全文获取类型
收费全文 | 523479篇 |
免费 | 7425篇 |
国内免费 | 2420篇 |
专业分类
电工技术 | 10693篇 |
技术理论 | 5篇 |
综合类 | 1714篇 |
化学工业 | 81493篇 |
金属工艺 | 19865篇 |
机械仪表 | 15153篇 |
建筑科学 | 13478篇 |
矿业工程 | 2438篇 |
能源动力 | 13034篇 |
轻工业 | 50003篇 |
水利工程 | 5013篇 |
石油天然气 | 9051篇 |
武器工业 | 250篇 |
无线电 | 61063篇 |
一般工业技术 | 98582篇 |
冶金工业 | 96857篇 |
原子能技术 | 9962篇 |
自动化技术 | 44670篇 |
出版年
2021年 | 4378篇 |
2019年 | 3898篇 |
2018年 | 6424篇 |
2017年 | 6229篇 |
2016年 | 6674篇 |
2015年 | 4983篇 |
2014年 | 8274篇 |
2013年 | 23785篇 |
2012年 | 13814篇 |
2011年 | 18694篇 |
2010年 | 14792篇 |
2009年 | 16377篇 |
2008年 | 17506篇 |
2007年 | 17524篇 |
2006年 | 15511篇 |
2005年 | 13952篇 |
2004年 | 13084篇 |
2003年 | 12564篇 |
2002年 | 12356篇 |
2001年 | 12580篇 |
2000年 | 11874篇 |
1999年 | 12237篇 |
1998年 | 28054篇 |
1997年 | 20554篇 |
1996年 | 16030篇 |
1995年 | 12261篇 |
1994年 | 11275篇 |
1993年 | 10850篇 |
1992年 | 8396篇 |
1991年 | 7980篇 |
1990年 | 7980篇 |
1989年 | 7788篇 |
1988年 | 7489篇 |
1987年 | 6303篇 |
1986年 | 6501篇 |
1985年 | 7387篇 |
1984年 | 6940篇 |
1983年 | 6485篇 |
1982年 | 5791篇 |
1981年 | 6117篇 |
1980年 | 5630篇 |
1979年 | 5749篇 |
1978年 | 5465篇 |
1977年 | 6151篇 |
1976年 | 7990篇 |
1975年 | 4803篇 |
1974年 | 4535篇 |
1973年 | 4628篇 |
1972年 | 3886篇 |
1971年 | 3453篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Hook T.B. Brown J. Cottrell P. Adler E. Hoyniak D. Johnson J. Mann R. 《Electron Devices, IEEE Transactions on》2003,50(9):1946-1951
Lateral scattering of retrograde well implants is shown to have an effect on the threshold voltage of nearby devices. The threshold voltage of both NMOSFETs and PMOSFETs increases in magnitude for conventional retrograde wells, but for triple-well isolated NMOSFETs the threshold voltage decreases for narrow devices near the edge of the well. Electrical data, SIMS, and SUPREM4 simulations are shown that elucidate the phenomenon. 相似文献
22.
A multi-level attention framework for tracking and segmentation of humans and objects under complex occlusions is investigated,
featuring an effective probabilistic appearance-based technique for pixel reclassification during object grouping and splitting.
A novel ’spatial-depth affinity metric’ is introduced in the conventional likelihood function, utilising information of both
spatial locations of pixels and dynamic depth ordering of the component objects in grouping. Depth ordering estimation is
achieved through a combination of top-down and bottom-up approach. Experiments on some realworld difficult scenarios of low
quality and highly compressed videos demonstrate the very promising results achieved. 相似文献
23.
Y Terashima H Ozaki R R Giri T Tano S Nakatsuji R Takanami S Taniguchi 《Water science and technology》2006,54(8):55-63
Environmental pollution by low concentrations of 2,4-Dichlorophenoxyacetic acid (2,4-D) is a concern these days due to ever increasingly stringent regulations. Photocatalysis with immobilized TiO2 fiber is a promising oxidation method. Laboratory experiments on photocatalytic degradation of 0.045 mmol l(-1) 2,4-D with the world's first high-strength TiO2 fiber catalyst were carried out in a continuous flow reactor in which the degradations were, in general, similar to those with high 2,4-D concentrations investigated elsewhere. Degradation and mineralization of 2,4-D were significantly enhanced with no initial pH adjustments. The rate constants for total organic carbon (TOC) without pH adjustment were about two-fold bigger than the pH adjustment cases. CO2 gas measurement and carbon mass-balance were carried out for the first time, where about 34% organic carbon converted into CO2 gas during four-hour oxidation. 2,4-Dichlorophenol (2,4-DCP), phenol, benzyl alcohol and two unknowns (RT = 2.65 and 3.78 min.) were detected as aromatic intermediates while Phenol was the new aromatic in HPLC analysis. Dechlorination efficiencies were high (> 70%) in all the cases, and more than 90% efficiencies were observed in chloride mass balance. Bigger flow rates and solution temperature fixed at 20 degrees C without pH adjustment greatly enhanced 2,4-D mineralization. These results can be an important basis in applying the treatment method for dioxin-contaminated water and wastewater. 相似文献
24.
