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   73521篇
  免费   5353篇
  国内免费   6926篇
化学   27105篇
晶体学   295篇
力学   7685篇
综合类   1245篇
数学   26034篇
物理学   23436篇
  2024年   112篇
  2023年   685篇
  2022年   1201篇
  2021年   1352篇
  2020年   1497篇
  2019年   1775篇
  2018年   1394篇
  2017年   1676篇
  2016年   1853篇
  2015年   1731篇
  2014年   2528篇
  2013年   4644篇
  2012年   2845篇
  2011年   3312篇
  2010年   2828篇
  2009年   4005篇
  2008年   4470篇
  2007年   4637篇
  2006年   4354篇
  2005年   3682篇
  2004年   3385篇
  2003年   3437篇
  2002年   3156篇
  2001年   2657篇
  2000年   2592篇
  1999年   2306篇
  1998年   2186篇
  1997年   1789篇
  1996年   1599篇
  1995年   1449篇
  1994年   1330篇
  1993年   1142篇
  1992年   1099篇
  1991年   867篇
  1990年   705篇
  1989年   623篇
  1988年   562篇
  1987年   449篇
  1986年   382篇
  1985年   458篇
  1984年   441篇
  1983年   215篇
  1982年   360篇
  1981年   410篇
  1980年   307篇
  1979年   293篇
  1978年   222篇
  1977年   208篇
  1976年   157篇
  1973年   111篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
The management of voice disorders may follow one of four approaches: surgical, pharmacological, technical aid, and/or voice therapy. The latter approach offers a wide variety of techniques, each based on certain theoretical beliefs. One of these techniques is the Smith Accent Method. The principles and goals of the Accent Method are presented. The results of its application are discussed. This technique proved effective for cases of functional voice disorders, vocal nodules, and some degrees of vocal fold paralysis.  相似文献   
42.
We shall prove here that any binary relation on a base E with cardinality n > 6 is reconstructible from its restrictions of cardinality 2, 3, 4 and (n - 1). This proof needs results of part I of this paper where we characterize any pair of relations R, R' which are 2-, 3- and 4-hypomorphic. As a corollary we obtain that any binary relation is (n - 4)-reconstructible (when n > 9).  相似文献   
43.
The morphology of blends of styrenic polymers in a matrix of 75% Nylon-6 prepared in a Brabender Plasti-Corder was examined by scanning electron microscopy. Styrene/acrylonitrile copolymers (SAN) form smaller particles as the AN level increases owing to the corresponding decrease in the SAN–polyamide interfacial tension. Various styrenic polymers containing functional groups, maleic anhydride or oxazoline type, that can react with Nylon-6 during melt processing were added to the SAN phase which also led to a decrease in the particle size owing to the graft copolymer formed in situ. The effects of functional group type, amount of functional groups per chain, amount of functional polymer added, and the miscibility of the styrene/maleic anhydride (SMA) and SAN copolymers on the morphology of the styrenic phase in the Nylon-6 matrix are described. © 1992 John Wiley & Sons, Inc.  相似文献   
44.
We proved in the first part [1] that plane geometry over Pythagorean fields is axiomatizable by quantifier-free axioms in a language with three individual constants, one binary and three ternary operation symbols. In this paper we prove that two of these operation symbols are superfluous.  相似文献   
45.
本文从影响消费的各个因素:居民收入、人口、教育、国家宏观政策等着手,对各因素进行了相关分析,运用多元统计中的岭回归估计法建立消费模型。从定量和定性分析的角度,分析了我国居民消费水平、居民收入、人口增长率、各层次教育、国家财政支出和银行利率等相关因素之间相互影响的数量变动关系和内在规律,就如何提高居民消费水平促进经济协调发展提出若干对策。  相似文献   
46.
1,2,3‐Triazole‐based polymers generated from the Cu(I)‐catalyzed cycloaddition between multivalent azides and acetylenes are effective adhesive materials for metal surfaces. The adhesive capacities of candidate mixtures of azide and alkyne components were measured by a modified peel test, using a customized adhesive tester. A particularly effective tetravalent alkyne and trivalent azide combination was identified, giving exceptional strength that matches or exceeds the best commercial formulations. The addition of Cu catalyst was found to be important for the synthesis of stronger adhesive polymers when cured at room temperature. Heating also accelerated curing rates, but the maximum adhesive strengths achieved at both room temperature and high temperature were the same, suggesting that crosslinking reaches the same advanced point in all cases. Polytriazoles also form adhesives to aluminum, but copper is bound more effectively, presumably because active Cu(I) ions may be leached from the surface to promote crosslinking and adhesion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5182–5189, 2007  相似文献   
47.
The paper outlines a procedure to identify the space-and time-dependent external nonstationary load acting on a closed circular cylindrical shell of medium thickness. Time-dependent deflections at several points of the shell are used as input data to solve the inverse problem. Examples of numerical identification of various nonstationary loads, including moving ones are presented. The relationship between the external load and the stress-strain state of the shell is described by the Volterra equation of the first kind. The identification problem is solved using Tikhonov's regularization method and Apartsin's h-regularization method __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 7, pp. 91–100, July 2008.  相似文献   
48.
Reduction of tetranuclear heterometallic complex Mo2Mg2 was simulated using the B3LYP and PBE density functional methods. The results of geometry calculations of the initial complex [MoVIO2Mg(MeOH)2(OMe)4]2 and a partially reduced MoV complex are in good agreement with experimental data. The reduced MoIII complex is characterized by a decrease in the binding energy of aqua ligands. Structural rearrangement of the complex with release of a coordination position at the Mo atoms requires small energy expenditure. One can assume that the reduction of the polynuclear complex causes overcrowding of its coordination sphere, which favors formation of dinitrogen complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 441–457, March, 2008.  相似文献   
49.
介绍了虚拟技术在实验教学改革中的作用与意义,探讨了电子信息系统实验教学改革的新思路与实现措施,并总结了实验教学改革的初步成果.  相似文献   
50.
§1. IntroductionIn the additive theory of prime numbers, one studies the representation of positive in-tegers by powers of primes. For the quadratic case, Hua [1] proved that each large integercongruent to 5 modulo 24 can be written as the sum of ?ve squ…  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