全文获取类型
收费全文 | 3683篇 |
免费 | 247篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 33篇 |
化学工业 | 868篇 |
金属工艺 | 107篇 |
机械仪表 | 139篇 |
建筑科学 | 141篇 |
矿业工程 | 11篇 |
能源动力 | 164篇 |
轻工业 | 624篇 |
水利工程 | 25篇 |
石油天然气 | 25篇 |
无线电 | 467篇 |
一般工业技术 | 616篇 |
冶金工业 | 145篇 |
原子能技术 | 30篇 |
自动化技术 | 538篇 |
出版年
2024年 | 16篇 |
2023年 | 54篇 |
2022年 | 59篇 |
2021年 | 146篇 |
2020年 | 103篇 |
2019年 | 103篇 |
2018年 | 182篇 |
2017年 | 126篇 |
2016年 | 171篇 |
2015年 | 133篇 |
2014年 | 159篇 |
2013年 | 512篇 |
2012年 | 140篇 |
2011年 | 154篇 |
2010年 | 171篇 |
2009年 | 183篇 |
2008年 | 115篇 |
2007年 | 88篇 |
2006年 | 96篇 |
2005年 | 49篇 |
2004年 | 49篇 |
2003年 | 35篇 |
2002年 | 42篇 |
2001年 | 98篇 |
2000年 | 94篇 |
1999年 | 93篇 |
1998年 | 120篇 |
1997年 | 116篇 |
1996年 | 41篇 |
1995年 | 27篇 |
1994年 | 24篇 |
1993年 | 20篇 |
1992年 | 19篇 |
1991年 | 28篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1981年 | 19篇 |
1978年 | 13篇 |
1976年 | 13篇 |
1975年 | 15篇 |
1915年 | 35篇 |
1913年 | 10篇 |
1912年 | 10篇 |
1911年 | 22篇 |
1910年 | 30篇 |
1909年 | 10篇 |
排序方式: 共有3933条查询结果,搜索用时 15 毫秒
91.
92.
Lutz Hofmann Tobias Fischer Thomas Werner Franz Selbmann Michael Rennau Ramona Ecke Stefan E. Schulz Thomas Geßner 《Microsystem Technologies》2016,22(7):1665-1677
This paper discusses approaches for the isolation of deep high aspect ratio through silicon vias (TSV) with respect to a Via Last approach for micro-electro-mechanical systems (MEMS). Selected TSV samples have depths in the range of 170…270 µm and a diameter of 50 µm. The investigations comprise the deposition of different layer stacks by means of subatmospheric and plasma enhanced chemical vapour deposition (PECVD) of tetraethyl orthosilicate; Si(OC2H5)4 (TEOS). Moreover, an etch-back approach and the selective deposition on SiN were also included in the investigations. With respect to the Via Last approach, the contact opening at the TSV bottom by means of a specific spacer-etching method have been addressed within this paper. Step coverage values of up to 74 % were achieved for the best of those approaches. As an alternative to the SiO2-isolation liners a polymer coating based on the CVD of Parylene F was investigated, which yields even higher step coverage in the range of 80 % at the lower TSV sidewall for a surface film thickness of about 1000 nm. Leakage current measurements were performed and values below 0.1 nA/cm2 at 10 kV/cm were determined for the Parylene F films which represents a promising result for the aspired application to Via Last MEMS-TSV. 相似文献
93.
94.
95.
In this paper, I review both mathematics education and CSCL literature and discuss how we can better take advantage of CSCL tools for developing mathematical proof skills. I introduce a model of proof in school mathematics that incorporates both empirical and deductive ways of knowing. I argue that two major forces have given rise to this conception of proving: a particular learning perspective promoted in reform documents and a genre of computer tools, namely dynamic geometry software, which affords this perspective of learning within the context of mathematical proof. Tracing the move from absolutism to fallibilism in the philosophy of mathematics, I highlight the vital role of community in the production of mathematical knowledge. This leads me to an examination of a certain CSCL tool whose design is guided by knowledge-building pedagogy. I argue that knowledge building is a suitable pedagogical approach for the proof model presented in this paper. Furthermore, I suggest software modifications that will better support learners’ participation in authentic proof tasks. 相似文献
96.
