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   720355篇
  免费   11079篇
  国内免费   4739篇
化学   350171篇
晶体学   8809篇
力学   25529篇
综合类   146篇
数学   78495篇
物理学   178357篇
无线电   94666篇
  2021年   5514篇
  2020年   6053篇
  2019年   6514篇
  2018年   7258篇
  2017年   6905篇
  2016年   11424篇
  2015年   8440篇
  2014年   11906篇
  2013年   30459篇
  2012年   23761篇
  2011年   29014篇
  2010年   19591篇
  2009年   20093篇
  2008年   28318篇
  2007年   29154篇
  2006年   27835篇
  2005年   25782篇
  2004年   23185篇
  2003年   20784篇
  2002年   20449篇
  2001年   20689篇
  2000年   17018篇
  1999年   13707篇
  1998年   12079篇
  1997年   11888篇
  1996年   11706篇
  1995年   10585篇
  1994年   10207篇
  1993年   9971篇
  1992年   10481篇
  1991年   10327篇
  1990年   9688篇
  1989年   9220篇
  1988年   9213篇
  1987年   8160篇
  1986年   7705篇
  1985年   10565篇
  1984年   10758篇
  1983年   8915篇
  1982年   9776篇
  1981年   9402篇
  1980年   9018篇
  1979年   9153篇
  1978年   9360篇
  1977年   9267篇
  1976年   9151篇
  1975年   8743篇
  1974年   8507篇
  1973年   8866篇
  1972年   5598篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
This paper explains the principle of a method which avoids printing of phantom resist lines due to undesired intensity minima appearing on Cr-less edge line phase-shifting masks. The method combines principles of grey-tone lithography and attenuated phase-shifting masks to give, what we call, a Cr-Less Attenuated Phase-shifting mask (CLAP). Rules for generating a CLAP design and a paradigm setup of a CLAP mask are presented. The capabilities and possible limitations of the CLAP method based on simulated results for a standard wafer stepper setup using the SOLID lithography simulator are being assessed.  相似文献   
62.
Many current implementations of protocols such as the Transmission Control Protocol/Internet Protocol (TCP/IP) are inefficient because data are often accessed more frequently than necessary. Three techniques that reduce the need for memory bandwidth are proposed. The techniques are copy-on-write, page remapping, and single-copy. Afterburner, a network-independent card that provides the services that are necessary for a single-copy protocol stack, is described. The card has 1 MByte of local buffers and provides a simple interface to a variety of network link adapters, including HIPPI and asynchronous transfer mode (ATM). Afterburner can support transfers to and from the link adapter card at rates up to 1 Gbit/s. An implementation of TCP/IP that uses the features provided by Afterburner to reduce the movement of data to a single copy is discussed. Measurements of the end-to-end performance of Afterburner and the single-copy implementation of TCP/IP are presented  相似文献   
63.
64.
Adam  J.A. 《Spectrum, IEEE》1994,31(10):24-26
The author focusses on advances in equipment that offset physically functional limitations. He discusses how disabled and elderly people are using aids that enhance mobility (walking a certain distance, lifting a weight, or climbing stairs) as well as sensory faculties (seeing print, hearing conversation, and speaking intelligibly)  相似文献   
65.
Fractal error for detecting man-made features in aerial images   总被引:3,自引:0,他引:3  
A technique is proposed for aiding photointerpreters in detecting man-made features in aerial reconnaissance images. The technique, which uses a metric called fractal error, is based on the observed propensity of natural image features to fit a fractional Brownian motion model. Man-made features usually do not fit this model well, and consequently the fractal error metric may be used as a discriminant function for detecting man-made scene features  相似文献   
66.
Empirical lifetime distributions sometimes have a bathtub-shaped failure rate. This paper deals with some models having a bathtub-shaped failure rate. The root-mean-square criterion is proposed for selection of the best model. Besides two criteria of optimum burn-in time are proposed. The comparison of some models with the general law of reliability is given to determine a burn-in time in a number of examples.  相似文献   
67.
New bounds are proposed for the Marcum Q-function, which is defined by an integral expression where the 0th-order modified Bessel function appears. The proposed bounds are derived by suitable approximations of the 0th-order modified Bessel function in the integration region of the Marcum Q-function. They prove to be very tight and outperform bounds previously proposed in the literature. In particular, the proposed bounds are noticeably good for large values of the parameters of the Marcum Q-function, where previously introduced bounds fail and where exact computation of the function becomes critical due to numerical problems  相似文献   
68.
69.
We consider the growth of a spherical crystal in a supersaturatedsolution. In the first part, existence and uniqueness resultsfor radially symmetric growth are obtained, provided that thesupersaturation is not too large; conversely, when the far-fieldsupersaturation exceeds a critical value, it is shown that theradially symmetric solution ceases to exist in finite time.In the second part, we examine the linear stability of a radiallysymmetric similarity solution (in which the radius grows ast?) to shape perturbations. The results are compared with previousquasi-static analyses, and, in particular, the critical radiusat which the crystal becomes unstable is found to be largerfor small supersaturations, but smaller for large supersaturations,than those predicted by the quasi-static analysis  相似文献   
70.
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