physical weathering and rainfall for (234U/238U), using rivers from South Island, New Zealand. These data allow interpretation of an existing speleothem (234U/238U) record and suggest that New Zealand glacier advance 13,000 years ago was influenced by increased rainfall rather than by Younger Dryas-like cooling. A model of seawater (234U/238U) during glacial cycles indicates that rejection of corals based on modern (234U/238U) +/- <0.01 is not merited and may reject the highest quality ages. 相似文献
40.