全文获取类型
收费全文 | 3187篇 |
免费 | 145篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 33篇 |
综合类 | 2篇 |
化学工业 | 631篇 |
金属工艺 | 59篇 |
机械仪表 | 89篇 |
建筑科学 | 167篇 |
矿业工程 | 17篇 |
能源动力 | 151篇 |
轻工业 | 289篇 |
水利工程 | 25篇 |
石油天然气 | 2篇 |
无线电 | 273篇 |
一般工业技术 | 625篇 |
冶金工业 | 274篇 |
原子能技术 | 18篇 |
自动化技术 | 681篇 |
出版年
2023年 | 22篇 |
2022年 | 45篇 |
2021年 | 66篇 |
2020年 | 54篇 |
2019年 | 63篇 |
2018年 | 66篇 |
2017年 | 78篇 |
2016年 | 100篇 |
2015年 | 87篇 |
2014年 | 117篇 |
2013年 | 204篇 |
2012年 | 202篇 |
2011年 | 263篇 |
2010年 | 173篇 |
2009年 | 167篇 |
2008年 | 192篇 |
2007年 | 164篇 |
2006年 | 130篇 |
2005年 | 118篇 |
2004年 | 109篇 |
2003年 | 90篇 |
2002年 | 83篇 |
2001年 | 76篇 |
2000年 | 45篇 |
1999年 | 36篇 |
1998年 | 72篇 |
1997年 | 58篇 |
1996年 | 40篇 |
1995年 | 47篇 |
1994年 | 32篇 |
1993年 | 16篇 |
1992年 | 19篇 |
1991年 | 20篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 15篇 |
1987年 | 11篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 12篇 |
1979年 | 18篇 |
1978年 | 8篇 |
1977年 | 13篇 |
1976年 | 12篇 |
1975年 | 13篇 |
1973年 | 8篇 |
排序方式: 共有3336条查询结果,搜索用时 62 毫秒
181.
Ionic liquids (ILs) are typically molten salts at temperatures lower than 100 °C. Because of their thermal and electrochemical properties, they are good candidates to replace the state-of-the-art electrolytes used in today's Li-ion batteries. These commercial batteries often suffer from hazards caused by possible misuse. Elevated voltages and high temperatures usually lead to electrolyte degradation due to parasitic reactions with the electrodes leading to gas (mainly CO2) evolution and may then eventually catch fire. Also, ILs are able to dissolve various gas molecules, making it possible to prevent a built-up of an overpressure inside the battery in case of undesired gas evolution. In this work, CO2 storage in two different ionic liquids, i.e. PYR14TFSI and [BMIm][BF4] is studied with regard to their respective Li-salt. Mixtures of ILs plus different concentrations of CO2 were made. Phase diagrams of the pressure vs. temperature of the systems “liquid + vapour” to liquid transitions are drawn. Data points from 1.5 bar to 70 bar are collected with a Cailletet apparatus. Both of the ILs show good CO2 dissolution ability; an increase of the temperature leads to an increase of the pressure needed to dissolve similar amounts of CO2. The presence of a Li-salt hampers gas storage, particularly for PYR14TFSI. A model based on the Langmuir adsorption theory is used to describe the solubility of the CO2 in [BMIm][BF4]. The PYR14TFSI IL does not obey the Langmuir-like solubility behaviour. Hence, the solubility then is described by the formation of discrete bonds between the CO2 and the solvent, similarly to the concept of adspecies and surface sites. 相似文献
182.
Scientific journals claim that correspondence sections are for post-publication peer review. We compared the conditions for
submission and the bibliometrics of letters-to-editors published in leading medical journals in 2002 and 2007 using journal-derived
information and data from PubMed and Journal Citation Reports. The median time limit for letter submissions decreased from
6 to 3.5 weeks, the median word limit from 400 to 350. The median number of letters per published article was near one in
both years. Only about half of the letters were followed by an author reply in either year. Electronic response systems were
available for four journals in 2007. 相似文献
183.
During the last decade, there has been an intensive debate on-going in Sweden about how power generation and use affect global warming. More precisely, the discussion has considered how electricity shall be assessed from an environmental and climate perspective in different situations. This article gives a critical analysis on the main viewpoints. A number of environmental-impact assessment principles are outlined and critically examined. Concepts like average electricity and marginal electricity are discussed, and Electricity Disclosure as a basis for evaluation is addressed. The impact from Emission Trading and Tradable Green Certificates is also considered. Recommendations to concerned stakeholders are given. The clash points in the Swedish debate are highlighted and thus made available to a broader audience outside Scandinavia. 相似文献
184.
This work constitutes detailed EIS (Electrochemical Impedance Spectroscopy) measurements on a PBI-based HT-PEM unit cell. By means of EIS the fuel cell is characterized in several modes of operation by varying the current density, temperature and the stoichiometry of the reactant gases. Using Equivalent Circuit (EC) modeling key parameters, such as the membrane resistance, charge transfer resistance and gas transfer resistance are identified, however the physical interpretation of the parameters derived from EC’s are doubtful as discussed in this paper. The EC model proposed, which is a modified Randles circuit, provides a reasonably good fit at all the conditions tested. The measurements reveal that the cell temperature is an important parameter, which influences the cell performance significantly, especially the charge transfer resistance proved to be very temperature dependent. The transport of oxygen to the Oxygen Reduction Reaction (ORR) likewise has a substantial effect on the impedance spectra, results showed that the gas transfer resistance has an exponential-like dependency on the air stoichiometry. Based on the present results and results found in recent publications it is still not clear what exactly causes the distinctive low frequency loop occurring at oxygen starvation. Contrary to the oxygen transport, the transport of hydrogen to the Hydrogen Oxidation Reaction (HOR), in the stoichiometry range investigated in this study, shows no measurable change in the impedance data. Generally, this work is expected to provide a basis for future development of impedance-based fuel cell diagnostic systems for HT-PEM fuel cell. 相似文献
185.
