全文获取类型
收费全文 | 2617篇 |
免费 | 142篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 32篇 |
综合类 | 8篇 |
化学工业 | 641篇 |
金属工艺 | 46篇 |
机械仪表 | 28篇 |
建筑科学 | 174篇 |
矿业工程 | 6篇 |
能源动力 | 74篇 |
轻工业 | 219篇 |
水利工程 | 20篇 |
石油天然气 | 5篇 |
无线电 | 257篇 |
一般工业技术 | 531篇 |
冶金工业 | 271篇 |
原子能技术 | 17篇 |
自动化技术 | 433篇 |
出版年
2023年 | 40篇 |
2022年 | 42篇 |
2021年 | 109篇 |
2020年 | 55篇 |
2019年 | 63篇 |
2018年 | 60篇 |
2017年 | 64篇 |
2016年 | 92篇 |
2015年 | 69篇 |
2014年 | 122篇 |
2013年 | 142篇 |
2012年 | 156篇 |
2011年 | 197篇 |
2010年 | 118篇 |
2009年 | 119篇 |
2008年 | 135篇 |
2007年 | 125篇 |
2006年 | 118篇 |
2005年 | 109篇 |
2004年 | 84篇 |
2003年 | 62篇 |
2002年 | 58篇 |
2001年 | 31篇 |
2000年 | 47篇 |
1999年 | 48篇 |
1998年 | 75篇 |
1997年 | 48篇 |
1996年 | 53篇 |
1995年 | 37篇 |
1994年 | 35篇 |
1993年 | 23篇 |
1992年 | 13篇 |
1991年 | 21篇 |
1990年 | 12篇 |
1989年 | 17篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 5篇 |
1976年 | 11篇 |
1973年 | 5篇 |
1916年 | 4篇 |
排序方式: 共有2762条查询结果,搜索用时 406 毫秒
1.
Christian Stephan Bernd 《AEUE-International Journal of Electronics and Communications》2006,60(1):20-24
Security for ad hoc network environments has received a lot of attention as of today. Previous work has mainly been focussing on secure routing, fairness issues, and malicious node detection. However, the issue of introducing and conserving trust relationships has received considerably less attention. In this article, we present a scalable method for the use of public key certificates and their revocation in mobile ad hoc networks (MANETs). With the LKN-ad hoc security framework (LKN-ASF) a certificate management protocol has been introduced, bringing PKI technology to MANETs. In addition a performance analysis of two different revocation approaches for MANETs will be presented. 相似文献
2.
Eich (1985) recently presented a distributed memory model in which the pattern of results used to support the levels-of-processing view of Craik and Lockhart (1972) was modeled by different degrees of similarity between the encoding context and the to-be-recalled item. We report two experiments in which both phonemic and semantic similarity were varied between pairs of words and incidental acquisition (rhyme vs. category judgments) was varied across the same pairs of items. In both experiments the manipulation of the acquisition task produced a difference in cued-recall performance for positive and negative rhyme and category judgments. Recall was better following a category encoding decision than following a rhyme decision. This difference was independent of the effects of similarity, which demonstrated that Eich's (1985) assumptions regarding the effects of similarity are not sufficient to account for the differences resulting from the manner in which subjects encode information. An alternative method of modeling the levels-of-processing effect within the framework of distributed memory models is proposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
3.
According to the knowledge partitioning framework, people sometimes master complex tasks by creating multiple independent parcels of partial knowledge. Research has shown that knowledge parcels may contain mutually contradictory information, and that each parcel may be used without regard to knowledge that is demonstrably present in other parcels. This article reports 4 experiments that investigated knowledge partitioning in categorization. When component boundaries of a complex categorization were identified by a context cue, a significant proportion of participants learned partial and independent categorization strategies that were chosen on the basis of context. For those participants, a strategy used in one context was unaffected by knowledge demonstrably present in other contexts, suggesting that knowledge partitioning in categorization can be complete. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
4.
We study experimentally and theoretically two polarization effects in a vertical cavity surface emitting laser submitted to optical feedback. In a first experiment, we obtain flips between two linearly polarized laser modes up to a frequency of 50 MHz using an external cavity with a polarizer. In a second experiment, polarization self modulation is demonstrated up to a frequency of 2.6 GHz, using a quarter wave plate instead. Numerical calculations, based on a four levels model for the active medium, show a good agreement with the experiments. 相似文献
5.
6.
Intact and ovariectomized oxytocin (OT)-deficient (OT-/-) and wild-type (OT+/+) mice were tested for consumption of 0.5 M NaCl solution or tap water in a 2-bottle choice test. During 3 days of acclimation, voluntary ingestion of NaCl was equal between genotypes. After overnight fluid deprivation, intact OT-/- mice ingested 2 times more NaCl solution than OT+/+ mice in the 6th hr, but not the 1 st hr, after reintroduction of fluid. Ovariectomized mice consumed less than intact mice after overnight fluid deprivation. When a 0.2 M NaCl solution was administered for 6 days in ovariectomized mice, OT-/- mice voluntarily consumed greater amounts than OT+/+ mice. After overnight fluid deprivation, consumption by OT-/- mice was 3 times that of OT+/+ mice at 1 hr and 2-fold greater after 6 hr. Enhanced intake of NaCl-containing solutions in female OT-/- mice suggests that central OT may be an important inhibitor of sodium consumption. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
Transport properties of 1,1-difluoroethane (R152a) 总被引:2,自引:0,他引:2
R. Krauss V. C. Weiss T. A. Edison J. V. Sengers K. Stephan 《International Journal of Thermophysics》1996,17(4):731-757
Based on reliable. carefully selected data sets. equations for the thermal conductivity and the viscosity of the refrigerant R 112a are presented. They are valid at temperatures from 240 to 440 K, pressures up to 20 MPa. and densities up to 1050 kg · m–3. including the critical region. 相似文献
8.
9.
Tihanyi P. Wagner D.K. Vollmer H.J. Roza A.J. Harding C.M. Davis R.J. Wolf E.D. 《Electronics letters》1987,23(15):772-773
We demonstrate, for the first time, laser diodes with anetched facet fabricated by chemically assisted ion beametching, producing 1?7 W pulsed and 470mW CW output power from one facet. The devices were coated and bonded junction-side-up and tested at room temperature. The single 40 ?m stripe, 300 ?m-long devices exhibit 94 mA threshold current and differential quantum efficiencies of 80% pulsed (78% CW). 相似文献
10.