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   26855篇
  免费   1719篇
  国内免费   27篇
电工技术   168篇
综合类   10篇
化学工业   5631篇
金属工艺   429篇
机械仪表   563篇
建筑科学   819篇
矿业工程   53篇
能源动力   521篇
轻工业   5480篇
水利工程   316篇
石油天然气   120篇
武器工业   1篇
无线电   1058篇
一般工业技术   4347篇
冶金工业   5415篇
原子能技术   70篇
自动化技术   3600篇
  2024年   67篇
  2023年   281篇
  2022年   277篇
  2021年   734篇
  2020年   667篇
  2019年   677篇
  2018年   1244篇
  2017年   1213篇
  2016年   1272篇
  2015年   972篇
  2014年   1118篇
  2013年   2313篇
  2012年   1777篇
  2011年   1580篇
  2010年   1285篇
  2009年   1102篇
  2008年   1152篇
  2007年   1060篇
  2006年   667篇
  2005年   566篇
  2004年   534篇
  2003年   512篇
  2002年   434篇
  2001年   328篇
  2000年   263篇
  1999年   313篇
  1998年   1898篇
  1997年   1189篇
  1996年   729篇
  1995年   395篇
  1994年   304篇
  1993年   318篇
  1992年   87篇
  1991年   74篇
  1990年   62篇
  1989年   60篇
  1988年   82篇
  1987年   73篇
  1986年   63篇
  1985年   72篇
  1984年   62篇
  1983年   35篇
  1982年   38篇
  1981年   60篇
  1980年   60篇
  1978年   30篇
  1977年   104篇
  1976年   207篇
  1975年   33篇
  1973年   38篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
ABSTRACT

In this paper, we review some algebraic control system. Precisely, linear and bilinear systems on Euclidean spaces and invariant and linear systems on Lie groups. The fourth classes of systems have a common issue: to any class, there exists an associated subgroup. From this object, we survey the controllability property. Especially, from those coming from our contribution to the theory.  相似文献   
2.
Wastewater treatment plant operators encounter complex operational problems related to the activated sludge process and usually respond to these by applying their own intuition and by taking advantage of what they have learnt from past experiences of similar problems. However, previous process experiences are not easy to integrate in numerical control, and new tools must be developed to enable re-use of plant operating experience. The aim of this paper is to investigate the usefulness of a case-based reasoning (CBR) approach to apply learning and re-use of knowledge gained during past incidents to confront actual complex problems through the IWA/COST Benchmark protocol. A case study shows that the proposed CBR system achieves a significant improvement of the benchmark plant performance when facing a high-flow event disturbance.  相似文献   
3.
Presents an obituary and information about the life and accomplishments of Josef Maria Bro?ek. Born August 14, 1913, in the ancient town of Melnik, in central Bohemia, today the Czech Republic, Josef spent his childhood in Poland (Warsaw, 1913- 1915) and in Siberia (1915-1920). His education in Czechoslovakia culminated with a thesis on "Memory, Its Measurement and Structure" and a PhD awarded in June 1937. In the history of psychology, his lifetime project bore the title "Historiography of Psychology Around the World," and it covered about 20 geographical areas. Extensive attention was devoted to institutional and organizational developments as journals, academic settings, archives, museums, research groups, conferences, and institutes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
4.
In this study chick embryo optic cups at HH stage 13 of development were analyzed under normal conditions and after inoculation with colchicine for 1, 2, 4, and 8 h. Several changes were seen after these periods of treatment: 1) modifications of the structure, with thicker regions in the cup and a general decrease in the total volume according to the duration of exposure to the drug (about 4 times less than normal, 5,035 x 10(3) microns 3 vs 1,334 x 10(3) microns 3 after 8 h of treatment); 2) enlargement of the ventricular cavity and its closure, due to failure of approximation of retinal and pigmentary layers; 3) failure of lens development, with delay and impairment of pit formation and deformation of all structures; lens volume was less than normal (about 4 times less, 2,148 x 10(3) microns 3 vs 658 x 10(3) microns 3 after 8 h of treatment); 4) a general segregation of the cells making up the structure, principally in the more active proliferating zones. The local alterations found are described.  相似文献   
5.
6.
INTRODUCTION: Even though there are few epidemiological studies evaluating the birth weights of different groups of malformed babies with chromosomal abnormalities, it is widely known that infants with trisomy 18, and to a lesser degree those with trisomy 13 and other chromosomal alterations, have low birth weights. PATIENTS AND METHODS: In this study we present the analysis of the birth weights and gestational ages of a large sample of babies (23,155 malformed and a similar number of nonmalformed babies), separating the different groups of chromosomal anomalies and comparing the weight in the clinical groups of malformed infants. RESULTS: Most of the groups with chromosomal abnormalities present lower birth weights in comparison to the other groups. CONCLUSIONS: The results of our study support the conclusion that the relationship between chromosomal alterations and low birth weight is sufficiently important that such a low birth weight in children with minor or major anomalies should be considered as one more indication to perform chromosomal analysis.  相似文献   
7.
Gamma delta T-Cells represent a minor subpopulation of T-lymphocytes in man and their role in normal and diseased human skin is unknown. This article is a comprehensive review of T-lymphocytes bearing the gamma delta T-cell receptor in normal and pathological human skin. Firstly, we have documented the occurrence of gamma delta T-cells in normal skin and in a range of reactive and malignant skin conditions. We have then discussed the experimental findings regarding the repertoire used by gamma delta T-cells in normal human skin and in cutaneous disorders with an increased percentage of gamma delta T-cells.  相似文献   
8.
9.
10.
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