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   21744篇
  免费   918篇
  国内免费   343篇
电工技术   499篇
综合类   586篇
化学工业   3729篇
金属工艺   554篇
机械仪表   770篇
建筑科学   926篇
矿业工程   181篇
能源动力   572篇
轻工业   2129篇
水利工程   261篇
石油天然气   190篇
武器工业   29篇
无线电   2400篇
一般工业技术   2810篇
冶金工业   4364篇
原子能技术   169篇
自动化技术   2836篇
  2023年   92篇
  2022年   196篇
  2021年   469篇
  2020年   269篇
  2019年   332篇
  2018年   384篇
  2017年   365篇
  2016年   398篇
  2015年   370篇
  2014年   593篇
  2013年   1067篇
  2012年   824篇
  2011年   1067篇
  2010年   774篇
  2009年   864篇
  2008年   826篇
  2007年   861篇
  2006年   743篇
  2005年   619篇
  2004年   696篇
  2003年   907篇
  2002年   1196篇
  2001年   1024篇
  2000年   596篇
  1999年   547篇
  1998年   1533篇
  1997年   973篇
  1996年   712篇
  1995年   482篇
  1994年   349篇
  1993年   392篇
  1992年   204篇
  1991年   160篇
  1990年   159篇
  1989年   150篇
  1988年   138篇
  1987年   118篇
  1986年   115篇
  1985年   157篇
  1984年   88篇
  1983年   92篇
  1982年   85篇
  1981年   107篇
  1980年   104篇
  1979年   61篇
  1978年   56篇
  1977年   124篇
  1976年   233篇
  1975年   55篇
  1973年   50篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
131.
132.
Cystic fibrosis (CF) is the most common lethal autosomal recessive disorder among Caucasians and is caused by abnormalities in the cystic fibrosis transmembrane conductance regulator gene (CFTR). CFTR gene encodes a chloride channel that regulates secretion in many exocrine tissues especially pancreatic and pulmonary tissues. The clinical presentation of cystic fibrosis is highly variable with isolated CAVD (congenital absence of vas deferens) and/or typical pancreatic and pulmonary manifestations. Over 500 mutations in the CFTR gene have been described and vary among different geographic locations. The severity of clinical manifestations and specially the pulmonary disease is poorly correlated with genotype. It is interesting to collect clinical and genetical data by analysing a larger cohort of CF patients. These results are likely to improve our understanding of the physiopathology of CF and the genetic counselling; particular biochemical defect could lead to more specific treatments in the future. From our 110 patients selected in Champagne-Ardenne country, we analysed the entire coding sequence of CFTR gene and detected 95% of CF mutations and in fact, 89.5% if we include the CAVD patients; 59.4% of CF mutations were detected for these patients. Three new mutations have been here reported. We found numerous CF mutations with a large distribution throughout the gene. Nevertheless, three exons are mainly involved: 10, 11 and 21. Relationships between the genotype and phenotype are difficult to assess.  相似文献   
133.
134.
The seroprevalence of HIV-1 and HIV-2 among pregnant women in Maputo, the capital of Mozambique, was compared between the years 1982/83, 1988 and 1990. None of the 432 serum samples collected in 1982/83 was positive for HIV antibodies whereas in 1988 the HIV-1 and HIV-2 seroprevalence was 0.4% (2/500) and 0.6% (3/500), respectively, and in 1990 0.6% (12/2014) and 0.2% (4/2014), respectively. These results indicate that HIV infection has been introduced recently in Maputo and is spreading at a slow rate among women.  相似文献   
135.
136.
137.
In this study several types of bottle materials (glass, PET (polyethylene terephthalate), PC (polycarbonate), HDPE (high density polyethylene), PP (polypropylene) and PVC (polyvinyl chloride)) were evaluated in order to be used as food refillables, comparing the residual chemical contamination after classical caustic washing. Bottles were contaminated with model chemicals (chloroxylenol and d-limonene) and caustic washed with varied process parameters using a simulated laboratory-scale washing procedure. After washing, the chemical-contaminated bottles were filled with water and stored for 28 days at 37 degrees C. The concentrations of the model chemicals in the water after storage were taken as a measure of chemical contamination. The influence of the cleaning parameters (temperature, caustic and commercial additive concentration) was studied using response surface methodology. Washing temperature showed a significant influence on the removal of absorbed chemicals from surfaces compared with the effect of the caustic and especially the additive concentration. Optimization of caustic cleaning for the cleaning process in question led to better cleaning effectiveness, although none of the different washing conditions were able to remove all absorbed chemicals out of the polymeric resins. Commercially available plastic refillables (PET and PC) showed the best chemical rinsability. Glass bottles, however, had in every case the best rinsing characteristics.  相似文献   
138.
A method of posterior mitral annulus remodeling is presented. The posterior annulus is divided into three segments, each segment encircled by a suture that is passed in a tourniquet. Coaptation of the leaflets can be achieved by tightening the tourniquets while the ventricle is being filled. This technique is simple and quick, avoids the use of foreign material, and requires less expertise and judgment than traditional annuloplasties.  相似文献   
139.
The oxidation of methanol on gold electrodes modified with polypyrrole and platinum is reported. These electrodes were characterized by cyclic voltammetry and by 12h polarizations in methanol solutions. They were found to give higher currents and lower rates of drift than electrodes of platinum and platinized gold. The effect of varying the amount of platinum deposited is also discussed.  相似文献   
140.
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