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   486969篇
  免费   4949篇
  国内免费   1659篇
化学   265000篇
晶体学   7155篇
力学   20123篇
综合类   12篇
数学   57071篇
物理学   144216篇
  2020年   3735篇
  2019年   4007篇
  2018年   4933篇
  2017年   4752篇
  2016年   7654篇
  2015年   5240篇
  2014年   7735篇
  2013年   21678篇
  2012年   16255篇
  2011年   20023篇
  2010年   13375篇
  2009年   13241篇
  2008年   18756篇
  2007年   19057篇
  2006年   18101篇
  2005年   16412篇
  2004年   14752篇
  2003年   13260篇
  2002年   13021篇
  2001年   14392篇
  2000年   11182篇
  1999年   8687篇
  1998年   7232篇
  1997年   7105篇
  1996年   6955篇
  1995年   6164篇
  1994年   5997篇
  1993年   5847篇
  1992年   6385篇
  1991年   6342篇
  1990年   6018篇
  1989年   5788篇
  1988年   6015篇
  1987年   5711篇
  1986年   5466篇
  1985年   7630篇
  1984年   7833篇
  1983年   6388篇
  1982年   6945篇
  1981年   6893篇
  1980年   6519篇
  1979年   6782篇
  1978年   6907篇
  1977年   6890篇
  1976年   6859篇
  1975年   6597篇
  1974年   6466篇
  1973年   6760篇
  1972年   4145篇
  1971年   3337篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Muonium in liquid SiCl has been observed for the first time at low temperature (−65°C) The observed polarization of muonium is as much as 25% of the total spin polarization and shows a fast relaxation rate.  相似文献   
992.
An exploratory Mössbauer spectroscopy study of the Fe-C system in the C rich region, prepared by high pressure-high temperature treatment near the graphite-diamond stability line, was made. The results obtained for the different processing conditions give no evidence of Fe intercalation in graphite. The presence of some water in the cell produced hydrated Fe complexes, which can explain the deleterious effect of water or hydrogen in the high pressure diamond synthesis.  相似文献   
993.
Eggenh&#;ffner  R.  Masini  R.  Bellingeri  E.  Cimberle  M. R.  Ferdeghini  C.  Costa  G. A.  Kaiser  E.  Signorelli  E. 《Il Nuovo Cimento D》1994,16(10):1659-1664
Il Nuovo Cimento D - The formation of Hg-based HTSC materials was investigated through the development of non-conventional techniques. The former was based on a singlestep synthesis at temperatures...  相似文献   
994.
It has previously been shown that nine of the most prominent procedures of interactive multiple objective programming can be considered as special cases of a common procedure called the unified algorithm. In this paper, we show how four additional procedures can be similarly included in the unified approach. Also, the paper presents a procedure-switching matrix that depicts the possibilities for switching from one procedure to another, one iteration to the next, in the unified algorithm if so directed by a user.  相似文献   
995.
Withanolides and related ergostane-type steroids.   总被引:1,自引:0,他引:1  
  相似文献   
996.
Non-Markovian Brownian motion in a periodic potential is studied by means of an electronic analogue simulator. Velocity spectra, the Fourier transforms of velocity autocorrelation functions, are obtained for three types of random force, that is, a white noise, an Ornstein—Uhlenbeck process, and a quasimonochromatic noise. The analogue results are in good agreement both with theoretical ones calculated with the use of a matrix-continued-fraction method, and with the results of digital simulations. An unexpected extra peak in the velocity spectrum is observed for Ornstein-Uhlenbeck noise with large correlation time. The peak is attributed to a slow oscillatory motion of the Brownian particle as it moves back and forth over several lattice spaces. Its relationship to an approximate Langevin equation is discussed.  相似文献   
997.
998.
The problems of determining and investigating the informative parameters of atmospheric electricity are discussed. It is shown that short-period variations in atmospheric electricity are ecologically significant. An automated system for monitoring atmospheric electricity and a method of processing the results of measurements are described. V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 88–98, May, 1998.  相似文献   
999.
1000.
The high resolution hyperfine spectroscopy, modulated adiabatic passage of oriented nuclei (MAPON), has been applied for the first time to high purity, elemental systems. Detailed comparisons between the electric quadrupole hyperfine interactions (EQI’s) and, in particular, their distributions, are obtained for60CoCo where the hosts are a single crystal of hcp cobalt and a polycrystalline cobalt foil of predominantly fcc character. For hcp Co, with the electronic magnetization, M, parallel to the c-axis, the mode value P/h=3e2qQ/4I(2I−1)h=−48.5(5) kHz. This fractional distribution implies the sharpest electric field gradient (efg) measured in a metal to date, using MAPON spectroscopy, in excess of two times sharper than that of the most dilute impurity efg in a crystallographically cubic ferromagnetic host. The mode efg is Vzz=−27.3(32)×1019 Vm−2. For the polycrystalline, predominantly fcc foil, prepared by quenching, the EQI mode value is P/h=−6.2(4) kHz with a FWHM of 12.0(7) kHz yielding a mode efg of Vzz=−3.5(5)×1019 Vm−2.  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