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   344658篇
  免费   9932篇
  国内免费   3719篇
电工技术   9457篇
技术理论   9篇
综合类   4958篇
化学工业   52537篇
金属工艺   14617篇
机械仪表   13684篇
建筑科学   13096篇
矿业工程   3061篇
能源动力   8825篇
轻工业   27691篇
水利工程   4000篇
石油天然气   8438篇
武器工业   556篇
无线电   44865篇
一般工业技术   61028篇
冶金工业   51030篇
原子能技术   6234篇
自动化技术   34223篇
  2022年   3505篇
  2021年   5108篇
  2020年   3851篇
  2019年   4047篇
  2018年   5683篇
  2017年   6036篇
  2016年   6061篇
  2015年   5243篇
  2014年   8036篇
  2013年   16284篇
  2012年   11742篇
  2011年   14335篇
  2010年   11836篇
  2009年   12504篇
  2008年   13069篇
  2007年   12933篇
  2006年   12380篇
  2005年   11210篇
  2004年   9598篇
  2003年   9189篇
  2002年   8525篇
  2001年   8455篇
  2000年   8412篇
  1999年   8773篇
  1998年   16551篇
  1997年   12119篇
  1996年   9804篇
  1995年   7820篇
  1994年   6884篇
  1993年   6434篇
  1992年   5185篇
  1991年   4734篇
  1990年   4441篇
  1989年   4123篇
  1988年   3935篇
  1987年   3335篇
  1986年   3223篇
  1985年   3717篇
  1984年   3472篇
  1983年   3091篇
  1982年   2908篇
  1981年   2998篇
  1980年   2798篇
  1979年   2675篇
  1978年   2511篇
  1977年   2977篇
  1976年   3566篇
  1975年   2330篇
  1974年   2321篇
  1973年   2326篇
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
51.
A method is proposed to generate categorical colour observer functions (individual colour matching functions) for any field size based on the CIE 2006 system of physiological observer functions. The method combines proposed categorical observer techniques of Sarkar et al with a physiologically-based individual observer model of Asano et al and a clustering technique to produce the optimal set of categorical observers. The number of required categorical observers varies depending on an application with as many as 50 required to predict individual observers' matches when a laser projector is viewed. However, 10 categorical observers are sufficient to represent colour-normal populations for personalized colour imaging. The proposed and recommended categorical observers represent a robust and inclusive technique to examine and quantify observer metamerism in any application of colorimetry.  相似文献   
52.
Polymer Bulletin - In this study, we synthesized a new ion-imprinted polymer (IIP) based on introduction of amidoxime groups in acrylonitrile, complexation with Cd2+ ions and polymerization with...  相似文献   
53.
The design of highly stable and efficient porous materials is essential for developing breakthrough hydrocarbon separation methods based on physisorption to replace currently used energy-intensive distillation/absorption technologies. Efforts to develop advanced porous materials such as zeolites, coordination frameworks, and organic polymers have met with limited success. Here, a new class of ionic ultramicroporous polymers (IUPs) with high-density inorganic anions and narrowly distributed ultramicroporosity is reported, which are synthesized by a facile free-radical polymerization using branched and amphiphilic ionic compounds as reactive monomers. A covalent and ionic dual-crosslinking strategy is proposed to manipulate the pore structure of amorphous polymers at the ultramicroporous scale. The IUPs exhibit exceptional selectivity (286.1–474.4) for separating acetylene from ethylene along with high thermal and water stability, collaboratively demonstrated by gas adsorption isotherms and experimental breakthrough curves. Modeling studies unveil the specific binding sites for acetylene capture as well as the interconnected ultramicroporosity for size sieving. The porosity-engineering protocol used in this work can also be extended to the design of other ultramicroporous materials for the challenging separation of other key gas constituents.  相似文献   
54.
55.
56.
57.
To improve the convertibility of reconfigurable manufacturing system (RMS), the concept of delayed reconfigurable manufacturing system (D-RMS) was proposed. RMS and D-RMS are both constructed around part family. However, D-RMS may suffer from ultra-long system problem with unacceptable idle machines using generic RMS part families. Besides, considering the complex basic system structure of D-RMS, machine selection of D-RMS should be addressed, including dedicated machine, flexible machine, and reconfigurable machine. Therefore, a system design method for D-RMS based on part family grouping and machine selection is proposed. Firstly, a part family grouping method is proposed for D-RMS that groups the parts with more former common operations into the same part family. The concept of longest relative position common operation subsequence (LPCS) is proposed. The similarity coefficient among the parts is calculated based on LPCS. The reciprocal value of the operation position of LPCS is adopted as the characteristic value. The average linkage clustering (ALC) algorithm is used to cluster the parts. Secondly, a machine selection method is proposed to complete the system design of D-RMS, including machine selection rules and the dividing point decision model. Finally, a case study is given to implement and verify the proposed system design method for D-RMS. The results show that the proposed system design method is effective, which can group parts with more former common operations into the same part family and select appropriate machine types.  相似文献   
58.
既有公共建筑能耗中,围护结构节能潜力巨大。以兰州某既有办公建筑为例,采用DeST-C软件模拟围护结构不同材料厚度、窗型,得出系列负荷,通过对数据分析、比较,得出如下结论:外墙外保温适宜材料为50mm的挤塑板,最大热负荷节能率为45.66%;屋面适宜保温材料为65mm的挤塑板,最大热负荷节能率为4.25%;外窗各个朝向全部更换玻璃,推荐选用内张膜中空玻璃(双膜),最大热负荷节能率为7.36%;单独更换南向外窗材料,推荐选用真空镀膜复合中空玻璃,最大热负荷节能率为1.78%。  相似文献   
59.
Lin  Haicheng  Huang  Wantong  Zhao  Kun  Qiao  Shuang  Liu  Zheng  Wu  Jian  Chen  Xi  Ji  Shuai-Hua 《Nano Research》2020,13(1):133-137
Nano Research - The isostructural and isoelectronic transition-metal-dichalcogenides 1T-TaS2 and 1T-TaSe2 are layered materials with intricate electronic structures. Combining the molecular beam...  相似文献   
60.
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