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   5411篇
  免费   91篇
  国内免费   16篇
电工技术   56篇
综合类   8篇
化学工业   661篇
金属工艺   119篇
机械仪表   103篇
建筑科学   47篇
矿业工程   15篇
能源动力   177篇
轻工业   185篇
水利工程   30篇
石油天然气   7篇
无线电   552篇
一般工业技术   832篇
冶金工业   2359篇
原子能技术   28篇
自动化技术   339篇
  2024年   13篇
  2023年   43篇
  2022年   79篇
  2021年   160篇
  2020年   82篇
  2019年   84篇
  2018年   121篇
  2017年   85篇
  2016年   101篇
  2015年   73篇
  2014年   110篇
  2013年   206篇
  2012年   130篇
  2011年   182篇
  2010年   144篇
  2009年   154篇
  2008年   141篇
  2007年   111篇
  2006年   110篇
  2005年   85篇
  2004年   66篇
  2003年   71篇
  2002年   55篇
  2001年   61篇
  2000年   64篇
  1999年   107篇
  1998年   705篇
  1997年   461篇
  1996年   297篇
  1995年   193篇
  1994年   172篇
  1993年   183篇
  1992年   66篇
  1991年   77篇
  1990年   56篇
  1989年   46篇
  1988年   58篇
  1987年   52篇
  1986年   46篇
  1985年   33篇
  1984年   32篇
  1983年   22篇
  1982年   37篇
  1981年   28篇
  1980年   39篇
  1979年   21篇
  1978年   14篇
  1977年   63篇
  1976年   137篇
  1973年   8篇
排序方式: 共有5518条查询结果,搜索用时 62 毫秒
31.
PURPOSE: To determine the radiologic characteristics of cystic dystrophy of the duodenal wall. MATERIALS AND METHODS: Ten patients with cystic dystrophy of the duodenal wall and chronic pancreatitis underwent ultrasonography (US) (n = 10), computed tomography (CT) (n = 10), endoscopic US (n = 5), and endoscopic retrograde cholangiopancreatography (ERCP) (n = 9). Cystic dystrophy of the duodenal wall was classified as either cystic or solid. The imaging findings were retrospectively analyzed and compared with findings at pancreatoduodenectomy (n = 10). RESULTS: The more frequent cystic type (n = 7) of cystic dystrophy of the duodenal wall was characterized by the presence of easily recognizable cystic lesions (diameter, more than 1 cm), located within the thickened wall of the second portion of the duodenum. The solid type (n = 3) of cystic dystrophy of the duodenal wall demonstrated fibrous thickening of the duodenal wall within which small cysts (diameter, less than 1 cm) were present. The intraduodenal cysts were usually elongated or bilobate with a thick wall. The thickening of the duodenal wall appeared as a solid layer between the duodenal lumen and the pancreas, hypoechoic at US, isoattenuating at unenhanced CT, and hypoattenuating in the early phase (after initiation of infusion of contrast material) and isoattenuating in the late phase (after completion of infusion) at contrast material-enhanced CT. Findings at retrospective analysis of CT and endoscopic US images were characteristic. CONCLUSION: Imaging modalities, notably CT and endoscopic US, helped establish the diagnosis of cystic dystrophy of the duodenal wall.  相似文献   
32.
Four parameters are defined to measure the performance of a teletext system, namely, the probability of delivering a message within specified time, the transmission efficiency, the average number of errors per page, and the throughput. Each of them is derived and computational results are presented taking the UK teletext system as an example. These parameters are compared in their ability to characterize the performance of the teletext system  相似文献   
33.
Radiation sickness manifestations have been studied in dogs exposed to electrons (electron energy 25 MeV) and gamma-neutron radiation (neutron energies of 0.37 and 1.2 MeV) in a wide dose range. Dose-response relationships have been calculated for mortality and some clinical manifestations of the intestinal and cerebral forms of radiation sickness. With regard to mortality, the highest effect has been observed for gamma-neutron radiation with a neutron energy of 1.2 MeV. For equal physical doses and for those equally effective in relation to mortality, clinical manifestations of damage are more prominent following exposure to electrons.  相似文献   
34.
Acyl-CoA:cholesterol acyltransferase (ACAT) is the enzyme largely responsible for intracellular cholesterol esterification. A systemic inhibitor of ACAT is believed to be able to slow or even reverse the atherosclerotic process. Towards that goal, a series of cyclic sulfides, derived from the hetero-Diels-Alder reaction of thioaldehydes with 1,3-dienes, and bearing carboxamide substituents, were prepared and evaluated for in vitro (in several tissues and species) and ex vivo ACAT inhibition. Minor changes in subsequent structure were found to have a significant effect in optimization of the biological activity of this series of compounds.  相似文献   
35.
Most nursing school curricula address the pathologic nature of illness, the nursing care of clients who are ill, the prevention of illness, and the promotion of health. There seems to be minimal discussion, however, both in nursing curricula and in textbooks, of the alleviation of suffering or of how nurses know that someone is suffering. The article describes a phenomenologic analysis of 12 nursing students' lived experiences of caring for individuals who were suffering. The voices of the students as they chronicled their experiences are exemplars of clinical scholarship as described in the literature.  相似文献   
36.
37.
38.
A gypsum wall assembly was exposed to an intense real‐scale compartment fire. For the wall assembly, temperatures were measured at the exposed face, within the stud cavity, and at the unexposed face during the fire exposure. Total heat flux gauges were used to measure the temporal variation of the energy incident on the walls, and cameras, both visual and infrared, were used to image the unexposed face of the wall assembly during the fire exposure. The behaviour of the wall assembly under the fire load is discussed as are current model results for a simulation of the fire test. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
39.
There are numerous physiological effects of spinal anaesthesia. This chapter focuses on the physiological effects that are of clinical relevance to the anaesthesiologist, and provides suggestions for successful management of this simple and popular technique. The mechanisms and clinical significance of spinal-anaesthesia-induced hypotension, bradycardia and cardiac arrest are reviewed. The increasing popularity of ambulatory spinal anaesthesia requires knowledge that long-acting local anaesthetics, such as bupivacaine, impair the ability to void far longer than short-acting local anaesthetics, such as lidocaine. The importance of thermoregulation during spinal anaesthesia, and the clinical consequences of spinal-anaesthesia-induced hypothermia are reviewed. Effects of spinal anaesthesia on ventilatory mechanics are also highlighted. Lastly, the sedative and minimum-alveolar-concentration-sparing effects of spinal anaesthesia are discussed to reinforce the need for the judicious use of sedation in the perioperative setting.  相似文献   
40.
The removal of Cu(II) by adsorption on fly ash has been found to be concentration, pH and temperature dependent. The kinetics of adsorption indicates the process to be diffusion controlled. The Langmuir constants have been calculated at different temperatures, and the adsorption has been found to be endothermic (ΔH = 15.652 kcal mol?1). The maximum removal is observed at pH 8.0, and variation in adsorption with pH has been explained on the basis of surface ionisation and complexation.  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