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   1342篇
  免费   38篇
  国内免费   5篇
化学   915篇
晶体学   3篇
力学   33篇
数学   192篇
物理学   242篇
  2021年   6篇
  2020年   10篇
  2019年   16篇
  2018年   12篇
  2017年   22篇
  2016年   30篇
  2015年   34篇
  2014年   35篇
  2013年   83篇
  2012年   55篇
  2011年   79篇
  2010年   46篇
  2009年   45篇
  2008年   90篇
  2007年   80篇
  2006年   80篇
  2005年   86篇
  2004年   79篇
  2003年   51篇
  2002年   49篇
  2001年   23篇
  2000年   21篇
  1999年   12篇
  1998年   9篇
  1997年   16篇
  1996年   22篇
  1995年   15篇
  1994年   13篇
  1993年   10篇
  1992年   13篇
  1991年   5篇
  1990年   12篇
  1989年   8篇
  1988年   8篇
  1987年   11篇
  1986年   13篇
  1985年   11篇
  1984年   24篇
  1983年   23篇
  1982年   13篇
  1981年   11篇
  1980年   9篇
  1979年   8篇
  1978年   7篇
  1977年   9篇
  1976年   10篇
  1975年   6篇
  1973年   10篇
  1967年   4篇
  1954年   4篇
排序方式: 共有1385条查询结果,搜索用时 31 毫秒
101.
A method for studying metal ion self-diffusion in oxides (or other inorganic compounds) is described. The method involves oxidation of an appropriate metal to form a dense, single-layered scale of the lowest valent oxide (e.g. MnO on Mn). The specimen is then treated in high vacuum, and the evaporation of metal diffusing through the scale is measured. From the rates of metal diffusion/evaporation as a function of scale thickness information about the defect structure is obtained. The metal ion self-diffusion coefficient is determined from the rate of metal transport (evaporation) through a scale with known thickness. The requirements and limitations of the method are discussed. The use of the method is illustrated for Mn self-diffusion in MnO at 1100°C. The self-diffusion coefficient of Mn in MnO is proportional to the square root of the oxygen pressure, DMn ∞ pO212, in t MnO phase field near the MnO/Mn3O4 phase boundary. It is also tentatively concluded that the predominating defects near the Mn/MnO phase boundary are manganese interstitials.  相似文献   
102.
The form of the nonrigid bender has changes that here we do render. We add, nicely paired, a term to J2 and regroup factors that are singular. As a result, the nonrigid bender Hamiltonian can now be set up using only Van Vleck perturbation theory, for any triatomic molecule (linear, quasi-linear, or bent). It can be used to calculate the rotation-vibration energies of the molecule to high J(?10) from the bending potential energy function and the stretch and stretch-bend force constants.  相似文献   
103.
Herein we describe the design, synthesis, and solution structure of a novel type of conjugate composed of a naturally occurring bio-active ligand bound to an artificial peptidomimetic backbone; in this first report on such functionalized foldamers we utilized a beta-peptide as backbone and a GalNAc carbohydrate residue as ligand.  相似文献   
104.
We report on a compact interferometer for the water-window soft-x-ray range that is suitable for operation with laser-plasma sources. The interferometer consists of a single diffractive optical element that focuses impinging x rays to two focal spots. The light from these two secondary sources forms the interference pattern. The interferometer was operated with a liquid-nitrogen jet laser-plasma source at lambda=2.88 nm. Scalar wave-field propagation was used to simulate the interference pattern, showing good correspondence between theoretical and experimental results. The diffractive optical element can simultaneously be used as an imaging optic, and we demonstrate soft-x-ray microscopy with interferometric contrast enhancement of a phase object.  相似文献   
105.
106.
Bromine-lithium exchange using tert-butyllithium at -78 degrees C initiates a cascade process whereby either xanthone derivatives or pentacyclic 13-azadibenzo[a,de]anthracenes are produced in high yields. The reaction proceeds via a sequential intramolecular trapping of organolithium intermediates.  相似文献   
107.
Pretreatment of polystyrene beads with a nonpolar organic solvent is the key for the generation of mechanically robust tablets consisting of neat functionalized polystyrene beads, both alone and in combination with solid reagents or catalysts. The novel dosing methodology provides accurately preweighed tablets in virtually any shape and size and with excellent disintegration properties, speeding up parallel solution and solid phase synthesis. The use of tablets is demonstrated in parallel Mitsunobu and acylation reactions.  相似文献   
108.
109.
This paper considers the problem of scheduling n jobs on m machines in an open shop environment so that the sum of completion times or mean flow time becomes minimal. It continues recent work by Bräsel et al. [H. Bräsel, A. Herms, M. Mörig, T. Tautenhahn, T. Tusch, F. Werner, Heuristic constructive algorithms for open shop scheduling to minmize mean flow time, European J. Oper. Res., in press (doi.10.1016/j.ejor.2007.02.057)] on constructive algorithms. For this strongly NP-hard problem, we present two iterative algorithms, namely a simulated annealing and a genetic algorithm. For the simulated annealing algorithm, several neighborhoods are suggested and tested together with the control parameters of the algorithm. For the genetic algorithm, new genetic operators are suggested based on the representation of a solution by the rank matrix describing the job and machine orders. Extensive computational results are presented for problems with up to 50 jobs and 50 machines, respectively. The algorithms are compared relative to each other, and the quality of the results is also estimated partially by a lower bound for the corresponding preemptive open shop problem. For most of the problems, the genetic algorithm is superior when fixing the same number of 30 000 generated solutions for each algorithm. However, in contrast to makespan minimization problems, where the focus is on problems with an equal number of jobs and machines, it turns out that problems with a larger number of jobs than machines are the hardest problems.  相似文献   
110.
The Carleson operator is closely related to the maximal partial sum operator for Fourier series. We study generalizations of this operator in one and several variables.  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