全文获取类型
收费全文 | 53491篇 |
免费 | 6166篇 |
国内免费 | 3225篇 |
专业分类
电工技术 | 15357篇 |
综合类 | 4554篇 |
化学工业 | 4007篇 |
金属工艺 | 2503篇 |
机械仪表 | 2887篇 |
建筑科学 | 4023篇 |
矿业工程 | 976篇 |
能源动力 | 1769篇 |
轻工业 | 6270篇 |
水利工程 | 1382篇 |
石油天然气 | 1271篇 |
武器工业 | 485篇 |
无线电 | 5766篇 |
一般工业技术 | 4884篇 |
冶金工业 | 2168篇 |
原子能技术 | 951篇 |
自动化技术 | 3629篇 |
出版年
2024年 | 314篇 |
2023年 | 977篇 |
2022年 | 1827篇 |
2021年 | 2037篇 |
2020年 | 2113篇 |
2019年 | 1777篇 |
2018年 | 1719篇 |
2017年 | 2257篇 |
2016年 | 2395篇 |
2015年 | 2529篇 |
2014年 | 3383篇 |
2013年 | 3295篇 |
2012年 | 4167篇 |
2011年 | 4417篇 |
2010年 | 3049篇 |
2009年 | 3195篇 |
2008年 | 2930篇 |
2007年 | 3480篇 |
2006年 | 3026篇 |
2005年 | 2433篇 |
2004年 | 1951篇 |
2003年 | 1598篇 |
2002年 | 1231篇 |
2001年 | 1146篇 |
2000年 | 987篇 |
1999年 | 826篇 |
1998年 | 652篇 |
1997年 | 516篇 |
1996年 | 449篇 |
1995年 | 398篇 |
1994年 | 316篇 |
1993年 | 257篇 |
1992年 | 229篇 |
1991年 | 156篇 |
1990年 | 136篇 |
1989年 | 112篇 |
1988年 | 83篇 |
1987年 | 71篇 |
1986年 | 45篇 |
1985年 | 45篇 |
1984年 | 47篇 |
1983年 | 24篇 |
1982年 | 32篇 |
1981年 | 14篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1965年 | 15篇 |
1964年 | 19篇 |
1963年 | 15篇 |
1957年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
21.
Yoon Carolyn; Feinberg Fred; Hu Ping; Gutchess Angela Hall; Hedden Trey; Chen Hiu-Ying Mary; Jing Qicheng; Cui Yao; Park Denise C. 《Canadian Metallurgical Quarterly》2004,19(3):379
Understanding how aging influences cognition across different cultures has been hindered by a lack of standardized, cross-referenced verbal stimuli. This study introduces a database of such item-level stimuli for both younger and older adults, in China and the United States, and makes 3 distinct contributions. First, the authors specify which item categories generalize across age and/or cultural groups, rigorously quantifying differences among them. Second, they introduce novel, powerful methods to measure between-group differences in freely generated ranked data, the rank-ordered logit model and Hellinger Affinity. Finally, a broad archive of tested, cross-linguistic stimuli is now freely available to researchers: data, similarity measures, and all stimulus materials for 105 categories and 4 culture-by-age groups, comprising over 10,000 fully translated unique item responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
22.
无磷洗涤剂的现状及存在问题 总被引:1,自引:0,他引:1
含磷洗涤剂中含的“磷”主要是STPP,作用很大但对环境的危害也很大,它是造成地表水体出现富营养化的重要原因之一,所以许多地方政府都在实行“禁磷”——禁止销售、使用含磷洗涤剂。现在我国使用的无磷洗涤剂中代磷助剂主要有3种,其中4A沸石用量最大,但它会对环境带来新的问题。主要介绍了含磷洗涤剂的危害及无磷洗涤剂的应用现状,指出了我国禁磷后将面临的问题。 相似文献
23.
J. Gegner Priv.‐Doz. Dr. W. Nierlich M. Brückner 《Materialwissenschaft und Werkstofftechnik》2007,38(8):613-623
Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology. 相似文献
24.
The State of the Art in Text Filtering 总被引:1,自引:0,他引:1
This paper develops a conceptual framework for text filtering practice and research, and reviews present practice in the field.
Text filtering is an information seeking process in which documents are selected from a dynamic text stream to satisfy a relatively
stable and specific information need. A model of the information seeking process is introduced and specialized to define text
filtering. The historical development of text filtering is then reviewed and case studies of recent work are used to highlight
important design characteristics of modern text filtering systems. User modeling techniques drawn from information retrieval,
recommender systems, machine learning and other fields are described. The paper concludes with observations on the present
state of the art and implications for future research on text filtering.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
25.
A centrifugal partition chromatograph (CPC) was used as a liquid-liquid catalytic reactor for the isomerisation of hexen-3-ol into ethylpropylketone with a water soluble rhodium catalyst. Global mass transfer coefficients were measured and shown to depend on both the nature of the solute and the flow rate. Liquid-liquid partition isotherms were also determined with the CPC using elution chromatography. Finally, a reactor model was derived to account for the experimental results obtained both under stationary and transient (pulse) conditions. A parameter sensitivity evaluation is also presented. 相似文献
26.
The Bi-system tapes and coils were prepared by the powder-in-tube method. The effect of processing and heat treatment on the properties of the tapes and coils was studied. It is found that the shearing stress produced by the rolling process may destroy the 2223 phase, and the destroyed 2223 phase cannot be recovered by heat treatment, whereas the pressing stress produced by the uniaxial pressing process only makes the 2223 phase grains break, and the broken 2223 phase can be closed by the heat treatment. TheJ
c values of the rolling samples, pressing sample, and the coil with a diameter of 35 mm are over 1.3×104, 2.5×104, and 4×103 A/cm2 (77 K, 0 T), respectively. 相似文献
27.
The paper addresses the design of two-level power system stabilizers using an optimal reduced order model whose state variables are torque angles and speeds. The reduced order model retains their physical meaning and is used to design a two-level linear feedback controller that takes into account the realities and constraints of electrical power systems. The two-level control strategy is used, and a global control signal is generated from the output variables to minimize the effect of interactions. The effectiveness of this controller is evaluated and a multimachine system is given as an example to illustrate the advantages of the proposed method. Responses of the system with a two-level scheme and an optimal reduced order scheme are included for comparative analysis. 相似文献
28.
29.
Learning a sequence of target locations when the sequence is uncorrelated with a sequence of responses and target location is not the response dimension (pure perceptual-based sequence learning) was examined. Using probabilistic sequences of target locations, the author shows that such learning can be implicit, is unaffected by distance between target locations, and is mostly limited to first-order transition probabilities. Moreover, the mechanism underlying learning affords processing of information at anticipated target locations and appears to be attention based. Implications for hypotheses of implicit sequence learning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
30.
小儿的心理状态与成人有着明显的差异,在其住院和接受医疗期间可出现严重的心理反应,导致植物神经功能紊乱,使机体低抗力下降,而削弱机体对麻药的耐受力,不利于麻醉诱导及管理,而且还会造成小儿的精神创伤。文章初步探讨了小儿麻醉心理学的有关问题。 相似文献