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   2727篇
  免费   73篇
  国内免费   16篇
化学   1659篇
晶体学   29篇
力学   87篇
综合类   3篇
数学   317篇
物理学   721篇
  2021年   16篇
  2020年   26篇
  2019年   25篇
  2018年   20篇
  2016年   38篇
  2015年   52篇
  2014年   47篇
  2013年   126篇
  2012年   123篇
  2011年   158篇
  2010年   78篇
  2009年   52篇
  2008年   132篇
  2007年   127篇
  2006年   132篇
  2005年   122篇
  2004年   85篇
  2003年   91篇
  2002年   95篇
  2001年   67篇
  2000年   59篇
  1999年   46篇
  1998年   36篇
  1997年   41篇
  1996年   48篇
  1995年   30篇
  1994年   36篇
  1993年   44篇
  1992年   37篇
  1991年   38篇
  1990年   23篇
  1989年   32篇
  1988年   31篇
  1987年   33篇
  1986年   37篇
  1985年   44篇
  1984年   46篇
  1983年   30篇
  1982年   35篇
  1981年   33篇
  1980年   29篇
  1979年   34篇
  1978年   35篇
  1977年   31篇
  1976年   30篇
  1975年   33篇
  1974年   30篇
  1973年   24篇
  1971年   22篇
  1967年   17篇
排序方式: 共有2816条查询结果,搜索用时 11 毫秒
61.
Some results are obtained for non-compact cases in topological vector spaces for the existence problem of solutions for some set-valued variational inequalities with quasi-monotone and lower hemi-continuous operators, and with quasi-semi-monotone and upper hemi-continuous operators. Some applications are given in non-reflexive Banach spaces for these existence problems of solutions and for perturbation problems for these set-valued variational inequalities with quasi-monotone and quasi-semi-monotone operators. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
62.
Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π0 production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions.  相似文献   
63.
In this paper, we deal with the digital output-measurement-feedbackH control problem for Pritchard-Salamon infinite-dimensionalsystems with unbounded input and output operators. A discretePopov-theory-based solution is given in terms of the solvabilityof Kalman-Szegö-Popov-Yakubovitch systems associated withthe equivalent discrete-time time-invariant system obtainedby lifting the T-periodic continuous-time system.  相似文献   
64.
The errors due to developmental finite difference approximations in the two-microphone acoustic intensity measurement technique are considered in this paper. Equations are developed which describe the errors in intensity measurements for point monopoles, dipoles, and lateral quadrupoles. High accuracy is shown possible with careful selection of measurement parameters for each of these sources. For a microphone separation of 8 mm approximation errors are shown to be less than 2 dB from 0 to 10 000 Hz. For the quadrupole source low frequency errors not present with other sources are demonstrated. A lower limiting frequency for intensity measurements is determined to prevent these low frequency errors.  相似文献   
65.
66.
67.
68.
Influence of the weak electric field on the electronic structure of the Fibonacci superlattice is considered. The electric field produces a nonlinear dynamics of the energy spectrum of the aperiodic superlattice. Mechanism of the nonlinearity is explained in terms of energy levels anticrossings. The multifractal formalism is applied to investigate the effect of weak electric field on the statistical properties of electronic eigenfunctions. It is shown that the applied electric field does not remove the multifractal character of the electronic eigenfunctions, and that the singularity spectrum remains non-parabolic, however with a modified shape. Changes of the distances between energy levels of neighbouring eigenstates lead to the changes of the inverse participation ratio of the corresponding eigenfunctions in the weak electric field. It is demonstrated, that the local minima of the inverse participation ratio in the vicinity of the anticrossings correspond to discontinuity of the first derivative of the difference between marginal values of the singularity strength. Analysis of the generalized dimension as a function of the electric field shows that the electric field correlates spatial fluctuations of the neighbouring electronic eigenfunction amplitudes in the vicinity of anticrossings, and the nonlinear character of the scaling exponent confirms multifractality of the corresponding electronic eigenfunctions.  相似文献   
69.
70.
The vertical electronic spectrum of formaldehyde has been studied by means of (SC)2-MR-SDCI and CCLR methods. Two basis sets of atomic natural orbitals (ANOs) complemented with a one-centre series of Rydberg orbitals were used. The first was taken from the CASPT2 study by Merchán, M., and Roos, B. O., 1995, Theoret. Chim. Acta, 92, 221, and may be described as C,O[4s3pld]/H[2slp] with a lslpld Rydberg series centred in the charge centroid of the 2B2 state of the cation. The second was a larger basis set that may be described as C,O[6s5p3d2f]/H[4s3p2d] + 3s3p3d in the same centre. The (SC)2 dressing may be applied efficiently to an MR-SDCI method and comparison with the dressed CAS-SDCI is satisfactory, in spite of the remarkable reduction in the CI space dimension. The consistency of the (SC)2-MR-SDCI results was tested also against the CCLR and CASPT2 results using the same basis sets and against the CCLR results using Dunning's aug- and daug-cc-pVQZ basis sets. The 3A1(π → π *) state is correctly placed as the second excited triplet while the highly multi-configurational nature of the 1A1(π → π *) state is confirmed as well as its greatly mixed valence-Rydberg nature. This state is predicted as lying under the 10 eV level, on top of the (ny → 3d) Rydberg states that are predicted in the 8.9–9.5eV region. The 5 1B2(ny → 4s) Rydberg state and the 1B2y → π*) also are predicted in this region. The triplet states also were calculated with the (SC)2-MR-SDCI method. The vertical ordering of the 2 1A1(ny → 3py) and 2 1B2(ny → 3pz) states is discussed, as well as that of the 1B1(σ → π*) and the Rydberg 1B1(ny → 3dxy) states. This work shows the highly reliable values that may be reached applying the dressing method along with a large basis set. Such a procedure is made possible using an MR-SDCI selection of spaces instead of the CAS-SDCI that was used up to now in most (SC)2 dressing applications.  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