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   554779篇
  免费   5962篇
  国内免费   1332篇
化学   280829篇
晶体学   8223篇
力学   26374篇
综合类   14篇
数学   75755篇
物理学   170878篇
  2021年   4281篇
  2020年   4793篇
  2019年   5220篇
  2018年   12765篇
  2017年   13230篇
  2016年   12950篇
  2015年   6779篇
  2014年   9712篇
  2013年   22424篇
  2012年   20438篇
  2011年   29926篇
  2010年   20214篇
  2009年   20139篇
  2008年   27043篇
  2007年   29304篇
  2006年   18096篇
  2005年   20731篇
  2004年   17325篇
  2003年   15736篇
  2002年   14220篇
  2001年   14936篇
  2000年   11368篇
  1999年   8765篇
  1998年   7342篇
  1997年   7035篇
  1996年   6815篇
  1995年   6126篇
  1994年   6047篇
  1993年   5849篇
  1992年   6481篇
  1991年   6615篇
  1990年   6312篇
  1989年   6162篇
  1988年   6126篇
  1987年   5941篇
  1986年   5635篇
  1985年   7239篇
  1984年   7458篇
  1983年   5948篇
  1982年   6059篇
  1981年   5954篇
  1980年   5535篇
  1979年   5951篇
  1978年   6222篇
  1977年   6068篇
  1976年   5973篇
  1975年   5535篇
  1974年   5520篇
  1973年   5526篇
  1972年   3916篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Some structural and spectroscopic features of rare earth orthoaluminates are examined.The trigonal→ orthorhombic transition is studied in a series of NdxSm1−xAlO3 compounds. The evolution of the crystal structure is followed by X-ray analysis and optical absorption. The free ion and crystal field parameters of Nd3+ (4f3 configuration) are determined in LuAlO3:Nd3+.The anomaly of the calculated splitting of the levels is slight, but well characterized in NdAlO3. The spin correlated crystal field and orbitally correlated crystal field models are tested as well as an empirical correction which was proposed earlier.  相似文献   
912.
In an effort to clarify the role of controlled oxygen exposure in the synthesis of LaBa2Cu3Oy samples which achieve zero resistivity above 90 K, we have prepared samples of La(1+x)Ba(2–x)Cu3Oy with x approximately equal to 0 and with y varying between 6.22 and 7.00. We find that for large values of y, 6.88相似文献   
913.
The structural relaxation time for series of various liquids (alkanes, aliphatic alcohols, and diols) are calculated from published data on the shear viscosity and the heat of evaporation per unit volume. Liquids having a 3D H-bond network (diols) are characterized by relaxation times one to two orders of magnitudes longer than those typical of liquids without such a network (alkanes and aliphatic alcohols).  相似文献   
914.
Anilinepropylsilica xerogel was obtained by using an appropriate organosilane and tetraethyl orthosilicate as precursor reagents. The gelation was carried out using HF and NaF as catalysts. The presence of Na+ (when NaF was used) resulted in a decrease in the final organic content of the materials. This effect was interpreted as an inhibition of the organosilane polycondensation possibly due to the Na+ interaction with the SiO- groups of the hydrolyzed organosilane. The presence of Na+ also results in morphological changes in the xerogels.  相似文献   
915.
Thermodynamic fluctuations in systems that are in nonequilibrium steady states are always spatially long ranged, in contrast to fluctuations in thermodynamic equilibrium. In the present paper we consider a fluid subjected to a stationary temperature gradient. Two different physical mechanisms have been identified by which the temperature gradient causes long-ranged fluctuations. One cause is the presence of couplings between fluctuating fields. Secondly, spatial variation of the strength of random forces, resulting from the local version of the fluctuation-dissipation theorem, has also been shown to generate long-ranged fluctuations. We evaluate the contributions to the long-ranged temperature fluctuations due to both mechanisms. While the inhomogeneously correlated Langevin noise does lead to long-ranged fluctuations, in practice, they turn out to be negligible as compared to nonequilibrium temperature fluctuations resulting from the coupling between temperature and velocity fluctuations.  相似文献   
916.
We prove some new evaluations for multiple polylogarithms of arbitrary depth. The simplest of our results is a multiple zeta evaluation one order of complexity beyond the well-known Broadhurst–Zagier formula. Other results we provide settle three of the remaining outstanding conjectures of Borwein, Bradley, and Broadhurst. A complete treatment of a certain arbitrary depth class of periodic alternating unit Euler sums is also given.  相似文献   
917.
A method of solving the problem of sound radiation from a plate with elements of different thickness in its plane is proposed, and the results obtained with this method are presented. It is shown that the main sources of sound radiation are the inhomogeneous flexural fields formed in the elements on both sides of their joint.  相似文献   
918.
919.
Modification of Paving Asphalts with Sulfur   总被引:2,自引:0,他引:2  
Sulfur dissolved in oil components of asphalt is a binder, filler, and chemical co-reagent at once. The structure of sulfur-extended asphalt depends on its formula and heating temperature. Road pavement based on sulfur-extended asphalt demonstrates higher durability as compared to that with the conventional binders.  相似文献   
920.
In this paper, we describe an aircraft loading problem submitted by the French military agency (DGA) as part of a more general military airlift planning problem. It can be viewed as a kind of bi-dimensional bin-packing problem, with heterogeneous bins and several additional constraints. We introduce two-phase methods for solving this NP-hard problem. The first phase consists in building good initial solutions, thanks to two fast algorithms: a list-based heuristic and a loading pattern generation method. Both algorithms call a constraint-based subroutine, able to determine quickly if the items already loaded can be reshuffled to accommodate a new object. The second phase improves these preliminary solutions using local search techniques. Results obtained on real data sets are presented.  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