全文获取类型
收费全文 | 15029篇 |
免费 | 1028篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 99篇 |
综合类 | 9篇 |
化学工业 | 5700篇 |
金属工艺 | 184篇 |
机械仪表 | 359篇 |
建筑科学 | 521篇 |
矿业工程 | 24篇 |
能源动力 | 415篇 |
轻工业 | 3760篇 |
水利工程 | 127篇 |
石油天然气 | 83篇 |
无线电 | 574篇 |
一般工业技术 | 1984篇 |
冶金工业 | 756篇 |
原子能技术 | 50篇 |
自动化技术 | 1421篇 |
出版年
2024年 | 49篇 |
2023年 | 198篇 |
2022年 | 1007篇 |
2021年 | 1117篇 |
2020年 | 470篇 |
2019年 | 484篇 |
2018年 | 544篇 |
2017年 | 598篇 |
2016年 | 622篇 |
2015年 | 500篇 |
2014年 | 659篇 |
2013年 | 1056篇 |
2012年 | 998篇 |
2011年 | 1100篇 |
2010年 | 841篇 |
2009年 | 780篇 |
2008年 | 725篇 |
2007年 | 680篇 |
2006年 | 520篇 |
2005年 | 388篇 |
2004年 | 335篇 |
2003年 | 304篇 |
2002年 | 275篇 |
2001年 | 175篇 |
2000年 | 116篇 |
1999年 | 147篇 |
1998年 | 188篇 |
1997年 | 147篇 |
1996年 | 138篇 |
1995年 | 101篇 |
1994年 | 79篇 |
1993年 | 81篇 |
1992年 | 76篇 |
1991年 | 59篇 |
1990年 | 40篇 |
1989年 | 39篇 |
1988年 | 47篇 |
1987年 | 33篇 |
1986年 | 48篇 |
1985年 | 42篇 |
1984年 | 31篇 |
1983年 | 26篇 |
1982年 | 21篇 |
1981年 | 20篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Ronald R. Delyser Sheila S. Thompson Jerry Edelstein Corinne Lengsfeld Albert J. Rosa Paul J. Rullkoetter Robert Whitman Margaret Whitt 《工程教育杂志》2003,92(3):269-273
A team of faculty members at the University of Denver changed the learning environment in key courses in the Department of Engineering from predominately teacher centered to student centered. Through this funded project new grading methods were implemented, classrooms were renovated and wired with studio layouts to facilitate learning, the Engineering Circuits Laboratory was rewired and instrumented for automated data acquisition and reporting, and two new pedagogical approaches were developed. At the onset of the project, six goals were established related to student learning. The introduction of industry standard hardware and software provided students with unprecedented hands‐on experience and project related activities stimulated faculty innovations in other current and future courses. Assessment results indicate that the new grading system improved the clarity of expectations for students before assignments were given resulting in increased reported motivation for learning in many courses. Even though course GPAs did not always reflect higher achievement on graded work, faculty members firmly believe that deeper understanding was achieved because more complex material was assimilated. 相似文献
13.
Scale selection using three different representations for images 总被引:1,自引:0,他引:1
J. Martinez-Baena J. A. García J. Fdez-Valdivia Rosa Rodriguez-Sanchez 《Pattern recognition letters》1997,18(14):1453-1467
14.
15.
16.
As in today’s knowledge society the Internet is playing an important role in the information literacy of university students
the goal of this paper is to analyse, after its first year on the Web, the informational impact of an e-learning resource
developed by Granada’s University lecturers (the e-COMS educational portal), a pioneer in Spain for training in information
literacy. From the objective and subjective data provided by the own portal and by it users, two different and complementary
kinds of analysis (functional and users’) are performed. Assessment of various capabilities, among which visibility and usability
stand out, is provided. The highly positive but improvable results offer a detailed analysis of the functional aspects of
the portal itself and of the users’ relations with this information resource. From these analyses strengths and weaknesses
are extracted and some proposals for improvement are derived. 相似文献
17.
