全文获取类型
收费全文 | 47073篇 |
免费 | 1987篇 |
国内免费 | 1931篇 |
专业分类
电工技术 | 1662篇 |
技术理论 | 18篇 |
综合类 | 5065篇 |
化学工业 | 5805篇 |
金属工艺 | 1342篇 |
机械仪表 | 2284篇 |
建筑科学 | 7748篇 |
矿业工程 | 3044篇 |
能源动力 | 1584篇 |
轻工业 | 3681篇 |
水利工程 | 2141篇 |
石油天然气 | 3917篇 |
武器工业 | 264篇 |
无线电 | 1701篇 |
一般工业技术 | 2293篇 |
冶金工业 | 4122篇 |
原子能技术 | 151篇 |
自动化技术 | 4169篇 |
出版年
2024年 | 92篇 |
2023年 | 306篇 |
2022年 | 804篇 |
2021年 | 1008篇 |
2020年 | 984篇 |
2019年 | 651篇 |
2018年 | 588篇 |
2017年 | 811篇 |
2016年 | 1021篇 |
2015年 | 1104篇 |
2014年 | 2659篇 |
2013年 | 2351篇 |
2012年 | 2942篇 |
2011年 | 3504篇 |
2010年 | 3005篇 |
2009年 | 2895篇 |
2008年 | 2475篇 |
2007年 | 3263篇 |
2006年 | 3366篇 |
2005年 | 3078篇 |
2004年 | 2630篇 |
2003年 | 2365篇 |
2002年 | 1921篇 |
2001年 | 1680篇 |
2000年 | 1425篇 |
1999年 | 990篇 |
1998年 | 728篇 |
1997年 | 517篇 |
1996年 | 399篇 |
1995年 | 285篇 |
1994年 | 223篇 |
1993年 | 148篇 |
1992年 | 131篇 |
1991年 | 81篇 |
1990年 | 69篇 |
1989年 | 64篇 |
1988年 | 37篇 |
1987年 | 29篇 |
1986年 | 35篇 |
1985年 | 44篇 |
1984年 | 27篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 21篇 |
1980年 | 15篇 |
1979年 | 15篇 |
1965年 | 11篇 |
1963年 | 10篇 |
1959年 | 11篇 |
1955年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
23.
24.
The Intellectual Development of Science and Engineering Students. Part 2: Teaching to Promote Growth
As college students experience the challenges of their classes and extracurricular activities, they undergo a developmental progression in which they gradually relinquish their belief in the certainty of knowledge and the omniscience of authorities and take increasing responsibility for their own learning. At the highest developmental level normally seen in college students (which few attain before graduation), they display attitudes and thinking patterns resembling those of expert scientists and engineers, including habitually and skillfully gathering and analyzing evidence to support their judgments. This paper proposes an instructional model designed to provide a suitable balance of challenge and support to advance students to that level. The model components are (1) variety and choice of learning tasks; (2) explicit communication and explanation of expectations; (3) modeling, practice, and constructive feedback on high‐level tasks; (4) a student‐centered instructional environment; and (5) respect for students at all levels of development. 相似文献
25.
26.
加快塑料技术中心建设提高新产品开发水平 总被引:2,自引:2,他引:0
对中国石油化工集团公司(简称中国石化)合成树脂生产及加工应用技术的现状进行了分析,指出中国石化应加快建设塑料加工应用技术中心,为塑料产品的加工用户提供高技术水平和快捷周到的技术服务,在合成树脂新产品开发和产品结构调整中发挥积极作用,以提高合成树脂产品的市场竞争力。 相似文献
27.
关于我国石油钻机技术的现状及其研发思考 总被引:13,自引:6,他引:7
介绍了我国石油钻机的技术现状,在肯定我国石油钻机发展所取得成绩的同时,指出我国石油钻机整体技术与国外钻机技术的差距,提出要把石油钻机作为国家战略装备来对待,加快我国石油钻机新技术、新产品研发工作,以满足我国石油工业发展的需要。 相似文献
28.
McWayne Christine M.; Fantuzzo John W.; McDermott Paul A. 《Canadian Metallurgical Quarterly》2004,40(4):633
The present concurrent study combined developmental and ecological considerations to examine the unique contribution of multiple preschool competencies to an indicator of early academic success. Participants included 195 Head Start children from 32 classrooms representative of a large, urban Head Start program. Dimensional (variable-centered) analyses revealed 3 distinct classroom competency dimensions (i.e., General Classroom Competencies, Specific Approaches to Learning, and Interpersonal Classroom Behavioral Problems). The first 2 of these dimensions were found to be uniquely associated with early academic success. Findings from typological (person-centered) analyses supported the dimensional findings. Typological analyses revealed 7 profiles of classroom competency distinguished by high scores on the dimensions of General Competencies and Approaches to Learning, and these profiles were found to relate differentially to the indicator of early academic success. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
29.
J. Gegner 《Materialwissenschaft und Werkstofftechnik》2003,34(3):290-297
Chemical Composition and Microstructure of Polymer‐Derived Glasses and Ceramics in the Si–C–O System. Part 2: Characterization of microstructure formation by means of high‐resolution transmission electron microscopy and selected area diffraction Liquid or solid silicone resins represent the economically most interesting class of organic precursors for the pyrolytic production of glass and ceramics materials on silicon basis. As dense, dimensionally stable components can be cost‐effectively achieved by admixing reactive filler powders, chemical composition and microstructure development of the polymer‐derived residues must be exactly known during thermal decomposition. Thus, in the present work, glasses and ceramics produced by pyrolysis of the model precursor polymethylsiloxane at temperatures from 525 to 1550 °C are investigated. In part 1, by means of analytical electron microscopy, the bonding state of silicon was determined on a nanometre scale and the phase separation of the metastable Si–C–O matrix into SiO2, C and SiC was proved. The in‐situ crystallization could be considerably accelerated by adding fine‐grained powder of inert fillers, such as Al2O3 or SiC, which permits effective process control. In part 2, the microstructure is characterized by high‐resolution transmission electron microscopy and selected area diffraction. Turbostratic carbon and cubic β‐SiC precipitate as crystallization products. Theses phases are embedded in an amorphous matrix. Inert fillers reduce the crystallization temperature by several hundred °C. In this case, the polymer‐derived Si–C–O material acts as a binding agent between the powder particles. Reaction layer formation does not occur. On the investigated pyrolysis conditions, no crystallization of SiO2 was observed. 相似文献
30.
新产品研发是建陶企业可持续发展的核心 总被引:2,自引:0,他引:2
新世纪我国建陶企业在整个国民经济的带动下将进一步发展,入世后经济全球化的市场竞争格局,建陶企业只有走新产口研发之路,严格企业管理,才会在日趋激烈的市场竞争中得以生存和可持续发展。 相似文献