全文获取类型
收费全文 | 1438篇 |
免费 | 56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 | 389篇 |
金属工艺 | 41篇 |
机械仪表 | 28篇 |
建筑科学 | 70篇 |
矿业工程 | 15篇 |
能源动力 | 22篇 |
轻工业 | 163篇 |
水利工程 | 1篇 |
石油天然气 | 11篇 |
无线电 | 82篇 |
一般工业技术 | 298篇 |
冶金工业 | 176篇 |
原子能技术 | 14篇 |
自动化技术 | 169篇 |
出版年
2021年 | 18篇 |
2020年 | 14篇 |
2019年 | 25篇 |
2018年 | 25篇 |
2017年 | 18篇 |
2016年 | 32篇 |
2015年 | 30篇 |
2014年 | 35篇 |
2013年 | 50篇 |
2012年 | 51篇 |
2011年 | 61篇 |
2010年 | 51篇 |
2009年 | 53篇 |
2008年 | 51篇 |
2007年 | 47篇 |
2006年 | 47篇 |
2005年 | 36篇 |
2004年 | 39篇 |
2003年 | 18篇 |
2002年 | 28篇 |
2001年 | 26篇 |
2000年 | 33篇 |
1999年 | 35篇 |
1998年 | 38篇 |
1997年 | 38篇 |
1996年 | 26篇 |
1995年 | 27篇 |
1994年 | 29篇 |
1993年 | 20篇 |
1992年 | 32篇 |
1991年 | 23篇 |
1989年 | 21篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1984年 | 25篇 |
1983年 | 25篇 |
1982年 | 23篇 |
1981年 | 11篇 |
1980年 | 21篇 |
1979年 | 20篇 |
1978年 | 15篇 |
1977年 | 15篇 |
1976年 | 25篇 |
1975年 | 27篇 |
1974年 | 19篇 |
1973年 | 19篇 |
1972年 | 13篇 |
1970年 | 11篇 |
排序方式: 共有1498条查询结果,搜索用时 31 毫秒
21.
Peter Werkhoff Wilfried Bretschneider Matthias Güntert Rudolf Hopp Horst Surburg 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1991,192(2):111-115
Summary The direct capillary gas Chromatographic separation oftrans--ionone andtrans--damascone enantiomers is reported using heptakis(2,3,6-tri-O-methyl)--cyclodextrin in polysiloxane as a suitable chiral stationary phase. The method described has been applied to determine the naturally occurring enantiomeric composition oftrans--ionone in the absolutes of the flowers ofBoronia megastigma Nees andOsmanthus fragrance Lour., Costus root oil (Saussurea lappa Clarke) as well as in odor concentrates of violet flowers (Viola odorata L.), fresh raspberries, carrots and vanilla pods. Furthermore, the optical purity oftrans--ionone in the solvent extracts of distilled alcoholic raspberry beverage, raspberry fruit juice concentrate and black tea was investigated.Trans--ionone was either isolated by headspace stripping in vacuo or by organic solvent extraction and subsequently enriched by multidimensional preparative Chromatographic techniques.Trans--damascone was isolated from Virginia tobacco extract and from black tea aroma and was enriched for direct chirospecific analysis by medium pressure liquid chromatography followed by multidimensional preparative capillary gas chromatography. The importance of chirality as an essential criterion for the discrimination of natural and nature-identical aromas is discussed briefly.
Chirale Analysen von Aroma-und etherischen Öl-Inhaltsstoffen Teil B. Direkte Trennung der Enantiomeren von trans--Ionon und trans--Damascon mittels Inklusionsgaschromatographie
Zusammenfassung Mit Heptakis(2,3,6-tri-O-methyl)--cyclodextrin in Polysiloxan als chiraler stationärer GC-Phase können die Enantiomeren vontrans--Ionon undtrans--Damascon direkt stereodifferenziert werden. Mit der beschriebenen Methode wird die Enantiomerenzusammensetzung vontrans--Ionon in den Absolues vonBoronia megastigma Nées undOsmanthus fragrance Lour., in Costuswurzelöl (Saussurea lappa Clarke), in den Headspace-Konzentraten von Veilchenblüten, frischen Himbeeren, Karotten und Vanilleschoten sowie in den Lösungsmittelextrakten von Himbeergeist, Himbeerfruchtsaftkonzentrat und schwarzem Tee bestimmt.Trans--Ionon wurde aus den genannten Naturprodukten mit Hilfe von multidimensionalen präparativen chromatographischen Trenntechniken angereichert und isoliert.Trans--Damascon wurde durch die Kombination MPLC/präparative Capillargaschromatographie aus Virginia Tabakextrakt und aus dem Aromastoffspektrum von schwarzem Tee erhalten und in s eine Enantiomeren aufgetrennt. Die Bedeutung der Chiralität als Beurteilungskriterium zur Unterscheidung natürlicher und naturidentischer Aromastoffe wird kurz diskutiert.相似文献
22.
