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   568147篇
  免费   5930篇
  国内免费   1607篇
化学   274010篇
晶体学   8009篇
力学   29169篇
综合类   13篇
数学   95928篇
物理学   168555篇
  2021年   3768篇
  2020年   4202篇
  2019年   4539篇
  2018年   20261篇
  2017年   20530篇
  2016年   16498篇
  2015年   6875篇
  2014年   8927篇
  2013年   20622篇
  2012年   21581篇
  2011年   36015篇
  2010年   23129篇
  2009年   23391篇
  2008年   30516篇
  2007年   34474篇
  2006年   16679篇
  2005年   20805篇
  2004年   17417篇
  2003年   16168篇
  2002年   13699篇
  2001年   13758篇
  2000年   10571篇
  1999年   8079篇
  1998年   6771篇
  1997年   6469篇
  1996年   6381篇
  1995年   5664篇
  1994年   5549篇
  1993年   5362篇
  1992年   5942篇
  1991年   6057篇
  1990年   5776篇
  1989年   5602篇
  1988年   5634篇
  1987年   5508篇
  1986年   5220篇
  1985年   6709篇
  1984年   6849篇
  1983年   5438篇
  1982年   5523篇
  1981年   5498篇
  1980年   5104篇
  1979年   5491篇
  1978年   5630篇
  1977年   5453篇
  1976年   5414篇
  1975年   4996篇
  1974年   4954篇
  1973年   4997篇
  1972年   3513篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
831.
Oximes of 4-(4-pyrazolyl)-3-buten-2-onees obtained by successive reaction of 3-aryl-4-formylpyrazoles with acetone and hydroxylamine at the treatment with iodine suffered an oxidative cyclization yielding 3-aryl-4-(5-isoxazolyl)pyrazoles.  相似文献   
832.
Possibilities of utilization of by-products formed in manufacture of epichlorohydrin are considered. A promising way to utilize wastes from production of epichlorohydrin by synthesis of 2,3-dichloropropene from 1,2,3-trichloropropane is suggested.  相似文献   
833.
834.
835.
836.
Polymer films with a dispersed liquid crystal were prepared by photopolymerization of (meth)acrylic monomers. The electrooptical properties of these films were studied. The influence exerted by the composition of the monomer mixture, cross-linking agents, and chain-transfer agent on the liquid crystal drop size and on the transmission of the polymer-liquid crystal films was examined.  相似文献   
837.
838.
We study the short-term staffing problem of systems that experience random, non-stationary demand. The typical method to accommodate changes in arrival rate is to use historical data to identify peak periods and associated forecasting for upcoming time windows. In this paper, we develop a method that instead detects change as it happens. Motivated by an automatic call distributor system in a call centre with time-varying arrivals, we propose a change detection algorithm based upon non-homogeneous Poisson processes. The proposed method is general and may be thought of as a feed-forward strategy, in which we detect a change in the arrival process, estimate the new magnitude of the arrival rate, and assign an appropriate number of servers to the tasks. The generalized likelihood ratio statistic is used and a recommendation for its decision limit is developed. Simulation results are used to evaluate the performance of the detector in the context of a telephone call centre.  相似文献   
839.
This paper considers a receiver set partitioning and sequencing problem in a wavelength division multiplexing single-hop lightwave network for multicasting traffic. The problem is analysed in the approach of uncapacitated single batch-processing machine scheduling. In the analysis, several solution properties are characterized with respect to a mean flow time measure, based upon which two heuristic algorithms are developed, along with a dynamic programming algorithm. Several numerical experiments show that the heuristic algorithms generate good schedules. The problem is extended to consider two measures simultaneously including the mean flow time and the number of transmissions, for which the proposed algorithms also perform well.  相似文献   
840.
A phantom composed of alanine dosimeter material has been constructed and depth–dose measurements made in a 10 MeV electron beam. The results have demonstrated the feasibility of using relative depth–dose measurements to determine stopping power ratios in materials of dosimetric interest. Experimental stopping power ratios for alanine dosimeter material and water agreed with the data of ICRU Report 37 within the uncertainty of the experiment (±1.2% at a 95% confidence level).  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