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   395篇
  免费   18篇
  国内免费   2篇
化学工业   37篇
金属工艺   5篇
机械仪表   11篇
建筑科学   14篇
能源动力   7篇
轻工业   98篇
水利工程   8篇
石油天然气   1篇
无线电   47篇
一般工业技术   77篇
冶金工业   43篇
自动化技术   67篇
  2022年   4篇
  2021年   10篇
  2020年   3篇
  2019年   3篇
  2018年   10篇
  2017年   7篇
  2016年   7篇
  2015年   9篇
  2014年   13篇
  2013年   30篇
  2012年   27篇
  2011年   32篇
  2010年   15篇
  2009年   12篇
  2008年   22篇
  2007年   30篇
  2006年   27篇
  2005年   26篇
  2004年   28篇
  2003年   23篇
  2002年   22篇
  2001年   1篇
  2000年   2篇
  1999年   9篇
  1998年   6篇
  1997年   3篇
  1996年   6篇
  1995年   7篇
  1994年   5篇
  1993年   2篇
  1990年   2篇
  1989年   1篇
  1988年   1篇
  1987年   2篇
  1985年   3篇
  1983年   1篇
  1981年   2篇
  1978年   1篇
  1977年   1篇
排序方式: 共有415条查询结果,搜索用时 453 毫秒
31.
In recent years, numerous foodborne outbreaks due to consumption of berry fruit contaminated by human enteric viruses have been reported. This European multinational study investigated possible contamination routes by monitoring the entire food chain for a panel of human and animal enteric viruses.  相似文献   
32.
L. A. Clark and D. Watson (1991) proposed a tripartite model of depression and anxiety that divides symptoms into 3 groups: symptoms of general distress that are largely nonspecific, manifestations of anhedonia and low positive affect that are specific to depression, and symptoms of somatic arousal that are relatively unique to anxiety. This model was tested by conducting separate factor analyses of the 90 items in the Mood and Anxiety Symptom Questionnaire (D. Watson & L. A. Clark, 1991) in 5 samples (3 student, 1 adult, 1 patient). The same 3 factors (General Distress, Anhedonia vs. Positive Affect, Somatic Anxiety) emerged in each data set, suggesting that the symptom structure in this domain is highly convergent across diverse samples. Moreover, these factors broadly corresponded to the symptom groups proposed by the tripartite model. Inspection of the individual item loadings suggested some refinements to the model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
33.
Despite the availability of several instruments to evaluate quality of life (QL) over time in patients with lung cancer, barriers in measurement remain. This methodological study used LCSS data (Lung Cancer Symptom Scale, a disease- and site-specific QL measure) to examine analysis methods to quantify QL where data needed for serial evaluation may be missing. Data from two large randomized trials, conducted at 30 centers, of a new combination chemotherapy regimen incorporating a new agent for patients (n = 673) with Stage III and IV non-small cell lung cancer were obtained for this study. QL had been prospectively measured at baseline, day 29, and every six weeks thereafter using the LCSS. For the slope analysis (SA) and area under the curve (AUC) analyses, an adjustment score of zero was used to indicate QL on the day of death (mortality adjustment) and each subsequent day until the end of the assessment period. Significant differences in QL, symptom scores and known prognostic factors at baseline were found in the attrition group. SA and AUC analysis allowed inclusion of 581 patients, giving an adequacy rate of 86%. By using a mortality adjustment, an additional 45 patients were included, increasing the inclusion rate to 93%. With the use of the mortality adjustment, QL was shown to decline over the interval, as opposed to rise if the adjustment had not been performed. The conclusions of the study were: (1) analysis for serial data using SA and AUC provides useful, but differing information; (2) when attrition (caused by death) is a factor, a mortality adjustment presented a more accurate assessment of QL as an endpoint; (3) more frequent evaluations of QL will capture rapid changes in patient status and reduce the attrition bias; (4) all patients should be followed until they die; and (5) QL should be given full consideration as a primary endpoint separate from survival.  相似文献   
34.
The disproportionately large number of traffic accidents of young novice drivers highlights the need for an effective driver education program. The Goals for Driving Education (GDE) matrix shows that driver education must target both lower and higher levels of driver competences. Research has indicated that current education programs do not emphasize enough the higher levels, for example awareness and insight. This has raised the importance of insight programs. On the Road (OtR), a Flemish post-license driver education program, is such an insight program that aims to target these higher levels. The program focus is on risky driving behavior like speeding and drink driving. In addition, the program addresses risk detection and risk-related knowledge. The goal of the study was to do an effect evaluation of this insight program at immediate post-test and 2 months follow-up. In addition, the study aimed to generalize the results of this program to comparable programs in order to make usable policy recommendations. A questionnaire based on the Theory of Planned Behavior (TPB) was used in order to measure participants’ safety consciousness of speeding and drink driving. Moreover, we focused on risk detection and risk-related knowledge. Participants (N = 366) were randomly assigned to a baseline—follow-up group or a post-test—follow-up group.  相似文献   
35.
