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   304962篇
  免费   3066篇
  国内免费   842篇
化学   165590篇
晶体学   4311篇
力学   12780篇
综合类   10篇
数学   36330篇
物理学   89849篇
  2020年   2508篇
  2019年   2669篇
  2018年   3493篇
  2017年   3506篇
  2016年   5323篇
  2015年   3508篇
  2014年   5181篇
  2013年   12527篇
  2012年   9832篇
  2011年   12045篇
  2010年   8214篇
  2009年   7862篇
  2008年   11197篇
  2007年   11343篇
  2006年   10788篇
  2005年   9728篇
  2004年   8922篇
  2003年   8020篇
  2002年   7842篇
  2001年   8006篇
  2000年   6233篇
  1999年   4886篇
  1998年   4358篇
  1997年   4372篇
  1996年   4105篇
  1995年   3797篇
  1994年   3975篇
  1993年   3668篇
  1992年   4122篇
  1991年   4083篇
  1990年   3964篇
  1989年   3815篇
  1988年   3898篇
  1987年   3757篇
  1986年   3625篇
  1985年   4816篇
  1984年   5123篇
  1983年   4289篇
  1982年   4464篇
  1981年   4360篇
  1980年   4342篇
  1979年   4248篇
  1978年   4583篇
  1977年   4479篇
  1976年   4488篇
  1975年   4133篇
  1974年   4162篇
  1973年   4293篇
  1972年   2993篇
  1971年   2496篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 4, pp. 581–587, April, 1991.  相似文献   
92.
It was shown that the reaction of o-hyroxyphenyldiphenylmethanol with benzaldehyde labeled with 17O and 18O isotopes proceeds in such a way that oxygen atoms of the starting phenoloalcohol are retained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 632–633, May, 1991.  相似文献   
93.
94.
It is proved that the variety of relevant disjunction lattices has the finite embeddability property. It follows that Avron's relevance logic RMI min has a strong form of the finite model property, so it has a solvable deducibility problem. This strengthens Avron's result that RMI min is decidable. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
95.
96.
The kinetics of radical copolymerization of acrylamide with lithium, sodium, and potassium 2-acrylamido-2-methylpropanesulfonates in concentrated aqueous solutions in the presence of potassium persulfate as initiating agent at pH 9 and 50°C was studied by dilatometry.  相似文献   
97.
In this paper we suggest a unique model for estimating the operating cost of each of three waste-collection systems. Under the traditional system, which is widely used, waste is typically collected in plastic bags and a three-man crew is needed on each vehicle. The other two systems require a one-man crew for vehicle collecting street containers. The side-loader system with fixed body automatically empties street containers into the vehicle body and empties the load at the disposal site. The side-loader system with demountable body allows the separation of the waste collection phase from transport to the disposal site, since the vehicle body can be demounted. We also present two case studies and show how the estimation of operating costs is a critical issue in decisions regarding the type of system to be used for waste collection.  相似文献   
98.
Procedures are discussed for production of rubber-bitumen compounds based on spent rubber items. A possibility of using these binders for paving is studied experimentally.  相似文献   
99.
In this paper necessary and sufficient conditions of null-controllability and approximate null-controllability are obtained for the wave equation on a half-axis. Controls solving these problems are found explicitly. Moreover, bang-bang controls solving the approximate null-controllability problem are constructed with the aid of solutions of a frequency extinguishing problem in the restricted band (−a,a) for this equation and the Markov power moment problem.  相似文献   
100.
We consider front solutions of the Swift–Hohenberg equation ∂ t u= -(1+ ∂ x 2)2 u + ɛ2 u -u 3. These are traveling waves which leave in their wake a periodic pattern in the laboratory frame. Using renormalization techniques and a decomposition into Bloch waves, we show the non-linear stability of these solutions. It turns out that this problem is closely related to the question of stability of the trivial solution for the model problem ∂ t u(x,t) = ∂ x 2 u (x,t)+(1+tanh(x-ct))u(x,t)+u(x,t) p with p>3. In particular, we show that the instability of the perturbation ahead of the front is entirely compensated by a diffusive stabilization which sets in once the perturbation has hit the bulk behind the front. Received: 23 February 2001 / Accepted: 27 August 2001  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