Graph edit distance is a powerful and flexible method for error-tolerant graph matching. Yet it can only be calculated for small graphs in practice due to its exponential time complexity when considering unconstrained graphs. In this paper we propose a quadratic time approximation of graph edit distance based on Hausdorff matching. In a series of experiments we analyze the performance of the proposed Hausdorff edit distance in the context of graph classification and compare it with a cubic time algorithm based on the assignment problem. Investigated applications include nearest neighbor classification of graphs representing letter drawings, fingerprints, and molecular compounds as well as hidden Markov model classification of vector space embedded graphs representing handwriting. In many cases, a substantial speedup is achieved with only a minor loss in accuracy or, in one case, even with a gain in accuracy. Overall, the proposed Hausdorff edit distance shows a promising potential in terms of flexibility, efficiency, and accuracy. 相似文献
23.
Tom Schrijvers Guido Tack Pieter Wuille Horst Samulowitz Peter J. Stuckey 《Constraints》2013,18(2):269-305
The ability to model search in a constraint solver can be an essential asset for solving combinatorial problems. However, existing infrastructure for defining search heuristics is often inadequate. Either modeling capabilities are extremely limited or users are faced with a general-purpose programming language whose features are not tailored towards writing search heuristics. As a result, major improvements in performance may remain unexplored. This article introduces search combinators, a lightweight and solver-independent method that bridges the gap between a conceptually simple modeling language for search (high-level, functional and naturally compositional) and an efficient implementation (low-level, imperative and highly non-modular). By allowing the user to define application-tailored search strategies from a small set of primitives, search combinators effectively provide a rich domain-specific language (DSL) for modeling search to the user. Remarkably, this DSL comes at a low implementation cost to the developer of a constraint solver. The article discusses two modular implementation approaches and shows, by empirical evaluation, that search combinators can be implemented without overhead compared to a native, direct implementation in a constraint solver. 相似文献
24.
Michael Herbst Swen Gottschalk Martin Reißel Horst Hardelauf Roy Kasteel Matthieu Javaux Jan Vanderborght Harry Vereecken 《Computers & Geosciences》2008,34(12):1958-1963
In this paper, we present a class of preconditioning methods for a parallel solution of the three-dimensional Richards equation. The preconditioning methods Jacobi scaling, block-Jacobi, incomplete lower–upper, incomplete Cholesky and algebraic multigrid were applied in combination with a parallel conjugate gradient solver and tested for robustness and convergence using two model scenarios. The first scenario was an infiltration into initially dry, sandy soil discretised in 500,000 nodes. The second scenario comprised spatially distributed soil properties using 275,706 numerical nodes and atmospheric boundary conditions. Computational results showed a high efficiency of the nonlinear parallel solution procedure for both scenarios using up to 64 processors. Using 32 processors for the first scenario reduced the wall clock time to slightly more than 1% of the single processor run. For scenario 2 the use of 64 processors reduces the wall clock time to slightly more than 20% of the 8 processors wall clock time. The difference in the efficiency of the various preconditioning methods is moderate but not negligible. The use of the multigrid preconditioning algorithm is recommended, since on average it performed best for both scenarios. 相似文献
25.
This paper investigates various ensemble methods for offline handwritten text line recognition. To obtain ensembles of recognisers, we implement bagging, random feature subspace, and language model variation methods. For the combination, the word sequences returned by the individual ensemble members are first aligned. Then a confidence-based voting strategy determines the final word sequence. A number of confidence measures based on normalised likelihoods and alternative candidates are evaluated. Experiments show that the proposed ensemble methods can improve the recognition accuracy over an optimised single reference recogniser. 相似文献
26.
