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   328篇
  免费   7篇
电工技术   8篇
化学工业   47篇
金属工艺   1篇
机械仪表   1篇
建筑科学   27篇
矿业工程   1篇
能源动力   61篇
轻工业   34篇
水利工程   2篇
无线电   17篇
一般工业技术   49篇
冶金工业   19篇
原子能技术   4篇
自动化技术   64篇
  2023年   2篇
  2022年   4篇
  2021年   8篇
  2020年   10篇
  2019年   4篇
  2017年   6篇
  2016年   3篇
  2015年   3篇
  2014年   4篇
  2013年   8篇
  2012年   14篇
  2011年   20篇
  2010年   19篇
  2009年   11篇
  2008年   19篇
  2007年   11篇
  2006年   13篇
  2005年   7篇
  2004年   8篇
  2003年   5篇
  2002年   8篇
  2001年   4篇
  2000年   3篇
  1998年   7篇
  1997年   8篇
  1996年   6篇
  1995年   2篇
  1994年   3篇
  1993年   10篇
  1992年   2篇
  1991年   3篇
  1990年   5篇
  1989年   3篇
  1987年   2篇
  1985年   8篇
  1984年   4篇
  1983年   4篇
  1982年   7篇
  1981年   14篇
  1980年   10篇
  1979年   11篇
  1978年   10篇
  1977年   4篇
  1976年   4篇
  1975年   3篇
  1973年   2篇
  1971年   2篇
  1970年   1篇
  1969年   1篇
  1967年   1篇
排序方式: 共有335条查询结果,搜索用时 15 毫秒
61.
In this paper, a new approach for detecting previously unencountered malware targeting mobile device is proposed. In the proposed approach, time-stamped security data is continuously monitored within the target mobile device (i.e., smartphones, PDAs) and then processed by the knowledge-based temporal abstraction (KBTA) methodology. Using KBTA, continuously measured data (e.g., the number of sent SMSs) and events (e.g., software installation) are integrated with a mobile device security domain knowledge-base (i.e., an ontology for abstracting meaningful patterns from raw, time-oriented security data), to create higher level, time-oriented concepts and patterns, also known as temporal abstractions. Automatically-generated temporal abstractions are then monitored to detect suspicious temporal patterns and to issue an alert. These patterns are compatible with a set of predefined classes of malware as defined by a security expert (or the owner) employing a set of time and value constraints. The goal is to identify malicious behavior that other defensive technologies (e.g., antivirus or firewall) failed to detect. Since the abstraction derivation process is complex, the KBTA method was adapted for mobile devices that are limited in resources (i.e., CPU, memory, battery). To evaluate the proposed modified KBTA method a lightweight host-based intrusion detection system (HIDS), combined with central management capabilities for Android-based mobile phones, was developed. Evaluation results demonstrated the effectiveness of the new approach in detecting malicious applications on mobile devices (detection rate above 94% in most scenarios) and the feasibility of running such a system on mobile devices (CPU consumption was 3% on average).  相似文献   
62.
During a fire at a power plant located in the coastal plain of Israel, PCBs were released to the atmosphere from a ruptured transformer. Since PCBs are probably carcinogenic to humans, this study was performed in order to assess the environmental contamination by PCBs via the atmospheric pathway and the need for remediation measures. The release conditions and the meteorological conditions which prevailed during the fire were analyzed. This provided the input to a Gaussian dispersion model used to estimate the downwind-contaminated sector as well as the location of the maximal concentration within this sector. A sampling plan was then devised and vegetation collected within this sector was analyzed for PCBs. A methodology was developed to convert PCB concentrations in vegetation to concentrations in the atmosphere. It allowed a reconstitution of the PCB source term to the atmosphere from the vegetation measurements. The PCB concentrations were found to be lower than the USEPA decontamination standards. Remediation measures were not needed beyond the plant fence.  相似文献   
63.
64.
