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   50565篇
  免费   1564篇
  国内免费   35篇
化学   29706篇
晶体学   273篇
力学   1087篇
数学   7556篇
物理学   13542篇
  2020年   615篇
  2019年   430篇
  2018年   511篇
  2017年   496篇
  2016年   1211篇
  2015年   983篇
  2014年   1120篇
  2013年   2384篇
  2012年   1936篇
  2011年   2363篇
  2010年   1289篇
  2009年   1089篇
  2008年   2250篇
  2007年   2174篇
  2006年   1956篇
  2005年   1757篇
  2004年   1398篇
  2003年   1215篇
  2002年   1142篇
  2001年   1007篇
  2000年   907篇
  1999年   675篇
  1998年   593篇
  1997年   586篇
  1996年   729篇
  1995年   649篇
  1994年   667篇
  1993年   743篇
  1992年   668篇
  1991年   481篇
  1990年   564篇
  1989年   471篇
  1988年   516篇
  1987年   514篇
  1986年   458篇
  1985年   617篇
  1984年   656篇
  1983年   560篇
  1982年   611篇
  1981年   592篇
  1980年   545篇
  1979年   514篇
  1978年   539篇
  1977年   499篇
  1976年   442篇
  1975年   442篇
  1974年   426篇
  1973年   430篇
  1967年   486篇
  1962年   388篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
111.
112.
The rotation-tunneling spectrum of the second most stable gGg conformer of ethylene glycol (1,2-ethanediol) in its ground vibrational state has been studied in selected regions between 77 and 579 GHz. Compared to the study of the more stable aGg conformer, a much larger frequency range was studied, resulting in a much extended frequency list covering similar quantum numbers, J?55 and Ka?19. While the input data were reproduced within experimental uncertainties up to moderately high values of J and Ka larger residuals remain at higher quantum numbers. The severe mixing of the states caused by the Coriolis interaction between the two tunneling substates is suggested to provide a considerable part of the explanation. In addition, a Coriolis interaction of the gGg ground vibrational state with an excited state of the aGg conformer may also contribute. Relative intensities of closely spaced lines have been investigated to determine the signs of the Coriolis constants between the two tunneling substates relative to the dipole moment components and to estimate the magnitudes of the dipole moment components and the energy difference between the gGg and the aGg conformers. Results of ab initio calculations on the total dipole moment and the vibrational spectrum were needed for these estimates. The current analysis is limited to transitions with quantum numbers J?40 and Ka?6 plus those having J?22 and Ka?17 which could be reproduced within experimental uncertainties. The results are aimed at aiding radioastronomers to search for gGg ethylene glycol in comets and in interstellar space.  相似文献   
113.
Capacity Constrained Transit Assignment with Common Lines   总被引:1,自引:0,他引:1  
This paper proposes the use of absorbing Markov chains to solve the capacity constrained transit network loading problem taking common lines into account. The approach handles congested transit networks, where some passengers will not be able to board because of the absence of sufficient space. The model also handles the common lines problem, where choice of route depends on frequency of arrivals. The mathematical formulation of the problem is presented together with a numerical example. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
114.
115.
Bionized nanoferrite (BNF) particles with high specific power absorption rates were synthesized in the size range of 20–100 nm by high-pressure homogenization for targeted cancer therapy with alternating magnetic fields. Several strategies were used to conjugate antibodies to the BNF particles. These strategies were compared using an immunoassay to find optimal conditions to reach a high immunoreactivity of the final antibody–particle conjugate.  相似文献   
116.
Standard ODE methods such as linear multistep methods encounter difficulties when applied to differential-algebraic equations (DAEs) of index greater than 1. In particular, previous results for index 2 DAEs have practically ruled out the use of all explicit methods and of implicit multistep methods other than backward difference formulas (BDFs) because of stability considerations. In this paper we embed known results for semi-explicit index 1 and 2 DAEs in a more comprehensive theory based on compound multistep and one-leg discretizations. This explains and characterizes the necessary requirements that a method must fulfill in order to be applicable to semi-explicit DAEs. Thus we conclude that the most useful discretizations are those that avoid discretization of the constraint. A freer use of e.g. explicit methods for the non-stiff differential part of the DAE is then possible.Dedicated to Germund Dahlquist on the occasion of his 70th birthdayThis author thanks the Centro de Estadística y Software Matemático de la Universidad Simón Bolivar (CESMa) for permitting her free use of its research facilities.Partial support by the Swedish Research Council for Engineering Sciences TFR under contract no. 222/91-405.  相似文献   
117.
118.
Montgomery and Vaughan improved a theorem of Erd?s and Fuchs for an arbitrary sequence. Sárközy extended this theorem of Erd?s and Fuchs for two arbitrary sequences which are "near" in a certain sense. Using the idea of Jurkat (differentiation of the generating function), we will extend similarly the result of Montgomery and Vaughan for "sufficiently near" sequences.  相似文献   
119.
120.
György Maróti 《ZDM》2003,35(2):63-68
This paper continues the discussion of teaching nondeterminism (see [6]) where we presented a didactic approach introducing the notion of nondeterministic automata. Although in this paper we use the same methodology we have to face up to new didactic challenges. Namely, teaching the subset construction requires answers to the question how can CAS be used in teaching the different phases of mathematical problem solving so that we can reach higher cognitive efficiency.  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