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   16184篇
  免费   756篇
  国内免费   949篇
化学   10182篇
晶体学   186篇
力学   547篇
综合类   101篇
数学   2296篇
物理学   4577篇
  2022年   210篇
  2021年   224篇
  2020年   226篇
  2019年   224篇
  2018年   219篇
  2017年   207篇
  2016年   375篇
  2015年   385篇
  2014年   449篇
  2013年   912篇
  2012年   735篇
  2011年   840篇
  2010年   643篇
  2009年   649篇
  2008年   816篇
  2007年   862篇
  2006年   720篇
  2005年   701篇
  2004年   672篇
  2003年   641篇
  2002年   678篇
  2001年   510篇
  2000年   477篇
  1999年   363篇
  1998年   263篇
  1997年   240篇
  1996年   244篇
  1995年   256篇
  1994年   240篇
  1993年   198篇
  1992年   187篇
  1991年   193篇
  1990年   203篇
  1989年   167篇
  1988年   151篇
  1987年   156篇
  1986年   130篇
  1985年   224篇
  1984年   243篇
  1983年   171篇
  1982年   183篇
  1981年   155篇
  1980年   157篇
  1979年   146篇
  1978年   115篇
  1977年   165篇
  1976年   146篇
  1975年   119篇
  1974年   113篇
  1973年   115篇
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
101.
In this work, effective, yet simple, recycling mechanisms for used scanning probe microscopy (SPM) tips were implemented. Comprising a tip profile characterization methodology and specific cleaning procedures, which decontaminate SPM tips whether the contamination nature is known or not, such routes were optimized during numerous tests with brand new, previously used, and already discarded categories of SPM tips. The results show that if the used tip suffered contamination only, but no physical damages, during its scanning lifetime, it becomes readily available for reutilization after the cleansing process, characterizing a recycling route. On the other hand, if the tip went through wear and breakages during its utilization, it still can be decontaminated, but may not be directly reutilized due to its inadequate physical profile. Nevertheless, the methodology developed in this work may yet be applied as part of a more complex recycling route.  相似文献   
102.
103.
A method is described for the determination of the antitumor agent iphosphamide and seven of its metabolites in the plasma of cancer patients by multiple ion monitoring (MIM) GC-MS, mainly using the electron capture chemical ionization mode, of stable methyl and/or trifluoroacetyl derivatives. The metabolites determined were 2- and 3-dechloroethyliphosphamide, 4-ketoiphosphamide, carboxyiphosphamide, iphosphamide mustard, and two previously undetected metabolites, chloroethylamine and 1,3-oxazolidine-2-one. The isolation of the acidic and neutral metabolites was performed by solid phase extraction on to C18 adsorbent at pH 4. The weakly acidic iphosphamide mustard, isolated under these conditions with a yield of ca 50%, was measured as a stable methyltrifluoroacetyl derivative, in contrast to the corresponding phosphoramide mustard of the isomer cyclophosphamide which decomposes during derivatization. Chloroethylamine and 1,3-oxazolidine-2-one were isolated with high yield by liquid extraction with ethyl acetate at pH 10. Selective measurement of several metabolite derivatives with similar retention times was performed by multiple ion monitoring MS of specific ion masses, using a methyl phenyl siloxane capillary column previously employed in the study of cyclophosphamide metabolites. Quantitation of metabolites in patient plasma samples could be performed in the concentration range 3 ng to 20 μg per ml of original plasma.  相似文献   
104.
105.
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   
106.
107.
New concepts for the study of incompressible plane or axisymmetric flows are analysed by the stream tube method. Flows without eddies and pure vortex flows are considered in a transformed domain where the mapped streamlines are rectilinear or circular. The transformation between the physical domain and the computational domain is an unknown of the problem. In order to solve the non-linear set of relevant equations, we present a new algorithm based on a trust region technique which is effective for non-convex optimization problems. Experimental results show that the new algorithm is more robust compared to the Newton-Raphson method.  相似文献   
108.
The paper deals with the global minimization of a differentiable cost function mapping a ball of a finite dimensional Euclidean space into an interval of real numbers. It is established that a suitable random perturbation of the gradient method with a fixed parameter generates a bounded minimizing sequence and leads to a global minimum: the perturbation avoids convergence to local minima. The stated results suggest an algorithm for the numerical approximation of global minima: experiments are performed for the problem of fitting a sum of exponentials to discrete data and to a nonlinear system involving about 5000 variables. The effect of the random perturbation is examined by comparison with the purely deterministic gradient method.  相似文献   
109.
110.
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