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   23278篇
  免费   965篇
  国内免费   322篇
电工技术   494篇
综合类   547篇
化学工业   4413篇
金属工艺   554篇
机械仪表   766篇
建筑科学   959篇
矿业工程   190篇
能源动力   664篇
轻工业   2260篇
水利工程   263篇
石油天然气   183篇
武器工业   27篇
无线电   2610篇
一般工业技术   3221篇
冶金工业   3814篇
原子能技术   177篇
自动化技术   3423篇
  2023年   157篇
  2022年   481篇
  2021年   611篇
  2020年   345篇
  2019年   409篇
  2018年   487篇
  2017年   450篇
  2016年   497篇
  2015年   429篇
  2014年   642篇
  2013年   1202篇
  2012年   931篇
  2011年   1186篇
  2010年   877篇
  2009年   940篇
  2008年   966篇
  2007年   931篇
  2006年   813篇
  2005年   676篇
  2004年   723篇
  2003年   950篇
  2002年   1224篇
  2001年   1042篇
  2000年   617篇
  1999年   555篇
  1998年   1367篇
  1997年   898篇
  1996年   657篇
  1995年   438篇
  1994年   329篇
  1993年   358篇
  1992年   199篇
  1991年   155篇
  1990年   149篇
  1989年   137篇
  1988年   139篇
  1987年   110篇
  1986年   113篇
  1985年   152篇
  1984年   86篇
  1983年   91篇
  1982年   87篇
  1981年   104篇
  1980年   101篇
  1979年   61篇
  1978年   52篇
  1977年   103篇
  1976年   193篇
  1975年   53篇
  1973年   52篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
The phase behavior of a hybrid polymer network (HPN) composed of poly[(propylene glycol maleate)-co-(propylene glycol phthalate)] crosslinked with styrene and polyester–urethane crosslinked with methylene-bis-ortho-chloroaniline was examined. The correlation between phase separation and impact strength of the HPNs is discussed. The composition of HPNs has an effect on their properties.  相似文献   
123.
The (2 w )! reversible transformations on w wires, i.e. reversible logic circuits with w inputs and w outputs, together with the action of cascading, form a group, isomorphic to the symmetric group S 2 w . Therefore, we investigate the group S n as well as one of its subgroups isomorphic to S n/2 × S n/2. We then consider the left cosets, the right cosets, and the double cosets generated by the subgroup. Each element of a coset can function as the representative of the coset. The coset can then be considered as the set of all group elements that differ from the representative by merely multiplying (either to the left or to the right or to both sides) by an arbitrary element of the subgroup. Different choices of the coset space and different choices of the coset representatives lead to six different syntheses for implementing an arbitrary reversible logic operation into hardware. Evaluation of all six methods, by means of three different cost functions (gate cost, switch cost, and quantum cost), leads to a best choice.  相似文献   
124.
The security of a deterministic quantum scheme for communication, namely the LM05 [1], is studied in presence of a lossy channel under the assumption of imperfect generation and detection of single photons. It is shown that the scheme allows for a rate of distillable secure bits higher than that pertaining to BB84 [2]. We report on a first implementation of LM05 with weak pulses.  相似文献   
125.
Probabilistic Visual Cryptography Schemes   总被引:1,自引:0,他引:1  
  相似文献   
126.
This study examines the presence of dental caries in a large sample of adult skeletons from the 19th century cemetery of St. Thomas' Anglican Church in Belleville, Ontario. The cemetery was used from 1821 to 1874. Caries prevalence and frequencies of diseased and missing teeth were calculated both by observing summary statistics of individual rates and by the total sample of teeth. Postmortem tooth loss is low in this sample and antemortem tooth loss is highest in first mandibular molars, all other molars and then premolars. Age at death, but not sex, was found to be significantly related to the overall Caries Rate while both age and sex were significantly associated with the Diseased-Missing Index. The increase in diseased and missing teeth in older individuals is expected while the sex difference is not explained by simple dietary factors. When compared to reports on British and American samples, caries and antemortem tooth loss in the St. Thomas' sample is most similar to a pre-1850 British group and higher than American samples. Although there is undoubtedly a complex of factors contributing to caries prevalence in this sample, more data are required from large historic samples, particularly from the American northeast and late 19th century Britain, to have a clearer understanding of the influence of diet, cultural, and environmental factors affecting caries rates in historic populations.  相似文献   
127.
128.
In this paper we analyze how supervised learning occurs in ecological neural networks, i.e. networks that interact with an autonomous external environment and, therefore, at least partially determine with their behavior their own input. Using an evolutionary method for selecting good teaching inputs we surprisingly find that to obtain a desired outputX it is better to use a teaching input different fromX. To explain this fact we claim that teaching inputs in ecological networks have two different effects: (a) to reduce the discrepancy between the actual output of the network and the teaching input, (b) to modify the network's behavior and, as a consequence, the network's learning experiences. Evolved teaching inputs appear to represent a compromise between these two needs. We finally show that evolved teaching inputs that are allowed to change during the learning process function differently at different stages of learning, first giving more weight to (b) and, later on, to (a).  相似文献   
129.
The immunoglobulin heavy chain (VH) gene family usage in experimental autoimmune myasthenia gravis (EAMG) model was investigated by RNA slot blot hybridization using VH gene family specific probes. Anti-acetylcholine receptor (AChR) monoclonal antibodies (mAbs) isolated from susceptible C57BL/6 and resistant BALB/c mice were found to be encoded by VH genes from at least six different families. The Vgam3.8 family was overrepresented in alpha-bungarotoxin blocking mAbs. Expression of cross-reactive idiotypes by anti-AChR mAbs was irrespective of the VH gene family usage. Strain dependent differences in susceptibility for EAMG were not reflected in an aberrant VH gene family usage of anti-AChR mAbs.  相似文献   
130.
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