全文获取类型
收费全文 | 3639篇 |
免费 | 132篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 40篇 |
综合类 | 5篇 |
化学工业 | 809篇 |
金属工艺 | 63篇 |
机械仪表 | 97篇 |
建筑科学 | 151篇 |
矿业工程 | 17篇 |
能源动力 | 63篇 |
轻工业 | 327篇 |
水利工程 | 28篇 |
石油天然气 | 13篇 |
无线电 | 297篇 |
一般工业技术 | 615篇 |
冶金工业 | 695篇 |
原子能技术 | 22篇 |
自动化技术 | 535篇 |
出版年
2023年 | 23篇 |
2022年 | 45篇 |
2021年 | 74篇 |
2020年 | 63篇 |
2019年 | 47篇 |
2018年 | 69篇 |
2017年 | 65篇 |
2016年 | 96篇 |
2015年 | 65篇 |
2014年 | 102篇 |
2013年 | 239篇 |
2012年 | 187篇 |
2011年 | 227篇 |
2010年 | 149篇 |
2009年 | 151篇 |
2008年 | 152篇 |
2007年 | 162篇 |
2006年 | 118篇 |
2005年 | 85篇 |
2004年 | 92篇 |
2003年 | 98篇 |
2002年 | 91篇 |
2001年 | 57篇 |
2000年 | 40篇 |
1999年 | 65篇 |
1998年 | 113篇 |
1997年 | 69篇 |
1996年 | 48篇 |
1995年 | 51篇 |
1994年 | 40篇 |
1993年 | 49篇 |
1992年 | 29篇 |
1991年 | 27篇 |
1990年 | 40篇 |
1989年 | 41篇 |
1988年 | 26篇 |
1987年 | 30篇 |
1986年 | 24篇 |
1985年 | 41篇 |
1984年 | 26篇 |
1983年 | 35篇 |
1982年 | 30篇 |
1981年 | 33篇 |
1980年 | 32篇 |
1979年 | 33篇 |
1978年 | 34篇 |
1977年 | 35篇 |
1976年 | 35篇 |
1975年 | 42篇 |
1974年 | 24篇 |
排序方式: 共有3777条查询结果,搜索用时 15 毫秒
61.
Recent proposals for multi-paradigm declarative programming combine the most important features of functional, logic and concurrent programming into a single framework. The operational semantics of these languages is usually based on a combination of narrowing and residuation. In this paper, we introduce a non-standard, residualizing semantics for multi-paradigm declarative programs and prove its equivalence with a standard operational semantics. Our residualizing semantics is particularly relevant within the area of program transformation where it is useful, e.g., to perform computations during partial evaluation. Thus, the proof of equivalence is a crucial result to demonstrate the correctness of (existing) partial evaluation schemes. 相似文献
62.
A set of perception experiments, using reiterant and lexicalised speech, was designed to perform a diagnostic of the relative implication of prosody in the segmentation and hierarchisation of speech. Both natural and synthetic intonation were evaluated. Then, two distance measures—correlation and root-mean-square distance on the acoustic parameters (F0, syllabic duration and intensity)—were applied to match the perception results. This objective vs. subjective comparison underlines which acoustic cues are used by listeners to judge the adequacy of prosody in performing a given function such as demarcation. Results can be summarized by a scale of the perceptual distance between two demarcation functions. This study also points out the ability of listeners to retrieve pertinent information on the basis of pure prosodic stimuli. 相似文献
63.
Albert A. Stahel 《International Transactions in Operational Research》2004,11(4):435-446
This paper presents two concepts: asymmetric warfare and dissymmetric warfare. NATO and US Military operations in recent wars in Kosovo and Afghanistan are analysed by means of comparison with old Chinese strategic thinking. No‐Loss‐Strategy and virtual warfare as well as the transformation from asymmetric to dissymmetric and from dissymmetric to asymmetric warfare are reflected upon. 相似文献
64.
George A. Sorial Albert D. Venosa Karen M. Koran Edith Holder Dennis W. King 《Canadian Metallurgical Quarterly》2004,130(10):1073-1084
The current U.S. Environmental Protection Agency protocol for testing the effectiveness of dispersants, the swirling flask test, has been found to give widely varying results in the hands of different testing laboratories. The sources of the ambiguities in the test were determined by considering several options in a rigorous systematic fashion. Options considered were variability among three operators and the variability and limitations of three analytical instruments in establishing a calibration curve for oil/dispersant mixtures. Other options included flask type, impact of operational variables (rotational speed, mixing time, settling time, and oil:dispersant ratio), development of a revised procedure for dispersant effectiveness, reproducibility and repeatability of the revised procedure, and development of selection criteria for screening of dispersants. A redesign of the test flask, which is characterized by having baffles with a stopcock at the bottom for sample collection, was deemed necessary to accomplish reproducibility within operator and between operators. The results indicated that the baffled flask provided a total coefficient of variation (variations within operator and between operators) less than 11% compared to above 100% in some cases for the swirling flask. 相似文献
65.
George A. Sorial Albert D. Venosa Karen M. Koran Edith Holder Dennis W. King 《Canadian Metallurgical Quarterly》2004,130(10):1085-1093
The current U.S. Environmental Protection Agency (EPA) protocol for testing the effectiveness of dispersants for use in treating oil spills on the open water, the swirling flask test (SFT), has been found to give widely varying results in the hands of different testing laboratories. Part I addressed the sources of the ambiguities in the EPA SFT and the development of a new test referred to as the baffled flask test (BFT). In this part of the series, further experiments were conducted for estimating the repeatability of three operators in determining the effectiveness of 18 dispersants by both the EPA SFT and the BFT methods. Overall statistical analysis of the results indicated that the coefficient of variation by the BFT was only 7.8% compared to 21.9% for the EPA SFT. The mean percent effectiveness of the EPA SFT was only 19.7% as compared to 64.6% for the BFT. Proposed selection criteria for screening of dispersants for listing on the National Contingency Plan Product Schedule have been developed. 相似文献
66.