The purpose of this study was to develop and validate a noninvasive pressure estimation technique based on subharmonic emissions from a commercially available ultrasound contrast agent and scanner, unlike other studies that have either adopted a single-element transducer approach and/ or use of in-house contrast agents. Ambient pressures were varied in a closed-loop flow system between 0 and 120 mmHg and were recorded by a solid-state pressure catheter as the reference standard. Simultaneously, the ultrasound scanner was operated in pulse inversion mode transmitting at 2.5 MHz, and the unprocessed RF data were captured at different incident acoustic pressures (from 76 to 897 kPa). The subharmonic data for each pulse were extracted using band-pass filtering with averaging, and subsequently processed to eliminate noise. The incident acoustic pressure most sensitive to ambient pressure fluctuations was determined, and then the ambient pressure was tracked over 20 s. In vivo validation of this technique was performed in the left ventricle (LV) of 2 canines. In vitro, the subharmonic signal could track ambient pressure values with r(2) = 0.922 (p < 0.001), whereas in vivo, the subharmonic signal tracked the LV pressures with r(2) > 0.790 (p < 0.001) showing a maximum error of 2.84 mmHg compared with the reference standard. In conclusion, a subharmonic ultrasound-based pressure estimation technique, which can accurately track left ventricular pressures, has been established.  相似文献   
36.
The satisfactory sealing of large reactor vessel flanges in petrochemical plant is a significant problem. It is necessary to accommodate relative flange movement of large pressure vessels and provide a system where adequate bolting can be applied. The leakage from a large flange can be a major contributor to plant emissions. Here a corrugated metal graphite covered gasket has been used to seal a flange 20 feet (6 m) in diameter on a high-temperature (450°C) reactor vessel. This has resulted in a significant reduction in emissions and plant maintenance. This feature is based on the submission by the winning team in the Fluid Sealing Association's 2003 Environmental Achievement Awards.  相似文献   
37.
Consideration of the eventual forced outage of individual power stations leads to a large number of possible states of the power generating system, all with their own probability. It is possible to design a stochastic method to properly take into account all of these possibilities and to weigh them accordingly. In broader energy models, instead of these stochastic techniques that require a considerable amount of calculation time, mostly approximative static simplified methods are applied. Up till now, these simplified techniques have not been validated. The scope of this paper is to check their validity. Therefore, two approaches are compared: a complete stochastic approach and a method based on the derated power (which is the nominal power multiplied with the average availability) of the individual plants. The conclusion of this comparison is that derated power may be used in energy modelling instead of the complicated stochastic approach. The error made is very small and the correlation between the unserved load probability functions obtained by both methods is excellent. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
38.
39.
A membrane‐assisted bioreactor (MBR) for sustained nitrite accumulation is presented, treating a synthetic wastewater with total ammonium nitrogen (TAN) concentrations of 1 kg N m?3 at a hydraulic retention time down to 1 day. Complete biomass retention was obtained by microfiltration with submerged hollow fibre membranes. A membrane flux up to 189.5 dm3 day?1 m?2 could be maintained at a suction pressure below 100 kPa. Nitrification was effectively blocked at the nitrite stage (nitritation), and nitrate concentration was less than 29 g N m?3. The rate of aeration was reduced to obtain a mixture of ammonium and nitrite, and after adjusting this rate the TAN/NO2‐N ratio in the reactor effluent was kept around unity, making it suitable for further treatment by anaerobic oxidation of ammonium with nitrite. After increasing again the rate of aeration, complete nitrification to nitrate recovered after 11 days. It is suggested that nitrite accumulation resulted from a combination of factors. First, the dissolved oxygen (DO) concentration in the reactor was always limited with concentrations below 0.1 g DO m?3, thereby limiting nitrification and preventing significant nitrate formation. The latter is attributed to the fact that ammonium‐oxidising bacteria cope better with low DO concentrations than nitrite oxidisers. Second, the MBR was operated at a high ammonia concentration of 7–54 g N m?3, resulting in ammonia inhibition of the nitrite‐oxidising microorganisms. Third, a temperature of 35 °C was reported to yield a higher maximum growth rate for ammonium‐oxidising bacteria than for nitrite‐oxidising bacteria. Nitrite oxidisers were always present in the MBR but were out‐competed under the indicated process conditions, which is reflected in low concentrations of nitrate. Oxygen limitation was shown to be the most important factor to sustain nitrite accumulation. Nevertheless, nitritation was possible at ambient temperature (22–24 °C), lower ammonia concentration (<7 g N m?3) and when using raw nitrogenous wastewater containing some biodegradable carbon. Overall, application of the MBR for nitritation was shown to be a reliable technology. © 2003 Society of Chemical Industry  相似文献   
40.
简介 由于拼写错误、意外的缩略语和其他不规则问题,实际的数据是“有问题”的。因此,在数据仓储项目中,很大一部分的时间和金钱都花费在了数据提取、数据转换和数据加载(ETL,Extraction、Transformation、Loading)阶段。在ETL阶段,新数据被清理、标准化,并使其与现有数据一致。在Microsoft SQL Server 2005中可用的模糊查找和模糊分组转换,有助于使ETL过程在遇到若干种在交际数据中观测到的常见错误时更易复原。它们解决一般的匹配和分组问题,而无需特定于域的规则和脚本的专家集合。通过为您的域自定义模糊查找和模糊分组,您可以利用Business Intelligence Development Studio内的通用数据清理算法,并避免创建复杂的自定义规则和代码。  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