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   358085篇
  免费   4460篇
  国内免费   699篇
电工技术   4982篇
综合类   2421篇
化学工业   57044篇
金属工艺   20304篇
机械仪表   13661篇
建筑科学   7095篇
矿业工程   4380篇
能源动力   5454篇
轻工业   17873篇
水利工程   5565篇
石油天然气   13424篇
武器工业   33篇
无线电   30183篇
一般工业技术   82901篇
冶金工业   41492篇
原子能技术   11486篇
自动化技术   44946篇
  2021年   3457篇
  2020年   2794篇
  2019年   3424篇
  2018年   20441篇
  2017年   19636篇
  2016年   16865篇
  2015年   4564篇
  2014年   6621篇
  2013年   12560篇
  2012年   12012篇
  2011年   19445篇
  2010年   16542篇
  2009年   14552篇
  2008年   15748篇
  2007年   16374篇
  2006年   7168篇
  2005年   7312篇
  2004年   7122篇
  2003年   6934篇
  2002年   6134篇
  2001年   5385篇
  2000年   5442篇
  1999年   4686篇
  1998年   9283篇
  1997年   7219篇
  1996年   5347篇
  1995年   4202篇
  1994年   3852篇
  1993年   4104篇
  1992年   3398篇
  1991年   3563篇
  1990年   3614篇
  1989年   3501篇
  1988年   3420篇
  1987年   3380篇
  1986年   3262篇
  1985年   3439篇
  1984年   3360篇
  1983年   3238篇
  1982年   3114篇
  1981年   3168篇
  1980年   3203篇
  1979年   3319篇
  1978年   3559篇
  1977年   3680篇
  1976年   4420篇
  1975年   3248篇
  1974年   3333篇
  1973年   3397篇
  1972年   3007篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Journal of Computer and Systems Sciences International - The problem of constructing a guaranteeing anticipating control for a shock isolator that protects an object on a movable base from impacts...  相似文献   
102.
High Temperature - Experimental findings suggest that a strongly ionized, arc He plasma of atmospheric pressure does not exist in the state of the local thermodynamic equilibrium (LTE) expected for...  相似文献   
103.
Strength of Materials - The paper addresses the investigation of high-strain rate compressive behavior of Al foams subjected to impact at the intermediate striking velocity ranged from 40 to...  相似文献   
104.
105.
The failure of frontline antibiotics in the clinic is one of the most serious threats to human health and requires a multitude of novel therapeutics and innovative approaches to treatment so as to curtail the growing crisis. In addition to traditional resistance mechanisms resulting in the lack of efficacy of many antibiotics, most chronic and recurring infections are further made tolerant to antibiotic action by the presence of biofilms. Herein, we report an expanded set of 5-benzylidene-4-oxazolidinones that are able to inhibit the formation of Staphylococcus aureus biofilms, disperse preformed biofilms, and, in combination with common antibiotics, are able to significantly reduce the bacterial load in a robust collagen-matrix model of biofilm infection.  相似文献   
106.
Over the last few years, the global biosurfactant market has raised due to the increasing awareness among consumers, for the use of biological or bio-based products. Because of their composition, it can be speculated that these are more biocompatible and more biodegradable than their chemical homologous. However, at the moment, no studies exist in the literature about the biodegradability of biosurfactants. In this work, a biosurfactant contained in a crude extract, obtained from a corn wet-milling industry stream that ferments spontaneously in the presence of lactic acid bacteria, was subjected to a biodegradation study, without addition of external microbial biomass, under different conditions of temperature (5–45 °C), biodegradation time (15–55 days), and pH (5–7). For that, a Box–Behnken factorial design was applied, which allowed to predict the percentage of biodegradation for the biosurfactant contained in the crude extract, between the range of the independent variables selected in the study, obtaining biodegradation values between 3 and 80%. The percentage of biodegradation for the biosurfactant was calculated based on the increase in the surface tension of samples of the crude extract. Furthermore, it was also possible to predict the variation in t1/2 for the biosurfactant (time to achieve the 50% of biodegradation) under different conditions.  相似文献   
107.
108.
Mobile software applications have to cope with a particular environment that involves small size, limited resources, high autonomy requirements, competitive business models and many other challenges. To provide development guidelines that respond to these needs, several practices have been introduced; however, it is not clear how these guidelines may contribute to solve the issues present in the mobile domain. Furthermore, the rapid evolution of the mobile ecosystem challenges many of the premises upon which the proposed practices were designed. In this paper, we present a survey of the literature on software assurance practices for mobile applications, with the objective of describing them and assessing their contribution and success. We identified, organized and reviewed a body of research that spans in three levels: software development processes, software product assurance practices, and software implementation practices. By carrying out this literature survey, we reviewed the different approaches that researchers on Software Engineering have provided to address the needs that raise in the mobile software development arena. Moreover, we review the evolution of these practices, identifying how the constant changes and modernization of the mobile execution environment has impacted the methods proposed in the literature. Finally, we introduced discussion on the application of these practices in a real productive setting, opening an area for further research that may determine if practitioners have followed the proposed assurance paradigms.  相似文献   
109.
Potentiometric sensors with plasticized poly(vinyl chloride) membranes based on β-lactam–tetraalkylammonium ion associates sensitive to penicillin antibiotics are proposed. The physicochemical characteristics (solubility product constants and dissociation constants) of active membrane components and the electrode, transport, and selective properties of the membranes of liquidand solid-contact sensors have been studied. The quantitative characteristics of membrane transport (penetrability, ion flux, and transport rate) have been evaluated. The main charge carriers in the membranes and at the membrane/solution interface have been determined from the membrane transport characteristics. The potentiometric sensors are shown to be applicable to the determination of penicillin antibiotics in biological fluids (blood serum and oral fluid) from patients with urinary tract infection.  相似文献   
110.
The authors have developed a procedure and a test bench for studying evolution of various nature physical fields in modeling geomedium fracture by fluids. The test bench performs synchronous recording of macro- and micro-deformation, heat and acoustic emission induced in physical models of geomedium under loading to discontinuity. The experimental procedure has been trialed. The analysis of the synchronized test data allows a conclusion on the existence of time–space relationship between different nature physical fields induced during failure of solids.  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