全文获取类型
收费全文 | 6024篇 |
免费 | 595篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 16篇 |
综合类 | 3篇 |
化学工业 | 2190篇 |
金属工艺 | 44篇 |
机械仪表 | 133篇 |
建筑科学 | 230篇 |
矿业工程 | 11篇 |
能源动力 | 162篇 |
轻工业 | 1995篇 |
水利工程 | 57篇 |
石油天然气 | 43篇 |
无线电 | 203篇 |
一般工业技术 | 745篇 |
冶金工业 | 166篇 |
原子能技术 | 8篇 |
自动化技术 | 617篇 |
出版年
2024年 | 20篇 |
2023年 | 84篇 |
2022年 | 393篇 |
2021年 | 452篇 |
2020年 | 243篇 |
2019年 | 279篇 |
2018年 | 279篇 |
2017年 | 285篇 |
2016年 | 307篇 |
2015年 | 223篇 |
2014年 | 339篇 |
2013年 | 481篇 |
2012年 | 453篇 |
2011年 | 496篇 |
2010年 | 367篇 |
2009年 | 350篇 |
2008年 | 300篇 |
2007年 | 268篇 |
2006年 | 195篇 |
2005年 | 145篇 |
2004年 | 126篇 |
2003年 | 98篇 |
2002年 | 85篇 |
2001年 | 42篇 |
2000年 | 49篇 |
1999年 | 49篇 |
1998年 | 34篇 |
1997年 | 29篇 |
1996年 | 22篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 17篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1932年 | 1篇 |
排序方式: 共有6623条查询结果,搜索用时 15 毫秒
131.
Abstract. Much of information technology (IT) implementation research has focused on individuals' acceptance of IT by examining their behaviour when faced with new IT and the antecedents of these behaviours. As they are frequently undertaken within a project framework, IT implementations also entail the application of project management practices in order to be successful. Based on the premise that antecedents of lower level theories are frequently determined by the outcomes of a higher level theory, the present paper illustrates how organizational-level decisions, examined from the perspective of economics theories, can help explain the antecedents of project risk management at the project and individual levels. To do so, the paper describes an IT implementation effort which went through three phases; the first two of which were abandoned versions of the same project. An organizational-level analysis of the case from an economics perspective and its project-level analysis from a risk management perspective show how organizational-level decisions influenced the antecedents at the project and individual levels, providing a more complete understanding of the IT implementation in question, an understanding which neither a theory approach nor a level perspective could provide on its own. 相似文献
132.
António V. Sousa Ana Maria Mendonça Aurélio Campilho 《Pattern Analysis & Applications》2008,11(3-4):409-423
This paper proposes a non-parametric method for the classification of thin-layer chromatographic (TLC) images from patterns represented in a dissimilarity space. Each pattern corresponds to a mixture of Gaussian approximation of the intensity profile. The methodology comprises various phases, including image processing and analysis steps to extract the chromatographic profiles and a classification phase to discriminate among two groups, one corresponding to normal cases and the other to three pathological classes. We present an extensive study of several dissimilarity-based approaches analysing the influence of the dissimilarity measure and the prototype selection method on the classification performance. The main conclusions of this paper are that, Match and Profile-difference dissimilarity measures present better results, and a new prototype selection methodology achieves a performance similar or even better than conventional methods. Furthermore, we also concluded that simplest classifiers, such as k-NN and linear discriminant classifiers (LDCs), present good performance being the overall classification error less than 10% for the four-class problem. 相似文献
133.
The different steps of the dehalogenation reaction carried out by LinB on three different substrates have been characterized using a combination of quantum mechanical calculations and molecular dynamics simulations. This has allowed us to obtain information in atomic detail about each step of the reaction mechanism, that is, substrate entrance and achievement of the near-attack conformation, transition state stabilization within the active site, halide stabilization, water molecule activation and subsequent hydrolytic attack on the ester intermediate with formation of alcohol, and finally product release. Importantly, no bias or external forces were applied during the whole procedure so that both intermediates and products were completely free to sample configuration space in order to adapt to the plasticity of the active site and/or search for an exit. Differences in substrate reactivity were found to be correlated with the ease of adopting the near-attack conformation and two different exit pathways were found for product release that do not interfere with substrate entrance. Additional support for the different entry and exit pathways was independently obtained from an examination of the enzyme's normal modes. 相似文献
134.
