全文获取类型
收费全文 | 5286篇 |
免费 | 246篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 79篇 |
综合类 | 17篇 |
化学工业 | 1218篇 |
金属工艺 | 172篇 |
机械仪表 | 106篇 |
建筑科学 | 301篇 |
矿业工程 | 24篇 |
能源动力 | 104篇 |
轻工业 | 448篇 |
水利工程 | 16篇 |
石油天然气 | 19篇 |
无线电 | 465篇 |
一般工业技术 | 936篇 |
冶金工业 | 978篇 |
原子能技术 | 79篇 |
自动化技术 | 584篇 |
出版年
2023年 | 39篇 |
2022年 | 52篇 |
2021年 | 98篇 |
2020年 | 73篇 |
2019年 | 94篇 |
2018年 | 92篇 |
2017年 | 85篇 |
2016年 | 138篇 |
2015年 | 120篇 |
2014年 | 172篇 |
2013年 | 240篇 |
2012年 | 189篇 |
2011年 | 231篇 |
2010年 | 163篇 |
2009年 | 187篇 |
2008年 | 165篇 |
2007年 | 184篇 |
2006年 | 170篇 |
2005年 | 149篇 |
2004年 | 144篇 |
2003年 | 132篇 |
2002年 | 123篇 |
2001年 | 82篇 |
2000年 | 117篇 |
1999年 | 131篇 |
1998年 | 258篇 |
1997年 | 182篇 |
1996年 | 162篇 |
1995年 | 102篇 |
1994年 | 93篇 |
1993年 | 98篇 |
1992年 | 64篇 |
1991年 | 68篇 |
1990年 | 56篇 |
1989年 | 62篇 |
1988年 | 52篇 |
1987年 | 57篇 |
1986年 | 50篇 |
1985年 | 43篇 |
1984年 | 47篇 |
1983年 | 54篇 |
1982年 | 34篇 |
1981年 | 37篇 |
1980年 | 53篇 |
1979年 | 43篇 |
1978年 | 51篇 |
1977年 | 67篇 |
1976年 | 94篇 |
1974年 | 42篇 |
1973年 | 33篇 |
排序方式: 共有5546条查询结果,搜索用时 0 毫秒
101.
Rudolf Treleano Hans-Dieter Belitz Harald Jugel und Herbert Wieser 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1978,167(5):320-323
Zusammenfassung 1-Aminocycloalkan-l-carbonsäuren mit Ringgrößen von 4–11 (ohne 10) wurden synthetisiert und auf ihre Geschmackseigenschaften untersucht. Süßer Geschmack tritt vom 4-Ring bis zum 8-Ring auf, beim 6-Ring ist der Schwellenwert minimal (c
Ssü=1–3 mmol/l). Bitter sind die Verbindungen vom 5-Ring bis zum 9-Ring, das Minimum des Schwellenwertes liegt beim 8-Ring (c
sbi=2–5 mmol/l). Die größeren Ringe sind bis zu Konzentrationen von 20 mmol/l ohne Geschmack. Beim 6-Ring löscht eine 2-Methylgruppe jeden Geschmackseindruck, während die 3- und 4-Methylverbindungen süß und bitter sind. Die 4-Äthylverbindung ist bitter aber nicht süß, die 4-tert.-Butylverbindung ist ohne Geschmack. 1-Aminonorbornan-1-carbonsäure ist süß (c
Ssü 50 mmol/l) und bitter (c
sbi=5–7mmo1/1), wobei der Schwellenwert für bitter fast eine Zehnerpotenz kleiner ist. tert.-Leucin ist ohne Geschmack. Die Ergebnisse werden im Zusammenhang mit früheren Untersuchungen an offenkettigen Aminosäuren diskutiert und in Modelle über sterische Voraussetzungen für Geschmack eingeordnet.
