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   43198篇
  免费   925篇
  国内免费   180篇
电工技术   523篇
综合类   631篇
化学工业   4632篇
金属工艺   586篇
机械仪表   861篇
建筑科学   831篇
矿业工程   390篇
能源动力   406篇
轻工业   2093篇
水利工程   594篇
石油天然气   55篇
武器工业   5篇
无线电   1972篇
一般工业技术   3418篇
冶金工业   21463篇
原子能技术   183篇
自动化技术   5660篇
  2023年   191篇
  2022年   114篇
  2021年   94篇
  2019年   51篇
  2018年   458篇
  2017年   673篇
  2016年   1054篇
  2015年   783篇
  2014年   435篇
  2013年   430篇
  2012年   2150篇
  2011年   2438篇
  2010年   680篇
  2009年   782篇
  2008年   621篇
  2007年   635篇
  2006年   576篇
  2005年   3364篇
  2004年   2578篇
  2003年   2057篇
  2002年   857篇
  2001年   742篇
  2000年   292篇
  1999年   627篇
  1998年   6186篇
  1997年   3825篇
  1996年   2513篇
  1995年   1463篇
  1994年   1080篇
  1993年   1109篇
  1992年   255篇
  1991年   308篇
  1990年   306篇
  1989年   283篇
  1988年   295篇
  1987年   224篇
  1986年   202篇
  1985年   174篇
  1984年   78篇
  1983年   89篇
  1982年   133篇
  1981年   180篇
  1980年   194篇
  1979年   60篇
  1978年   102篇
  1977年   612篇
  1976年   1324篇
  1975年   100篇
  1973年   46篇
  1971年   49篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
81.
Ultrasound imaging allows the evaluation of the degree of emergency of a patient. However, in some instances, a well-trained sonographer is unavailable to perform such echography. To cope with this issue, the Mobile Tele-Echography Using an Ultralight Robot (OTELO) project aims to develop a fully integrated end-to-end mobile tele-echography system using an ultralight remote-controlled robot for population groups that are not served locally by medical experts. This paper focuses on the user interface of the OTELO system, consisting of the following parts: an ultrasound video transmission system providing real-time images of the scanned area, an audio/video conference to communicate with the paramedical assistant and with the patient, and a virtual-reality environment, providing visual and haptic feedback to the expert, while capturing the expert's hand movements. These movements are reproduced by the robot at the patient site while holding the ultrasound probe against the patient skin. In addition, the user interface includes an image processing facility for enhancing the received images and the possibility to include them into a database.  相似文献   
82.
This study examined associations of temperament at ages 6 to 12 with body-mass index (BMI) and waist circumference (WC) at ages 24 to 30 years. The participants were 619 men and women derived from the population-based Cardiovascular Risk in Young Finns Study. Temperament was operationalized as (negative) emotionality, sociability, and activity. High emotionality predicted increased BMI, independently of WC, and independently of childhood and adulthood risk factors for adult obesity. None of the temperament dimensions had any associations with WC after controlling for BMI. The findings suggest that temperamental difficulty in childhood may be a useful risk indicator for general body mass in adulthood, and the mechanisms relating temperament with body mass should be further explored. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
83.
Motivated by a study of similar problems stated for factors of words, we study forbidden subwords of a language or a word. A procedure for obtaining the set of all words avoiding a given set of subwords is presented. On the other hand, an algorithm for computing the set of minimal forbidden subwords for a word is given. The case of a two-letter alphabet appears to be particularly interesting and it is considered separately.  相似文献   
84.
85.
A Discfilter with 10 and 18 microm filter openings, respectively, was placed in parallel to a flotation plant for separation of biological flocs from a post-denitrifying Kaldnes Moving Bed Process, the last treatment step at the municipal wastewater treatment plant at Sj?unda, Malm?, Sweden. The effluent concentrations from the 10 and 18 microm filter were 2-5 and 2-8 mg SS L(-1), respectively, which is comparable to, or better than, the flotation plant. Comparison with experiences from activated sludge plants shows that the Discfilter works especially well after the Kaldnes process. Particle size distribution (PSD) studies show that particles larger than the filter openings of 10 and 18 microm are separated with approximately 90% efficiency, whereas most of the smaller particles pass the filter. This fact indicates that the major particle separation mechanism is physical blocking. These findings point to the possibility of improving the prediction of the separation efficiency by combining measurements of turbidity and suspended solids with particle size analysis.  相似文献   
86.
Ohne Zusammenfassung  相似文献   
87.
This paper presents an analysis of the data collected in the ambient vibration test of the International Guadiana cable-stayed Bridge, which links Portugal and Spain, based on different output-only identification techniques: peak-picking, frequency domain decomposition, covariance-driven stochastic subspace identification, and data-driven stochastic subspace identification. The purpose of the analysis is to compare the performance of the four techniques and evaluate their efficiency in dealing with specific challenges involved in the modal identification of the tested cable-stayed bridge, namely the existence of closely spaced modes, the perturbation produced by the local vibration of stay-cables, and the variation of modal damping coefficients with wind velocity. The identified natural frequencies and mode shapes are compared with the corresponding modal parameters provided by a previously developed numerical model. Additionally, the variability of some modal damping coefficients is related with the variation of the wind characteristics and associated with a component of aerodynamic damping.  相似文献   
88.
The preoxidation of a highly polluted waste pharmaceutical fermentation broth using wet air oxidation (WAO) has been studied as a possible method for the effective removal of organics. The applied (pre)treatment method should enhance the biotreatability of the pharmaceutical fermentation broth in terms of reduced initial toxicity and higher biodegradability. Preliminary experiments in the pilot biological treatment plant were successful only at low organic loads, whereas the system collapses at higher ones. The characterization of the fermentation broth was started by common physicochemical analysis, whereas several bioassays were used to determine its impact on biological treatment plants and the environment. Toxicity prior to and after WAO was determined using the acute Vibrio fischeri test, measurement of inhibition of O2 consumption, and the Daphnia magna acute test. Ready biodegradability of the treated and untreated broth has also been assessed. WAO experiments were accomplished in the 2?L batch reactor at different temperatures (240/280°C) and operating pressures. WAO experiments confirmed reduction of the toxicity toward microorganisms, whereas oxidized wastewater was more toxic to daphnids. Biodegradability of the oxidized broth has also been enhanced. Further work has been focused on designing appropriate combination of WAO and biological processes.  相似文献   
89.
90.
After considering the stabilization of a specific class of stochastic nonlinear systems in a companion paper, in this second part, we address the classical question of when is a stabilizing (in probability) controller optimal and show that for every system with a stochastic control Lyapunov function it is possible to construct a controller which is optimal with respect to a meaningful cost functional. Then we return to the problem from Part I and design an optimal backstepping controller whose cost functional includes penalty on control effort and which has an infinite gain margin.  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