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   589815篇
  免费   6757篇
  国内免费   1726篇
电工技术   10850篇
综合类   543篇
化学工业   90288篇
金属工艺   23428篇
机械仪表   18778篇
建筑科学   12920篇
矿业工程   3246篇
能源动力   15566篇
轻工业   48310篇
水利工程   6123篇
石油天然气   11451篇
武器工业   44篇
无线电   67480篇
一般工业技术   116141篇
冶金工业   111670篇
原子能技术   13278篇
自动化技术   48182篇
  2021年   5301篇
  2020年   3964篇
  2019年   5141篇
  2018年   8745篇
  2017年   8744篇
  2016年   9359篇
  2015年   5895篇
  2014年   9851篇
  2013年   27893篇
  2012年   15769篇
  2011年   21398篇
  2010年   17029篇
  2009年   19069篇
  2008年   19709篇
  2007年   19577篇
  2006年   17563篇
  2005年   15602篇
  2004年   14806篇
  2003年   14599篇
  2002年   14172篇
  2001年   13920篇
  2000年   13173篇
  1999年   13603篇
  1998年   34139篇
  1997年   23654篇
  1996年   18255篇
  1995年   13772篇
  1994年   12088篇
  1993年   12075篇
  1992年   8957篇
  1991年   8349篇
  1990年   8489篇
  1989年   8044篇
  1988年   7706篇
  1987年   6750篇
  1986年   6685篇
  1985年   7599篇
  1984年   7061篇
  1983年   6377篇
  1982年   5906篇
  1981年   6053篇
  1980年   5710篇
  1979年   5512篇
  1978年   5532篇
  1977年   6231篇
  1976年   8096篇
  1975年   4794篇
  1974年   4512篇
  1973年   4666篇
  1972年   3922篇
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
61.
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications.  相似文献   
62.
63.
The hydrogen annealing process has been used to improve surface roughness of the Si-fin in CMOS FinFETs for the first time. Hydrogen annealing was performed after Si-fin etch and before gate oxidation. As a result, increased saturation current with a lowered threshold voltage and a decreased low-frequency noise level over the entire range of drain current have been attained. The low-frequency noise characteristics indicate that the oxide trap density is reduced by a factor of 3 due to annealing. These results suggest that hydrogen annealing is very effective for improving device performance and for attaining a high-quality surface of the etched Si-fin.  相似文献   
64.
Current features are considered in the calculation of carrying capacities for constructions in engineering plant (EP). Methods and algorithms are described for EP calculations with comprehensive incorporation of the effects from technological and working defects on the behavior of structures under standard and emergency conditions. __________ Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 8, pp. 38–40, August, 2006.  相似文献   
65.
66.
Phase equilibria involving spinel solid solutions, delafossite, and hematite in the Fe–Cu–O system are studied by emf measurements in solid-electrolyte galvanic cells. The results demonstrate that, above 1250 K, Fe3O4 and CuFe2O4 form a continuous series of solid solutions. At lower temperatures, the solid solution disproportionates with the formation of delafossite and Fe2O3, and two spinel solid solutions appear: one based on Fe3O4 and the other based on Cu2FeO4. The compositions of the spinel phases in equilibrium with delafossite and Fe2O3 are determined in the range 1100–1250 K.  相似文献   
67.
68.
The primary objective of this project is to identify gaps, whether real or perceived, that hinder effective groundwater management in New Zealand. These gaps show as gaps in information, gaps in implementation, gaps in technological and management tools, and gaps in understanding of fundamental processes. The secondary objective is to propose a management strategy to close the identified gaps. Several methods are used to meet these objectives: surveys distributed to selected staff in each regional council; the review of various written reports; the analysis of land-use databases; and private consultation within each regional council. Results show that groundwater management in New Zealand is generally reactionary with the main gaps being in strategic planning and national guidelines. Most gaps appear to be predominantly information and implementation issues. In some cases there are gaps in the understanding of fundamental processes within an aquifer system, including the long-term effects of land-use on groundwater quality. An adaptive management approach is suggested as a means of closing these gaps.  相似文献   
69.
70.
Modeling aviation baggage screening security systems: a case study   总被引:1,自引:0,他引:1  
Aviation security protects vital national interests, as well as passengers and aircraft. Key components of an aviation security system include baggage and passenger screening devices and operations. Determining how and where to assign (deploy) such devices can be quite challenging. Moreover, even after such systems are in place, it can be difficult to measure their effectiveness. This paper describes how discrete optimization models can be used to address these questions, based on three performance measures that quantify the effectiveness of airport baggage screening security device systems. These models are used to solve for optimal airport baggage screening security device deployments considering the number of passengers on a set of flights who have not been cleared using a security risk assessment system in use by the Federal Aviation Administration (i.e., passengers whose baggage is subjected to screening), the number of flights in this set, and the size of the aircraft for such flights. Several examples are provided to illustrate these results, including an example that uses data available from the Official Airline Guide.  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