全文获取类型
收费全文 | 3406篇 |
免费 | 173篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 36篇 |
综合类 | 11篇 |
化学工业 | 854篇 |
金属工艺 | 81篇 |
机械仪表 | 49篇 |
建筑科学 | 195篇 |
矿业工程 | 8篇 |
能源动力 | 105篇 |
轻工业 | 272篇 |
水利工程 | 23篇 |
石油天然气 | 17篇 |
无线电 | 294篇 |
一般工业技术 | 758篇 |
冶金工业 | 273篇 |
原子能技术 | 30篇 |
自动化技术 | 577篇 |
出版年
2023年 | 47篇 |
2022年 | 77篇 |
2021年 | 157篇 |
2020年 | 73篇 |
2019年 | 82篇 |
2018年 | 93篇 |
2017年 | 85篇 |
2016年 | 126篇 |
2015年 | 93篇 |
2014年 | 163篇 |
2013年 | 229篇 |
2012年 | 229篇 |
2011年 | 248篇 |
2010年 | 147篇 |
2009年 | 155篇 |
2008年 | 178篇 |
2007年 | 176篇 |
2006年 | 157篇 |
2005年 | 132篇 |
2004年 | 113篇 |
2003年 | 81篇 |
2002年 | 77篇 |
2001年 | 50篇 |
2000年 | 61篇 |
1999年 | 51篇 |
1998年 | 59篇 |
1997年 | 55篇 |
1996年 | 58篇 |
1995年 | 39篇 |
1994年 | 45篇 |
1993年 | 25篇 |
1992年 | 19篇 |
1991年 | 18篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 13篇 |
1977年 | 5篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有3583条查询结果,搜索用时 15 毫秒
1.
Journal of Materials Science - Phase separation is a relevant mode of transformation for microstructure development in multicomponent alloys. Its occurrence can drastically alter the composition... 相似文献
2.
3.
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
4.
Vladimir Rozenshtein Alexander Berg Haim Levanon Uwe Krueger Dietmar Stehlik Yuri Kandrashkin Art Van Der Est 《Israel journal of chemistry》2003,43(3-4):373-381
Light-induced spin-polarized transient EPR spectra are reported for several water-soluble copper porphyrins. The spectra are assigned to the doublet ground state, with emissive spin polarization resulting from photoexcitation and subsequent electronic relaxation. In contrast to other systems for which polarization of a doublet ground state has been observed, the exchange interactions in the copper porphyrins are strong and the geometry is fixed. It is proposed that intersystem crossing from the photoexcited trip-doublet to the trip-quartet state can lead to net polarization of the spin system and that this polarization is maintained during electronic decay, possibly via charge-transfer and exciplex states. The intensity of the observed spin polarization is essentially independent of the molecular orientation in the external field, but is strongly dependent on the nature of the charged peripheral groups. Possible reasons for this behavior are discussed. 相似文献
5.
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
6.
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
7.
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
8.
9.
铁电纳米粒子悬浮在向列相液晶母体中,增强介电各向异性,而且对施加的电场信号敏感。本文也展示了纳米粒子对所述复合材料可实现的总的相变的作用。这种方法也许可应用于设计新型显示材料。 相似文献
10.
Nemenchinskaya Ekaterina O. Kondratenko Yuri V. Sadovsky Michael G. 《Open Systems & Information Dynamics》2004,11(2):161-175
The new method of a gap recovery in symbol sequences is presented. A covering is combined from the suitable reasonably short strings of the parts of a sequence available for observation. Two criteria are introduced to choose the best covering. It must yield the maximum of entropy of a frequency dictionary developed over the sequence obtained due to the recovery, if an overlapping combined from the copies of strings from the available parts of the sequence exists. The second criterion identifies the best covering in case when one has to use any string to cover the gap; here the best covering must yield the minimum of specific entropy of the frequency dictionary developed over the available parts of the sequence against the one developed over the entire sequence obtained due to the recovery. Kirdin kinetic machine which is the ideal fine-grained structureless computer has been used to resolve the problem of the reconstruction of a gap in symbol sequence. 相似文献