全文获取类型
收费全文 | 4426篇 |
免费 | 288篇 |
专业分类
4714篇 |
出版年
2023年 | 30篇 |
2022年 | 66篇 |
2021年 | 136篇 |
2020年 | 120篇 |
2019年 | 129篇 |
2018年 | 159篇 |
2017年 | 148篇 |
2016年 | 173篇 |
2015年 | 266篇 |
2014年 | 286篇 |
2013年 | 348篇 |
2012年 | 391篇 |
2011年 | 334篇 |
2010年 | 206篇 |
2009年 | 174篇 |
2008年 | 232篇 |
2007年 | 226篇 |
2006年 | 213篇 |
2005年 | 174篇 |
2004年 | 131篇 |
2003年 | 134篇 |
2002年 | 96篇 |
2001年 | 66篇 |
2000年 | 53篇 |
1999年 | 57篇 |
1998年 | 28篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 18篇 |
1994年 | 13篇 |
1993年 | 14篇 |
1992年 | 17篇 |
1991年 | 22篇 |
1990年 | 13篇 |
1989年 | 23篇 |
1988年 | 15篇 |
1987年 | 25篇 |
1986年 | 11篇 |
1985年 | 23篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 12篇 |
1974年 | 8篇 |
排序方式: 共有4714条查询结果,搜索用时 0 毫秒
11.
12.
Thymosin-beta 4 gene. Preliminary characterization and expression in tissues, thymic cells, and lymphocytes 总被引:1,自引:0,他引:1
J Gómez-Márquez M Dosil F Segade X R Bustelo J G Pichel F Dominguez M Freire 《Journal of immunology (Baltimore, Md. : 1950)》1989,143(8):2740-2744
A cDNA for rat thymosin-beta 4 was used to investigate the expression of this gene in different tissues, thymic cells, and lymphocytes. Hybridization analysis of total RNA from 13 rat tissues demonstrated the presence of an 800 nucleotides-long mRNA in all the tissues surveyed, with the highest levels in spleen, thymus, and lung. Examination of thymic cells showed that the thymosin-beta 4 gene is predominantly expressed in thymocytes. The thymosin-beta 4 mRNA was also studied in Ig+ and Ig- lymphocytes, being fourfold more abundant in Ig- than Ig+ splenic lymphocytes, whereas similar levels were found in both types of blood cells. The analysis of RNA from T cells at different maturation stages evidenced slight differences in their thymosin-beta 4 mRNA content, indicating that thymosin-beta 4 gene expression is not clearly related to the differentiation process of T cells. All these results do not support the roles for thymosin-beta 4 in cellular immunity and differentiation of lymphoid cells, suggesting a more general function for this peptide. Preliminary characterization of the human beta 4 gene by restriction analysis disclosed a complicated pattern consistent with multiple genes and/or introns. The analysis of genomic DNA from different species ranging from humans to Escherichia coli showed that this gene is only highly conserved in mammals. 相似文献
13.
Maria de Fatima Bonaldo Pierre Jelenc Long Su Lee Lawton M. -T. Wu Dorothy Warburton Marcelo Bento Soares 《Human genetics》1996,97(4):441-452
A study was conducted on the feasibility of isolating genes and pseudogenes that map to chromosome 13 by a hybridization-based approach using a 13-specific library and pools of repeat-free cDNA clones. Five pairs of cDNA and chromosome 13 genomic clones were identified and characterized. Partial or full-length sequence was derived from all cDNAs, and database searches were performed for putative gene identification. Partial sequence was also obtained from the chromosome 13 genomic clones for comparison with those of the hybridizing cDNAs. As a result of these analyses we identified three genes, a putative homologue of a porcine mRNA encoding an unidentified hepatic protein, a putative homologue of a yeast integral membrane protein, and a gene for a translationally controlled tumor protein, and two processed pseudogenes, ribosomal proteins L23a and S3a. The latter was formerly identified as the v-fos transformation effector gene, Fte-1, and recently cited as a possible candidate for the BRCA2 gene on chromosome 13. All genes and pseudogenes were localized to cytogenetic bands by in situ hybridization of metaphase chromosomes with probes derived from the chromosome 13 genomic clones. 相似文献
14.
Immunogenic tumor cell variant P35 was obtained by mutagen treatment of mouse mastocytoma P815. It express a potent new antigen recognized by syngeneic cytolytic T lymphocytes (CTL). This antigen is the result of a point mutation in a gene that is expressed by most healthy cells. A decapeptide encoded by the region spanning the mutation sensitized P815 cells to the relevant CTL, whereas the homologous decapeptide corresponding to the normal sequence did not. Only the mutant decapeptide was capable of enhancing the expression of the Dd-presenting molecule at the cell surface, indicating that the mutation generates a motif which enables the antigenic peptide to bind to Dd.
