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   5883篇
  免费   207篇
  国内免费   33篇
化学   3666篇
晶体学   23篇
力学   192篇
数学   1198篇
物理学   1044篇
  2023年   58篇
  2022年   136篇
  2021年   180篇
  2020年   156篇
  2019年   153篇
  2018年   129篇
  2017年   116篇
  2016年   242篇
  2015年   229篇
  2014年   240篇
  2013年   334篇
  2012年   412篇
  2011年   465篇
  2010年   270篇
  2009年   247篇
  2008年   375篇
  2007年   340篇
  2006年   310篇
  2005年   296篇
  2004年   232篇
  2003年   179篇
  2002年   188篇
  2001年   70篇
  2000年   46篇
  1999年   63篇
  1998年   51篇
  1997年   64篇
  1996年   48篇
  1995年   48篇
  1994年   46篇
  1993年   36篇
  1992年   25篇
  1991年   29篇
  1990年   22篇
  1989年   19篇
  1988年   22篇
  1987年   25篇
  1986年   19篇
  1985年   25篇
  1984年   22篇
  1983年   13篇
  1982年   22篇
  1981年   12篇
  1980年   14篇
  1979年   14篇
  1978年   15篇
  1977年   9篇
  1976年   6篇
  1973年   7篇
  1972年   5篇
排序方式: 共有6123条查询结果,搜索用时 15 毫秒
921.
Many beautiful experiments have been addressed to test standard quantum mechanics against local realistic models. Even if a strong evidence favouring standard quantum mechanics is emerged, a conclusive experiment is still lacking, because of low detection efficiencies. Recently, experiments based on pseudoscalar mesons have been proposed as a way for obtaining a conclusive experiment. In this paper, we investigate if this result can effectively be obtained. Our conclusions, based on a careful analysis of the proposed set ups, are that this will not be possible due to intrinsic limitations of these kind of experiments.  相似文献   
922.
923.
We compare Euler-Poincaré reduction in principal fibre bundles, as a constrained variational problem on the connections of this fibre bundle and constraint defined by the vanishing of the curvature of the connection, with the corresponding problem of Lagrange. Under certain cohomological condition we prove the equality of the sets of critical sections of both problems with the one obtained by application of the Lagrange multiplier rule. We compute the corresponding Cartan form and characterise critical sections as the set of holonomic solutions of the Cartan equation and, in particular, under a certain regularity condition for the problem, we prove the holonomy of any solution of this equation.  相似文献   
924.
In the present work, we describe a collection system for the off-line coupling of capillary isoelectric focusing (CIEF) with matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. In this system, the capillary effluent is directly deposited in fractions onto the MALDI target via the use of a sheath liquid. The collected fractions are subsequently supplemented with matrix and further analysed by MALDI-TOF mass spectrometry for mass assignment. The experimental set-up includes a fiber optic based UV detector operating at 280 nm, which allows the study of the influence of the sheath liquid composition on the CIEF separation. The influence of the carrier ampholyte concentration on the protein MALDI spectra was also evaluated and the feasibility of the collection method was finally demonstrated with a mixture of four standard proteins.  相似文献   
925.
We study the separability of the Neumann-Rosochatius system on the n-dimensional sphere using the geometry of bi-Hamiltonian manifolds. Its well-known separation variables are recovered by means of a separability condition relating the Hamiltonian with a suitable (1,1) tensor field on the sphere. This also allows us to iteratively construct the integrals of motion of the system.  相似文献   
926.
Interpretando il problema del filtraggio a tempo discreto come generalizzazione della inferenza statistica Bayesiana, si ottengono condizioni necessarie per l'esistenza di filtri a dimensione finita; tali condizioni generalizzano analoghe condizioni note in Statistica per l'esistenza di statistiche sufficienti a dimensione finita. Viewing the discrete-time filtering problem as generalization of Bayesian statistical inference, we obtain necessary conditions for the existence of a finite-dimensional filter; these conditions generalize those known in Statistics for the existence of a sufficient statistic of fixed finite dimension.
(Conferenza tenuta il 29 maggio 1989)  相似文献   
927.
Graphene is described at low energy by a massless Dirac equation whose eigenstates have definite chirality. We show that the tendency of Coulomb interactions in lightly doped graphene to favor states with larger net chirality leads to suppressed spin and charge susceptibilities. Our conclusions are based on an evaluation of graphene's exchange and random-phase-approximation correlation energies. The suppression is a consequence of the quasiparticle chirality switch which enhances quasiparticle velocities near the Dirac point.  相似文献   
928.
Low‐power light upconversion is a highly desirable feature for a broad range of applications and new materials enabling this process are sought in both bulk and particulate form. Here, the preparation of upconverting nanoparticles is reported from a methacrylic terpolymer bearing diphenylanthracene and meso‐phenoxytris(heptyl)porphyrin pendant groups by a microemulsion technique. The use of a terpolymer in which the upconvering dye molecules are covalently attached mitigates some of the drawbacks of triplet–triplet annihilation upconverting nanoparticles made by other techniques, in particular dye leakage from the nanoparticles, and limited control of the sensitizer and emitter concentration within each nanoparticle. Size and morphology of the new upconverting nanoparticles are investigated by dynamic light scattering and transmission electron microscopy and elucidated their upconverting properties by luminescence spectroscopy.

  相似文献   

929.
By linkage of 1,5-naphthalenedisulfonate (1,5-NDS) anion fluorophore, 3D cucurbit[7]uril (CB[7]) framework has been constructed. The maximum solid-state fluorescence wavelength of the CB[7] framework exhibits blue-shift from 406 to 340 nm in comparison with that of 1,5-NDS, which was ascribed to increased excited energy from 0.10 to 0.13 eV according to theoretical calculations.  相似文献   
930.
We study a class of fractional p-Laplacian problems with weights which are possibly singular on the boundary of the domain. We provide existence and multiplicity results as well as characterizations of critical groups and related 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