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   1124篇
  免费   24篇
  国内免费   1篇
电工技术   11篇
化学工业   134篇
金属工艺   8篇
机械仪表   9篇
建筑科学   35篇
矿业工程   3篇
能源动力   15篇
轻工业   125篇
水利工程   5篇
石油天然气   2篇
无线电   88篇
一般工业技术   162篇
冶金工业   436篇
原子能技术   9篇
自动化技术   107篇
  2022年   10篇
  2021年   17篇
  2020年   13篇
  2019年   17篇
  2018年   7篇
  2017年   18篇
  2016年   12篇
  2015年   19篇
  2014年   17篇
  2013年   45篇
  2012年   27篇
  2011年   27篇
  2010年   35篇
  2009年   20篇
  2008年   33篇
  2007年   30篇
  2006年   20篇
  2005年   24篇
  2004年   17篇
  2003年   22篇
  2002年   27篇
  2001年   19篇
  2000年   18篇
  1999年   36篇
  1998年   93篇
  1997年   82篇
  1996年   48篇
  1995年   32篇
  1994年   33篇
  1993年   35篇
  1992年   23篇
  1991年   10篇
  1990年   17篇
  1989年   18篇
  1988年   15篇
  1987年   11篇
  1986年   15篇
  1985年   9篇
  1984年   9篇
  1982年   10篇
  1981年   8篇
  1979年   11篇
  1978年   6篇
  1977年   17篇
  1976年   19篇
  1973年   12篇
  1971年   6篇
  1970年   9篇
  1968年   8篇
  1965年   7篇
排序方式: 共有1149条查询结果,搜索用时 15 毫秒
101.
Field-programmable gate arrays (FPGAs) are becoming an increasingly important implementation medium for digital logic. One of the most important keys to using FPGAs effectively is a complete, automated software system for mapping onto the FPGA architecture. Unfortunately, many of the tools necessary require different techniques than traditional circuit implementation options, and these techniques are often developed specifically for only a single FPGA architecture. In this paper we describe automatic mapping tools for Triptych, an FPGA architecture with improved logic density and performance over commercial FPGAs. These tools include a simulated-annealing placement algorithm that handles the routability issues of fine-grained FPGAs, and an architecture-adaptive routing algorithm that can easily be retargeted to other FPGAs. We also describe extensions to these algorithms for mapping asynchronous circuits to Montage, the first FPGA architecture to completely support asynchronous and synchronous interface applications  相似文献   
102.
The present study examines the concentrations of vanadium, bromine and sulphur contained within cryofixed/freeze dried blood cells of the ascidian Phallusia philippinensis (Millar, 1975). Elemental profiles of seven cell types were obtained using the National University of Singapore nuclear microscope. Morula cells were found to contain the following mean values; 0.8% vanadium, 3.5% bromine and 6.1% sulphur. Signet ring cells contained 0.5% vanadium, 2.4% bromine and 1.5% sulphur. Compartment cells had 0.1% vanadium, 2.1% bromine and 2.4% sulphur. Other less abundant cell types such as lymphocytes, macrogranular amoebocytes, carotenoid pigment cells and granular amoebocytes were also analysed and found to contain 0.4%, 0.7%, 0.2% and 1.0% vanadium, 2.0%, 1.6%, 0.6% and 1.2% bromine and 1.3%, 1.5%, 0.3% and 4.3% sulphur respectively. Sulphur occurred in high levels in all cell types, which could indicate its involvement in the vanadium concentration process, while bromine, incorporated into complexes, may be utilised for anti-fouling rather than as a deterrent to predators.  相似文献   
103.
Atrial natriuretic peptide (ANP) is produced and secreted by atrial cells. We measured calf capillary filtration rate with prolonged venous-occlusion plethysmography of supine healthy male subjects during pharmacologic infusion of ANP (48 pmol/kg/min for 15 min; n = 6) and during placebo infusion (n = 7). Results during infusions were compared to prior control measurements. ANP infusion increased plasma [ANP] from 30 +/- 4 to 2,568 +/- 595 pmol/l. Systemic hemoconcentration occurred during ANP infusion: mean hematocrit and plasma colloid osmotic pressure increased 4.6 and 11.3%, respectively, relative to preinfusion baseline values (p < 0.05). Mean calf filtration, however, was significantly reduced from 0.15 to 0.08 ml/100 ml/min with ANP. Heart rate increased 20% with ANP infusion, whereas blood pressure was unchanged. Calf conductance (blood flow/arterial pressure) and venous compliance were unaffected by ANP infusion. Placebo infusion had no effect relative to prior baseline control measurements. Although ANP induced systemic capillary filtration, in the calf, filtration was reduced with ANP. Therefore, pharmacologic ANP infusion enhances capillary filtration from the systemic circulation, perhaps at upper body or splanchnic sites or both, while having the opposite effect in the leg.  相似文献   
104.