Relationsships between structure and taste in amino acids with cyclic side chains
Summary 1-Aminocycloalkane-1-carboxylic acids with ring sizes of 4–11 (excluding 10) were synthesized and tested for their taste properties. The compounds with 4- to 8-membered rings are sweet, with threshold values going through a minimum for the 6-membered ring (c tsw = l-3 mM/l). The compounds with 5- to 9-membered rings are bitter. Here the threshold value reaches a minimum for the 8-membered ring (c tbi=2–5 mM/l). The larger rings are without taste up to concentrations of 20 mmol/l. With the 6-membered ring a 2-methyl group abolishes any taste impression, whereas the 3- and 4-methyl compounds are sweet and bitter. The 4-ethyl compound is bitter but not sweet, the 4-tert.-butyl compound has no taste. 1-Aminonorbornane-l-carboxylic acid is sweet (c tsw 50mM/l) and bitter (c tbi= 5–7 mM/l), withc tbi being significantly smaller thanc tsw. tert-Leucine is without taste. The results are discussed in relation to previous investigations into steric prerequisites for taste in the amino acid series.相似文献
102.
Just how insoluble are monoterpenes? 总被引:16,自引:0,他引:16
Jeffrey D. Weidenhamer Francisco A. Macias Nikolaus H. Fischer G. Bruce Williamson 《Journal of chemical ecology》1993,19(8):1799-1807
Prior generalizations about the ecological roles of monoterpenes may be misleading if based on the presumed insolubility of monoterpenes in water. We determined the aqueous solubility of 31 biologically active monoterpenes by gas chromatography. While hydrocarbons were of low solubility (< 35 ppm), oxygenated monoterpenes exhibited solubilities one or two orders of magnitude higher, with ranges of 155–6990 ppm for ketones and of 183–1360 ppm for alcohols. Many monoterpenes are phytotoxic in concentrations under 100 ppm, well below the saturated aqueous concentrations of oxygenated monoterpenes. Therefore, even dilute, unsaturated solutions of monoterpenes, occurring naturally in plant tissues and soil solutions, may act as potent biological inhibitors. 相似文献
103.
Michael Würsch Giacomo Ghezzi Matthias Hert Gerald Reif Harald C. Gall 《Computing》2012,94(11):857-885
The Semantic Web provides a standardized, well-established framework to define and work with ontologies. It is especially apt for machine processing. However, researchers in the field of software evolution have not really taken advantage of that so far. In this paper, we address the potential of representing software evolution knowledge with ontologies and Semantic Web technology, such as Linked Data and automated reasoning. We present Seon, a pyramid of ontologies for software evolution, which describes stakeholders, their activities, artifacts they create, and the relations among all of them. We show the use of evolution-specific ontologies for establishing a shared taxonomy of software analysis services, for defining extensible meta-models, for explicitly describing relationships among artifacts, and for linking data such as code structures, issues (change requests), bugs, and basically any changes made to a system over time. For validation, we discuss three different approaches, which are backed by Seon and enable semantically enriched software evolution analysis. These techniques have been fully implemented as tools and cover software analysis with web services, a natural language query interface for developers, and large-scale software visualization. 相似文献
104.
Zusammenstellung von Schrifttumsangaben für die Änderung der freien Standardenthalpien der Reaktionen , Mo + O2 ? MoO2 und in Eisenschmelzen. Neubestimmung der Temperaturabhängigkeiten der Größen ΔGoCr2O3, ΔGoMoO2 und ΔGoO im Eisen bei Temperaturen zwischen 1460 bzw. 1530 und 1725 °C. Nachweis der Anwendbarkeit der neu ermittelten thermodynamischen Funktionen durch EMK-Parallelmessungen an ThO2 (Y2O3)- und ZrO2 (MgO)-Festelektrolytzellen mit Cr-Cr2O3- und Mo-MoO2-Referenzelektroden in Reineisenschmelzen bei 1600 °C. Ermittlung des Parameters pe′ der Elektronenteilleitfähigkeit für einen teilstabilisierten ZrO2-Festelektrolyten mit einem Stoffmengengehalt von 5% MgO. 相似文献
105.
B. Witzigmann V. Laino M. Luisier U.T. Schwarz H. Fischer G. Feicht W. Wegscheider C. Rumbolz A. Lell V. Harle 《Photonics Technology Letters, IEEE》2006,18(15):1600-1602
The temperature dependent spectral gain in InGaN-GaN multiple quantum-well structures with 10% In content is investigated. Mode gain is measured in a temperature range between 239 K and 312 K using the Hakki-Paoli technique and compared to simulations. The simulation accounts for temperature-dependent polarization dephasing, and hence homogeneous broadening, in a rigorous fashion, without any fit parameter. It is found that the evolution of the gain spectrum with temperature at different drive currents can be modeled using a temperature-independent single value for inhomogeneous broadening. The resulting compositional fluctuations are compared to structural measurements. 相似文献
106.
