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   436579篇
  免费   6084篇
  国内免费   1543篇
电工技术   7438篇
综合类   337篇
化学工业   65809篇
金属工艺   17766篇
机械仪表   13638篇
建筑科学   10324篇
矿业工程   2677篇
能源动力   11242篇
轻工业   38943篇
水利工程   4839篇
石油天然气   9480篇
武器工业   27篇
无线电   51655篇
一般工业技术   86872篇
冶金工业   77733篇
原子能技术   9581篇
自动化技术   35845篇
  2021年   3694篇
  2020年   2786篇
  2019年   3495篇
  2018年   5999篇
  2017年   6052篇
  2016年   6613篇
  2015年   4175篇
  2014年   7061篇
  2013年   19711篇
  2012年   11730篇
  2011年   15922篇
  2010年   12616篇
  2009年   14091篇
  2008年   14632篇
  2007年   14557篇
  2006年   13056篇
  2005年   11897篇
  2004年   11198篇
  2003年   11000篇
  2002年   10426篇
  2001年   10861篇
  2000年   9915篇
  1999年   10417篇
  1998年   25176篇
  1997年   17631篇
  1996年   13390篇
  1995年   10186篇
  1994年   8879篇
  1993年   8993篇
  1992年   6657篇
  1991年   6388篇
  1990年   6159篇
  1989年   5981篇
  1988年   5883篇
  1987年   4905篇
  1986年   4885篇
  1985年   5776篇
  1984年   5285篇
  1983年   4913篇
  1982年   4485篇
  1981年   4504篇
  1980年   4376篇
  1979年   4269篇
  1978年   4130篇
  1977年   4530篇
  1976年   5494篇
  1975年   3680篇
  1974年   3453篇
  1973年   3623篇
  1972年   2999篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
84.
85.
86.
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   
87.
88.
Fluorescent nanodiamonds (fNDs) containing nitrogen vacancy (NV) centers are promising candidates for quantum sensing in biological environments. This work describes the fabrication and implementation of electrospun poly lactic‐co‐glycolic acid (PLGA) nanofibers embedded with fNDs for optical quantum sensing in an environment, which recapitulates the nanoscale architecture and topography of the cell niche. A protocol that produces uniformly dispersed fNDs within electrospun nanofibers is demonstrated and the resulting fibers are characterized using fluorescent microscopy and scanning electron microscopy (SEM). Optically detected magnetic resonance (ODMR) and longitudinal spin relaxometry results for fNDs and embedded fNDs are compared. A new approach for fast detection of time varying magnetic fields external to the fND embedded nanofibers is demonstrated. ODMR spectra are successfully acquired from a culture of live differentiated neural stem cells functioning as a connected neural network grown on fND embedded nanofibers. This work advances the current state of the art in quantum sensing by providing a versatile sensing platform that can be tailored to produce physiological‐like cell niches to replicate biologically relevant growth environments and fast measurement protocols for the detection of co‐ordinated endogenous signals from clinically relevant populations of electrically active neuronal circuits.  相似文献   
89.
Wastewater treatment plant operators encounter complex operational problems related to the activated sludge process and usually respond to these by applying their own intuition and by taking advantage of what they have learnt from past experiences of similar problems. However, previous process experiences are not easy to integrate in numerical control, and new tools must be developed to enable re-use of plant operating experience. The aim of this paper is to investigate the usefulness of a case-based reasoning (CBR) approach to apply learning and re-use of knowledge gained during past incidents to confront actual complex problems through the IWA/COST Benchmark protocol. A case study shows that the proposed CBR system achieves a significant improvement of the benchmark plant performance when facing a high-flow event disturbance.  相似文献   
90.
This report compares the enterococci count on samples obtained with Azide NutriDisk (AND) (sterile, dehydrated culture medium) and Slanetz and Bartley (SB) medium when exposed to a variable in incubation time and temperature. Three experiments were performed to examine the recovery of enterococci on AND and SB media using membrane filtration with respect to: (a) incubation time; (b) incubation temperature; and (c) a combination of the two. Presumptive counts were observed at 37, 41, 46 and 47 degrees C and at 20, 24, 28 and 48 h. These were compared to AWWA standard method 9230 C (44 degrees C, 44 h). Samples were confirmed using Kanamycin Aesculin Azide (KAA) agar. Friedman's ANOVA and Students t-test analysis indicated higher enumeration of enterococci when grown on AND (p = 0.45) than SB (p = < 0.001) at all temperatures with a survival threshold at 47 degrees C. Significant results for AND medium were noted at 20 h (p = 0.021), 24 h (p = 0.278) and 28 h (p = 0.543). The study concluded that the accuracy of the AND medium at a greater time and temperature range provided flexibility in incubator technology making it an appropriate alternative to SB medium for monitoring drinking water using field testing kits in developing countries.  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