全文获取类型
收费全文 | 22081篇 |
免费 | 1400篇 |
国内免费 | 19篇 |
专业分类
电工技术 | 366篇 |
综合类 | 54篇 |
化学工业 | 4805篇 |
金属工艺 | 639篇 |
机械仪表 | 533篇 |
建筑科学 | 970篇 |
矿业工程 | 131篇 |
能源动力 | 477篇 |
轻工业 | 2870篇 |
水利工程 | 163篇 |
石油天然气 | 53篇 |
无线电 | 1322篇 |
一般工业技术 | 5530篇 |
冶金工业 | 1899篇 |
原子能技术 | 202篇 |
自动化技术 | 3486篇 |
出版年
2023年 | 282篇 |
2022年 | 240篇 |
2021年 | 492篇 |
2020年 | 418篇 |
2019年 | 391篇 |
2018年 | 739篇 |
2017年 | 760篇 |
2016年 | 814篇 |
2015年 | 656篇 |
2014年 | 926篇 |
2013年 | 1685篇 |
2012年 | 1045篇 |
2011年 | 1240篇 |
2010年 | 1066篇 |
2009年 | 978篇 |
2008年 | 1079篇 |
2007年 | 1049篇 |
2006年 | 767篇 |
2005年 | 613篇 |
2004年 | 525篇 |
2003年 | 516篇 |
2002年 | 508篇 |
2001年 | 417篇 |
2000年 | 375篇 |
1999年 | 297篇 |
1998年 | 660篇 |
1997年 | 450篇 |
1996年 | 375篇 |
1995年 | 291篇 |
1994年 | 220篇 |
1993年 | 218篇 |
1992年 | 162篇 |
1991年 | 130篇 |
1990年 | 118篇 |
1989年 | 101篇 |
1988年 | 110篇 |
1987年 | 90篇 |
1986年 | 75篇 |
1985年 | 182篇 |
1984年 | 184篇 |
1983年 | 118篇 |
1982年 | 127篇 |
1981年 | 155篇 |
1980年 | 121篇 |
1979年 | 100篇 |
1978年 | 100篇 |
1977年 | 109篇 |
1976年 | 163篇 |
1975年 | 90篇 |
1974年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Hydrogenation of canola oil in the presence of nickel and the methyl benzoate-chrome carbonyl complex 总被引:1,自引:0,他引:1
L. J. Rubin S. S. Köseoglu L. L. Diosady W. F. Graydon 《Journal of the American Oil Chemists' Society》1986,63(12):1551-1557
Canola oil was hydrogenated using a mixture of homogeneous methyl benzoate-Cr(CO)3 and heterogeneous nickel catalysts. The effect of the methyl benzoate-Cr(CO)3_to-nickel ratio on the activity, specific isomerization index, linoleate and linolenate selectivities, and fatty acid composition
was evaluated, and the results compared with those obtained with commercial nickel catalyst and methyl benzoate-Cr(CO)3 used individually. At higher chromium-to-nickel ratios the activity of nickel was inhibited and the system behaved essentially
like the pure chrome complex, while at low chromium-to-nickel ratios the characteristics of the nickel predominated. In a
short transition zone relatively high reaction rates were obtained with significantly reducedtrans-isomer levels in the product. In a broader sense, it may be possible to combine a homogeneous and heterogeneous catalyst
while retaining the advantages of both. We may thus be able to design catalyst systems for specific applications. 相似文献
103.
Different qualities of concrete have been fire tested using different geometries of the specimens as well as different load levels and load configurations. The main objective with the study was to examine a test methodology consisting of a full‐scale test and different small scale‐tests for determining the probability of spalling and the amount of spalling of fire exposed concrete structures. A reference specimen was defined as a one‐sided fire exposed slab with the dimensions 1800 × 1200 mm2 giving an exposed area of 1500 × 1200 mm2. A number of concrete qualities with different probabilities for spalling, were tested using the reference specimen. These tests showed that the reference specimens worked well giving the expected test results. Small specimens were manufactured in different shapes with the same concrete as the one used in the reference tests. These small specimens were tested either at the same time as the reference specimens in the large furnace or afterwards on a small‐scale furnace where the fire exposed surface was 450 × 360 mm2. The test results clearly show the increased probability and the increased amount of spalling by using external compressive loading. The results also show that by using pre‐stress through bars or wires the load can be lost due to heating of the bars/wires which results in a decreased amount of spalling. The boundary of the specimen also affects the amount of spalling. The spalling around the edges was in all tests less than the spalling on the central parts of the exposed area. It could also be noted that the spalling did not pass completely through any of the specimens. The reason for this is probably that the water/vapour could migrate out from the unexposed surface of the specimen. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
104.
105.
This paper describes the spatial distribution of customer demand, supply of customer services and facility investment, as the outcome of a three-level game-like interaction between customers (e.g., shoppers), suppliers (e.g., retailers) and developers (e.g., landlords). Treating both the suppliers and developers at each centre as competitors, oligopolistic equilibria of the Nash-Stackelberg type are developed, and conditions for their existence and uniqueness established. Uncertain customer demand is specified in probabilistic terms, representing the suppliers' perception of expected customer behaviour. 相似文献
106.
107.
108.
Jörg Ziercke 《Informatik-Spektrum》2008,31(1):62-64
Zusammenfassung Die rasante Entwicklung des Internets bewirkt neben einer sich verst?rkenden Internationalisierung von Terrorismus und Organisierter
Kriminalit?t einen Strukturwandel weltweiter Kommunikation und Datenspeicherung. 相似文献
109.
In current desktop user interfaces, selection is usually accomplished easily with a mouse or a similar two-dimensional locator. In wearable computing, however, controlling two dimensions simultaneously gets significantly harder: a change in one dimension results easily in an undesired change in the other dimension as well when the user is occupied with a parallel task – such as walking. We present a way to overcome this problem by applying one-dimensional selection for graphical user interfaces in head-worn displays. Our new interaction technique allows a wearable computer user to perform object selection tasks easily and accurately. The technique is based on a visible circle on the screen. The user controls the circle, altering its radius with a one-dimensional valuator. The midpoint of the circle is in the middle of the screen. The object currently on the perimeter of the circle is highlighted and can be selected. Our preliminary usability evaluation, applying our custom evaluation method designed especially for walking users, indicates that the proposed technique is usable also when walking. 相似文献
110.
Global competition, commitment to the Kyoto Protocol and a deregulated, integrated European electricity market will in all probability increase the demand for energy efficiency on the part of companies in Sweden. Investment decisions are an important part of meeting the new demands, because they decide the future efficiency of industrial energy systems. The objective of this study is to investigate, from a managerial perspective, the need to improve decision support in some industries, which can help to facilitate and improve investment decisions concerning energy efficiency. This work has been conducted through in-depth interviews with representatives for a number of energy-intensive companies and non-energy-intensive companies from different sectors. One need that was identified was the improvement of working methods in order to support the decision-making process. Here, external players seem to be playing an increasingly important role. Access to correct information, better follow-up activities, and transparent, understandable calculations are also considered to be important. The study will form the foundation for subsequent work on decision support and energy efficiency in industry. 相似文献