全文获取类型
收费全文 | 9295篇 |
免费 | 1470篇 |
国内免费 | 1365篇 |
专业分类
化学 | 7474篇 |
晶体学 | 137篇 |
力学 | 466篇 |
综合类 | 149篇 |
数学 | 961篇 |
物理学 | 2943篇 |
出版年
2024年 | 35篇 |
2023年 | 159篇 |
2022年 | 302篇 |
2021年 | 341篇 |
2020年 | 410篇 |
2019年 | 412篇 |
2018年 | 338篇 |
2017年 | 316篇 |
2016年 | 495篇 |
2015年 | 535篇 |
2014年 | 614篇 |
2013年 | 793篇 |
2012年 | 810篇 |
2011年 | 770篇 |
2010年 | 687篇 |
2009年 | 597篇 |
2008年 | 693篇 |
2007年 | 598篇 |
2006年 | 512篇 |
2005年 | 460篇 |
2004年 | 356篇 |
2003年 | 298篇 |
2002年 | 270篇 |
2001年 | 242篇 |
2000年 | 180篇 |
1999年 | 142篇 |
1998年 | 92篇 |
1997年 | 73篇 |
1996年 | 57篇 |
1995年 | 61篇 |
1994年 | 45篇 |
1993年 | 61篇 |
1992年 | 57篇 |
1991年 | 42篇 |
1990年 | 34篇 |
1989年 | 23篇 |
1988年 | 23篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 21篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1979年 | 8篇 |
1977年 | 8篇 |
1975年 | 11篇 |
1974年 | 12篇 |
1972年 | 11篇 |
1971年 | 7篇 |
1969年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The aggregation and packing of a membrane-disruptive beta-hairpin antimicrobial peptide, protegrin-1 (PG-1), in the solid state are investigated to understand its oligomerization and hydrogen-bonding propensity. Incubation of PG-1 in phosphate buffer saline produced well-ordered nanometer-scale aggregates, as indicated by 13C and 15N NMR line widths, chemical shifts, and electron microscopy. Two-dimensional 13C and 1H spin diffusion experiments using C-terminus strand and N-terminus strand labeled peptides indicate that the beta-hairpin molecules in these ordered aggregates are oriented parallel to each other with like strands lining the intermolecular interface. In comparison, disordered and lyophilized peptide samples are randomly packed with both parallel and antiparallel alignments. The PG-1 aggregates show significant immobilization of the Phe ring near the beta-turn, further supporting the structural ordering. The intermolecular packing of PG-1 found in the solid state is consistent with its oligomerization in lipid bilayers. This solid-state aggregation approach may be useful for determining the quaternary structure of peptides in general and for gaining insights into the oligomerization of antimicrobial peptides in lipid bilayers in particular. 相似文献
72.
The palladium-catalyzed hydrostannolysis of α-disubstituted allyl β-keto esters yields the corresponding tributyltin β-keto carboxylates which loose carbon dioxide at very moderate temperature, thus leading to the regiospecific formation of tributyltin tetrasubstituted enolates. 相似文献
73.
Three novel supramolecular arrays of zigzag polyaromatic salts are reported. Both the conformation and disposition of the dications are subjected to various noncovalent interactions. Thus, the presence or absence of the π‐π interacting enclathrated molecules, the efficient packing and the involved hydrogen bonding interactions of anions, as well as the increased hydrophobic property of the dications themselves exert influence. 相似文献
74.
Shen R Lin CT Bowman EJ Bowman BJ Porco JA 《Journal of the American Chemical Society》2003,125(26):7889-7901
The total synthesis and stereochemical assignment of the potent antitumor macrolide lobatamide C, as well as synthesis of simplified lobatamide analogues, is reported. Cu(I)-mediated enamide formation methodology has been developed to prepare the highly unsaturated enamide side chain of the natural product and analogues. A key fragment coupling employs base-mediated esterification of a beta-hydroxy acid and a salicylate cyanomethyl ester. Three additional stereoisomers of lobatamide C have been prepared using related synthetic routes. The stereochemistry at C8, C11, and C15 of lobatamide C was assigned by comparison of stereoisomers and X-ray analysis of a crystalline derivative. Synthetic lobatamide C, stereoisomers, and simplified analogues have been evaluated for inhibition of bovine chromaffin granule membrane V-ATPase. The salicylate phenol, enamide NH, and ortho-substitution of the salicylate ester have been shown to be important for V-ATPase inhibitory activity. 相似文献
75.
A New Reaction-controlled Phase-transfer Catalyst System 总被引:1,自引:0,他引:1
MingQiangLI XiGaoJIAN GuiMeiWANG YanYU 《中国化学快报》2004,15(3):350-352
A new reaction-controlled phase-transfer catalyst system was designed and synthesized.In this system, heteropolytungstate [C7H7N(CH3)3]9PW9O34 was used for catalytic epoxidation of cyclohexene with H2O2 as the oxidant. The conversion of H2O2 was 100% and the yield of cyclohexene oxide was 87.1% based on cyclohexene. Infrared spectra showed that both fresh catalyst and the recovered catalyst do have completely same absorption peak, indicating the structure of catalyst is very stability and can be recycled. 相似文献
76.
77.
Nan Yan FU Mei Li PANG Yao Feng YUAN Ji Tao WANG* Department of Chemistry National Key Laboratory of Elemento-organic Chemistry Nankai University Tianjin 《中国化学快报》2002,13(10)
A highly efficient catalyst indium (III) tribromide is used to synthesize 5-alkoxy- carbonyl-4-hydrocarbyl-3,4-dihydropyrimidin-2(1H)-ones by a three-component coupling of β-keto ester, aldehydes and urea through improved Biginelli reaction. 相似文献
78.
Yang G Miao R Jin C Mei Y Tang H Hong J Guo Z Zhu L 《Journal of mass spectrometry : JMS》2005,40(8):1005-1016
Interaction of carboplatin with cytochrome c (Cyt. c) has been investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). ESI-MS studies revealed that the ring-opened adducts of carboplatin with Cyt. c were formed in the stoichiometric ratio of 1:1 and 2:1 at pH 5.0 and 37 degrees C and in the stoichiometric ratio of 1:1 only at pH 7.0 and 37 degrees C. It was also found that Cyt. c could be cleaved by carboplatin at pH 2.5 and 50 degrees C. The cleaved fragments of Cyt. c were determined by ESI-MS and MS/MS analysis to be Glu66 approximately Met80, Ac-Gly01 approximately Met65, Glu66 approximately Glu104, Ac-Gly01 approximately Met80 and Ile81 approximately Glu104. The carboplatin prefers to anchor to Met65 first, then to Met80. To further confirm the binding site of Met, AcMet-Gly was used as the model molecule to investigate its interaction with carboplatin and its hydrolysis reaction. On the basis of species detected during the reaction monitored by ESI-MS, a possible pathway of the cleavage reaction was proposed. 相似文献
79.
Unlabeled fluoroimmunoassay with a europium chelate is described. The recommended method is simple because the complicated labeling process is omitted. The recovery of some samples ranges from 91 to 111%. The relative standard deviation of the method is less than 10%. The detection limit is about 10−10mol liter−1antigen. 相似文献
80.