At present, there is an unprecedented level of interest in the properties and structures of complexes consisting of DNA mixed with oppositely charged cationic liposomes (CLs). The interest arises because the complexes mimic natural viruses as chemical carriers of DNA into cells in worldwide human gene therapy clinical trials. However, since our understanding of the mechanisms of action of CL-DNA complexes interacting with cells remains poor, significant additional insights and discoveries will be required before the development of efficient chemical carriers suitable for long-term therapeutic applications. Recent studies describe synchrotron X-ray diffraction, which has revealed the liquid crystalline nature of CL-DNA complexes, and three-dimensional laser-scanning confocal microscopy, which reveals CL-DNA pathways and interactions with cells. The importance of the liquid crystalline structures in biological function is revealed in the application of these modern techniques in combination with functional transfection efficiency measurements, which shows that the mechanism of gene release from complexes in the cell cytoplasm is dependent on their precise liquid crystalline nature and the physical and chemical parameters (for example, the membrane charge density) of the complexes. In [section sign] 5, we describe some recent new results aimed at developing bionanotube vectors for gene delivery.  相似文献   
65.
This paper details the Box-Jenkins approach to forecasting time series and applies it to short-term natural gas marketed production and crude petroleum production in the United States. After establishing the efficacy of the approach for forecasting the two series of interest, monthly forecasts for 1978 are made. The results indicate that natural gas production in 1978 will increase by 2·8 per cent over the 1977 level while crude petroleum production will fall by 4·0 per cent.  相似文献   
66.
67.
68.
Abstract

Problem, research strategy, and findings: Despite growing interest by practitioners in using exploratory scenarios within urban planning practice, there are few detailed guidelines for how to do this. Through the discussion of five case examples, we illustrate different approaches to linking exploratory scenarios to different planning contexts. We conclude by observing that to directly inform a plan, regardless of the specific approach taken, exploratory scenarios in urban planning must incorporate stakeholder values and not only rely on expert judgment and analysis.

Takeaway for practice: Exploratory scenarios are effective for analyzing uncertainty within a planning process. However, exploratory scenarios can be incorporated into planning practice in different ways, ranging from workshops among experts that aim to cultivate general learning to complex projects that result in highly detailed scenarios and recommendations for plans. Practitioners can draw on the cases we present to inspire planning methods for particular projects, taking into account specific contexts and goals.  相似文献   
69.
Synchronized external pulsation is proposed as a method to improve tolerance to acceleration stress. This technique uses a modified anti-G suit which is pressurized and depressurized synchronously with the heart cycle. The feasibility of the procedure has been studied using a computer model of the cardiovascular system which includes the effects of Gz stress, and contains simulations of baroreceptor control of heart rate and venous tone. Model predictions indicate that for unprotected subjects, carotid pressure at eye level (ophthalmic artery pressure) decreases to 20 mmHg (beginning of central light loss) at approximately +3.6 Gz. Applying standard anti-G suit pressure to the model increases this level to 5.3 Gz. When synchronized external pulsation of 2 psi is superimposed on the standard anti-G suit pressure, the tolerance to acceleration stress is further augmented by at least 0.9 G above the protection afforded by the standard anti-G suit alone. A set of preliminary experiments on human subjects to test the feasibility of using the technique in the high-G environment has also been carried out. The results under various protection modes compare favorably to the model predictions. Our results suggest that the computer model presented here is a useful tool for studying cardiovascular responses under +GZ stress. It also indicates that using synchronized external pulsation pressure superimposed on the standard anti-G suit pressure may offer extra protection to acceleration stress.  相似文献   
70.
This study is concerned with the assessing the impact that inaccuracy in the measurement of the dependent variable and one or more of the independent variables has on the estimate of the price elasticity of demand for diesel fuel by farmers in the United States. Two diagnostics – the regression coefficient bounds and the bias correction factor — are introduced to assess the effect that such measurement errors have on the estimated coefficients of the diesel fuel demand relationship.  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