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   101847篇
  免费   9869篇
  国内免费   10988篇
化学   39404篇
晶体学   486篇
力学   8728篇
综合类   1653篇
数学   35794篇
物理学   36639篇
  2023年   857篇
  2022年   1706篇
  2021年   1973篇
  2020年   2276篇
  2019年   2417篇
  2018年   2156篇
  2017年   2567篇
  2016年   2945篇
  2015年   2733篇
  2014年   3984篇
  2013年   6999篇
  2012年   4519篇
  2011年   5342篇
  2010年   4593篇
  2009年   6158篇
  2008年   6659篇
  2007年   6837篇
  2006年   6169篇
  2005年   5275篇
  2004年   4605篇
  2003年   4682篇
  2002年   4282篇
  2001年   3529篇
  2000年   3473篇
  1999年   3100篇
  1998年   2841篇
  1997年   2303篇
  1996年   2006篇
  1995年   1787篇
  1994年   1647篇
  1993年   1416篇
  1992年   1382篇
  1991年   1065篇
  1990年   905篇
  1989年   821篇
  1988年   727篇
  1987年   596篇
  1986年   504篇
  1985年   599篇
  1984年   577篇
  1983年   297篇
  1982年   474篇
  1981年   511篇
  1980年   392篇
  1979年   409篇
  1978年   305篇
  1977年   285篇
  1976年   228篇
  1974年   167篇
  1973年   173篇
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
41.
This article explores the questions of long time orbital stability in high order Sobolev norms of plane wave solutions to the NLSE in the defocusing case.  相似文献   
42.
In this paper, we study the global (in time) existence of small data solutions to the Cauchy problem for the semilinear wave equation with friction, viscoelastic damping, and a power nonlinearity. We are interested in the connection between regularity assumptions for the data and the admissible range of exponents p in the power nonlinearity.  相似文献   
43.
This paper is dedicated to studying the following Schrödinger–Poisson system Δ u + V ( x ) u K ( x ) ϕ | u | 3 u = a ( x ) f ( u ) , x 3 , Δ ϕ = K ( x ) | u | 5 , x 3 . Under some different assumptions on functions V(x), K(x), a(x) and f(u), by using the variational approach, we establish the existence of positive ground state solutions.  相似文献   
44.
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   
45.
ABSTRACT

A new density functional for the study of associating inhomogeneous fluids based on Wertheim's first-order thermodynamic perturbation theory is presented and compared to the most currently used associating density functionals. This functional is developed using the weighted density approximation in the range of association of hard spheres. We implement this functional within the framework of classical density functional theory together with modified fundamental measure theory to account for volume exclusion of hard spheres. This approach is tested against molecular simulations from literature of pure associating hard spheres and mixtures of non-associationg and associating hard spheres with different number of bonding sites close to a hard uniform wall. Furthermore, we compare and review our results with the performance of associating functionals from literature, one based on fundamental measure theory and the inhomogeneous version of Wertheim's perturbation theory. Results obtained with classical DFT and the three functionals show excellent agreement with molecular simulations in systems with one hard wall. For the cases of small pores where only one or two layers of fluid are allowed discrepancies between results with classical DFT and molecular simulations were found.  相似文献   
46.
刘静松 《化学教育》2020,41(9):12-16
分析学生对二氧化碳的3个典型学科认知障碍,以“二氧化碳的捕捉”为情境,通过“尝试捕捉二氧化碳”“谁在捕捉二氧化碳”“捕捉背后的原理”等3个主要环节,实现对学科认知障碍的突破,展示了一种新的中考复习教学思路。  相似文献   
47.
This paper deals with the Cauchy–Dirichlet problem for the fractional Cahn–Hilliard equation. The main results consist of global (in time) existence of weak solutions, characterization of parabolic smoothing effects (implying under proper condition eventual boundedness of trajectories), and convergence of each solution to a (single) equilibrium. In particular, to prove the convergence result, a variant of the so-called ?ojasiewicz–Simon inequality is provided for the fractional Dirichlet Laplacian and (possibly) non-analytic (but C1) nonlinearities.  相似文献   
48.
基于时变Copula模型,获得预测方差,确定单个基金收益率序列的边缘分布.利用常见的静态Copula和时变Copula模型对基金收益率序列间两两相依关系进行建模并进行对比分析.应用研究表明,基于MCMC方法的时变Copula模型能更有效地度量基金收益率序列的风险.  相似文献   
49.
50.
We give a sheaf theoretic interpretation of Potts models with external magnetic field, in terms of constructible sheaves and their Euler characteristics. We show that the polynomial countability question for the hypersurfaces defined by the vanishing of the partition function is affected by changes in the magnetic field: elementary examples suffice to see non-polynomially countable cases that become polynomially countable after a perturbation of the magnetic field. The same recursive formula for the Grothendieck classes, under edge-doubling operations, holds as in the case without magnetic field, but the closed formulae for specific examples like banana graphs differ in the presence of magnetic field. We give examples of computation of the Euler characteristic with compact support, for the set of real zeros, and find a similar exponential growth with the size of the graph. This can be viewed as a measure of topological and algorithmic complexity. We also consider the computational complexity question for evaluations of the polynomial, and show both tractable and NP-hard examples, using dynamic programming.  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