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   363821篇
  免费   6337篇
  国内免费   1472篇
电工技术   5272篇
综合类   2533篇
化学工业   53771篇
金属工艺   13334篇
机械仪表   10828篇
建筑科学   9929篇
矿业工程   1140篇
能源动力   8974篇
轻工业   36243篇
水利工程   3603篇
石油天然气   2344篇
武器工业   9篇
无线电   44150篇
一般工业技术   67120篇
冶金工业   56826篇
原子能技术   3791篇
自动化技术   51763篇
  2022年   1310篇
  2021年   2550篇
  2020年   1983篇
  2019年   2257篇
  2018年   17507篇
  2017年   16469篇
  2016年   13514篇
  2015年   3674篇
  2014年   5027篇
  2013年   14438篇
  2012年   11627篇
  2011年   20206篇
  2010年   16636篇
  2009年   14838篇
  2008年   16726篇
  2007年   17447篇
  2006年   9379篇
  2005年   9393篇
  2004年   9049篇
  2003年   8861篇
  2002年   7725篇
  2001年   7468篇
  2000年   6854篇
  1999年   7334篇
  1998年   18813篇
  1997年   12858篇
  1996年   9618篇
  1995年   7158篇
  1994年   6220篇
  1993年   6068篇
  1992年   4191篇
  1991年   3983篇
  1990年   3749篇
  1989年   3573篇
  1988年   3456篇
  1987年   2745篇
  1986年   2651篇
  1985年   3341篇
  1984年   2960篇
  1983年   2680篇
  1982年   2488篇
  1981年   2556篇
  1980年   2346篇
  1979年   2158篇
  1978年   1986篇
  1977年   2348篇
  1976年   3082篇
  1975年   1664篇
  1974年   1552篇
  1973年   1633篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
Indoor body-area channel model for narrowband communications   总被引:1,自引:0,他引:1  
Using wireless sensors placed on a person to continuously monitor health information is a promising new application. At the same time, new low-power wireless standards such as Bluetooth and Zigbee have been proposed for short range, low data-rate communication matching the requirements of these bio-medical applications. However, there are currently few measurements or models describing propagation around the body. To address this problem, electromagnetic waves near the torso are measured and a statistical model is derived for communication in the 915 MHz and 2.45 GHz industrial, scientific and medical bands associated with Zigbee and Bluetooth. Measurement setup and statistical analysis are described.  相似文献   
122.
There are some foods that contain mutagenic or carcinogenic agents, some of which occur naturally and others that may be formed during preparation or cooking. Several foods such as legumes, also contain natural antimutagens and/or anticarcinogens. Lupine is one such legume that contains high amounts of protein (40%) and oils (14%). About 90 species of lupine have been reported throughout Mexico. However, the use of this crop as a source of food has been limited by the presence of antinutritional agents such as phenolic compounds (PC), carbohydrates (CH) and quinolizidinic alkaloids (Qas). It has also been suggested that consuming these compounds can affect human health and may even reduce the risk of disease. The objective of this work was to determine the effect of PC, CH and Qas, isolated and quantified from Lupinus campestris on the mutagenicity of 1-nitropyrene (1-NP) as a model mutagen and we used the Salmonella typhimurium tester strain YG1024 by the Kado microsuspension method. The results indicate that L. campestris seeds have 11 mg (+)catechin equivalent g(-1) seed coat; 120.3 mg g(-1) seeds and 2.13 mg g(-1) seeds of PC, CH and Qas, respectively. 1-NP mutagenicity was inhibited by 86% for PC, 76% for CH and 75% for Qas at concentrations of 200, 512 and 13.6 microg/tube, respectively.  相似文献   
123.
The structure of the recently introduced Brazilian government programme for monitoring pesticide residues in six major agricultural products is described. Residues found from the analysis of samples of tomatoes and strawberries are discussed in detail. The much greater frequency of detection of pesticide residues, many of which are not approved for use in Brazil, in produce being sold on the domestic market, as opposed to that produced for export, is of major concern. It is perceived that this new monitoring programme will become permanent and be used to underpin enforcement actions that will need to be taken to reduce the numbers of incidents of illegal residues occurring, particularly in fresh fruits and vegetables.  相似文献   
124.
Neutron-irradiated quartz crystal is one of the interesting materials for the study of the glassy dynamics. The temperature and frequency dependence of the sound velocity in amorphous materials at temperatures above the low-temperature maximum is not well understood. In this paper we present the results of our measurements of the variation of the ultrasound velocity (270 – 650 MHz) in neutron-irradiated quartz crystals with different irradiation doses in temperature range 5 - 35 K. We have found that the temperature dependence of the ultrasound velocity is linear in the sample with a dose < 10 19 n/cm2 and is sublinear in samples with a dose > 10 19 n/cm2 . We discuss our results in the framework of the different theoretical approaches. PACS numbers: 61.43. j, 62.65.+k, 63.  相似文献   
125.
126.
127.
128.
129.
A high-gain ballistic hot-electron device is described. The GaAs-AlGaAs heterostructure device, with a 21-mm-thick pseudomorphic In 0.12Ga0.88As base, had a current gain of 27 at 77 K and 41 at 4.2 K. As characteristically seen in ballistic devices, transfer into the L valley limited the maximum gain. The Γ-L valley separation in the strained In0.12Ga0.88As was estimated to be about 380 meV  相似文献   
130.
The TELEMAC project brings new methodologies from the Information and Science Technologies field to the world of water treatment. TELEMAC offers an advanced remote management system which adapts to most of the anaerobic wastewater treatment plants that do not benefit from a local expert in wastewater treatment. The TELEMAC system takes advantage of new sensors to better monitor the process dynamics and to run automatic controllers that stabilise the treatment plant, meet the depollution requirements and provide a biogas quality suitable for cogeneration. If the automatic system detects a failure which cannot be solved automatically or locally by a technician, then an expert from the TELEMAC Control Centre is contacted via the internet and manages the problem.  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