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   21363篇
  免费   815篇
  国内免费   319篇
电工技术   465篇
综合类   549篇
化学工业   3751篇
金属工艺   546篇
机械仪表   728篇
建筑科学   862篇
矿业工程   181篇
能源动力   564篇
轻工业   2083篇
水利工程   245篇
石油天然气   177篇
武器工业   27篇
无线电   2369篇
一般工业技术   2790篇
冶金工业   4168篇
原子能技术   168篇
自动化技术   2824篇
  2023年   110篇
  2022年   339篇
  2021年   469篇
  2020年   265篇
  2019年   333篇
  2018年   383篇
  2017年   357篇
  2016年   397篇
  2015年   347篇
  2014年   526篇
  2013年   1012篇
  2012年   792篇
  2011年   970篇
  2010年   751篇
  2009年   816篇
  2008年   804篇
  2007年   825篇
  2006年   713篇
  2005年   608篇
  2004年   687篇
  2003年   899篇
  2002年   1188篇
  2001年   1018篇
  2000年   594篇
  1999年   554篇
  1998年   1476篇
  1997年   953篇
  1996年   701篇
  1995年   469篇
  1994年   341篇
  1993年   376篇
  1992年   200篇
  1991年   158篇
  1990年   152篇
  1989年   138篇
  1988年   133篇
  1987年   111篇
  1986年   116篇
  1985年   153篇
  1984年   87篇
  1983年   93篇
  1982年   86篇
  1981年   105篇
  1980年   100篇
  1979年   61篇
  1978年   50篇
  1977年   116篇
  1976年   219篇
  1975年   54篇
  1973年   52篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
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   
73.
74.
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   
75.
76.
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   
77.
The degradation due to stress induced voiding of nitride passivated Al-1 wt.% Si and Ti/TN/ Al-1wt.% Si-0.5 wt. % Cu/Ti/TN interconnects with widths ranging between 0.4 and 1.2 μm was studied by in-situ conventional high resolution resistance measurements (HRRM) during storage at temperatures between 168 and 240°C. The conventional measurements on Al-Si lines, which lasted more than one year, clearly showed that the interconnect lifetime decreases with decreasing line width. With HRRM the degradation due to stress induced voiding can be detected much sooner and with much more detail. From the HRRM it is clear that the resistance changes during storage often happen in jumps and that the degradation has a rather complex alloy, line width and temperature dependence. Both for 0.4 and 0.6 μm wide Al---Si lines more degradation occurred for storage at 175 °C compared to storage at 200 °C. For the Al---Si---Cu stacks the degradation of 0.4 μm wide lines was worse for storage at 240°C compared to storage at 200 °C, but the opposite was true for the 0.6 μm wide lines.  相似文献   
78.
Memory cost is responsible for a large amount of the chip and/or board area of customized video and image processing system realizations. In this paper, we present a novel technique-founded on data-flow analysis which allows one to address the problem of background memory size evaluation for a given nonprocedural algorithm specification, operating on multidimensional signals with affine indexes. Most of the target applications are characterized by a huge number of signals, so a new polyhedral data-flow model operating on groups of scalar signals is proposed. These groups are obtained by a novel analytical partitioning technique, allowing to select a desired granularity, depending on the application complexity. The method incorporates a way to tradeoff memory size with computational and controller complexity  相似文献   
79.
Pb1–x Ca x [(Co0.5W0.5)0·05Ti0.95]O3 ceramics with x = 0.24, 0.30 and 0.35, are prepared by a solid state reaction of oxides. Deviations from nominal chemical compositions and formation of segregated phases different from modified lead titanate perovskites, are studied. Pyro- and non-pyroelectric currents excited in the material by a thermal wave are investigated and related to mobility of electrical charges in the materials.  相似文献   
80.
The conclusions are put forward that are adopted by a discussion group preparing the framework for a limitation policy of the radon problem in Belgium. Existing and future situations are treated in a coherent policy that is adequate for practical implementation. An action level is defined, together with a hierachy of levels for new constructions. The decision logic for the acceptance of building materials is explained.  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