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   449篇
  免费   2篇
化学   184篇
晶体学   2篇
力学   14篇
数学   21篇
物理学   230篇
  2021年   3篇
  2020年   7篇
  2019年   4篇
  2018年   4篇
  2017年   3篇
  2016年   7篇
  2015年   4篇
  2014年   11篇
  2013年   25篇
  2012年   11篇
  2011年   17篇
  2010年   11篇
  2009年   16篇
  2008年   10篇
  2007年   16篇
  2006年   11篇
  2005年   15篇
  2004年   10篇
  2003年   4篇
  2002年   13篇
  2001年   12篇
  2000年   8篇
  1999年   15篇
  1996年   3篇
  1995年   6篇
  1994年   5篇
  1993年   10篇
  1992年   12篇
  1991年   9篇
  1990年   4篇
  1989年   8篇
  1988年   7篇
  1987年   5篇
  1986年   5篇
  1985年   12篇
  1984年   6篇
  1983年   11篇
  1982年   8篇
  1981年   10篇
  1980年   9篇
  1979年   7篇
  1978年   8篇
  1977年   13篇
  1976年   12篇
  1975年   3篇
  1974年   3篇
  1973年   5篇
  1972年   4篇
  1971年   3篇
  1968年   4篇
排序方式: 共有451条查询结果,搜索用时 15 毫秒
341.
We investigated the kinetics of autophobic dewetting, caused by differences in entropy, of a polymer melt slipping on a monolayer of end-grafted identical molecules (polymer brush). From simultaneous measures of the dewetted distance and the width of the resulting rim, we obtained in real time and quantitatively the slippage length and the contact angle, a measure of the "incompatibility" between identical molecules. Furthermore, we could directly relate a decrease in the slippage length in the course of the experiments at elevated temperatures to temporal or permanent attachment of polymers from the melt to the brush.  相似文献   
342.
In this paper, the generating relations for a set of hypergeometric functions ,,,m (x) are obtained by using the representation of the Lie group SL(2,C) giving a suitable interpretation to the index m in order to derive the elements of Lie algebra. The principle interest in our results lies in the fact that a number of special cases would inevitably yield too many new and known results of the theory of special functions, namely the Laguerre, even and odd generalized Hermite, Meixner, Gottlieb, and Krawtchouk polynomials.  相似文献   
343.

A simple, efficient, and eco-friendly protocol for the synthesis of 1,3-oxazine derivatives, viz. 7-aryl-7,8-dihydro-6H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-e][1,3]oxazines and 3-aryl-3,4-dihydro-2H- naphtho[2,3-e][1,3]oxazine-5,10-diones, involving one-pot multicomponent condensation reaction of various amines and formaldehyde with sesamol/2-hydroxy-1,4-naphthoquinone, respectively, catalyzed by a choline chloride–oxalic acid deep eutectic solvent has been developed. The method offers several advantages, including mild reaction conditions, simple operating procedure, recyclable and biodegradable catalyst, short reaction times, and excellent yields of the target products.

  相似文献   
344.
A set of density dependent nucleon-nucleon (N-N) interactions has been examined in nuclear matter calculations by varying spin-isospin contributions. Two sets of potentials have been considered. One having a density dependentσ-function type short range part followed by one term long range Gaussian part while the other having a density dependentσ-function part followed by two Gaussian terms. The strength parameters of the potential have been fitted to the saturation properties of nuclear matter, i.e. binding energy per particle of 15.5 MeV atk F=1.35 fm−1. Several sets of these two potentials have been generated by varying the strength parameterM of Majorana exchange operatorP M. It is seen thatM indirectly controls the spin, iso-spin contribution to the interaction potential and thus affects the nuclear matter properties such as compressibility and symmetry energy considerably, while variation of these quantities with the range parameterμ for givenM is moderate at lowM values while at higherM values it is quite large.  相似文献   
345.
346.
The spectrum of chlorine excited in the presence of argon has been photographed with a 21-ft. grating spectrograph in the first order. Two band systems in the region 2600–2390 Å and 2365–2239 Å are observed which appear to be respectively analogous to the 2950–2670 Å and 2660–2590 Å systems of bromine reported earlier by Venkateswarlu and Verma. The wavelengths and the wavenumbers of all the bands in the system 2600–2390 Å are given. The vibrational scheme along with the corresponding Franck-Condon parabola is also given. The analysis suggests that the lower state of the system is the 3π(O u +_ state established by Elliott at 17658 cm.?1 and that the upper state is at 67773 cm.?1 The vibrational constants obtained arew 0′ = 246·6 cm.?1,w 0x 0′ = 0·615 cm.?1,w 0″ = 255·2 cm.?1,w 0x 0″ = 5·5 cm.?1,w 0y 0″ = ?0·0155 cm.?1 andw 0z 0″ = 0·00115 cm.?1  相似文献   
347.
Density functional theory can envisage a vast assortment of molecular possessions such as molecular structures, vibrational frequencies, molecular energies, ionization energies, polar, electric and magnetic properties etc. The efficacy of this method relies on the study of electronic parameters to categorize the reactive sites to comprehend the plausible action of these scaffolds. Further it also facilitates the correlation between the structural characteristics of drug and their inhibition efficiency against infectious microorganisms. In light of the above facts, we have studied the structural parameters such as energy (total), variation of electron density over highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), charge distribution, absolute electronegativity (χ), softness/hardness (σ/ɳ) and fraction of electron transfer (ΔN) of some previously synthesized heterocycles.  相似文献   
348.
We used a terahertz (THz) quantum cascade laser (QCL) as an integrated injection seeded source and amplifier for THz time-domain spectroscopy. A THz input pulse is generated inside a QCL by illuminating the laser facet with a near-IR pulse from a femtosecond laser and amplified using gain switching. The THz output from the QCL is found to saturate upon increasing the amplitude of the THz input power, which indicates that the QCL is operating in an injection seeded regime.  相似文献   
349.
Using a representation for Lie groups closely associated with thermal problems, we derive the algebraic rules of the real-time formalism for thermal quantum field theories, the so-called thermo-field dynamics (TFD), including the tilde conjugation rules for interacting fields. These thermo-group representations provide a unified view of different approaches for finite-temperature quantum fields in terms of a symmetry group. On these grounds, a path integral formalism is constructed, using Bogoliubov transformations, for bosons, fermions and non-abelian gauge fields. The generalization of the results for quantum fields in topology is addressed.  相似文献   
350.
Relations among the magnetic moments of charmed and uncharmed baryons are derived in the framework of SU(4) and SU(8) symmetries. The SU(3) resultμ (Σ o)=−μ(Λ) is not present in SU(4), but is obtained in SU(8). Higher order effects are further considered to improve the situation.  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