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   74525篇
  免费   6003篇
  国内免费   2892篇
电工技术   4695篇
综合类   7225篇
化学工业   4743篇
金属工艺   2359篇
机械仪表   2827篇
建筑科学   11776篇
矿业工程   1737篇
能源动力   1540篇
轻工业   13838篇
水利工程   4949篇
石油天然气   2303篇
武器工业   342篇
无线电   9716篇
一般工业技术   3801篇
冶金工业   3676篇
原子能技术   513篇
自动化技术   7380篇
  2024年   425篇
  2023年   1109篇
  2022年   1841篇
  2021年   2335篇
  2020年   2350篇
  2019年   1932篇
  2018年   1767篇
  2017年   2204篇
  2016年   2264篇
  2015年   2609篇
  2014年   5242篇
  2013年   4347篇
  2012年   5388篇
  2011年   5659篇
  2010年   4450篇
  2009年   4660篇
  2008年   4225篇
  2007年   4982篇
  2006年   4525篇
  2005年   3745篇
  2004年   3261篇
  2003年   2919篇
  2002年   2567篇
  2001年   1910篇
  2000年   1513篇
  1999年   1172篇
  1998年   804篇
  1997年   620篇
  1996年   548篇
  1995年   454篇
  1994年   362篇
  1993年   257篇
  1992年   234篇
  1991年   138篇
  1990年   112篇
  1989年   100篇
  1988年   74篇
  1987年   68篇
  1986年   37篇
  1985年   45篇
  1984年   35篇
  1983年   19篇
  1982年   19篇
  1981年   13篇
  1980年   21篇
  1978年   5篇
  1977年   6篇
  1976年   4篇
  1975年   4篇
  1959年   14篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
81.
近年来太钢由于烧结技术进步,烧结矿质量不断改善,固体燃耗降低,促进了高炉炉料结构的优化。为高炉技术经济指标提高奠定了基础。  相似文献   
82.
A test chamber has been developed in order to provide a small and simple emission testing facility capable of testing construction products in a climate where the important climatic parameters such as temperature, ventilation rate and air velocity can be varied independently around typical indoor values. The test chamber CLIMPAQ is made of panes of window glass. Other main surface materials are stainless steel and eloxated aluminium. The chamber has a volume of 50.9 litres and is designed to meet the requirements for quantifying air pollution. In this investigation human subjects acted as air pollution judges, and chemical characterization of the air pollution was carried out. Carpet, linoleum, wall paint and seal- ant were tested simultaneously in the CLIMPAQ and in four other chambers ranging from a full-scale chamber of 28 m3 to a field and laboratory emission cell of 3.5· 10?5m3. Product ranking is the same in all chambers for the sensory measurements. Emission rates based on sensory measurements differ for all products less than 100 % except for tests in a 3-litre chamber where emission rates were higher. Chemical measurements differ up to approximately 10 times for the same product in different chambers. Deviations appear to be the result of different environmental parameters in the various chambers. Low air concentrations or high specific ventilation rates seem to increase emissions, while differences in air velocities and sink properties may also be the cause of differences in emission rates.  相似文献   
83.
全金属反射光学系统结构的有限元分析   总被引:3,自引:1,他引:2  
用有限元分析方法对全金属反射光学系统在各种受力状态下的变形、应力及固有频率做了全面的分析,并给出了结构多次优化后的分析结果。  相似文献   
84.
Diced green bell peppers were soaked in a solution of hydrochloric acid or calcium chloride, air-dried to 50% moisture, held in CO2 at 5.8 MPa for 1, 3 or 5 min, and puffed by abruptly releasing the CO2 pressure. Treatment with 1% CaCl2 increased the size of puffed-dried products as compared to a control; however, HCl treatments did not. The treatment with 1 or 2% CaCl2 reduced shrinkage as compared to the control. The 1% CaCl2 treatment may have increased the CO2 saturation rate.  相似文献   
85.
就民用建筑设计部门设计图纸质量抽查中出现的问题,进行了剖析并提出了注意事项。  相似文献   
86.
