全文获取类型
收费全文 | 87158篇 |
免费 | 1748篇 |
国内免费 | 2962篇 |
专业分类
化学 | 54347篇 |
晶体学 | 44篇 |
力学 | 1433篇 |
综合类 | 53篇 |
数学 | 2497篇 |
物理学 | 25460篇 |
无线电 | 8034篇 |
出版年
2023年 | 201篇 |
2022年 | 210篇 |
2021年 | 180篇 |
2020年 | 150篇 |
2019年 | 140篇 |
2018年 | 198篇 |
2017年 | 139篇 |
2016年 | 261篇 |
2015年 | 274篇 |
2014年 | 461篇 |
2013年 | 400篇 |
2012年 | 7041篇 |
2011年 | 9718篇 |
2010年 | 1886篇 |
2009年 | 642篇 |
2008年 | 7347篇 |
2007年 | 7580篇 |
2006年 | 7627篇 |
2005年 | 7455篇 |
2004年 | 6233篇 |
2003年 | 4541篇 |
2002年 | 4076篇 |
2001年 | 3063篇 |
2000年 | 3312篇 |
1999年 | 1243篇 |
1998年 | 558篇 |
1997年 | 473篇 |
1996年 | 1428篇 |
1995年 | 1102篇 |
1994年 | 1271篇 |
1993年 | 1517篇 |
1992年 | 1427篇 |
1991年 | 719篇 |
1990年 | 769篇 |
1989年 | 768篇 |
1988年 | 673篇 |
1987年 | 735篇 |
1986年 | 748篇 |
1985年 | 942篇 |
1984年 | 558篇 |
1983年 | 439篇 |
1982年 | 399篇 |
1981年 | 357篇 |
1980年 | 262篇 |
1979年 | 165篇 |
1976年 | 136篇 |
1975年 | 220篇 |
1974年 | 124篇 |
1958年 | 153篇 |
1956年 | 143篇 |
排序方式: 共有10000条查询结果,搜索用时 394 毫秒
191.
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
192.
A Novel Contactless Method for Characterization of Semiconductors:Surface Electron Bean Induced Voltage in Scanning Electron Microscopy
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
193.
V. A. KHATSKEVICH V.A. SENDEROV 《数学学报(英文版)》2006,22(6):1687-1694
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
194.
195.
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
197.
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
198.
1IntroductionAtpresent,astheerbiumdopedamplifiershavesucesfulybeenappliedtoopticalfiberlinks,thelonghaulhighbitrateofoptic... 相似文献
199.
在重点说明影响传输光纤设计的主要问题的同时,简要介绍了各种升级方式所面临的主要技术挑战,并详细说明这些挑战对传输光纤提出的技术要求。 相似文献
200.