Oztop E 《Neural computation》2006,18(12):3119-3138
It is known that any dichotomy of {-1, 1}n can be learned (separated) with a higher-order neuron (polynomial function) with 2n inputs (monomials). In general, less than 2n monomials are sufficient to solve a given dichotomy. In spite of the efforts to develop algorithms for finding solutions with fewer monomials, there have been relatively fewer studies investigating maximum density (Pi(n)), the minimum number of monomials that would suffice to separate an arbitrary dichotomy of {-1, 1}n . This article derives a theoretical (upper) bound for this quantity, superseding previously known bounds. The main theorem here states that for any binary classification problem in {-1, 1}n (n > 1), one can always find a polynomial function solution with 2n -2n/4 or fewer monomials. In particular, any dichotomy of {-1, 1}n can be learned by a higher-order neuron with a fan-in of 2n -2n/4 or less. With this result, for the first time, a deterministic ratio bound independent of n is established as Pi(n)/2n < or = 0 75. The main theorem is constructive, so it provides a deterministic algorithm for achieving the theoretical result. The study presented provides the basic mathematical tools and forms the basis for further analyses that may have implications for neural computation mechanisms employed in the cerebral cortex. 相似文献
97.
Eftychios G. Christoforou Nikolaos V. Tsekos Alpay Özcan 《Journal of Intelligent and Robotic Systems》2006,47(2):175-196
The effective integration of robotics together with magnetic resonance (mr) technology is expected to facilitate the real-time guidance of various diagnostic and therapeutic interventions. Specially designed robotic manipulators are required for this purpose, the development of which is a challenging task given the strong magnetic fields and the space limitations that characterize the mr scanning environment. A prototype mr-compatible manipulator is presented, designed to operate inside cylindrical mr scanners. It was developed for the study of minimally invasive diagnostic and therapeutic interventions in the abdominal and thoracic area with real-time mr image guidance. Initial tests were performed inside a high-field clinical mr scanner and included mr-compatibility tests and phantom studies on image-guided targeting. 相似文献
98.
Sparse nonlinear classification and regression models in reproducing kernel Hilbert spaces (RKHSs) are considered. The use of Mercer kernels and the square loss function gives rise to an overdetermined linear least-squares problem in the corresponding RKHS. When we apply a greedy forward selection scheme, the least-squares problem may be solved by an order-recursive update of the pseudoinverse in each iteration step. The computational time is linear with respect to the number of the selected training samples. 相似文献
99.
Four different types of high-density polyethylenes were blended with expanded perlite at different compositions. -aminopropyltriethoxysilane was applied to perlite (2 wt%) from ether and water solutions to enhance the interfacial adhesion between the polymer and the filler. It was shown that silane treatment advances the yield stress with improving dispersion and increasing the interfacial adhesion of the filler with the polymer matrix. The experimental results were then checked with the expression of Turcsanyiet al.'s. 相似文献
100.
Sevan Platin Elif Ö. Özer Ugur Akman Öner Hortaçsu 《Journal of the American Oil Chemists' Society》1994,71(8):833-837
Effects of temperature (at 35, 45 or 55°C) and pressure (10–110 atm) on the relative distribution coefficients of the twelve
key components of spearmint oil (essential oil ofMentha cardiaca; Scotch spearmint) at equilibrium in dense CO2 were investigated under conditions ranging from subcritical to supercritical regions. Effects of vapor pressure, molecular
weight and polarity of the key components on their equilibrium distributions in sub/supercritical CO2 are discussed. At 35°C, all key components of spearmint oil are equally soluble in dense CO2 within the 12–102 atm pressure region. At 45 and 55°C, the key components are equally soluble for pressures greater than
about 60 atm. However, around either 45°C/27 atm or 55°C/35 atm conditions, the relative distribution coefficients of all
monoterpene hydrocarbons and of isomenthone (an oxygenated monoterpene) exhibit maxima, which are due to significantly higher
vapor pressures of these components and significantly lower solvating power of the dense-gas solvent at these particular temperatures
and pressures. Vapor-pressure effects, coupled with the decrease in solvating power, dominate the effects of polarity and
molecular mass of the key components. Deterpenation of spearmint oil with dense CO2 is possible around either 45°C/27 atm or 55°C/35 atm, where the monoterpene hydrocarbons tend to concentrate in the CO2-rich phase. 相似文献