We sought to estimate the impact of maternal HIV testing and prenatal care on the potential to reduce vertical transmission through zidovudine (AZT) use by HIV-infected mothers. We evaluated the prepartum maternal HIV diagnosis rate, prenatal care, disease stage, and vertical transmission rate (from a two-part mixture model) using New York State Medicaid and vital statistics data for HIV-infected mothers and their singletons in 1985-90. We used published data to estimate the effect of AZT on vertical transmission and expert input to define other parameters for the model. Our HIV-infected (N = 1514) had a vertical transmission rate of 27.0%. HIV was diagnosed prepartum for 39.5% of women in 1990. Transmission would have been 22.2% if AZT had been taken only by the subset of women diagnosed prepartum with HIV and receiving prenatal care by 34 weeks gestation (86.7%). Transmission would have dropped to 11.2% if all women had been diagnosed prepartum with HIV and received adequate prenatal care. The observed deficiencies in prenatal care and maternal HIV diagnosis rates in this Medicaid population-based cohort must be addressed to realize the promise of AZT to reduce vertical transmission.  相似文献   
105.
引言 我工作时喜欢有点背景音乐,会打开Windows Media Player,按下PLAY键来播放音乐.但有电话打进来时,我希望能不用鼠标在桌面上到处找Media Player图标来调低音量或按暂停键.  相似文献   
106.
The pseudouridine residues of ribosomal RNA   总被引:3,自引:0,他引:3  
  相似文献   
107.
The effects of loss of resources and illness symptoms on experienced anger, anger expression, and supporter's anger was studied among patients with severe chronic breathing disorder. Both illness symptoms and resource loss were related to greater anger. Angry feelings, in turn, led to more angry behavior. This angry behavior, in turn, resulted in increased anger of supporters. This process illustrates how chronic stress depletes both personal resources and social resources, making the individual increasingly vulnerable to further stressful experiences, inevitably to be confronted in chronic stress sequences. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
108.
Greenhouse gas emissions are likely to rise faster than growth in population and more than double for water supply and wastewater services over the next 50 years in South East Queensland (SEQ), Australia. New sources of water supply such as rainwater tanks, recycled water, and desalination currently have greater energy intensity than traditional sources. In addition, direct greenhouse gas emissions from reservoirs and wastewater treatment and handling have potentially the same magnitude as emissions from the use of energy. Centralized and decentralized water supply and wastewater systems are considered for a scenario based upon a government water supply strategy for the next 50 years. Many sources of data have large uncertainties which are estimated following the IPCC Good Practice Guidelines. Important sources of emissions with large uncertainties such as rainwater tanks and direct emissions were identified for further research and potential mitigation of greenhouse gas emissions.  相似文献   
109.
Carbon electrodes coupled with electrochemical detection have been used extensively for the investigation of biogenic amines. Herein we report the fabrication and characterization of carbonaceous electrodes prepared from pyrolyzed parylene C (PPC) films. High-aspect ratio carbonaceous microelectrodes have been prepared by masking PPC coated pipets with an insulating parylene C film. PPC thin film electrodes were characterized electrochemically, spectroscopically, and with electron microscopy. The procedures described here offer a route to fabrication of thin film carbon electrodes that can be patterned and produced in parallel. These electrodes are similar to carbon electrodes derived from pyrolyzed photoresist films but do not require spin-coating or lithography and can readily coat three-dimensional surfaces.  相似文献   
110.
Vitamins are essential to human health, and dietary supplements containing vitamins are widely used by individuals hoping to ensure they have adequate intake of these important nutrients. Measurement of vitamins in nutritional formulations is necessary to monitor regulatory compliance and in studies examining the nutrient intake of specific populations. Liquid chromatographic methods, primarily with UV absorbance detection, are well established for both fat- and water-soluble measurements, but they do have limitations for certain analytes and may suffer from a lack of specificity in complex matrices. Liquid chromatography-mass spectrometry (LC-MS) provides both sensitivity and specificity for the determination of vitamins in these matrices, and simultaneous analysis of multiple vitamins in a single analysis is often possible. In this work, LC-MS methods were developed for both fat- and water-soluble vitamins and applied to the measurement of these analytes in two NIST Standard Reference Materials. When possible, stable isotope labeled internal standards were employed for quantification.  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