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   271597篇
  免费   2128篇
  国内免费   636篇
化学   144942篇
晶体学   4172篇
力学   11985篇
综合类   9篇
数学   30031篇
物理学   83222篇
  2019年   2323篇
  2018年   3133篇
  2017年   3126篇
  2016年   4539篇
  2015年   2726篇
  2014年   4348篇
  2013年   10825篇
  2012年   8181篇
  2011年   10013篇
  2010年   7162篇
  2009年   6955篇
  2008年   9415篇
  2007年   9635篇
  2006年   9022篇
  2005年   8200篇
  2004年   7538篇
  2003年   6846篇
  2002年   6780篇
  2001年   7405篇
  2000年   5719篇
  1999年   4417篇
  1998年   3924篇
  1997年   3895篇
  1996年   3655篇
  1995年   3386篇
  1994年   3547篇
  1993年   3254篇
  1992年   3736篇
  1991年   3742篇
  1990年   3650篇
  1989年   3535篇
  1988年   3634篇
  1987年   3541篇
  1986年   3352篇
  1985年   4450篇
  1984年   4728篇
  1983年   3928篇
  1982年   4093篇
  1981年   4008篇
  1980年   3978篇
  1979年   3965篇
  1978年   4255篇
  1977年   4182篇
  1976年   4235篇
  1975年   3904篇
  1974年   3963篇
  1973年   4096篇
  1972年   2873篇
  1971年   2419篇
  1970年   2200篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
In vitro and in vivo proton T1 data are reported that demonstrate that the paramagnetic copper-D-penicillamine complex can be applied as a potential contrast agent to magnetic resonance imaging.  相似文献   
952.
The exchange of gramicidin between liposomes made of two different kinds of phospholipids has been studied using a fluorescent probe (pyranine). The experimentally observed rate of exchange is compared with that of nigericin, which is a simple carrier. Possible reasons for the difference in the rate of exchange are discussed and probable mechanisms suggested. It is proposed that gramicidin exchanges between vesicles by a contact mechanism.  相似文献   
953.
Electron energy distribution functions (eedf) in CO2 laser discharge (He—CO2—N2—CO mixture) have been calculated by solving the Boltzmann equation in the presence of given concentrations of excited (vibrational and electronic) states. The results show a well structured eedf as a result of second kind collisions coming from metastable electronic states of N2 and He as well as a strong dependence of rate coefficients for CO2 dissociation and for the ionization of the different species.  相似文献   
954.
Gamma rays of199Au obtained after double neutron capture in197Au were measured at the ILL high flux reactor. A level scheme up to 1770 keV excitation energy is established. The result is compared with IBFM and Boson-Fermion-Symmetry calculations.  相似文献   
955.
Parity violation effects have been studied at 40 neutron p-wave resonances of the even-even nuclei238U and232Th. Of these 11 show parity violation effects larger than 2 standard deviations, making parity violation a rather common phenomenon. Parity mixing up to 10% has been found. The root-mean squared matrix elements for parity violation derived from these resonances are M=0.58 (+0.50/-0.25) meV for238U, respectively 1.39 (+0.35/-0.38) meV for232Th.  相似文献   
956.
Summary A review of the correlations between gravitational-wave detectors and particle detectors during SN1987A is given. The correlation between the Maryland and Rome g.w. detectors with the Mont Blanc neutrino detector is illustrated. This correlation extends during a period of one or two hours centred at 2∶45 UT of 23 February 1987, with the ?neutrino? signals delayed by (1.1±0.5) s and with a probability of the order of 10−5 to be accidental. Using the data obtained with the Kamiokande and IMB detectors, with the same statistical choices and procedures for the data analysis used previously, the above result is confirmed with a probability of the order of 10−3 or 10−4 that the additional correlation be accidental. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.  相似文献   
957.
The general centered form for multi-variate polynomials is investigated and a computing procedure is proposed that results in a certain superset. Based on this procedure the optimal centered forms for monomials and for some special cases of polynomials are investigated.  相似文献   
958.
Periodic Nodal Surfaces (PNS) of Fourier series are derived and classified as fundamental invariants of structured matter. Relationships to periodic minimal surfaces PMS and to periodic zero potential surfaces (POPS) are given. A basic set of cubic PNS is represented in arithmetic form. The special importance of the invariance of the zeros to the type of the potential is stressed.  相似文献   
959.
In this note, we consider a class of two-point boundary value problems involving a pa- rameter in one of the boundary conditions. We shall show that if we know the solution corresponding to a particular value of the parameter, then the solution for any other value of the parameter can be obtained by a simple algebraic method.  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