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   42136篇
  免费   580篇
  国内免费   788篇
电工技术   724篇
综合类   51篇
化学工业   6378篇
金属工艺   3094篇
机械仪表   1386篇
建筑科学   864篇
矿业工程   151篇
能源动力   1429篇
轻工业   2266篇
水利工程   356篇
石油天然气   1386篇
无线电   3976篇
一般工业技术   10665篇
冶金工业   7219篇
原子能技术   788篇
自动化技术   2771篇
  2021年   340篇
  2020年   276篇
  2019年   374篇
  2018年   665篇
  2017年   657篇
  2016年   743篇
  2015年   539篇
  2014年   807篇
  2013年   2387篇
  2012年   1405篇
  2011年   1884篇
  2010年   1489篇
  2009年   1781篇
  2008年   1624篇
  2007年   1768篇
  2006年   1400篇
  2005年   1226篇
  2004年   1178篇
  2003年   1078篇
  2002年   1066篇
  2001年   1119篇
  2000年   964篇
  1999年   999篇
  1998年   2115篇
  1997年   1658篇
  1996年   1440篇
  1995年   983篇
  1994年   757篇
  1993年   774篇
  1992年   597篇
  1991年   572篇
  1990年   525篇
  1989年   485篇
  1988年   369篇
  1987年   402篇
  1986年   364篇
  1985年   381篇
  1984年   305篇
  1983年   300篇
  1982年   301篇
  1981年   296篇
  1980年   349篇
  1979年   341篇
  1978年   294篇
  1977年   415篇
  1976年   629篇
  1975年   308篇
  1974年   292篇
  1973年   311篇
  1972年   272篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
A clinical case control study to identify prognostic factors present at hospital admission associated with early sequelae and fatal outcome of acute Japanese encephalitis (JE) was carried out in Gusi county, Henan Province, central China from June to September 1991. A total of 70 patients with laboratory-confirmed acute JE were studied, of whom 3 cases died and 33 cases had neurological or psychiatric sequelae at the end of three months follow-up. The results showed that acute JE at younger age, with higher body temperature, high white cell count in CSF, and deep coma present at hospital admission were markers for unfavorable outcomes (sequelae or fatal). A history of the vaccination was not correlated with the early sequelae and fatal outcome of the disease. The paper suggests that early diagnosis and treatment and universal JE vaccination for all susceptible populations are keys for decreasing incidence of sequelae and fatal outcome of acute JE.  相似文献   
112.
113.
An analysis of a wide rectangular radiating slot excited by a microstrip line is described. Coupled integral equations are formulated to find the electric current distribution on the feed line and the electric field in the aperture. The solution is based on the method of moments and using the space domain Sommerfeld-type Green's function. The information about the input impedance or reflection coefficient is extracted from the electric current distribution on the microstrip line utilizing the matrix pencil technique. The theoretical analysis is described and data are presented and compared with other theoretical and experimental results  相似文献   
114.
The oxygen absorption process in highly aligned YBa2Cu3Ox samples in air and in pure oxygen was studied at several constant temperatures. The process can be expressed in two steps, a chemical reaction controlled step and a diffusion controlled step. The kinetic equations are as follows respectively:
(1 − at) ln(1 − at) + at = kDt

The activation energy was calculated using an Arrhenius equation. The technical conditions of heat treatment for oxygen absorption of highly aligned YBa2Cu3Ox crystals are discussed.  相似文献   

115.
The finite-element method (FEM) exhibits a reduced convergence rate when used for the analysis of geometries containing sharp edges where the electromagnetic field is singular. The convergence of the method can be-improved by introducing singular elements that model analytically predicted singular behavior. A number of authors have developed singular elements that are compatible with the scalar FEM. In this paper, we propose a new singular element that is compatible with edge-based vector finite elements and can cope with any order of singularity while preserving the sparsity of the FEM equations. Edge-based singular elements more correctly model singular fields and thus require fewer unknowns, while avoiding the introduction of spurious modes in the numerical solution. Numerical results verify that the convergence of the FEM is significantly improved  相似文献   
116.
Here we present a case of a patient with a massive ossification of annulus fibrosus and longitudinal ligament at the level C3-C4, C4-C5 and C5-C6, also called the Van Swaay bridge. One can observe a propulsion of the pharingeal tissue at the level of the massive Van Swaay bridge between C5 and C6 which caused pressure and dysphagia.  相似文献   
117.
Inflammation of a mixture of Furnon-3KhP refractory mortar prepared using a binary reducer consisting of metallic Al and Mg powders is considered. It is shown that the inflammation temperature can be decreased by 100 – 150°C. Mechanical characteristics of refractory bricks joined by the mortar are determined.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 10, pp. 16 – 19, October, 1996.  相似文献   
118.
The alarm lists presented to control center operators are usually difficult to interpret. The authors present an expert system that processes the alarm lists in Portuguese control centers. This system makes an intelligent synthesis of the available information and presents it in a flexible and structured way. It uses an original approach to deal with temporal reasoning and real-time constraints. The system incorporates an explanation module that enables its use as a tutor for novice operators  相似文献   
119.
MCF7 and ZR75-1 breast cancer cells grow as adherent monolayers in tissue culture. Treatment with the serum serine protease plasmin causes them to detach and to grow as floating multicellular spheroids. Two plasmin activators, urokinase plasminogen activator and streptokinase, induce the same growth pattern changes in the presence of plasminogen. Serum contains also plasminogen activator inhibitors. Aged serum, deficient in plasminogen activator inhibitors, converts spontaneously monolayer breast cancer cells into multicellular spheroids which readily revert to monolayer growth after addition of fresh serum. Urokinase blocks the reversion. The formation of multicellular spheroids does not affect the proliferative rate of breast tumor cells but endows tumor cells with increased resistance to the chemotherapeutic drugs, doxorubicin and paclitaxel.  相似文献   
120.
This case report describes an accessory hepatic duct (AHD) identified by intraoperative cholangiography during excisional surgery of a choledochal cyst (CC). The accessory duct was divided and reconstructed successfully to the Roux-en-Y jejunal loop. The postoperative course was uneventful, and follow-up abdominal sonography revealed neither evidence of biliary tract obstruction nor atrophic changes of the liver. It is advocated that an AHD should be meticulously reconstructed if it is divided during excisional surgery of a CC.  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