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   685579篇
  免费   6686篇
  国内免费   1503篇
化学   335115篇
晶体学   9789篇
力学   35917篇
综合类   16篇
数学   100293篇
物理学   212638篇
  2021年   5758篇
  2020年   6424篇
  2019年   7248篇
  2018年   13838篇
  2017年   14021篇
  2016年   15996篇
  2015年   8251篇
  2014年   13216篇
  2013年   28572篇
  2012年   24575篇
  2011年   33039篇
  2010年   23631篇
  2009年   23788篇
  2008年   30630篇
  2007年   31946篇
  2006年   23121篇
  2005年   23001篇
  2004年   20483篇
  2003年   18814篇
  2002年   18059篇
  2001年   18603篇
  2000年   14523篇
  1999年   11073篇
  1998年   9577篇
  1997年   9225篇
  1996年   8842篇
  1995年   7944篇
  1994年   7900篇
  1993年   7671篇
  1992年   8243篇
  1991年   8623篇
  1990年   8340篇
  1989年   8189篇
  1988年   7991篇
  1987年   7944篇
  1986年   7457篇
  1985年   9365篇
  1984年   9613篇
  1983年   7843篇
  1982年   8084篇
  1981年   7786篇
  1980年   7294篇
  1979年   8008篇
  1978年   8219篇
  1977年   8157篇
  1976年   8179篇
  1975年   7504篇
  1974年   7346篇
  1973年   7513篇
  1972年   5722篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
933.
Applied Magnetic Resonance - We examined by electron spin resonance (ESR) spectroscopy the thermal decay of radicals as induced by γ-irradiation on pepper. Upon irradiation, the satellite...  相似文献   
934.
A nonlinear (in the cubic approximation) relaxation equation of state is derived for a rod containing cracks partially filled with an incompressible viscous liquid. The nonlinear effects of the self-action and interaction of low-and high-frequency longitudinal elastic waves propagating in such a rod are studied for the cases of identical and size-varied cracks. Linear and nonlinear acoustic parameters characterizing the self-action and interaction of elastic waves in a cracked rod are determined.  相似文献   
935.
The structure of neutron-rich beryllium isotopes has been investigated using different heavy-ion-induced transfer reactions. In neutron transfer reactions, the population of final states shows a strong sensitivity to the chosen core nucleus, i.e., the target nuclei 9Be or 10Be, respectively. Molecular rotational bands up to high excitation energies are observed with 9Be as the core due to its pronounced 2α-cluster structure, whereas only a few states at low excitation energies are populated with 10Be as the core. For 11Be, a detailed investigation has been performed for the three states at 3.41, 3.89, and 3.96 MeV, which resulted in the most probable spin-parity assignments 3/2+, 5/2?, and 3/2?, respectively. Furthermore, we have studied particle-hole states of 16C using the 13C(12C, 9C)16C reaction and found 14 previously unknown states. Using the 12C(12C, 9C)15C reaction, five new states were observed for 15C.  相似文献   
936.
We describe in detail fundamental properties of continuity modules of various orders in the spaces L p of functions defined on a finite segment. We establish some general estimates of seminorms in terms of continuity modules with the best known constants. An example of application of these results to the best approximations is considered. Bibliography: 32 titles.  相似文献   
937.
Considering the importance of the X-ray production cross sections for the determination of the element concentrations in a given material, we have measured them experimentally for Al Si, Sc, Ti, V, Fe, Co, Ni and Cu bombarded by protons with energies ranging from 40 to 180 keV. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
938.
We investigate analytically and numerically the influence of the type of the photorefractive nonlinear response on the periodic states (attractors) which occur during feedback controlled 2W-coupling and correspond to almost 100% diffraction efficiency of the dynamic index grating. In addition to the case of the local response typical, for example, for LiNbO3 crystals we consider the cases of nonlocal (diffusive) response (BaTiO3, SBN) and resonant response (DC-biased BSO, BTO, and BGO crystals). It is shown that the conditions for the transition to the periodic states and their apparent characteristics are strongly different for the two limiting cases above. Received 16 July 2002 / Received in final form 29 October 2002 Published online 4 March 2003  相似文献   
939.
The uptake of technetium on bentonite materials has been studied from the point of view of the characterization of long-term radioactive elements behavior in nuclear waste repository. It is generally known that bentonite materials show an excellent cation-exchange capacity and on the other hand a poor uptake of anions. The aim of our research has been to find out the conditions suitable for technetium sorption on selected bentonite under oxidizing conditions. The influence of the addition of different materials (e.g., activated carbon, graphite, Fe2+, Fe) with bentonite, the effect of solid:aqueous phase ratio and a pH value on the percentage of technetium uptake and on the K d values were tested.This revised version was published online in November 2005 with corrections to the Cover Date.  相似文献   
940.
Many problems arising in practical applications lead to linear programming problems. Hence, they are fundamentally tractable. Recent interior-point methods can exploit problem structure to solve such problems very efficiently. Infeasible interior-point predictor–corrector methods using floating-point arithmetic sometimes compute an approximate solution with duality gap less than a given tolerance even when the problem may not have a solution. We present an efficient verification method for solving linear programming problems which computes a guaranteed enclosure of the optimal solution and which verifies the existence of the solution within the computed interval.  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