全文获取类型
收费全文 | 232128篇 |
免费 | 4279篇 |
国内免费 | 662篇 |
专业分类
电工技术 | 4318篇 |
综合类 | 150篇 |
化学工业 | 33844篇 |
金属工艺 | 8147篇 |
机械仪表 | 6178篇 |
建筑科学 | 5045篇 |
矿业工程 | 817篇 |
能源动力 | 5398篇 |
轻工业 | 19805篇 |
水利工程 | 2019篇 |
石油天然气 | 2961篇 |
武器工业 | 13篇 |
无线电 | 28620篇 |
一般工业技术 | 43166篇 |
冶金工业 | 53193篇 |
原子能技术 | 3722篇 |
自动化技术 | 19673篇 |
出版年
2021年 | 2075篇 |
2020年 | 1636篇 |
2019年 | 2061篇 |
2018年 | 3553篇 |
2017年 | 3497篇 |
2016年 | 3614篇 |
2015年 | 2573篇 |
2014年 | 3918篇 |
2013年 | 10662篇 |
2012年 | 6502篇 |
2011年 | 8001篇 |
2010年 | 6474篇 |
2009年 | 7191篇 |
2008年 | 7482篇 |
2007年 | 7445篇 |
2006年 | 6497篇 |
2005年 | 6043篇 |
2004年 | 5912篇 |
2003年 | 5710篇 |
2002年 | 5479篇 |
2001年 | 5713篇 |
2000年 | 5296篇 |
1999年 | 5872篇 |
1998年 | 17884篇 |
1997年 | 11847篇 |
1996年 | 8941篇 |
1995年 | 6392篇 |
1994年 | 5498篇 |
1993年 | 5582篇 |
1992年 | 3590篇 |
1991年 | 3460篇 |
1990年 | 3375篇 |
1989年 | 3194篇 |
1988年 | 2932篇 |
1987年 | 2374篇 |
1986年 | 2420篇 |
1985年 | 2757篇 |
1984年 | 2443篇 |
1983年 | 2157篇 |
1982年 | 2028篇 |
1981年 | 2192篇 |
1980年 | 1941篇 |
1979年 | 1752篇 |
1978年 | 1739篇 |
1977年 | 2297篇 |
1976年 | 3320篇 |
1975年 | 1485篇 |
1974年 | 1423篇 |
1973年 | 1386篇 |
1972年 | 1147篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Mechanical property-grain size relationships have been examined for squeeze cast Al-4.5% Cu alloy, for an aluminium alloy with a composition corresponding to wrought 7010, and for a magnesium alloy AZ91. The general trend of the results obtained showed that the tensile properties and the fatigue strength improved as grain size decreased and the reverse was found to be the case for the fatigue crack propagation resistance and fracture energy of these castings. However, the results also showed that no simple common relationship existed between grain size and the tensile properties of the different alloys. The results are discussed in respect of their microstructures. 相似文献
993.
994.
Student O. Z. Rusyn B. P. Kysil' B. V. Kobasyar M. I. Stakhiv T. P. Markov A. D. 《Materials Science》2003,39(1):17-24
We give a quantitative estimate of changes in the structure of 15Kh2MFA steel after its long-term exposure to the combined action of high temperature, tensile stresses, and hydrogen as the factors of degradation of this steel under conditions of oil hydrocracking. Under laboratory conditions, we study the effect of high-temperature hydrogen degradation of 15Kh2MFA heat-resistant steel on changes in the quantitative characteristics of its structural elements, in particular, in the dimension and average distance between carbides as well as in their orientation from one grain to another. Algorithms for the solution of the formulated problems are described, and the possibilities of proposed approaches for the quantitative automatic processing of metallographic images are shown. 相似文献
995.
The authors model the optical properties of metallic quantum wells with thicknesses in the range of a few nanometers. A simple picture that includes only single electron transitions predicts strong absorption lines at frequencies associated with allowed interband transitions. This strong absorption feature can be in the near infrared for metal films several monolayers thick. The model is extended to include collective electron interactions by solving simultaneously Schroedinger's and Poisson's equations. It is found that the single electron picture does not change appreciably for frequencies above the bulk plasma frequency of the metal. For frequencies at or below the plasma frequency, however, the absorption is reduced in strength and becomes nearly featureless 相似文献
996.
997.
Nakamura K. Oguri T. Atsumo T. Takada M. Ikemoto A. Suzuki H. Nishigori T. Yamazaki T. 《Solid-State Circuits, IEEE Journal of》1992,27(11):1504-1510
The authors report a 4 M word×1 b/1 M word×4 b BiCMOS SRAM that can be metal mask programmed as either a 6-ns access time for an ECL 100 K I/O interface to an 8-ns access time for a 3.3-V TTL I/O interface. Die size is 18.87 mm×8.77 mm. Memory cell size is 5.8 μm×3.2 μm. In order to achieve such high-speed address access times the following technologies were developed: (1) a BiCMOS level converter that directly connects the ECL signal level to the CMOS level; (2) a high-speed BiCMOS circuit with low threshold voltage nMOSFETs; (3) a design method for determining the optimum number of decoder gate stages and the optimum size of gate transistors; (4) high-speed bipolar sensing circuits used at 3.3-V supply voltage; and (5) 0.55-μm BiCMOS process technology with a triple-well structure 相似文献
998.
999.
1000.
Y. Fujishiro T. Sato A. Okuwaki 《Journal of materials science. Materials in medicine》1995,6(3):172-176
Coating of hydroxyapatite on various metal plates was carried out by a homogeneous precipitation technique using hydrothermal reactions in Ca(edta)2-–NaH2PO4 at 140–200°C and pH 3.4–10.0. Hydroxyapatite films were formed on the surface of the iron plates in solutions at an initial pH above 4.7, whereas aggregates consisting of needle-like hydroxyapatite crystal radiating from a point in the form of flower deposited as islands on the surface of aluminum, copper and titanium plates. The upper part of the film formed on the surface of the iron plates consisted of needle-like hydroxyapatite particles whereas the bottom of the film consisted of spherical hydroxyapatite particles. The length of the needle-like hydroxyapatite particles increased with decreasing concentration of Ca(edta)2-. 相似文献