The performance of the energy consumption of an electronic valve and a classical thermostatic valve has been compared when these expansion valves are adopted in a vapour compression plant subjected to a cold store. The main aim is to verify experimentally which type of expansion valve would be preferable from energy point of view when a classical thermostat or a fuzzy logic algorithm are used as the control system for the refrigeration capacity. The fuzzy logic‐based control is able to modulate continuously the compressor speed through an inverter. The results show that with a fuzzy algorithm, the thermostatic expansion valve allows an energy saving of about 8% in comparison with the electronic valve. When on–off control is used, the electric energy consumption obtained both with the electronic valve and with the thermostatic valve is comparable. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
25.
The effects of the cuticle and epicuticular waxes of grapefruit, strawberry and apple on the photodegradation and penetration of chlorpyrifos-methyl were studied. Photodegradation experiments were conducted by exposing the insecticide to the light of a xenon lamp in the presence of a film of wax extracted from the fruit surface. The half-life of chlorpyrifos-methyl irradiated in absence of waxes was 9.6 min. The half-lives of pesticide irradiated in the presence of wax extracts of apple, grapefruit and strawberry were 83, 34 and 26 min, respectively. In penetration studies, fruit with and without wax layers were treated with an aqueous suspension of pesticide. The penetration of the pesticide from the cuticle to the pulp was measured after 24 h. Samples without wax contained a higher total amount of insecticide than those with wax. No pesticide was detected in samples of apple and grapefruit pulp. Residues were detected in all fractions of strawberry. The waxes and cuticle appear to have some effect on the photodegradation and penetration of chlorpyrifos-methyl in fruit samples. 相似文献
26.
27.
Kruk Menno R.; Halász József; Meelis Wout; Haller József 《Canadian Metallurgical Quarterly》2004,118(5):1062
Aggressive behavior induces an adrenocortical stress response, and sudden stressors often precipitate violent behavior. Experiments in rats revealed a fast, mutual, positive feedback between the adrenocortical stress response and a brain mechanism controlling aggression. Stimulation of the aggressive area in the hypothalamus rapidly activated the adrenocortical response, even in the absence of an opponent and fighting. Hypothalamic aggression, in turn, was rapidly facilitated by a corticosterone injection in rats in which the natural adrenocortical stress response was prevented by adrenalectomy. The rapidity of both effects points to a fast, mutual, positive feedback of the controlling mechanisms within the time frame of a single conflict. Such a mutual facilitation may contribute to the precipitation and escalation of violent behavior under stressful conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
28.
This study investigates the citation patterns in the journal, Medical Principles and Practice from its inception in 1989 through 2000 (volumes 1-9). The data set includes 4740 references appended to the 221 original
research articles. All of the citations were entered into a ProCite database for analysis. Specifically, this study addresses:
(1) bibliometric patterns of cited works in terms of publication format, subject scatter, authorship characteristics, age
of citations, geographic distribution, and language distribution; (2) productivity of journal titles; (3) the role of self-citation;
and (4) how selected bibliometric indicators apply. Some of the findings include: journal articles are most frequently cited;
English language publications dominate the literature; there is a trend of multiple authorship; and the pattern of aging is
below the norm for medical literature. The results of the study can provide a benchmark to measure the user behavior of a
particular group of researchers as well as for the provision of collection development and management decisions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
29.
30.
S.M. Savaresi F.L. Taroni F. Previdi S. Bittanti 《Mechatronics, IEEE/ASME Transactions on》2004,9(3):569-579
The problem considered in this paper is the design and tuning of the control system of a power-split continuously variable transmission (CVT) used in high-power tractors. Power-split CVTs are characterized by the combination of a traditional mechanical transmission and by a continuously-variable transmission. This guarantees, at the same time, smooth variations of the transmission-ratio and high efficiency of the overall transmission system. The control architecture of an hydrostatic power-split CVT is constituted by three main parts: 1) servo-controller on the current of the valve which drives the hydraulic transmission; 2) a servo-controller on the hydraulic transmission-ratio; and 3) a synchronizer which coordinates the hydraulic and the mechanical parts of the CVT. In this work, these three controllers are fully developed, including: design, implementation, and evaluation on an experimental system. 相似文献