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   2040篇
  免费   63篇
  国内免费   9篇
电工技术   16篇
综合类   73篇
化学工业   75篇
金属工艺   23篇
机械仪表   64篇
建筑科学   420篇
矿业工程   12篇
能源动力   46篇
轻工业   492篇
水利工程   22篇
石油天然气   23篇
武器工业   4篇
无线电   74篇
一般工业技术   181篇
冶金工业   121篇
原子能技术   24篇
自动化技术   442篇
  2025年   9篇
  2024年   31篇
  2023年   41篇
  2022年   39篇
  2021年   82篇
  2020年   77篇
  2019年   53篇
  2018年   50篇
  2017年   59篇
  2016年   90篇
  2015年   84篇
  2014年   115篇
  2013年   140篇
  2012年   125篇
  2011年   125篇
  2010年   133篇
  2009年   128篇
  2008年   91篇
  2007年   99篇
  2006年   107篇
  2005年   74篇
  2004年   64篇
  2003年   55篇
  2002年   47篇
  2001年   30篇
  2000年   22篇
  1999年   21篇
  1998年   18篇
  1997年   15篇
  1996年   14篇
  1995年   8篇
  1994年   11篇
  1993年   7篇
  1992年   5篇
  1991年   5篇
  1990年   4篇
  1989年   3篇
  1986年   2篇
  1985年   4篇
  1984年   2篇
  1981年   3篇
  1980年   3篇
  1977年   1篇
  1974年   2篇
  1973年   1篇
  1972年   2篇
  1968年   2篇
  1965年   2篇
  1963年   1篇
  1958年   3篇
排序方式: 共有2112条查询结果,搜索用时 15 毫秒
101.
Influent and effluent samples originating from two wastewater treatment plants (WWTPs) (treating hospital wastewater and domestic wastewater, Belgium) have been analyzed in order to estimate their steroid hormone content. The natural estrogens estrone (E1), 17β-estradiol (E2), and the synthetic 17α-ethinylestradiol (EE2) together with other steroid hormones progesterone (P) and testosterone (T) metabolites were detected in these samples. The hormone concentrations in both the hospital and the domestic WWTP samples were not significantly different and ranged from <0.2?ng EE2/L to 114?ng EE2/L, from <0.2?ng E1/L to 58?ng E1/L and from <0.2?ng P/L to >100?ng P/L. E2 was detected once at a concentration of 17?ng/L. In the domestic WWTP which comprises a conventional activated sludge treatment in parallel with a membrane bioreactor, no differences in estrogen removal efficiency could be observed for both treatments. In comparison to chemical analysis data, the Yeast Estrogen Screen (YES) appears to underestimate the influent estrogen concentrations, probably due to influent toxicity for the YES. Effluent estrogen concentrations, on the other hand, were overestimated by the YES test, probably due to the presence of other estrogenic compounds in the effluent.  相似文献   
102.
Recent advances in hardware technology have led to the development of low cost, power efficient and more feature rich devices that are amongst the most critical parts of communication networks. These devices or sensors can now sense data with more accuracy, process it by themselves and send it to the neighboring node or the sink node. However, robust and reliable security mechanisms are not yet properly implemented on these sensors due to their limited energy and computation power. Sensors also play a very important role in eHealthcare systems where ubiquitous patient monitoring is performed. As data is generated from the sensor nodes, reliable, secure and attack-resistant data acquisition and transmission is important for an efficient eHealthcare systems. This survey focuses on security issues of sensors data acquisition and transmission protocols, describing their main security features and comparing them in the context of a secure eHealthcare system. A taxonomy of open issues and future challenges is also discussed with respect to specific security metrics described in the paper.  相似文献   
103.
The analytical energy performance of an advanced energy optimized-ventilation constrained control approach to variable air volume systems was compared to four other controls. The other controls are either currently used or have been proposed in the literature. The advanced control demonstrated its potential to meet the ventilation requirements of ASHRAE Standard 62–1989 for every zone of the building with minimal energy consumption.

The analytical work was carried out in a single story prototypical commercial building. The building was analyzed in five US cities to provide insight into the impact of climate on the performance of the advanced control. The advanced control consumed less total energy, considerably less in some cities, than the other four controls. The advanced control provides an excellent opportunity to apply to buildings new automation equipment and software never attempted before.  相似文献   

104.
Abstract The amount of volatile organic compounds (VOCs) in indoor air, usually called TVOC (total volatile organic compounds), has been measured using different definitions and techniques which yield different results. This report recommends a definition of TVOC referring to a specified range of VOCs and it proposes a method for the measurement of this TVOC entity. Within the specified range, the measured concentrations of identified VOCs (including 64 target compounds) are summed up, concentrations of non-identified compounds in toluene equivalents are added and, together with the identified VOCs, they give the TVOC value. The report reviews the TVOC concept with respect to its usefulness for exposure assessment and control and for the prediction of health or comfort effects. Although the report concludes that at present it is not possible to use TVOC as an effect predictor, it affirms the usefulness of TVOC for characterizing indoor pollution and for improving source control as required from the points of view of health, comfort, energy efficiency and sustainability.  相似文献   
105.
