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   3081篇
  免费   36篇
电工技术   13篇
综合类   1篇
化学工业   166篇
金属工艺   10篇
机械仪表   19篇
建筑科学   81篇
矿业工程   1篇
能源动力   41篇
轻工业   221篇
水利工程   17篇
石油天然气   32篇
无线电   104篇
一般工业技术   161篇
冶金工业   2115篇
原子能技术   18篇
自动化技术   117篇
  2023年   6篇
  2022年   8篇
  2021年   15篇
  2019年   9篇
  2018年   19篇
  2017年   24篇
  2016年   18篇
  2015年   19篇
  2014年   27篇
  2013年   65篇
  2012年   35篇
  2011年   54篇
  2010年   40篇
  2009年   30篇
  2008年   54篇
  2007年   43篇
  2006年   57篇
  2005年   48篇
  2004年   39篇
  2003年   56篇
  2002年   39篇
  2001年   35篇
  2000年   37篇
  1999年   89篇
  1998年   615篇
  1997年   360篇
  1996年   256篇
  1995年   150篇
  1994年   115篇
  1993年   117篇
  1992年   35篇
  1991年   28篇
  1990年   50篇
  1989年   50篇
  1988年   37篇
  1987年   26篇
  1986年   24篇
  1985年   38篇
  1984年   16篇
  1983年   8篇
  1982年   10篇
  1981年   25篇
  1980年   30篇
  1979年   7篇
  1978年   13篇
  1977年   58篇
  1976年   136篇
  1975年   8篇
  1974年   6篇
  1973年   4篇
排序方式: 共有3117条查询结果,搜索用时 15 毫秒
101.
The authors investigated the relationship between stress at initial cancer diagnosis and treatment and subsequent quality of life (QoL). Women (n = 112) randomized to the assessment-only arm of a clinical trial were initially assessed after breast cancer diagnosis and surgery and then reassessed at 4 months (during adjuvant treatment) and 12 months (postadjuvant treatment). There were 3 types of stress measured: number of stressful life events (K. A. Matthews et al., 1997), cancer-related traumatic stress symptoms (M. J. Horowitz, N. Wilner, & W. Alvarez, 1979), and perceived global stress (S. Cohen, T. Kamarck, & R. Mermelstein, 1983). Using hierarchical multiple regressions, the authors found that stress predicted both psychological and physical QoL (J. E. Ware, K. K. Snow, & M. Kosinski, 2000) at the follow-ups (all ps  相似文献   
102.
Most network applications assume continuous connectivity-an assumption that does not “migrate” to wireless environments. The authors present the design of a communication layer for mobile computing that dynamically adapts to changes in network connections. Our work was part of AMIGOS (Advanced Mobile Integration in General Operating Systems), a collaboration between researchers at the University of Copenhagen in Denmark and the University of Minho in Portugal. The AMIGOS project provides transparent support for semi connected operations on mobile computers running a standard operating system; the project home page is at http://www.econ.cbs.dk/people/birger/AMIGOS/. Briefly, our design lets a mobile user connect a mobile host to a LAN, then disconnect the host from it. The user then can reconnect, for example, via a Global System for Mobile Communications (GSM) cellular modem without losing TCP/IP connections. We want to allow existing TCP/IP based applications to be used in a mobile environment, without application modifications  相似文献   
103.
The aim of this study was to determine the role of the formation of radicals and hydrogen peroxide in the viscosity loss of beta-glucan extracts from oat and barley. Radicals derived from endogenous H2O2 were formed spontaneously in all extracts. The decomposition of H2O2 by catalase had little or no effect on the viscosity, and the radical formation detected and measured by electron spin resonance (ESR) spectroscopy did not predict the shelf life of crude beta-glucan extracts. The addition of FeSO4 accelerated the radical formation and viscosity loss, revealing the sensitivity of the extract viscosity towards catalysts for oxidation. Using 50% cadoxen in the extracts slowed down the viscosity loss in all extracts but still led to a 10–70% decrease of the initial viscosities during 4 weeks of storage. The results suggest that the viscosity loss may be a result from multiple mechanisms including chemical reactions during storage as well as aggregation and conformational changes.  相似文献   
104.
Commercially available graphitized carbon nanofibers and multi-walled carbon nanotubes, two carbon materials with very different structure, have been functionalized in a nitric–sulfuric acid mixture. Further on, the materials have been platinized by a microwave assisted polyol method. The relative degree of graphitization has been estimated by means of Raman spectroscopy and X-ray diffraction while the relative concentration of oxygen containing groups has been estimated by X-ray photoelectron spectroscopy, which resulted in a graphitic character trend: Pt/GNF > Pt/F-GNF ? Pt/MWCNT > Pt/F-MWCNT. Transmission electron microscopy showed that the Pt particle size is around 3 nm for all samples, which was similar to the crystallite size obtained by X-ray diffraction. The activity towards electrochemical reduction of oxygen has been quantified using the thin-film rotating disk electrode, which has shown that all the samples have a better activity than the commercially available electrocatalysts. The trend obtained for the graphitic character maintained for the electrochemical activity, while the reverse trend has been obtained for the accelerated ageing test. Long-term potential cycling has demonstrated that the functionalization improves the stability for multi-walled carbon nanotubes, at the cost of decreased activity.  相似文献   
105.
106.
107.
108.
In future mobile communications many antennas will coexist on the device. This creates a number of problems related to bandwidth, efficiency, and correlation. Remedies are discussed in the paper, and attention is called to the promising area of adaptive matching, which also can solve problems related to the user.  相似文献   
109.
110.
Polychlorinated biphenyl (PCB) contamination of buildings continues to pose an exposure threat, even decades after their application in the form of calks and other building materials. In this research, we investigate the ability of clothing to sorb PCBs from contaminated air and thereby influence exposure. The equilibrium concentration of PCB‐28 and PCB‐52 was quantified for nine used clothing fabrics exposed for 56 days to air in a Danish apartment contaminated with PCBs. Fabric materials included pure materials such as cotton and polyester, or blends of polyester, cotton, viscose/rayon, and/or elastane. Air concentrations were fairly stable over the experimental period, with PCB‐28 ranging from 350 to 430 ng/m3 and PCB‐52 ranging from 460 to 550 ng/m3. Mass accumulated in fabric ranged from below detection limits to 4.5 mg/g of fabric. Cotton or materials containing elastane sorbed more than polyester materials on a mass basis. Mass‐normalized partition coefficients above detection limits ranged from 105.7 to 107.0 L/kg. Clothing acts as a reservoir for PCBs that extends dermal exposure, even when outside or in uncontaminated buildings.  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