全文获取类型
收费全文 | 1553篇 |
免费 | 56篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 17篇 |
综合类 | 3篇 |
化学工业 | 436篇 |
金属工艺 | 41篇 |
机械仪表 | 28篇 |
建筑科学 | 73篇 |
矿业工程 | 15篇 |
能源动力 | 23篇 |
轻工业 | 169篇 |
水利工程 | 1篇 |
石油天然气 | 11篇 |
无线电 | 84篇 |
一般工业技术 | 328篇 |
冶金工业 | 196篇 |
原子能技术 | 14篇 |
自动化技术 | 174篇 |
出版年
2021年 | 19篇 |
2020年 | 14篇 |
2019年 | 25篇 |
2018年 | 26篇 |
2017年 | 17篇 |
2016年 | 35篇 |
2015年 | 30篇 |
2014年 | 37篇 |
2013年 | 51篇 |
2012年 | 53篇 |
2011年 | 64篇 |
2010年 | 53篇 |
2009年 | 61篇 |
2008年 | 53篇 |
2007年 | 47篇 |
2006年 | 51篇 |
2005年 | 43篇 |
2004年 | 41篇 |
2003年 | 21篇 |
2002年 | 28篇 |
2001年 | 28篇 |
2000年 | 38篇 |
1999年 | 38篇 |
1998年 | 41篇 |
1997年 | 38篇 |
1996年 | 30篇 |
1995年 | 27篇 |
1994年 | 31篇 |
1993年 | 20篇 |
1992年 | 32篇 |
1991年 | 25篇 |
1989年 | 21篇 |
1988年 | 16篇 |
1987年 | 13篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 26篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1978年 | 16篇 |
1977年 | 15篇 |
1976年 | 28篇 |
1975年 | 36篇 |
1974年 | 19篇 |
1973年 | 24篇 |
1972年 | 14篇 |
1971年 | 16篇 |
1970年 | 19篇 |
排序方式: 共有1613条查询结果,搜索用时 15 毫秒
11.
The classical two-film model for mass transfer between two fluid phases can only be used to describe the steady state mass transfer mechanism. Both the penetration and the film-penetration model are also valid solely when only one diffusion boundary layer exists at the interface between the phases. With a view to surmounting the limitations of the above models a new model has been developed for the mass transfer between two fluid phases with two diffusion boundary layers at the interface. The new model is based on the two-film concept and the Danckwerts distribution function, and is also able to simulate the unsteady state mass transfer mechanism between two fluid phases with two different boundary layers. 相似文献
12.
Helga Hinze Helmut Holzer 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1985,180(2):117-120
Summary When nitrite or sulfite are applied to yeast cells below pH 5.0, an enormous intracellular accumulation occurs. It is assumed that nitrite and sulfite penetrate the cell membrane in their undissociated forms as nitrous acid (pK = 3.3) or sulfurous acid (pK =1.8), respectively. Due to the neutral intracellular pH they are trapped inside the cell in their anionic forms, which are impermeable to the cell membrane. It has previously been shown that sulfite causes a rapid depletion of the ATP content of yeast cells [Schimz, K. L. and Holzer, H. (1979) resp. Hinze et al. as above]. Similarly, millimolar concentrations of nitrite decrease the ATP level to less than 10% of the initial value. Nitrite and sulfite in combination deplete the ATP content of yeast cells much stronger than expected for the sum of the separate effects of these compounds (synergistic effect).
Akkumulation von Nitrit und Sulfit in Hefezellen und synergistischer Abfall des intrazellulären ATP-Gehalts
Zusammenfassung Wenn Hefezellen mit Nitrit oder Sulft bei pH-Werten unter 5,0 inkubiert werden, beobachtet man eine starke intracelluläre Akkumulation von Nitrit, bzw. Sulfit. Es ist anzunehmen, daß Nitrit und Sulfit in ihrer undissoziierten Form als salpetrige Säure (pK=3,3) bzw. schweflige Säure (pK=1,8) penetrieren und dann in den Zellen durch Neutralisation zu den anionischen Formen, die die Zellmembran nicht mehr permeieren können, abgefangen werden. Ähnlich dem früher beschriebenen raschen Abfall des ATP-Gehaltes nach Zusatz von Sulfit in Hefe [Schimz, KL und Holzer H (1979) Arch Microbiol 121:225–229] und in Bakterien [Hinze H, Maier K, Holzer H (1981) Z Lebensm Unters Forsch 172:389-392] verursacht auch Nitrit einen raschen Abfall des ATP-Gehaltes in Hefe auf weniger als 10 % des Anfangswertes. Werden Nitrit und Sulfit in Kombination verabreicht, so beobachtet man einen wesentlich stärkeren Abfall des ATP-Gehaltes als er aus der Summe der Einzeleffekte von Nitrit, bzw. Sulfit zu erwarten wäre (Synergistischer Effekt).相似文献
13.
Mikhail GelferRoland H Horst H.Henning Winter Amy M HeintzShaw Ling Hsu 《Polymer》2003,44(8):2363-2371
The effect of molecular architecture on the evolution of viscoelastic properties during crystallization was investigated using ethylene-hexene copolymers manufactured via metallocene (M-LLDPE) and Ziegler-Natta (ZN-LLDPE) processes. Differences in branching distribution were shown to have a drastic effect on the viscoelastic properties near the gel point. It is shown that the branching distribution rather than branch content is the determining parameter for the evolution of the rheological properties during isothermal and non-isothermal crystallization, and for the width of the solidification interval. We developed a partial melting technique for the preparation of stable critical gels of LLDPE whose viscoelastic properties correspond to the intermediate state between melt and solid. Local molecular conformation and crystallinity in these gels were characterized by Raman spectroscopy, which shows that the transition from melt-like to solid-like rheological behavior (physical gelation) in LLDPE occurs at a very low overall crystallinity of less than 5%. 相似文献
14.
15.
16.
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
17.
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
18.
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
19.
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
20.
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