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   5719篇
  免费   158篇
  国内免费   89篇
电工技术   76篇
综合类   125篇
化学工业   444篇
金属工艺   153篇
机械仪表   121篇
建筑科学   302篇
矿业工程   33篇
能源动力   82篇
轻工业   332篇
水利工程   42篇
石油天然气   61篇
武器工业   24篇
无线电   329篇
一般工业技术   559篇
冶金工业   2986篇
原子能技术   42篇
自动化技术   255篇
  2023年   18篇
  2022年   56篇
  2021年   67篇
  2020年   59篇
  2019年   68篇
  2018年   64篇
  2017年   68篇
  2016年   62篇
  2015年   61篇
  2014年   73篇
  2013年   152篇
  2012年   144篇
  2011年   167篇
  2010年   127篇
  2009年   146篇
  2008年   136篇
  2007年   146篇
  2006年   145篇
  2005年   115篇
  2004年   113篇
  2003年   103篇
  2002年   82篇
  2001年   59篇
  2000年   68篇
  1999年   153篇
  1998年   875篇
  1997年   548篇
  1996年   345篇
  1995年   229篇
  1994年   184篇
  1993年   236篇
  1992年   51篇
  1991年   59篇
  1990年   55篇
  1989年   62篇
  1988年   54篇
  1987年   47篇
  1986年   45篇
  1985年   47篇
  1984年   32篇
  1983年   25篇
  1982年   45篇
  1981年   43篇
  1980年   38篇
  1979年   27篇
  1978年   32篇
  1977年   102篇
  1976年   191篇
  1975年   19篇
  1974年   19篇
排序方式: 共有5966条查询结果,搜索用时 46 毫秒
41.
42.
43.
网络信息安全技术综述   总被引:10,自引:0,他引:10  
李彦旭  巴大志  成立 《半导体技术》2002,27(10):9-12,28
阐述了网络信息安全的三个组成方面,具体分析了在实际应用中的网络安全技术手段,探讨了国内外研究开发网络信息安全技术的现状、发展趋势及我们所应着重采取的策略.  相似文献   
44.
Hereditary susceptibility to sarcoidosis is suggested by ethnic preponderance, familial clustering, and multigenerational involvement. The genetics of sarcoidosis cannot be adequately addressed in small samples of patients; a large-scale study with stratification for patient phenotypic differences is necessary. A study that uses both genetic marker and environmental data would be able to control for and examine different causative mechanisms. Until such a well-designed, comprehensive study is carried out, we are left with interesting patterns of disease in families and uncertain allelic associations.  相似文献   
45.
We present the first case of esophagogastric devascularization and esophagogastric transection using a stapler through laparoscopic surgery. The procedure was performed in a 71-year-old diabetic woman with alcoholic liver cirrhosis (Child-Pugh B class), portal hypertension, bleeding grade III esophageal varices, and a previous bleeding episode. The surgical technique was carried out without problems, and the patient had an excellent postoperative condition. Esophagogastric devascularization with esophageal transection using a stapler through laparoscopic surgery is a feasible technique that accomplishes the same and all objectives of the open procedure. Operative time in both methods is the same, whereas surgical trauma, inmunologic depletion, amount of transfused blood, pain, use of analgesics, and hospital stay are reduced in the laparoscopic technique.  相似文献   
46.
Catechol-O-methyltransferase (COMT) is one of the major mammalian enzymes involved in the metabolic degradation of catecholamines and is considered a candidate for several psychiatric disorders and symptoms, including the psychopathology associated with the 22q11 microdeletion syndrome. By means of homologous recombination in embryonic stem cells, a strain of mice in which the gene encoding the COMT enzyme has been disrupted was produced. The basal concentrations of brain catecholamines were measured in the striatum, frontal cortex, and hypothalamus of adult male and female mutants. Locomotor activity, anxiety-like behaviors, sensorimotor gating, and aggressive behavior also were analyzed. Mutant mice demonstrated sexually dimorphic and region-specific changes of dopamine levels, notably in the frontal cortex. In addition, homozygous COMT-deficient female (but not male) mice displayed impairment in emotional reactivity in the dark/light exploratory model of anxiety. Furthermore, heterozygous COMT-deficient male mice exhibited increased aggressive behavior. Our results provide conclusive evidence for an important sex- and region-specific contribution of COMT in the maintenance of steady-state levels of catecholamines in the brain and suggest a role for COMT in some aspects of emotional and social behavior in mice.  相似文献   
47.
48.
复合微粒高性能混凝土的二级界面显微结构及耐久性研究   总被引:8,自引:0,他引:8  
巴恒静  冯奇  杨英姿 《硅酸盐学报》2003,31(11):1043-1047
将天然纳米纤维材料及活性球形掺合料复合应用于高性能混凝土中,用以改善高性能混凝土的二级界面,探讨胶凝材料的颗粒紧密堆积及显微结构。对混凝土力学性能的研究表明:改善混凝土的二级界面,可以大幅度提高其抗弯强度和弹性模量;对耐久性的研究表明,由于加入了纳米纤维材料,改善了体系颗粒级配及二级界面显微结构,增加了体系密实度,是提高混凝土抗冻性、抗渗性的有效途径。因而,研究高性能混凝土的二级界面显微结构,对于提高高性能混凝土的宏观物理力学性能及耐久性存在巨大潜能。  相似文献   
49.
Negative consequences are an important component of the substance use change process, yet no standardized measure exists to assess consequences of use. This study evaluated the psychometric properties of the Inventory of Drug Use Consequences, a self-report measure assessing drinking and drug use consequences. Participants (N=252) were assessed at entry into outpatient substance abuse treatment. Items loaded strongly on 1 factor, and internal consistency of the total scale was high. Fifteen items with the highest correlations with the total scale were chosen to represent the construct. The shortened measure exhibited good internal consistency, convergent and discriminant validity, and detected change over time and may be the measure of substance use consequences that is lacking in the field. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
50.
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