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   61720篇
  免费   21001篇
  国内免费   1841篇
化学   67629篇
晶体学   231篇
力学   3124篇
综合类   76篇
数学   4753篇
物理学   8749篇
  2024年   426篇
  2023年   4332篇
  2022年   2162篇
  2021年   3188篇
  2020年   5297篇
  2019年   3047篇
  2018年   2968篇
  2017年   1201篇
  2016年   6480篇
  2015年   6332篇
  2014年   5933篇
  2013年   6472篇
  2012年   4883篇
  2011年   2799篇
  2010年   4516篇
  2009年   4405篇
  2008年   2212篇
  2007年   1783篇
  2006年   1102篇
  2005年   868篇
  2004年   659篇
  2003年   476篇
  2002年   478篇
  2001年   377篇
  2000年   302篇
  1999年   425篇
  1998年   303篇
  1997年   377篇
  1996年   373篇
  1995年   389篇
  1994年   297篇
  1993年   429篇
  1992年   244篇
  1991年   227篇
  1990年   187篇
  1989年   178篇
  1988年   204篇
  1980年   220篇
  1979年   195篇
  1978年   202篇
  1977年   321篇
  1976年   377篇
  1975年   471篇
  1974年   483篇
  1973年   298篇
  1972年   374篇
  1971年   362篇
  1970年   548篇
  1969年   421篇
  1968年   470篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
The chemical mechanism of the precipitation of lead titanium peroxohydroxide particles in a solution of nitrilotriacetate (NTA) complexes of lead and titanium peroxo-hydroxide is envisioned as the interaction between cations of lead hydroxide and anions of polymeric titanium peroxo-hydroxide.  相似文献   
92.
The common methods for calculating the mass transfer across liquid-liquid interfaces in technical applications take into account the mass transfer resistances within the bulk phases. The transfer resistance of the interface and a possible coupling between the momentum and the mass transport is not taken into account. In the present paper a survey is given of theoretical approaches which can describe this coupling and the additional mass transfer resistance. A theory is proposed by Hampe which can be used to explain the coupling between momentum and mass transport employing thermodynamics of irreversible processes. On the basis of this work, the influence of the dilatation of a flat interface on the mass transfer is deduced. It is also concluded from this theory that the diffusion coefficients within the bulk phases are coupled near the thermodynamic equilibrium.  相似文献   
93.
94.
To improve aircraft crash safety, conditions critical to occupants survival during a crash must be known. In view of the importance of this problem, studies of post-crash dynamic behavior of victims are necessary in order to reduce severe injuries. In this study, crash dynamics program SOM-LA/TA, incorporating a dynamic model of the human body with a finite element model of the seat structure was used. Modifications were performed in the program for reconstruction of an occupant's head impact with the interior walls or bulkhead. A viscoelastic-type contact force model was used to represent the compliance characteristics of the bulkhead. Correlated studies of analytical simulations with impact sled test results were accomplished. A parametric study of the coefficients in the contact force model was then performed in order to obtain the correlations between the coefficients and the Head Injury Criteria. A measure of optimal values for the bulkhead compliance and displacement requirements was thus achieved in order to keep the possibility of a head injury as little as possible. This information could in turn be used in the selection of suitable materials for the bulkhead, instrument panel, or interior walls of an aircraft.  相似文献   
95.
96.
97.
98.
Let E, F be two Banach spaces, and B(E, F), Φ(E, F), SΦ(E, F) and R(E,F) be the bounded linear, Fredholm, semi-Frdholm and finite rank operators from E into F, respectively. In this paper, using the continuity characteristics of generalized inverses of operators under small perturbations, we prove the following result Let ∑ be any one of the following sets {T ∈ Φ(E, F) IndexT =const, and dim N(T) = const.}, {T ∈ SΦ(E, F) either dim N(T) = const. < ∞ or codim R(T) = const.< ∞} and {T ∈ R(E, F) RankT =const.<∞}. Then ∑ is a smooth submanifold of B(E, F) with the tangent space TA∑ = {B ∈ B(E,F) BN(A) (∪) R(A)} for any A ∈ ∑. The result is available for the further application to Thom's famous results on the transversility and the study of the infinite dimensional geometry.  相似文献   
99.
This paper seeks to solve the difficult nonlinear problem in financial markets on the complex system theory and the nonlinear dynamics principle, with the data-model-concept-practice issue-oriented reconstruction of the phase space by the high frequency trade data. In theory, we have achieved the differentiable manifold geometry configuration, discovered the Yang-Mills functional in financial markets, obtained a meaningful conserved quantity through corresponding space-time non-Abel localization gauge symmetry transformation, and derived the financial solitons, which shows that there is a strict symmetry between manifold fiber bundle and guage field in financial markets. In practical applications of financial markets, we have repeatedly carried out experimental tests in a fluctuant evolvement, directly simulating and validating the existence of solitons by researching the price fluctuations (society phenomena) using the same methods and criterion as in natural science and in actual trade to test the stock Guangzhou Proprietary and the futures Fuel Oil in China. The results demonstrate that the financial solitons discovered indicates that there is a kind of new substance and form of energy existing in financial trade markets, which likely indicates a new science paradigm in the economy and society domains beyond physics.   相似文献   
100.
Malyngamide X ( 1 ), the first (7R)‐lyngbic acid connected to a new tripeptide backbone, was isolated from the Thai sea hare Bursatella leachii. The gross structure of 1 was established on the basis of 1D and 2D NMR and mass spectroscopic data. Combination of the NMR spectroscopic experiments with α‐methoxy‐α‐(trifluoromethyl)phenylacetic acid esters, 2,2,2‐trifluoro‐1‐(9‐anthryl)ethanol chiral solvating agent, and molecular mechanics of 1 and the synthetic molecular fragments allowed us to determine the absolute stereochemistry of all six stereogenic centers without hydrolytic degradation of the compound. Compound 1 displayed moderate cytotoxic, antitubercular, and antimalarial properties.  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