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   222982篇
  免费   17101篇
  国内免费   8801篇
电工技术   12606篇
技术理论   18篇
综合类   13833篇
化学工业   37853篇
金属工艺   11848篇
机械仪表   13638篇
建筑科学   17887篇
矿业工程   6346篇
能源动力   6373篇
轻工业   13821篇
水利工程   3720篇
石油天然气   13099篇
武器工业   1536篇
无线电   26390篇
一般工业技术   27188篇
冶金工业   11122篇
原子能技术   2422篇
自动化技术   29184篇
  2024年   923篇
  2023年   3528篇
  2022年   6098篇
  2021年   8458篇
  2020年   6444篇
  2019年   5420篇
  2018年   6075篇
  2017年   6933篇
  2016年   5936篇
  2015年   8211篇
  2014年   10226篇
  2013年   12597篇
  2012年   13479篇
  2011年   14690篇
  2010年   12856篇
  2009年   12447篇
  2008年   12219篇
  2007年   11523篇
  2006年   12070篇
  2005年   10649篇
  2004年   7254篇
  2003年   6324篇
  2002年   5791篇
  2001年   5445篇
  2000年   5697篇
  1999年   6366篇
  1998年   5454篇
  1997年   4720篇
  1996年   4276篇
  1995年   3670篇
  1994年   2975篇
  1993年   2234篇
  1992年   1785篇
  1991年   1388篇
  1990年   1076篇
  1989年   917篇
  1988年   723篇
  1987年   528篇
  1986年   369篇
  1985年   270篇
  1984年   168篇
  1983年   127篇
  1982年   145篇
  1981年   96篇
  1980年   80篇
  1979年   42篇
  1978年   28篇
  1977年   25篇
  1976年   40篇
  1973年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
An analytical method is presented for calculating the resonant frequency andQ-factor of a superconducting dielectric disk resonator operating in millimeter-wave regime with whispering-gallery mode. Resonant frequency shift due to the optical generation of quasi-particles in superconducting film is investigated as a function of photon flux. An optically tunable resonant frequency of about 500 MHz is estimated, and good agreement is found between numerical results and experimental ones.  相似文献   
92.
本文推导了在修正双极坐标系下的Navier-Stokes方程和讨论了它的基本流的扰动解  相似文献   
93.
The tail-flick (TF) technique was used to assess the antinociceptive properties of nifedipine (NIF) given intraperitoneally (i.p.). First, the most suitable intensity of the noxious stimulus (temperature of the bulb) has been ascertained and used in the main study. Male Sprague-Dawley rats received NIF, dissolved in dimethyl sulfoxide (DMSO) at the doses of 0.0, 0.5, 2, 5, 10 and 15 mg/kg, or control with no injection. For the main study, the noxious stimulus was limited to 15 sec (cut-off time) and TF latencies were recorded up to 120 min. The antinociceptive response was expressed as the area under the curve for each rat and analyzed by one-way ANOVA. The antinociceptive response to the lower doses of NIF (0.5 and 2 mg/kg) did not differ from control (no injection) and DMSO alone. Significance was found at 5, 10 and 15 mg NIF with no difference among the doses. However, there was an increasing tendency of the mean values from 0.5 to 15 mg NIF resulting in a positive correlation. The correlation coefficient was 0.32483 (p = 0.015) and regression equation Y = (19.37) x dose + 1320. Our data suggest that spinal mechanisms are involved in NIF-induced antinociception.  相似文献   
94.
文中解决了2-重自补图的计数问题,获得了具有p个顶点的2-重自补图的数目是其中Z(A)表示置换群A的圈指标,S ̄(2)_p表示p次对称群的对群.  相似文献   
95.
Epidemiological studies have linked dietary fiber to the prevention of human colorectal cancer and suggest that short chain fatty acids such as butyric acid, which is produced by fermentation of dietary fiber in the large intestine, may be an important mediator of the protective effects of fiber. We investigated the role of Bcl-2 deregulation on the sensitivity of colorectal carcinoma cells to undergo butyrate-induced apoptosis. Here we report an inverse relationship between the levels of Bcl-2 and the sensitivity of colorectal carcinoma cell lines to undergo apoptosis in response to butyrate. Overexpression of Bcl-2 in colorectal carcinoma DiFi cells resulted in suppression of butyrate-induced apoptosis and enhanced cell survival in response to butyrate. Butyrate-induced apoptosis was accompanied by inhibition of expression of a 30 kDa protein (p30, immunorecognized by anti-Bcl-2 mAb) and this cellular effect of butyrate was inhibited by Bcl-2 overexpression. These findings suggest that deregulation of Bcl-2 in human colorectal carcinoma cells confers resistance to induction of apoptosis by butyrate, a dietary micronutrient.  相似文献   
96.
The purpose of this study is to investigate the precipitation characteristics of σ phase in the fusion zone of stainless steel welds at various welding passes during a tungsten are welding (GTAW) process. The morphology, quantity, and chemical composition of the δ-ferrite and σ phase were analyzed using optical microscopy (OM), a ferritscope (FS), a X-ray diffractometer (XRD), scanning electron microscopy (SEM), an electron probe micro-analyzer (EPMA), and a wavelength dispersive spectrometer (WDS), respectively. Massive δ-ferrite was observed in the fusion zone of the first pass welds during welding of dissimilar stainless steels. The σ phase precipitated at the inner δ-ferrite particles and decreased δ-ferrite content during the third pass welding. The σ and δ phases can be stabilized by Si element, which promoted the phase transformation of σ→ϱ+λ2 in the fusion zone of the third pass welds. It was found that the σ phase was a Fe−Cr−Si intermetallic compound found in the fusion zone of the third pass welds during multi-pass welding.  相似文献   
97.
含油废水处理   总被引:10,自引:0,他引:10  
赵亚乾  徐培 《水处理技术》1995,21(4):227-230
在水量水质调查的基础上,本文提出了以出水回用为目的的含油废水隔油调节沉淀-混凝沉淀-砂滤处理工艺,动态模型试验表明,废水中油和COD的去除率分别达到95%和90%,出水浊度低于2,此水质完全可回用于有关生产车间。  相似文献   
98.
99.
100.
该文较详细地介绍了I.O.T管的发展历程,其特点及工作方式。  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