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   173340篇
  免费   16902篇
  国内免费   12084篇
化学   92800篇
晶体学   1832篇
力学   11907篇
综合类   666篇
数学   43445篇
物理学   51676篇
  2024年   225篇
  2023年   1999篇
  2022年   2333篇
  2021年   3417篇
  2020年   4115篇
  2019年   3877篇
  2018年   13090篇
  2017年   12642篇
  2016年   10389篇
  2015年   5454篇
  2014年   6069篇
  2013年   7834篇
  2012年   12660篇
  2011年   19330篇
  2010年   11922篇
  2009年   11962篇
  2008年   12902篇
  2007年   14256篇
  2006年   5771篇
  2005年   5887篇
  2004年   5094篇
  2003年   4819篇
  2002年   3622篇
  2001年   2454篇
  2000年   2226篇
  1999年   2198篇
  1998年   1921篇
  1997年   1700篇
  1996年   1745篇
  1995年   1479篇
  1994年   1313篇
  1993年   1094篇
  1992年   945篇
  1991年   834篇
  1990年   694篇
  1989年   556篇
  1988年   430篇
  1987年   391篇
  1986年   387篇
  1985年   307篇
  1984年   229篇
  1983年   188篇
  1982年   166篇
  1981年   116篇
  1980年   105篇
  1979年   68篇
  1978年   56篇
  1973年   42篇
  1914年   45篇
  1909年   41篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
951.
952.
A group of machines for processing a set of jobs in a manufacturing system is often located in a serial line. An efficient strategy for locating these machines such that the total travel distance or the cost of transporting the jobs is minimized is desired. In this research, the assumption of a linear line with equally spaced machine location is relaxed. This research addressed problems of locating unique machines. It is found that the machine distances possess unique properties in this type of a problem. Utilizing these properties, heuristic strategies are proposed to obtain efficient solution where optimal methods are expected to be computationally prohibitive. A lower bound for the optimum solution is also proposed. Results are encouraging.  相似文献   
953.
The paper proves some general facts on commutators that refer to Fuglede-Putnam classical theorem in the spectral theory of not necessarily selfadjoint operators.  相似文献   
954.
Stimulated Raman adiabatic passage (STIRAP) has been successfully extended to multilevel system. During the STIRAP process, the intermediate levels have notable population which is detrimental if these levels could decay to other levels through spontaneous emission. This paper proposes a novel method to reduce the intermediate level population during the STIRAP process. A complete population transfer can be achieved in this modified STIRAP even if the intermediate level decays to other levels.  相似文献   
955.
Those who have worked in the Royal Institution of Great Britain have, since its foundation in 1799, made significant contributions to scientific knowledge, to its practical application, and to its communication to a wide variety of audiences. Such work cannot be carried out in an architectural vacuum, and in this paper we examine how the buildings of the Royal Institution, 20 and 21 Albemarle Street in central London, have shaped the work undertaken within its walls and how, on a number of occasions, the buildings have been reconfigured to take account of the evolving needs of scientific research and communication. This paper is based on the Conservation Plan of the Royal Institution that we wrote during 2003. The Conservation Plan did not examine the land owned by the Royal Institution to the north (i.e., 22 and 23 Albemarle Street; for this area see Richard Garnier, “Grafton Street, Mayfair,” Georgian Group Journal 13 (2003), 210–272), but it did discuss 18 and 19 Albemarle Street. In this paper we concentrate on the core Royal Institution buildings at 20 and 21 Albemarle Street. Other studies of the relationship of architecture,space, and science include Crosbie Smith and Jon Agar, ed., Making Space for Science: Territorial Themes in the Shaping of Knowledge (Basingstoke: Macmillan, 1997); Peter Galison and Emily Thompson, ed., The Architecture of Science (Cambridge, Mass.: MIT Press, 1999); and Sophie Forgan,“The architecture of science and the idea of a university,” Studies in History and Philosophy of Science 20 (1989), 405–434. Frank A.J.L. James is Professor of the History of Science at the Royal Institution; he has written widely on the history of nineteenth-century science in its social and cultural contexts and is editor of the Correspondence of Michael Faraday. He is President of the British Society for the History of Science. Anthony Peers is an Associate of Rodney Melville and Partners where he works in the field of building conservation as an architectural historian. He is a Council member of the Ancient Monument Society.  相似文献   
956.
Summary. Free radical couplings from furan, as cheap starting material, were studied in view of developing a rapid strategy en route to the synthesis of derivatives of nonactin. The chain containing the alcohol function was introduced in one or two steps in 86% yield. For the introduction of the second chain with the ester function two different coupling methods were tested. Starting from the advanced intermediates obtained nonactin derivatives can be prepared by catalytic hydrogenation of the furan ring.  相似文献   
957.
A Yang–Mills theory in a purely symplectic framework is developed. The corresponding Euler–Lagrange equations are derived and first integrals are given. We relate the results to the work of Bourgeois and Cahen on preferred symplectic connections.  相似文献   
958.
This paper describes work carried out with hospital consultants in Lancaster District Health Authority to develop and use computerized waiting list management models. The ‘what if?’ models produced have been found to be a very useful tool in the constructive debate about problems faced by consultants and managers, and of the options available to them.  相似文献   
959.
睾酮是国际奥委会规定禁用的99种兴奋剂之一,由于睾酮是内源性激素,因此不能靠定性来判断运动员是否服用了睾酮,在人体激素代谢中,产生睾酮差向异构体——表睾酮,在男性黄种人中睾酮与表睾酮浓度比约为1:1,白种人中略高一些,根据这一情况,国际奥委会规定,人尿中睾酮与表睾酮之间浓度比不得超过6:1,尿中排泄出的睾酮和表睾酮是以葡  相似文献   
960.
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