全文获取类型
收费全文 | 294210篇 |
免费 | 23412篇 |
国内免费 | 15535篇 |
专业分类
电工技术 | 19142篇 |
技术理论 | 56篇 |
综合类 | 40765篇 |
化学工业 | 30865篇 |
金属工艺 | 10436篇 |
机械仪表 | 16074篇 |
建筑科学 | 40643篇 |
矿业工程 | 15973篇 |
能源动力 | 9019篇 |
轻工业 | 14960篇 |
水利工程 | 14851篇 |
石油天然气 | 11969篇 |
武器工业 | 3024篇 |
无线电 | 19763篇 |
一般工业技术 | 22206篇 |
冶金工业 | 18053篇 |
原子能技术 | 2903篇 |
自动化技术 | 42455篇 |
出版年
2024年 | 949篇 |
2023年 | 3048篇 |
2022年 | 5466篇 |
2021年 | 6643篇 |
2020年 | 7107篇 |
2019年 | 6044篇 |
2018年 | 5826篇 |
2017年 | 6986篇 |
2016年 | 8159篇 |
2015年 | 9023篇 |
2014年 | 16322篇 |
2013年 | 15384篇 |
2012年 | 19229篇 |
2011年 | 20749篇 |
2010年 | 16556篇 |
2009年 | 17272篇 |
2008年 | 16373篇 |
2007年 | 20971篇 |
2006年 | 19807篇 |
2005年 | 17267篇 |
2004年 | 14662篇 |
2003年 | 13081篇 |
2002年 | 10841篇 |
2001年 | 9118篇 |
2000年 | 7724篇 |
1999年 | 6346篇 |
1998年 | 4807篇 |
1997年 | 4232篇 |
1996年 | 3877篇 |
1995年 | 3327篇 |
1994年 | 2951篇 |
1993年 | 2228篇 |
1992年 | 1989篇 |
1991年 | 1473篇 |
1990年 | 1285篇 |
1989年 | 1159篇 |
1988年 | 923篇 |
1987年 | 619篇 |
1986年 | 497篇 |
1985年 | 406篇 |
1984年 | 387篇 |
1983年 | 284篇 |
1982年 | 260篇 |
1981年 | 205篇 |
1980年 | 159篇 |
1979年 | 136篇 |
1978年 | 88篇 |
1977年 | 91篇 |
1975年 | 62篇 |
1955年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
The interaction of different metal oxides such as Co3O4, NiO, Al2O3, Cr2O3, Fe2O3 and SiO2 with Na2SO4 at a temperature of 1100 and 1200 K in flowing oxygen has been studied. The thermogravimetric studies for each system were
carried out as a function of Na2SO4 in the mixture. The presence of different constituents in the reaction products were identified by X-ray diffraction analysis
and the morphologies of the reaction products were characterized using metallography and scanning electron microscopy (SEM).
The formation of products was also investigated by thermodynamic computation of free energies of the reactions and the study
of relevant equilibrium phase diagrams. The soluble species in the aqueous solutions of the reaction products were determined
quantitatively using atomic absorption spectrophotometry.
The high temperature interaction products usually contain a 3-phase structure namely, Na2O·M2O
x
, M2O
x
and metal sulphide and/or metal sulphate. The formation of Na2O·M2O
x
depends upon the solid state solubility of metal oxide in the molten salt at high temperatures. Under limited solubility
conditions Na2O·M2O
x
is invariably formed, but as soon as this condition is relaxed the oxide. M2O
x
, precipitates and forms a separate phase. 相似文献
132.
Reconstruction of an original continuous curve and the estimation of its parameters from the digitized version of the curve
is a challenging problem, as quantization always causes some loss of information. In this paper, we have developed a scheme
for reconstruction which is applicable to a class of curves having at the most two parameters. The class of curves for which
the scheme works has also been characterized. We have shown that for one-parameter curves the exact domain of values of the
parameter can be obtained. But in the two-parameter case, only the smallest rectangle containing the domain can be realised.
The distinctive feature of our scheme is that it provides a unified approach to solve the reconstruction and the domain-finding
problem for a class of curves. 相似文献
133.
Results from applying the model on a sample of contractors, the majority of whom were international and operating in Egypt, reinforces the credibility of the developed methodology, claim the authors. 相似文献
134.
With this volume, the 47-year old Canadian Journal of Psychology takes a new name and makes a renewed commitment. In retitling the journal the Canadian Journal of Experimental Psychology, the intention is to reflect more clearly what has always been the major goal of the journal--to publish the best new research in experimental psychology, both Canadian and international, in both French and English. I am honoured to become the tenth editor of the major journal for experimental psychology in Canada. CJP has served the field very well; my primary goal is to ensure that CJEP continues to do so. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
135.
Sensitivity analysis is used to show how uncertainties in basic factors, such as heat transfer, pressure drop, compressor efficiency, and thermophysical properties, influence the result of heat pump cycle performance estimations. By comparing the results of this analysis with uncertainty levels of estimations and experimental determinations, it is established to what extent improvements in accuracy are needed. The investigation was carried out for several different applications and, as working fluids, both pure substances and non-azeotropic mixtures were examined. It was found that evaporation heat transfer and compressor efficiency are two areas where improvements are needed. It is also shown that estimates using very accurate, substance-specific, equations of state differ from those using more general types by up to 1 % for COP and 2% for capacity. 相似文献
136.
A semi-analytic boundary element method for parabolic problems 总被引:1,自引:0,他引:1
A new semi-analytic solution method is proposed for solving linear parabolic problems using the boundary element method. This method constructs a solution as an eigenfunction expansion using separation of variables. The eigenfunctions are determined using the dual reciprocity boundary element method. This separation of variables-dual reciprocity method (SOV-DRM) allows a solution to be determined without requiring either time-stepping or domain discretisation. The accuracy and computational efficiency of the SOV-DRM is found to improve as time increases. These properties make the SOV-DRM an attractive technique for solving parabolic problems. 相似文献
137.
138.
Dmitri E. Nikonov George I. Bourianoff Paolo A. Gargini 《Journal of Superconductivity and Novel Magnetism》2006,19(6):497-513
Quantum limits of power dissipation in spintronic computing are estimated. A computing element composed of a single electron
in a quantum dot is considered. Dynamics of its spin due to external magnetic field and interaction with adjacent dots are
described via the Bloch equations. Spin relaxation due to magnetic noise from various sources is described as coupling to
a reservoir. Resulting dissipation of energy is calculated and is shown to be much less than the thermal limit, ∼kT per bit,
if the rate of spin relaxation is much slower than the switching rate. Clues on how to engineer an energy efficient spintronic
device are provided. 相似文献
139.
陈金强 《数字社区&智能家居》2007,(9):1460-1461
中等职业学校一般开设VB、VC及数据库等涉及程序设计的计算机课程。本文拟就程序设计中一题多解的教学方法进行探讨。 相似文献
140.
W D Tiner 《International Journal of Project Management》1985,3(1):13-18
In order to control a project, construction management requires project information. This is obtained through accounting, estimating, cost management and scheduling functions which produce project reports. These reports are best obtained by subdividing the project into small parts. The ways in which each of these functions subdivides a project in order to produce its reports is discussed, together with a means of interrelating this information with a technique known as the work breakdown structure. 相似文献