全文获取类型
收费全文 | 1649篇 |
免费 | 124篇 |
国内免费 | 61篇 |
出版年
2023年 | 7篇 |
2022年 | 48篇 |
2021年 | 69篇 |
2020年 | 40篇 |
2019年 | 57篇 |
2018年 | 56篇 |
2017年 | 42篇 |
2016年 | 71篇 |
2015年 | 106篇 |
2014年 | 115篇 |
2013年 | 117篇 |
2012年 | 150篇 |
2011年 | 121篇 |
2010年 | 82篇 |
2009年 | 68篇 |
2008年 | 69篇 |
2007年 | 82篇 |
2006年 | 64篇 |
2005年 | 73篇 |
2004年 | 55篇 |
2003年 | 57篇 |
2002年 | 48篇 |
2001年 | 38篇 |
2000年 | 20篇 |
1999年 | 32篇 |
1998年 | 16篇 |
1997年 | 7篇 |
1996年 | 11篇 |
1995年 | 13篇 |
1994年 | 15篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 13篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 9篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1980年 | 1篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有1834条查询结果,搜索用时 62 毫秒
171.
Three mono- and dinuclear nickel complexes with dichalcogenolate o-carboranyl ligands were synthesized and characterized by X-ray crystallography. The reactions of Ni(COD)2(COD=1,5-octadiene) with [(THF)3LiE2C2B10H10Li(THF)]2 (E=S, Se) in THF in the presence of air in different ratios afforded the mono- and dinuclear nickel complexes of formulae Li(THF)4]2[Ni(E2C2B10H10)2] (E=S, 1a; E=Se, 1b) and [Li(THF)4]2[Ni2(E2C2B10H10)3] (E=S, 2a; E=Se, 2b). In 2a, two nickel atoms are connected by one chalcogen (η1,η2-S2C2B10H10) bridging ligand with strong metal-metal interaction. Complex of formula (PPh3)2Ni(S2C2B10H10) · 0.5THF (3a) was also obtained from the reaction of (PPh3)2NiCl2 and [(THF)3LiS2C2B10H10Li(THF)]2. 相似文献
172.
Miyazaki M Dobrzyn A Man WC Chu K Sampath H Kim HJ Ntambi JM 《The Journal of biological chemistry》2004,279(24):25164-25171
173.
Determination of the topological shape of integral membrane protein light-harvesting complex LH2 from photosynthetic bacteria in the detergent solution by small-angle X-ray scattering
下载免费PDF全文
![点击此处可从《Biophysical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The topological shape of the integral membrane protein light-harvesting complex LH2 from photosynthetic bacteria Rhodobacter spheroides 2.4.1 in detergent solution has been determined from synchrotron small-angle X-ray scattering data using direct curve-fitting by the ellipsoid, ab initio shape determination methods of simulated annealing algorithm and multipole expansion, respectively. The results indicate that the LH2 protein in aqueous solution is encapsulated by a monolayered detergent shell. The detergent-stabilized structure has the shape of an oblate plate, with a thickness of 40 A, a long axis of 110 A, and a short axis of 85 A. After correction for the detergent shell, the shape of the LH2 core is also an oblate plate with a height of 40 A, a long axis of 80 A, and a short axis of 55 A. In contrast to the cylindrical crystal structure with a height of 40 A and a diameter of 68 A, the molecular shape of the LH2 complex in detergent solution clearly deviates from the ringlike crystal structure, with an eccentricity found to be 0.59-consistent with the result of single molecular spectroscopy study of the isolated single LH2 molecules. 相似文献
174.
In this paper, we analyzed the pH-induced changes in the conformational states of the manganese-stabilizing protein (MSP) of photosystem II. Distinct conformational states of MSP were identified using fluorescence spectra, far-UV circular dichroism, and pressure-induced unfolding at varying suspension pH values, and four different conformational states of MSP were clearly distinguished using the center of fluorescence spectra mass when suspension pH was altered from 2 to 12. MSP was completely unfolded at a suspension pH above 11 and partly unfolded below a pH of 3. Analysis of the center of fluorescence spectral mass showed that the MSP structure appears stably folded around pH 6 and 4. The conformational state of MSP at pH 4 seems more stable than that at pH 6. Studies of peak positions of tryptophan fluorescence and MSP-bound 1-anilinonaphthalene-8-sulfonic acid fluorescence spectra supported this observation. A decrease in the suspension pH to 2 resulted in significant alterations in the MSP structure possibly because of protonation of unprotonated residues at lower pH, suggesting the existence of a large number of unprotonated amino acid residues at neutral pH possibly useful for proton transport in oxygen evolution. The acidic pH-induced conformational changes of MSP were reversible upon increase of pH to neutral pH; however, N-bromosuccinimide modification of tryptophan (Trp241) blocks the recovery of pH-induced conformational changes in MSP, implying that Trp241 is a key residue for the unfolded protein to form a functional structure. Thus, pH-induced structural changes of stable MSP (pH 6-4) may be utilized to analyze its functionality as a cofactor for oxygen evolution. 相似文献
175.
