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   1620869篇
  免费   25334篇
  国内免费   7118篇
电工技术   35013篇
综合类   6523篇
化学工业   277792篇
金属工艺   66085篇
机械仪表   46222篇
建筑科学   48626篇
矿业工程   11743篇
能源动力   50627篇
轻工业   126576篇
水利工程   16369篇
石油天然气   38123篇
武器工业   153篇
无线电   200166篇
一般工业技术   301645篇
冶金工业   218494篇
原子能技术   34471篇
自动化技术   174693篇
  2021年   15792篇
  2020年   12140篇
  2019年   14874篇
  2018年   18457篇
  2017年   17863篇
  2016年   22926篇
  2015年   17865篇
  2014年   29063篇
  2013年   88754篇
  2012年   38539篇
  2011年   53223篇
  2010年   45495篇
  2009年   53110篇
  2008年   49006篇
  2007年   46716篇
  2006年   47077篇
  2005年   42555篇
  2004年   43959篇
  2003年   43609篇
  2002年   42341篇
  2001年   39561篇
  2000年   37560篇
  1999年   37575篇
  1998年   61877篇
  1997年   49731篇
  1996年   42138篇
  1995年   34734篇
  1994年   31918篇
  1993年   31924篇
  1992年   27198篇
  1991年   24455篇
  1990年   24653篇
  1989年   23798篇
  1988年   22339篇
  1987年   20462篇
  1986年   19834篇
  1985年   23154篇
  1984年   22855篇
  1983年   20818篇
  1982年   19696篇
  1981年   19897篇
  1980年   18527篇
  1979年   18848篇
  1978年   18155篇
  1977年   18843篇
  1976年   21354篇
  1975年   16304篇
  1974年   15688篇
  1973年   15833篇
  1972年   13303篇
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
41.
42.
Trust is the key element of commerce, both for traditional models and — more recently — for eCommerce. Unlike its traditional counterpart, eCommerce relies on trust being created and maintained with the help of digital devices and services. Convergence brings significant changes to the way people interact through digital media by offering ubiquitous and seamless communication. This has a significant impact on the way trust is established and maintained, with consequent impact upon eCommerce. This paper identifies a number of the most important challenges to trust in eCommerce as well as trust-related aspects of key enablers of eCommerce. From this perspective, the paper studies an impact of convergence on trust within eCommerce to identify several positive relationships.  相似文献   
43.
44.
Stormwater quality simulation models are useful tools for the design and management of sewer systems. Modelling results are highly sensitive to experimental data used for calibration. This sensitivity is examined for three modelling approaches of various complexities (site mean concentration approach, event mean concentration approach and build-up, washoff and transport modelling approach) applied to a typical case study (design of a dry detention tank), accounting for the variability of calibration data and their effect on simulation results. Calibrated models with different calibration data sets were used to simulate 3 years of rainfall with different retention tank specific volumes. Annual pollutant load interception efficiencies were determined. Simulations results revealed (i) that there is no advantage in using the EMC model compared to the SMC model and (ii) that the BWT model resulted in higher design ratios than those given by the SMC/hydraulic approach. For both EMC and BWT models, using an increasing number n of events for calibration leads to narrower confidence intervals for the design ratios. It is crucial for design ratios to account for successive storm events in chronological order and to account for the maximum allowable flow to be transferred to the downstream WWTP.  相似文献   
45.
An inventory analysis of rural pollution loads in China.   总被引:1,自引:0,他引:1  
Rural pollution has attracted increasing attention over the past decade for its important consequences on surface and groundwater quality. This is particularly so in China due to the wide and effective control of industrial and municipal wastewater discharges over the past decade. Based on the discussion of rural activities in China, this paper develops a new method of inventory analysis through the definition of elementary unit (EU). This inventory analysis approach is then applied to estimate the total rural pollution loads of COD, TN and TP, as well as their spatial distributions in China. Further analysis is also conducted to investigate the correlations between rural pollution loads and agricultural production outputs, as well as population. It is found that China's agriculture is developing largely at the cost of environment quality, and a high population, as well as the increasing demand for agricultural products, is one of the dominant driving forces. The constructed EKC, which describes the relationship between rural pollution loads and agricultural income, also reveals that current agricultural development in China is mostly far from de-locked from the environmental problem.  相似文献   
46.
It was found that vanadyl porphyrin complexes synthesized from petroleum metal porphyrin concentrates stimulated epoxidation during the olefin oxygenation process. The yields of obtained oxiranes turned out to be 38–75%, depending on the olefin structure. An epoxidation mechanism that suggests the formation of a protonated dioxygen adduct as an intermediate during oxygenation of olefins in the presence of vanadyl porphyrin complexes was proposed. An analogy is drawn between the epoxide formation reaction upon the catalytic oxygenation of olefins and the Prilezhaev reaction.  相似文献   
47.
Presented here are details of the development of a novel membrane integrated circuit (IC) probe card structure based on microsystems technology. The device design allows probing of both solder bumps and pads. A self-limiting sensor was integrated to prolong device lifetime. Comparison with and discussion of the use of modelling is made. Possible enhancements to the probing structure are discussed to improve alignment and measurements. Also shown is data using our microsystems probe card to access a simple IC device. Our device has a contact resistance of less than 0.5 Ω for a force of 0.004 N. A method to implement our probing structure for commercial application and the potential developments which can be made to improve its ease of use are then discussed.  相似文献   
48.
The Magnitogorsk Metallurgical Combine has conducted a study of the effect of technological factors on the hydrogen content of chromium-nickel-molybdenum steel after vacuum degassing. It was established that the most important factor is the hydrogen content of the steel before the degassing operation. The study also determined the effects of the circulation coefficient, the duration of the degassing operation, and the vacuum used in the treatment. __________ Translated from Metallurg, No. 7, pp. 68–69, July, 2006.  相似文献   
49.
50.
Kowalik  J. 《Computer》2006,39(3):104-103
Isolating applied mathematics from computer science harms the profession and those who depend on it.  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