全文获取类型
收费全文 | 6796篇 |
免费 | 590篇 |
国内免费 | 6篇 |
出版年
2023年 | 17篇 |
2022年 | 84篇 |
2021年 | 165篇 |
2020年 | 85篇 |
2019年 | 95篇 |
2018年 | 162篇 |
2017年 | 126篇 |
2016年 | 217篇 |
2015年 | 371篇 |
2014年 | 418篇 |
2013年 | 476篇 |
2012年 | 590篇 |
2011年 | 533篇 |
2010年 | 328篇 |
2009年 | 257篇 |
2008年 | 413篇 |
2007年 | 393篇 |
2006年 | 320篇 |
2005年 | 318篇 |
2004年 | 311篇 |
2003年 | 212篇 |
2002年 | 223篇 |
2001年 | 209篇 |
2000年 | 146篇 |
1999年 | 116篇 |
1998年 | 59篇 |
1997年 | 36篇 |
1996年 | 49篇 |
1995年 | 33篇 |
1994年 | 32篇 |
1993年 | 25篇 |
1992年 | 56篇 |
1991年 | 36篇 |
1990年 | 40篇 |
1989年 | 35篇 |
1988年 | 33篇 |
1987年 | 37篇 |
1986年 | 24篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 20篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 21篇 |
1978年 | 20篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1974年 | 17篇 |
1969年 | 13篇 |
排序方式: 共有7392条查询结果,搜索用时 46 毫秒
991.
Described are further studies directed towards elucidating the mechanism of the nitric oxide reduction of the copper(II) model system, Cu(dmp)2(2+) (I, dmp=2,9-dimethyl-1,10-phenanthroline). The reaction of I with NO in methanol results in the formation of Cu(dmp)2+ (II) and methyl nitrite (CH3ONO), with a second order rate constant kNO=38.1 M-1 s-1 (298K). The activation parameters for this reaction in buffered aqueous medium were measured to be DeltaH(double dagger)=41.6 kJ/mol and DeltaS(double dagger)=-82.7 kJ/mol deg. The addition of azide ion (N3-) as a competing nucleophile results in a marked acceleration in the rate of the copper(II) reduction. Analysis of the kinetics for the NO reduction of the bulkier Cu(dpp)(2)2+ (IV, dpp=2,9-diphenyl-1,10-phenanthroline) and the stronger oxidant, Cu(NO2-dmp)2(2+) (V, NO2-dmp=5-nitro-2,9-dimethyl-1,10-phenanthroline), gave the second order rate constants kNO=21.2 and 29.3 M-1 s-1, respectively. These results argue against an outer sphere electron transfer pathway and support a mechanism where the first step involves the formation of a copper-nitrosyl (Cu(II)-NO or Cu(I)-NO+) adduct. This would be followed by the nucleophilic attack on the bound NO and the labilization of RONO to form the nitrite products and the cuprous complex. 相似文献
992.
Law Peter K. Haider Kh. Fang G. Jiang S. Chua F. Lim Y.T. Sim E. 《Molecular and cellular biochemistry》2004,263(1):173-178
Bioengineering the regenerative heart may provide a novel treatment for heart failure. On May 14, 2002, a 55-year-old man suffering from ischemic myocardial infarction received 25 injections carrying 465 million cGMP-produced pure myoblasts into his myocardium after coronary artery bypass grafting. As on August 28, 2002, his EKG was normal and showed no arrhythmia. His ejection fraction increased by 13%. He no longer experienced shortness of breath and angina as he did before the treatment. Three myogenesis mechanisms were elucidated with 17 human/porcine xenografts using cyclosporine as immunosuppressant. Some myoblasts developed to become cardiomyocytes. Others transferred their nuclei into host cardiomyocytes through natural cell fusion. As yet others formed skeletal myofibers with satellite cells. De novo production of contractile filaments augmented the heart contractility. Human myoblasts transduced with VEGF165 gene produced six times more capillaries in porcine myocardium than in placebo. Xenograft rejection was not observed for up to 20 weeks despite cyclosporine discontinuation at 6 weeks. Pros and cons of autografts vs. allografts are compared to guide future development of heart cell therapy. (Mol Cell Biochem 263: 173–178, 2004) 相似文献
993.
