全文获取类型
收费全文 | 16179篇 |
免费 | 41篇 |
国内免费 | 41篇 |
专业分类
系统科学 | 70篇 |
丛书文集 | 108篇 |
教育与普及 | 28篇 |
理论与方法论 | 56篇 |
现状及发展 | 5794篇 |
研究方法 | 756篇 |
综合类 | 9131篇 |
自然研究 | 318篇 |
出版年
2013年 | 186篇 |
2012年 | 231篇 |
2011年 | 564篇 |
2010年 | 101篇 |
2008年 | 258篇 |
2007年 | 333篇 |
2006年 | 333篇 |
2005年 | 309篇 |
2004年 | 299篇 |
2003年 | 279篇 |
2002年 | 287篇 |
2001年 | 690篇 |
2000年 | 675篇 |
1999年 | 370篇 |
1994年 | 47篇 |
1992年 | 340篇 |
1991年 | 272篇 |
1990年 | 297篇 |
1989年 | 316篇 |
1988年 | 285篇 |
1987年 | 268篇 |
1986年 | 290篇 |
1985年 | 311篇 |
1984年 | 270篇 |
1983年 | 245篇 |
1982年 | 203篇 |
1981年 | 188篇 |
1980年 | 211篇 |
1979年 | 502篇 |
1978年 | 391篇 |
1977年 | 365篇 |
1976年 | 302篇 |
1975年 | 348篇 |
1974年 | 496篇 |
1973年 | 376篇 |
1972年 | 386篇 |
1971年 | 491篇 |
1970年 | 607篇 |
1969年 | 413篇 |
1968年 | 448篇 |
1967年 | 377篇 |
1966年 | 384篇 |
1965年 | 259篇 |
1959年 | 135篇 |
1958年 | 225篇 |
1957年 | 162篇 |
1956年 | 115篇 |
1955年 | 115篇 |
1954年 | 110篇 |
1948年 | 89篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
801.
Ubiquitin-proteasome pathway as a primary defender against TRAIL-mediated cell death 总被引:3,自引:0,他引:3
Kim S Choi K Kwon D Benveniste EN Choi C 《Cellular and molecular life sciences : CMLS》2004,61(9):1075-1081
Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptotic cell death as well as expression of proinflammatory genes such as CXCL8 in malignant human astrocytoma cells. However, the molecular mechanisms that determine the fate of cells are not yet understood. The ubiquitin (Ub)-proteasome pathway regulates a wide range of cellular functions through degradation of various regulatory proteins; given this, we hypothesized that this pathway may play a central role in TRAIL-mediated signaling. We demonstrate here that inhibition of the Ub-proteasome pathway enhanced TRAIL-mediated cell death of human astrocytoma CRT-MG cells within hours by blocking degradation of active caspase-8 and -3. Proteasome inhibitors suppressed TRAIL-mediated activation of NF-B; however, inhibition of the NF-B pathway alone was not sufficient to enhance TRAIL-mediated cell death. Collectively, these results suggest that the Ub-proteasome pathway may play an important role as an antiapoptotic surveillance system by eliminating activated caspases as well as mediating NF-B-dependent signals.Received 30 December 2003; received after revision 9 February 2004; accepted 13 February 2004 相似文献
802.
803.
804.
Mignot C Boespflug-Tanguy O Gelot A Dautigny A Pham-Dinh D Rodriguez D 《Cellular and molecular life sciences : CMLS》2004,61(3):369-385
Alexander disease (AXD) is the first primary astrocytic disorder. This encephalopathy is caused by dominant mutations in the glial fibrillary acidic protein (GFAP) gene, encoding the main intermediate filament of astrocyte. Pathologically, this neurodegenerative disease is characterised by dystrophic astrocytes containing intermediate filament aggregates associated with myelin abnormalities.More than 20 GFAP mutations have been reported. Many of them cluster in highly conserved regions between several intermediate filaments. Contrary to other intermediate filament-related diseases, AXD seems to be the consequence of a toxic gain of function induced by aggregates. This is supported by the phenotype of mice overexpressing human GFAP. Nevertheless, GFAP null mice display myelin abnormalities and blood-brain barrier dysfunction that are present in AXD.Given the pivotal role of astrocytes in brain physiology, there are many possibilities for astrocytes to dysfunction and to impair the functions of other cells. Physiopathological hypotheses are discussed in the frame of AXD.Received 11 April 2003; received after revision 22 July 2003; accepted 31 July 2003Both authors contributed equally to this work. 相似文献
805.
