全文获取类型
收费全文 | 99371篇 |
免费 | 8298篇 |
国内免费 | 6658篇 |
出版年
2024年 | 185篇 |
2023年 | 1120篇 |
2022年 | 2637篇 |
2021年 | 4581篇 |
2020年 | 2986篇 |
2019年 | 3693篇 |
2018年 | 3698篇 |
2017年 | 2699篇 |
2016年 | 3762篇 |
2015年 | 5760篇 |
2014年 | 6732篇 |
2013年 | 7506篇 |
2012年 | 8683篇 |
2011年 | 8009篇 |
2010年 | 4870篇 |
2009年 | 4331篇 |
2008年 | 5211篇 |
2007年 | 4681篇 |
2006年 | 4022篇 |
2005年 | 3434篇 |
2004年 | 2946篇 |
2003年 | 2647篇 |
2002年 | 2360篇 |
2001年 | 2043篇 |
2000年 | 1977篇 |
1999年 | 1832篇 |
1998年 | 1073篇 |
1997年 | 976篇 |
1996年 | 1001篇 |
1995年 | 907篇 |
1994年 | 855篇 |
1993年 | 644篇 |
1992年 | 977篇 |
1991年 | 774篇 |
1990年 | 716篇 |
1989年 | 613篇 |
1988年 | 472篇 |
1987年 | 404篇 |
1986年 | 369篇 |
1985年 | 334篇 |
1984年 | 240篇 |
1983年 | 215篇 |
1982年 | 130篇 |
1981年 | 127篇 |
1980年 | 91篇 |
1979年 | 149篇 |
1978年 | 85篇 |
1977年 | 95篇 |
1975年 | 113篇 |
1974年 | 116篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Plant Molecular Biology - 相似文献
2.
Plant somatic cells have the capability to switch their cell fates from differentiated to undifferentiated status under proper
culture conditions, which is designated as totipotency. As a result, plant cells can easily regenerate new tissues or organs
from a wide variety of explants. However, the mechanism by which plant cells have such remarkable regeneration ability is
still largely unknown. In this study, we used a set of meristem-specific marker genes to analyze the patterns of stem cell
differentiation in the processes of somatic embryogenesis as well as shoot or root organogenesis in vitro. Our studies furnish preliminary and important information on the patterns of the de novo stem cell differentiation during various types of in vitro organogenesis. 相似文献
3.
Wen-Yeh Hsieh Tang-Ching Kuan Kun-Shan Cheng Yan-Chiou Liao Mu-Yuan Chen Pei-Heng Lin Yuan-Chang Hsu Chen-Yi Huang Wei-Hua Hsu Sheng-Yao Yu Chih-Sheng Lin 《International journal of biological sciences》2012,8(8):1197-1205
Objective: Pleural effusion is common problem, but the rapid and reliable diagnosis for specific pathogenic effusions are lacking. This study aimed to identify the diagnosis based on clinical variables to differentiate pleural tuberculous exudates from other pleural effusions. We also investigated the role of renin-angiotensin system (RAS) and matrix metalloproteinase (MMPs) in the pathogenesis of pleural exudates.Experimental design: The major components in RAS and extracellular matrix metabolism, including angiotensin converting enzyme (ACE), ACE2, MMP-2 and MMP-9 activities, were measured and compared in the patients with transudative (n = 45) and exudative (n = 80) effusions. The exudative effusions were come from the patients with tuberculosis (n = 20), pneumonia (n = 32), and adenocarcinoma (n = 28).Results: Increased ACE and equivalent ACE2 activities, resulting in a significantly increased ACE/ACE2 ratio in exudates, were detected compared to these values in transudates. MMP-9 activity in exudates was significantly higher than that in transudates. The significant correlation between ACE and ACE2 activity that was found in transudates was not found in exudates. Advanced analyses showed significantly increased ACE and MMP-9 activities, and decreased ACE2 activity in tuberculous pleural effusions compared with those in pneumonia and adenocarcinoma effusions. The results indicate that increased ACE and MMP-9 activities found in the exudates were mainly contributed from a higher level of both enzyme activities in the tuberculous pleural effusions.Conclusion: Interplay between ACE and ACE2, essential functions in the RAS, and abnormal regulation of MMP-9 probably play a pivotal role in the development of exudative effusions. Moreover, the ACE/ACE2 ratio combined with MMP-9 activity in pleural fluid may be potential biomarkers for diagnosing tuberculous pleurisy. 相似文献
4.
5.
6.
7.
8.
A Yersinia pseudotuberculosis protein which cross-reacts with HLA-B27 总被引:10,自引:0,他引:10
J H Chen D H Kono Z Yong M S Park M M Oldstone D T Yu 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(9):3003-3011
The most-debated question in the investigation of the spondyloarthropathies has been whether there is molecular mimicry between host HLA-B27 antigens and the arthritis-causing pathogens. We have generated a monoclonal anti-HLA-B27 antibody in our laboratory and have used a radioimmunoassay to screen a panel of bacterial species. Two strains of Yersinia pseudotuberculosis were found to be highly reactive. The cross-reactive Yersinia component was identified by Western blot to be a 19,000 component. A preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis chromatography apparatus was constructed to isolate milligram quantities of this component. To verify that the component carried the HLA-B27-specific epitope, rabbits were hyperimmunized with the purified materials. Affinity-purified antibodies from one of the immunized rabbits indeed carried anti-HLA-B27 activity. Last, antibodies generated against synthetic peptides derived from the HLA-B27.1 amino acid sequence were tested against the Yersinia component. Positive reactivity was found with antibodies generated against a peptide spanning residues 69-83 of the HLA-B27.1 protein. Since this resides in the segment responsible for the allotypic specificity of the antigen, these experiments establish the presence of molecular mimicry to a high degree of confidence. 相似文献
9.
Ting‐Hang Liu Chia‐Lin Chyan Feng‐Yin Li Ying‐Jie Chen Jason T. C. Tzen 《Biotechnology progress》2011,27(6):1760-1767
It has been demonstrated that caleosin alone is sufficient to stabilize artificial oil bodies. A series of recombinant caleosins, mutated with 3, 5, 8, 11, 13, 15, and 17 extra Lys residues and over‐expressed in Escherichia coli, were used as carrier proteins to render biotin as a hapten on the surface of artificial oil bodies for antibody production. Biotinylation levels of the recombinant caleosins were step‐wisely elevated as the number of extra Lys residues increased, and the biotinylated Lys residues were identified by mass spectrometric analysis. Polyclonal antibodies against biotin were successfully generated in rats injected with artificial oil bodies constituted with each of the biotinylated caleosins. Moreover, those generated via the biotinylated caleosins with eight or more extra Lys residues no longer recognized caleosin. It appears that engineered Lys‐rich caleosins are suitable carrier proteins for the production of antibodies against small molecules. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011 相似文献
10.