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   9056篇
  免费   338篇
  国内免费   38篇
电工技术   123篇
综合类   23篇
化学工业   2108篇
金属工艺   168篇
机械仪表   233篇
建筑科学   574篇
矿业工程   31篇
能源动力   172篇
轻工业   778篇
水利工程   53篇
石油天然气   12篇
武器工业   1篇
无线电   591篇
一般工业技术   1460篇
冶金工业   1554篇
原子能技术   71篇
自动化技术   1480篇
  2023年   51篇
  2022年   119篇
  2021年   143篇
  2020年   105篇
  2019年   120篇
  2018年   169篇
  2017年   110篇
  2016年   192篇
  2015年   191篇
  2014年   249篇
  2013年   567篇
  2012年   399篇
  2011年   547篇
  2010年   410篇
  2009年   392篇
  2008年   436篇
  2007年   427篇
  2006年   365篇
  2005年   315篇
  2004年   296篇
  2003年   221篇
  2002年   230篇
  2001年   175篇
  2000年   165篇
  1999年   161篇
  1998年   270篇
  1997年   204篇
  1996年   163篇
  1995年   143篇
  1994年   125篇
  1993年   140篇
  1992年   130篇
  1991年   77篇
  1990年   92篇
  1989年   79篇
  1988年   94篇
  1987年   66篇
  1986年   55篇
  1985年   79篇
  1984年   94篇
  1983年   61篇
  1982年   68篇
  1981年   85篇
  1980年   68篇
  1979年   86篇
  1978年   68篇
  1977年   68篇
  1976年   56篇
  1975年   58篇
  1973年   48篇
排序方式: 共有9432条查询结果,搜索用时 218 毫秒
961.
We have designed a 5×5 mm2 position sensitive solid-state photomultiplier (PS-SSPM) using a complementary metal-oxide-semiconductor (CMOS) process that provides imaging capability on the micro-pixel level. The PS-SSPM has 11,664 micro-pixels total, with each having an active area and micro-pixel pitch of 30×30 μm2 and 44.3 μm, respectively. The PS-SSPM was then examined for its performance characteristics such as its energy and spatial resolution, and LYSO scintillator array imaging capabilities. When coupled to 5×5×3 mm3 LYSO, the energy resolution at 511 keV (22Na) was measured as a function of bias, and corrected for the PS-SSPM non-linear output. The resolution is 14% (FWHM) at 511 keV with 30 V bias. The LYSO coincidence timing resolution was 9.4 ns (FWHM) at 511 keV. Spatial resolution studies were conducted using a focused (∼30 μm beam spot diameter) pulsed 635 nm diode laser. Scintillator array imaging studies were conducted at 511 keV using a 6×6 LYSO array, having 500 μm pixels (530 μm pitch) and 5 mm tall.  相似文献   
962.
Advanced treatment techniques, like ozone, activated carbon and TiO2 in combination with UV, are proposed to improve removal efficiency of micropollutants during wastewater treatment. In a meta-analysis of peer-reviewed literature, we found significantly reduced overall ecotoxicity of municipal wastewaters treated with either ozone (n = 667) or activated carbon (=113), while TiO2 and UV was not yet assessed. As comparative investigations regarding the detoxification potential of these advanced treatment techniques in municipal wastewater are scarce, we assessed them in four separate Gammarus-feeding trials with 20 replicates per treatment. These bioassays indicate that ozone concentrations of approximately 0.8 mg ozone/mg DOC may produce toxic transformation products. However, referred effects are removed if higher ozone concentrations are used (1.3 mg ozone/mg DOC). Moreover, the application of 1 g TiO2/l and ambient UV consistently reduced ecotoxicity. Although activated carbon may remove besides micropollutants also nutrients, which seemed to mask its detoxification potential, this treatment technique reduced the ecotoxicity of the wastewater following its amendment with nutrients. Hence, all three advanced treatment techniques are suitable to reduce the ecotoxicity of municipal wastewater mediated by micropollutants and may hence help to meet the requirements of the European Water Framework Directive.  相似文献   
963.
964.
965.
Carbon nanotubes and graphene are outstanding materials of the 21st century with a broad spectrum of applications. However, major challenges are faced such as the intrinsically low solubility of both sp2 carbon allotropes. To overcome this hurdle the potential of noncovalent functionalization is summarized with a special focus on the establishment of the perylene bisimide unit as aromatic anchor to the graphitic surface. Rational surfactant design is unmasked as the key to solubilization of the carbon allotropes, while at the same time tailoring their surface properties, or even electronic properties in a fully reversible fashion.  相似文献   
966.
967.
968.
969.
970.
Air mass origin as determined by back trajectories often aids in explaining some of the short-term variability in the atmospheric concentrations of semivolatile organic contaminants. Airsheds, constructed by amalgamating large numbers of back trajectories, capture average air mass origins over longer time periods and thus have found use in interpreting air concentrations obtained by passive air samplers. To explore some of their key characteristics, airsheds for 54 locations on Earth were constructed and compared for roundness, seasonality, and interannual variability. To avoid the so-called "pole problem" and to simplify the calculation of roundness, a "geodesic grid" was used to bin the back-trajectory end points. Departures from roundness were seen to occur at all latitudes and to correlate significantly with local slope but no strong relationship between latitude and roundness was revealed. Seasonality and interannual variability vary widely enough to imply that static models of transport are not sufficient to describe the proximity of an area to potential sources of contaminants. For interpreting an air measurement an airshed should be generated specifically for the deployment time of the sampler, especially when investigating long-term trends. Samples taken in a single season may not represent the average annual atmosphere, and samples taken in linear, as opposed to round, airsheds may not represent the average atmosphere in the area. Simple methods are proposed to ascertain the significance of an airshed or individual cell. It is recommended that when establishing potential contaminant source regions only end points with departure heights of less than ~700 m be considered.  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