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   1479610篇
  免费   25727篇
  国内免费   6978篇
电工技术   34188篇
综合类   6371篇
化学工业   269052篇
金属工艺   63827篇
机械仪表   41244篇
建筑科学   45373篇
矿业工程   11317篇
能源动力   50229篇
轻工业   108032篇
水利工程   14805篇
石油天然气   37415篇
武器工业   132篇
无线电   195577篇
一般工业技术   279195篇
冶金工业   154250篇
原子能技术   33861篇
自动化技术   167447篇
  2021年   15541篇
  2020年   11800篇
  2019年   14557篇
  2018年   15167篇
  2017年   14453篇
  2016年   20964篇
  2015年   17242篇
  2014年   28613篇
  2013年   87776篇
  2012年   34430篇
  2011年   46302篇
  2010年   41794篇
  2009年   50295篇
  2008年   43503篇
  2007年   40396篇
  2006年   43767篇
  2005年   38242篇
  2004年   40675篇
  2003年   40727篇
  2002年   39776篇
  2001年   36684篇
  2000年   35255篇
  1999年   34289篇
  1998年   42420篇
  1997年   37438篇
  1996年   34160篇
  1995年   30053篇
  1994年   28385篇
  1993年   28205篇
  1992年   25911篇
  1991年   23005篇
  1990年   23324篇
  1989年   22394篇
  1988年   20929篇
  1987年   19206篇
  1986年   18589篇
  1985年   21828篇
  1984年   22161篇
  1983年   20139篇
  1982年   19187篇
  1981年   19292篇
  1980年   17879篇
  1979年   18410篇
  1978年   17637篇
  1977年   17302篇
  1976年   18159篇
  1975年   15935篇
  1974年   15437篇
  1973年   15510篇
  1972年   12973篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
A case of endometrioid carcinoma arising from endometriosis of the sigmoid colon is reported. The patient had been treated with unopposed continuous estrogen injection for twenty years after bilateral salpingo-oophorectomy because of severe endometriosis. The pathology, pertinent literature and implications of the present case are discussed.  相似文献   
902.
903.
Dissolved organic carbon (DOC) dynamics were investigated over a two year period in the Upper Rhǒne River to examine the role of side-arms in providing DOC to the main channel in relation to discharge fluctuations, especially floods. Concentrations of DOC are shown to remain low in space and in time (average 1.5 mg ?1) and to be more related to global hydrological events (precipitation) than to any local flushing for backwaters during floods. The results do not support the general assumption that side-arms are the providers of DOC to the main channel.  相似文献   
904.
905.
36%渗乐乳油     
陈洪超  简锡贤 《农药》1995,34(9):13-14
36%渗乐乳油田HP-1增效剂与乐果及其他助剂调配而成。五年田间小区和大田药效试验证明:36%渗乐乳油高效,安全,用量少,对各类蚜虫防效优异。  相似文献   
906.
Results of the drift hole mobility in strained and unstrained SiGe alloys are reported for Ge fractions varying from 0 to 30% and doping levels of 1015-1019 cm-3. The mobilities are calculated taking into account acoustic, optical, alloy, and ionized-impurity scattering. The mobilities are then compared with experimental results for a boron doping concentration of 2×1019 cm-3. Good agreement between experimental and theoretical values is obtained. The results show an increase in the mobility relative to that of silicon  相似文献   
907.
We report a 7.6-mW single-frequency fiber laser operating at 1545 nm, using for the first time an Er3+:Yb3+ doped fiber and a fiber grating output coupler. The laser did not exhibit self-pulsation, which is a typical problem in short three-level fiber lasers, and had a relative intensity noise (RIN) level below -145.5 dB/Hz at frequencies above 10 MHz. The linewidth of the laser was limited by the relaxation oscillation sidebands in the optical spectrum and was typically less than 1 MHz  相似文献   
908.
A new equation is derived for the rotational oscillations of a deep massive foundation flexibly restrained in the ground. An error in the corresponding equation published in the literature is indicated. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 7–8, November–December, 1996.  相似文献   
909.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9  相似文献   
910.
Cellulose diacetate and triacetate films 6–55 µm thick with a total porosity of 0.8–2% were prepared by pouring a solution on an immobile surface and by calendering. Sorption of H2S and CO2 gases and acetone vapors on these films was investigated in static and dynamic conditions. It was shown that films 6–10 µm thick prepared by calendering should be used for purification of air from H2S and CO2 and films 15–20 µm thick prepared by pouring should be used for removal of acetone vapors.Engels Institute of Technology, Saratov State University. Translated from Khimicheskie Volokna, No. 6, pp. 44–46, November–December, 1995.  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