Albert Saputra Hossein Talebi Duc Tran Carolin Birk Chongmin Song 《International journal for numerical methods in engineering》2017,109(5):697-738
Digital imaging technologies such as X‐ray scans and ultrasound provide a convenient and non‐invasive way to capture high‐resolution images. The colour intensity of digital images provides information on the geometrical features and material distribution which can be utilised for stress analysis. The proposed approach employs an automatic and robust algorithm to generate quadtree (2D) or octree (3D) meshes from digital images. The use of polygonal elements (2D) or polyhedral elements (3D) constructed by the scaled boundary finite element method avoids the issue of hanging nodes (mesh incompatibility) commonly encountered by finite elements on quadtree or octree meshes. The computational effort is reduced by considering the small number of cell patterns occurring in a quadtree or an octree mesh. Examples with analytical solutions in 2D and 3D are provided to show the validity of the approach. Other examples including the analysis of 2D and 3D microstructures of concrete specimens as well as of a domain containing multiple spherical holes are presented to demonstrate the versatility and the simplicity of the proposed technique. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
67.
C(18) phases prepared by different synthetic pathways are examined by solid-state NMR spectroscopy. Silane functionality is clearly indicated by (29)Si CP/MAS NMR spectroscopy. Order and mobility of the alkyl chains are investigated with high-speed (1)H MAS and (13)C CP/MAS NMR spectroscopy. Differences in coverage are monitored by (1)H line widths,( 13)C chemical shifts, (13)C cross-polarization constants, and (1)H relaxation times in the rotating frame. It is shown that C(18) phases prepared by the surface polymerization technique exhibit a more regular surface coverage than sorbents prepared by conventional polymeric synthesis. The findings from solid-state NMR investigations are discussed in the context of liquid chromatography (LC) separations of linear and bulky polycyclic aromatic hydrocarbon (PAH) solutes. 相似文献
68.
Albert Weichselbraun 《Journal of Intelligent Information Systems》2011,37(2):119-137
One key property of the Semantic Web is its support for interoperability. Recent research in this area focuses on the integration
of multiple data sources to facilitate tasks such as ontology learning, user query expansion and context recognition. The
growing popularity of such machups and the rising number of Web APIs supporting links between heterogeneous data providers
asks for intelligent methods to spare remote resources and minimize delays imposed by queries to external data sources. This
paper suggests a cost and utility model for optimizing such queries by leveraging optimal stopping theory from business economics:
applications are modeled as decision makers that look for optimal answer sets. Queries to remote resources cause additional
cost but retrieve valuable information which improves the estimation of the answer set’s utility. Optimal stopping optimizes
the trade-off between query cost and answer utility yielding optimal query strategies for remote resources. These strategies
are compared to conventional approaches in an extensive evaluation based on real world response times taken from seven popular
Web services. 相似文献
69.
One-order-statistic estimators are derived for the shape parameter K of the limited distribution function F1(x, ?, K) = 1 - (? - x)K and the Pareto distribution function F2(y, ?, K) = 1 - (y - ?)-K, given the location parameters ? and ?, respectively. Similar estimators are derived for the scale parameters v1 and Vn, of the Type II asymptotic distributions of smallest and largest values, F3(w, v1, K) = 1 - exp[-(w/v1)-K] and F4(z, vn K) = exp [-(z/vn)-K], given the shape parameter K and assuming the location parameter is zero. The one-order-statistic estimators are K?|? = -1/Cmn 1n(? - xmn) for the limited distribution, K?|? = 1/Cmn 1n(ymn - ?) for the Pareto distribution, ?1|K = Cmn-1/K Wmn and ?n|K = Cmn-1/K Zn-m+1,n for the Type II distributions of smallest and largest values, where Xmn, Ymn, Wmn, Zmn are the mth order statistics of samples of size n from the respective distributions and Cmn is the coefficient for a one-order-statistic estimator of the scale parameter of an exponential distribution, which has been tabled in an earlier paper. It is shown that exact confidence bounds can be easily derived for these parameters using exact confidence bounds for the scale parameter of the exponential distribution. Use of the estimators is illustrated by numerical examples. 相似文献
70.
In most cases, product development is not inventing a product completely new and from scratch, it typically either adds a few newly developed sub-functions to mainly known sub-functions, or it generates invention based on new combinations of already existing and slightly modified sub-functions. This synthesis is ideally based on a preceding and comprehensive system analysis that is necessary to define promising directions for advancement in further product development. In analysis as well as in synthesis the design engineer needs creativity—either to be able to recognize which functions are realized in a given system that is subject to analysis or to be able to think up new ways how a desired function could be realized in a system. The main cognitive mechanism for creativity is analogy and this mechanism in turn is based on schemas and mental models. In microsystems development, micro specific obstacles accrue when using analogies. In this work, the authors derive the nature and source of these obstacles and their implications on microsystems development. To overcome these obstacles, a functions catalogue is proposed. This catalogue can directly be used to add an external source for analogies during system synthesis. By transferring a method called geometrical similarity search to microsystems technology and combining it with the functions catalogue, system analysis can be supported as well. 相似文献