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   3617篇
  免费   208篇
  国内免费   1篇
电工技术   109篇
综合类   5篇
化学工业   976篇
金属工艺   80篇
机械仪表   126篇
建筑科学   111篇
矿业工程   11篇
能源动力   141篇
轻工业   535篇
水利工程   16篇
石油天然气   15篇
无线电   213篇
一般工业技术   862篇
冶金工业   39篇
原子能技术   13篇
自动化技术   574篇
  2023年   28篇
  2022年   33篇
  2021年   95篇
  2020年   68篇
  2019年   87篇
  2018年   128篇
  2017年   129篇
  2016年   157篇
  2015年   118篇
  2014年   180篇
  2013年   391篇
  2012年   246篇
  2011年   276篇
  2010年   210篇
  2009年   167篇
  2008年   176篇
  2007年   140篇
  2006年   114篇
  2005年   73篇
  2004年   43篇
  2003年   65篇
  2002年   52篇
  2001年   38篇
  2000年   44篇
  1999年   39篇
  1998年   30篇
  1997年   24篇
  1996年   33篇
  1995年   28篇
  1994年   37篇
  1993年   28篇
  1992年   24篇
  1991年   25篇
  1990年   21篇
  1989年   22篇
  1988年   15篇
  1987年   13篇
  1985年   40篇
  1984年   39篇
  1983年   34篇
  1982年   26篇
  1981年   38篇
  1980年   35篇
  1979年   27篇
  1978年   25篇
  1977年   22篇
  1976年   21篇
  1975年   15篇
  1973年   15篇
  1972年   15篇
排序方式: 共有3826条查询结果,搜索用时 15 毫秒
71.
72.
The anodic oxidation of formic acid was studied on platinum distributed in the form of small particles in a porous substrate modified by metal adatoms deposited at underpotentials. The rate of the reaction was greatly enhanced on the commercial catalyst Powercat 3000 (PC 3000). The hydrogen adsorption and the underpotential deposition of several metals at PC 3000 were shown to be dissimilar to that at smooth polycrystalline Pt. Steady-state and long-term experiments were performed to determine the stability of this electrode.  相似文献   
73.
This work considers structural and compression mechanical properties of three Ti3Al-based alloys processed by powder metallurgy. Mechanically alloyed powders were compacted by hot-pressing to non-porous homogenous compacts. Prior to compression tests, all compacts were homogenized by a solution treatment at 1050°C (α + β region) for 1h, followed by water quenching. The compression tests were performed from room temperature to 500°C in vacuum at a strain rate of 2.4 × 10−3 s−1. Detailed microstructural characterization has been evaluated by scanning electron microscopy (SEM), followed by electron dispersive spectroscopy (EDS) and X-ray diffraction analysis. Fracture topography was examined by SEM. The Ti3Al-Nb alloy exhibits the highest ductility in the whole temperature range, whereas addition of Mo to Ti3Al-Nb alloy yields the highest ultimate compression strength. A correlation between ductility and the fracture mode exists for all materials.  相似文献   
74.
Stress stability testing represents an important part of the drug development process. It is used as an important tool for the identification of degradation products and degradation pathways, as well as for the assessment of changes in physical form of drug molecules. The impact of excipients on the stability of olanzapine confirms that levels of impurities and degradants are limiting parameters and are therefore used for stability evaluation. The major degradation product of olanzapine was identified as 2-methyl-5,10-dihydro-4H-thieno[2,3-b][1,5]benzodiazepine-4-one (III). The structure of III was determined by using LC-MS, IR and NMR. Compatibility and stress stability results demonstrated that tablet formulations of olanzapine are sensitive to temperature and moisture. In samples protected from moisture, the increase in concentration of III was shown to be highly temperature dependent and the degradation followed zero-order kinetics. In addition, studies of olanzapine with excipients and in formulated tablets revealed polymorphic phase changes in some samples, influenced by a combination of stress temperature and humidity conditions. Polymorphic transitions were monitored using x-ray powder diffraction (XRPD) analysis and exhibited no correlation between the phase change (appearance of a new polymorph) and the degradation process.  相似文献   
75.
This paper presents the concept of decomposition as applied to the control synthesis of multivariable mechanical systems, in which the coupling among the subsystems can be very strong. The system class considered contains subsystems with powered degrees of freedom, as well as subsystems without their own actuators. Global control is introduced to diminish the influence of coupling on the stability of the whole system. The procedure is illustrated by simulation of two examples, one in robotics, the other in biomechanics.  相似文献   
76.
Survey of Intelligent Control Techniques for Humanoid Robots   总被引:8,自引:0,他引:8  
This paper focusses on the application of intelligent control techniques (neural networks, fuzzy logic and genetic algorithms) and their hybrid forms (neuro-fuzzy networks, neuro-genetic and fuzzy-genetic algorithms) in the area of humanoid robotic systems. It represents an attempt to cover the basic principles and concepts of intelligent control in humanoid robotics, with an outline of a number of recent algorithms used in advanced control of humanoid robots. Overall, this survey covers a broad selection of examples that will serve to demonstrate the advantages and disadvantages of the application of intelligent control techniques.  相似文献   
77.
In this paper, a novel self‐organizing network (SON) based similarity index and its application for the optimization of sampling locations in an existing river water quality monitoring network (WQMN) is presented. A rationalization of the River Danube WQMN on its stretch through Serbia was performed using the proposed SON2‐based similarity index. A high‐dimensional dataset was used, which is composed of 18 water quality parameters that were collected during the period 2002–2010 at 17 monitoring locations. The SON‐based seasonal classification that divides 12 months into the cold, moderate, and warm seasons was employed, whereas its second application on each seasonal class yielded subclasses that were used to compare the monitoring locations. The obtained SON2‐based similarity index can be utilized for analysing seasonal variations, as well as overall similarities among neighbouring sites. Based on the calculated similarities of locations and characteristics of the River Danube basin a rationalized WQMN, which uses 30% less monitoring sites, has been proposed.  相似文献   
78.
In this paper we present an electromagnetism (EM) metaheuristic for solving NP hard Maximum Betweenness Problem (MBP). A new encoding scheme with appropriate objective functions is implemented. Specific representation of the individuals enables the EM operators to explore the searching space in a way that achieves high quality solutions. An effective 1-swap based local search procedure improved by the specific caching technique is performed on each EM point. The algorithm is tested both on real and artificial instances from the literature. Experimental results show that the proposed EM approach achieves all previously known optimal solutions, except one, and achieves the best-known solutions or outperforms other approaches on all large-scale instances, except two. Provided statistical analysis indicates that the EM approach is significantly better than other approaches.  相似文献   
79.
Nelson Goodman’s highly influential book Languages of Art argued that that all visual experience is merely a cultural construct. In presenting his thesis Goodman relied on a series of geometrical arguments intended to show that the geometrical construction of perspective does not rely on the geometry of light rays. In this article I analyze the geometrical validity of Goodman’s arguments.  相似文献   
80.
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