176.
We propose a general method of designing an experiment when there are potentially failing trials. We use polynomial models and the Michaelis-Menten model as examples and construct different types of optimal designs under a broad class of response probability functions. We show that the usual optimal designs, that assume all observations are available at the end of the experiment, can be quite inefficient if the anticipated missingness pattern is not accounted for at the design stage. We also investigate robustness properties of the proposed designs to specification of their nominal values and the response probability functions. 相似文献
177.
178.
Song Q Naidong W 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2006,830(1):135-142
Bioanalytical methods using liquid/liquid extraction (LLE) and liquid chromatography with electrospray tandem mass spectrometry (LC-MS/MS) are widely used. The organic extracts need to be evaporated and reconstituted, hampering further improvement of throughput and automation. In this study, we demonstrated a novel approach of eliminating these two steps in 96-well LLE by using hydrophilic interaction chromatography with MS/MS (HILIC-MS/MS) on silica column with high organic/low aqueous mobile phase. Omeprazole, its metabolite 5-OH omeprazole, and internal standard desoxyomeprazole, were extracted from 0.05 ml of human plasma using 0.5 ml of ethyl acetate in a 96-well plate. A portion (0.1 ml) of the ethyl acetate extract was diluted with 0.4 ml of acetonitrile and 10 microl was injected onto a Betasil silica column (50 mm x 3.0 mm, 5 microm) and detected by API 3000 and 4000 with (+) ESI. Mobile phase with linear gradient elution consists of acetonitrile, water, and formic acid (from 95:5:0.1 to 73.5:26.5:0.1 in 2 min). The flow rate was 1.5 ml/min with total run time of 2.75 min. The method was validated for a low limit of quantitation at 2.5 ng/ml for both analytes. The method was also validated for specificity, reproducibility, stability and recovery. Lack of adverse matrix effect and carry-over was also demonstrated. The inter-day precision and accuracy of the quality control samples at low, medium and high concentration levels were <4.4% relative standard deviation (R.S.D.) and 4.1% relative error (R.E.) for omeprazole, and 4.5% R.S.D. and 5.6% R.E. for 5-OH omeprazole, respectively. 相似文献
179.
Alterations in DNA methylation and genome structure in two rice mutant lines induced by high pressure 总被引:2,自引:0,他引:2
Sile Shen Zhenwei Wang Xiaohui Shan Hua Wang Ling Li Xuyun Lin Likun Long Kenan Weng Bao Liu Guangtian Zou 《中国科学:生命科学英文版》2006,49(2):97-104
Pressure is expected to be an important parameter to affect characteristics of matters and control rate and equilibrium of chemical reactions. As a fundamental thermodynamic variable, it also has effects on bio-macromolecules and a lot of physiological an… 相似文献
180.
Deepa Alex Emilia Conceição Leong Zai‐Jun Zhang Gloria Tse Ho Yan Shuk‐Han Cheng Chi‐Weng Leong Zhen‐Hua Li Kai‐Heng Lam Shun‐Wan Chan Simon Ming‐Yuen Lee 《Journal of cellular biochemistry》2010,109(2):339-346
Angiogenesis plays an important role in the development of neoplastic diseases such as cancer. Resveratrol and its derivatives exert antiangiogenic effects, but the mechanisms of their actions remain unclear. The aim of this study was to evaluate the antiangiogenic activity of resveratrol and its derivative trans‐3,5,4′‐trimethoxystilbene in vitro using human umbilical vein endothelial cells (HUVECs) and in vivo using transgenic zebrafish, and to clarify their mechanisms of action in zebrafish by gene expression analysis of the vascular endothelial growth factor (VEGF) receptor (VEGFR2/KDR) and cell‐cycle analysis. trans‐3,5,4′‐Trimethoxystilbene showed significantly more potent antiangiogenic activity than that of resveratrol in both assays. In zebrafish, trans‐3,5,4′‐trimethoxystilbene caused intersegmental vessel regression and downregulated VEGFR2 mRNA expression. Trans‐3,5,4′‐trimethoxystilbene also induced G2/M cell‐cycle arrest, most specifically in endothelial cells of zebrafish embryos. We propose that the antiangiogenic and vascular‐targeting activities of trans‐3,5,4′‐trimethoxystilbene result from the downregulation of VEGFR2 expression and cell‐cycle arrest at G2/M phase. J. Cell. Biochem. 109: 339–346, 2010. © 2009 Wiley‐Liss, Inc. 相似文献