107.
Minna Karstunen Harald Krenn Simon J. Wheeler Mirva Koskinen Rachid Zentar 《Canadian Metallurgical Quarterly》2005,5(2):87-97
This paper investigates the influence of anisotropy and destructuration on the behavior of a test embankment on soft clay. The test embankment at Murro, Finland, was commissioned in 1993 by the Finnish Road Administration and has been monitored for over 10?years. The construction and consolidation of Murro test embankment is analyzed with finite element method using three different constitutive models to represent the soft soil. The results are compared with field observations. The constitutive models used include two recently proposed constitutive models, namely S-CLAY1 that accounts for initial and plastic strain induced anisotropy and its extension, called S-CLAY1S. The S-CLAY1S model accounts, additionally, for interparticle bonding and degradation of bonds. For comparison, the test embankment is also analyzed using the isotropic Modified Cam Clay model. The simulations demonstrate that for this type of problem, it is important to account for the anisotropy, whereas destructuration appears to have less influence on predicted deformations. However, only a model incorporating destructuration can explain the decrease in undrained shear strength during consolidation that was measured in field. 相似文献
108.
During and after rolling or flattening of metal strips and plates the permissible deviations from flatness are described by the permissible absolute wave height and the flatness index. Both values can be determined on a measuring table while the material is not subjected to global tension. Because this procedure is expensive, time‐consuming and allows measurement only at discrete positions along the strip length, on‐line flatness measuring systems are used which can detect the distribution of longitudinal tensile stresses distributed across the strip width allowing for the calculation of the flatness index. This value does not always agree with the value obtained directly by measuring on the table even when the measurement of the longitudinal tensile stress distribution operates perfectly. It can be shown that the measurement of the tensile stress distribution does not give a direct indication on the wave height in the tension‐free state determined on the measuring table. To explain the relationship between tensile stress distribution in the strip and the flatness measurement on the measuring table, the buckling behavior is analysed both with and without dead load for simple symmetrical residual stress distributions resulting, e.g., from the rolling process. Based on the knowledge of the distribution of the longitudinal residual stresses across the strip width, the flatness index and the wave height can be determined by using a specialized finite element model. If the direct measurement is performed under action of dead load, large differences between the directly and indirectly obtained flatness index are observed. Below a certain limit of the intensity of the residual stress distribution the strips and plates lie flat on the measuring table. Above this limit the strip lying on the table exhibits post‐bucking deformations. In the latter case, the wave height increases with strip thickness and intensity of residual stresses. 相似文献
109.
N. K. Simha F. D. Fischer O. Kolednik J. Predan G. X. Shan 《International Journal of Fracture》2005,135(1-4):73-93
This paper describes a theoretical model and related computational methods for examining the influence of inhomogeneous material
properties on the crack driving force in elastic and elastic-plastic materials. Following the configurational forces approach,
the crack tip shielding or anti-shielding due to smooth (e.g. graded layer) and discontinuous (e.g. bimaterial interface)
distributions in material properties are derived. Computational post-processing methods are described to evaluate these inhomogeneity
effects. The utility of the theoretical model and computational methods is demonstrated by examining a bimaterial interface
perpendicular to a crack in elastic and elastic-plastic compact tension specimens. 相似文献
110.
In this paper analytic formulae are derived to estimate conservatively the unavailability of a two out of four digital safety Instrumentation and Control (I&C) system with recurrent tests. The analytic formulae disclose the influence of the different parameters on the system’s unavailability. In particular, the choice of a proper test interval is essential to guarantee the required low unavailability. The extraordinary self-checking capabilities of digital systems are taken into account by use of an appropriate failure model together with the treatment of dependent failures of the integrated software–hardware system. The underlying methodology is approved by licensing experts of nuclear facilities in Germany. 相似文献