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   17411篇
  免费   2703篇
  国内免费   1987篇
化学   12758篇
晶体学   186篇
力学   1199篇
综合类   136篇
数学   2051篇
物理学   5771篇
  2024年   39篇
  2023年   321篇
  2022年   534篇
  2021年   541篇
  2020年   625篇
  2019年   653篇
  2018年   514篇
  2017年   530篇
  2016年   744篇
  2015年   748篇
  2014年   927篇
  2013年   1148篇
  2012年   1521篇
  2011年   1564篇
  2010年   1065篇
  2009年   938篇
  2008年   1086篇
  2007年   988篇
  2006年   987篇
  2005年   805篇
  2004年   614篇
  2003年   552篇
  2002年   553篇
  2001年   463篇
  2000年   354篇
  1999年   379篇
  1998年   305篇
  1997年   287篇
  1996年   315篇
  1995年   243篇
  1994年   218篇
  1993年   180篇
  1992年   177篇
  1991年   180篇
  1990年   134篇
  1989年   126篇
  1988年   86篇
  1987年   79篇
  1986年   83篇
  1985年   60篇
  1984年   60篇
  1983年   45篇
  1982年   32篇
  1981年   31篇
  1980年   29篇
  1978年   24篇
  1977年   25篇
  1976年   23篇
  1974年   20篇
  1973年   26篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
121.
We apply the theory developed in quantum cosmology to a model of charged generalized Brans–Dicke gravity. This is a quantum model of gravitation interacting with a charged Brans–Dicke type scalar field which is considered in the Pauli frame. The Wheeler–DeWitt equation describing the evolution of the quantum Universe is solved in the semiclassical approximation by applying the WKB approximation. The wave function of the Universe is also obtained by applying both the Vilenkin-like and the Hartle–Hawking-like boundary conditions. We then make predictions from the wave functions and infer that the Vilenkin's boundary condition is more reasonable in the Brans–Dicke gravity models leading a large vacuum energy density at the beginning of the inflation.  相似文献   
122.
关于RNP和SCS的若干等价条件   总被引:1,自引:0,他引:1  
使用切片方法,讨论了Banach空间中有界闭凸子集的RNP和SCS的若干等价条件.  相似文献   
123.
The singularly perturbed boundary value problem for a class of semilinearsingular equation is considered. Using a simple and special method the asym-ptotic behavior of solution is studied.  相似文献   
124.
A necessary condition is derived for a quadratic form ptGp to be minimal among all permutations of the nonnegative nontrivial vector p. The quadratic form arises from the stability problem of a fixed-fixed taut string loaded with masses at equidistant points.  相似文献   
125.
126.
Great interests have been accumulated in recent years in the chemistry and biochemistry of nitric oxide (NO) since the remarkable discoveries of its key roles in a wide range of human physiological processes. To elucidate the mechanistic details of NO migration from its donor to its acceptor, it is necessary to determine the Y-NO bind energy that registers the thermodynamic driving force for NO release and capture. In this paper the heterolytic and homolytic N-NO bond dissociation energies [ i. e., △Hhet(N-NO) and △Hhomo(N-NO)] for ten N-nitroso-p-substituted-benzensulfonyl methylamines in acetonitrile are offered, which were obtained from titration calorimetry and thermodynamic cycles, respectively (Scheme 1).  相似文献   
127.
本文讨论了温度、相变、应力间的耦合关系,给出了铸坯在考虑相变时的热弹塑性蠕变的本构关系,以及计算铸坯内应力的有限元迭代公式。  相似文献   
128.
Two previously unknown metabolites of halofantrine, a candidate anti-malarial drug, have been isolated by thin-layer chromatography from the plasma of dogs administered a single oral dose of 60 mg/kg. Their identifies were investigated after trimethylsilylation by gas chromatography-mass spectrometry under electron-impact and negative-ion chemical ionization conditions. The structural assignment was further confirmed by using a combination of elemental composition analysis of all the isotope peaks at low mass resolution and isotope pattern matching. These two metabolites were formed by modification of the dibutylaminopropyl side-chain of the parent compound involving deamination and oxidation or reduction.  相似文献   
129.
1H chemical shift changes of sodium 4-decyl naphthalene sulfonate (SDNS) at 313 K show that its critical micellar concentration lies between 0.82 and 0.92 mmol/dm3, which is in the same range as that of the previous study at 298 K. The spin–lattice relaxation time, spin–spin relaxation time and two-dimensional nuclear Overhauser enhancement spectroscopy experiments give information about the structure of the SDNS micelle and the dynamics of the molecules in the micelle. The size of the SDNS micelle remains almost unchanged in the temperature range from 298 to 313 K as deduced by analyzing the self-diffusion coefficient. Special arrangement of the naphthyl rings of SDNS in the micelles affects the packing of these hydrophobic chains. The methylene groups of the alkyl chain nearest the naphthalene groups penetrate into the aromatic region, which results in a more tightly packed hydrophobic micellar core than that of sodium dodecyl sulfonate.  相似文献   
130.
Examination of the aerial parts of a Chinese herbal medicine yielded a novel metabolite, perforatumone 1, which is characterized by its unique carbon skeleton. Its structure was determined by detailed spectroscopic analysis.  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