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   349686篇
  免费   3177篇
  国内免费   801篇
电工技术   6357篇
综合类   238篇
化学工业   50401篇
金属工艺   15889篇
机械仪表   10775篇
建筑科学   6924篇
矿业工程   2495篇
能源动力   7118篇
轻工业   22226篇
水利工程   4241篇
石油天然气   10515篇
武器工业   19篇
无线电   40013篇
一般工业技术   72238篇
冶金工业   70130篇
原子能技术   9847篇
自动化技术   24238篇
  2021年   2669篇
  2019年   2700篇
  2018年   4817篇
  2017年   4888篇
  2016年   5215篇
  2015年   3031篇
  2014年   5298篇
  2013年   13731篇
  2012年   8306篇
  2011年   10962篇
  2010年   8909篇
  2009年   10163篇
  2008年   10598篇
  2007年   10553篇
  2006年   9360篇
  2005年   8733篇
  2004年   8505篇
  2003年   8231篇
  2002年   8000篇
  2001年   8381篇
  2000年   7895篇
  1999年   8298篇
  1998年   21673篇
  1997年   14864篇
  1996年   11294篇
  1995年   8374篇
  1994年   7306篇
  1993年   7430篇
  1992年   5379篇
  1991年   5286篇
  1990年   5328篇
  1989年   5104篇
  1988年   4849篇
  1987年   4215篇
  1986年   4323篇
  1985年   4644篇
  1984年   4277篇
  1983年   3977篇
  1982年   3699篇
  1981年   4001篇
  1980年   3677篇
  1979年   3761篇
  1978年   3866篇
  1977年   4240篇
  1976年   5571篇
  1975年   3503篇
  1974年   3479篇
  1973年   3489篇
  1972年   3099篇
  1971年   2712篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
103.
104.
Continuous simulation is performed using the US Environmental Protection Agency (USEPA) Storm Water Management Model (SWMM) to evaluate regional differences around the United States in hydrologic and water quality performance of wet-weather controls. Controls are characterised as being limited by peak inflow rate (i.e. any device with little or no storage, such as screens, filters and some proprietary devices) or by storage capacity (e.g., ponds, tanks). For flow-limited devices, results are presented in the form of percentage of annual runoff volume captured (passing through the device) for a given inflow capacity. For storage-limited devices, results are presented in two forms: percentage of annual runoff volume captured as a function of unit basin size and drawdown (drain) time, and as a percentage of total suspended solids captured, for the same two variables. Regional differences are apparent, driven mainly by variations in rainfall patterns around the country.  相似文献   
105.
106.
This paper presents the assessment of the efficiency of the main biological nitrogen transformation processes in a shallow well-oxygenated river and conditions under which they are active and stabilise. The process dynamics was studied with the help of mathematical modelling of 2 years on-line data series measured in a reach of the Toess River, Switzerland. The algal nitrogen uptake was very stable and unaffected by most but frequent flood events. Daylight photosynthetic nitrogen uptake stabilised at 6 mgN mstreambed(-2) h(-1) (15 degrees C), dark uptake on storage products at rates of 0.5-2.5 mgN mstreambed(-2) h(-1). Nitrogen uptake by heterotrophic bacteria in the hyporheic zone was relatively constant at a level of 1.5-3.5 mgN mstreambed(-2) h(-1). Streambed nitrification could establish only during periods with average an daily concentration of at least 0.3 g(NH4-N) m(-3) in river water for several weeks. The maximum nitrification rate was 35 mgN mstreambed(-2) h(-1) for 3 g(NH4-N) m(-3). The effects of reduced nitrification in the WWTP and of river banks shading on a sudden ammonium peak were simulated. A river reach endangered by ammonium spills should be kept open to sun to favour ammonium uptake by algae. In-stream nitrification reduces ammonium peaks efficiently but leads to toxic nitrite concentrations.  相似文献   
107.
We analyze the non-Fermi liquid behavior in the proximity of the quantum phase transition induced by the strong polarization of the electrons due to local magnetic moments in Ni x Pd1-x alloys. We use the renormalization group approach introduced by Hertz–Mi11is–Moriya (HMM) to estimate the temperature dependence of the electrical resistivity for the case of three dimensional itinerant ferromagnets. We study two different cases, namely, the clean and disordered ferromagnets, and argue that at the present time more experimental data are needed to decide if the HMM theory can accurately describe the physical properties in Ni x Pd1-x alloys.  相似文献   
108.
109.
110.
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