全文获取类型
收费全文 | 1401篇 |
免费 | 59篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 12篇 |
综合类 | 1篇 |
化学工业 | 274篇 |
金属工艺 | 32篇 |
机械仪表 | 36篇 |
建筑科学 | 49篇 |
矿业工程 | 1篇 |
能源动力 | 50篇 |
轻工业 | 86篇 |
水利工程 | 12篇 |
石油天然气 | 1篇 |
无线电 | 187篇 |
一般工业技术 | 231篇 |
冶金工业 | 242篇 |
原子能技术 | 16篇 |
自动化技术 | 234篇 |
出版年
2023年 | 8篇 |
2022年 | 9篇 |
2021年 | 10篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 23篇 |
2017年 | 27篇 |
2016年 | 36篇 |
2015年 | 28篇 |
2014年 | 51篇 |
2013年 | 97篇 |
2012年 | 72篇 |
2011年 | 70篇 |
2010年 | 59篇 |
2009年 | 58篇 |
2008年 | 51篇 |
2007年 | 66篇 |
2006年 | 53篇 |
2005年 | 51篇 |
2004年 | 51篇 |
2003年 | 45篇 |
2002年 | 41篇 |
2001年 | 33篇 |
2000年 | 35篇 |
1999年 | 25篇 |
1998年 | 63篇 |
1997年 | 55篇 |
1996年 | 38篇 |
1995年 | 29篇 |
1994年 | 26篇 |
1993年 | 21篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 13篇 |
1989年 | 22篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 11篇 |
1982年 | 5篇 |
1979年 | 4篇 |
1977年 | 7篇 |
1976年 | 19篇 |
1975年 | 2篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1964年 | 2篇 |
排序方式: 共有1464条查询结果,搜索用时 437 毫秒
101.
J. E. S. Fransson G. Smith J. Askne H. Olsson 《International journal of remote sensing》2013,34(14):2777-2791
The use of spaceborne synthetic aperture radar (SAR) systems to estimate stem volume and biomass in boreal forests has shown some promising results, but with saturation of the radar backscatter at relatively low stem volumes and limited accuracy of stem volume estimation. These limitations have motivated evaluation of more advanced methods, such as interferometry. The results presented in this study show that ERS interferometry, under favourable conditions, may be used to estimate stem volume at stand level with saturation level and accuracy useful for operational forestry management planning in boreal forests. Five interferograms were analysed, covering a test site located in the central part of Sweden with stem volume in the range of 0-305 m3 ha-1. The best interferogram showed a linear relationship between stem volume and coherence with a root mean square error (RMSE) of approximately 26 m3 ha-1, corresponding to 20% of the average stem volume, throughout the range of stem volume. No saturation was observed up to the maximum stem volume. However, the sensitivity of coherence to stem volume varied considerably between the interferograms. Finally, four SPOT XS images were evaluated and compared with the stem volume estimations obtained from the interferograms, resulting in a relative RMSE of about 24% of the stem volume, for the best case. The estimation of stem volume using coherence data was found to be better than optical data for stem volumes exceeding about 110 m3 ha-1. The statistical analysis was performed using linear regression models with cross-validation. 相似文献
102.
Niall Robert Hamilton James Wood Alexander Galloway Mikael Brian Olsson Robbie Yuxuan Zhang 《Journal of Nuclear Materials》2013,432(1-3):42-51
At the heart of any procedure for modelling and assessing the design or failure of dissimilar material brazed joints there must be a basic understanding of the metallurgy and mechanics of the joint. This paper is about developing this understanding and addressing the issues faced with modelling and predicting failure in real dissimilar material brazed joints and the challenges still to be overcome in many cases. An understanding of the key metallurgical features of such joints in relation to finite element modelling is presented in addition to a study of the mechanics and stress state at an abrupt interface between two materials. A discussion is also presented on why elastic singularities do not exist based on a consideration of the assumption of an abrupt change in material properties and plasticity in the vicinity of the joint. In terms of modelling real dissimilar material brazed joints; there are several barriers to accurately capturing the stress state in the region of the joint and across the brazed layer and these are discussed in relation to a metallurgical study of a real dissimilar material brazed joint. However, this does not preclude using a simplified modelling approach with a representative braze layer in design and failure assessment away from the interface. In addition modelling strategies and techniques for assessing the various failure mechanisms of dissimilar material brazed joints are discussed. The findings from this paper are applicable to dissimilar material brazed joints found in a range of applications; however the references listed are primarily focussed on work in fusion research and development. 相似文献
103.
