全文获取类型
收费全文 | 751099篇 |
免费 | 9857篇 |
国内免费 | 2375篇 |
专业分类
化学 | 354015篇 |
晶体学 | 9419篇 |
力学 | 28437篇 |
综合类 | 19篇 |
数学 | 79885篇 |
物理学 | 194310篇 |
无线电 | 97246篇 |
出版年
2021年 | 5507篇 |
2020年 | 6209篇 |
2019年 | 6516篇 |
2018年 | 7956篇 |
2017年 | 7667篇 |
2016年 | 12506篇 |
2015年 | 8329篇 |
2014年 | 12621篇 |
2013年 | 32064篇 |
2012年 | 24157篇 |
2011年 | 29908篇 |
2010年 | 20856篇 |
2009年 | 21678篇 |
2008年 | 29313篇 |
2007年 | 30251篇 |
2006年 | 28638篇 |
2005年 | 26349篇 |
2004年 | 24261篇 |
2003年 | 21835篇 |
2002年 | 21310篇 |
2001年 | 23273篇 |
2000年 | 18520篇 |
1999年 | 15139篇 |
1998年 | 13052篇 |
1997年 | 12639篇 |
1996年 | 12363篇 |
1995年 | 11291篇 |
1994年 | 11031篇 |
1993年 | 10611篇 |
1992年 | 11540篇 |
1991年 | 11483篇 |
1990年 | 10813篇 |
1989年 | 10356篇 |
1988年 | 10280篇 |
1987年 | 9097篇 |
1986年 | 8705篇 |
1985年 | 11415篇 |
1984年 | 11555篇 |
1983年 | 9442篇 |
1982年 | 9737篇 |
1981年 | 9677篇 |
1980年 | 9129篇 |
1979年 | 9461篇 |
1978年 | 9598篇 |
1977年 | 9550篇 |
1976年 | 9341篇 |
1975年 | 8850篇 |
1974年 | 8720篇 |
1973年 | 8854篇 |
1972年 | 5915篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Z. V. Golubenko A. S. Kamzin L. P. Ol’khovik M. M. Khvorov Z. I. Sizova V. P. Shabatin 《Physics of the Solid State》2002,44(9):1698-1702
Magnetization and remagnetization processes in a close-packed nanodispersed barium hexaferrite powder sample in the magnetically stable state were analyzed. Reversibility effects were discussed in terms of interparticle interaction. Judging from the magnetization curve and the parameters characterizing remagnetization irreversibility, the sample under study is a model system of small Stoner-Wohlfarth particles. 相似文献
992.
993.
994.
An analysis of events in the tunneling junction shows that the interaction of one-electron processes in a many-electron system may be a source of scale-invariant low-frequency fluctuations of conductivity (the interaction consists in that the quantum probability of an electron transition depends on fast random changes in the environment in the course of the transition, including the changes caused by analogous transitions). The theory relates flicker fluctuations in the tunneling conductivity to the discrete character of the spectrum of electron states and explains the nonlinearity of the noise-current characteristic observed in nanocomposites. 相似文献
995.
M.V. Kossov 《The European Physical Journal A - Hadrons and Nuclei》2002,14(3):377-392
Photonuclear interaction cross-sections from the GEANT4 database are approximated for all nuclei and all energies (from the
hadron production threshold to about 40 TeV). The approximation methods in the giant-dipole resonance region, nucleon resonance
region, and high-energy region are improved with respect to existing approximations. As an application of the approximation
for photonuclear cross-sections, an improved method of calculating electronuclear cross-sections is developed. The interaction
cross-section of virtual photons with nuclei at high Q2 are approximated and a simple algorithm for describing the electronuclear reactions, including high-Q2 scattering, is proposed.
Received: 22 February 2002 / Accepted: 6 May 2002 相似文献
996.
Chemical bonding in isolated molecules and crystals of zwitterionic pentacoordinate silicon chelates
The electronic structures of a number of zwitterionic pentacoordinate silicon chelates were investigated using the results of X-ray diffraction studies and quantum-chemical calculatoins by the MPW1PW91/6-311G(d) method. The topological analysis of the electron density distribution function and the study in the framework of the natural bond orbital partitioning scheme showed that the character of chemical bonding in the axial fragments of the molecules under consideration changes from dative to three-center, four-electron as the silicon atom assumes a trigonal-bipyramidal coordination. 相似文献
997.
Timinskas A. Cheshunene A. Kurtinaitene M. Skominas V. 《Russian Journal of Applied Chemistry》2002,75(6):911-914
Conditions under which anodized aluminum is treated first in a dilute solution of phosphoric acid and then in a fluoroborate immersion solution in order to deposit a multilayer system of cobalt and copper in the pores in the oxide were studied. 相似文献
998.
A.R. DegheidyM.T. Attia M. Sallah 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,74(3):285-297
The time-independent radiative transfer problem in a scattering and absorbing planar random medium with general boundary conditions and internal energy source is considered. The medium is assumed to consist of two randomly mixed immiscible fluids, with the mixing statistics described as a two-state homogeneous Markov process. The problem is solved in terms of the solution of the corresponding free-source problem with simple boundary conditions which is solved using Pomraning-Eddington approximation in the deterministic case. A formalism, developed to treat radiative transfer in statistical mixtures, is used to obtain the ensemble-averaged solution. The average partial heat fluxes are calculated in terms of the albedoes of the source-free problem. Results are obtained for isotropic and anisotropic scattering for specular and diffused reflecting boundaries. 相似文献
999.
L.V. Zolotukhina Ye.V. ZabolotskayaYe.V. Arkhipova M.G. Zuev 《Journal of Physics and Chemistry of Solids》2002,63(3):415-418
Phase equilibria in the Sc2O3-V2O5-Nb2O5-Ta2O5 system and properties of ScNb2−2xTa2xVO9 phases were studied by X-ray phase analysis, optical and radio spectroscopy. A continuous series of solid solutions was shown to exist at 0≤x≤1. V(IV) centers with different crystallographic surrounding were detected for all the considered compositions. A correlation between the number of V(IV) ions and the width of the forbidden gap in the solid solutions was found. 相似文献
1000.
Advances in the management and control of optical Internet 总被引:15,自引:0,他引:15
Given the ever increasing demand for network bandwidth, and the phenomenal advances in optical wavelength division multiplexing (WDM) networking technologies, a major component of the next generation Internet will be an Internet protocol (IP)-based optical WDM network. As IP over WDM networking technologies mature, a number of important architectural, management and control issues have surfaced. These issues need to be addressed before a true next generation optical Internet can emerge. We enumerate some of the key architectural, management and control issues and discuss corresponding approaches and advances made toward addressing these issues. We first review the different IP/WDM networking architectural models and their tradeoffs. We outline and discuss several management and control issues and corresponding approaches related to the configuration, fault, and performance management of IP over dynamic WDM networks. We present an analysis and supporting simulation results demonstrating the potential benefits of dynamic IP over WDM networks. We then discuss the issues related to IP/WDM traffic engineering in more detail, and present the approach taken in the NGI SuperNet Network Control and Management Project funded by DARPA. In particular, we motivate and present an innovative integrated traffic-engineering framework for reconfigurable IP/WDM networks. It builds on the strength of multiprotocol label switching for fine-grain IP load balancing, and on the strength of reconfigurable WDM networking for reducing the IP network's weighted-hop-distance, and for expanding the bottleneck bandwidth 相似文献