994.
Characterization of an Escherichia coli O157:H7 O-Antigen Deletion Mutant and Effect of the Deletion on Bacterial Persistence in the Mouse Intestine and Colonization at the Bovine Terminal Rectal Mucosa
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Haiqing Sheng Ji Youn Lim Maryann K. Watkins Scott A. Minnich Carolyn J. Hovde 《Applied microbiology》2008,74(16):5015-5022
995.
Lim do H Kim J Kim S Carthew RW Lee YS 《Biochemical and biophysical research communications》2008,371(3):525-530
The Drosophila RNase III enzyme Dicer-2 processes double-stranded RNA (dsRNA) precursors into small interfering RNAs (siRNAs). It also interacts with the siRNA product and R2D2 protein to facilitate the assembly of an RNA-induced silencing complex (RISC) that mediates RNA interference. Here, we characterized six independent missense mutations in the dicer-2 gene. Four mutations (P8S, L188F, R269W, and P365L) in the DExH helicase domain reduced dsRNA processing activity. Two mutations were located within an RNase III domain. P1496L caused a loss of dsRNA processing activity comparable to a null dicer-2 mutation. A1453T strongly reduced both dsRNA processing and RISC activity, and decreased the levels of Dicer-2 and R2D2 proteins, suggesting that this mutation destabilizes Dicer-2. We also found that the carboxyl-terminal region of R2D2 is essential for Dicer-2 binding. These results provide further insight into the structure-function relationship of Dicer, which plays a critical role in the siRNA pathway. 相似文献
996.
Lim SY Chung WY Lee HK Park MS Park HG 《Biochemical and biophysical research communications》2008,376(4):633-636
The fluorogenic 1,3-Huisgen dipolar cycloaddition reaction was used as part of a novel immobilization strategy of PNA capture probes on a microarray. By using this click chemistry, azidocoumarin-anchored PNA probes were immobilized on phenyl acetylene-modified glass slides with the simultaneous generation of the fluorescent triazolylcoumarin moiety. Since the emitting moieties are generated in the immobilization reaction itself, fluorescent signals can be used to directly monitor the integrity of immobilization in a nondestructive manner. By using this strategy, PNA microarrays were prepared and successfully employed to perform microarray-based diagnosis of selected mutations in the breast cancer susceptibility gene BRCA1. 相似文献
997.
Cnu is a nucleoid protein that has a high degree of sequence homology with Hha/YmoA family proteins, which bind to chromatin and regulate the expression of Escherichia coli virulence genes in response to changes in temperature or ionic strength. Here, we determined its solution structure and dynamic properties and mapped H-NS binding sites. Cnu consists of three alpha helices that are comparable with those of Hha, but it has significant flexibility in the C-terminal region and lacks a short alpha helix present in Hha. Upon increasing ionic strength, the helical structure of Cnu is destabilized, especially at the ends of the helices. The dominant H-NS binding sites, located at helix 3 as in Hha, reveal a common structural platform for H-NS binding. Our results may provide structural and dynamic bases for the similarity and dissimilarity between Cnu and Hha functions. 相似文献
998.
999.
Hee-Kyun Lim Pham Tuan Linh Cheong-Hee Hong Kyeong-Ho Kim Jong-Seong Kang 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,755(1-2)
The enantiomeric separation of metoprolol and its metabolites in human urine was undertaken using capillary electrophoresis (CE). Resolution of the enantiomers was achieved using carboxymethyl-β-cyclodextrin (CM-β-CD) as the chiral selector. A 100-mM acetate buffer (pH 4.0) containing 5% 2-propanol and 10 mM CM-β-CD resulted in the optimum separation of the metoprolol enantiomers and its acidic metabolite in human urine. Following a single metoprolol oral administration of 100 mg racemic metoprolol tartrate, stereoselective pharmacokinetic analysis showed that urinary acidic metabolite 3 of metoprolol accounted for 62.3% of the dose with an R/S ratio of 1.23 and urinary unchanged metoprolol 1 accounted for 6.3% of the dose with an R/S ratio of 0.72. 相似文献
1000.