全文获取类型
收费全文 | 12571篇 |
免费 | 918篇 |
国内免费 | 669篇 |
专业分类
14158篇 |
出版年
2023年 | 114篇 |
2022年 | 275篇 |
2021年 | 450篇 |
2020年 | 309篇 |
2019年 | 360篇 |
2018年 | 386篇 |
2017年 | 310篇 |
2016年 | 443篇 |
2015年 | 650篇 |
2014年 | 786篇 |
2013年 | 895篇 |
2012年 | 1004篇 |
2011年 | 964篇 |
2010年 | 573篇 |
2009年 | 508篇 |
2008年 | 590篇 |
2007年 | 569篇 |
2006年 | 515篇 |
2005年 | 490篇 |
2004年 | 417篇 |
2003年 | 425篇 |
2002年 | 354篇 |
2001年 | 269篇 |
2000年 | 263篇 |
1999年 | 215篇 |
1998年 | 139篇 |
1997年 | 128篇 |
1996年 | 123篇 |
1995年 | 125篇 |
1994年 | 99篇 |
1993年 | 96篇 |
1992年 | 159篇 |
1991年 | 127篇 |
1990年 | 96篇 |
1989年 | 99篇 |
1988年 | 86篇 |
1987年 | 67篇 |
1986年 | 68篇 |
1985年 | 81篇 |
1984年 | 56篇 |
1983年 | 46篇 |
1982年 | 33篇 |
1981年 | 25篇 |
1979年 | 34篇 |
1978年 | 29篇 |
1977年 | 36篇 |
1976年 | 25篇 |
1974年 | 28篇 |
1973年 | 20篇 |
1971年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Comparison of 16S rRNA sequences from the family Pasteurellaceae: phylogenetic relatedness by cluster analysis 总被引:2,自引:0,他引:2
The taxonomy of the family Pasteurellaceae has remained controversial despite investigations of biochemistry, serology, and nucleic acid relatedness. In an attempt to resolve some of this confusion, we have partially sequenced the 16S rRNAs of seven members of the family, representing all three genera. The sequences were aligned, similarity scores calculated, and single, average and complete linkage cluster analysis of the resulting distance matrix performed. In this way, an evolutionary branching pattern of these closely related species was reconstructed, and the approximate phylogenetic position of the family determined. Actinobacillus (Haemophilus) actinomycetemcomitans clustered with Haemophilus instead of Actinobacillus, supporting transfer of this species to the genus Haemophilus. Thus cluster analysis of phylogenetic relatedness was found to be particularly useful for studying closely related organisms, and could be performed using a microcomputer. 相似文献
22.
23.
J L Gu I D Goldfine J R Forsayeth P De Meyts 《Biochemical and biophysical research communications》1988,150(2):694-701
Two monoclonal antibodies to the insulin receptor, MA-5 and MA-20, unlike other monoclonal antibodies, do not mimick the accelerating effect of insulin on the dissociation of 125I-insulin from the receptors (negative cooperativity). On the contrary, MA-5 and MA-20 markedly slow down the dissociation rate. We show now that MA-5 and MA-20 are potent antagonists of the negative cooperativity induced by insulin, and reverse the insulin-induced acceleration whether added simultaneously with insulin or after insulin. The reversal of the insulin-induced acceleration is almost immediate. These data strengthen the concept therefore that the insulin-receptor complex has access to alternative conformational states that can be stabilized by ligand-induced site-site interactions. 相似文献
24.
25.
Stanley W. Watson Eberhard Bock Frederica W. Valois John B. Waterbury Ursula Schlosser 《Archives of microbiology》1986,144(1):1-7
A new chemolithotrophic nitrite-oxidizing bacterium, for which the name Nitrospira marina is proposed, was isolated from the Gulf of Maine. N. marina is a Gramnegative curved rod which may form spirals with 1 to 12 turns. Cells have a unique periplasmic space and lack intracytoplasmic membranes and carboxysomes. N. marina is an obligate chemolithotroph, but best growth is obtained in a mixotrophic medium. N. marina may be one of the most prevalent nitrite-oxidizing bacteria in some oceanic environments. Type strain is field with American Type Culture Collection (ATCC 43039). 相似文献
26.
The application of 1H-nuclear Overhauser enhancement, 1H-spin-lattice-relaxation-time and 1H-chemical shift measurements for the assessment of the conformational preferences of oligosaccharides are briefly reviewed. It is demonstrated that additivity rules, for the correlation of the chemical shifts of similar hydrogen atoms in different oligosaccharides, can be useful in the conformational analysis of oligosaccharides when the differential chemical shifts are greater than 0.1 ppm. These often can be attributed to specific interunit deshielding of a hydrogen atom by an oxygen atom with which it is in strong nonbonded interaction. HSEA calculations are used to demonstrate that differential chemical shifts of less than 0.1 ppm can have origins that are not significant to the overall conformational preferences of the oligosaccharides which are being compared. Both shielding and deshielding effects can arise from a change in the orientation of a substituent group as the result of the introduction of a sugar on a neighboring unit. It is demonstrated that substituent groups, such as hydroxymethyl and acetamido groups, on occasions, should be treated in HSEA calculations as freely rotating about their linkage to a pyranose ring. 相似文献
27.
28.
29.
Zusammenfassung Beidseitige Adrenalektomie und Hypophysektomie führen bei der Ratte zu gleichartigen histologischen Veränderungen in der Zona externa infundibuli. In beiden Fällen treten in der normalerweise weitgehend goniorinegativen Zona externa infundibuli große Mengen gomoripositiver Granula auf. Sie scheinen Fasern anzugehören, die senkrecht zur Längsachse des Infundibulum verlaufen.Die Befunde werden als weiterer Hinweis dafür betrachtet, daß die gomoripositiven Substanzen der Zona externa infundibuli eine Bedeutung für die Steuerung der Nebennierenrindenfunktion haben.
Studies on the functional morphology of the neurohypophysisII. Comparison of histological changes in the median eminence of the rat after bilateral adrenalectomy and hypophysectomy
Summary Bilateral adrenalectomy and hypophysectomy in the rat produce similar histological changes in the outer layer of the median eminence. In both cases, abundant gomoripositive granules are observed in the outer layer, which normally reacts gomorinegative. The gomoripositive granules seem to belong to fibres running vertically through the infundibulum.These findings are regarded as a further indication, that the gomoripositive substances of the outer layer of the median eminence play a significant role in controlling adrenocortical function.相似文献
30.