全文获取类型
收费全文 | 12696篇 |
免费 | 988篇 |
国内免费 | 919篇 |
专业分类
14603篇 |
出版年
2024年 | 35篇 |
2023年 | 167篇 |
2022年 | 387篇 |
2021年 | 676篇 |
2020年 | 458篇 |
2019年 | 533篇 |
2018年 | 579篇 |
2017年 | 372篇 |
2016年 | 523篇 |
2015年 | 772篇 |
2014年 | 910篇 |
2013年 | 900篇 |
2012年 | 1168篇 |
2011年 | 1058篇 |
2010年 | 595篇 |
2009年 | 519篇 |
2008年 | 641篇 |
2007年 | 496篇 |
2006年 | 468篇 |
2005年 | 395篇 |
2004年 | 314篇 |
2003年 | 273篇 |
2002年 | 249篇 |
2001年 | 219篇 |
2000年 | 210篇 |
1999年 | 227篇 |
1998年 | 112篇 |
1997年 | 112篇 |
1996年 | 96篇 |
1995年 | 119篇 |
1994年 | 112篇 |
1993年 | 80篇 |
1992年 | 119篇 |
1991年 | 101篇 |
1990年 | 91篇 |
1989年 | 63篇 |
1988年 | 70篇 |
1987年 | 50篇 |
1986年 | 51篇 |
1985年 | 62篇 |
1984年 | 33篇 |
1983年 | 19篇 |
1982年 | 25篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 14篇 |
1978年 | 15篇 |
1977年 | 11篇 |
1974年 | 11篇 |
1968年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
In chloroplasts, tetramethyl-p-hydroquinone supports high rates of phosphorylation-coupled, noncyclic electron flow through Photosystem I to methylviologen. The reaction is totally sensitive to dibromothymoquinone, indicating an electron donation to the plastoquinone region of the photosynthetic chain. The uncoupled electron flow rate exceeds 1000 μequivalents per hour per mg chlorophyll. The phosphorylation efficiency () at the optimal pH of 8 is 0.6–0.65. Presumably this ratio represents the efficiency of energy coupling in the electron transfer step plastoquinone → cytochrome f. 相似文献
3.
An iso-random Bi Bi mechanism has been proposed for adenylate kinase. In this mechanism, one of the enzyme forms can bind the substrates MgATP and AMP, whereas the other form can bind the products MgADP and ADP. In a catalytic cycle, the conformational changes of the free enzyme and the ternary complexes are the rate-limiting steps. The AP(5)A inhibition equations derived from this mechanism show theoretically that AP(5)A acts as a competitive inhibitor for the forward reaction and a mixed noncompetitive inhibitor for the backward reaction. 相似文献
4.
5.
Isolation and characterization of a new 40-kilodalton protein from bovine cardiac muscle 总被引:1,自引:0,他引:1
A new protein having a subunit weight of 40,000 has been purified from myosin-extracted bovine cardiac myofibrils. Its amino acid composition and isoelectric point are distinct from actin, eu-actinin, and a variety of sarcoplasmic proteins of similar size. Affinity-purified antibodies made to this protein only react with a single 40-kDa protein band from cardiac myofibrils on immunoblots. The anti-40-kDa protein also shows cross-reactivities with cardiac myofibrils from rabbits, rats, and chickens. Immunofluorescence studies demonstrate that the 40-kDa protein is localized at the Z-bands of cardiac myofibrils and at the intercalated discs. The antibody did not react with skeletal muscle myofibrils by immunofluorescence or immunoblotting. It appears that the 40-kDa protein may play a role in the strong attachments between adjacent myofibrils in cardiac muscle. 相似文献
6.
Barry W. Duceman Dolly Ness Roberto Rende Michael J. Chorney Rakesh Srivastava Daniel S. Greenspan Julian Pan Sherman M. Weissman F. Carl Grumet 《Immunogenetics》1986,23(2):90-99
The JY328 clone was identified in a human genomic library using cDNA corresponding to mRNA for HLA-B7 as a probe. The L/328 cell line was established by cotransformation of mouse Ltk– cells with the herpes thymidine kinase gene and clone JY328. On Northern blots, RNA from,L/328 strongly hybridized to an HLA class I probe, and an antigen was recognized by an anti-HLA class I framework antibody on the cell surface. A DNA probe corresponding to a segment of intron 7 was developed by comparing the nucleotide sequence of clone JY328 with that of other HLA class I-type genes. Using the radiolabeled probe to screen Southern blots of DNA from families with siblings exhibiting intra-HLA recombinations, a restriction fragment length polymorphism was revealed —a 1.4 kb BstE II band not present in all individuals. A corresponding fragment was apparent in the base sequence of clone JY328. The occurrence of this band on Southern blots established that JY328 maps distinct from and centromeric to the HLA-C locus and near to the HLA-B locus. Antibody absorption studies and cytotoxicity tests indicated that the JY328 gene product was not an HLA-B antigen but that it did specifically absorb CW7-specific antibody. In sum, these results suggest a novel, polymorphic HLA class I gene which expresses a product serologically similar to HLA-Cw7 but which does not map within the corresponding locus. 相似文献
7.
T. C. Pan T. H. Lin C. L. Tseng M. H. Yang C. W. Huang 《Biological trace element research》1993,39(2-3):117-128
Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Though extensive epidemiological
study has implicated that high arsenic content in artesian well water of the endemic area, bears some important connection
with the disease, the etiology of the disease is still unknown. In this study, attention is paid to multielement determination
in order to find out whether the trace elements in hair of Blackfoot disease patients are different from those of the controls.
Experimental results indicate that the concentrations of As and Se in hair of patients are significantly higher than those
of the controls, but Ca and Zn are significantly lower than those of the controls. The possible connection of these elements
with the etiology of the disease is discussed. 相似文献
8.
9.
The present paper describes isolation and purification ofa-hemolysin ofEscherichia coli. The optimum production medium was found to be the Todd—Hewitt broth. Out of thirteen fractions obtained after separation
on Sephadex G-200, two fractions possessed the highest relative specific activity. 相似文献
10.
本文选用金黄地鼠的微血管,利用显微高速摄影技术,放大微观流场和血细胞,连续地“冻结”短瞬间的变化状态,把物理图象呈现在胶片上,经图像分析和数据处理,从定性及定量方面研究血液微流变学,为生命科学和医学研究提供了又一种新的方法。 相似文献