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   307675篇
  免费   3100篇
  国内免费   477篇
电工技术   5768篇
综合类   341篇
化学工业   47322篇
金属工艺   15282篇
机械仪表   12356篇
建筑科学   6705篇
矿业工程   2039篇
能源动力   5776篇
轻工业   25921篇
水利工程   3472篇
石油天然气   6152篇
武器工业   32篇
无线电   31314篇
一般工业技术   62556篇
冶金工业   50451篇
原子能技术   6787篇
自动化技术   28978篇
  2021年   2106篇
  2019年   2019篇
  2018年   11058篇
  2017年   11529篇
  2016年   8020篇
  2015年   2692篇
  2014年   3985篇
  2013年   10242篇
  2012年   8533篇
  2011年   15867篇
  2010年   13878篇
  2009年   13377篇
  2008年   13620篇
  2007年   15666篇
  2006年   6954篇
  2005年   9309篇
  2004年   7674篇
  2003年   7179篇
  2002年   6299篇
  2001年   5629篇
  2000年   5516篇
  1999年   5328篇
  1998年   12582篇
  1997年   8905篇
  1996年   6873篇
  1995年   5340篇
  1994年   4767篇
  1993年   4648篇
  1992年   3683篇
  1991年   3413篇
  1990年   3593篇
  1989年   3473篇
  1988年   3310篇
  1987年   2895篇
  1986年   2933篇
  1985年   3375篇
  1984年   3220篇
  1983年   2896篇
  1982年   2738篇
  1981年   2822篇
  1980年   2721篇
  1979年   2624篇
  1978年   2686篇
  1977年   2950篇
  1976年   3806篇
  1975年   2368篇
  1974年   2242篇
  1973年   2376篇
  1972年   1970篇
  1971年   1858篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
141.
The patent literature concerning thermal spraying for biomedical applications is reviewed in this contribution. The patents were compiled from multiple databases search spanning the 2005-2018 period. For clarity and ease of reading, the results have been grouped into sections according to four individual material groups (apatites, titanium, oxide ceramics, other), with the secondary sorting criterion being related to the specific bioapplication areas (maxillofacial, orthopedic, methods). Lastly, the patents are grouped according to the selected thermal spray method within the individual subsections. In the paper, recent R&D trends in this field are further identified and briefly commented.  相似文献   
142.
Estimation of earth-fill dam height and dimension of spillway are strongly depend on accurate evaluation of dam overtopping reliability. Ideally, whole random and effective variables on overtopping should be considered for dam overtopping reliability assessment. However, taking into account all affecting random variables as well as overtopping reliability assessment using algorithms such as Monte Carlo (MC) could be excessively time consuming and impossible in some cases. In this study, new approach has been introduced as conditional reliability method and it has been tried to reduce the simulations time significantly by using combination of rainfall threshold theory, SUFI (Sequential Uncertainty Fitting) and MC methods. According two defined indexes, the obtain results shown, the relative error of new approach in computation of Jamishan dam overtopping reliability is less than 0.23%. Also, time saving in new method against to regular MC method is more than 87%. So, the new introduced method has more efficiency with acceptable accuracy for assessment of dam overtopping reliability. In addition, among hydrological and hydraulic uncertainties, hydrological uncertainties have more effect on overtopping reliability.  相似文献   
143.
144.
145.
We study a maritime inventory routing problem, in which shipments between production and consumption nodes are carried out by a fleet of vessels. The vessels have specific capacities and can be chartered under different agreements. The inventory levels of all consumption nodes and some production nodes should be maintained within specified bounds; for the remaining production nodes, orders should be picked up within pre-defined time windows. We propose a discrete-time mixed-integer programming model. In the face of new information and uncertainty, this optimization model has to be re-solved, as the horizon is rolled forward. We discuss how to account for different sources of uncertainty. We present a rolling-horizon reoptimization framework that allows us to study different policies that impact the quality of the implemented solution, so we can identify the optimal set of policies.  相似文献   
146.
147.
In optimization of transient problems, a robust, stable, and efficient numerical scheme for time integration is of much importance. Recently, the mixed Lag  相似文献   
148.
149.
Understanding the sources and composition of organic aerosol (OA) in indoor environments requires rapid measurements, since many emissions and processes have short timescales. However, real-time molecular-level OA measurements have not been reported indoors. Here, we present quantitative measurements, at a time resolution of five seconds, of molecular ions corresponding to diverse aerosol-phase species, by applying extractive electrospray ionization mass spectrometry (EESI-MS) to indoor air analysis for the first time, as part of the highly instrumented HOMEChem field study. We demonstrate how the complex spectra of EESI-MS are screened in order to extract chemical information and investigate the possibility of interference from gas-phase semivolatile species. During experiments that simulated the Thanksgiving US holiday meal preparation, EESI-MS quantified multiple species, including fatty acids, carbohydrates, siloxanes, and phthalates. Intercomparisons with Aerosol Mass Spectrometer (AMS) and Scanning Mobility Particle Sizer suggest that EESI-MS quantified a large fraction of OA. Comparisons with FIGAERO-CIMS shows similar signal levels and good correlation, with a range of 100 for the relative sensitivities. Comparisons with SV-TAG for phthalates and with SV-TAG and AMS for total siloxanes also show strong correlation. EESI-MS observations can be used with gas-phase measurements to identify co-emitted gas- and aerosol-phase species, and this is demonstrated using complementary gas-phase PTR-MS observations.  相似文献   
150.
The shaping of the toroidal cutting section of end mills is considered. Methods are devised for selecting the positional parameters in shaping the helical rake surface on the toroidal section. Relations are established between the geometric parameters of the end mill in the toroidal section.  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