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   746篇
  免费   21篇
  国内免费   4篇
化学   462篇
晶体学   2篇
力学   10篇
数学   99篇
物理学   198篇
  2023年   4篇
  2022年   18篇
  2021年   26篇
  2020年   23篇
  2019年   17篇
  2018年   22篇
  2017年   23篇
  2016年   24篇
  2015年   25篇
  2014年   29篇
  2013年   60篇
  2012年   56篇
  2011年   60篇
  2010年   25篇
  2009年   30篇
  2008年   38篇
  2007年   36篇
  2006年   41篇
  2005年   39篇
  2004年   34篇
  2003年   31篇
  2002年   23篇
  2001年   8篇
  2000年   6篇
  1999年   7篇
  1998年   7篇
  1997年   6篇
  1996年   6篇
  1995年   5篇
  1994年   11篇
  1993年   4篇
  1992年   4篇
  1991年   4篇
  1990年   2篇
  1989年   1篇
  1988年   1篇
  1987年   1篇
  1986年   1篇
  1985年   1篇
  1983年   3篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
  1972年   1篇
  1966年   1篇
排序方式: 共有771条查询结果,搜索用时 0 毫秒
751.
Abstract

C-phosphorylation of N,N-dimethylhydrazones and N,N-dimethyl-N′-arylamidines by phosphorus tribromide was first accomplished. It directs to the formation of novel types of functional P(III) derivatives (1–3)  相似文献   
752.
753.
754.
We investigate the rate of convergence of general global random search (GRS) algorithms. We show that if the dimension of the feasible domain is large then it is impossible to give any guarantee that the global minimizer is found by a general GRS algorithm with reasonable accuracy. We then study precision of statistical estimates of the global minimum in the case of large dimensions. We show that these estimates also suffer the curse of dimensionality. Finally, we demonstrate that the use of quasi-random points in place of the random ones does not give any visible advantage in large dimensions.  相似文献   
755.
We derive an asymptotic formula for the number of pairs of consecutive fractions a0=q0 and a=q in the Farey sequence of order Q such that a=q; q=Q; and (Q - q0)=q lie each in prescribed subintervals of the interval [0; 1]. We deduce the leading term in the asymptotic formula for `the hyperbolic lattice point problem" for the modular group PSL(2; Z ), the number of images of a given point under the action of the group in a given circle in the hyperbolic plane.  相似文献   
756.
A Radon–Nikodym type theorem for positive orthosymmetric bilinear operators is proved. The main tools are based upon homogeneous functional calculus on vector lattices and the concept of square of vector lattice.  相似文献   
757.
An approach to non-convex multi-objective optimization problems is considered where only the values of objective functions are required by the algorithm. The proposed approach is a generalization of the probabilistic branch-and-bound approach well applicable to complicated problems of single-objective global optimization. In the present paper the concept of probabilistic branch-and-bound based multi-objective optimization algorithms is discussed, and some illustrations are presented.  相似文献   
758.
A two-person game with a Nash equilibrium is formulated for optimal control problems with a free right end and a linear differential system. The game is reduced to the calculation of a fixed point of an extremal mapping, which in turn is reduced to a variational inequality with linear constraints generated by systems of linear differential controllable processes. An extra-gradient iterative method is proposed for calculating the Nash equilibrium of the dynamic game. The convergence of the method is proved.  相似文献   
759.
A practical method for the synthesis of 2-selenoxo-1,2,3,4-tetrahydro-4-quinazolinone was reported. The latter compounds were found to undergo facile oxidation with H2O2 into corresponding diselenides. Novel organoselenium derivatives were characterized by the 1H, 77Se, and 13C NMR spectroscopies, high-resolution electrospray ionization mass spectrometry, IR, elemental analyses (C, H, N), and X-ray diffraction analysis for several of them. Novel heterocycles exhibited multiple remarkable chalcogen bonding (ChB) interactions in the solid state, which were studied theoretically.  相似文献   
760.
New hybrids of 4-amino-2,3-polymethylenequinoline with different sizes of the aliphatic ring linked to butylated hydroxytoluene (BHT) by enaminoalkyl (7) or aminoalkyl (8) spacers were synthesized as potential multifunctional agents for Alzheimer’s disease (AD) treatment. All compounds were potent inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with selectivity toward BChE. Lead compound 8c, 2,6-di-tert-butyl-4-{[2-(7,8,9,10- tetrahydro-6H-cyclohepta[b]quinolin-11-ylamino)-ethylimino]-methyl}-phenol exhibited an IC50(AChE) = 1.90 ± 0.16 µM, IC50(BChE) = 0.084 ± 0.008 µM, and 13.6 ± 1.2% propidium displacement at 20 μM. Compounds possessed low activity against carboxylesterase, indicating likely absence of clinically unwanted drug-drug interactions. Kinetics were consistent with mixed-type reversible inhibition of both cholinesterases. Docking indicated binding to catalytic and peripheral AChE sites; peripheral site binding along with propidium displacement suggest the potential of the hybrids to block AChE-induced β-amyloid aggregation, a disease-modifying effect. Compounds demonstrated high antioxidant activity in ABTS and FRAP assays as well as inhibition of luminol chemiluminescence and lipid peroxidation in mouse brain homogenates. Conjugates 8 with amine-containing spacers were better antioxidants than those with enamine spacers 7. Computational ADMET profiles for all compounds predicted good blood-brain barrier distribution (permeability), good intestinal absorption, and medium cardiac toxicity risk. Overall, based on their favorable pharmacological and ADMET profiles, conjugates 8 appear promising as candidates for AD therapeutics.  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