全文获取类型
收费全文 | 10397篇 |
免费 | 260篇 |
国内免费 | 46篇 |
专业分类
化学 | 7022篇 |
晶体学 | 125篇 |
力学 | 352篇 |
数学 | 1056篇 |
物理学 | 2148篇 |
出版年
2022年 | 57篇 |
2021年 | 77篇 |
2020年 | 96篇 |
2019年 | 104篇 |
2018年 | 81篇 |
2017年 | 68篇 |
2016年 | 197篇 |
2015年 | 175篇 |
2014年 | 179篇 |
2013年 | 472篇 |
2012年 | 483篇 |
2011年 | 566篇 |
2010年 | 326篇 |
2009年 | 256篇 |
2008年 | 477篇 |
2007年 | 515篇 |
2006年 | 545篇 |
2005年 | 479篇 |
2004年 | 407篇 |
2003年 | 386篇 |
2002年 | 379篇 |
2001年 | 191篇 |
2000年 | 182篇 |
1999年 | 122篇 |
1998年 | 130篇 |
1997年 | 174篇 |
1996年 | 202篇 |
1995年 | 133篇 |
1994年 | 154篇 |
1993年 | 172篇 |
1992年 | 141篇 |
1991年 | 108篇 |
1990年 | 105篇 |
1989年 | 129篇 |
1988年 | 123篇 |
1987年 | 102篇 |
1986年 | 104篇 |
1985年 | 149篇 |
1984年 | 158篇 |
1983年 | 110篇 |
1982年 | 140篇 |
1981年 | 138篇 |
1980年 | 124篇 |
1979年 | 115篇 |
1978年 | 120篇 |
1977年 | 115篇 |
1976年 | 93篇 |
1975年 | 118篇 |
1974年 | 106篇 |
1973年 | 94篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The method of path integration is applied to the analysis of wave propagation in both a graded-index optical waveguide and in an otherwise homogeneous infinite medium whose refractive indices have random statistical inhomogeneities superposed upon a regular variation of refractive index with suitable averaged properties. The authors use techniques originally employed in the context of electron propagation in a set of random scatterers to calculate the averaged Green function describing paraxial wave propagation in a medium whose refractive index has statistical inhomogeneities. The concept of an averaged density of modes is introduced, and the paper presents detailed calculations of this quality for two limiting case. In the first, the correlation length associated with the distribution of inhomogeneities is zero along the direction of propagation. In the second, the Feynman variational technique is used to describe the propagator in a medium whose statistical inhomogeneities have an infinite correlation length along the direction of propagation. Comments are made about the intermediate case which is of greater relevance to real waveguides. 相似文献
992.
Philip Rabinowitz 《Israel Journal of Mathematics》1986,56(1):66-74
Conditions are given which insure convergence for all Riemann-integrable functions of interpolatory product integration rules
and their companion rules based on the Gauss, Radau or Lobatto points with respect to a generalized smooth Jacobi weight function. 相似文献
993.
We study the effective dielectric constant of a dilute, polydisperse suspension of spheres embedded in a uniform background. We consider a frequency region where the dipole polarizability of individual spheres exhibits a resonance. We evaluate the effective dielectric constant to second order in the volume fraction employing the dipole approximation, which in previous work has been shown to be applicable in resonance. We apply our results to suspensions of spheres with identical and uniform dielectric constant, assuming a log-normal distribution of sphere radii. 相似文献
994.
Philip E. Gill Walter Murray Michael A. Saunders John A. Tomlin Margaret H. Wright 《Discrete Optimization》2008,5(2):151-158
We pay homage to George B. Dantzig by describing a less well-known part of his legacy–his early and dedicated championship of the importance of systems optimization in solving complex real-world problems. 相似文献
995.
An extended data set of extreme ultraviolet images of the solar corona provided by the SOHO spacecraft is analyzed using statistical methods common to studies of self-organized criticality (SOC) and intermittent turbulence (IT). The data exhibit simultaneous hallmarks of both regimes: namely, power-law avalanche statistics as well as multiscaling of structure functions for spatial activity. This implies that both SOC and IT may be manifestations of a single complex dynamical process entangling avalanches of magnetic energy dissipation with turbulent particle flows. 相似文献
996.
We construct the low-energy theory of a doped Mott insulator, such as the high-temperature superconductors, by explicitly integrating over the degrees of freedom far away from the chemical potential. For either hole or electron doping, a charge 2e bosonic field emerges at low energy. The charge 2e boson mediates dynamical spectral weight transfer across the Mott gap and creates a new charge e excitation by binding a hole. The result is a bifurcation of the electron dispersion below the chemical potential as observed recently in angle-resolved photoemission on Pb-doped Bi2Sr2CaCu2O8+delta (Pb2212). 相似文献
997.
