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   3628篇
  免费   97篇
  国内免费   2篇
化学   2386篇
晶体学   39篇
力学   72篇
数学   259篇
物理学   971篇
  2023年   37篇
  2022年   62篇
  2021年   61篇
  2020年   90篇
  2019年   105篇
  2018年   69篇
  2017年   59篇
  2016年   128篇
  2015年   73篇
  2014年   122篇
  2013年   238篇
  2012年   238篇
  2011年   292篇
  2010年   176篇
  2009年   146篇
  2008年   216篇
  2007年   181篇
  2006年   162篇
  2005年   140篇
  2004年   110篇
  2003年   75篇
  2002年   75篇
  2001年   60篇
  2000年   57篇
  1999年   46篇
  1998年   29篇
  1997年   23篇
  1996年   38篇
  1995年   29篇
  1994年   35篇
  1993年   43篇
  1992年   29篇
  1991年   27篇
  1989年   19篇
  1988年   21篇
  1987年   27篇
  1986年   21篇
  1985年   19篇
  1984年   31篇
  1983年   20篇
  1982年   22篇
  1981年   30篇
  1980年   19篇
  1979年   27篇
  1978年   16篇
  1977年   18篇
  1976年   16篇
  1975年   15篇
  1973年   11篇
  1957年   13篇
排序方式: 共有3727条查询结果,搜索用时 15 毫秒
31.
32.
33.
Effects of Hall current on a steady hydromagnetic (MHD) fully developed flow in a rotating environment within a parallel plate channel in the presence of an inclined magnetic field is studied. From an extension of literature [13] subject to a forced oscillation it is observed that the present paper is methodically more correct to work first in the steady state where forced oscillation becomes insignificant and then new results are expected for an unsteady MHD flow under the influence of a pulse-oscillator. Exact solutions of the governing equations are obtained in a closed form. The graphical representation for the velocity and the induced magnetic field are depicted graphically and the heat transfer at both the plates are presented in tables.  相似文献   
34.
This work reports isothermal reversible variation of magnetization in nanoporous Pd-Ni alloys subjected to continuous charging and discharging of the sample in aprotic electrolyte medium. Polarizing metal surface with excess charge also finds strain in the nanoporous structure using the sample as working electrode. Therefore, it is proposed that pressure induced by strain is the key parameter for the observed reversible magnetization in the transition metal alloys.  相似文献   
35.
We show that, when a turbid medium with a layered fluorophore distribution is excited by linearly polarized light, measurement of angle-resolved polarized fluorescence can provide depth-resolved fluorescence measurements.  相似文献   
36.
Using an algebraic technique based on the Lie algebra of the group SO(2, 1) the eigenvalues of the triple-well anharmonic oscillator are calculated for all ranges of the coupling constant. Approximate analytic formulas for the eigenvalues up to second order are given. The results obtained are compared with those of other authors.  相似文献   
37.
We present exact explicit expressions for the row spin-spin correlation functions 00 n0 in the isotropicd= 2 Ising model, in terms of elliptic integrals, forn 5. We also give a general structural formula for 00 n0.  相似文献   
38.
Contributions to the spin-lattice relaxation time (T 1) and the spin-spin relaxation time (T 2) due to critical fluctuations (CF) have been determined in para-azoxyanisole (PAA) from the corresponding proton relaxation times measured at 60 MHz over a temperature range of about 35 °K above the nematic-isotropic transition temperatureT C .In determining the CF contributions, the procedure followed here is the same as the present authors used earlier for a similar study in p-methoxybenzylidene p-n butylaniline (MBBA). Like that in MBBA at 14 MHz, a maximum in the CF contribution toT 1, has been observed. Following a recent theory we identify this contribution toT 1 arising from the nonlocal part of CF, and we call thisT 1)CFN. The correlation time associated with this nonlocal part of CF, CFN, has been determined at different temperatures fromT 1)CFN. The temperature dependence of CFN is in good agreement with the Landau-de Gennes theory and is consistent with that observed earlier in MBBA. The temperature dependence ofT 2)CF is also in reasonable agreement with the above behavior of CFN. However, ourT 2)CF data can also be fitted to a temperature dependence expected from a contribution toT 2)CF arising from the local part of CF, such a fitting is comparatively poorer than the former. Since ourT 2)CF data are neither sufficiently accurate nor elaborate, no attempt has been made here to separate these two contributions, nonlocal and local parts of CF, which have been predicted from theoretical considerations. A behavior similar to that of ourT 2)CF is also shown by the earlier data of Cabane and Clark obtained from14N resonance when their data are processed properly.Work done with the financial support of the Consiglio Nazionale delle Ricerche granted through the Gruppo Nazionale di Struttura della Materia to the Istituto di Fisica, Università dell' AquilaA preliminary report of this work was presented at the Fifth International Symposium on Magnetic Resonance held at Bombay, India, January 14–18, 1974  相似文献   
39.
G B Mitra  T B Ghosh 《Pramana》1987,29(3):285-301
The fourth central moment of an X-ray diffraction profile from an aggregate of distorted crystallites has been expressed by Mitra (1964a) as a function of the crystallite size, strain and strain gradients in the specimen. While the usual methods of line profile analysis yield information regarding either the apparent strain or the rms strain, the present study provides additional information regarding strain distribution in the form of strain derivatives and rms displacements of atoms over a given distancet in the direction of study. The strain parameters like 〈ee′〉, 〈ee″〉 have been obtained from fourth moment of the strain profile against range plots. The strain parameters thus obtained have subsequently been used to determine the rms displacements of the atoms. Alloys of copper and zinc at different stages of cold working and annealing have been studied by this method. The results have been discussed in the light of dislocation distribution, polygonisation and grain growth as well as distortion waves in the distorted crystals.  相似文献   
40.
Rotational structure of a series of new absorption bands of PO in the region 1850 to 1600 Å has been analyzed from a spectrum taken at high resolution. The bands are attributed to an electronic transition P2Π-X2Π, where P2Π is a new valence state of PO. Some of these bands have been found to be perturbed. A qualitative account of these perturbations is presented. A probable electron-configuration π3π12 has been suggested for the new state. From the predissociation observed in the higher vibrational levels of P an upper limit of 48 885 cm?1 (X2Π, T0 = 0) for the ground state dissociation energy has been obtained.  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