Smith NJ Chan HW Osborne JE Thomas WG Hannan RD 《Cellular and molecular life sciences : CMLS》2004,61(21):2695-2703
Activation of the type 1 angiotensin II receptor (AT(1)R) is associated with the aetiology of left ventricular hypertrophy, although the exact intracellular signalling mechanism(s) remain unclear. Transactivation of the epidermal growth factor receptor (EGFR) has emerged as a central mechanism by which the G protein-coupled AT(1)R, which lacks intrinsic tyrosine kinase activity, can stimulate the mitogen-activated protein kinase signalling pathways thought to mediate cardiac hypertrophy. Current studies support a model whereby AT(1)R-dependent transactivation of EGFRs on cardiomyocytes involves stimulation of membrane-bound metalloproteases, which in turn cleave EGFR ligands such as heparin-binding EGF from a plasma membrane-associated precursor. Numerous aspects of the 'triple membrane-passing signalling' paradigm of AT(1)R-induced EGFR transactivation remain to be characterised, including the identity of the specific metalloproteases involved, the intracellular mechanism for their activation and the exact EGFR subtypes required. Here we examine how 'hijacking' of the EGFR might explain the ability of the AT(1)R to elicit the temporally and qualitatively diverse responses characteristic of the hypertrophic phenotype, and discuss the ramifications of delineating these pathways for the development of new therapeutic strategies to combat cardiac hypertrophy. 相似文献
806.
DNA mutations and aberrations are a problem for all forms of life. Eukaryotes specifically have developed ways of identifying and repairing various DNA mutations in a complex and refractory chromatin environment. The chromatin structure is much more than a packaging unit for DNA; it is dynamic. Cells utilize and manipulate chromatin for gene regulation, genome organization and maintenance of genome integrity. Once a DNA aberration has occurred, the various DNA repair machineries interact with chromatin proteins, such as the histone variant H2A.X, and chromatin remodeling machines of the SWI/SNF family to gain access and repair the lesion in a timely manner. Recent studies have thus begun to address the roles of chromatin proteins in DNA repair as well as to dissect the functions of DNA repair machinery in vitro on more physiological, nucleosomal templates. 相似文献
807.
Gelsolin superfamily proteins: key regulators of cellular functions 总被引:10,自引:0,他引:10
Silacci P Mazzolai L Gauci C Stergiopulos N Yin HL Hayoz D 《Cellular and molecular life sciences : CMLS》2004,61(19-20):2614-2623
Cytoskeletal rearrangement occurs in a variety of cellular processes and involves a wide spectrum of proteins. Among these, the gelsolin superfamily proteins control actin organization by severing filaments, capping filament ends and nucleating actin assembly [1]. Gelsolin is the founding member of this family, which now contains at least another six members: villin, adseverin, capG, advillin, supervillin and flightless I. In addition to their respective role in actin filament remodeling, these proteins have some specific and apparently non-overlapping particular roles in several cellular processes, including cell motility, control of apoptosis and regulation of phagocytosis (summarized in table 1). Evidence suggests that proteins belonging to the gelsolin superfamily may be involved in other processes, including gene expression regulation. This review will focus on some of the known functions of the gelsolin superfamily proteins, thus providing a basis for reflection on other possible and as yet incompletely understood roles for these proteins. 相似文献
808.
809.
Alternative splicing of Bcl-2-related genes: functional consequences and potential therapeutic applications 总被引:6,自引:0,他引:6
Apoptosis is a morphologically distinct form of cell death. It is executed and regulated by several groups of proteins. Bcl-2 family proteins are the main regulators of the apoptotic process acting either to inhibit or promote it. More than 20 members of the family have been identified so far and most have two or more isoforms. Alternative splicing is one of the major mechanisms providing proteomic complexity and functional diversification of the Bcl-2 family proteins. Pro- and anti-apoptotic Bcl-2 family members should function in harmony for the regulation of the apoptosis machinery, and their relative levels are critical for cell fate. Any mechanism breaking down this harmony by changing the relative levels of these antagonistic proteins could contribute to many diseases, including cancer and neurodegenerative disorders. Recent studies have shown that manipulation of the alternative splicing mechanisms could provide an opportunity to restore the proper balance of these regulator proteins. This review summarises current knowledge on the alternative splicing products of Bcl-2-related genes and modulation of splicing mechanisms as a potential therapeutic approach.Received 5 January 2004; received after revision 31 March 2004; accepted 6 April 2004 相似文献
810.
The function of protein and RNA molecules depends on complex epistatic interactions between sites. Therefore, the deleterious effect of a mutation can be suppressed by a compensatory second-site substitution. In relating a list of 86 pathogenic mutations in human tRNAs encoded by mitochondrial genes to the sequences of their mammalian orthologs, we noted that 52 pathogenic mutations were present in normal tRNAs of one or several nonhuman mammals. We found at least five mechanisms of compensation for 32 pathogenic mutations that destroyed a Watson-Crick pair in one of the four tRNA stems: restoration of the affected Watson-Crick interaction (25 cases), strengthening of another pair (4 cases), creation of a new pair (8 cases), changes of multiple interactions in the affected stem (11 cases) and changes involving the interaction between the loop and stem structures (3 cases). A pathogenic mutation and its compensating substitution are fixed in a lineage in rapid succession, and often a compensatory interaction evolves convergently in different clades. At least 10%, and perhaps as many as 50%, of all nucleotide substitutions in evolving mammalian tRNAs participate in such interactions, indicating that the evolution of tRNAs proceeds along highly epistatic fitness ridges. 相似文献