全文获取类型
收费全文 | 650篇 |
免费 | 22篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 6篇 |
综合类 | 2篇 |
化学工业 | 142篇 |
金属工艺 | 22篇 |
机械仪表 | 29篇 |
建筑科学 | 18篇 |
矿业工程 | 1篇 |
能源动力 | 50篇 |
轻工业 | 23篇 |
水利工程 | 12篇 |
无线电 | 42篇 |
一般工业技术 | 190篇 |
冶金工业 | 65篇 |
原子能技术 | 8篇 |
自动化技术 | 67篇 |
出版年
2023年 | 12篇 |
2022年 | 17篇 |
2021年 | 23篇 |
2020年 | 25篇 |
2019年 | 30篇 |
2018年 | 43篇 |
2017年 | 27篇 |
2016年 | 32篇 |
2015年 | 17篇 |
2014年 | 39篇 |
2013年 | 51篇 |
2012年 | 36篇 |
2011年 | 57篇 |
2010年 | 34篇 |
2009年 | 40篇 |
2008年 | 29篇 |
2007年 | 25篇 |
2006年 | 21篇 |
2005年 | 17篇 |
2004年 | 6篇 |
2003年 | 13篇 |
2002年 | 4篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 1篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有677条查询结果,搜索用时 15 毫秒
61.
Dichalcogenides with the common formula MX(2) are layered materials with electrical properties that range from semiconducting to superconducting. Here, we describe optimal imaging conditions for the optical detection of ultrathin, two-dimensional dichalcogenide nanocrystals containing single, double and triple layers of MoS(2), WSe(2) and NbSe(2). A simple optical model is used to calculate the contrast for nanolayers deposited on wafers with varying thicknesses of SiO(2). The model is extended for imaging using the green channel of a video camera. Using AFM and optical imaging we confirm that single layers of MoS(2) and WSe(2) can be detected on 90 and 270 nm SiO(2) using optical means. By measuring contrast under broadband green illumination we are also able to distinguish between nanostructures containing single, double and triple layers of MoS(2) and WSe(2.) We observe and discuss discrepancies in the case of NbSe(2). 相似文献
62.
A lecture theatre with dimension 16 m × 8.4 m × 3.6 m located at Roorkee (28.58°N, 77.20°E) in the northern region of India, is selected to calculate the monthly and annual cooling load (kWh) and cooling capacity of air conditioning system by a computer simulation. The paper also presents the results of a study investigating the effect of different glazing systems on windows and the reduction in building cooling load. DesignBuilder software has been used for the computer simulation for calculating the cooling load. The paper aims to investigate the reduction in thermal gains and cooling load requirements by varying the U-values of different glazing types, insulating the ceiling, providing cool roofs, interior and exterior insulation on walls, and replacing the conventional fluorescent tube lamp (FTL) by energy efficient compact fluorescent lamp (CFL). Installation of false ceiling, wall insulation, different glazing types and lighting systems are cost effective with normalized annual saving ranging from 17% to 19.8% from this retrofitting project. Furthermore, the study also highlights the potential of reducing the emission of CO2 and equivalent carbon credit. Retrofitting techniques strongly influence the level of energy saving, although the payback period is generally quite long of order 8 years. 相似文献
63.
We study the multisubband electron mobility in a barrier delta doped AlχGal-χAs parabolic quantum well structure under the influence of an applied electric field perpendicular to the interface plane. We consider the alloy fraction χ = 0.3 for barriers and vary x from 0.0 to 0.1 for the parabolic well. Electrons diffuse into the well and confine within the triangular like potentials near the interfaces due to Coulomb interaction with ionized donors. The parabolic structure potential, being opposite in nature, partly compensates the Coulomb potential. The external electric field further amends the potential structure leading to an asymmetric potential profile. Accordingly the energy levels, wave functions and occupation of subbands change. We calculate low temperature electron mobility as a function of the electric field and show that when two subbands are occupied, the mobility is mostly dominated by ionised impurity scattering mediated by intersubband effects. As the field increases transition from double subband to single subband occupancy occurs. A sudden enhancement in mobility is obtained due to curtailment of intersubband effects. Thereafter the mobility is governed by both impurity and alloy disorder scatterings. Our analysis of mobility as a function of the electric field for different structural parameters shows interesting results. 相似文献
64.
R. Sahoo 《Particulate Science and Technology》2005,23(3):285-296
Single-particle breakage tests of South Blackwater and Ensham coal from the Bowen Basin area in Queensland were conducted by a computer-monitored twin-pendulum device to measure the energy utilization pattern of the breakage particles. Three particle sizes (-16.0 + 13.2 mm, -13.2 + 11.2 mm, -11.2 + 9.5 mm) of each coal were tested by a pendulum device at five input energy levels to measure the specific comminution energy. When particles were tested at constant input energy, the variation of comminution energy between the same size broken particles of Ensham coal was minimal, because Ensham coal is a softer and higher friability coal, which absorbs more input energy than harder coal during breakage tests. For different particle sizes, the specific comminution energy increases linearly with the input energy and the fineness of the breakage products increases with the specific comminution energy.The size distribution graphs are curved but approach linearity in the finer region. At a constant input energy, the twin pendulum breakage product results show that the fineness of the products increases with decrease in particle size and South Blackwater coal produced finer products than the Ensham coal. The t-curves are the family of size distribution curves, which can describe the product size distribution of the breakage particles during single-particle breakage tests. 相似文献
65.
66.
67.
Graft copolymerization of methyl methacrylate (MMA) onto cotton–cellulose has been carried out using hexavalent chromium Cr(VI) as initiator. Aqueous-methanolic solution of perchloric acid has been chosen as the reaction medium. The effect of monomer, initiator, acid, reaction medium, and temperature on the graft percentage has been found out. The reactions have also been carried out in the presence of polymerization, inhibitors, and retarders, such as hydroquinone and transition metal salts like CuSO4, FeCl3, etc. The grafted samples, after exhaustive separation of homopolymers and purification, were subjected to various chemical, mechanical, and thermal testings. The results of various analyses have been compared with the reference, and the improvement in the graft has been evaluated. A suitable mechanism for the grafting processes has been suggested, in accordance with the experimental results. 相似文献
68.
69.
Summary In a recent paper [H. F. MOED, E. GARFIELD: In basic science the percentage of “authoritative”references decreases as bibliographies
become shorter. Scientometrics 60 (3) (2004) 295-303] the authors show, experimentally, the validity of the statement in the
title of their paper. In this paper we give a general informetric proof of it, under certain natural conditions. The proof
is given both in the discrete and the continuous setting. An easy corollary of this result is that the fraction of non-authoritative
references increases as bibliographies become shorter. This finding is supported by a set of data of the journal Information
Processing and Management (2002 + 2003) with respect to the fraction of conference proceedings articles in reference lists. 相似文献
70.