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   10582篇
  免费   418篇
  国内免费   16篇
化学   6429篇
晶体学   198篇
力学   224篇
数学   1603篇
物理学   2562篇
  2023年   80篇
  2022年   187篇
  2021年   248篇
  2020年   257篇
  2019年   325篇
  2018年   220篇
  2017年   208篇
  2016年   433篇
  2015年   333篇
  2014年   416篇
  2013年   796篇
  2012年   643篇
  2011年   689篇
  2010年   498篇
  2009年   437篇
  2008年   548篇
  2007年   494篇
  2006年   438篇
  2005年   345篇
  2004年   287篇
  2003年   270篇
  2002年   214篇
  2001年   184篇
  2000年   157篇
  1999年   119篇
  1998年   123篇
  1997年   92篇
  1996年   90篇
  1995年   125篇
  1994年   74篇
  1993年   59篇
  1992年   84篇
  1991年   53篇
  1990年   77篇
  1989年   67篇
  1988年   71篇
  1987年   66篇
  1986年   74篇
  1985年   104篇
  1984年   120篇
  1983年   73篇
  1982年   70篇
  1981年   84篇
  1980年   88篇
  1979年   61篇
  1978年   71篇
  1977年   71篇
  1976年   64篇
  1975年   60篇
  1974年   52篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Journal of Optimization Theory and Applications - We consider a distributionally robust formulation of stochastic optimization problems arising in statistical learning, where robustness is with...  相似文献   
2.
3.
4.
5.
Silver-mediated α-dC–Ag+–β-dC hybrid base pairs decorated with 5-iodo- or 5-octadiynyl residues are well accommodated in duplex DNA. A strong Tm increase and favorable thermodynamic data for duplex DNA were observed after addition of silver ions. The phenomenon is particularly obvious when both nucleobases of the base pairs are functionalized. Neither the position of the base pair, nor the type of 5-substituent had a negative influence. On the contrary, functionalization of conventional silver-mediated β-dC–Ag+–β-dC homo base pairs showed a negative impact induced by the bulky substituents. To this end, cytosine modified 12-mer oligodeoxynucleotides were prepared by solid-phase synthesis employing new α-anomeric 2′-deoxycytidine phosphoramidites. A multigram scale synthesis was developed for 5-iodo-α-d -2′-deoxycytidine ( 1 ) employing the direct glycosylation of cytosine with Hoffer's α-d -halogenose followed by separation of anomeric DMT nucleosides. Regarding base-pair stability and functionalization silver-mediated α/β-dC hybrid base pairs were found to be superior to β/β-dC homo pairs. According to their extraordinary properties, they might find applications in DNA diagnostics, material science, or nanotechnology.  相似文献   
6.
Exposure of cimetidine (CIM) to dry heat (160–180 °C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics.  相似文献   
7.
Mąkosza  M.  Fedoryński  M. 《Russian Chemical Bulletin》2021,70(11):2045-2050
Russian Chemical Bulletin - The discovery and studies of chemistry of dichlorocarbene and other electron deficient carbenes are discussed.  相似文献   
8.
The present paper is a continuation of comprehensive study regarding to synthesis and properties of pyrazoles and their derivatives. In its framework an experimental and theoretical studies of thermal decomposition of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline were performed. It was found, that the decompositions of the mentioned pyrazoline system in the solution and at the melted state proceed via completely different molecular mechanisms. These mechanisms have been explained in the framework of the Molecular Electron Density Theory (MEDT) with the computational level of B3LYP/6-31G(d). A Bonding Evolution Theory (BET) examination of dehydrochlorination of the 3,3-diphenyl-4-(trichloromethyl)-5-nitropyrazoline permits elucidation of the molecular mechanism. It was found, that on the contrary for most known HCl extrusion processes in solution, this reaction is realised via single-step mechanism.  相似文献   
9.
The analysis of electrophilicity indexes and the results of potential energy surface (PES) simulations for the reaction pathways proved that the [2 + 3] cycloadditions of nitroallylic systems with nitrones should be considered nonpolar reactions. Our simulations proved that the reactions always proceed via a one‐step mechanism through a prereaction complex. Although the symmetry of respective transition states is quite varied, their polarity is low and does not change when a polar medium is introduced to the reaction environment. When the polarity of the reaction medium increases, the kinetic pathway preference does not change. The regiochemistry of the cycloadditions tested may, however, be controlled to some extent by steric effects.  相似文献   
10.
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