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   47941篇
  免费   6275篇
  国内免费   4682篇
化学   25185篇
晶体学   460篇
力学   1804篇
综合类   278篇
数学   4228篇
物理学   11470篇
无线电   15473篇
  2024年   163篇
  2023年   967篇
  2022年   1313篇
  2021年   1646篇
  2020年   1644篇
  2019年   1558篇
  2018年   1385篇
  2017年   1442篇
  2016年   1878篇
  2015年   2115篇
  2014年   2412篇
  2013年   3160篇
  2012年   3635篇
  2011年   3800篇
  2010年   2872篇
  2009年   2895篇
  2008年   3105篇
  2007年   2929篇
  2006年   2651篇
  2005年   2322篇
  2004年   1808篇
  2003年   1492篇
  2002年   1467篇
  2001年   1176篇
  2000年   1050篇
  1999年   945篇
  1998年   786篇
  1997年   723篇
  1996年   734篇
  1995年   606篇
  1994年   545篇
  1993年   509篇
  1992年   479篇
  1991年   396篇
  1990年   337篇
  1989年   251篇
  1988年   227篇
  1987年   151篇
  1986年   182篇
  1985年   196篇
  1984年   131篇
  1983年   82篇
  1982年   95篇
  1981年   66篇
  1980年   64篇
  1979年   73篇
  1978年   58篇
  1976年   54篇
  1974年   53篇
  1973年   52篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Boundedness of commutators on homogeneous Herz spaces   总被引:9,自引:0,他引:9  
The boundedness on homogeneous Herz spaces is established for a large class of linear commutators generated by BMO(R n ) functions and linear operators of rough kernels which include the Calderón-Zygmund operators and the Ricci-Stein oRfiUatory singular integrals with rough kernels. Project supponed in pan by the National h’atural Science Foundation of China (Grant No. 19131080) and the NEDF of China.  相似文献   
62.
本文概述了离子注入过程中污染产生的原因和防止污染的措施,特别强调了对微粒污染和金属污染的防护以满足ULSI加工对离子注入的要求。  相似文献   
63.
An authenticated multiple-key agreement protocol is proposed. The protocol is not only secure against the unknown-key attack but also more efficient than other protocols.  相似文献   
64.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication  相似文献   
65.
Coplanar waveguide-fed uniplanar bow-tie antenna   总被引:3,自引:0,他引:3  
The design of coplanar waveguide (CPW)-fed bow-tie antenna for the 2.4-GHz ISM band is described. A coplanar waveguide-to-coplanar strips (CPW-to-CPS) balun is used to obtain the balanced feed line for the printed bow-tie. An analysis method based on the mixed potential integral equation method is used to characterize the input characteristics of the bow-tie antenna. The numerical results obtained are in good agreement with the experimental data. Through experiments with bow-tie antennas of various extended angles, the bow-tie antenna with a 90° extended angle exhibits the widest bandwidth in the desired frequency band which has a bandwidth of 17% for a VSWR <1.5:1  相似文献   
66.
Color image retrieval based on hidden Markov models   总被引:1,自引:0,他引:1  
In this correspondence, a new approach to retrieving images from a color image database is proposed. Each image in the database is represented by a two-dimensional pseudo-hidden Markov model (2-D PHMM), which characterizes the chromatic and spatial information about the image. In addition, a flexible pictorial querying method is used, by which users can paint the rough content of the desired images in a query picture. Image matching is achieved by comparing the query picture with each 2-D PHMM in the database. Experimental results show that the proposed approach is indeed effective.  相似文献   
67.
Identifies the basic technological components of multimedia communications. Among these technologies, multimedia processing and transmission already benefit heavily from VLSI advances. in fact, these two technologies could not have matured without special-purpose VLSI chips. We have examined basic processing required in these technologies and some VLSI architectures. The focus has been on standard-compliant VLSI chips, because the eventual goal of communications is to allow everyone to reach others without constraints. There are still a number of evolving standards, which means that we might witness yet another wave of VLSI chips for multimedia communications  相似文献   
68.
Summary A supersonic jet spectrum of 9,10-dichloroanthracene is measured by stimulated-emission-pumping fluorescence dip spectrometry and conventional fluorescence spectrometry. The performance obtained is compared for these spectrometric methods, providing same information concerned with the energy level of the ground state. The former is more preferential for measurement of a high-resolution spectrum, since the spectral resolution is determined by the linewidth of the dumping laser. On the other hand, the latter is more preferential for measurement with better sensitivity at the expense of the spectral resolution, since the fluorescence throughput can be improved by increasing the slit width of the monochromator.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday  相似文献   
69.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data.  相似文献   
70.
The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order.  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