Guidelines for the incremental identification of aspects in requirements specifications 总被引:1,自引:0,他引:1
Jorge García-Duque Martín López-Nores José J. Pazos-Arias Ana Fernández-Vilas Rebeca P. Díaz-Redondo Alberto Gil-Solla Manuel Ramos-Cabrer Yolanda Blanco-Fernández 《Requirements Engineering》2006,11(4):239-263
The desired principle of separation of concerns in software development can be jeopardized by the so-called crosscutting concerns, which tend to be scattered over (and tangled with) the functionality of the modular units of a system. The correct identification of such concerns (and their encapsulation into separate artifacts) is thereby considered a way to improve software understanding and evolution. Pursuing a proper management of concerns from the requirements engineering stage can greatly benefit the entire software life-cycle. In this paper, we propose conceptual guidelines on how to perform the identification of crosscutting concerns in the process of building requirements specifications. We argue that the identification must be carried out in an incremental way, to encapsulate apart the crosscutting concerns even if they have not emerged completely yet.
相似文献
Yolanda Blanco-FernándezEmail: |
135.
Annelise E. Gerbase José R. Gregório Márcia Martinelli Márcia C. Brasil Ana N. F. Mendes 《Journal of the American Oil Chemists' Society》2002,79(2):179-181
We studied the methyltrioxorhenium (MTO)-CH2Cl2/H2O2 biphasic system for epoxidizing soybean oil. The reactions were optimized (reactant ratio, time, and temperature), which
resulted in a better performance (higher conversion and selectivity) than those described in the literature. Total doublebond
conversion and 95% selectivity were obtained in 2 h at room temperature. Furthermore, it was possible to reach desired epoxidation
degrees by changing the oxidant and MTO amounts. The rhenium-epoxidized soybean oil remained stable in the absence of stabilizers
for up to 30 d when stored at mild conditions. 相似文献
136.
In this paper, we present several algorithms related with the computation of the homology of groups, from a geometric perspective (that is to say, carrying out the calculations by means of simplicial sets and using techniques of Algebraic Topology). More concretely, we have developed some algorithms which, making use of the effective homology method, construct the homology groups of Eilenberg–MacLane spaces K(G,1) for different groups G, allowing one in particular to determine the homology groups of G. 相似文献
137.
Arranging office space into a single open room offers advantages in terms of easy exchange of information and interaction among coworkers, but reduces privacy and acoustic comfort. Thus, the purpose of this work was to evaluate the acoustic quality of a real open-plan office and to propose changes in the room to improve the acoustic conditioning of this office. The computational model of the office under study was calibrated based on RT and STI measurements. Predictions were made of the RT and STI, which generated the radius of distraction r(D), and the rate of spatial decay of sound pressure levels per distance doubling DL(2) in the real conditions of the office and after modifications of the room. The insertion of dividers between work stations and an increase in the ceiling's sound absorption improved the acoustic conditions in the office under study. 相似文献
138.
139.
Ana Garcia-Armada 《Wireless Communications, IEEE Transactions on》2006,5(1):57-60
Adaptive OFDM has the potential of providing bandwidth-efficient communications in hostile propagation environments. Currently, bit loading algorithms use M-ary quadrature amplitude modulation of the OFDM sub-carriers, where the number of bits per symbol modulating each of them is obtained in order to maximize the performance. SNR gap approximation for M-QAM signaling makes the algorithms simpler to implement. However, in some circumstances it may be preferable to use. M-ary phase shift keying. In this letter an approximation is derived for M-PSK similar to the SNR gap of M-QAM so that bit loading algorithms can be extended to this type of modulation. In addition, the performance obtained when using M-PSK is compared to that of M-QAM in a practical situation. 相似文献
140.
Pollution Buildup on Road Surfaces 总被引:1,自引:0,他引:1
Samples of sediment found on an urban road in Aberdeen (Scotland) were collected by washing designated surfaces. This method, called the “wet” method, was capable of collecting sediment of the smallest particle size range that is normally left behind by traditional sampling techniques using dry vacuuming. Over 17 months (mainly on a weekly basis), 66 samples were collected and analyzed for sediment loading, particle size distribution, concentration of heavy metals (Zn, Cu, Pb, Cd) in four sediment size fractions, and several dissolved pollutants in the effluent collected from washing (NO3?,?SO42?,?PO43?,?Cl?,?F?,?NH4+, total organic carbon, total carbon). Standard statistical methods, including multiple regressions, were used to determine relationships amongst different sediment characteristics. It was found that sediment loading, as well as concentrations of Cl? and SO42?, were highest in the winter months, especially when snow was present on the road surface. It was observed that 66% of total road sediment loading was found within a 0.5 m strip next to the curb. The average sediment particle sizes found were smaller than those previously recorded in the literature. As expected, the concentrations of heavy metals were highest in the smallest particle size fraction analyzed (<63?μm), and this occurred during the summer months when less sediment was available on the street surface. The antecedent dry weather period had a very weak and negative influence on the loading rate of the smallest particle size fraction next to the curb. 相似文献