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   13957篇
  免费   483篇
  国内免费   46篇
电工技术   184篇
综合类   24篇
化学工业   3335篇
金属工艺   242篇
机械仪表   342篇
建筑科学   801篇
矿业工程   38篇
能源动力   346篇
轻工业   1133篇
水利工程   82篇
石油天然气   22篇
武器工业   1篇
无线电   1167篇
一般工业技术   2291篇
冶金工业   2061篇
原子能技术   130篇
自动化技术   2287篇
  2023年   74篇
  2022年   174篇
  2021年   225篇
  2020年   150篇
  2019年   180篇
  2018年   253篇
  2017年   212篇
  2016年   315篇
  2015年   275篇
  2014年   362篇
  2013年   816篇
  2012年   607篇
  2011年   802篇
  2010年   620篇
  2009年   611篇
  2008年   643篇
  2007年   638篇
  2006年   581篇
  2005年   473篇
  2004年   464篇
  2003年   360篇
  2002年   373篇
  2001年   280篇
  2000年   268篇
  1999年   238篇
  1998年   417篇
  1997年   329篇
  1996年   268篇
  1995年   243篇
  1994年   218篇
  1993年   220篇
  1992年   185篇
  1991年   115篇
  1990年   141篇
  1989年   122篇
  1988年   139篇
  1987年   111篇
  1986年   80篇
  1985年   158篇
  1984年   152篇
  1983年   114篇
  1982年   110篇
  1981年   163篇
  1980年   114篇
  1979年   135篇
  1978年   85篇
  1977年   104篇
  1976年   100篇
  1975年   99篇
  1973年   73篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
This paper explores the linkage between the entrepreneurial orientation of established firms and the development of radical innovation. Through five case studies in firms involved in radical innovation, three propositions are developed, suggesting that proactiveness, risk‐taking and autonomy stimulate the development of radical innovation, whereas competitive aggressiveness does not necessarily do so, as radical innovations are directed towards the creation of entirely new arenas of business, where existing competitors are not present.  相似文献   
2.
3.
In-service fracture of helicopter windshields was studied. Simulated catastrophic fracture tests were conducted by firing alumina and steel spheres onto stationary tempered and as-received glass panels. The results were studied by Hertzian analysis and modified Auerbach's relations. Thermally tempered glass shows much higher impact resistance than that estimated from superposition of residual stresses. Subcritical impact sites exhibit slow crack growth in tempered plates, eventually leading to fracture of the entire plate.  相似文献   
4.
This paper presents an enhanced approach to predictive modeling for determining tool-wear in end-milling operations based on enhanced-group method of data handling (e-GMDH). Using milling input parameters (speed, feed, and depth-of-cut) and response (tool wear), the data for the model is partitioned into training and testing datasets, and the training dataset is used to realize a predictive model that is a function of the input parameters and the coefficients determined. In our approach, we first present a methodology for modeling, and then develop predictive model(s) of the problem being solved in the form of second-order equations based on the input data and coefficients realized. This approach leads to some generalization because it becomes possible to predict not only the test data obtained during experimentation, but other test data outside the experimental results can also be used. Moreover, this approach makes it easy to present the realized solution in a form that can be further optimized for the input parameters using some optimization techniques. The results realized using our e-GMDH method are promising, and the comparative study presented shows that the e-GMDH outperforms polynomial neural network (PNN); moreover, it is more flexible than the conventional GMDH, which tends to produce nonlinear solutions even for simple problems. In the investigation, the extended particle swarm optimization (PSO) technique was applied to obtain the optimal parameters. Consequently, the modeling approach is extremely useful in realizing a computer-aided process-planning system in an advanced manufacturing environment.  相似文献   
5.
A Kanban system facilitates lean principles in a simple and effective way. While reportedly successful in many manufacturing firms, the conventional Kanban systems using physical cards suffer from human errors, limited tracking capability, and so on. To make the information flow leaner, software providers add new features to their existing programs for manufacturing systems to computerize Kanban activities. As Web-based technologies advance rapidly, developing an entirely Web-based Kanban system appears to be feasible and promising. This paper presents the advantages, limitations, and challenges of Web-based Kanban systems. An experimental program has been developed based on PHP+MySQL, a popular Web programming platform. The server-executed program features cross-platform compatibility, real-time tracking and performance monitoring, and greatly enhanced information contents compared to physical Kanbans. Human errors are minimized by the automated transactions; nevertheless, the interfacing and data maintenance require further research efforts.  相似文献   
6.
Roasting coffee led to a drop in the ochratoxin A (OTA) concentration, as measured by the reference method, especially for dark type roasts. The way the beverage was prepared also affected the OTA content, which could paradoxically be higher than that of the initial roasted coffee. Assays on the thermal stability of pure OTA showed that it ought to be found in larger quantities in roasted coffee. This suggested that OTA was masked by reactions with the substrate during roasting. The absence of OTA in green coffee is therefore the best guarantee of safety.  相似文献   
7.
8.
Theophylline pellets were coated with Eudragit RS 30 D in a miniature fluid-bed pan coater called MiniWiD developed recently. The dispersions were plasticized with varying amounts of triethyl citrate (TEC), dibutyl phthalate (DBP), and polyethylene glycol 6000 (PEG) and applied at different temperatures ranging from 25 to 45 °C. Theophylline release was tested by dissolution using the USP Apparatus 2 (paddle) in 0.1 N hydrochloric acid under sink conditions over 6 hours.

At a coating level of 4 % (0.7 mg/cm2) sustained-release profiles were obtained from dispersions plasticized with TEC or DBP. By reducing the amount of plasticizer from 20 to 10%, films with higher permeabilities were obtained. This effect was compensated by tempering the pellets at 50 deg;C for 24 hours. The coating temperature had little effect on the dissolution profiles of TEC-plasticized films and no effect on films with DBP.

Coatings plasticized with 20% PEG were applied at temperatures ranging from 25 to 45 °C. These films required a coating level of about 18 % (3.3 mg/cm2) to provide comparable sustained-release properties. In contrast to DBP and TEC, a strong influence of the coating temperature on the release rates was observed in which higher temperatures led to slower release rates. This behavior can be explained by the minimum film-forming temperature (MFT). Since PEG does not lower the MFT of Eudragit RS 30 D, the application of these films below the MFT of 45 °C is associated with a lower degree of film formation.  相似文献   
9.
10.
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