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   4376篇
  免费   113篇
  国内免费   20篇
化学   2816篇
晶体学   39篇
力学   82篇
数学   844篇
物理学   728篇
  2023年   42篇
  2022年   95篇
  2021年   125篇
  2020年   98篇
  2019年   122篇
  2018年   132篇
  2017年   111篇
  2016年   152篇
  2015年   121篇
  2014年   125篇
  2013年   271篇
  2012年   236篇
  2011年   302篇
  2010年   193篇
  2009年   193篇
  2008年   241篇
  2007年   227篇
  2006年   224篇
  2005年   214篇
  2004年   176篇
  2003年   137篇
  2002年   116篇
  2001年   73篇
  2000年   53篇
  1999年   38篇
  1998年   38篇
  1997年   35篇
  1996年   27篇
  1995年   22篇
  1994年   25篇
  1993年   32篇
  1992年   17篇
  1991年   32篇
  1990年   17篇
  1989年   16篇
  1987年   16篇
  1986年   20篇
  1985年   22篇
  1984年   30篇
  1983年   20篇
  1982年   20篇
  1981年   27篇
  1980年   22篇
  1979年   25篇
  1978年   26篇
  1977年   27篇
  1975年   20篇
  1974年   15篇
  1958年   13篇
  1955年   15篇
排序方式: 共有4509条查询结果,搜索用时 15 毫秒
21.
If p is an arbitrary parabolic subsuperalgebra of g = gl(m + n), p(m), a character formula for the generic finite-dimensional irreducible g-module, such that p is the stabilizer of its lowest weight space, is announced. Furthermore, an estimate for the character of any finite-dimensional irreducible g-module in terms of its highest weight with respect to a distinguished Borel subsuperalgebra is presented (inequality (4)) and a sufficient condition for this to be an equality is found. In this way, two generalizations of the Kac character formula for typical modules are obtained: a formula concerning an arbitrary Borel subsuperalgebra ((1)) and a more effective formula ((3)) for the special case of a distinguished Borel subsuperalgebra. The complete proofs will appear in [14].Partially supported by Contract 911/11.04.88 with the Bulgarian Ministry of Culture, Science, and Education.  相似文献   
22.
23.
The two-band memory-function conductivity formula is derived from the quantum kinetic equation in the pseudogap state of underdoped cuprates. The conduction electrons are described by using the adiabatic version of the nested Fermi liquid model, and the effects of Mott correlations are taken into account phenomenologically. The linear dependence of the low-temperature effective number of conduction electrons on the doping level δ (for not too large δ) is found to be in agreement with experimental observation. The momentum distribution function turns out to play an important role in describing temperature effects. The closing of the antiferromagnetic pseudogap at temperatures of the order of room temperature is shown to be a direct consequence of a relatively large width of the quasiparticle peak in this distribution function. The coupling of conduction electrons to external magnetic fields is included in the two-band transport equations in the usual semiclassical way. It is shown that the low-temperature Hall number is proportional to δ as well (again for not too large δ) and that it exhibits singular behaviour when the Fermi surface changes from the hole-like shape into the electron-like shape.  相似文献   
24.
We show that if F, X are two locally convex spaces and h: F → R?, ?: F × X → R are two convex functionals satisfying h(y) = ?(y, x0) (y?F) for some x0?X, then, under suitable assumptions, the computation of inf h(F) can be reduced to the computation of inf ?(H) on certain hyperplanes H of F × X. We give some applications.  相似文献   
25.
We generalize the concept of a space of numerical events in such a way that this generalization corresponds to arbitrary orthomodular posets whereas spaces of numerical events correspond to orthomodular posets having a full set of states. Moreover, we show that there is a natural one-to-one correspondence between orthomodular posets and certain posets with sectionally antitone involutions. Finally, we characterize orthomodular lattices among orthomodular posets.  相似文献   
26.
We present an analytic model of jet quenching, based on the (D)GLV energy loss formalism, to describe the system size dependence of QGP-induced parton absorption in relativistic heavy ion collisions. Numerical simulations of the transverse momentum dependence of jet quenching are given for central Au+Au and Cu+Cu reactions. Low p Tdijet correlations are shown to be sensitive to the reappearance of the lost energy as soft hadrons. At high p Twe find that the attenuation of dihadrons is similar to that of single inclusive particles. Comparison to recent data from PHENIX and STAR is given as a test of the jet quenching theory.  相似文献   
27.
Abstract

The i.r. spectra of N-phenylphthalimide and 15N-phenylphthalimide have been measured in 4000–100 cm?1 frequency range as KBr and polyethylene pellets and as chloroform solutions. The Raman spectra (4000–50) cm?1 of microcrystalline powder of the of the same compounds have also been investigated.

A detailed assignment of most of the observed frequencies has been proposed on the basis of the group vibrational concept, isotopic shift data and analogies with the spectra of related molecules. Some literature data have been discussed and some frequencies are reassigned.  相似文献   
28.
Time-resolved single-crystal diffraction performed with synchrotron radiation shows that the 53(1) micros phosphorescent state, generated in the crystalline phase of trimeric {[3,5-(CF3)(2)Pyrazolate]Cu}(3) molecules by exposure to 355 nm of light at 17 K, is due to the formation of an excimer rather than the shortening of the intramolecular Cu...Cu distances within the trimeric units, or the formation of a continuous chain of interacting molecules. One of the intermolecular Cu...Cu distances contracts by 0.56 Angstroms from 4.018(1) to 3.46(1) Angstroms;, whereas the interplanar spacing of the trimers is reduced by 0.65 Angstroms; from 3.952(1) to 3.33(1) Angstroms. Density-functional theory calculations support the formation of a Cu...Cu bond through the intermetallic transfer of a Cu 3d electron to a molecular orbital with a large 4p contribution on the reacting Cu atoms.  相似文献   
29.
Bilateral cochlear implant patients are unable to localize as well as normal hearing listeners. Although poor sensitivity to interaural time differences clearly contributes to this deficit, it is unclear whether deficits in terms of interaural level differences are also a contributing factor. In this study, localization was tested while manipulating interaural time and level cues using head-related transfer functions. The results indicate that bilateral cochlear implant users' ability to localize based on interaural level differences is actually greater than that of untrained normal hearing listeners.  相似文献   
30.
The shape of supramolecular aggregates based on stereoisomers of p‐tert‐butyl thiacalix[4]arenes functionalized with secondary, tertiary amide and hydrazide groups at the lower rim in cone, partial cone and 1,3‐alternate conformations with several metal cations were investigated by atomic force microscopy. The examined p‐tert‐butyl thiacalix[4]arenes form host–guest complexes; dimers, spherics ellipsoids and elongated nanoscale particles depending on the conformation of macrocycles, the nature of the binding centers and the nature of the metal cation. Only associates formed by p‐tert‐butyl thiacalix[4]arenes with morpholide groups at the lower rim in cone conformation with silver cations exhibited a higher antimicrobial activity. Copyright © 2012 John Wiley & Sons, Ltd.  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