The assessment of the glycemic index (GI) seems to be an important parameter to take into account in order to better understand the physiologic effects of foods with high carbohydrate levels. Among cereals, which are major sources of carbohydrates, spelt (Triticum spelta L.) has been considered as particularly interesting from a nutritional point of view. The aim of this study was to evaluate in vivo the GI of white spelt bread in healthy subjects. The wheat (Triticum aestivum L.) white bread was used as reference food. To avoid differences in the production of both breads, spelt and wheat breads were baked under the same controlled conditions. Results showed that the glycemic profile of spelt white bread was not different from that of wheat white bread (GI of 93 ± 9). The area under the glycemic curve significantly and negatively correlated to fasting glycemia and carbohydrate intake during evening meals preceding the test. In conclusion, the glycemic response to spelt bread was similar to that of wheat bread. However, in order to avoid more inter-individual variability, our data supports the importance to propose standardised carbohydrate content for the last meal before evaluating the GI of food.  相似文献   
106.
This paper presents an estimate of the externalities produced in the Mexico City Metropolitan Area (MCMA) through the impacts on health caused by secondary pollutants attributed to seven electric power plants located outside this area. An original method was developed to make possible a simplified application of the impact pathway approach to estimate the damage costs in the specified area. Our estimate shows that the annual costs attributed to secondary pollutants total 71 million USD (min/max 20/258 million USD). Finally, this paper discusses basic ideas on the implications for energy policy arising from this exercise in externality valuation.  相似文献   
107.
《辐射防护》2022,(2):169-172
Dose Estimation for Exposure to Radioactive Fallout from Nuclear Detonations Steven L.Simon1,AndréBouville2,Harold L.Beck3,Lynn R.Anspaugh4,Kathleen M.Thiessen5,F.Owen Hoffman5,Sergey Shinkarev6(1.National Cancer Institute,National Institutes of Health,Bethesda,MD;2.National Cancer Institute,National Institutes of Health,Bethesda,MD(retired);3.US Department of Energy(retired),New York,NY;4.Department of Radiology,University of Utah(Emeritus),Henderson,NV;5.Oak Ridge Center for Risk Analysis,Inc.,Oak Ridge,TN.  相似文献   
108.
The objective of this work was to determine the organic and total mercury contents in twelve fish species used in preparing sashimi in Japanese restaurants and estimate the exposure to organic mercury due to the consumption of this food. The mercury species were quantified by atomic absorption with thermal decomposition and amalgamation. Total mercury was analyzed directly, whereas organic mercury was quantified after extraction with toluene in an acid medium using a microwave assisted system. Needlefish and tuna showed the highest levels of mercury species and salmon and mullet the lowest levels. The mean ratios between MeHg+/total Hg were 93% and 87% for sandperch and octopus, respectively, indicating that the most toxic form (organic Hg) predominates in these species. Exposure to methylmercury was estimated based on the PTWI and the results showed that the ingestion of 2 portions of needlefish and tuna exceeded the values established by 100%.  相似文献   
109.
A fortified food that was rich in protein, vitamins and iron made of chickpea, bovine lung and corn was developed with the aim of controlling iron-deficiency anaemia in children from poorer areas. It was tested in Teresina, State of Piauí, Northeastern Brazil, on a population with high anaemia prevalence. Two local daycare units with similar characteristics were selected and the children at one of them received a 30 g pack three times a week, representing a total iron daily intake of 6.96 mg. The other daycare unit was followed as a control. The capillary haemoglobin concentration was determined for the children at both daycare units, at the beginning of the study and after a two-month intervention period. The mean haemoglobin concentration in the test group at the beginning of the intervention was 11.8 g/dL, which increased to 13.1 g/dL at the end of the intervention. In the control group these figures remained practically constant (11.6–11.8 g/dL). These represented a dramatic and significant drop in anaemia prevalence, from 61.5% to 11.5% in the test group, and an insignificant reduction (63.1–57.7%) in the control group. The acceptance of the fortified snack was excellent and no undesirable effects were observed.  相似文献   
110.
Informed by data on the dose-response effect, the authors assessed use of psychotherapy in the Veterans Health Administration (VA). The authors identified 410,923 patients with newly diagnosed depression, anxiety, or posttraumatic stress disorder using VA databases (October 2003 through September 2004). Psychotherapy encounters were identified by Current Procedural Terminology codes for the 12 months following patients' initial diagnosis. Psychotherapy was examined for session exposure received within the 12-month follow-up period and time (in days) between diagnosis and treatment. Of the cohort, 22% received at least one session of psychotherapy; 7.9% received four or more sessions; 4.2% received eight or more sessions; and 2.4% received 13 or more sessions. Delays between initial mental health diagnosis and initiation of care averaged 57 days. Patient variables including age, marital status, income, travel distance, psychiatric diagnosis, and medical-illness burden were significantly related to receipt of psychotherapy. Treatment delays and general underuse of psychotherapy services are potential missed opportunities for higher-quality psychotherapeutic care in integrated health care settings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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