全文获取类型
收费全文 | 592038篇 |
免费 | 6881篇 |
国内免费 | 1726篇 |
专业分类
电工技术 | 10864篇 |
综合类 | 544篇 |
化学工业 | 90942篇 |
金属工艺 | 23476篇 |
机械仪表 | 18841篇 |
建筑科学 | 12993篇 |
矿业工程 | 3253篇 |
能源动力 | 15660篇 |
轻工业 | 48907篇 |
水利工程 | 6141篇 |
石油天然气 | 11467篇 |
武器工业 | 44篇 |
无线电 | 67572篇 |
一般工业技术 | 116417篇 |
冶金工业 | 111833篇 |
原子能技术 | 13286篇 |
自动化技术 | 48405篇 |
出版年
2021年 | 5420篇 |
2020年 | 4032篇 |
2019年 | 5209篇 |
2018年 | 8816篇 |
2017年 | 8842篇 |
2016年 | 9438篇 |
2015年 | 5960篇 |
2014年 | 9942篇 |
2013年 | 28077篇 |
2012年 | 15926篇 |
2011年 | 21556篇 |
2010年 | 17156篇 |
2009年 | 19183篇 |
2008年 | 19818篇 |
2007年 | 19673篇 |
2006年 | 17642篇 |
2005年 | 15657篇 |
2004年 | 14853篇 |
2003年 | 14646篇 |
2002年 | 14204篇 |
2001年 | 13949篇 |
2000年 | 13189篇 |
1999年 | 13618篇 |
1998年 | 34199篇 |
1997年 | 23684篇 |
1996年 | 18282篇 |
1995年 | 13799篇 |
1994年 | 12108篇 |
1993年 | 12091篇 |
1992年 | 8967篇 |
1991年 | 8353篇 |
1990年 | 8492篇 |
1989年 | 8048篇 |
1988年 | 7718篇 |
1987年 | 6753篇 |
1986年 | 6689篇 |
1985年 | 7606篇 |
1984年 | 7067篇 |
1983年 | 6380篇 |
1982年 | 5910篇 |
1981年 | 6057篇 |
1980年 | 5716篇 |
1979年 | 5516篇 |
1978年 | 5533篇 |
1977年 | 6232篇 |
1976年 | 8105篇 |
1975年 | 4795篇 |
1974年 | 4512篇 |
1973年 | 4666篇 |
1972年 | 3923篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
S. V. Doronin 《Chemical and Petroleum Engineering》2006,42(7-8):461-464
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
72.
73.
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
74.
75.
Thomas S. Lowry John C. Bright Murray E. Close Christina A. Robb Paul A. White Stewart G. Cameron 《国际水资源开发杂志》2003,19(4):579-592
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
76.
77.
Sheldon H. Jacobson Julie L. Virta Jon M. Bowman John E. Kobza John J. Nestor 《IIE Transactions》2003,35(3):259-269
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
78.
Introduces the current issue of the American Psychologist, which examines the ramifications of the Brown vs. Board of Education decision and its sequelae over the last 50 years, with a special focus on the mixed role of psychological research and practice. Despite the great strides toward a more just society since May 17, 1954, inequities remain in schooling, in social relations, and in economic opportunity. How will history judge American psychology 50 years from now vis-a-vis the possibilities it helped create via Brown? The articles in this special issue suggest several important directions of research and action our field will need to take if the verdict of history is to be a positive one. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
79.
End-to-end congestion control schemes: utility functions, random losses and ECN marks 总被引:1,自引:0,他引:1
We present a framework for designing end-to-end congestion control schemes in a network where each user may have a different utility function and may experience noncongestion-related losses. We first show that there exists an additive-increase-multiplicative-decrease scheme using only end-to-end measurable losses such that a socially optimal solution can be reached. We incorporate round-trip delay in this model, and show that one can generalize observations regarding TCP-type congestion avoidance to more general window flow control schemes. We then consider explicit congestion notification (ECN) as an alternate mechanism (instead of losses) for signaling congestion and show that ECN marking levels can be designed to nearly eliminate losses in the network by choosing the marking level independently for each node in the network. While the ECN marking level at each node may depend on the number of flows through the node, the appropriate marking level can be estimated using only aggregate flow measurements, i.e., per-flow measurements are not required. 相似文献
80.
Use of citric acid for heavy metals extraction from contaminated sewage sludge for land application.
Recent studies revealed that organic acids such as citric and oxalic acids seemed to be more promising as chemical extracting agents for removal of heavy metals from contaminated sludge, since they are biodegradable and can attain a higher metal extraction efficiency at mildly acidic pH compared to other extracting agents. Results of a lab-scale study on the efficiency of citric acid in the extraction of chromium (Cr), copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn) from anaerobically digested sludge, revealed that citric acid seemed to be highly effective in extracting Cr (at 100%), Cu (at 88%), Ni (at 98%) and Zn (at 100%) at pH 2.33, mostly at 5 days leaching time except for Cu and Zn, which are at 1 day and 2 h contact times respectively. Lead removal at the same pH was also high at 95% but at a longer leaching time of 11 days. At pH 3, citric acid seemed to be highly effective in extracting Pb (at 100%) at 1 day leaching time, although higher removals were also attained for Ni (70%) and Zn (80%) at only 2 h leaching time. Chemical speciation studies showed that Cr, Cu and Ni in the sludge sample seem to predominate in residual fractions, while Pb and Zn were found mostly bound to organic and inorganic matter forms, hence the potential of the sludge for land application. 相似文献