Andreas Wüstefeld Götz Bokelmann Christophe Zaroli Guilhem Barruol 《Computers & Geosciences》2008,34(5):515-528
We present a graphical user interface to facilitate the processing of teleseismic shear-wave splitting observations. In contrast to a fully automated technique, we present a manual, per-event approach that maintains user control during the sequence of processing. The SplitLab environment is intended to undertake the repetitive processing steps while enabling the user to focus on quality control and eventually the interpretation of the results. Pre-processing modules of SplitLab create a database of events and link the corresponding seismogram files. The seismogram viewer tool uses this database to perform the measurement interactively. Post-processing of the combined results of such a project includes a viewer and export option. Our emphasis lies in the application to teleseismic shear-wave splitting analysis, but our code can be extended easily for other purposes. SplitLab can be downloaded at http://www.gm.univ-montp2.fr/splitting/. 相似文献
27.
Hendrik Voigt Aaron Rigoni Evgeniy Boltynjuk Mohammed Reda Chellali Bonnie Tyler Harald Rösner Sergiy Divinski Horst Hahn Gerhard Wilde 《Advanced functional materials》2023,33(44):2302386
Comprehensive analyses of the atomic structure using advanced analytical transmission electron microscopy-based methods combined with atom probe tomography confirm the presence of distinct glass–glass interfaces in a columnar Cu-Zr nanoglass synthesized by magnetron sputtering. These analyses provide first-time in-depth characterization of sputtered film nanoglasses and indicate that glass–glass interfaces indeed present an amorphous phase with reduced mass density as compared to the neighboring amorphous regions. Moreover, dedicated analyses of the diffusion kinetics by time-of-flight secondary ion mass spectroscopy (ToF SIMS) prove significantly enhanced diffusivity, suggesting fast transport along the low density glass–glass interfaces. The present results further indicate that sputter deposition is a feasible technique for reliable production of nanoglasses and that some of the concepts proposed for this new class of glassy materials are applicable. 相似文献
28.
Horst Kesselmeier Inga Tschiersch Klaus Henning Beate Stoffels Sebastian Kutscha 《AI & Society》1998,12(1-2):55-63
Today technology design can no longer be understood as a design process on a green site. Design and implementation of new technology are always dependent on existing technology and the way it is used by people. In this respect Software-Engineering has also changed to the characteristics of normal technology design taking into account existing computer systems. Experiences show that the conditions and needs of such Software-Reengineering projects are highly complex and differ in their special characteristics ranging from aspects of quality of existing system documentation to organizational structures of the computer departments concerned. The Task-Artifact Cycle presented here gives a suitable reengineering approach emphasizing both analysis and design in Software-Reengineering. 相似文献
29.
Rieder C Kröger T Schumann C Hahn HK 《IEEE transactions on visualization and computer graphics》2011,17(12):1812-1821
Percutaneous radiofrequency ablation (RFA) is becoming a standard minimally invasive clinical procedure for the treatment of liver tumors. However, planning the applicator placement such that the malignant tissue is completely destroyed, is a demanding task that requires considerable experience. In this work, we present a fast GPU-based real-time approximation of the ablation zone incorporating the cooling effect of liver vessels. Weighted distance fields of varying RF applicator types are derived from complex numerical simulations to allow a fast estimation of the ablation zone. Furthermore, the heat-sink effect of the cooling blood flow close to the applicator's electrode is estimated by means of a preprocessed thermal equilibrium representation of the liver parenchyma and blood vessels. Utilizing the graphics card, the weighted distance field incorporating the cooling blood flow is calculated using a modular shader framework, which facilitates the real-time visualization of the ablation zone in projected slice views and in volume rendering. The proposed methods are integrated in our software assistant prototype for planning RFA therapy. The software allows the physician to interactively place virtual RF applicator models. The real-time visualization of the corresponding approximated ablation zone facilitates interactive evaluation of the tumor coverage in order to optimize the applicator's placement such that all cancer cells are destroyed by the ablation. 相似文献
30.
Florian Sahling Lisbeth Buschkühl Horst Tempelmeier Stefan Helber 《Computers & Operations Research》2009
This paper presents a new algorithm for the dynamic multi-level capacitated lot sizing problem with setup carry-overs (MLCLSP-L). The MLCLSP-L is a big-bucket model that allows the production of any number of products within a period, but it incorporates partial sequencing of the production orders in the sense that the first and the last products produced in a period are determined by the model. We solve a model which is applicable to general bill-of-material structures and which includes minimum lead times of one period and multi-period setup carry-overs. Our algorithm solves a series of mixed-integer linear programs in an iterative so-called fix-and-optimize approach. In each instance of these mixed-integer linear programs a large number of binary setup variables is fixed whereas only a small subset of these variables is optimized, together with the complete set of the inventory and lot size variables. A numerical study shows that the algorithm provides high-quality results and that the computational effort is moderate. 相似文献