Rosa RicciardiChristine Gaillet Guylaine DucouretFrançoise Lafuma Françoise Lauprêtre 《Polymer》2003,44(11):3375-3380
The structure and rheological behavior of atactic poly(vinyl alcohol) (a-PVA) hydrogels prepared by freeze/thaw cycles were investigated as a function of polymer concentration and number of freeze/thaw cycles. The presence of phases with different mobilities was observed using 13C CP/MAS and DP/MAS NMR experiments. The degree of crystallinity of the a-PVA-rich phase was determined by 1H NMR free decay experiments. Measurements of the shear storage and loss modulus were performed at a fixed frequency of 1 Hz and a strain value of 0.1%, i.e. under conditions where the deformation imposed on the gel structure is entirely reversible. Results thus obtained showed that an increase in the number of freeze/thaw cycles induces an increase in the degree of crystallinity in the polymer-rich phase together with an increase in the storage modulus. The a-PVA hydrogels became more fragile as the number of freeze/thaw cycles was increased. Moreover, both the percentage of protons in a rigid environment measured by 1H NMR and the storage modulus values tended to a limiting value after six freeze/thaw cycles. These results show that the first five or six freeze/thaw cycles play a very important role in determining the hydrogel structure and rheological properties. A more detailed comparison of NMR and rheological data led to the conclusion that the storage modulus is mainly controlled by the a-PVA crystallinity while the hydrogen bond interactions have a much smaller contribution. 相似文献
18.
The influence of school- and age-related variables was examined separately on 2 tasks involving elementary quantitative skills: conservation of number and mental addition. Performance on these tasks was compared by using a cutoff design with 3 groups of kindergarten and Grade 1 children who differed in age but not amount of schooling (grade), in schooling but not age, or in both age and schooling. The effects of age and schooling were distinct. On conservation of number, performance improved as a function of age but not schooling. On mental arithmetic, accuracy improved with schooling rather than age but children's use of various solution procedures (e.g., retrieval, counting) was not influenced by schooling. Thus, in the domain of elementary mathematical skills, the influence of schooling can be very specific, and age-related variables other than schooling play an important role in the development of elementary mathematical skills. Results illustrate the utility of the cutoff design for investigating instructional and developmental influences on cognitive development. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
19.
Venezuela's vast natural resource base has largely shaped the nation's economic and energy-use patterns. Major opportunities exist for improving the efficiency of energy use in Venezuela and, consequently, restraining the growth of energy-related carbon emissions. This paper presents a detailed report of one potential development path for Venezuela and estimates the ensuing levels of energy demand and CO2 emissions associated with pursuing this path through the year 2025. The results indicate that by adopting a development strategy that incorporates structural changes in the economy, fuel-switching measures and improved end-use efficiencies, Venezuela can introduce energy efficiency and carbon restraints as part of its economic development process. 相似文献
20.
Izard Carroll E.; Fantauzzo Christina A.; Castle Janine M.; Haynes O. Maurice; Rayias Maria F.; Putnam Priscilla H. 《Canadian Metallurgical Quarterly》1995,31(6):997
Four studies examined aspects of the differential emotions theory (DET) hypothesis of expressive behavior development. In Study 1, facial-expressive movements of 108 2.5–9-mo-old infants were video recorded in positive and negative mother–infant interactions (conditions). As expected, Max-specified full-face and partial expressions of interest, joy, sadness, and anger were morphologically stable between the 2 ages. Studies 1 and 2 confirmed predicted differential responding to mother sadness and anger expressions and to composite positive and negative conditions. Discrete negative expressions exceeded negative blends, and the amount of both expression types remained stable across ages. Studies 3 and 4 provided varying degrees of support for the social validity of Max-specified infant negative affect expressions. Conclusions include revisions and clarifications of DET. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献