Correspondence to: T. Boon. 相似文献
15.
Neuza Domingues André R. A. Marques Rita Diogo Almeida Calado Inês S. Ferreira Cristiano Ramos José Ramalho Maria I. L. Soares Telmo Pereira Luís Oliveira José R. Vicente Louise H. Wong Inês C. M. Simões Teresa M. V. D. Pinho e Melo Andrew Peden Cláudia Guimas Almeida Clare E. Futter Rosa Puertollano Winchil L. C. Vaz Otília V. Vieira 《Traffic (Copenhagen, Denmark)》2023,24(7):284-307
16.
Joana Pais De Faria Vitor H. Paiva Sara N. Veríssimo Catarina S. Lopes Rita Soares João Oliveira Ivo dos Santos Ana C. Norte Jaime A. Ramos 《Ibis》2023,165(1):312-321
Gulls, as largely flexible opportunistic individuals, have been increasingly breeding in many cities around the world, but it is still unclear whether urban habitats are of equal or higher quality than traditional natural habitats or represent an ecological trap with immediate reproductive benefits but longer-term detrimental consequences to health. Here we present a study of breeding parameters (nest density, egg dimensions, clutch size, hatching success and adult body condition) and physiological parameters (erythrocyte sedimentation rate, heterophil/lymphocyte ratio, haemoglobin concentration and measurements of oxidative stress) as indicators of the general health condition of Yellow-legged Gull Larus michahellis adults and chicks from natural and urban colonies. Yellow-legged Gulls in the largest urban area (Porto) laid smaller eggs and clutches, showed a significantly lower occurrence of inflammatory processes in chicks, and showed a slower early chick growth than in the natural colony of Deserta. This suggests that urban gulls might be facing important trade-offs between the advantages of breeding in lower density urban colonies, with fewer intraspecific interactions and a lower disease transmission probability, and the disadvantages of having an anthropogenic diet usually lower in nutritional value. 相似文献
17.
Certain partly ordered protein conformations, commonly called “moltenglobule states,” are widely believed to represent protein folding intermediates. Recentstructural studies of molten globule states ofdifferent proteins have revealed features whichappear to be general in scope. The emergingconsensus is that these partly ordered forms exhibit a high content of secondary structure, considerable compactness, nonspecific tertiary structure, and significant structural flexibility. These characteristics may be used to define ageneral state of protein folding called “the molten globule state,” which is structurally andthermodynamically distinct from both the native state and the denatured state. Despite exaatensive knowledge of structural features of afew molten globule states, a cogent thermodynamic argument for their stability has not yetbeen advanced. The prevailing opinion of thelast decade was that there is little or no enthalpy difference or heat capacity differencebetween the molten globule state and the unfolded state. This view, however, appears to beat variance with the existing database of protein structural energetics and with recent estimates of the energetics of denaturation of α-lactalbumin, cytochrome c, apomyoglobin, and T4 lysozyme. We discuss these four proteins at length. The results of structural studies, together with the existing thermodynamic values for fundamental interactions in proteins, provide the foundation for a structural thermodynamic framework which can account for the observed behavior of molten globule states. Within this framework, we analyze the physical basis for both the high stability of several molten globule states and the low probability of other protential folding intermediates. Additionally, we consider, in terms of reduced enthalpy changes and disrupted cooperative interactions, the thermodynamic basis for the apparent absence of a thermally induced, cooperative unfolding transition for some molten globule states. © 1993 Wiley-Liss, Inc. 相似文献
18.
Rafael Fogaça de Almeida Aline Castro Rodrigues Lucena Michel Batista Fabricio Klerynton Marchini Lyris Martins Franco de Godoy 《Proteomics》2023,23(16):2200230
Post-translational methylation of proteins, which occurs in arginines and lysines, modulates several biological processes at different levels of cell signaling. Recently, methylation has been demonstrated in the regulation beyond histones, for example, in the dynamics of protein-protein and protein-nucleic acid interactions. However, the presence and role of non-histone methylation in Trypanosoma cruzi, the etiologic agent of Chagas disease, has not yet been elucidated. Here, we applied mass spectrometry-based-proteomics (LC-MS/MS) to profile the methylproteome of T. cruzi epimastigotes, describing a total of 1252 methyl sites in 824 proteins. Functional enrichment and protein-protein interaction analysis show that protein methylation impacts important biological processes of the parasite, such as translation, RNA and DNA binding, amino acid, and carbohydrate metabolism. In addition, 171 of the methylated proteins were previously reported to bear phosphorylation sites in T. cruzi, including flagellar proteins and RNA binding proteins, indicating that there may be an interplay between these different modifications in non-histone proteins. Our results show that a broad spectrum of functions is affected by methylation in T. cruzi, indicating its potential to impact important processes in the biology of the parasite and other trypanosomes. 相似文献
19.
20.