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   196320篇
  免费   2201篇
  国内免费   757篇
化学   108670篇
晶体学   3301篇
力学   7898篇
综合类   32篇
数学   18546篇
物理学   60831篇
  2016年   2333篇
  2015年   1744篇
  2014年   2466篇
  2013年   7925篇
  2012年   5365篇
  2011年   6742篇
  2010年   4494篇
  2009年   4440篇
  2008年   6061篇
  2007年   6236篇
  2006年   5991篇
  2005年   5476篇
  2004年   5014篇
  2003年   4468篇
  2002年   4343篇
  2001年   5798篇
  2000年   4412篇
  1999年   3550篇
  1998年   2775篇
  1997年   2802篇
  1996年   2759篇
  1995年   2544篇
  1994年   2415篇
  1993年   2303篇
  1992年   2803篇
  1991年   2684篇
  1990年   2629篇
  1989年   2662篇
  1988年   2598篇
  1987年   2596篇
  1986年   2409篇
  1985年   3272篇
  1984年   3283篇
  1983年   2715篇
  1982年   2909篇
  1981年   2845篇
  1980年   2754篇
  1979年   2897篇
  1978年   3139篇
  1977年   2959篇
  1976年   2896篇
  1975年   2753篇
  1974年   2701篇
  1973年   2719篇
  1972年   1759篇
  1971年   1466篇
  1968年   1929篇
  1967年   2129篇
  1966年   1920篇
  1965年   1497篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Antiproton-proton annihilation at rest in a gaseous H2 target at NTP into the final state π+ π? K ± π? (K 0) with an undetectedK 0 or \(\bar K^0 \) has been investigated. We observe theE(1420) resonance in the invariant mass spectrum (K 0)miss K ± π? with massM E =1413±8 MeV/c2 and widthГ E =62 ± 16MeV/c2 and find evidence for the production of thef 1(1285). The absolute branching ratio of \(\bar p\) p → π+ π? E 0,E 0K 0 L K ± π ? at (61±6)%P wave annihilation is (3.0±0.9)·10?4 of all annihilations. The observed suppression of theE production fromP wave with respect to theS wave together with some simple selection rules suggest that the quantum numbers of theE(1420) areJ pc=0?+ and not I++.  相似文献   
992.
Backward proton and pion production is studied in ν and \(\bar v\) charged current interactions in neon. The results are compared with other experiments and theory. The complete backward proton data is compatible with protons produced by reinteractions in the nucleus. However in events with only one proton, muon variables appear correlated to those for the backward proton, as expected by the two-nucleon correlation model.  相似文献   
993.
Evidence is presented that \(\bar p\) p annihilation proceeds via the formation of two jets, with average transverse momentum of the order of the nucleon mass. The implications of this behaviour is linked to the measured cross sections and multiplicities, and explanations for it have been sought in the underlying gluon and quark constituents of the \(\bar p\) p system. The confrontation of the suggested constituent mechanisms and experimental data lead to the concept that charm meson production may play a significant role in the \(\bar p\) p experiments at the highest available energies.  相似文献   
994.
This paper proposes a new type of high permittivity whispering gallery mode cylindrical dielectric resonators with a geometry which is very suitable for use in microstrip type integrated circuits. These oversized resonators, together with high Q factors and ease of fabrication, are potentially interesting for millimeter wave integrated filters and oscillators. In this paper, we report an experimental investigation of such resonators carried out in Ka band (26.5–40 GHz). Measured results including resonant frequencies and loaded quality factors will be presented. Application to millimeter wave filters will also be demonstrated.  相似文献   
995.
A kinematically correct treatment of the full transition amplitude for many-body hypernuclear production is presented. By an example of (+, K+) reaction, effects of the spin-flip amplitude and its interference with the spin-non-flip amplitude are demonstrated and specified for 12 C.Dedicated to Academician Václav Votruba on the occasion of his eightieth birthday.The discussions with many colleagues are appreciated, in particular those with R. Mach, L. Majling and T. Motoba were of much use.  相似文献   
996.
Considering a system ofN identical interacting particles, which obey Fermi-Dirac or Bose-Einstein statistics, we derive new formulas for correlation functions of the type (whereB j is diagonal in the free-particle states) in the thermodynamic limit. Thereby we apply and extend a superoperator formalism, recently developed for the derivation of long-time tails in semiclassical systems. As an illustrative application, the Boltzmann equation value of the time-integrated correlation functionC(t) is derived in a straightforward manner. Due to exchange effects, the obtained t-matrix and the resulting scattering cross section, which occurs in the Boltzmann collision operator, are now functionals of the Fermi-Dirac or Bose-Einstein distribution.  相似文献   
997.
We calculate the moments t q , whereq is not necessarily an integer, of the first passage time to trapping for a simple diffusion problem in one dimension. If a characteristic length of the system isL and t q ~L (q) asL, then we show that there is a phase transition atq=q c such that whenq<q c ,(g)=0, and forq>q c , (q) is a linear function ofq. These analytical results can be used to explain results for large moments for diffusion on a hierarchic structure. We also show how to calculate noninteger moments in terms of characteristic functions.  相似文献   
998.
Büttiker and Landauer studied scattering off an oscillating rectangular barrier in order to shed light on the time aspects of tunneling. The expression for the traversal time resulting from this study is controversial. In addition, doubts have recently been expressed on technical aspects of their work. In an attempt to clarify these issues, we investigate a generalization of their model to arbitrary oscillating barriers,V(x, t)=V 0(x)+V 1(x)cos t. In the process, we confirm that Büttiker and Landauer's work is technically sound. However, we show, by several examples, that no direct general relation exists between the characteristic frequency of an oscillating barrier and the duration of the tunneling process. For a wide range of realistic parameters this characteristic frequency does not even exist.This paper is dedicated to E. G. D. Cohen.  相似文献   
999.
1000.
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