全文获取类型
收费全文 | 2846篇 |
免费 | 176篇 |
出版年
2021年 | 17篇 |
2018年 | 45篇 |
2017年 | 27篇 |
2016年 | 52篇 |
2015年 | 94篇 |
2014年 | 125篇 |
2013年 | 123篇 |
2012年 | 191篇 |
2011年 | 181篇 |
2010年 | 106篇 |
2009年 | 96篇 |
2008年 | 133篇 |
2007年 | 153篇 |
2006年 | 136篇 |
2005年 | 131篇 |
2004年 | 102篇 |
2003年 | 108篇 |
2002年 | 134篇 |
2001年 | 72篇 |
2000年 | 70篇 |
1999年 | 47篇 |
1998年 | 34篇 |
1997年 | 31篇 |
1996年 | 24篇 |
1995年 | 18篇 |
1994年 | 19篇 |
1993年 | 27篇 |
1992年 | 47篇 |
1991年 | 45篇 |
1990年 | 45篇 |
1989年 | 40篇 |
1988年 | 42篇 |
1987年 | 35篇 |
1986年 | 33篇 |
1985年 | 24篇 |
1984年 | 23篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 18篇 |
1980年 | 16篇 |
1979年 | 24篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 15篇 |
1975年 | 20篇 |
1974年 | 13篇 |
1973年 | 18篇 |
1971年 | 28篇 |
1970年 | 24篇 |
1969年 | 22篇 |
排序方式: 共有3022条查询结果,搜索用时 31 毫秒
1.
Julia Nonnenmann Renate Stirner Julia Roider Maria C. Jung Kathrin Schr?dl Johannes R. Bogner Rika Draenert 《Journal of virology》2014,88(13):7678-7682
Myeloid-derived suppressor cells (MDSC) are immature myeloid cells with immunosuppressive function. Compared to the level in healthy controls (HC), no elevation of MDSC in chronic hepatitis C (cHEP-C) patients was found, and there was no difference in MDSC based on genotype or viral load (P > 0.25). Moreover, MDSC of cHEP-C patients inhibited CD8 T cell function as efficiently as MDSC of HC did. Since we detected neither quantitative nor qualitative differences in MDSC of cHEP-C patients relative to those of HC, we postulate that MDSC in peripheral blood are most likely not significant regarding immune dysfunction in cHEP-C. 相似文献
2.
3.
Thorsten Stoeck Harald Welter Dagmar Seitz-Bender Jürgen Kusch & Helmut J. Schmidt 《Zoologica scripta》2000,29(1):75-82
Morphologically indistinguishable sibling species also known as syngens are a characteristic taxonomic feature of the ciliate genus Paramecium . This has been convincingly demonstrated for the P. aurelia species complex. For a long time this feature has also been assumed for P. caudatum . Classical morphology based techniques of taxonomic analysis are often inefficient to study sibling specie. We therefore investigated 14 P. caudatum strains of seven supposedly different syngens using random amplified polymorphic DNA (RAPD)-fingerprinting and amplified ribosomal DNA restriction analyses (ARDRA, Riboprinting). The RAPD patterns revealed by five different random primers were similar between the different strains of the same syngen (similarity index ranging from 73 to 91%) and also between strains of supposedly different syngens (similarity index ranging from 67 to 91%). The amplified 18S rRNA-fragments of supposedly different syngens, as well as the restriction patterns of these fragments digested by five different endonucleases, were identical for all investigated P. caudatum stains. Consequently we reject the sibling species hypothesis for P. caudatum . According to our molecular analysis, P. caudatum is not a species complex, but just one single species. 相似文献
4.
5.
Effect of Energy Under-Reporting on Secular Trends of Dietary Patterns in a Mediterranean Population
Anna N. Funtikova Santiago F. Gomez Montserrat Fitó Roberto Elosua Alejandra A. Benítez-Arciniega Helmut Schr?der 《PloS one》2015,10(5)
BackgroundDiet is an important factor in the prevention of chronic diseases. Analysis of secular trends of dietary patterns can be biased by energy under-reporting. Therefore, the objective of the present study was to analyse the impact of energy under-reporting on dietary patterns and secular trends in dietary patterns defined by cluster analysis.ResultsThree clusters, “healthy”, “mixed” and “western”, were identified for both surveys. The “mixed” cluster was the predominant cluster in both surveys. Excluding EUR reduced the proportion of the “mixed” cluster up to 6.40% in the 2000 survey; this caused secular trend increase in the prevalence of the “mixed” pattern. Cross-classification analysis of all participants and PER’ data showed substantial agreement in cluster assignments: 68.7% in 2000 and 84.4% in 2005. Excluding EUR did not cause meaningful (≥15%) changes in the “healthy” pattern. It provoked changes in consumption of some food groups in the “mixed” and “western” patterns: mainly decreases of unhealthy foods within the 2000 and increases of unhealthy foods within the 2005 surveys. Secular trend effects of EUR were similar to those within the 2005 survey. Excluding EUR reversed the direction of secular trends in consumption of several food groups in PER in the “mixed” and “western” patterns.ConclusionsEUR affected distribution of participants between dietary patterns within and between surveys, secular trends in food group consumption and amount of food consumed in all, but not in the “healthy” pattern. Our findings emphasize threats from energy under-reporting in dietary data analysis. 相似文献
6.
T Helander T Timonen P Kalliom?ki J Schr?der 《Journal of immunology (Baltimore, Md. : 1950)》1991,147(6):2063-2067
Different populations of unstimulated and IL-2-activated PBL were used in binding and killing assays against somatic mouse/human lymphocyte cell hybrids containing different human chromosomes. Unstimulated PBL effector cells showed low binding and killing activity to both cell hybrids and mouse parental cell lines. However, IL-2-activated killer (LAK) cells bound strongly to, and effectively killed, cell hybrids carrying human chromosome 6, but were inefficient in both assays to mouse parental cells and to cell hybrids not carrying human chromosome 6. These results show that human LAK cells but not endogenous NK cells bind and kill mouse/human lymphocyte hybrids containing human chromosome 6. We thus suggest that LAK cells recognize ligands encoded by genes on chromosome 6. 相似文献
7.
8.
Jan Gundlach Achim Dickmanns Kathrin Schr?der-Tittmann Piotr Neumann Jan Kaesler Jan Kampf Christina Herzberg Elke Hammer Frank Schwede Volkhard Kaever Kai Tittmann J?rg Stülke Ralf Ficner 《The Journal of biological chemistry》2015,290(5):3069-3080
The cyclic dimeric AMP nucleotide c-di-AMP is an essential second messenger in Bacillus subtilis. We have identified the protein DarA as one of the prominent c-di-AMP receptors in B. subtilis. Crystal structure analysis shows that DarA is highly homologous to PII signal transducer proteins. In contrast to PII proteins, the functionally important B- and T-loops are swapped with respect to their size. DarA is a homotrimer that binds three molecules of c-di-AMP, each in a pocket located between two subunits. We demonstrate that DarA is capable to bind c-di-AMP and with lower affinity cyclic GMP-AMP (3′3′-cGAMP) but not c-di-GMP or 2′3′-cGAMP. Consistently the crystal structure shows that within the ligand-binding pocket only one adenine is highly specifically recognized, whereas the pocket for the other adenine appears to be promiscuous. Comparison with a homologous ligand-free DarA structure reveals that c-di-AMP binding is accompanied by conformational changes of both the fold and the position of the B-loop in DarA. 相似文献
9.