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   33376篇
  免费   1098篇
  国内免费   251篇
化学   22983篇
晶体学   229篇
力学   793篇
数学   5531篇
物理学   5189篇
  2022年   217篇
  2021年   424篇
  2020年   526篇
  2019年   492篇
  2018年   382篇
  2017年   375篇
  2016年   841篇
  2015年   741篇
  2014年   816篇
  2013年   1767篇
  2012年   1904篇
  2011年   2381篇
  2010年   1158篇
  2009年   1020篇
  2008年   2025篇
  2007年   2052篇
  2006年   2014篇
  2005年   1880篇
  2004年   1608篇
  2003年   1391篇
  2002年   1299篇
  2001年   415篇
  2000年   407篇
  1999年   371篇
  1998年   343篇
  1997年   372篇
  1996年   498篇
  1995年   356篇
  1994年   318篇
  1993年   294篇
  1992年   290篇
  1991年   250篇
  1990年   218篇
  1989年   218篇
  1988年   243篇
  1987年   201篇
  1986年   187篇
  1985年   356篇
  1984年   355篇
  1983年   255篇
  1982年   331篇
  1981年   338篇
  1980年   316篇
  1979年   300篇
  1978年   268篇
  1977年   244篇
  1976年   220篇
  1975年   224篇
  1974年   224篇
  1973年   228篇
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
121.
122.
N. David Mermin 《Pramana》1998,51(5):549-565
I list several strong requirements for what I would consider a sensible interpretation of quantum mechanics and discuss two simple recent theorems which have important implications for such an interpretation. My talk will not clear everything up; indeed, you may conclude that it has not cleared anything up. But I hope it will provide a different perspective from which to view some old and vexing puzzles (or, if you believe nothing needs to be cleared up, some ancient verities.)  相似文献   
123.
124.
Nonequilibrium statistical mechanics close to equilibrium is studied using SRB states and a formula [10] for their derivatives with respect to parameters. We write general expressions for the thermodynamic fluxes (or currents) and the transport coefficients, generalizing the results of [4, 5]. In this framework we give a general proof of the Onsager reciprocity relations. Received: 2 December 1996 / Accepted: 13 March 1997  相似文献   
125.
In this paper a statistical multiplexer that processes a mixture of real-time and non-real-time traffic is studied under bursts of traffic. Different scheduling algorithms are compared under conditions when one of the classes of traffic has a sudden increase in its arrival rate during a short period of time. The results show a difference in the way the scheduling disciplines studied behave under short overloads of traffic even though the scheduling algorithms had been set up to give similar performance under steady-state arrivals. The lifetime of real-time packets is shown to have a great effect on the way in which the performance of the scheduling algorithms compare.Robert Lackman is an IBM employee in the IBM Resident Study Program.  相似文献   
126.
127.
Dibutyltin-3-hydroxyflavone, Bu2Sn(of), is a new fluorescence probe inhibitor of F1F0-ATPase and oxidative phosphorylation which inhibits by titration of an unidentified component of F0. Its site of action is closely related to that of the trialkyltins and of venturicidin. This F0 component is part of a pool of this component which is present in the heart mitochondrial inner membrane at levels of 5–7 nmol (mg protein)?1 [18 ± 3 Bu2Sn(of) sites per mol F1F0-ATPase]. However, ATPase activity in submitochondrial particles is near maximally inhibited by titration of approx. three Bu2Sn(of) sites per mol F1F0-ATPase. Over 60% (60–80%) of the Bu2Sn(of) interaction sites can be lost during the purification of F1F0-ATPase from submitochondrial particles. The number of Bu2Sn(of) interaction sites in various F1F0-ATPase preparations is variable. The high numbers of Bu2Sn(of) sites per mol F1F0-ATPase for heart mitochondria (18–21) and submitochondrial particles (15–19.5) decline in ATP synthase (11–15) to the low values obtained in Complex V (7–10.5) and the minimal values observed in highly purified F1F0?ATPase (3.5–5.6), thus indicating a variable dissociable component or cofactor of ATP synthase. The Bu2Sn(of) interaction site, a component of ATP synthase, is responsive to the redox status of the respiratory chain and the interaction with Bu2Sn(of) is with the reduced form of this component. Fluorescence titration studies show that this component is in redox equilibrium with the ubiquinone pool of the respiratory chain. It is proposed that this redox component serves as an inhibitor titratable cofactor pool which cycles through an F0 interaction site (or sites) via a system which serves as an energy-transfer link between the respiratory chain and ATP synthase.  相似文献   
128.
This paper presents an active patch array designed at 24 GHz. It can be used as a front-end component for a phased array. A series resonant array structure is chosen which is compact and easy excite. With 5 elements, the array proved a 12-dB antenna gain. A power amplifier and a low noise amplifier are designed on a single GaAs chip (PALNA). Bias switch is used in the PALNA, which greatly reduces the switch loss in a transceiver and increases the efficiency. 20-dB small signal gain is achieved in both power amplifier and low noise amplifier. The active patch array is built by the combination of the patch array and PALNA. The measured active gain of this antenna is 35-dB for the PA mode and 31-dB for the LNA mode. This active patch array can obtain an EIRP of 34 dBm with a total radiated power of 22dBm and a maximum PAE of 32%. To check the noise performance, we applied sources at both normal temperature and 77K (liquid nitrogen) and extracted the noise figure (3.5 dB) of the active antenna by the Y factor method. The results proved that the active antenna is working efficiently as both a transmitting and receiving antenna.  相似文献   
129.
130.
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