首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4244篇
  免费   109篇
  国内免费   10篇
电工技术   46篇
综合类   5篇
化学工业   1031篇
金属工艺   79篇
机械仪表   86篇
建筑科学   292篇
矿业工程   6篇
能源动力   102篇
轻工业   401篇
水利工程   26篇
石油天然气   23篇
无线电   241篇
一般工业技术   680篇
冶金工业   786篇
原子能技术   58篇
自动化技术   501篇
  2022年   46篇
  2021年   42篇
  2020年   42篇
  2019年   50篇
  2018年   53篇
  2017年   73篇
  2016年   83篇
  2015年   54篇
  2014年   97篇
  2013年   283篇
  2012年   138篇
  2011年   197篇
  2010年   181篇
  2009年   156篇
  2008年   182篇
  2007年   184篇
  2006年   174篇
  2005年   143篇
  2004年   134篇
  2003年   125篇
  2002年   101篇
  2001年   87篇
  2000年   68篇
  1999年   66篇
  1998年   91篇
  1997年   79篇
  1996年   55篇
  1995年   63篇
  1994年   69篇
  1993年   57篇
  1992年   51篇
  1991年   49篇
  1990年   58篇
  1989年   66篇
  1988年   60篇
  1987年   36篇
  1986年   59篇
  1985年   59篇
  1984年   63篇
  1983年   53篇
  1982年   52篇
  1981年   55篇
  1980年   46篇
  1979年   57篇
  1978年   58篇
  1977年   46篇
  1976年   44篇
  1975年   34篇
  1974年   32篇
  1973年   37篇
排序方式: 共有4363条查询结果,搜索用时 15 毫秒
101.
Replies to the comments by R. A. R. Gurung (see record 2003-03405-011) and J. Li (see record 2003-03405-012) regarding comments on the article by R. G. Tweed and D. R. Lehman (2001) which stated that a Confucian-Socratic framework provides a structure for analyzing culture-influenced aspects of academic learning. In this article, Tweed and Lehman argued that these ancient exemplars model approaches to learning continue to differentiate students within a modern Canadian postsecondary context. In this reply, Tweed and Lehman advise caution in how Gurung placed their Confucian-Socratic framework within the context of prior theory on education and epistemological development because these models were developed exclusively in the West. Furthermore, Tweed and Lehman believe that Li's argument misinterpreted their article, and that they should of consistently used the term "personal reform" rather than "behavioral reform" in order to communicate the depth of personal change envisioned by Confucius. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
102.
Performance variability across repeated task administrations may be an important indicator of age-related cognitive functioning. In the present investigation, the authors examined whether age differences and change in inconsistency were related to 6-year (3 occasion) cognitive change. Inconsistency scores were computed from 4 reaction time tasks performed by 446 older adults (54-89 years). Replicating previous cross-sectional results, greater inconsistency was observed for older participants even after controlling for differences in response speed. New longitudinal results demonstrated (a) associations between inconsistency at baseline measurement and 6-year change in cognitive performance; (b) longitudinal change in inconsistency; and (c) intraindividual covariation between 6-year change in inconsistency and 6-year change in level of cognitive function. These findings support the view that performance variability serves as a marker of cognitive aging. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
103.
104.
In this paper we present adsorption isotherms of carbon dioxide on five different activated carbons from CHEMVIRON CARBON Belgium (Centaur HSV, BPL 410, F30-470, WS 42, Reactivated) and on a carbon molecular sieve from BERGBAU FORSCHUNG Gmbh (CMS II). The temperature is 303 K and the pressure ranges from 100 kPa up to 4000 kPa. Such conditions correspond to relative pressures ranging from 0.01 to 0.5. We also provide, for the same six sorbents, the nitrogen isotherms at 77 K (pressure: 0.001 to 100 kPa, relative pressure: 10-5 to 1). A theoretical treatment based on the Dubinin-Radushkevich and Stoeckli concept is presented and applied to the experimental results in order to obtain the micropore size distribution function (considered as Gaussian) of each sorbent. Using the CO2 data, it is possible to point out important structural differences between the six carbons. The theoretical treatment provides micropore size distribution functions in agreement with what is physically expected. Using N2 data, the structural differences are not so well marked. As a consequence, the structural parameters provided by the theoretical treatment are not reliable: except for the total micropore volume, they fluctuate strongly when changing the relative pressure domain of the used data.  相似文献   
105.
106.
The hydration of tricalcium silicate at 25°C was accelerated by seeding with 5 wt% tricalcium germanate. Based on heat evolution, seeding resulted in the elimination of the induction period. However, the shape of the hydration peak remained the same. Because tricalcium germanate hydrates first, the microstructure of the calcium silicate hydrate which subsequently forms is influenced by the calcium germanate hydrate morphology. Calcium silicate hydrate formed in the presence of calcium germanate hydrate exhibits the morphology typical of the latter. Acceleration of hydration and morphological variation indicate heteroepitaxial growth.  相似文献   
107.
A general survey of fluorinated phosphazene polymers starting from their synthesis in 1965 to recent times is presented. Various types of fluorinated phosphazenes are described depending on the way fluorine atoms are connected to the polyphosphazene skeleton. The characterization, properties and practical utilization of these compounds in different domains are critically discussed.  相似文献   
108.
Summary: It was demonstrated that it is possible to produce prepolymers with a number‐average degree of polymerisation on the order of 5–40 directly in a liquid‐liquid dispersion in less than three hours. It was also shown that prepolymers made via this route and rapidly crystallised by the addition of a dispersant at ambient temperature are more porous than prepolymers made in an industrial liquid melt process.

SEM micrograph of prepolymers pLL‐PTA with \overline {DP} _{\rm n} = 28, dp ∈ 63–125 μm.  相似文献   

109.
Precise and accurate knowledge of the optical properties of amorphous silica is important because of the increasing application of SiO2 in optical and electrooptical devices, including photolithography masks for semiconductor fabrication, recently as a potential 157 nm mask substrate. The optical properties in the vacuum ultraviolet (VUV) region have been investigated, because they convey detailed information on the electronic structure and interatomic bonding of the material. In this work, we have combined spectroscopic ellipsometry and VUV spectroscopy to directly determine the optical functions of SiO2 in this range, thereby reducing the uncertainty in the low-energy extrapolation of the data, essential for Kramers–Kronig analysis of VUV reflectance. We report the complex optical properties of SiO2, over the range of 1.5 to 42 eV, showing improved agreement with theory when contrasted with earlier results. In addition to the features previously reported at 10.4, 11.6, 14.03, and 17.10 eV, new interband transitions have been observed at 21.3 eV along with O 2 s transitions at 32 eV. We found the bulk plasma peak to be 23.7 eV in the energy loss function spectrum. Based on the magnitude of these new results, the Hamaker constant for SiO2|Vacuum|SiO2 is 71.6 zJ, which is larger than the previously reported value of 66 zJ.  相似文献   
110.
This work examines the correlation between the 1H‐NMR T2 relaxation constant and the mechanical properties of aged crosslinked polyolefin cable insulation. T2 experiments on unswollen samples could not differentiate between unaged and highly aged materials; all exhibited 1H T2 constants of approximately 0.5 ms. To accentuate the effects of aging, samples were swollen in various solvents. Unaged samples had T2 values of approximately 15 ms in good solvents. With thermal aging, T2 values decreased as the ultimate tensile elongation decreased. However, the correlation between T2 and elongation differed for samples irradiated with high‐energy radiation and for materials aged above versus below the crystalline melting temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2578–2582, 2003  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号