Specifying OLAP Cubes on XML Data 总被引:6,自引:0,他引:6
Mikael R. Jensen Thomas H. Møller Torben Bach Pedersen 《Journal of Intelligent Information Systems》2001,17(2-3):255-280
On-Line Analytical Processing (OLAP) enables analysts to gain insight about data through fast and interactive access to a variety of possible views on information, organized in a dimensional model. The demand for data integration is rapidly becoming larger as more and more information sources appear in modern enterprises. In the data warehousing approach, selected information is extracted in advance and stored in a repository, yielding good query performance. However, in many situations a logical (rather than physical) integration of data is preferable. Previous web-based data integration efforts have focused almost exclusively on the logical level of data models, creating a need for techniques focused on the conceptual level. Also, previous integration techniques for web-based data have not addressed the special needs of OLAP tools such as handling dimensions with hierarchies. Extensible Markup Language (XML) is fast becoming the new standard for data representation and exchange on the World Wide Web. The rapid emergence of XML data on the web, e.g., business-to-business (B2B) e-commerce, is making it necessary for OLAP and other data analysis tools to handle XML data as well as traditional data formats.Based on a real-world case study, this paper presents an approach to specification of OLAP DBs based on web data. Unlike previous work, this approach takes special OLAP issues such as dimension hierarchies and correct aggregation of data into account. Also, the approach works on the conceptual level, using Unified Modeling Language (UML) as a basis for so-called UML snowflake diagrams that precisely capture the multidimensional structure of the data. An integration architecture that allows the logical integration of XML and relational data sources for use by OLAP tools is also presented. 相似文献
104.
Shitvov A. P. Olsson T. El Banna B. Zelenchuk D. E. Schuchinsky A. G. 《Microwave Theory and Techniques》2010,58(2):356-362
105.
Stacy M. Trey Mikael Lundström Daniel Ståhlberg Mats Johansson 《Progress in Organic Coatings》2009,64(2-3):238-246
Sheet molded compound (SMC) is a highly filled, glass fiber reinforced, thermoset material used in trim and body panel automotive parts. When SMC-substrates are coated with conventional thermally cured paints, inherent porosity and entrapped volatiles of the substrate result in popping (“paint pops”) defects. UV-curable primers (UVP) provide an order of magnitude reduction of paint defects in SMC coatings, but typically have poor adhesion. Mercaptan polymers have a long history, dating back to 1928, of use in adhesives and sealant applications. The present study investigates a series of UVPs, showing the effect of resin functionality and thiol functional additive content on the adhesion of the coatings to SMC substrates. The SMC formulation is also considered when evaluating UVP adhesion, regarding variables such as surface chemistry, morphology, and surface area. The present study brings to light how adhesion of acrylate UVP can be enhanced with mercaptan moieties in additive amounts. The effect is most apparent on SMC substrates that have been treated to expose inorganic fillers as opposed to untreated surfaces of polyester. Additionally annealing the films boosts adhesion, but only in thiol containing formulations. This is a result of the decrease in Tgs and modulus of the films with the addition of mercaptans, thus providing better contact with the substrate in comparison to non-thiol containing formulations. 相似文献
106.
Amplification of ultrashort optical pulses in semiconductor laser amplifiers is shown to result in considerable spectral broadening and distortion as a result of the nonlinear phenomenon of self-phase modulation (SPM). The physical mechanism behind SPM is gain saturation, which leads to intensity-dependent changes in the refractive index in response to variations in the carrier density. The effect of the shape and the initial frequency chirp of input pulses on the shape and the spectrum of amplified pulses is discussed in detail. Particular attention is paid to the case in which the input pulsewidth is comparable to the carrier lifetime so that the saturated gain has time to recover partially before the trailing edge of the pulse arrives. The experimental results, performed by using picosecond input pulses from a 1.52-μm mode-locked semiconductor laser, are in agreement with the theory. When the amplified pulse is passed through a fiber, it is initially compressed because of the frequency chirp imposed on it by the amplifier. This feature can be used to compensate for fiber dispersion in optical communication systems 相似文献
107.
