全文获取类型
收费全文 | 7292篇 |
免费 | 1007篇 |
国内免费 | 1篇 |
专业分类
8300篇 |
出版年
2021年 | 89篇 |
2016年 | 114篇 |
2015年 | 192篇 |
2014年 | 199篇 |
2013年 | 287篇 |
2012年 | 334篇 |
2011年 | 327篇 |
2010年 | 208篇 |
2009年 | 213篇 |
2008年 | 303篇 |
2007年 | 296篇 |
2006年 | 266篇 |
2005年 | 229篇 |
2004年 | 244篇 |
2003年 | 233篇 |
2002年 | 242篇 |
2001年 | 232篇 |
2000年 | 229篇 |
1999年 | 192篇 |
1998年 | 78篇 |
1997年 | 85篇 |
1996年 | 80篇 |
1995年 | 63篇 |
1994年 | 71篇 |
1993年 | 66篇 |
1992年 | 127篇 |
1991年 | 136篇 |
1990年 | 153篇 |
1989年 | 131篇 |
1988年 | 138篇 |
1987年 | 121篇 |
1986年 | 126篇 |
1985年 | 141篇 |
1984年 | 109篇 |
1983年 | 124篇 |
1982年 | 99篇 |
1981年 | 81篇 |
1980年 | 83篇 |
1979年 | 113篇 |
1978年 | 87篇 |
1977年 | 75篇 |
1976年 | 71篇 |
1975年 | 87篇 |
1974年 | 85篇 |
1973年 | 83篇 |
1972年 | 84篇 |
1971年 | 67篇 |
1970年 | 86篇 |
1969年 | 76篇 |
1967年 | 70篇 |
排序方式: 共有8300条查询结果,搜索用时 0 毫秒
81.
β-Maltosylamine has been synthesized for the first time. It is an effective specific inhibitor of sweet potato β-amylase. This result extends the observation that 1-aminoglycosides are specific inhibitors of exoglycosidases which hydrolyze the corresponding glycose and also demonstrates that an enzyme acting with inversion, as well as those acting with retention of anomeric configuration, can be inhibited by glycosylamines. Maltosylamine, which acts as a reversible inhibitor of β-amylase, appears to be directed to the active site since it protects the essential sulfhydryl group of the enzyme from inactivation by N-ethylmaleimide. 相似文献
82.
M Ehrich J E Aswell R L van Tassell T D Wilkins A R Walker N J Richardson 《Mutation research》1979,64(4):231-240
The incidence of mutagens in the feces of 3 South-African populations at different risk levels for colon cancer has been determined. Lyophilized fecal samples were extracted with ether and the mutagenicity of the extracts determined using the Salmonella/mammalian microsome mutagenicity test. 19% of the samples from urban white South-Africans, a population at a high risk for colon cancer, were mutagenic using Salmonella typhimurium strain TA100. This incidence was significantly greater (p less than 0.001) than the incidence of mutagen excretion in the low-risk populations of urban blacks (2%) and rural blacks (0%). This pattern was also obtained using Salmonella typhimurium strain TA98. The incidence of mutagen excretion for urban whites was 10%, as compared to 5% and 2% for urban and rural blacks, respectively. 相似文献
83.
84.
Peter G Walker 《BMJ (Clinical research ed.)》1981,283(6287):384
85.
Sustained swimming speeds and myotomal muscle function in the trout, Salmo gairdneri 总被引:1,自引:0,他引:1
Rainbow trout were trained for 3–4 weeks in a flume at swimming speeds of 1, 2 and 3 l s−1 . For each experiment growth rates were estimated and by measuring the hypertrophy of red and mosaic skeletal muscle fibres their function was described at particular swimming speeds and compared with earlier experiments on coalfish using the same technique.
Maximum growth, compared with controls in still water, occurred at swimming speeds of 1 l s−1 . At this speed the trout mosaic muscle fibres hypertrophied by 40% but the red muscle fibres showed only a 25% hypertrophy. It is suggested that natural swimming speeds are close to 1Ls−l and the trout mosaic fibres are better adapted for use at this speed in comparison with coalfish white muscle fibres. 相似文献
Maximum growth, compared with controls in still water, occurred at swimming speeds of 1 l s
86.
J H Dussault P Walker J D Dubois F Labrie 《Canadian journal of physiology and pharmacology》1977,55(5):1091-1097
87.
C Wastell J Colin T Wilson E Walker J Gleeson R Zeegen 《BMJ (Clinical research ed.)》1977,2(6091):851-853
A consecutive series of 100 men with uncomplicated duodenal ulcer was randomly divided into two groups: one group of 52 underwent proximal gastric vagotomy (PGV), the other group (48) underwent PGV with pyloroplasty (PGVP). Preoperative peak acid output (PAOP) was measured in all patients. Those with a higher preoperative PAOP were significantly more likely to develop recurrent ulceration. Three patients developed recurrent ulceration after PGV and seven after PGVP. Dumping was both more common and more severe after PGVP than PGV. An overall satisfactory result was achieved in 92% after PGV and 81% after PGVP. We conclude that combining pyloroplasty with PGV has no appreciable advantages. 相似文献
88.
Structural and functional studies of the endothelial activation antigen endothelial leucocyte adhesion molecule-1 using a panel of monoclonal antibodies. 总被引:14,自引:0,他引:14
R Pigott L A Needham R M Edwards C Walker C Power 《Journal of immunology (Baltimore, Md. : 1950)》1991,147(1):130-135
We have produced a panel of mAb to the endothelial activation Ag endothelial leucocyte adhesion molecule-1 (ELAM-1), using both a conventional immunization protocol and one involving immunosuppression. By constructing ELAM-1 mutants we have demonstrated that seven of these antibodies recognize epitopes within the lectin domain of ELAM-1 and that one binds within the complement regulatory protein domains. These studies also suggest that the EGF-like domain is important in maintaining the conformation of the neighbouring lectin domain. In functional studies, U937 cells bound to Cos cells expressing either ELAM-1 or ELAM-1 with the complement regulatory protein domains deleted. No adhesion was observed to Cos cells expressing ELAM-1 mutants lacking either the lectin or EGF-like domains. The fact that antibodies directed against the lectin domain can inhibit adhesion suggest that this domain is directly involved in cell binding. 相似文献
89.
Annexin IV (endonexin) has been purified from chicken liver and crystallized by the vapour diffusion method. Crystals which diffract to at least 2.2 A have been obtained. They belong to space group R3 and have unit cell dimensions of a = b = 99.4 A, c = 96.2 A, alpha = 90 degrees, beta = 90 degrees, gamma = 120 degrees. There is one molecule of 32,500 Da per asymmetric unit. 相似文献
90.