Artuso M Blusk S Butt J Li J Menaa N Mountain R Nisar S Randrianarivony K Sia R Skwarnicki T Stone S Wang JC Zhang K Bonvicini G Cinabro D Dubrovin M Lincoln A Asner DM Edwards KW Naik P Briere RA Ferguson T Tatishvili G Vogel H Watkins ME Rosner JL Adam NE Alexander JP Cassel DG Duboscq JE Ehrlich R Fields L Galik RS Gibbons L Gray R Gray SW Hartill DL Heltsley BK Hertz D Jones CD Kandaswamy J Kreinick DL Kuznetsov VE Mahlke-Krüger H Mohapatra D Onyisi PU Patterson JR Peterson D Pivarski J 《Physical review letters》2007,99(19):191801
Using a 281 pb{-1} data sample collected at the psi(3770) with the CLEO-c detector, we present the first absolute branching fraction measurement of the decay D0-->K(-)pi(+)pi(-)e(+)nu(e) at a statistical significance of about 4.0 standard deviations. We find 10 candidates consistent with the decay D0-->K(-)pi(+)pi(-)e(+)nu(e). The probability that a background fluctuation accounts for this signal is less than 4.1 x 10{-5}. We find B(D0-->K(-)pi(+)pi(-)e(+)nu(e)) = [2.8{-1.1}{+1.4}(stat)+/-0.3(syst)]x10{-4}. By restricting the invariant mass of the hadronic system to be consistent with K1(1270), we obtain the product of branching fractions B(D{0}-->K{1}{-}(1270)e{+}nu{e})xB(K1-(1270)-->K{-}pi{+}pi{-})=[2.5{-1.0}{+1.3}(stat)+/-0.2(syst)]x10{-4}. Using B(K1-(1270)-->K{-}pi{+}pi{-})=(33+/-3)%, we obtain B(D{0}-->K{1}{-}(1270)e{+}nu{e})=[7.6{-3.0}{+4.1}(stat)+/-0.6(syst)+/-0.7]x10{-4}. The last error accounts for the uncertainties in the measured K1-(1270)-->K{-}pi{+}pi{-} branching fractions. 相似文献
998.
Navasardyan T Adams GS Ahmidouch A Angelescu T Arrington J Asaturyan R Baker OK Benmouna N Bertoncini C Blok HP Boeglin WU Bosted PE Breuer H Christy ME Connell SH Cui Y Dalton MM Danagoulian S Day D Dodario T Dunne JA Dutta D El Khayari N Ent R Fenker HC Frolov VV Gan L Gaskell D Hafidi K Hinton W Holt RJ Horn T Huber GM Hungerford E Jiang X Jones M Joo K Kalantarians N Kelly JJ Keppel CE Kubarovski V Li Y Liang Y Malace S Markowitz P McGrath E McKee P Meekins DG Mkrtchyan H Moziak B 《Physical review letters》2007,98(2):022001
A large data set of charged-pion (pi+/-) electroproduction from both hydrogen and deuterium targets has been obtained spanning the low-energy residual-mass region. These data conclusively show the onset of the quark-hadron duality phenomenon, as predicted for high-energy hadron electroproduction. We construct several ratios from these data to exhibit the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark-->pion production mechanisms. 相似文献
999.
Yang Z Chak P Bristow AD van Driel HM Iyer R Aitchison JS Smirl AL Sipe JE 《Optics letters》2007,32(7):826-828
Highly efficient second-harmonic generation can be achieved by harnessing resonance effects in microring resonator structures. We propose an angular quasi-phase-matching scheme based on the position dependence of polarization inside the ring resonator. 相似文献
1000.
Flaws in composite laminates may result in a severe loss of static and dynamic strength. Such flaws may be inherent or gained by misadventure. The extent of this loss can be influenced by several factors including loading, laminate stacking sequence, lamina properties, flaw size and damage type.In this study, the free-edge delamination of a laminated composite under compression loading is investigated. Computational, analytical and experimental tests are performed on a graphite/epoxy laminate AS4/3501-6 containing near surface edge defects and the crack opening behaviour is investigated.The computational analysis consists of a three dimensional finite element model where the plies can be catered for individually and interply delamination modelled. In the experimental investigations, a delamination is simulated by inserting teflon film at appropriate locations during the lay-up process. 相似文献