全文获取类型
收费全文 | 4563篇 |
免费 | 30篇 |
专业分类
电工技术 | 11篇 |
综合类 | 1篇 |
化学工业 | 221篇 |
金属工艺 | 36篇 |
机械仪表 | 33篇 |
建筑科学 | 38篇 |
矿业工程 | 2篇 |
能源动力 | 26篇 |
轻工业 | 218篇 |
水利工程 | 20篇 |
石油天然气 | 2篇 |
无线电 | 139篇 |
一般工业技术 | 144篇 |
冶金工业 | 3518篇 |
原子能技术 | 8篇 |
自动化技术 | 176篇 |
出版年
2023年 | 7篇 |
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2018年 | 21篇 |
2017年 | 18篇 |
2016年 | 17篇 |
2015年 | 17篇 |
2014年 | 29篇 |
2013年 | 48篇 |
2012年 | 43篇 |
2011年 | 54篇 |
2010年 | 40篇 |
2009年 | 44篇 |
2008年 | 52篇 |
2007年 | 57篇 |
2006年 | 41篇 |
2005年 | 47篇 |
2004年 | 39篇 |
2003年 | 46篇 |
2002年 | 45篇 |
2001年 | 41篇 |
2000年 | 37篇 |
1999年 | 140篇 |
1998年 | 1058篇 |
1997年 | 624篇 |
1996年 | 399篇 |
1995年 | 244篇 |
1994年 | 184篇 |
1993年 | 212篇 |
1992年 | 46篇 |
1991年 | 68篇 |
1990年 | 55篇 |
1989年 | 70篇 |
1988年 | 74篇 |
1987年 | 73篇 |
1986年 | 48篇 |
1985年 | 42篇 |
1984年 | 15篇 |
1983年 | 18篇 |
1982年 | 21篇 |
1981年 | 35篇 |
1980年 | 45篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1977年 | 78篇 |
1976年 | 177篇 |
1974年 | 8篇 |
1970年 | 6篇 |
排序方式: 共有4593条查询结果,搜索用时 15 毫秒
51.
Bioactive peptides and carbohydrates are sourced from a myriad of plant, animal and insects and have huge potential for use as food ingredients and pharmaceuticals. However, downstream processing bottlenecks hinder the potential use of these natural bioactive compounds and add cost to production processes. This review discusses the health benefits and bioactivities associated with peptides and carbohydrates of natural origin and downstream processing methodologies and novel processes which may be used to overcome these. 相似文献
52.
Mathematical models for single electrode reversible heat and non-isothermal electromotive force (EMF) of a solid oxide fuel cell (SOFC) are developed. These models estimate the volumetric reversible heat generation and EMF of electrochemical reactions, within each electrode at local conditions of temperature and pressure, based on entropy change of half reactions. The resulting equations are thermodynamically consistent. They inherently obey the conservation of energy law as the electrochemical energy released added to the heat of reactions at each electrode equate the enthalpy change of the reacted species. The equations are implemented to model electrodes in a tubular micro- solid oxide fuel cell (TμSOFC). The thermodynamic consistency of the model is numerically confirmed as the enthalpy of the reactants equates the electric energy released by the cell plus the sum of electrode heats plus electrolyte Ohmic heat. The effect of thermal gradients on the cell's overall EMF is found to be negligible. The reversible and irreversible heat generation of each electrode are distinguished. Overall, the anode is found to be endothermic, and the cathode exothermic. 相似文献
53.
The European rabbit (Oryctolagus cuniculus) uses the secretion of the chin gland in the maintenance of social status. Previous work has concentrated on secretion collected directly from the animal. In this study, the analysis was conducted by collecting scent marks made by free-ranging animals. Scent marks were found to be concentrated at the center of the area controlled by a social group, and at the boundaries between two adjacent social groups. Only the mark from dominant animals could be identified. Marks were also collected from the skin of rabbits, where they had been placed by the dominant individual. The mark found on the head of a subordinate animal may, in the future, be used to identify the dominant animal of the social group, who placed the mark. 相似文献
54.
55.
