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   1521632篇
  免费   27562篇
  国内免费   6933篇
电工技术   34223篇
综合类   6482篇
化学工业   269943篇
金属工艺   64100篇
机械仪表   42734篇
建筑科学   47058篇
矿业工程   11369篇
能源动力   50205篇
轻工业   117898篇
水利工程   15466篇
石油天然气   37286篇
武器工业   136篇
无线电   196298篇
一般工业技术   287912篇
冶金工业   170385篇
原子能技术   33793篇
自动化技术   170839篇
  2021年   15502篇
  2019年   14608篇
  2018年   14840篇
  2017年   14036篇
  2016年   21050篇
  2015年   17358篇
  2014年   28765篇
  2013年   87872篇
  2012年   36166篇
  2011年   48457篇
  2010年   42201篇
  2009年   50361篇
  2008年   45357篇
  2007年   42587篇
  2006年   45609篇
  2005年   39881篇
  2004年   42438篇
  2003年   42285篇
  2002年   41338篇
  2001年   38374篇
  2000年   36639篇
  1999年   35619篇
  1998年   46960篇
  1997年   40593篇
  1996年   36344篇
  1995年   31506篇
  1994年   29559篇
  1993年   29107篇
  1992年   26535篇
  1991年   23629篇
  1990年   23873篇
  1989年   22948篇
  1988年   21450篇
  1987年   19721篇
  1986年   19185篇
  1985年   22572篇
  1984年   22691篇
  1983年   20567篇
  1982年   19425篇
  1981年   19490篇
  1980年   18095篇
  1979年   18743篇
  1978年   17923篇
  1977年   17992篇
  1976年   19541篇
  1975年   16110篇
  1974年   15647篇
  1973年   15719篇
  1972年   13209篇
  1971年   11842篇
排序方式: 共有10000条查询结果,搜索用时 703 毫秒
891.
FeO-doped TiO2 nanoparticle photocatalysts were immobilized onto the surface of fibrous activated carbon (ACF) via a sol-gel process. As an adsorbent and photocatalyst, FeO-TiO2 on immobilized ACFs (FeO-TiO2/ACF) greatly improved the photocatalysis rate of hydrogen production as compared with pure TiO2 and ACF-TiO2 under UV irradiation and visible light. The addition of ACFs surface significantly reduced the photogenerated pairs of electrons-hole recombination, thereby promoting the photocatalysis action of doped photo-metal oxides of FeO-TiO2. Co-doping of FeO onto the lattice of the TiO2 approach can improve the absorption activity of visible light through photo-metal oxide of TiO2 and further enhance hydrogen production under visible light. The photocatalytic fabrics (FeO-TiO2/ACF) were effortlessly split out from the experimental solution for re-utilization and exhibited high stability even after five complete regeneration cycles.  相似文献   
892.
Bakry  A. R.  Hashim  M. D.  Elwy  A. M. 《Radiochemistry》2020,62(3):359-367
Radiochemistry - Leaching of uranium and REEs with oxalic acid from the Egyptian Abu-Tartur phosphate rock (PR) was studied. The effect exerted on the leaching process by oxalic acid concentration,...  相似文献   
893.
Technical Physics Letters - The magnetoelectric (ME) effect in a planar amorphous ferromagnet–piezoelectric lead zirconate titanate (PZT) composite structure can be effectively excited by...  相似文献   
894.
895.
896.
897.
A new constitutive equation of thermoelasticity for crystals is presented based on the interatomic potential and solid mechanics at finite temperature. Using the new constitutive equation, the calculations for crystal copper and graphene are carried out under different loading paths at different temperatures. The calculated results are in good agreement with those of the previous thermoelasticity constitutive equation based on quantum mechanics, which clearly indicates that our new constitutive equation of thermoelasticity is correct. A lot of comparisons also show that the present theory is more concise and efficient than the previous thermal stress theory in the practical application.  相似文献   
898.
899.
The aims of this experiment were (1) to compare the effects of a soybean meal with an enzymatic treatment (ESBM) to reduce the concentration of antinutritional factors versus a standard soybean meal (SBM) on foregut and small intestine digestion in weaned dairy calves and (2) to estimate the endogenous losses of crude protein (CP) in the small intestine. Our hypothesis was that a diet containing ESBM instead of SBM would improve ruminal and small intestine digestion and absorption of nutrients. A T-cannula was placed in the duodenum, and a second T-cannula was installed in the distal ileum of 12 Holstein calves at approximately 3 wk of age. Calves were weaned on d 42, and on d 50 they were assigned randomly to a quadruplicated 3 × 3 Latin square with 10-d periods. Digesta samples were collected on d 7 and 8 from the ileum and d 9 and 10 from the duodenum. The diets were fed for ad libitum intake and consisted of a calf starter (CS) of 20% CP with SBM as the main source of protein (CTRL), and an isonitrogenous CS with an ESBM instead of SBM (ENZT). A third diet with a low content of CP (10%) and no soy protein was fed to estimate endogenous N losses and digestibilities of test ingredients. Flows and digestibilities of nutrients were compared between CTRL and ENZT and their test ingredients (SBM vs. ESBM, respectively). Duodenal net flows of CP and total AA as well as ruminal microbial protein synthesis per kilogram of digested CP were greater, and flow of nonprotein N and CP true (corrected by endogenous and microbial flows) foregut digestibility were lower with ENZT than CTRL. The apparent small intestine digestibilities of CP and total AA were greater for ESBM than SBM, but there were no differences between the CTRL and ENZT diets. We observed no differences in digestibilities at the duodenum or ileum of starch or NDF, but true small intestine digestibilities of CP and all AA were greater with ENZT than CTRL. Total endogenous protein losses in the small intestine estimated from calves fed the low-CP with no soy protein diet were 37 ± 1.5 g of CP and 29 ± 1.4 g of AA/kg of DMI. These values may be considered the basal endogenous losses as they are similar to values obtained with the regression method, which estimates N losses when dietary N is null. Our results indicated that the inclusion of an ESBM improved the efficiency of ruminal microbial protein synthesis per digested kilogram of organic matter and CP, and increased CP and AA absorption in the small intestine despite a greater proportion of undigested dietary protein entering the duodenum.  相似文献   
900.
Jatropha oil is a promising nonedible feedstock for producing renewable diesel. In this work, the hydrotreatment processing of jatropha oil was investigated. Instead of using conventional alumina-supported Co–Mo, Ni–Mo, and Ni–W catalysts that need sulfidation pretreatment, noble metals such as Pd and Ru were chosen. Trials were performed in an isothermal trickle-bed reactor and the reaction conditions were as follows: temperature 603–663?K, weight hourly space velocity (WHSV) 1 to 4/h, pressure 1.5–3?MPa, and H2/oil ratio 200–800 (v/v). Yield of n-C15 to n-C18 hydrocarbons was maximized (70.3 and 43.8% for Pd/Al2O3 and Ru/Al2O3, respectively) at the following conditions: T?=?663 K, WHSV?=?2/h, P?=?3?MPa, and H2/oil ratio?=?600 (v/v). Since Ru favored cracking reactions to a larger extent than Pd, the yield of C15 to C18 hydrocarbons over Ru/Al2O3 was lowered. Using simple first-order plots for oil conversion, activation energies for the hydrotreating process over Pd/Al2O3 and Ru/Al2O3 were found and they were equal to 109 and 121?kJ/mol, correspondingly.  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