全文获取类型
收费全文 | 808篇 |
免费 | 37篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 17篇 |
综合类 | 1篇 |
化学工业 | 179篇 |
金属工艺 | 4篇 |
机械仪表 | 21篇 |
建筑科学 | 24篇 |
能源动力 | 74篇 |
轻工业 | 76篇 |
水利工程 | 6篇 |
石油天然气 | 17篇 |
无线电 | 94篇 |
一般工业技术 | 164篇 |
冶金工业 | 85篇 |
原子能技术 | 17篇 |
自动化技术 | 70篇 |
出版年
2023年 | 21篇 |
2022年 | 38篇 |
2021年 | 70篇 |
2020年 | 25篇 |
2019年 | 40篇 |
2018年 | 31篇 |
2017年 | 22篇 |
2016年 | 43篇 |
2015年 | 28篇 |
2014年 | 36篇 |
2013年 | 59篇 |
2012年 | 36篇 |
2011年 | 50篇 |
2010年 | 29篇 |
2009年 | 27篇 |
2008年 | 23篇 |
2007年 | 30篇 |
2006年 | 7篇 |
2005年 | 15篇 |
2004年 | 16篇 |
2003年 | 13篇 |
2002年 | 9篇 |
2001年 | 8篇 |
2000年 | 9篇 |
1999年 | 11篇 |
1998年 | 34篇 |
1997年 | 21篇 |
1996年 | 14篇 |
1995年 | 6篇 |
1994年 | 14篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1966年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有849条查询结果,搜索用时 0 毫秒
71.
CHANGES IN ASPHALT CHEMISTRY AND DURABILITY DURING OXIDATION AND POLYMER MODIFICATION 总被引:1,自引:0,他引:1
The Gulf Countries' environmental conditions are very severe. The temperature zoning study indicate that more than half of Gulf areas experience a maximum seven consecutive days pavement temperature of 76°C (Al-Abdul Wahhab et al., 1997). This has resulted in damage to the road networks in the form of cracking, rutting and deformation. Polymer modification of asphalt is required to increase the resistance to permanent deformation at relatively high temperatures without adversely affecting the properties of the asphalts at low temperature. In this work chemical and performance-related properties of fresh, oxidized, and polymer modified asphalts were evaluated. The physical properties and performance characteristics of asphalts were found to depend on the chemical composition of asphalt. The interactions of polar functionalities actually present or formed during oxidative aging or due to polymer modification, influence the viscosity and related flow properties. The changes in composition of fresh, oxidized and polymer-modified asphalts can be clearly identified from Infrared spectroscopy. NMR spectroscopy enables detailed information about the Carbon-and-hydrogen-types and average molecular/structural parameters of asphalt without separating it into different components. 相似文献
72.
S. Afaque M. H. Ansari M. S. Ahmad M. S. Siddiqui 《Journal of the American Oil Chemists' Society》1989,66(9):1334-1337
Substituted oxathiolane and thioether derivatives have been synthesized from an allylic oxo fatty acid ester. The reaction
of methyl 4-oxo-trans-2-octadecenoate with 3-mercaptopropan-1,2-diol (1-thioglycerol) affords methyl 4-(3′-hydroxymethyl-1′,4′-oxathiolane)-2(3)-(O-mercaptopropan-1″,2″-diol)-octadecanoate
(II), methyl 4-oxo-2(3)-(O-mercaptopropan-1′,2′-diol)-octadecanoate (III), methyl 4-(3′-hydroxy-l′,5′-oxathiane)-2 (3)-(S-mercaptopropan-1″,2″-diol)-octadecanoate
(IV), methyl 4-oxo-2(3)-(S-mercaptopropan-1′, 2′diol)-octadecanoate (V) and methyl 4-(3′-hydroxymethyl-1′, 4′-oxathiolane)-2(3)-(S-mercaptopropan-1″,
2″-diol)-octadecanoate (VI). Structures of the individual reaction products have been established on the basis of spectral
data and microanalyses. 相似文献
73.
G.J. Hutchings R. Wells S. Feast M.R.H. Siddiqui D.J. Willock F. King C.H. Rochester D. Bethell P.C.B. Page 《Catalysis Letters》1997,46(3-4):249-254
Modification of zeolite H-Y by dithiane oxides (2-R-1,3-dithiane 1-oxide, R = H, CH3, C6H5) is shown to enhance significantly its activity for the acid-catalysed gas phase dehydration of butan-2-ol. The rate enhancement
is observed for catalysts that are prepared using two commercial samples of zeolite H-Y. The origin of this effect is examined
using in situ FTIR spectroscopy and 27Al and 29Si MAS NMR spectroscopy studies of the modified zeolite. The rate enhancement is considered to result from a specific interaction
between the dithiane oxide modifier with both the extra-framework and framework aluminium in the zeolite.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
74.
Curing kinetics of anisotropic conductive adhesive film 总被引:1,自引:0,他引:1
Polymer-based conductive-adhesive materials have become widely used in many electronic packaging interconnect applications,
such as chip-on-glass, chip-on-flex, etc. Among all the conductive-adhesive materials, anisotropic conductive adhesive film
(ACF) is an attractive interconnect material because of its fine pitch capability. Anisotropic conductive-adhesive film is
a thermosetting, epoxy matrix impregnated with a small amount of electrically conductive particles. During component assembly,
the epoxy resin is cured to provide mechanical connection, and the conducting medium provides electrical connection in the
z direction. The thermal cure process is critical to develop the ultimate electrical and mechanical properties of the ACF.
