全文获取类型
收费全文 | 45226篇 |
免费 | 149篇 |
国内免费 | 435篇 |
专业分类
化学 | 29202篇 |
晶体学 | 3篇 |
力学 | 207篇 |
综合类 | 5篇 |
数学 | 568篇 |
物理学 | 13923篇 |
无线电 | 1902篇 |
出版年
2023年 | 17篇 |
2022年 | 17篇 |
2021年 | 22篇 |
2020年 | 13篇 |
2019年 | 13篇 |
2018年 | 28篇 |
2017年 | 21篇 |
2016年 | 32篇 |
2015年 | 31篇 |
2014年 | 46篇 |
2013年 | 42篇 |
2012年 | 3776篇 |
2011年 | 5393篇 |
2010年 | 900篇 |
2009年 | 177篇 |
2008年 | 4089篇 |
2007年 | 4206篇 |
2006年 | 4263篇 |
2005年 | 4150篇 |
2004年 | 3341篇 |
2003年 | 2457篇 |
2002年 | 2181篇 |
2001年 | 1499篇 |
2000年 | 1737篇 |
1999年 | 483篇 |
1998年 | 233篇 |
1997年 | 223篇 |
1996年 | 810篇 |
1995年 | 599篇 |
1994年 | 756篇 |
1993年 | 956篇 |
1992年 | 839篇 |
1991年 | 400篇 |
1990年 | 416篇 |
1989年 | 313篇 |
1988年 | 230篇 |
1987年 | 227篇 |
1986年 | 235篇 |
1985年 | 227篇 |
1984年 | 59篇 |
1983年 | 54篇 |
1982年 | 52篇 |
1981年 | 37篇 |
1980年 | 26篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1976年 | 15篇 |
1975年 | 26篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
CAI Xiang bao 《中国邮电高校学报(英文版)》2003,10(2)
1 IntroductionMaterialswithPhotonicBandGaps (PBG’s)havebeenwidelystudiedboththeoreticallyandex perimentallyinthepastfew years[1~ 4] .Theexis tenceofgaps,which prohibitthepropagationofelectromagnetic (EM )wavesinacertainrangeoffrequencies,canhavesignificantimpactsbothinsci enceandtechnology .Manypracticalapplicationsofthesestructureshavebeensuggestedanddemon strated ,suchasPhotonicCrystal (PC)microcavi ties[5] ,infraredPC[6] ,PClens[7] ,suppressingspontaneousemission ,manipulatinglight… 相似文献
2.
ON THE UNIQUENESS OF THE WEAK SOLUTIONS OF A QUASILINEAR HYPERBOLIC SYSTEM WITH A SINGULAR SOURCE TERM 下载免费PDF全文
This paper is a continuation of the authors'previous paper[1].In this paper the authorsprove,assuming additional conditions on the initial data,some results about the existence anduniqueness of the entropy weak solutions of the Cauchy problem for the singular hyperbolicsystem a_t+(au)_x_2au/x=0,u_t+1/2(a~2+u~2)_x=0,x>0,t≥0. 相似文献
3.
一、Telc02.0的业务和技术范例
当连通性成为日常生活的必须,网络运营商的挑战正在逐渐显现,那就是通过使用基于刚络的能力提供独特的价值以占据新收入链的重要部分。网络运营商必须专注于差异化,运用业界(包括最大的电信实体,全球移动通讯系统[GSM]协会)称之为Telco2.0的业务和技术范例。 相似文献
4.
CAO Wei-feng WANG Wen-boBeijing University of Posts Telecommunications Beijing P.R. China 《中国邮电高校学报(英文版)》2005,12(4)
1IntroductionCurrently,smart antenna technology can greatly en-hance system performance and i mprove the system ca-pacity so that it has been considered as a keytechnologyinthe third generation wireless communicationsystems .The researches on channel model , beamforming algo-rithms and receive algorithms have been widely carriedout and a great many of proposition have beensubmittedtothe 3th Generation Project Partner (3GPP) . Fromthe viewpoint of link-level and system-level research,many asp… 相似文献
5.
John P. kotter 《IT时代周刊》2007,(24):76-77
在拥有了多年大权在握、呼风唤雨的经历之后。相当一部分企业领导人很难从容地放弃权力。这时。董事会必须采取行动,不仅要帮助退休领导人选择和培养好接班人。更要积极参与管理层交接班的全过程。 相似文献
6.
Quan Sen JIU Department of Mathematics Capital Normal University Beijing P.R.China Cheng HE Institute of Applied Mathematics Academy of Mathematics System Sciences Chinese Academy of Sciences Beijing P.R.China 《应用数学学报(英文版)》2004,(4)
In this paper we are interested in the sufficient conditions which guarantee the regularityof solutions of 3-D ideal magnetohydrodynamic equations in the arbitrary time interval [0,T].Fivesufficient conditions are given.Our results are motivated by two main ideas:one is to control theaccumulation of vorticity alone;the other is to generalize the corresponding geometric conditions of3-D Euler equations to 3-D ideal magnetohydrodynamic equations. 相似文献
7.
Electron Spin Resonance Studies of Mn^2+ in Freshwater Snail Shells: Pomacea Canaliculata Lamarck and Fossilized Snail Shell 下载免费PDF全文
N.Udomkan S.Meejoo P.Limsuwan P.Winotai Y.Chaimanee 《中国物理快报》2005,22(7):1780-1783
We study paramagnetic Mn^2 ions present in the nowadays shells of univalve freshwater snails of Pomacea canaliculata lamarck (PCL) and the fossilized freshwater snail (FFS), Viviparus. All these shells are abundant in Thailand. The PCL shells were ground into fine powder. A set of seven samples were then separately annealed for 2 h in air atmosphere at different annealing temperatures while the FFS powder was characterized as-received. The PCL shells mainly consist of aragonite and a fraction of calcite. The heat treatments of the PCL powder samples at temperature higher than 450℃ resulted in an irreversible phase transformation from aragonite to calcite. However, it is found that the FFS shell is mainly made of calcite, with a minor fraction of aragonite. The crystal structure of the high-temperature-annealed PCL samples are quite similar to that of FFS, which indicates that the metamorphosis (aragonite→calcite) in the FFS shell had occurred but was not yet completed, although it had remained under the pressure and temperature of the Earth‘s crusts over millions of years. Our detailed ESR spectral analyses of PCL and FFS show that Mn^2 ions enter the Ca^2 sites during a biomineralization process. Simulated ESR parameters of PCL-500 of Mn^2 at a uniaxial site of calcite are reported. It is surprising to And that the ratio of Mn^2 concentration present in FFS to those in PCL shells evaluated from ESR spectra is as much as 10:1. 相似文献
8.
1IntroductionIndesktopvideoconferencingsystems,therearetwokindsofdata:continuousmediastreamanduser′sdatathatneedtobetransmite... 相似文献
9.
1 IntroductionSince 1 990 ,chaoticsynchronization[1~ 4] andchaoticcontrolling[5~6] havereceivedagreatdealofattention[7~1 1 ] ,andchaoticsynchronizationisaphenomenonofinterestinfieldsfromelectronicstocommunication[1 2 ] ,andfrombiophysicstoneuro science[1 3] .Ifchaoticsync… 相似文献
10.