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   107661篇
  免费   11083篇
  国内免费   7225篇
电工技术   8463篇
技术理论   4篇
综合类   9621篇
化学工业   15306篇
金属工艺   7055篇
机械仪表   7582篇
建筑科学   7971篇
矿业工程   3527篇
能源动力   3144篇
轻工业   9737篇
水利工程   2794篇
石油天然气   4345篇
武器工业   1317篇
无线电   12489篇
一般工业技术   11666篇
冶金工业   4305篇
原子能技术   1546篇
自动化技术   15097篇
  2024年   576篇
  2023年   1688篇
  2022年   3733篇
  2021年   4875篇
  2020年   3583篇
  2019年   2821篇
  2018年   3007篇
  2017年   3378篇
  2016年   3220篇
  2015年   4744篇
  2014年   5751篇
  2013年   6841篇
  2012年   7921篇
  2011年   8571篇
  2010年   7834篇
  2009年   7286篇
  2008年   7438篇
  2007年   7074篇
  2006年   6381篇
  2005年   5388篇
  2004年   3956篇
  2003年   3251篇
  2002年   3429篇
  2001年   2942篇
  2000年   2335篇
  1999年   1631篇
  1998年   1127篇
  1997年   938篇
  1996年   846篇
  1995年   739篇
  1994年   623篇
  1993年   482篇
  1992年   352篇
  1991年   277篇
  1990年   208篇
  1989年   175篇
  1988年   142篇
  1987年   81篇
  1986年   71篇
  1985年   46篇
  1984年   37篇
  1983年   20篇
  1982年   24篇
  1981年   29篇
  1980年   29篇
  1979年   21篇
  1976年   8篇
  1975年   7篇
  1959年   14篇
  1951年   11篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
13.
基于AutoCAD的二次开发环境下,建立幻灯片库,在AutoCAD本身所包含的程序帮助下,将已建好的幻灯片库嵌入到AutoCAD用户专用下拉菜单中.给设计者创造属于自己的开发环境,使AutoCAD在建筑电气设计中的使用更加灵活,极大的提高设计效率.  相似文献   
14.
15.
A three-dimensional zinc phosphate compound with DFT topology, designated as ZnPO4-EU1, has been synthesized by an ionothermal approach from the system HF-ZnO–P2O5-choline chloride-imidazolidone. Ethylenediamine, derived from decomposition of the imidazolidone component of the deep-eutectic solvent (DES) itself, is delivered to the synthesis and serves as an appropriate template for ZnPO4-EU1. Experiments in which the synthesis conditions were varied showed that ZnPO4-EU1 may be prepared over a wide molar ratio of P/Zn = 0.55–13.0. Powder X-ray diffraction patterns have been obtained at intervals to track the crystallization process of this material. The experimental data show that Zn3(PO4)2 · 4H2O (a dense phase) was first isolated from the DES after reaction for 1 h. Subsequently, the pure phase of ZnPO4-EU1 was obtained with increasing crystallization time from 12 h to 72 h. The experimental results show that the nucleation and crystallization take place with relatively low levels of solvent degradation, demonstrating that zinc phosphate with a three-dimensional framework can be synthesized by in situ generation of an appropriate template using an unstable DES at high temperatures (150–200 °C).  相似文献   
16.
Polyetherimide (PEI) substrate for next‐generation high density optical data storage is fabricated and characterized. Cover‐layer incident or first‐surface recording configurations do not require optical properties of the substrate, which are the prerequisite conditions for the conventional material of polycarbonate (PC). Instead of the optical properties, good mechanical properties with a sufficient transcribability are required. Even though PEI has higher glass transition temperature than that of PC, a microscopic transcribability of PEI is comparable with PC by laminating a thermal insulation layer on the backside of a stamper to retard the heat flow. A macroscopic warpage of PEI substrate is smaller than that of PC substrates, which reduces tilt and servo burden. The lowest critical speed coupled with the flutter of PEI substrate is larger than that of PC substrate because of the mechanical properties of PEI. POLYM. ENG. SCI., 48:97–101, 2008. © 2007 Society of Plastics Engineers  相似文献   
17.
Many approaches have been proposed to enhance software productivity and reliability. These approaches typically fall into three categories: the engineering approach, the formal approach and the knowledge-based approach. But the optimal gain in software productivity cannot be obtained if one relies on only one of these approaches. This paper describes the work in knowledge-based software engineering conducted by the authors for the past 10 years. The final goal of the research is to develop a paradigm for software engineering which integrates the three approaches mentioned above. A knowledge-based tool which can support the whole process of software development is provided in this paper.  相似文献   
18.
In this paper we design an experiment which can be depicted as a simple scenario, a very limited 'world'. In this world, there are an actor that can pursue a project and an observer that is keeping its eyes on the actor. We try to show in the experiment that the observer can to some degree understand the actor based on its knowledge and some metaphors, i.e. understand what the actor is doing and why. As the conclusion of this experiment, we try to show some features of 'understanding'. These are (1) that 'understanding' has to be based on some preliminary knowledge; (2) that 'understanding' is a process of incremental learning; (3) that, as for symbolic systems, some metaphors are necessary for mapping real entities into concepts in mind.  相似文献   
19.
It is found that an acoustic wave which is nearly polarized in the shear horizontal (SH) direction can propagate along the X axis of a Z-cut lithium niobate plate if the ratio h/λ, where h=plate thickness and λ=acoustic wavelength, is less than about 0.5. Attractive properties of this quasi-SH wave include: (1) phase velocity nearly constant for all values of h/λ; (2) ability to propagate in contact with a liquid medium; and (3) electromechanical coupling coefficient as high as 0.15. These properties make the wave attractive for use in a variety of sensor and signal processing applications. An example of sensor applications is illustrated by using the wave to measure conductivity of liquids (aqueous KCl solution). The frequency of a 12-MHz quasi-SH mode oscillator fabricated on a 0.48 wavelength thick Z-X lithium niobate plate is found to vary by more than 80 kHz for variation in KCI concentration from 0 to 0.15%  相似文献   
20.
Permeation of zidovudine (3'-azido-3'-deoxythymidine, AZT) and probenecid from oily bases containing an alcohol through rat skin was examined. Isopropyl myristate (IPM), as an oily vehicle, showed a penetration enhancing effect for AZT and probenecid. Ethanol, n-propanol, and n-butanol were used as additives in IPM and were examined for their own permeation and the enhancing effect on the permeation of AZT and probenecid. The skin permeation of AZT and probenecid from IPM was enhanced by addition of the alcohol in IPM. The degree of the enhancement was decreased with increasing lipophilicity of the alcohol used. me permeation rate of the drug from those systems was shown to be governed by penetration-enhancing effects of the oily base and alcohol, and the penetration of the alcohol itself through the skin.  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