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   36346篇
  免费   1301篇
  国内免费   63篇
电工技术   371篇
综合类   29篇
化学工业   7240篇
金属工艺   725篇
机械仪表   738篇
建筑科学   1964篇
矿业工程   114篇
能源动力   1054篇
轻工业   2887篇
水利工程   430篇
石油天然气   117篇
武器工业   5篇
无线电   2477篇
一般工业技术   6114篇
冶金工业   6601篇
原子能技术   269篇
自动化技术   6575篇
  2023年   214篇
  2022年   442篇
  2021年   683篇
  2020年   464篇
  2019年   617篇
  2018年   781篇
  2017年   695篇
  2016年   834篇
  2015年   757篇
  2014年   1040篇
  2013年   2372篇
  2012年   1680篇
  2011年   2091篇
  2010年   1651篇
  2009年   1548篇
  2008年   1800篇
  2007年   1774篇
  2006年   1591篇
  2005年   1439篇
  2004年   1174篇
  2003年   1122篇
  2002年   1052篇
  2001年   703篇
  2000年   550篇
  1999年   595篇
  1998年   583篇
  1997年   575篇
  1996年   549篇
  1995年   572篇
  1994年   525篇
  1993年   511篇
  1992年   501篇
  1991年   288篇
  1990年   418篇
  1989年   389篇
  1988年   319篇
  1987年   355篇
  1986年   310篇
  1985年   418篇
  1984年   416篇
  1983年   318篇
  1982年   295篇
  1981年   281篇
  1980年   269篇
  1979年   270篇
  1978年   247篇
  1977年   225篇
  1976年   207篇
  1975年   194篇
  1974年   173篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Studied the differences in moral orientation in terms of gender specific modes of reasoning, in 2 experiments. In Exp 1, 32 Ss (aged 24–55 yrs) were read the "Heinz dilemma," and asked 3 questions regarding it. Deliberative and justificatory strategies were identified on the basis of the presence or absence of the higher level knowledge structures. In Exp 2, 40 undergraduates were presented with "Michael and Kohlberg Heinz dilemma," followed by a set of relevant questions. Male Ss preferred to apply a norm or rule in their solutions, while females rejected the application of a norm and sought alternative solutions. This was replicated in Exp 2, but the pattern was reversed with female Ss preferring to apply a norm. Males were divided in their use of either strategy indicating that although, genders differed in their judgments as to which norms or rules to apply; once adopted, norms and rules were used in similar ways. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
22.
23.
There is ample evidence that people cannot generate random series when instructed to do so. Rather, they produce sequences with too few symmetries and long runs and too many alternations among events. The authors propose a psychological theory to account for these findings, which assumes that subjects generate nonrandom sequences that locally represent theoretical random series subject to a constraint on their short-term memory. Closed-form expressions are then derived for the major statistics that have been used to test for deviations from randomness. Results from 3 experiments with 2 and 3 equiprobable alternatives support the model on both the individual and group levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
24.
25.
Anti-virus (AV) products and other fingerprint-based systems are typical of the applications used to enforce security. AV products are probably the first step that most organizations take to protect their systems and enhance security. Many small to medium organizations rely almost entirely on AV products.  相似文献   
26.
Collaborative filtering (CF) involves predicting the preferences of a user for a set of items given partial knowledge of the user's preferences for other items, while leveraging a database of profiles for other users. CF has applications e.g. in predicting Web sites a person will visit and in recommending products. Fundamentally, CF is a pattern recognition task, but a formidable one, often involving a huge feature space, a large data set, and many missing features. Even more daunting is the fact that a CF inference engine must be capable of predicting any (user-selected) items, given any available set of partial knowledge on the user's other preferences. In other words, the model must be designed to solve any of a huge (combinatoric) set of possible inference tasks. CF techniques include memory-based, classification-based, and statistical modelling approaches. Among these, modelling approaches scale best with large data sets and are the most adept at handling missing features. The disadvantage of these methods lies in the statistical assumptions (e.g. feature independence), which may be unjustified. To address this shortcoming we propose a new model-based CF method, based on the maximum entropy principle. For the MS Web application, the new method is demonstrated to outperform a number of CF approaches, including naive Bayes and latent variable (cluster) models, support vector machines (SVMs), and the (Pearson) correlation method.  相似文献   
27.
Water and sediment samples from 29 locations in the Detroit and St. Clair rivers were analyzed for the highly toxic tri-n-butyltin (Bu3Sn+) species and for the less toxic di-n-butyltin (Bu2Sn2+) and n-butyltin (BuSn3+) species and inorganic tin. In general, locations sampled in the St. Clair River were less contaminated with butyltin species than those in the Detroit River. Inorganic tin and BuSn3+ were detected in over 90% of all subsurface water samples, while Bu2Sn2+ and Bu3Sn+ were detected in 45 and 28% of the same samples, respectively. The highest concentration ofBu3Sn+ in subsurface water, 5.9 × 10?10 mol Sn/L, was at the mouth of the Ecorse River, a tributary of the Detroit River. The three butyltin species and inorganic tin were also detected in 23–46% of all sediment samples. The highest concentrations of Bu3Sn+ in sediment were found close to the mouths of the River Rouge, another tributary of the Detroit River, and the Ecorse River, and were 6.2 × I0–7 and 1.7 × I0–7 mol Sn/kg dry weight, respectively, for the top 2 cm of sediment.  相似文献   
28.
29.
30.
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