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   410436篇
  免费   5033篇
  国内免费   1376篇
电工技术   7690篇
综合类   333篇
化学工业   61226篇
金属工艺   16602篇
机械仪表   13855篇
建筑科学   8506篇
矿业工程   2157篇
能源动力   11787篇
轻工业   28972篇
水利工程   4293篇
石油天然气   7923篇
武器工业   17篇
无线电   50435篇
一般工业技术   84148篇
冶金工业   75567篇
原子能技术   9251篇
自动化技术   34083篇
  2022年   2633篇
  2021年   4006篇
  2020年   3044篇
  2019年   3924篇
  2018年   6636篇
  2017年   6612篇
  2016年   7122篇
  2015年   4496篇
  2014年   7430篇
  2013年   20514篇
  2012年   11818篇
  2011年   15691篇
  2010年   12450篇
  2009年   14096篇
  2008年   14374篇
  2007年   14086篇
  2006年   12697篇
  2005年   11347篇
  2004年   10723篇
  2003年   10620篇
  2002年   10067篇
  2001年   9900篇
  2000年   9263篇
  1999年   9659篇
  1998年   24631篇
  1997年   16893篇
  1996年   12934篇
  1995年   9623篇
  1994年   8462篇
  1993年   8475篇
  1992年   6099篇
  1991年   5750篇
  1990年   5721篇
  1989年   5361篇
  1988年   5076篇
  1987年   4455篇
  1986年   4331篇
  1985年   4833篇
  1984年   4442篇
  1983年   4008篇
  1982年   3668篇
  1981年   3749篇
  1980年   3442篇
  1979年   3332篇
  1978年   3347篇
  1977年   3762篇
  1976年   4867篇
  1975年   2854篇
  1974年   2668篇
  1973年   2737篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
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   
54.
55.
56.
Translated from Kibernetika i Sistemnyi Analiz, No. 3, pp. 172–176, May–June, 1994  相似文献   
57.
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   
58.
A novel class of narrow-band tunable wavelength filters is proposed and evaluated. Wavelength selectivity of the proposed filters Is derived from the finite time response of an optical nonlinearity. The nonlinearity is gain saturation in semiconductor optical amplifier structures. The filters are shown to have very narrow passbands tunable over the entire semiconductor gain bandwidth. The key to filter implementation is a device configuration in which the wave-mixing products can be isolated from the amplified inputs. Three integrated optics compatible configurations are considered and shown to have high filter throughputs 34 to 180% and subangstrom bandwidths  相似文献   
59.
The technological process of cold forging applied for the first time in the production of the casing of the internal joint with races is described. The process operations of cold forging and the annealing and carburizing regimes for this part me described.  相似文献   
60.
A fiber optic ring network, such as fiber distributed data interface (FDDI), can be operated over multiple wavelengths on its existing fiber plant consisting of point-to-point fiber links. Using wavelength division multiplexing (WDM) technology, FDDI nodes can be partitioned to operate over multiple subnetworks, with each subnetwork operating independently on a different wavelength, and inter-subnetwork traffic forwarding performed by a bridge. For this multiwavelength version of FDDI, which we refer to as wavelength distributed data interface (WDDI), we examine the necessary upgrades to the architecture of a FDDI node, including its possibility to serve as a bridge. The main motivation behind this study is that, as network traffic scales beyond (the single-wavelength) FDDI's information-carrying capacity, its multiwavelength version, WDDI, can gracefully accommodate such traffic growth. A number of design choices exist in constructing a good WDDI network. Specifically, we investigate algorithms using which, based on prevailing traffic conditions, partitioning of nodes into subnetworks can be performed in an optimized fashion. Our algorithms partition the nodes into subrings, such that the total traffic flow in the network and/or the network-wide average packet delay is minimized  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