全文获取类型
收费全文 | 653821篇 |
免费 | 7538篇 |
国内免费 | 1114篇 |
专业分类
电工技术 | 11753篇 |
综合类 | 552篇 |
化学工业 | 102977篇 |
金属工艺 | 27749篇 |
机械仪表 | 20919篇 |
建筑科学 | 14481篇 |
矿业工程 | 5158篇 |
能源动力 | 16047篇 |
轻工业 | 50902篇 |
水利工程 | 8341篇 |
石油天然气 | 18434篇 |
武器工业 | 42篇 |
无线电 | 68279篇 |
一般工业技术 | 135158篇 |
冶金工业 | 112212篇 |
原子能技术 | 17340篇 |
自动化技术 | 52129篇 |
出版年
2021年 | 6048篇 |
2019年 | 5824篇 |
2018年 | 10243篇 |
2017年 | 10422篇 |
2016年 | 10940篇 |
2015年 | 6732篇 |
2014年 | 11486篇 |
2013年 | 29339篇 |
2012年 | 17658篇 |
2011年 | 23654篇 |
2010年 | 19005篇 |
2009年 | 21212篇 |
2008年 | 21532篇 |
2007年 | 21187篇 |
2006年 | 18454篇 |
2005年 | 16777篇 |
2004年 | 15955篇 |
2003年 | 15568篇 |
2002年 | 15128篇 |
2001年 | 14738篇 |
2000年 | 14137篇 |
1999年 | 13864篇 |
1998年 | 32334篇 |
1997年 | 23354篇 |
1996年 | 18120篇 |
1995年 | 13877篇 |
1994年 | 12514篇 |
1993年 | 12334篇 |
1992年 | 9580篇 |
1991年 | 9363篇 |
1990年 | 9263篇 |
1989年 | 8937篇 |
1988年 | 8627篇 |
1987年 | 7881篇 |
1986年 | 7652篇 |
1985年 | 8556篇 |
1984年 | 7800篇 |
1983年 | 7534篇 |
1982年 | 6801篇 |
1981年 | 6990篇 |
1980年 | 6720篇 |
1979年 | 6912篇 |
1978年 | 6904篇 |
1977年 | 7519篇 |
1976年 | 9454篇 |
1975年 | 6288篇 |
1974年 | 6094篇 |
1973年 | 6203篇 |
1972年 | 5397篇 |
1971年 | 4976篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The requirements on an object-oriented DBMS for management of information in a large, complex enterprise are presented. These requirements aid in the achievement of an environment characterized by data sharing, open architectures, application and data portability, and assurance of data integrity. They were defined from the point of view of a user of the DBMS; therefore they describe the expected functionality of the DBMS and do not specify the method of implementation to achieve this functionality. They encompass requirements on the data model, query and data manipulation languages, the system architecure, interfaces to the system, change management, and transaction management. 相似文献
992.
Using a continuous, in-line, nondestructive technique based on the maximum bubble pressure method, the surface tension of
the wash water in a mechanical dishwashing machine has been monitored. This technique has enabled surface tension to be used
as a controlled variable, providing feedback to regulate the amount of surfactant added. Assuming the mechanical force of
the water spray is adequate to remove bound soil from the dish surface, the food soil may be titrated against surfactant,
providing an indirect indication as to when the dishes are clean. This technique also could be applied to a recirculated wash
solution for in-place cleaning. 相似文献
993.
994.
995.
996.
