首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   829篇
  免费   51篇
化学   629篇
晶体学   7篇
力学   37篇
数学   42篇
物理学   165篇
  2023年   3篇
  2022年   14篇
  2021年   15篇
  2020年   20篇
  2019年   11篇
  2018年   10篇
  2017年   13篇
  2016年   38篇
  2015年   31篇
  2014年   31篇
  2013年   41篇
  2012年   58篇
  2011年   44篇
  2010年   40篇
  2009年   43篇
  2008年   49篇
  2007年   54篇
  2006年   44篇
  2005年   54篇
  2004年   49篇
  2003年   24篇
  2002年   34篇
  2001年   24篇
  2000年   12篇
  1999年   11篇
  1998年   8篇
  1997年   6篇
  1996年   10篇
  1995年   11篇
  1994年   8篇
  1993年   4篇
  1992年   8篇
  1991年   6篇
  1990年   3篇
  1989年   1篇
  1988年   2篇
  1987年   7篇
  1986年   3篇
  1985年   7篇
  1984年   8篇
  1983年   1篇
  1982年   1篇
  1981年   8篇
  1980年   1篇
  1976年   4篇
  1972年   1篇
  1968年   1篇
  1967年   2篇
  1966年   1篇
  1938年   1篇
排序方式: 共有880条查询结果,搜索用时 31 毫秒
11.
We report a new synthesis of thiazoles from a cyclocondensation reaction between dimethyl N-(ethoxycarbonylmethyl)iminodithiocarbonate (EMIC), carbon disulfide and alkylation of intermediate thiazole-2-thiolate with alkyl halides.  相似文献   
12.
[reaction: see text] Data on the apparent dipole moment of thianthrene-5-oxide (1) and (1)H NMR spectra in different solvents support the conformational mobility of 1, which flaps between two limit boat conformations with the sulfinyl group in pseudoequatorial and pseudoaxial positions, respectively. The conformational equilibrium of 1 occurs too fast for the (1)H NMR (500 MHz) time-scale even at -130 degrees C, and the equilibrium constant has not been determined. The apparent dipole moments of 1 in n-hexane and 1,4-dioxane and the (1)H NMR spectra of 1 and the model compounds cis- and trans-thianthrene-5,10-dioxides (2) and thianthrene (5) in different solvents and at various temperatures confirm that the relative position of the conformational equilibrium of 1 is solvent-dependent, and more polar solvents favor the conformation with the sulfoxide group in the pseudoaxial position (1(')(ax)). Variable-temperature (1)H NMR spectra have established the interconversion barrier of trans-2 and confirmed that the conformational equilibrium of cis-2 is strongly displaced toward the conformation with both sulfinyl groups in the pseudoequatorial position. The (1)H NMR data support the transannular interaction of the functional groups in 1 and trans-2.  相似文献   
13.
Central European Journal of Operations Research - Agri-food production must increase while food waste needs to be reduced for improving the position of farmers. To do so it is necessary to...  相似文献   
14.
15.
An efficient procedure for third-order electron propagator calculations of ionization energies and electron affinities is reported. Diagonal self-energy expressions that are suitable for large molecules are empolyed. The outer-valence Green's function method also is implemented. An integral transformation program for direct and semidirect algorithms is modified to store only nonzero integrals according to Abelian point group symmetry. Contributions to self-energy matrix elements that depend on electron repulsion integrals with four virtual orbital indices are computed in a direct way. Intermediate batches of integrals are created by sort procedures while avoiding storage of transformed integrals in the main memory. This method permits calculation of electron binding energies for C with a 231 atomic orbital basis and for Zn(C5H5)2 with a 220 atomic orbital basis on an IBM RISC/6000 Model 550. During these calculations, the CPU is engaged approximately 90% of the time. © 1995 John Wiley & Sons, Inc.  相似文献   
16.
17.
18.
The cytochrome P450 superfamily of enzymes catalyzes a broad range of oxidative processes involved in the metabolism of fatty acids, biosynthesis of sterols, and elimination of drugs and xenobiotics. Application of the unique properties of P450 enzymes as fine biocatalysts in biotechnology is limited due to their thermal instability and the requirement for auxiliary electron-donor proteins and cofactors. CYP119, a thermophilic P450 enzyme from Sulfolobus solfataricus, was characterized some time ago, but no high-temperature redox partners have been available for it. Here we report reconstitution of CYP119 with a novel high-temperature electron-donor system consisting of a ferredoxin and 2-oxoacid:ferredoxin oxidoreductase from Sulfolobus tokodaii strain 7 that, unlike all other known P450 electron-donor partners, utilizes coenzyme-A and pyruvic acid rather than NADH or NADPH as the source of electrons. The oxidation of lauric acid by the reconstituted system increased 16-fold as the temperature increased from 25 to 70 degrees C and was functional for more than 30 min at the higher temperature. This first in vitro high-temperature P450 catalytic system is a key step in the development of practical high-temperature monooxygenase systems.  相似文献   
19.
This article presents a variation of the integral transform method to evaluate multicenter bielectronic integrals (12|34), with 1s Slater‐type orbitals. It is proved that it is possible to define, out of the expression of (12|34) given by the integral transform method, a function F(q) that has the property of having a unique Q, such that F(Q) = (12|34). Therefore, F(q) may be used to calculate (12|34). It is shown that the evaluation of F(Q) turns out to be simpler than the three‐dimensional integral involved in the calculation of (12|34), and an algorithm is presented to calculate Q. The results show that relative errors on the order of 10?3 or lower are obtained very efficiently. In addition, it is shown that the proposed algorithm is very stable. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004  相似文献   
20.
Studying protein components of large intracellular complexes by in-cell NMR has so far been impossible because the backbone resonances are unobservable due to their slow tumbling rates. We describe a methodology that overcomes this difficulty through selective labeling of methyl groups, which possess more favorable relaxation behavior. Comparison of different in-cell labeling schemes with three different proteins, calmodulin, NmerA, and FKBP, shows that selective labeling with [(13)C]methyl groups on methionine and alanine provides excellent sensitivity with low background levels at very low costs.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号