全文获取类型
收费全文 | 60331篇 |
免费 | 4933篇 |
国内免费 | 31篇 |
专业分类
65295篇 |
出版年
2022年 | 413篇 |
2021年 | 854篇 |
2020年 | 528篇 |
2019年 | 638篇 |
2018年 | 831篇 |
2017年 | 771篇 |
2016年 | 1357篇 |
2015年 | 2392篇 |
2014年 | 2512篇 |
2013年 | 3336篇 |
2012年 | 4237篇 |
2011年 | 4245篇 |
2010年 | 2755篇 |
2009年 | 2440篇 |
2008年 | 3531篇 |
2007年 | 3590篇 |
2006年 | 3391篇 |
2005年 | 3419篇 |
2004年 | 3355篇 |
2003年 | 3148篇 |
2002年 | 3116篇 |
2001年 | 711篇 |
2000年 | 531篇 |
1999年 | 729篇 |
1998年 | 865篇 |
1997年 | 597篇 |
1996年 | 602篇 |
1995年 | 591篇 |
1994年 | 572篇 |
1993年 | 596篇 |
1992年 | 535篇 |
1991年 | 463篇 |
1990年 | 389篇 |
1989年 | 405篇 |
1988年 | 402篇 |
1987年 | 338篇 |
1986年 | 340篇 |
1985年 | 395篇 |
1984年 | 444篇 |
1983年 | 374篇 |
1982年 | 459篇 |
1981年 | 409篇 |
1980年 | 363篇 |
1979年 | 240篇 |
1978年 | 293篇 |
1977年 | 284篇 |
1976年 | 231篇 |
1975年 | 216篇 |
1974年 | 236篇 |
1973年 | 219篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
122.
Peter D. Shargool 《Plant cell reports》1985,4(4):206-209
Studies to determine the role of histidine in catalysis by L-argininosuccinate synthetase (EC 6. 3. 4. 5) were carried out with the enzyme isolated from soybean cell suspension cultures. These experiments utilized analogues of the substrates citrulline and aspartate to investigate substrate binding, and to determine which portion of the molecule were required for binding at the active site of the enzyme. Photooxidation studies using rose bengal were carried out to define the importance of histidine residues for catalysis. These studies suggest that an active site histidine residue has an important role to play in the formation of argininosuccinate by this enzyme. 相似文献
123.
Bernhard Knig Patricia A. DiNitto Peter M. Blumberg 《Journal of cellular biochemistry》1985,29(1):37-44
The major phorbol ester receptor is the Ca++-activated, phospholipid-dependent protein kinase C. Diacylglycerol stimulates protein kinase C in a fashion similar to the phorbol esters. Likewise, it inhibits phorbol ester binding competitively. Both results suggest that diacylglycerol is the/an endogenous phorbol ester analogue. Alternatively, the diacylglycerol might simply be acting to modify the phospholipid environment of the protein. If diacylglycerol were indeed functioning as an analogue, it should interact with the receptor stoichiometrically. This interaction can be quantitated by measuring the perturbation in apparent diacylglycerol binding affinity as a function of the ratio of diacylglycerol to receptor. We report here that 1,2-dioleoylglycerol interacts with the receptor with the predicted stoichiometry. 相似文献
124.
125.
126.
Weight differences, brood reduction, and sibling competition among nestling Stonechats Saxicola torquata (Aves: Turdidae) 总被引:1,自引:0,他引:1
Weight differences within broods of nestling birds are commonly assumed to be the outcome of a parental strategy of selectively starving one or more offspring so as to enhance the survival of the remaining chicks. This study examined patterns of development of nestling Stonechats to reveal the significance of weight hierarchies in determining the relative growth and survival of siblings. Although Stonechat broods display obvious weight hierarchies, the results show that a low rank does not strongly influence survival within the nest, especially early in the nestling period, and in small broods. Low ranking chicks were more likely to leave the nest at lighter weights, however. A proximate mechanism for the establishment of weight hierarchies was investigated, involving competition among nestlings for advantageous positions in the nest, in which the heavier siblings were more successful. 相似文献
127.
Bernhard Reinicke Peter Blümel Harald Labischinski Peter Giesbrecht 《Archives of microbiology》1985,141(4):309-314
In contrast to what has been postulated, penicillin G at its optimal lytic concentration of 0.1 g per ml did not lead to a detectable activation of autolytic wall processes in staphylococci in terms of the release of uniformly labelled wall fragments from cells pretreated with the drug for 1 h. Rather a considerable inhibition of this release was observed. A similarly profound inhibition of the release of peptidoglycan fragments occurred when staphylococci pretreated for 1 h with 0.1 g penicillin per ml acted as a source of crude autolysins on peptidoglycan isolated from labelled normal cells of the same strain. This clearly demonstrated that the overall inhibition of autolytic wall processes caused by penicillin was mainly due to a decreased total autolysin action rather than to an altered wall structure. Furthermore, no substantial penicillin-induced inhibition of the incorporation of 14C-N-acetylglucosamine into the staphylococcal wall could be observed before bacteriolysis started, i. e., approximately during the first 80 min of penicillin action. These results are not consistent with any of the models hitherto proposed for the action of penicillin.Dedicated to Prof. Dr. Gerhart Drews on the occasion of his 60th birthday 相似文献
128.
Energy flow and the vertical structure of real ecosystems 总被引:4,自引:0,他引:4
Peter Yodzis 《Oecologia》1984,65(1):86-88
Summary Three possible explanations for the well-known limitation of food chain lengths to two or three links for the most part are subjected to an empirical test, using the fact that ectotherms, especially invertebrates, tend to have higher production efficiencies than endotherms. The data are consistent with the hypothesis that food chain lengths are limited by the availability of energy. 相似文献
129.
J.Lane Cameron Peter V. Fankboner 《Journal of experimental marine biology and ecology》1984,81(2):193-209
Tentacle structure and function in the pentacula larva, juvenile, and adult life stages of Parastichopus californiens (Stimpson) were examined via light and electron microscopy. Food particle adherance to the tentacle surface is mediated by an adhesive material in the case of the pentacula larva and additionally by mechanical entrapment in juvenile and adult animals. Mechanical entrapment is of secondary importance to adhesion during feeding. 相似文献
130.
Steven P. Butcher Peter J. Roberts James F. Collins† 《Journal of neurochemistry》1984,43(4):1039-1045
Abstract: The effects of ions on the binding of the excitatory amino acid analogue dl -[3 H]2-amino-4-phosphon-obutyrate to l -glutamate-sensitive sites on rat brain synaptic membranes was investigated. The divalent cations manganese, magnesium, strontium, and particularly calcium, produced a marked enhancement in specific binding. However, this effect was manifest only in the presence of added chloride, or to a lesser extent, with bromide ions. Application of saturation analysis revealed that both chloride and calcium acted to increase the binding site density in a concentration-dependent manner, without affecting the dissociation constant. The only other ionic species found to have a significant effect on 2-amino-4-phosphonobutyrate binding was sodium, which produced an apparent reduction in site affinity, without modifying the binding site density. Although the significance of these striking ionic effects is as yet unknown, it seems feasible that chloride (and possibly also calcium) ions may serve a role in regulating the interaction of excitatory amino acids with their physiological receptors. 相似文献