教师的职业道德是贯穿教育全过程的精神支柱,它对学生和社会都会有深远的激励和影响作用;而熟练掌握专业知识和教育理论知识是教师业务能力的本质要求。新时期的创新型教师都必须不断地在这两个方面进行提升才能够符合时代的要求。  相似文献   
87.
Stability of large-scale coal-fired MHD channels is studied by (1) linearized stability analysis, and (2) time-dependent 1-D analysis. The channel length is 15 m with 600 electrode pairs, and the output power ranges from 220.6 MW through 258.7 MW. Linearized stability analyses show that the Faraday channels operated with fixed loading resistance are stable, whereas the two waves of u and u–a (u, a: gas and sound velocity) become unstable in the Faraday channel with fixed loading factor. Two waves of u and u–a are unstable in the diagonal channel with fixed loading current and the u + a wave becomes unstable in the diagonal channel with fixed electrode current. Time-dependent one-dimensional analyses indicate that the Faraday channels with fixed load resistance are smooth without growth of fluctuation. The diagonal channels with fixed electrode current are smooth with no fluctuation, though the linear theory indicates that the u + a wave is unstable. The diagonal channel with fixed load current suffers large disturbance along the latter half of the channel, being consistent with the linearized analysis which indicates that the u - a and u waves are unstable.  相似文献   
88.
Abstract This study deals with the modeling of air pollution in apartments from laboratory measurements of source strengths, using formaldehyde and Total Volatile Organic Compounds (TVOCs) as model pollutants. The sources in two test apartments were grouped into two: building-related sources and occupant-related sources. The measured source strengths and ventilation rates were used for the prediction of concentrations expected in the apartments. These predictions were compared to measurements in the apartment over 12 months. The conclusions were that the model predictions based on emission rates measured in the laboratory can be used to predict the long-term concentration of the two model pollutants in the apartments. Considering the measured differences in ventilation between the apartments, an occupant emission rate of between 0.2 and 0.3 mg/h/kg body weight could be estimated. Based on previous suggested limits of acceptable exposures of humans to VOCs, an acceptable average emission rate of VOCs from building materials in general was estimated to be about 30 (μ/m2/h. The modeling showed that during the first 200 days, building materials dominated the emissions. After this, sources relating to the occupants dominated. On average about half of the VOC pollution originated from the building materials.  相似文献   
89.
90.
Monitoring water quality in reservoirs with IRS-1A-LISS-I   总被引:1,自引:1,他引:0  
An attempt has been made to quantify the relationship between the variation in IRS-IA-LISS-I (Indian Remote Sensing Satellite-1A Linear Imaging Self-Scanning System) radiance data and field measured change in secchi disc depth. Secchi disc depth was measured for 47 predetermined sampling locations on reservoir surface water. At extinction depth (secchi depth), water samples were collected from all the sampling locations. Suspended sediments of eight locations representing various reaches of the reservoir were selected for mineralogical, particle size and optical properties analysis. The LISS-I radiance value in band 1 (0.45–0.52µm) band 2 (0-52–0.59 µm) and band 3 (0.62–0.68 µm) were used in a regression analysis. The absorption infrared band 4 (0.77–0.86 µm) was not included in the analysis. In these, the dependable variable was secchi depth (SD) and the LISS-I-radiance data was the estimator variable. Forty-seven data sets of 20 October 1988 from Tawa reservoir surface water were used to obtain an estimator equation for SD. The verification of the estimator equation was tested by applying it to a data set of 21 measurements of 28 September 1988 for this reservoir. The coefficient of correlation between observed and estimated values for the 28 September 1988 data set wasr=0.92 for SD, indicating that the equation could accurately predict the water clarity (SD) for this reservoir on new occasions from IRS-IA-LISS-I spectral data. It is shown that mineral composition and optical properties of suspended sediments influence the reflected radiance of water quality. It is concluded that IRS-IA-LISS-I data provide a useful means of mapping water quality in reservoir.  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