全文获取类型
收费全文 | 105754篇 |
免费 | 6555篇 |
国内免费 | 15篇 |
专业分类
112324篇 |
出版年
2022年 | 763篇 |
2021年 | 1545篇 |
2020年 | 1266篇 |
2019年 | 1416篇 |
2018年 | 2657篇 |
2017年 | 2387篇 |
2016年 | 3224篇 |
2015年 | 4260篇 |
2014年 | 4549篇 |
2013年 | 5901篇 |
2012年 | 6851篇 |
2011年 | 6173篇 |
2010年 | 4152篇 |
2009年 | 3419篇 |
2008年 | 5043篇 |
2007年 | 4822篇 |
2006年 | 4677篇 |
2005年 | 3950篇 |
2004年 | 4005篇 |
2003年 | 3534篇 |
2002年 | 3299篇 |
2001年 | 2715篇 |
2000年 | 2523篇 |
1999年 | 2060篇 |
1998年 | 1016篇 |
1997年 | 765篇 |
1996年 | 777篇 |
1995年 | 719篇 |
1994年 | 659篇 |
1992年 | 1247篇 |
1991年 | 1171篇 |
1990年 | 1111篇 |
1989年 | 1176篇 |
1988年 | 978篇 |
1987年 | 1003篇 |
1986年 | 919篇 |
1985年 | 968篇 |
1984年 | 792篇 |
1983年 | 707篇 |
1982年 | 593篇 |
1979年 | 798篇 |
1978年 | 603篇 |
1977年 | 591篇 |
1975年 | 694篇 |
1974年 | 757篇 |
1973年 | 720篇 |
1972年 | 655篇 |
1970年 | 623篇 |
1969年 | 687篇 |
1968年 | 647篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
T Abe S Alemá R Miledi 《Proceedings of the Royal Society of London. Series B, Containing papers of a Biological character. Royal Society (Great Britain)》1980,207(1169):487-490
It has recently been claimed that our beta-bungarotoxin preparation contained three contaminants, including a postsynaptic toxin. We have extended our purification procedure and found no evidence of such contaminants. 相似文献
122.
123.
124.
The antigen-antibody interaction occurring previous to the triggering of the immunological response is analyzed as a relational process in terms of lattices. Accordingly, this process is expressed as a lattice belonging to a pseudo-Boolean algebraic variety. The Heyting arrow operation, which appears in this kind of algebra, is used to analyze behaviors between non-comparable biological states expressed by the lattice. The resulting states coming from the arrows are connected with the influence of increasing and decreasing energies involved in the linking process. 相似文献
125.
126.
127.
David Dávila Silvia Fernández Ignacio Torres-Alemán 《The Journal of biological chemistry》2016,291(5):2510-2523
Disruption of insulin-like growth factor I (IGF-I) signaling is a key step in the development of cancer or neurodegeneration. For example, interference of the prosurvival IGF-I/AKT/FOXO3 pathway by redox activation of the stress kinases p38 and JNK is instrumental in neuronal death by oxidative stress. However, in astrocytes, IGF-I retains its protective action against oxidative stress. The molecular mechanisms underlying this cell-specific protection remain obscure but may be relevant to unveil new ways to combat IGF-I/insulin resistance. Here, we describe that, in astrocytes exposed to oxidative stress by hydrogen peroxide (H2O2), p38 activation did not inhibit AKT (protein kinase B) activation by IGF-I, which is in contrast to our previous observations in neurons. Rather, stimulation of AKT by IGF-I was significantly higher and more sustained in astrocytes than in neurons either under normal or oxidative conditions. This may be explained by phosphorylation of the phosphatase PTEN at the plasma membrane in response to IGF-I, inducing its cytosolic translocation and preserving in this way AKT activity. Stimulation of AKT by IGF-I, mimicked also by a constitutively active AKT mutant, reduced oxidative stress levels and cell death in H2O2-exposed astrocytes, boosting their neuroprotective action in co-cultured neurons. These results indicate that armoring of AKT activation by IGF-I is crucial to preserve its cytoprotective effect in astrocytes and may form part of the brain defense mechanism against oxidative stress injury. 相似文献
128.
F. Šrámek 《Biologia Plantarum》1999,42(4):582-582
129.
De novo-synthesized ceramide signals apoptosis in astrocytes via extracellular signal-regulated kinase. 总被引:10,自引:0,他引:10
Recent observations support the importance of ceramide synthesis de novo in the induction of apoptosis. However, the downstream targets of de novo-synthesized ceramide are unknown. Here we show that palmitate incorporated into ceramide and induced apoptotic DNA fragmentation in astrocytes. These effects of palmitate were exacerbated when fatty acid breakdown was uncoupled and were not evident in neurons, which show a very low capacity to take up and metabolize palmitate. Palmitate-induced apoptosis of astrocytes was prevented by L-cycloserine and fumonisin B1, two inhibitors of ceramide synthesis de novo, and by PD098059, an inhibitor of the extracellular signal-regulated kinase (ERK) cascade. Accordingly, palmitate activated ERK by a process that was dependent on ceramide synthesis de novo and Raf-1, but independent of kinase suppressor of Ras. Other potential targets of ceramide in the control of cell fate, namely, c-Jun amino-terminal kinase, p38 mitogen-activated protein kinase, and protein kinase B, were not significantly affected in astrocytes exposed to palmitate. Results show that the Raf-1/ERK cascade is the selective downstream target of de novo-synthesized ceramide in the induction of apoptosis in astrocytes and also highlight the importance of ceramide synthesis de novo in apoptosis of astrocytes, which might have pathophysiological relevance. 相似文献
130.
Prakash Bhuta Stanislav Chládek 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1982,698(2):167-172
The effect of the antibiotics thiostrepton and micrococcin on EF-Tu-catalyzed (ribosome-dependent) GTP hydrolysis in the presence of A-Phe, C-A-Phe, or C-C-A-Phe (related to the sequence of the 3′-terminus of aminoacyl-tRNA)(System I) or by methanol (‘uncoupled GTPase’, System II) was investigated. In System I, thiostrepton increases the binding affinities of the effectors to the EF-Tu·GTP·70 S ribosome complex, as well as the extent of the GTP hydrolysis, while the KGTPm is virtually unchanged. Similarly, in the uncoupled system (System II) and in the absence of effectors, thiostrepton significantly increases VGTPmax, whereas KGTPm remains unaffected. Micrococcin is without any effect in both systems. The ‘uncoupled GTPase’ (in System II) is also strongly inhibited by C-A-Phe. The results indicate the crucial role of the EF-Tu site which binds the aminoacylated C-C-A terminus of aminoacyl-tRNA in promoting GTP hydrolysis. It follows that the binding of the model effectors (such as C-C-A-Phe) to that site is favorably influenced by the interaction of thiostrepton with the 50 S ribosomal subunit, whereas thiostrepton, per se, does not influence the affinity of EF-Tu for GTP. 相似文献