Triton polymers are commercial surfactants whose molecular weight distributions are conventionally determined by means of high-performance liquid chromatography (HPLC). However, in the case of the important octylphenol ethoxylates [p-C8H17-C6H4-O-(CH2CH2O)n-H], HPLC cannot resolve individual oligomers of high molecular weight Triton surfactants (e.g., greater than 2000 u or so; u = unified atomic mass unit). In this paper, we show that laser desorption Fourier transform ion cyclotron resonance mass spectrometry (LD/FT/ICR/MS) provides a simple and accurate measure of such Triton surfactant molecular weight distributions up to at least 3500 u, based on a single-shot laser pulse measurement of a few seconds duration. Comparison of LD/FT/ICR/MS and HPLC molecular weight distributions of low molecular weight surfactants shows that laser desorption/ionization produces minimal fragmentation and thus offers an accurate measure of the relative abundances of the neutral oligomers, without the need for prior chromatographic separation of the components. Moreover, for all Triton polymer molecular weight distributions (700-3000 u), LD/FT/ICR/MS provides much more highly resolved profiles of oligomer relative abundances. Finally, LD/FT/ICR/MS reveals the presence of poly(ethylene oxide) side products of the polymerization process, which are not observed by HPLC with conventional ultraviolet absorption detection. 相似文献
997.
Analysis on the effectiveness of the 20-H rule for printed-circuit-board layout to reduce edge-radiated coupling 总被引:1,自引:0,他引:1
Montrose M.I. Er-Ping Li Hong-Fang Jin Wei-Liang Yuan 《Electromagnetic Compatibility, IEEE Transactions on》2005,47(2):227-233
This paper presents the quantified study of the electromagnetic radiation mechanism of the 20-H rule using a numerical approach that has not yet been systematically addressed. The 20-H rule is a rule-of-thumb layout technique recommended to minimize radiated fields propagating from the edges of a printed circuit board (PCB) coupling onto nearby structures. Propagating electromagnetic fields may corrupt adjacent cable assemblies, sheet metal enclosures, and aperture openings. The magnitude of this design rule is investigated using the full-wave finite-difference time-domain (FDTD) method. An analysis on whether benefits exist from use of this rule is examined and under what conditions the rule is valid when correctly implemented. The purpose of this paper is to provide insight into the validity of the 20-H rule, recognizing that every PCB will have different simulation results. FDTD is used to capture a snapshot view of field propagation. This view allows one to determine the validity of the 20-H rule at a single point of time within a dynamic structure and what may be expected when digital components are finally added to a PCB assembly, which generally negates simulated results. 相似文献
998.
V. V. Andrikanis B. V. Andreev K. B. Rudyak F. V. Karpeko A. V. Ivanov N. N. Parsent’ev V. S. Nikitchenko G. V. Danilov I. A. Sinel’nikov 《Chemistry and Technology of Fuels and Oils》2006,42(3):229-234
Increasing attention at oil refineries is being focused on solving environmental problems caused by stiffening of the requirements
for emissions of harmful substances into air and water. Advanced technologies that reduce the effect of industrial enterprises
on the environment to the minimum are becoming increasingly in demand. Treatment of process wastewaters to remove hydrogen
sulfide and ammonia is one such problem of the modern refinery with cat crackers.
__________
Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 3, pp. 52–55, May–June, 2006. 相似文献
999.
Several coats, such as gray cast iron, cast iron alloyed with nickel and copper, nickel-aluminum, Nichrome (nickel-chromium
alloy), bronze, etc., have been investigated. Corrosion resistance of coats in a medium based on drilling mud and sodium chloride
and sulfate solutions has been checked. Alloyed cast iron admixed with tin-based compounds showed the best results.
__________
Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 3, pp. 43–44, March, 2006. 相似文献
1000.
Troya A. Maharatna K. Krstic M. Grass E. Jagdhold U. Kraemer R. 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(2):672-686
In this paper, we propose low-power designs for the synchronizer and channel estimator units of the Inner Receiver in wireless local area network systems. The objective of the work is the optimization, with respect to power, area, and latency, of both the signal processing algorithms themselves and their implementation. Novel circuit design strategies have been employed to realize optimal hardware and power efficient architectures for the fast Fourier transform, arc tangent computation unit, numerically controlled oscillator, and the decimation filters. The use of multiple clock domains and clock gating reduces the power consumption further. These blocks have been integrated into an experimental digital baseband processor for the IEEE 802.11a standard implemented in the 0.25mum- 5-metal layer BiCMOS technology from Institute for High Performance Microelectronics. 相似文献