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   419篇
  免费   17篇
  国内免费   3篇
化学   249篇
力学   5篇
数学   80篇
物理学   105篇
  2021年   3篇
  2019年   4篇
  2016年   12篇
  2015年   12篇
  2014年   6篇
  2013年   22篇
  2012年   25篇
  2011年   32篇
  2010年   11篇
  2009年   12篇
  2008年   26篇
  2007年   15篇
  2006年   20篇
  2005年   22篇
  2004年   17篇
  2003年   12篇
  2002年   16篇
  2001年   6篇
  2000年   5篇
  1999年   3篇
  1997年   7篇
  1996年   5篇
  1995年   8篇
  1994年   3篇
  1993年   6篇
  1992年   3篇
  1991年   3篇
  1989年   8篇
  1987年   3篇
  1986年   6篇
  1985年   3篇
  1984年   5篇
  1983年   3篇
  1982年   8篇
  1981年   5篇
  1980年   4篇
  1979年   3篇
  1977年   7篇
  1976年   4篇
  1975年   4篇
  1974年   7篇
  1973年   3篇
  1939年   2篇
  1931年   2篇
  1930年   2篇
  1927年   2篇
  1923年   2篇
  1885年   2篇
  1884年   2篇
  1881年   2篇
排序方式: 共有439条查询结果,搜索用时 15 毫秒
91.
We consider the problem of constraining a particle to a smooth compact submanifold Σ of configuration space using a sequence of increasing potentials. We compare the classical and quantum versions of this procedure. This leads to new results in both cases: an unbounded energy theorem in the classical case, and a quantum averaging theorem. Our two step approach, consisting of an expansion in a dilation parameter, followed by averaging in normal directions, emphasizes the role of the normal bundle of Σ, and shows when the limiting phase space will be larger (or different) than expected. Received: 16 November 2000 / Accepted: 2 February 2001  相似文献   
92.
In the neutral title complex, trans‐bis(2,2′‐imino­di­ethanol‐N,O)­bis­(iso­thio­cyanato)­nickel(II), [Ni(NCS)2(C4H11NO2)2], the iso­thio­cyanate ions and the di­ethanol­amine mol­ecules act as mono­dentate and bi­dentate ligands, respectively. The NiII ion exhibits a distorted octahedral configuration with crystallographically imposed inversion symmetry and NNCS—Ni—Namine and NNCS—Ni—Oamine bond angles of 88.78 (10) and 89.44 (10)°, respectively. The Ni—N bond distances are in the range 2.069 (3)–2.096 (2) Å. The mol­ecules are linked by hydrogen bonds to form a three‐dimensional infinite lattice.  相似文献   
93.
Line beam excimer laser annealing (ELA) is a well-known technique for thin Si-film crystallization and established in LTPS mass production. With introduction of sequential lateral solidification (SLS) some aspects such as crystalline quality, throughput and flexibility regarding the substrate size could be improved, but for OLED manufacturing still further process development is necessary. This paper discusses line beam ELA and SLS-techniques that might enable process engineers to make polycrystalline-silicon (poly-Si) films with a high degree of uniformity and quality as required for system on glass (SOG) and active matrix organic light emitting displays (AMOLED). Equipment requirements are discussed and compared to previous standards. SEM-images of process examples are shown in order to demonstrate the viability.  相似文献   
94.
A review is given of the principles, key developments and representative applications of small electrodes in flow-through electrochemical (ec) detectors having very low effective dead volume (<10 μl) for voltammetric and amperometric detection in flowing solutions. Emphasis is placed on factors contributing to high sensitivity, reliability and selectivity of ec detection as an integral part of larger analytical systems utilizing continuously flowing, unsegmented streams, e.g., flow-injection and liquid chromatographic analyses. Solid and mercury electrodes are considered under potentiostatic and potentiodynamic control. A review is given also of auxiliary chemical and photolytic derivatizations coupled to ec detection. The majority of the literature on the subject relates to liquid chromatography with electrochemical detection (l.c./ec); however, applications to these concepts to specific examples in flow-injection systems, as well as for on-line process control, should be obvious. Details of chromatographic separations and design of total analytical systems are not reviewed.  相似文献   
95.
We discuss the perturbation of continuum eigenvalues without analyticity assumptions. Among our results, we show that generally a small perturbation removes these eigenvalues in accordance with Fermi's Golden Rule. Thus, generically (in a Baire category sense), the Schrödinger operator has no embedded non-threshold eigenvalues.Supported in part by NSF Grant DMS 8602826  相似文献   
96.
97.
98.
We investigated the simultaneous chiral separation of nine amphetamine type stimulants (dl-norephedrine, dl-norpseudoephedrine, dl-ephedrine, dl-pseudoephedrine, dl-amphetamine, dl-methamphetamine, dl-methylenedioxyamphetamine (MDA), dl-methylenedioxymethamphetamine (MDMA), and dl-methylenedioxyethylamphetamine (MDEA)) by capillary electrophoresis using highly sulfated gamma-cyclodextrin (SU(XIII)-gamma-CD) as a chiral selector. Three different approaches using SU(XIII)-gamma-CD with 50 mM phosphate background electrolyte were designed; (I) high CD concentration (10 mM SU(XIII)-gamma-CD) at neutral pH (pH 7.0) in the normal polarity mode, (II) low CD concentration (1.0 mM) at low pH (pH 2.6) in the normal polarity mode and (III) high CD concentration at low pH (pH 2.6) in the reversed-polarity mode. In mode (II), the effects of adding three neutral CDs (beta-CD, dimethyl-beta-CD and hydroxypropyl-beta-CD) were also investigated. The best separation was obtained after optimizing mode (III) as follows: run buffer of 10 mM SU(XIII)-gamma-CD with 50 mM phosphate background electrolyte at pH 2.6, applied voltage of -12 kV and capillary temperature of 15 degrees C.  相似文献   
99.
New high-level quantum chemical calculations have been undertaken to understand the rates and mechanisms of the reactive and associative channels for the reactants C2H2(+) + H2. The reactive channel, which produces C2H3(+) + H, has been shown to be slightly endothermic, confirming earlier calculations at a somewhat lower level and in agreement with some recent experimental work. The associative channel, leading to C2H4+, has been shown to proceed via a transition state with negative energy relative to the reactants, so that association is predicted to be efficient. This result is in conflict with an earlier theoretical study but in agreement with low-temperature experimental measurements.  相似文献   
100.
We have investigated the reactions between 2,3,5,6-tetrakis(α-pyridyl)pyrazine (TPP) and CrCl3 · 6H2O in 1:2 and 2.6:1 (CrIII:TPP) stoichiometric ratios. The resulting products, [Cr(TPP)Cl3] (1) and [(CrCl3)2-μ-TPP] (2), respectively, have been characterized by elemental and thermogravimetric analyses, molar conductivities, vibrational and electronic spectroscopy, and powder e.p.r. spectroscopy at room temperature. In both (1) and (2), TPP behaves as a tridentate ligand. Whereas (1) is a monometallic species with three uncoordinated nitrogen atoms, (2) is bimetallic with TPP as a bridging ligand.  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