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   73473篇
  免费   5394篇
  国内免费   2775篇
电工技术   3879篇
技术理论   6篇
综合类   4427篇
化学工业   12690篇
金属工艺   3949篇
机械仪表   4803篇
建筑科学   5190篇
矿业工程   2404篇
能源动力   2232篇
轻工业   4769篇
水利工程   1000篇
石油天然气   5279篇
武器工业   460篇
无线电   7652篇
一般工业技术   9433篇
冶金工业   3932篇
原子能技术   750篇
自动化技术   8787篇
  2024年   301篇
  2023年   1263篇
  2022年   2104篇
  2021年   2904篇
  2020年   2198篇
  2019年   1960篇
  2018年   2297篇
  2017年   2503篇
  2016年   2075篇
  2015年   2694篇
  2014年   3438篇
  2013年   4215篇
  2012年   4343篇
  2011年   4855篇
  2010年   4170篇
  2009年   3950篇
  2008年   3851篇
  2007年   3711篇
  2006年   3792篇
  2005年   3430篇
  2004年   2284篇
  2003年   2083篇
  2002年   1868篇
  2001年   1636篇
  2000年   1799篇
  1999年   2048篇
  1998年   1769篇
  1997年   1425篇
  1996年   1406篇
  1995年   1186篇
  1994年   957篇
  1993年   717篇
  1992年   546篇
  1991年   428篇
  1990年   327篇
  1989年   254篇
  1988年   226篇
  1987年   142篇
  1986年   120篇
  1985年   96篇
  1984年   66篇
  1983年   40篇
  1982年   42篇
  1981年   30篇
  1980年   25篇
  1979年   13篇
  1977年   7篇
  1976年   8篇
  1975年   5篇
  1945年   4篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Eighty-six children who completed immunization with the two trivalent poliovirus vaccines, live attenuated (OPV) and enhanced potency inactivated (EIPV), in one of four schedules (OPV-OPV-OPV, EIPV-EIPV-EIPV, EIPV-OPV-OPV, and EIPV-EIPV-OPV) at 1 year of age were monitored serologically over the subsequent 4 years and challenged with OPV at 5 years of age. Each of the immunization groups exhibited an initial 10- to 100-fold decline in neutralizing antibody to poliovirus types 1, 2, and 3 during the first 2 years of follow-up; thereafter antibody titers stabilized. The EIPV-EIPV-OPV group maintained the highest antibody levels throughout the observation period, including the response to OPV challenge at 5 years of age. These data suggest that immunization with OPV, EIPV, and combinations of the two vaccines confers long-term immunity. Optimal systemic immunity was associated with two or more doses of EIPV.  相似文献   
102.
103.
We describe a case of positional dyspnea due to compression of the tracheobronchial tree by an extensive thoracic aneurysm. In a 77-year-old woman with long-standing systemic hypertension, intermittent anterior chest pain gradually developed over several years. She had no history of asthma or thoracic trauma. She was admitted to our hospital because of sudden, severe shortness of breath. The breathlessness was markedly worse when she lay on her back or on her right side. On physical examination, she was in acute respiratory distress with cyanosis, severe hypertension (180/110 mmHg), tachycardia, and inspiratory stridor. A chest X-ray film showed loss of volume and nearly complete radiopacity of the left hemithorax. Arterial blood gas analysis revealed an arterial oxygen partial pressure of 54.8 mmHg, a carbon dioxide partial pressure of 39.8 mmHg, and an oxygen saturation of 84.5 percent on room air. Computed tomographic examination of the thorax showed dilation of the aortic arch and descending aorta, and marked compression of the trachea and the left main bronchus. Examination with a fiberoptic bronchoscope revealed extrinsic compression of the trachea just proximal to the carina. The patient's symptoms stabilized. However, she did not undergo surgery because of her age and because of the size of the aneurysm. She died due to rupture of the aneurysm.  相似文献   
104.
采用P型InP衬底新月型结构制备了1.48μm大功率激光器,该激光器与单模光纤耦合输出功率大于40mW。  相似文献   
105.
A class of algorithms has been developed which detects QRS complexes in the electrocardiogram (ECG). The algorithms employ nonlinear transforms derived from multiplication of backward differences (MOBD). The algorithms are evaluated with the American Heart Association ECG database, and comparisons are made with the algorithms reported by Okada (1979) and by Hamilton and Tompkins (1986). The MOBD algorithms provide a good performance tradeoff between accuracy and response time, making this type of algorithm desirable for real-time microprocessor-based implementation  相似文献   
106.
By using scanning polarization force microscopy,the deliquescence process and the atomic steps on the cleavage surface of CaCO3 in air were studied in situ.Under an exposure to medium umidity(-57%),the sloiw step movement has been observed.  相似文献   
107.
108.
A crucial step in manufacturing microcircuits is the wire bonding process in which a very thin gold wire must be formed to connect two surfaces in the microcircuit. The quality of the wire bond can be measured by visual inspection and a pull test—both of which are high-reliability, high-cost approaches to statistical process control. Westinghouse wanted to develop a high-reliability, low-cost quality assurance system. In this paper, we report on a year-long study to construct a neural network model that is capable of predicting the quality of wire bonds. The results of our modeling efforts reveal that neural networks are useful tools for statistical process control problems.  相似文献   
109.
Synthesis of ultrafine LiCoO2 powders by the sol-gel method   总被引:8,自引:0,他引:8  
Ultrafine high-temperature (HT) LiCoO2 powders were synthesized by the sol-gel method using polyacrylic acid (PAA) as a chelating agent. The decomposition process of the gel precursor was examined to determine the crystallization temperature and the dependence of the physicochemical properties of HT-LiCoO2 powders on the PAA quantity was extensively investigated. Polycrystalline HT-LiCoO2 powders, composed of very uniformly sized ultrafine particulates with an average particle size of 30–50 nm and a specific surface area of 2.3–17 m2g–1, could be obtained at the lower calcination temperature of 550 °C and the shorter calcination time of 1 h compared to the solid-state reaction.  相似文献   
110.
本文旨在通过对玻璃钢管道及其标准的发展历史、产品特点、基本设计原理、质量影响因素及选用时应注意的事项等方面的介绍,使用户与工程设计人员对该产品有一个比较全面的了解,以便更好地选用并受益于这种管材。  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