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   598509篇
  免费   7602篇
  国内免费   2072篇
电工技术   10776篇
综合类   478篇
化学工业   88920篇
金属工艺   22363篇
机械仪表   18775篇
建筑科学   13678篇
矿业工程   2634篇
能源动力   16835篇
轻工业   50889篇
水利工程   5806篇
石油天然气   9536篇
武器工业   22篇
无线电   73767篇
一般工业技术   116913篇
冶金工业   113224篇
原子能技术   11667篇
自动化技术   51900篇
  2022年   3335篇
  2021年   5238篇
  2020年   3989篇
  2019年   5017篇
  2018年   8334篇
  2017年   8336篇
  2016年   8999篇
  2015年   5943篇
  2014年   9821篇
  2013年   29133篇
  2012年   16266篇
  2011年   22330篇
  2010年   17632篇
  2009年   19902篇
  2008年   20527篇
  2007年   20327篇
  2006年   18394篇
  2005年   16578篇
  2004年   15863篇
  2003年   15692篇
  2002年   14722篇
  2001年   14919篇
  2000年   13832篇
  1999年   14736篇
  1998年   36936篇
  1997年   25640篇
  1996年   19528篇
  1995年   14642篇
  1994年   12807篇
  1993年   12804篇
  1992年   9110篇
  1991年   8638篇
  1990年   8484篇
  1989年   8002篇
  1988年   7695篇
  1987年   6536篇
  1986年   6331篇
  1985年   7382篇
  1984年   6728篇
  1983年   6103篇
  1982年   5616篇
  1981年   5725篇
  1980年   5325篇
  1979年   5067篇
  1978年   4914篇
  1977年   5639篇
  1976年   7237篇
  1975年   4246篇
  1974年   3984篇
  1973年   4121篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Communication network design is becoming increasingly complex, involving making networks more usable, affordable, and reliable. To help with this, we have proposed an expert network designer (END) for configuring, modeling, simulating, and evaluating large structured computer networks, employing artificial intelligence, knowledge representation, and network simulation tools. We present a neural network/knowledge acquisition machine-learning approach to improve the END's efficiency in solving the network design problem and to extend its scope to acquire new networking technologies, learn new network design techniques, and update the specifications of existing technologies  相似文献   
82.
83.
84.
Malignant bone pain: pathophysiology and treatment   总被引:1,自引:0,他引:1  
2-acetyl aminofluorene (AAF) reacts in acidic conditions with nitrous fume yielding N-nitroso-AAF (N-NO-AAF), as previously described, that exerts more toxic and mutagenic effects than its parental compound. In this study, the effect of sodium nitrite (NaNO2) on the tumorigenicity of AAF in rats fed with AAF and NaNO2 was observed. Wistar rats were divided into five groups: group I served as control; group II were treated with NaNO2 (0.3%); group III was given 0.02% AAF alone; groups IV and V received both AAF and NaNO2 (0.2 and 0.3% respectively) in their diet for 12 weeks. At the end of the experiment, all rats in groups III, IV and V developed early stage phenomena of hepatocellular carcinoma, including hepatomegaly with variable-sized foci and neoplastic nodules. Severe damage was observed in the rats treated with AAF and NaNO2. Feeding of AAF (0.02%) for 3 months elevated the levels of c-Fos, c-Jun and c-Myc proteins in the rat livers. The AAF-induced c-Jun, c-Fos and c-Myc expressions were significantly magnified (P < 0.001) by NaNO2. These data confirmed that the strengthening of AAF-induced hepatocarcinogenesis by NaNO2 should be associated with its enhancing effect on the AAF-induced increases in the expressions of c-Jun, c-Fos and c-Myc.  相似文献   
85.
Approaches to using visual language in a cultural context can be placed on a continuum, with global (universal) on one end and culture-focused on the other. Each approach reveals contrasting assumptions about three central design issues: perception, aesthetics and pragmatics. The global approach is characterized by attempts to invent an objective, universal visual language or to define such a language through perceptual principles and empirical research. The culture-focused perspective is founded on the principle that visual communication is intimately bound to experience and hence can function only within a given cultural context, to which designers must be sensitive. While the modernist, universal approach has been losing ground to the postmodern, culture-focused approach, the two complement each other in a variety of ways and, depending on the rhetorical situation, offer pragmatic benefits and drawbacks  相似文献   
86.
87.
88.
Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 172–176, May–June, 1994  相似文献   
89.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period  相似文献   
90.
An experimental and theoretical analysis of the nonlinear coupling mechanism between the two solitary pulses circulating in a two-color femtosecond laser is presented. Two operation regimes; synchronized; and nonsynchronized; and a hysteresis of the transition between the two regimes are clearly observed; while independent modelocking and tunability of the output pulse trains is found in both regimes. Pulses in the range from 15 to 100 fs are synchronized with a timing jitter below 2 fs. The combined effects of cross-phase modulation and negative group velocity dispersion are shown to be responsible for the strong pulse correlation in the synchronized regime. Our experimental observations are in agreement with numerical simulations, thus confirming the theoretical model  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