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   30151篇
  免费   4177篇
  国内免费   2090篇
化学   5099篇
晶体学   105篇
力学   5118篇
综合类   507篇
数学   12598篇
物理学   12991篇
  2024年   65篇
  2023年   280篇
  2022年   732篇
  2021年   809篇
  2020年   968篇
  2019年   880篇
  2018年   822篇
  2017年   1093篇
  2016年   1269篇
  2015年   938篇
  2014年   1616篇
  2013年   2421篇
  2012年   1689篇
  2011年   1959篇
  2010年   1711篇
  2009年   2049篇
  2008年   1922篇
  2007年   1879篇
  2006年   1590篇
  2005年   1401篇
  2004年   1283篇
  2003年   1090篇
  2002年   1065篇
  2001年   863篇
  2000年   813篇
  1999年   706篇
  1998年   640篇
  1997年   482篇
  1996年   406篇
  1995年   380篇
  1994年   358篇
  1993年   300篇
  1992年   270篇
  1991年   206篇
  1990年   177篇
  1989年   138篇
  1988年   131篇
  1987年   139篇
  1986年   119篇
  1985年   142篇
  1984年   142篇
  1983年   75篇
  1982年   100篇
  1981年   66篇
  1980年   37篇
  1979年   42篇
  1978年   31篇
  1977年   32篇
  1976年   16篇
  1973年   23篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
191.
A new approach to the study of the Jaynes–Cummings sum, which determines the atomic inversion in quantum model of a single two-level atom interacting with a single mode of the quantized radiation field, based on the number theory theorems on approximation of trigonometric sums is presented.   相似文献   
192.
综合运用国内外多种测量量表对大学生的心理素质进行诊断与测试 ,并应用多元统计分析方法对其心理素质结构主因素进行定量分析 ,在此基础上建立了心理素质诊断模型 ,并运用该模型对实际问题进行了分析 .  相似文献   
193.
We consider two classes of integrable nonlinear hyperbolic systems on Lie algebras. These systems generalize the principal chiral model. Each system is related to a pair of compatible Lie brackets and has a Lax representation, which is determined by the direct sum decomposition of the Lie algebra of Laurent series into the subalgebra of Taylor series and the complementary subalgebra corresponding to the pair. New examples of compatible Lie brackets are given.  相似文献   
194.
We study asymptotic properties of solutions to an extension to arbitrary dimensions of the astrophysical model proposed by Chavanis et al. to explain phenomena of gravitational collapse in clouds of self-gravitating particles. In particular, we show that in the two-dimensional case the solutions can be continued to global ones, while in three space dimensions large data of negative energy blow up in a finite time. Relations between isothermal, Streater's energy-transport and the present models are also studied.  相似文献   
195.
This paper proposes a method for estimation of a class of partially linear single-index models with randomly censored samples. The method provides a flexible way for modelling the association between a response and a set of predictor variables when the response variable is randomly censored. It presents a technique for “dimension reduction” in semiparametric censored regression models and generalizes the existing accelerated failure-time models for survival analysis. The estimation procedure involves three stages: first, transform the censored data into synthetic data or pseudo-responses unbiasedly; second, obtain quasi-likelihood estimates of the regression coefficients in both linear and single-index components by an iteratively algorithm; finally, estimate the unknown nonparametric regression function using techniques for univariate censored nonparametric regression. The estimators for the regression coefficients are shown to be jointly root-n consistent and asymptotically normal. In addition, the estimator for the unknown regression function is a local linear kernel regression estimator and can be estimated with the same efficiency as all the parameters are known. Monte Carlo simulations are conducted to illustrate the proposed methodology.  相似文献   
196.
The multivariate model, where not only parameters of the mean value of the observation matrix, but also some other parameters occur in constraints, is considered in the paper. Some basic inference is presented under the condition that the covariance matrix is either unknown, or partially unknown, or known. Supported by the grant of the Council of Czech Republic MSM 6 198 959 214.  相似文献   
197.
针对合同的动态性,提出利用基于演化博弈建立定价模型。考虑到决策群体中个体的认识误差,对所建立的定价模型进行修正,建立带偏离的定价模型并分析了偏离对均衡解的影响。最后将以上模型应用实例进行比较分析。  相似文献   
198.
刘汉中 《运筹与管理》2007,16(6):123-127
本文首先对回报率与交易量之间的关系进行了研究,发现并不存在非对称的数量关系,但存在双向的葛兰杰因果关系;同时将交易量对波动率的解释能力进行了研究,发现在沪市交易量对波动率具有解释力,而在深市交易量对波动率没有解释力。  相似文献   
199.
200.
A multi-dimensional transient drift-diffusion model for (at most) three charged particles, consisting of the continuity equations for the concentrations of the species and the Poisson equation for the electric potential, is considered. The diffusion terms depend on the concentrations. Such a system arises in electrophoretic modeling of three species (neutrally, positively and negatively charged) and in semiconductor theory for two species (positively charged holes and negatively charged electrons). Diffusion terms of degenerate type are also possible in semiconductor modeling. For the initial boundary value problem with mixed Dirichlet - Neumann boundary conditions and general reaction rates, a global existence result is proved. Uniqueness of solutions follows in the Dirichlet boundary case if the diffusion terms are uniformly parabolic or if the initial and boundary densities are strictly positive. Finally, we prove that solutions exist which are positive uniformly in time and globally bounded if the reaction rates satisfy appropriate growth conditions.  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