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   30185篇
  免费   2478篇
  国内免费   1416篇
电工技术   1747篇
技术理论   1篇
综合类   1986篇
化学工业   4640篇
金属工艺   1454篇
机械仪表   1785篇
建筑科学   2167篇
矿业工程   911篇
能源动力   768篇
轻工业   2485篇
水利工程   543篇
石油天然气   1761篇
武器工业   206篇
无线电   2796篇
一般工业技术   2977篇
冶金工业   3535篇
原子能技术   320篇
自动化技术   3997篇
  2024年   142篇
  2023年   505篇
  2022年   891篇
  2021年   1196篇
  2020年   863篇
  2019年   738篇
  2018年   843篇
  2017年   933篇
  2016年   828篇
  2015年   1106篇
  2014年   1477篇
  2013年   1795篇
  2012年   1864篇
  2011年   2140篇
  2010年   1829篇
  2009年   1767篇
  2008年   1787篇
  2007年   1616篇
  2006年   1542篇
  2005年   1382篇
  2004年   922篇
  2003年   762篇
  2002年   716篇
  2001年   625篇
  2000年   613篇
  1999年   656篇
  1998年   1211篇
  1997年   795篇
  1996年   590篇
  1995年   426篇
  1994年   360篇
  1993年   311篇
  1992年   169篇
  1991年   108篇
  1990年   93篇
  1989年   60篇
  1988年   75篇
  1987年   66篇
  1986年   33篇
  1985年   16篇
  1984年   13篇
  1983年   13篇
  1982年   12篇
  1981年   15篇
  1980年   34篇
  1979年   4篇
  1977年   27篇
  1976年   99篇
  1975年   5篇
  1959年   2篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
61.
62.
The postbuckling behavior of plates on an elastic foundation is studied by using the boundary element method (BEM). A new fundamental solution of lateral deflection is derived through the resolution theory of a differential operator, and a set of boundary element formulae in incremental form is presented. By using these formulae, the BEM solution procedure becomes relatively simple. The results of a number of numerical examples are compared with existing solutions and good agreement is observed. It shows that the proposed method is effective for solving the postbuckling problems of plates with arbitrary shape and various boundary conditions.  相似文献   
63.
Zinc ferrite is a promising sensor material. In this paper, thin films of nanocrystalline zinc ferrite were deposited on alumina substrates by nebulization of a 0.01-M solution of a mixture of ZnCl/sub 2/ and FeCl/sub 3/ in ethanol (Zn:Fe=1:2) followed by pyrolysis and annealing in flowing air. The resulting films were characterized by X-ray diffraction and scanning electron microscopy, and the gas-sensing properties of as-deposited films were also investigated.  相似文献   
64.
农村电网的无功功率补偿   总被引:1,自引:0,他引:1  
阐述农村电网无功补偿的意义 .针对农村电网和农村用户的特点 ,提出在农网改造中 ,对各级电力线路 ,以提高农村电网的功率因数 ,保证农网安全、可靠和经济运行 .和电力用户进行无功补偿的方法  相似文献   
65.
以往双侧向测井仪动态范围小,测量精度低,为此开发了DLL23XA双侧向测井仪。该仪器主要单元采用厚膜电路,稳定性、一致性好;深、浅屏流源采用可变功率控制,提高了仪器的动态范围。仪器采用3506P例进行数据传输,可方便地配接各种地面系统。  相似文献   
66.
Recent evidence indicates few differences between patients recruited through advertising and by consultation referral, and there is some suggestion that those recruited through advertising are more representative of the target community population. However little has been reported on differences in placebo response and compliance in these two patient groups. We conducted a retrospective chart review of 49 patients with major depressive disorder (MDD), recruited through advertising or consultation, randomized to placebo in five clinical trials. Variables included demographics, clinical history, efficacy, compliance, and completion data. Homogeneity was demonstrated for most variables. Differences in placebo groups included significantly lower Hamilton Rating Scale for Depression (HAM-D) scores for the advertisement group throughout the trials. Advertisement patients were also more likely to be early placebo responders and in remission at Days 14 and 28. No differences were found in completion rates or reasons for early termination. Compliance was excellent for both groups. Early placebo response of the advertisement group reinforces the need for trials of at least 8 weeks. In addition, consultation patients may have a more severe illness and be treatment resistant, suggesting they are less generalizable to community practice populations.  相似文献   
67.
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   
68.
秦岭  章静 《电信科学》1993,9(6):32-35
本文介绍了集传真技术、通信技术、微型计算机技术于一体的微机传真系统,提出了微机传真系统在硬件接口及报表识别上的实现方法。  相似文献   
69.
70.
一个表示和运用非功能性需求的框架   总被引:1,自引:0,他引:1  
本文分析了一个软件开发进程中表示和运用非功能性需求的综合框架,该框架的目的是开发一套技术以调整软件开发进程中的设计决策,从而强调了依据非功能需求,探索合理化的软件开发进程。  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