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   8153篇
  免费   474篇
  国内免费   225篇
化学   6062篇
晶体学   58篇
力学   258篇
综合类   15篇
数学   1043篇
物理学   1416篇
  2023年   86篇
  2022年   104篇
  2021年   122篇
  2020年   199篇
  2019年   175篇
  2018年   125篇
  2017年   115篇
  2016年   268篇
  2015年   221篇
  2014年   244篇
  2013年   436篇
  2012年   541篇
  2011年   617篇
  2010年   318篇
  2009年   281篇
  2008年   512篇
  2007年   529篇
  2006年   518篇
  2005年   444篇
  2004年   394篇
  2003年   360篇
  2002年   332篇
  2001年   160篇
  2000年   98篇
  1999年   91篇
  1998年   83篇
  1997年   101篇
  1996年   103篇
  1995年   77篇
  1994年   81篇
  1993年   111篇
  1992年   68篇
  1991年   59篇
  1990年   83篇
  1989年   52篇
  1988年   47篇
  1987年   42篇
  1986年   38篇
  1985年   74篇
  1984年   61篇
  1983年   39篇
  1982年   70篇
  1981年   60篇
  1980年   49篇
  1979年   48篇
  1978年   45篇
  1977年   28篇
  1976年   40篇
  1975年   24篇
  1974年   19篇
排序方式: 共有8852条查询结果,搜索用时 15 毫秒
991.
992.
Nearly half of all strategic alliances fail (Park and Russo, 1996; Dyer et al., 2001), often because of opportunistic behavior by one party or the other. We use a tournament and simulation to study strategies in an iterated prisoner's dilemma game with exit option to shed light on how a firm should react to an opportunistic partner. Our results indicate that a firm should give an alliance partner a second chance following an opportunistic act but that subsequent behavior should be contingent on the value of the next best opportunity outside the alliance. Firms should be more forgiving if the potential benefits from the alliance exceed other opportunities. The strategies were also found to be robust across a wide range of game lengths. The implications of these results for alliance strategies are discussed. Steven E. Phelan received his PhD in economics from La Trobe University (Australia) in 1998. Following five years at the University of Texas at Dallas, he joined the faculty of the University of Nevada Las Vegas in 2003. Dr. Phelan's research interests include competitive dynamics, organizational efficiency, acquisition and alliance performance, and entrepreneurial competence. His methods of choice to study these phenomena include agent-based modelling, experimental game theory, and event studies. Prior to joining academia, Dr. Phelan held executive positions in the telecommunications and airline industries and was a principal partner in Bridges Management Group, a consultancy specializing in strategic investment decisions. Richard J. Arend is a graduate of the University of British Columbia's doctoral program in Policy Analysis and Strategy. He is on the Management faculty of the University of Nevada, Las Vegas, arriving most recently from the Management faculty of New York University's Stern School of Business. Dr. Arend's interests lie in the analysis of unusual modes of firm value creation and destruction, where he has published in several top journals. He is a professional engineer with work and consulting experience in aerospace and computing. Darryl A. Seale joined the faculty of UNLV in 1999, following three years at Kent State University and the University of Alabama in Huntsville. Prior to Alabama, he completed his Ph.D. and M.S. degrees in Business Administration at the University of Arizona, his M.B.A. from Penn State University, and spent over ten years in management and market planning positions in the health care industry. Professor Seale's research interests include strategic decision making, bargaining and negotiation, and behavioral game theory. His research has been funded by the National Science Foundation and has been published in top-tier journals including Management Science, OBHDP, Games and Economic Behavior, and Strategic Management Journal. His teaching interests include business policy/strategy, managerial decision making, and bargaining and negotiation.  相似文献   
993.
We unify various constructions and contribute to the theory of singular symmetric functionals on Marcinkiewicz function/operator spaces. This affords a new approach to the non-normal Dixmier and Connes-Dixmier traces (introduced by Dixmier and adapted to non-commutative geometry by Connes) living on a general Marcinkiewicz space associated with an arbitrary semifinite von Neumann algebra. The corollaries to our approach, stated in terms of the operator ideal L(1,∞) (which is a special example of an operator Marcinkiewicz space), are: (i) a new characterization of the set of all positive measurable operators from L(1,∞), i.e. those on which an arbitrary Connes-Dixmier trace yields the same value. In the special case, when the operator ideal L(1,∞) is considered on a type I infinite factor, a bounded operator x belongs to L(1,∞) if and only if the sequence of singular numbers {sn(x)}n?1 (in the descending order and counting the multiplicities) satisfies . In this case, our characterization amounts to saying that a positive element xL(1,∞) is measurable if and only if exists; (ii) the set of Dixmier traces and the set of Connes-Dixmier traces are norming sets (up to equivalence) for the space , where the space is the closure of all finite rank operators in L(1,∞) in the norm ∥.∥(1,∞).  相似文献   
994.
Two-photon resonant multiphoton ionization has been used to prepare rotationally cooled and selected CH3I+ ions with controlled vibrational and electronic distributions. These ions are photodissociated by a second laser. The highly simplified photodissociation spectrum displays a clear dissociation threshold as well as bands hidden in earlier spectra. The data suggests corrections to previously determined vibrational constants.  相似文献   
995.
Summary In this paper a fundamental set of solutions is determined for certain nth order linear differential equations.  相似文献   
996.
997.
998.
A lane of traffic approaches an intersection where a traffic signal mediates between two possibilities: continued travel on that lane, or a turn onto a one-way street. Movement stops temporarily whenever a vehicle arrives at the intersection during a period permitting the alternative that is not the driver's intention. A simple model is presented which mathematically verifies the intuition that this type of signal cannot allow traffic to move efficiently during the rush-hour.  相似文献   
999.
Aryl benzoates are reduced to 1,4-dihydroaromatics with Na/NH3 in the presence of water.  相似文献   
1000.
Using Fourier transform infrared spectroscopy, the ethene yield from the reaction of C2H5 radicals with O2 has been determined to be 1.50 ± 0.09%, 0.85 ± 0.11%, and <0.1% at total pressures of 25, 50, and 700 torr, respectively. Additionally, the rate constant of the reaction of C2H5 radicals with molecular chlorine was measured relative to that with molecular oxygen. (1) A ratio k6/k7 = 1.99 ± 0.14 was measured at 700 torr total pressure which, together with the literature value of k7 = 4.4 × 10?12 cm3 molecule?1s?1, yields k6 = (8.8 ± 0.6) × 10?12 cm3 molecule?1s?1. Quoted errors represent 2σ. These results are discussed with respect to previous kinetic and mechanistic studies of C2H5 radicals.  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