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   86508篇
  免费   1770篇
  国内免费   2960篇
化学   56258篇
晶体学   40篇
力学   1442篇
综合类   47篇
数学   2503篇
物理学   23086篇
无线电   7862篇
  2023年   202篇
  2022年   210篇
  2021年   180篇
  2020年   164篇
  2019年   136篇
  2018年   199篇
  2017年   141篇
  2016年   264篇
  2015年   276篇
  2014年   456篇
  2013年   398篇
  2012年   7572篇
  2011年   10358篇
  2010年   1933篇
  2009年   652篇
  2008年   7430篇
  2007年   7907篇
  2006年   7920篇
  2005年   7567篇
  2004年   6097篇
  2003年   4473篇
  2002年   4067篇
  2001年   2878篇
  2000年   2994篇
  1999年   1182篇
  1998年   543篇
  1997年   441篇
  1996年   1187篇
  1995年   964篇
  1994年   1077篇
  1993年   1288篇
  1992年   1171篇
  1991年   599篇
  1990年   667篇
  1989年   634篇
  1988年   592篇
  1987年   680篇
  1986年   663篇
  1985年   833篇
  1984年   551篇
  1983年   439篇
  1982年   388篇
  1981年   359篇
  1980年   266篇
  1979年   169篇
  1976年   130篇
  1975年   214篇
  1958年   175篇
  1957年   123篇
  1956年   143篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
A sharp coefficient estimate,distortion theorem and the radius of convexityare determined for the class R(α,β,A,B) of function f(z)=z+(?)anzn satisfyingthe condition |(f′(z)-1)/(Bf′(z)-[B+(A-B)(1-α)])|<β for some α,β(0≤α<1,0<β≤1) and -1≤A相似文献   
182.
IntroductionThe interest in polyoxometalates that are widelyused in medical chemistry, catalyst reactions, and ma-terial sciences stems from their complicated aggregatesformed by means of corner-, edge- and face-sha-ring[1—4]. The exploitation of new str…  相似文献   
183.
The present paper deals with the long-time behavior of a class of nonautonomous retarded semilinear parabolic differential equations. When the time delays are small enough and the spectral gap conditions hold, the inertial manifolds of the nonautonomous retard parabolic equations are constructed by using the Lyapunov-Perron method.  相似文献   
184.
朱世秋  E.I.RAU 《中国物理快报》2002,19(9):1329-1332
We present a novel contactless and nondestructive method called the surface electron beam induced voltage (SEBIV) method for characterizing semiconductor materials and devices.The SEBIV method is based on the detection of the surface potential induced by electron beams of scanning electron microscopy (SEM).The core part of the SEBIV detection set-up is a circular metal detector placed above the sample surface.The capacitance between the circular detector and whole surface of the sample is estimated to be about 0.64pf.It is large enough for the detection of the induced surface potential.The irradiation mode of electron beam (e-beam) influences the signal generation When the e-beam irradiates on the surface of semiconductors continuously,a differential signal is obtained.The real distribution of surface potentials can be obtained when a pulsed e-beam with a fixed frequency is used for irradiation and a lock-in amplifier is employed for detection.The polarity of induced potential depends on the structure of potential barriers and surface states of samples.The contrast of SEBIV images in SEM changes with irradiation time and e-beam intensity.  相似文献   
185.
The operator sets, which are the subject of this paper, have been studied in many papers where, under different restrictions on the generating operators, convexity, compactness in the weak operator topology, and nonemptiness were proved for sets of different classes under study. Then the results obtained were used in these papers to solve several applied problems. Namely, they played the key role in establishing the dichotomy of nonautonomous dynamical systems, with either continuous or discrete time. In the present paper, we generalize and sharpen the already known criteria and obtain several new criteria for convexity, compactness, and nonemptiness of several special operator sets. Then, using the assertions obtained, we construct examples of sets of the form under study which are nonconvex, noncompact in the weak operator topology, as well as empty, and are generated by "smooth" operators of a special class. The existence problem for such sets remained open until the authors of this paper announced some of its results.  相似文献   
186.
高压热处理对氧沉淀低温形核的影响   总被引:2,自引:2,他引:0  
研究了外加高压(1GPa)下对450℃热处理硅片中氧沉淀行为的影响.透射电镜观察表明相对于大气压下热处理的样品,高压处理的样品会产生密度更高、尺寸更小的氧沉淀,表明高压有利于小直径氧沉淀的生成.电学性能测试表明,高压下处理的样品其热施主生成浓度和生成速率远远高于常压下处理的样品,这表明热施主与低温热处理过程中生成的高浓度氧沉淀核心有密切的关系.  相似文献   
187.
188.
当前,与Intenert相连的网络数量的增长速度十分迅猛。预计,在专用局域网或“内部网”中,In-ternet技术的应用增长规模会更大。据估计,三分之二的现有LAN正在使用Novell NetWare,而且有越来越多的LAN将与Internet或企业内部网相连接。为了帮助用户在保护其在NetWare上的投资的同时,能够利用Internet/Intra-  相似文献   
189.
The thermal conduction and Navier-Stokes equations are usedto obtain the stress field generated by a chopped electron beam incident ona disk sample.The piezoelectric equation is then used to obtain the out-put signal of the transducer coupled to the sample.The results lead to aconsideration of the signal generation mechanism and spatial resolution inscanning electron acoustic microscopy(SEAM).It is shown that atime-variant heat source generated both a thermal wave and an acousticwave simultaneously,and thermal-to-acoustic wave mode conversion oc-cured on the boundary surfaces depends on the amplitudes and the gra-dients at boundary surfaces of both heat source and thermal waves.It isargued that the spatial resolution of a imaging system operated in thenear field,such as SEAM and thermal wave microscope,is dependent onthe distance between the heat source and scatterer and,at best,the lateralresolution in SEAM is of the order of the diameter of the focal spot ofthe electron beam.  相似文献   
190.
1IntroductionAtpresent,astheerbiumdopedamplifiershavesucesfulybeenappliedtoopticalfiberlinks,thelonghaulhighbitrateofoptic...  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