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   227766篇
  免费   45875篇
  国内免费   34715篇
化学   104799篇
晶体学   1815篇
力学   10495篇
综合类   528篇
数学   19276篇
物理学   81302篇
综合类   90141篇
  2024年   901篇
  2023年   3357篇
  2022年   4273篇
  2021年   4922篇
  2020年   6057篇
  2019年   8305篇
  2018年   8069篇
  2017年   8572篇
  2016年   10606篇
  2015年   10617篇
  2014年   11996篇
  2013年   14398篇
  2012年   15276篇
  2011年   16850篇
  2010年   17782篇
  2009年   17424篇
  2008年   11405篇
  2007年   10369篇
  2006年   9023篇
  2005年   8614篇
  2004年   8744篇
  2003年   6954篇
  2002年   6362篇
  2001年   6123篇
  2000年   5210篇
  1999年   6740篇
  1998年   5999篇
  1997年   5797篇
  1996年   5845篇
  1995年   5779篇
  1994年   5518篇
  1993年   5269篇
  1992年   4621篇
  1991年   4110篇
  1990年   3450篇
  1989年   3276篇
  1988年   3053篇
  1987年   1952篇
  1986年   1800篇
  1985年   1256篇
  1984年   1160篇
  1983年   486篇
  1982年   993篇
  1981年   791篇
  1980年   807篇
  1979年   540篇
  1978年   537篇
  1977年   638篇
  1976年   1049篇
  1972年   532篇
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
961.
In this paper the classical theorem of Zareckii about regular relations is generalized and an intrinsic characterization of regularity is obtained. Based on the generalized Zareckii theorem and the intrinsic characterization of regularity, the authors give a characterization of monotone normality of ordered spaces. A new proof of the Urysohn-Nachbin lemma is presented which is quite different from the classical one.  相似文献   
962.
The effect of an applied magnetic field on an inhomogeneous superconductor is studied and the value of the upper critical magnetic field Hc3 at which superconductivity can nucleate is estimated. In addition, the authors locate the concentration of the order parameter, which depends on the inhomogeneous term a(x). Unlikely to the homogeneous case, the order parameter may concentrate in the interior of the superconducting material, due to the influence of the inhomogeneous term a(x).  相似文献   
963.
The notion of a fuzzy retract was introduced by Rodabaugh (1981). The notion of a fuzzy pairwise retract was introduced in 2001. Some weak forms and some strong forms of α-continuous mappings were introduced in 1988 and 1997. The authors extend some of these forms to the L-fuzzy bitopological setting and construct various α-fuzzy pairwise retracts. The concept of weakly induced spaces in the case L = [0,1] was introduced by Martin (1980). Liu and Luo (1987) generalized this notion to the case that L is an arbitrary F-lattice and introduced the notion of induced L-fts. Several results are obtained, especially, for L-valued pairwise stratification spaces.  相似文献   
964.
The existence and uniqueness results of fully coupled forward-backward stochastic differential equations with stopping time (unbounded) is obtained. One kind of comparison theorem for this kind of equations is also proved.  相似文献   
965.
A modified backward difference time discretization is presented for Galerkin approximations for nonlinear hyperbolic equation in two space variables. This procedure uses a local approximation of the coefficients based on patches of finite elements with these procedures, a multidimensional problem can be solved as a series of one‐dimensional problems. Optimal order H01 and L2 error estimates are derived. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007  相似文献   
966.
In the present paper, some types of general solutions of a first-order nonlinear ordinary differential equation with six degree are given and a new generalized algebra method is presented to find more exact solutions of nonlinear differential equations. As an application of the method and the solutions of this equation, we choose the (2 + 1) dimensional Boiti Leon Pempinelli equation to illustrate the validity and advantages of the method. As a consequence, more new types and general solutions are found which include rational solutions and irrational solutions and so on. The new method can also be applied to other nonlinear differential equations in mathematical physics.  相似文献   
967.
A novel method, entitled the discrete global descent method, is developed in this paper to solve discrete global optimization problems and nonlinear integer programming problems. This method moves from one discrete minimizer of the objective function f to another better one at each iteration with the help of an auxiliary function, entitled the discrete global descent function. The discrete global descent function guarantees that its discrete minimizers coincide with the better discrete minimizers of f under some standard assumptions. This property also ensures that a better discrete minimizer of f can be found by some classical local search methods. Numerical experiments on several test problems with up to 100 integer variables and up to 1.38 × 10104 feasible points have demonstrated the applicability and efficiency of the proposed method.  相似文献   
968.
Through arylsulfonyl activation of thiourea, efficient synthesis of oligomeric guanidines can be achieved in either solution or solid-phase. Incorporation of TFA-sensitive arylsulfonyl groups, such as Pbf, during the synthesis greatly simplifies deprotection procedures for obtaining the final oligomeric guanidine products.  相似文献   
969.
970.
在前文研究的基础上,经试验,证明Ag(Ⅰ)与巯萘剂(TN)反应生成非电活性物质,导致电活性物质DTN电流降低。在最佳条件下,Ag(Ⅰ)浓度在3.7×10~(-8)~4.5×10(-7)mol/L范围内与DTN电流峰高降低值成线性关系,检出限为2.2×10~(-8)mol/L(相当于2.4ng/ml)Ag(Ⅰ)。方法用于纯镍和氢氧化钾中痕最银的测定,结果满意。  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