We report on the measurement of second-harmonic signals from hyperplastic parenchyma and stroma in malignant human prostate tissue under femtosecond pulsed illumination in the wavelength range from 730 to 870 nm. In particular, the relationship of the second-harmonic generation to the excitation wavelength is measured. The result in these two regions behaves considerably differently and thus provides a possible indicator for identifying tissue components and malignancy. 相似文献
186.
A total of 890 samples of fresh produce obtained from Norwegian markets were examined in order to assess the bacteriological quality of the products and their potential public health risk. The samples comprised lettuce, pre-cut salads, growing herbs, parsley and dill, mushrooms and strawberries. The samples were analysed for the presence of thermotolerant coliform bacteria (TCB), Escherichia coli O157, Salmonella spp., Listeria monocytogenes, Staphylococcus spp., and Yersinia enterocolitica. Neither Salmonella spp. nor E. coli O157 were isolated. For all product groups included, TCB were isolated from a small proportion of samples. Three samples harboured L. monocytogenes; one of the isolates belonging to serogroup 1 (champignons) and two of the isolates belonging to serogroup 4 (Chinese leaves and strawberries). Staphylococci were isolated from a relatively large proportion of the samples of strawberries and mushrooms. However, only four isolates were identified as S. aureus (non-toxinogenic). By the use of PCR, the presence of Y. enterocolitica was indicated in a few of the samples of lettuce, whilst no positive samples were found using a culturing method. The study shows that the occurrence of pathogenic bacteria and TCB in the products analysed was quite low. Nevertheless, the results indicate that the type of products analysed may contain pathogenic bacteria and thereby represent a risk to the consumers in regard to food-borne diseases. 相似文献
187.
In this paper a method for fitting open surfaces to data obtained from images is presented using a level set representation
of the surface. This is done by tracking a curve, representing the boundary, on the implicitly defined surface. This curve
is given as the intersection of the level set describing the surface and an auxiliary level set. These two level sets are
propagated using the same motion vector field. Special care has to be taken in order for the surfaces not to intersect at
other places than at the desired boundary. Methods for accomplishing this are presented and a fast scheme for finding initial
values is proposed. This method gives a piecewise linear approximation of the initial surface boundary using a partition of
the convex hull of the recovered 3D data. With the approach described in this paper, open surfaces can be fitted to e.g. point
clouds obtained using structure from motion techniques. This paper solves an important practical problem since in many cases
the surfaces in the scene are open or can only be viewed from certain directions. Experiments on several data sets support
the method. 相似文献
188.
Stankiewicz Brian J.; Legge Gordon E.; Mansfield J. Stephen; Schlicht Erik J. 《Canadian Metallurgical Quarterly》2006,32(3):688
The authors describe 3 human spatial navigation experiments that investigate how limitations of perception, memory, uncertainty, and decision strategy affect human spatial navigation performance. To better understand the effect of these variables on human navigation performance, the authors developed an ideal-navigator model for indoor navigation whose optimizing algorithm uses a partially observable Markov decision process. The model minimizes the number of actions (translations and rotations) required to move from an unknown starting state to a specific goal state in indoor environments that have perceptual ambiguity. The authors compared the model's performance with that of the human observer to measure human navigation efficiency. Experiment 1 investigated the effect of increasing the layout size on spatial way-finding efficiency and found that participants' efficiencies decreased as layout size increased. The authors investigated whether this reduction in navigation efficiency was due to visual perception (Experiment 2), memory, spatial updating strategy, or decision strategy (Experiment 3). (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
189.
An overview of JML tools and applications 总被引:3,自引:0,他引:3
Lilian Burdy Yoonsik Cheon David R. Cok Michael D. Ernst Joseph R. Kiniry Gary T. Leavens K. Rustan M. Leino Erik Poll 《International Journal on Software Tools for Technology Transfer (STTT)》2005,7(3):212-232
The Java Modeling Language (JML) can be used to specify the detailed design of Java classes and interfaces by adding annotations to Java source files. The aim of JML is to provide a specification language that is easy to use for Java programmers and that is supported by a wide range of tools for specification typechecking, runtime debugging, static analysis, and verification.This paper gives an overview of the main ideas behind JML, details about JML’s wide range of tools, and a glimpse into existing applications of JML. 相似文献
190.
Yijun Yu Jianguo Lu John Mylopoulos Weiwei Sun Jing‐Hao Xue Erik H. D'Hollander 《Software》2005,35(1):1-14
In name and in practice, the World‐Wide Web (hereafter Web) is used around the World beyond English‐speaking areas. This creates a tremendous need to internationalize standard terminology used in the technologies that make the Web possible. Existing efforts on XML internationalization (i18n) and localization (i10n) have focused on the content of XML documents instead of the terms used in markup (annotations) such as elements and attributes. The SGML standard ISO 8879 supports the use of Unicode (ISO 10646) throughout a document, including markups. However, most elements and attributes of XML documents are still defined in English, thereby limiting their use among non‐English speakers. This paper presents an XSLT‐based method that can completely localize the markup of XML documents into different natural languages. We also describe how the proposed technique can be applied to translation problems in programming (e.g. C and Java) or documentation (e.g. LATEX or other formatting languages) so that a program or a document can be converted to and from an XML format. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献