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   690710篇
  免费   9952篇
  国内免费   1806篇
电工技术   12522篇
综合类   755篇
化学工业   106181篇
金属工艺   26218篇
机械仪表   20265篇
建筑科学   16641篇
矿业工程   3369篇
能源动力   17952篇
轻工业   63253篇
水利工程   6976篇
石油天然气   12629篇
武器工业   68篇
无线电   76266篇
一般工业技术   131438篇
冶金工业   136518篇
原子能技术   14353篇
自动化技术   57064篇
  2021年   6250篇
  2020年   4482篇
  2019年   5834篇
  2018年   9903篇
  2017年   9686篇
  2016年   10274篇
  2015年   6990篇
  2014年   11646篇
  2013年   31189篇
  2012年   18493篇
  2011年   25373篇
  2010年   20030篇
  2009年   22397篇
  2008年   22955篇
  2007年   22808篇
  2006年   20037篇
  2005年   18195篇
  2004年   17480篇
  2003年   17143篇
  2002年   16442篇
  2001年   16418篇
  2000年   15400篇
  1999年   16127篇
  1998年   41344篇
  1997年   28940篇
  1996年   22165篇
  1995年   16741篇
  1994年   14622篇
  1993年   14284篇
  1992年   10454篇
  1991年   9732篇
  1990年   9822篇
  1989年   9489篇
  1988年   8895篇
  1987年   7914篇
  1986年   7827篇
  1985年   8816篇
  1984年   8276篇
  1983年   7370篇
  1982年   6961篇
  1981年   7078篇
  1980年   6768篇
  1979年   6554篇
  1978年   6428篇
  1977年   7576篇
  1976年   9922篇
  1975年   5611篇
  1974年   5270篇
  1973年   5440篇
  1972年   4493篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
In the editorial by J.C. Bezdek (ibid., p.1), an example is presented to demonstrate differences between fuzzy membership and probability. The authors argue that probability can be used in a way much more closely analogous to this use of fuzzy membership, weakening the argument for the latter  相似文献   
983.
First break picking is a pattern recognition problem in seismic signal processing, one that requires much human effort and is difficult to automate. The authors' goal is to reduce the manual effort in the picking process and accurately perform the picking. Feedforward neural network first break pickers have been developed using backpropagation training algorithms applied either to an encoded version of the raw data or to derived seismic attributes which are extracted from the raw data. The authors summarize a study in which they applied a backpropagation fuzzy logic system (BPFLS) to first break picking. The authors use derived seismic attributes as features, and take lateral variations into account by using the distance to a piecewise linear guiding function as a new feature. Experimental results indicate that the BPFLS achieves about the same picking accuracy as a feedforward neural network that is also trained using a backpropagation algorithm; however, the BPFLS is trained in a much shorter time, because there is a systematic way in which the initial parameters of the BPFLS can be chosen, versus the random way in which the weights of the neural network are chosen  相似文献   
984.
Qualitative representation of spatial knowledge in two-dimensional space   总被引:3,自引:0,他引:3  
Various relation-based systems, concerned with the qualitative representation and processing of spatial knowledge, have been developed in numerous application domains. In this article, we identify the common concepts underlying qualitative spatial knowledge representation, we compare the representational properties of the different systems, and we outline the computational tasks involved in relation-based spatial information processing. We also describesymbolic spatial indexes, relation-based structures that combine several ideas in spatial knowledge representation. A symbolic spatial index is an array that preserves only a set of spatial relations among distinct objects in an image, called the modeling space; the index array discards information, such as shape and size of objects, and irrelevant spatial relations. The construction of a symbolic spatial index from an input image can be thought of as a transformation that keeps only a set of representative points needed to define the relations of the modeling space. By keeping the relative arrangements of the representative points in symbolic spatial indexes and discarding all other points, we maintain enough information to answer queries regarding the spatial relations of the modeling space without the need to access the initial image or an object database. Symbolic spatial indexes can be used to solve problems involving route planning, composition of spatial relations, and update operations.  相似文献   
985.
Robotica is a computer aided design package for robotic manipulators developed in the Coordinated Science Laboratory at the University of Illinois at Urbana-Champaign. It encapsulates over 30 functions into a Mathematica package allowing efficient symbolic and numeric calculation of kinematic and dynamic equations for multi-degree-of-freedom manipulators. An X-Windows front end that utilizes the interprocess communication features of Mathematica 2.1 has also been created for ease of use. This paper describes the most important features of the package and how they are used  相似文献   
986.
987.
In 50 patients auditory threshold and brain stem evoked potential studies were carried out before and after myelography. Due to the analysis of amplitudes and latencies of auditory brain stem measurements, significant functional disorders of the hearing organ and the auditory pathway could be demonstrated. In most of the patients these functional disorders were found to be subclinical, whereas 12 patients showed alterations extending from a subjectively slight hearing loss to an audiometrically objectified acute hearing loss depending on its intensity in each case. The reasons of these functional disorders could not be clarified. An open cochlear aqueduct through which perilymph enters the subarachnoidal space leading to a secondary endolymphatic hydrops can be considered as the cause in cases where manifest symptoms develop. The changes in brain stem audiometry can be additionally explained by changes in osmolality of the inner ear fluids which may lead to the development of an endolymphatic hydrops.  相似文献   
988.
989.
Family nursing, always a component of nursing, has been recently receiving increased attention through publications, educational programs, clinical practice settings and family nursing research. Nurses are in the best position to assist families experiencing the illness of a loved one, but often lack the skills and confidence necessary to assist with the psychosocial needs. The purpose of this paper is to describe the development and implementation of a family nursing program within a large, tertiary care facility. The program's evaluation is ongoing but early outcomes indicate that day-to-day nursing practice has been positively influenced and improved job satisfaction may result.  相似文献   
990.
This report details procedures to measure annihilation anxiety, a concept derived from Freud's 1926 formulation of traumatic anxiety. A 25-item pencil-and-paper inventory administered to patient and to nonpatient samples is described, along with a brief summary of earlier findings. The delineation of nine interrelated experiential components of annihilation anxiety provides the background for the construction of Rorschach and TAT measures of the concept. Findings comparing the pencil-and-paper inventory and the projective test measures are presented as well as examples of responses judged to reflect annihilation anxiety from Rorschach and TAT protocols.  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