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   524篇
  免费   36篇
化学   353篇
力学   9篇
数学   68篇
物理学   130篇
  2022年   3篇
  2021年   13篇
  2020年   14篇
  2019年   11篇
  2018年   5篇
  2017年   5篇
  2016年   25篇
  2015年   19篇
  2014年   21篇
  2013年   24篇
  2012年   30篇
  2011年   32篇
  2010年   19篇
  2009年   26篇
  2008年   30篇
  2007年   27篇
  2006年   26篇
  2005年   19篇
  2004年   20篇
  2003年   10篇
  2002年   28篇
  2001年   14篇
  2000年   10篇
  1999年   12篇
  1998年   7篇
  1997年   7篇
  1995年   7篇
  1994年   3篇
  1993年   3篇
  1992年   3篇
  1991年   6篇
  1990年   3篇
  1989年   4篇
  1986年   3篇
  1985年   5篇
  1984年   4篇
  1983年   2篇
  1982年   4篇
  1981年   4篇
  1980年   6篇
  1979年   4篇
  1978年   3篇
  1977年   3篇
  1976年   5篇
  1975年   3篇
  1974年   3篇
  1973年   6篇
  1970年   2篇
  1969年   3篇
  1905年   3篇
排序方式: 共有560条查询结果,搜索用时 46 毫秒
31.
Propagation of Aharonov-Bohm matter waves and light waves in moving media is characterized by the interaction electromagnetic momentum. Thus, recent models of light propagation in moving rarefied media justify and call for an optical experiment of the Mascart-Jamin type, capable of testing the modern interpretations of ether drift experiments.  相似文献   
32.
The distribution and the origin of carbon and nitrogen in sediments of an Italian lagoon--located north-east of Ravenna town--were investigated. From 1957 to 1976, the lagoon had been affected by a strong industrial pollution due to an important petrochemical complex. At present, industrial and domestic waste waters undergo a treatment process before being discharged into the lagoon. Sediment samples from 10 locations throughout the lagoon were analysed, in order to document the spatial and vertical distribution of C and N. Data show a very strong variability (organic carbon content varies between 8.9% and 0.14%) and the highest values were found in the immediate vicinity of the industrial discharge. Sediment organic matter shows allochthonous origin in proximity of industrial discharge and autochthonous origin in the remaining areas.  相似文献   
33.
We report the diastereoselective addition of a wide range of nucleophiles to chiral pyrazolines to provide facile access to a range of useful densely functionalized building blocks for asymmetric synthesis. Coupled with the asymmetric cycloaddition reaction of Me(3)SiCHN(2) to chiral acrylates, access to these chiral heterocycles is considerably expanded.  相似文献   
34.
We want in this note to clarify some aspects of the Machian foundation of the concept of mass in classical mechanics; specifically, we show how the relations of transitivity for the mass-ratios, necessary for a well grounded definition of mass, can be derived from Machian postulates.  相似文献   
35.
The computations performed in a previous paper for hypothetical structures of the site active in the polymerization of olefins at the (110) surfaces of TiCl3-α are extended to edges, steps and reliefs on (111) surfaces of all the layered modifications of TiCl3. Our computations suggest that edges, steps and reliefs of all the layered modifications of TiCl3 should behave similarly in providing active sites; polymerization should occur on these more exposed sites because of the much lower activation energies than for plain surfaces. A unique general model emerges: lower steric repulsions appear to be implied for a coordination of the polymeric chain on the more hindered octahedral position at a titanium atom and this, in turn, causes a chiral orientation of the first carbon-carbon bond of the chain. This orientation may be the main factor in determining the stereospecificity.  相似文献   
36.
The existence of solutions of a nonlinear parabolic equation describing the gravitational interaction of particles is studied for the initial data in spaces of (generalized) pseudomeasures. This approach permits us to relax regularity assumptions on the initial conditions and to prove asymptotic stability results for the above problem.Mathematics Subject Classification (2000):35B40, 35K15, 82C21  相似文献   
37.
The sigma-enynyl complex [TpRu(C(Ph)=C(Ph)C identical to CPh)(P-MeiPr2)] efficiently catalyses the regioselective cyclization of alpha,omega-alkynoic acids to yield endocyclic enol lactones having ring size up to 12 atoms.  相似文献   
38.
We consider the maximum function f resulting from a finite number of smooth functions. The logarithmic barrier function of the epigraph of f gives rise to a smooth approximation g of f itself, where >0 denotes the approximation parameter. The one-parametric family g converges – relative to a compact subset – uniformly to the function f as tends to zero. Under nondegeneracy assumptions we show that the stationary points of g and f correspond to each other, and that their respective Morse indices coincide. The latter correspondence is obtained by establishing smooth curves x() of stationary points for g , where each x() converges to the corresponding stationary point of f as tends to zero. In case of a strongly unique local minimizer, we show that the nondegeneracy assumption may be relaxed in order to obtain a smooth curve x().  相似文献   
39.
Morales  P.  Mazarío  F. García  Guerra  P. Jiménez 《Order》2000,17(1):43-60
Let (X, F) be an Alexandroff space, let A(F) be the Boolean subalgebra of 2 X generated by F, let G be a Hausdorff commutative topological lattice group and let rbaF(A(F), G) denote the set of all order bounded F-inner regular finitely additive set functions from A(F) into G. Using some special properties of the elements of rbaF(A(F), G), we extend to this setting the first decomposition theorem of Alexandroff.  相似文献   
40.
In a recent article [M. Consoli, E. Costanzo, Phys. Lett. A 333 (2004) 355], M. Consoli and E. Costanzo have investigated classical and modern aether drift experiments and explored the narrow window for detection of a preferred reference frame. This Letter proposes an easy to perform variant of Fizeau's experiment, which may confirm or deny Consoli–Costanzo's claims.  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