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   260292篇
  免费   3191篇
  国内免费   824篇
电工技术   5130篇
综合类   330篇
化学工业   37262篇
金属工艺   10260篇
机械仪表   8498篇
建筑科学   6106篇
矿业工程   1076篇
能源动力   6397篇
轻工业   22862篇
水利工程   2561篇
石油天然气   3908篇
武器工业   68篇
无线电   34742篇
一般工业技术   50147篇
冶金工业   46545篇
原子能技术   5418篇
自动化技术   22997篇
  2021年   2044篇
  2019年   2035篇
  2018年   3471篇
  2017年   3536篇
  2016年   3733篇
  2015年   2323篇
  2014年   4050篇
  2013年   11301篇
  2012年   6575篇
  2011年   8883篇
  2010年   6988篇
  2009年   7855篇
  2008年   8678篇
  2007年   8622篇
  2006年   7808篇
  2005年   7143篇
  2004年   6889篇
  2003年   6739篇
  2002年   6373篇
  2001年   6469篇
  2000年   6173篇
  1999年   6254篇
  1998年   14244篇
  1997年   10269篇
  1996年   8113篇
  1995年   6414篇
  1994年   5713篇
  1993年   5585篇
  1992年   4555篇
  1991年   4212篇
  1990年   4055篇
  1989年   3782篇
  1988年   3627篇
  1987年   3173篇
  1986年   3073篇
  1985年   3616篇
  1984年   3387篇
  1983年   3039篇
  1982年   2859篇
  1981年   2959篇
  1980年   2761篇
  1979年   2648篇
  1978年   2501篇
  1977年   2947篇
  1976年   3558篇
  1975年   2316篇
  1974年   2315篇
  1973年   2319篇
  1972年   1849篇
  1971年   1746篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
91.
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   
92.
We analyze the non-Fermi liquid behavior in the proximity of the quantum phase transition induced by the strong polarization of the electrons due to local magnetic moments in Ni x Pd1-x alloys. We use the renormalization group approach introduced by Hertz–Mi11is–Moriya (HMM) to estimate the temperature dependence of the electrical resistivity for the case of three dimensional itinerant ferromagnets. We study two different cases, namely, the clean and disordered ferromagnets, and argue that at the present time more experimental data are needed to decide if the HMM theory can accurately describe the physical properties in Ni x Pd1-x alloys.  相似文献   
93.
94.
The operation of a torsional oscillator for detection, of flow-driven textural transitions in, 3He-A is described. The detection technique, tracking the shift of the resonant frequency of the torsional oscillator, allows us to observe textural changes and the presence of vortices in zero magnetic field. It relies on. the anisotropic superfluid density of 3He-A and its change due to reorientation of the Î-texture caused by counterflow.  相似文献   
95.
96.
A newly developed membrane performance enhancer (MPE) was used to prevent membrane fouling in a membrane bioreactor (MBR) process. It transpired that 1,000 mg/l of MPE reduced polysaccharide levels from 41 mg/I to 21 mg/I on average under the experimental condition. Repeated experiments also confirmed that 50-1,000 mg/l of MPE could reduce membrane fouling significantly and increase the intervals between membrane cleanings. Depending on MPE dosages and experimental conditions, trans-membrane pressure (TMP) increase was suppressed for 20-30 days, while baseline TMP surged within a few days. In addition, MPE allowed MBR operation even at 50,000 mg/l of total solid and reduced permeate COD. However, no evidence of toxicity for sludge was found from respiratory works.  相似文献   
97.
The biochemical composition can be seen as a good indicator of both the biodegradability and the methane potential of a given waste. The work presented here is an attempt to elaborate a typology of wastes and to compare it to the anaerobic degradation characteristics. The first data indicate that there is a link between the ligno-cellulosic content of the waste and the biodegradability. When dealing with application to anaerobic digestion processes, having a tool to predict the ability of the waste to be degraded could be of the greatest interest for preventing failures, estimating biogas production, methane content, or for the management of co-digestion processes.  相似文献   
98.
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   
99.
100.
Long-term trends in alpine and prairie snow pack accumulation and melt are affecting streamflow within the Oldman River Basin in southern Alberta, Canada. Unchecked rural and urban development also has contributed to changes in water quality, including enhanced microbial populations and increased waterborne pathogen occurrence. In this study we look at changing environment within the Oldman River Basin and its impact on water quality and quantity. The cumulative effects include a decline in net water supplies, and declining quality resulting in increased risk of disease. Our data indicates that decreases in the rate of flow of water can result in sedimentation of bacterial contaminants within the water column. Water for ecosystems, urban consumption, recreation and distribution through irrigation is often drawn from waterholding facilities such as dams and weirs, and concern must be expressed over the potential for contaminate build-up and disproportionate potential of these structures to pose a risk to human and animal health. With disruption of natural flow rates for water resulting from environmental change such as global warming and/or human intervention, increased attention needs to be paid to use of best management practices to protect source water supplies.  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