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   9134篇
  免费   171篇
  国内免费   8篇
电工技术   70篇
综合类   2篇
化学工业   589篇
金属工艺   84篇
机械仪表   51篇
建筑科学   58篇
矿业工程   3篇
能源动力   91篇
轻工业   345篇
水利工程   17篇
石油天然气   15篇
无线电   276篇
一般工业技术   473篇
冶金工业   6810篇
原子能技术   32篇
自动化技术   397篇
  2023年   19篇
  2022年   29篇
  2021年   69篇
  2020年   51篇
  2019年   45篇
  2018年   83篇
  2017年   78篇
  2016年   74篇
  2015年   53篇
  2014年   114篇
  2013年   201篇
  2012年   111篇
  2011年   170篇
  2010年   115篇
  2009年   167篇
  2008年   144篇
  2007年   106篇
  2006年   101篇
  2005年   88篇
  2004年   90篇
  2003年   63篇
  2002年   65篇
  2001年   54篇
  2000年   56篇
  1999年   244篇
  1998年   2161篇
  1997年   1244篇
  1996年   804篇
  1995年   420篇
  1994年   374篇
  1993年   426篇
  1992年   67篇
  1991年   110篇
  1990年   92篇
  1989年   93篇
  1988年   94篇
  1987年   99篇
  1986年   91篇
  1985年   86篇
  1984年   15篇
  1983年   23篇
  1982年   50篇
  1981年   64篇
  1980年   48篇
  1979年   8篇
  1978年   20篇
  1977年   168篇
  1976年   333篇
  1975年   17篇
  1955年   7篇
排序方式: 共有9313条查询结果,搜索用时 361 毫秒
111.
Mass treatment of the human population with niclosamide was carried out in 2 villages in rural Guatemala where Taenia solium was endemic, to determine how this would affect the epidemiology of the parasite. Intestinal taeniasis was diagnosed by microscopy and coproantigen testing, and porcine cysticercosis by a specific Western blot. Before mass treatment, the prevalence of human taeniasis was 3.5%; 10 months after treatment it was 1%, a significant decrease (P < 10(-4)). All tapeworms that could be identified to the species level were T. solium. Similarly, the seroprevalence of antibodies to cysticercosis in pigs declined from 55% before treatment to 7% 10 months after treatment, once again a significant decrease (P < 10(-6)). These effects were seen in both villages. The possible use of mass chemotherapy as a tool in the control of T. solium is discussed.  相似文献   
112.
113.
The β-hydroxyacyl-CoA-dehydrogenase (HADH) activity of unfrozen and thawed frog legs was investigated. The enzyme was extracted by either immersing frog legs in phosphate buffer 0.1 M, pH 6.0 at 25°C for 15 min or pressing them between trichinoscopy glasses. The enzyme activity was assayed using acetoacetyl-CoA as substrate and measured spectrophotometrically at 340 nm. It was possible by both extraction methods to distinguish between thawed and unfrozen samples although when the juice was obtained by pressing the HADH activity of the dilution was ~ 1.5 times higher than that obtained by immersion. The HADH activity was significantly higher (P≤0·001) in frozen-thawed frogs than in unfrozen legs because during freezing there is a release of HADH. No significative differences were found in the HADH activity in samples frozen in the temperature range -10 to -196°C. HADH activity was not affected by the storage time in crushed ice up to 6 days.  相似文献   
114.
The available surgical and non-surgical therapy options for treatment of gallstone disease are presented. Conventional cholecystectomy is regarded as standard therapy of symptomatic cholecystolithiasis. Other modes of therapy may be indicated under certain circumstances, depending on the results of imaging procedures. In this context conventional X-ray examination, oral and intravenous cholecystography, sonography, computed tomography, endoscopic retrograde cholangiography/cholecystography, and magnetic resonance imaging are discussed and their influence on therapeutic decisions is explained.  相似文献   
115.
116.
117.
Wind energy conversion systems (WECS) produce fluctuating output power, which may cause voltage fluctuations and flicker. Flicker assessment in networks may be difficult since its evaluation requires long computing time and special procedures to calculate the flicker severity index, Pst. In this paper, a frequency domain method to study flicker propagation is presented. This method is based on propagation of frequency components from WECS output currents throughout the grid. In this way, a fast flicker analysis in a network of any size can be performed. Also, an algorithm for flicker measurement in the frequency domain, which allows Pst calculation, is proposed. Several study cases have been performed, and results have been compared with time domain simulations, showing good agreement between them  相似文献   
118.
We analyzed the first 5 years of surveillance data from the Established Population for the Epidemiologic Studies of the Elderly (EPESE) in the Piedmont of North Carolina (n = 4162) to estimate the effect of a global self-rating of health on survival. Covariates used in Cox proportional hazard models included sociodemographic factors, chronic medical conditions, activities of daily living, use of health services, health risk behaviors, cognitive function, affective mood, and negative life events. Adjusted risk of mortality associated with poor (compared to excellent) self-ratings of health was significantly elevated among urban men only. Confounders of the association between survival and overall health assessment varied widely by subgroup. Pooled estimates from heterogeneous populations may mask significant subgroup differences both in the pattern of variables that mediate crude risk and also in the magnitude of residual risk of global self-ratings of health.  相似文献   
119.
120.
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