Temkin H. Olsson N. Abeles J. Logan R. Panish M. 《Quantum Electronics, IEEE Journal of》1986,22(2):286-293
We report a detailed study of the excess noise induced in index-guided InGaAsP laser structures by reflection feedback. The phenomena of high-frequency noise (1-5 GHz), low-frequency noise (< 100 MHz), and intensity fluctuations are shown to have a common physical origin in the unusual instability of the coupled laser-external cavity system. After a randomly occurring light intensity drop, the light output recovers in 10-15 steps, each corresponding to an external cavity roundtrip (high-frequency noise); the total recovery time corresponds to the low-frequency noise. The instability, and the subsequent noise, can be suppressed under conditions of very strong feedback such as obtained for lasers with anti-reflection-coated facets. The reflection noise characteristics are shown to be largely independent of the laser structure and structure modifications such as distributed feedback. 相似文献
108.
Carole M. McNamee Ronald A. Olsson 《International journal of parallel programming》1990,19(5):357-387
This paper presents source-level transformations that improve the performance of programs using synchronous and asynchronous message passing primitives, including remote call to an active process (rendezvous). It also discusses the applicability of these transformations to shared memory and distributed environments. The transformations presented reduce the need for context switching, simplify the specific form of communication, and/or reduce the complexity of the given form of communication. One additional transformation actually increases the number of processes as well as the number of context switches to improve program performance. These transformations are shown to be generalizable. Results of hand-applying the transformations to SR programs indicate reductions in execution time exceeding 90% in many cases. The transformations also apply to many commonly occurring synchronization patterns and to other concurrent programming languages such as Ada and Concurrent C. The long term goal of this effort is to include such transformations as an otpimization step, performed automatically by a compiler.This work was supported by NSF under Grant Number CCR88-10617. 相似文献
109.
Simon M. M. Pedersen Caroline Nebel Niels Chr. Nielsen Henrik J. Andersen Johan Olsson Magnus Simrén Lena Öhman Ulla Svensson Hanne C. Bertram Anders Malmendal 《European Food Research and Technology》2011,233(6):1013-1021
In the present study, the use of gas chromatography mass spectrometry (GC–MS)-based metabonomics to characterize blood serum
in an intervention study of patients suffering from the common gastrointestinal disorder irritable bowel syndrome (IBS) was
investigated. The patients included in the study consumed an acidified milk product with (n = 30) or without probiotics (n = 31) (Lactobacillus paracasei F19, Lactobacillus acidophilus LA-5 and Bifidobacterium lactis BB-12) for an 8-week period, and blood serum samples were collected before and after the intervention. Acidified milk is
commonly used as a delivering vector for probiotics in commercial consumer settings. The serum samples were extracted and
derivatized using N-Methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA), and GC–MS analysis was carried out. Multivariate data analysis including principal
component analysis (PCA), orthogonal partial least squares-discriminant analysis (OPLS-DA), and S-plot was applied on the
obtained GC–MS data, which revealed higher serum lactate, glutamine, proline creatinine/creatine, and aspartic acid levels
and lower serum glucose levels after the intervention period for both treatment groups. Consequently, the present study indicated
an effect of acidified milk consumption on the plasma metabolite profile, which was independent of a concomitant intake of
probiotics. In addition, the present study demonstrates that GC–MS is a useful analytical technique for metabonomics studies
of blood serum. 相似文献
110.
Anders Olsson Jan Oscarsson Erik Serrano Bo Källsner Marie Johansson Bertil Enquist 《Holz als Roh- und Werkstoff》2013,71(3):319-333
Machine strength grading of structural timber is based upon relationships between so called indicating properties (IPs) and bending strength. However, such relationships applied on the market today are rather poor. In this paper, new IPs and a new grading method resulting in more precise strength predictions are presented. The local fibre orientation on face and edge surfaces of wooden boards was identified using high resolution laser scanning. In combination with knowledge regarding basic wood material properties for each investigated board, the grain angle information enabled a calculation of the variation of the local MOE in the longitudinal direction of the boards. By integration over cross-sections along the board, an edgewise bending stiffness profile and a longitudinal stiffness profile, respectively, were calculated. A new IP was defined as the lowest bending stiffness determined along the board. For a sample of 105 boards of Norway spruce of dimension 45 × 145 × 3,600 mm³, a coefficient of determination as high as 0.68–0.71 was achieved between this new IP and bending strength. For the same sample, the coefficient of determination between global MOE, based on the first longitudinal resonance frequency and the board density, and strength was only 0.59. Furthermore, it is shown that improved accuracy when determining the stiffness profiles of boards will lead to even better predictions of bending strength. The results thus motivate both an industrial implementation of the suggested method and further research aiming at more accurately determined board stiffness profiles. 相似文献