Brian S. Hayes James C. Seferis George A. Parker 《Polymer Engineering and Science》2000,40(6):1344-1349
Low temperature cure cyanate ester resin systems were developed and modified with epoxy‐terminated butadiene acrylonitrile rubber (ETBN) and impregnated into woven glass fabric. Mode I and mode II interlaminar fracture toughness values of the cured laminates were evaluated as a function of rubber concentration. Mode I fracture toughness increased to almost twice that of the unmodified system, while mode II fracture toughness remained essentially unchanged. Composite samples were subjected to aging experiments in water and the absorption/desorption behavior was investigated as was the effect on thermal performance. The presence of rubber was found to reduce the rate of matrix deterioration but also caused a substantial increase in water uptake. It was found that although the addition of rubber to the matrices decreased the unconditioned (dry) Tg all specimens showed the same reduction in Tg, after equilibrium water absorption. 相似文献
56.
57.
Magic-angle spinning (MAS) 13C nuclear magnetic resonance (NMR) spectroscopy is a convenient method for nondestructive, quantitative characterization of
seed oil composition. We describe results for intact hybrid and transformed canola seeds. The MAS 13C NMR technique complements and agrees with gas chromatography results. The spectral resolution approaches that of neat, liquid
oils. MAS 13C NMR data allow quantitative analysis of major oil components, including saturates and oleic, linoleic, and linolenic acyl
chains. 13C NMR directly and quantitatively elucidates, triglyceride regiochemistry and acyl chain cis-trans isomers that cannot be quickly detected by other methods. MAS 13C NMR can serve as the primary method for development of near-infrared seed oil calibrations. These NMR methods are nondestructive
and attractive for plant-breeding programs or other studies (e.g., functional genomics) where loss of seed viability is inconvenient. 相似文献
58.
Spawning habits of fall Chinook salmon in the Hanford Reach of the Columbia River have been documented with annual aerial surveys since 1948. We developed a series of models analysing these data, exploring the influence of environmental factors on the timing of redd construction. These models included a logistic regression and a dynamic modelling approach, with combinations of day of year (as a surrogate for environmental cues such as day length), water temperature and discharge as potential explanatory factors. Results of these analyses indicate that day of year was the strongest predictor of the timing of redd construction, but with significant modifying effects of water temperature and discharge. The dynamic modelling approach provides substantial advantages over a traditional logistic regression, including (1) the ability to treat data collected at non‐synchronous time intervals in a consistent fashion and (2) the ability to easily implement complex functions (e.g., threshold responses) relating behaviour to environmental cues. Evaluation of the series as a whole indicates that the median date of redd construction has increased over time, from approximately day 299 in 1950 to day 307 in 2010, as has the temperature on Oct 1 (16.3 °C–18.1 °C). The degree to which these changes are caused by climate change or dam operations is uncertain, however. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
59.
The spectacular recent economic growth in the Asia-Pacific region in general, and in many of the economies of Northeast Asia in particular, has spurred a vast expansion in the need for energy services, and an expansion in the demand for the fuels that help to supply these services. Future projections suggest that the growth of fossil fuel use in Northeast Asia, especially in China, will have major consequences for financial and fuel markets and pollution both regionally and globally. Before the project described in this paper was initiated, there was no ongoing forum for energy experts from all of the countries of the region to meet, informally and in an unofficial capacity, to discuss openly and in a targeted fashion the energy situations in their countries, and to work together to evaluate the energy efficiency costs and benefits of different ways of meeting regional demand. The Asian Energy Security (AES) project provides such a forum, and as such constitutes a unique resource in the engagement of the countries of Northeast Asia on the topic of energy security. 相似文献
60.
“Energy Security” has typically, to those involved in making energy policy, meant mostly securing access to oil and other fossil fuels. With increasingly global, diverse energy markets, however, and increasingly transnational problems resulting from energy transformation and use, old energy security rationales are less salient, and other issues, including climate change and other environmental, economic, and international considerations are becoming increasingly important. As a consequence, a more comprehensive operating definition of “Energy Security” is needed, along with a workable framework for analysis of which future energy paths or scenarios are likely to yield greater Energy Security in a broader, more comprehensive sense. Work done as a part of the Nautilus Institute's “Pacific Asia Regional Energy Security” (PARES) project developed a broader definition of Energy Security, and described an analytical framework designed to help to compare the energy security characteristics – both positive and negative – of different quantitative energy paths as developed using software tools such as the LEAP (Long-range Energy Alternatives Planning) system. 相似文献