In this paper, the curing reaction of ACF was studied with a differential scanning calorimeter (DSC) under isothermal conditions
in the range of 120–180°C. An autocatalyzed kinetic model was used to describe the curing reaction. The rate constant and
the reaction orders were determined and used to predict the progress of the curing reaction. A good agreement is found between
the proposed kinetic model and the experimental reaction-rate data. The reaction-rate constants were correlated with the isothermal
temperature by the Arrhenius equation. The glass-transition temperature also has been studied as a function of cure degree
and moisture absorption. 相似文献
75.
The last-observation-carried-forward imputation method is commonly used for imputting data missing due to dropouts in longitudinal clinical trials. The method assumes that outcome remains constant at the last observed value after dropout, which is unlikely in many clinical trials. Recently, random-effects regression models have become popular for analysis of longitudinal clinical trial data with dropouts. However, inference obtained from random-effects regression models is valid when the missing-at-random dropout process is present. The random-effects pattern-mixture model, on the other hand, provides an approach that is valid under more general missingness mechanisms. In this article we describe the use of random-effects pattern-mixture models under different patterns for dropouts. First, subjects are divided into groups depending on their missing-data patterns, and then model parameters are estimated for each pattern. Finally, overall estimates are obtained by averaging over the missing-data patterns and corresponding standard errors are obtained using the delta method. A typical longitudinal clinical trial data set is used to illustrate and compare the above methods of data analyses in the presence of missing data due to dropouts. 相似文献
76.
Bhutan's energy and environmental situation and approaches to development are reviewed and analyzed in this paper. Conservation of natural resources and human happiness have been placed as central strategic policy themes and have been given high priority in the national development plans of Bhutan. Bhutan's unique approach to development via Gross National Happiness (GNH) or the Middle Path of development is being facilitated by the Royal Government of Bhutan as a tool to balance poverty alleviation, environmental conservation and development. However, challenges exist due to the constraints of resources, good governance, legal frameworks, and human capacity. This paper reviews selected sustainable energy projects (e.g. energy from renewables or energy conservation) in Bhutan and finds that in fact, Bhutan's renewable energy resources (e.g. water and forests) which have proved to be indispensable for development are vulnerable due to the adverse impacts of climate change and environmental degradation. Appropriate measures in order to reduce potential environmental degradation and mitigate climate change impacts have been acknowledged globally and these have potential for application in Bhutan. For example, implementation of sustainable energy projects under the Clean Development Mechanism (CDM) of the Kyoto Protocol could offer an opportunity for mitigating climate change impacts and also contributing to sustainable development. 相似文献
77.
An attempt has been made in this paper to estimate the reliability of an s-out-of-k system with non-identical component strengths when component strengths follow an exponential distribution. A further assumption is made that all the components are subjected to a common random stress which also follow an exponential distribution. Bayes and maximum likelihood estimators of such system reliability are considered. A Bayes estimate is obtained by using Lindley's approximation. Comparisons are made on the basis of efficiency and Pitman nearness probability through a Monte-Carlo study. 相似文献
78.
79.
S. Reaz Ahmed S. K. Deb Nath M. Wahhaj Uddin 《International journal for numerical methods in engineering》2005,64(6):729-750
Optimum design of tire‐tread sections is an important practical issue. However, useful study of the problem that can suggest a reliable guideline for determining the optimum tread sections had hardly been made in the past. The present paper describes a new analysis of the state of stresses in tire‐tread sections in contact with the road surface, taking special care of the boundary conditions. Based on the analysis, a method is proposed to determine the optimum tread shapes for avoiding lateral slippage between tires and roads. The displacement potential function formulation, an ideal mathematical model for the practical stress problems, has been used in conjunction with finite‐difference method of solution. For the present analysis, lateral slipping in absence of frictional resistance as well as the no‐slip conditions of the tire‐tread contact surface have been considered along with a large number of tread aspect ratios. The present computational approach proves to be a powerful tool for determining the optimum tread shapes for avoiding the lateral slippage of tire‐treads. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
80.
In Vitro Antiamoebic Activity Evaluation and Docking Studies of Metronidazole–Triazole Hybrids 下载免费PDF全文
Dr. Beena Negi Dr. K. Kranthi Raj Shadab Miyan Siddiqui Dr. Dittakavi Ramachandran Dr. Amir Azam Prof. Diwan S. Rawat 《ChemMedChem》2014,9(11):2439-2444
An in‐house database of 520 compounds was docked against Entamoeba histolytica thioredoxin reductase (EhTrR), a promising target for the treatment of amoebiasis. Amongst these, some metronidazole (MTZ)–triazole hybrids were ranked high, with docking scores from ?10.23 to ?7.56. Studies of the binding orientations and conformations show that the head groups of MTZ–triazole hybrids interact with the arginine residues within the binding pocket of EhTrR, making it clear that such is the optimal and most reliable orientation for this class of compounds. The top‐ten MTZ–triazole hybrids were then selected for evaluation of their activity against the HM1:IMSS strain of amoeba. The most active compound, 2‐pyridyl‐(1,2,3‐triazolyl)metronidazole 10 , with an IC50 value of 8.4 nM , was significantly more active than the standard drug MTZ alone. Docking studies revealed that compound 10 may act as an EhTrR inhibitor with activity in the nanomolar range and satisfactory ADME properties; it is a suitable candidate to be carried forward as a potential lead in the discovery of drugs to combat amoebiasis. 相似文献