全文获取类型
收费全文 | 19412篇 |
免费 | 1432篇 |
国内免费 | 1577篇 |
专业分类
22421篇 |
出版年
2024年 | 48篇 |
2023年 | 330篇 |
2022年 | 664篇 |
2021年 | 1094篇 |
2020年 | 677篇 |
2019年 | 914篇 |
2018年 | 808篇 |
2017年 | 569篇 |
2016年 | 880篇 |
2015年 | 1162篇 |
2014年 | 1473篇 |
2013年 | 1540篇 |
2012年 | 1838篇 |
2011年 | 1594篇 |
2010年 | 1029篇 |
2009年 | 883篇 |
2008年 | 965篇 |
2007年 | 822篇 |
2006年 | 677篇 |
2005年 | 595篇 |
2004年 | 493篇 |
2003年 | 444篇 |
2002年 | 390篇 |
2001年 | 295篇 |
2000年 | 298篇 |
1999年 | 306篇 |
1998年 | 197篇 |
1997年 | 199篇 |
1996年 | 191篇 |
1995年 | 151篇 |
1994年 | 137篇 |
1993年 | 96篇 |
1992年 | 142篇 |
1991年 | 115篇 |
1990年 | 102篇 |
1989年 | 77篇 |
1988年 | 52篇 |
1987年 | 31篇 |
1986年 | 28篇 |
1985年 | 42篇 |
1984年 | 18篇 |
1983年 | 23篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
我们采用RT-PCR方法克隆了2个APl同源基因全长cDNA,分别命名为MAPl-1(GenBank accession No.FJ529206)和MAPl-2(GenBank accession No.FJ529207).MAPl-1编码247个氨基酸,开放阅读框长度为741 bp,蛋白质分子量为28.54kD,等电点为8.31;MAPl-2编码248个氨基酸,开放阅读框长度为744 bp,蛋白质分子量为28.78 kD,等电点为8.70.同源性分析表明,它们的核苷酸序列与其它木本植物APl同源基因的一致性为72%~81%.实验分析表明,MAPl-1和MAPl-2第1至第61个氨基酸含有一个MADS盒结构域,第88至第178个为K盒结构域;两个基因均定位于细胞核,且功能位点分布存在着不同,推测这两个基因在花器官发育过程中的功能存在差异.蛋白二级结构预测显示,MAPl-1蛋白有12个a-螺旋,4个β折叠区,14个β-转角;而MAPl-2蛋白有11个a-螺旋,5个β折叠区,15个β-转角:其大多数氨基酸具有亲水性.本研究有助于进一步了解芒果的开花分子机理及成花的生物学发育阶段. 相似文献
73.
74.
Aptamer selection for the detection of Escherichia coli K88 总被引:2,自引:0,他引:2
In this study, the first group of single-stranded DNA aptamers that are highly specific to enterotoxigenic Escherichia coli (ETEC) K88 was obtained from an enriched oligonucleotide pool by the SELEX (Systematic Evolution of Ligands by Exponential Enrichment) procedure, during which the K88 fimbriae protein was used as the target and bovine serum albumin as counter targets. These aptamers were applied successfully in the detection of ETEC K88. They were then grouped under different families based on the similarity of their secondary structure and the homology of their primary sequence. Four sequences from different families were deliberately chosen for further characterization by fluorescence analysis. Having the advantage of high sensitivity, fluorescence photometry was selected as single-stranded DNA quantification method during the SELEX process. Aptamers with the highest specificity and affinity were analyzed to evaluate binding ability with E. coli. Since ETEC K88 is the only type of bacterium that expressed abundant K88 fimbriae, the selected aptamers against the K88 fimbriae protein were able to specifically identify ETEC K88 among other bacteria. This method of detecting ETEC K88 by aptamers can also be applied to bacteria other than ETEC K88. 相似文献
75.
76.
Jian Xiao Xiaoyan Zhu Bin He Yufeng Zhang Bo Kang Zhinong Wang Xin Ni 《Journal of biomedical science》2011,18(1):35
Background
Autophagy plays a significant role in myocardial ischemia-reperfusion (IR) injury. So it is important to inhibit autophagy to protect cardiomyocytes besides anti-apoptosis. MiRNA has been demonstrated to protect cardiomyocytes against apoptosis during IR, while whether it has anti-autophagy effect has not been known. The aim of this study was to investigate whether miR-204 regulated autophagy by regulating LC3-II protein, which is the marker of autophagosome during myocardial IR injury. 相似文献77.
Separation strategies based on size-selective precipitation of DNA fragments with polyethylene glycol (PEG) have been used for achieving desired DNA interval in automated sample preparation for next-generation sequencing. By varying PEG concentration, DNA fragments of different sizes can be precipitated onto surfaces of carboxyl-coated paramagnetic particles selectively, and therefore, the desired DNA interval can be obtained. However, one of the crucial points in this approach is to determine the critical PEG concentration for DNA fragment of a certain size. The aim of this work was to develop a convenient and reliable method for accurately determining the critical PEG concentration. In our method, at a fixed concentration of sodium chloride (NaCl), recovered DNA samples obtained with different PEG concentrations were directly quantified, and their concentrations as a function of the PEG concentration were fitted by the logistic function. The critical PEG value was easily and accurately determined from the fitted logistic function. The repeatability and stability of the critical PEG value were assessed, showing an excellent reliability of the method. Based on this method, critical PEG values of different-size DNA fragments were determined at different NaCl concentrations. The effectiveness of the method was also demonstrated by selective precipitation of DNA fragments. 相似文献
78.
79.
80.
Ji-Fu Wei Xiao-long Wei Qiu-Yu Chen Tian Huang Li-Ya Qiao Wan-Yu Wang Yu-Liang Xiong Shao-Heng He 《Biochimica et Biophysica Acta (BBA)/General Subjects》2006
A novel phospholipase A2 (PLA2) with Asn at its site 49 was purified from the snake venom of Protobothrops mucrosquamatus by using SP-Sephadex C25, Superdex 75, Heparin-Sepharose (FF) and HPLC reverse-phage C18 chromatography and designated as TM-N49. It showed a molecular mass of 13.875 kDa on MALDI-TOF. TM-N49 does not possess enzymatic, hemolytic and hemorrhagic activities. It fails to induce platelet aggregation by itself, and does not inhibit the platelet aggregation induced by ADP. However, it exhibits potent myotoxic activity causing inflammatory cell infiltration, severe myoedema, myonecrosis and myolysis in the gastrocnemius muscles of BALB/c mice. Phylogenetic analysis found that that TM-N49 combined with two phospholipase A2s from Trimeresurus stejnegeri, TsR6 and CTs-R6 cluster into one group. Structural and functional analysis indicated that these phospholipase A2s are distinct from the other subgroups (D49 PLA2, S49 PLA2 and K49 PLA2) and represent a unique subgroup of snake venom group II PLA2, named N49 PLA2 subgroup. 相似文献