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   11043篇
  免费   315篇
  国内免费   40篇
电工技术   121篇
综合类   22篇
化学工业   2109篇
金属工艺   169篇
机械仪表   230篇
建筑科学   578篇
矿业工程   31篇
能源动力   171篇
轻工业   774篇
水利工程   54篇
石油天然气   11篇
武器工业   1篇
无线电   593篇
一般工业技术   1443篇
冶金工业   3546篇
原子能技术   70篇
自动化技术   1475篇
  2023年   58篇
  2022年   120篇
  2021年   144篇
  2020年   108篇
  2019年   120篇
  2018年   168篇
  2017年   110篇
  2016年   191篇
  2015年   191篇
  2014年   249篇
  2013年   563篇
  2012年   397篇
  2011年   545篇
  2010年   410篇
  2009年   389篇
  2008年   432篇
  2007年   421篇
  2006年   364篇
  2005年   312篇
  2004年   291篇
  2003年   228篇
  2002年   228篇
  2001年   173篇
  2000年   166篇
  1999年   214篇
  1998年   877篇
  1997年   557篇
  1996年   374篇
  1995年   291篇
  1994年   229篇
  1993年   270篇
  1992年   151篇
  1991年   108篇
  1990年   121篇
  1989年   109篇
  1988年   119篇
  1987年   88篇
  1986年   77篇
  1985年   103篇
  1984年   95篇
  1983年   62篇
  1982年   74篇
  1981年   97篇
  1980年   88篇
  1979年   85篇
  1978年   72篇
  1977年   112篇
  1976年   138篇
  1975年   59篇
  1973年   47篇
排序方式: 共有10000条查询结果,搜索用时 0 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.
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   
4.
5.
Midden and Dahl, in a recent paper, have presented important data on the inactivation of bacteria by singlet oxygen. In analyzing the data, use was made of a theory published earlier by the present author. The purpose of this paper is to point out that theory and experiment can be brought into better agreement by assuming that the interaction of singlet oxygen with the bacteria takes place in an essentially lipid environment rather than aqueous.  相似文献   
6.
7.
Nickel molybdate catalysts used in several different upgrading reactions of coal-derived materials from low-rank Australian coals have been regenerated and their activity assessed using a number of physical and chemical techniques. Regeneration of spent coked catalysts for 20 hours in air at 450°C was sufficient to restore chemical hydrogenation activity to catalyst used for pre-asphaltene, asphaltene and oil upgrading, provided poisoning of the catalyst surface by other impurities, principally chlorine-containing molecules, had not occurred.  相似文献   
8.
Soft sediments from the Detroit River were analyzed for the USEPA priority pollutants to generally characterize contaminant distribution. Forty-three were detected. Highest heavy metal concentrations were found in the Trenton Channel and immediately downstream of Grosse Ile. They ranged from an area mean (N = 2) of 0.19 mg/kg mercury to 338.7 mg/kg zinc (dry weight). Polynuclear aromatic hydrocarbons ranged from 0.1 mg/kg to 38.8 mg/kg (mean, N = 2) with the highest levels near Grosse Ile. PCBs ranged from 0.015 mg/kg to 1.7 mg/kg (mean, N = 2). Organochlorine pesticides were not detected except for a trace of heptachlor in one sample. Sediment contamination in the Detroit River is widespread with higher concentrations on the U.S. side downstream of the Rouge River and in the Trenton Channel. The significance of these in-place pollutants to biota and as a source to Lake Erie is still unknown.  相似文献   
9.
10.
A new technique for understanding the organization of complex circuits in the vertebrate brain, scanning laser photostimulation, is described. This approach is based on the photolysis of a caged form of the excitatory neurotransmitter glutamate. Computer-controlled photostimulation and whole cell recording in brain slices allow the construction of detailed maps of the position, strength, sign and number of inputs converging on a single postsynaptic neuron. Scanning laser photostimulation offers many advantages over current techniques: spatial resolution is superb, fibers of passage are not activated, and thousands of presynaptic locations can be stimulated. This review describes the technique of photostimulation, outlines the instrumentation, necessary to implement it, and discusses the interpretation of photostimulation-derived data. Several examples of applications, ranging from mapping circuits in the mammalian visual cortex to determining receptor distributions on single neurons are considered. Although still in its early stages, scanning laser photostimulation offers neuroscientists a powerful tool for determining the organization and function of local brain circuits.  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