全文获取类型
收费全文 | 5057篇 |
免费 | 314篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 119篇 |
综合类 | 20篇 |
化学工业 | 1285篇 |
金属工艺 | 102篇 |
机械仪表 | 85篇 |
建筑科学 | 354篇 |
矿业工程 | 26篇 |
能源动力 | 127篇 |
轻工业 | 438篇 |
水利工程 | 33篇 |
石油天然气 | 5篇 |
无线电 | 399篇 |
一般工业技术 | 1006篇 |
冶金工业 | 475篇 |
原子能技术 | 25篇 |
自动化技术 | 877篇 |
出版年
2023年 | 60篇 |
2022年 | 104篇 |
2021年 | 165篇 |
2020年 | 128篇 |
2019年 | 111篇 |
2018年 | 136篇 |
2017年 | 119篇 |
2016年 | 172篇 |
2015年 | 184篇 |
2014年 | 199篇 |
2013年 | 320篇 |
2012年 | 290篇 |
2011年 | 364篇 |
2010年 | 291篇 |
2009年 | 243篇 |
2008年 | 262篇 |
2007年 | 233篇 |
2006年 | 183篇 |
2005年 | 174篇 |
2004年 | 119篇 |
2003年 | 113篇 |
2002年 | 100篇 |
2001年 | 85篇 |
2000年 | 70篇 |
1999年 | 70篇 |
1998年 | 113篇 |
1997年 | 80篇 |
1996年 | 83篇 |
1995年 | 57篇 |
1994年 | 50篇 |
1993年 | 40篇 |
1992年 | 39篇 |
1991年 | 27篇 |
1990年 | 20篇 |
1989年 | 30篇 |
1988年 | 27篇 |
1986年 | 23篇 |
1985年 | 23篇 |
1984年 | 21篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 24篇 |
1978年 | 16篇 |
1977年 | 34篇 |
1976年 | 37篇 |
1974年 | 26篇 |
1973年 | 23篇 |
1972年 | 18篇 |
1971年 | 16篇 |
排序方式: 共有5376条查询结果,搜索用时 15 毫秒
21.
Ohne Zusammenfassung 相似文献
22.
In the following paper at first general concepts which have to be considered for the accomplishment of a 3D fatigue crack propagation simulation by the FE‐method in real structures are introduced. In doing so numerical aspects concerning the necessary mesh generation as well as fracture mechanical issues will be discussed. Furthermore the 3D crack simulation program ADAPCRACK3D, which has been developed at the Institute of Applied Mechanics at University of Paderborn, is presented in its general functionality. The simulation example of the crack propagation in a shutter ring of a hydraulic press shows the practical relevance of both the implemented algorithms and fracture mechanical concepts. 相似文献
23.
Modified (α‐diimine)nickel(II) catalysts are suitable for ethylene oligomerization reactions. Due to the mechanism (“chain running”), the formation of double‐bond isomers and branched olefins can be observed. The obtained oligomer mixtures show a Schulz–Flory distribution. Increasing ethylene pressure favors the selectivity of α‐olefin formation. The same effect can be observed when Lewis bases like thiophene or furane are added to the oligomerization reaction mixture. These results can be related to an interaction of the additives with the catalytic active species during the oligomerization process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1356–1361, 2003 相似文献
24.
Part 1 of this contribution reported on the effects of system properties on heat transfer between heating or cooling surfaces and bubbling fluidized beds. This investigation produced four correlations which define the respective maximum heat transfer. Part 2 of this study suggests that the heat transfer between exchanger surfaces and bubbling fluidized beds depends on superficial gas velocity, expressed as dimensionless excess gas velocity. The present paper shows that heat transfer coefficients in circulating fluidized beds can be predicted by evaluation of a state diagram, which combines three dimensionless groups: Nusselt number, Archimedes number and a dimensionless pressure gradient. A comparison of coal combustion experiments with own cold model measurements indicates that the radiative component of heat transfer coefficients is only evident at very low dimensionless pressure gradients. 相似文献
25.
Markus Stolze 《Knowledge》1994,7(4):271-273
System development is strongly influenced by the perspectives used by system developers. Current development methods for knowledge-based systems are based on an information processing perspectives of experts and users which has been criticized by a number of researchers. The paper argues that work-oriented development of knowledge-based systems requires the parallel use of multiple perspectives (including the information processing perspective), and that the use of any single perspective is potentially dangerous. As an example of the importance of using multiple perspectives, thepaper presents the situated action perspective, and shows how it complements the information processing perspective. 相似文献
26.
F. Otto 《Theory of Computing Systems》1995,28(4):363-384
Examples of one-rule trace-rewriting systems are given that are confluent but not strongly confluent. This contrasts with the situation for one-rule string-rewriting systems as well as with the situation for one-rule commutative string-rewriting systems. 相似文献
27.
Dipl.-Phys. Andreas Neuber M. Sc. Guenther Carlos Krieger Dipl.-Ing. Markus Tacke Prof. Dr.-Ing Johannes Janicka 《Forschung im Ingenieurwesen》1996,62(7-8):188-194
Zusammenfassung Die laserspektroskopischen Me?methoden laserinduzierte Fluoreszenz und spontane Ramanspektroskopie werden eingesetzt zur Messung
der Konzentrationen von Stickoxid, Hydroxyl sowie der chemischen Hauptkomponenten und der Temperatur. Betrachtet wird die
thermische Umsetzung von Wasserstoff mit Luftsauerstoff. Es wird die experimentelle Vorgehensweise und Problematik dargestellt.
Ebenso wird der Weg der Modellierung und Berechnung turbulenter Verbrennungsvorg?nge am konkreten Beispiel skizziert. Die
Annahme chemischen Gleichgewichts stellt sich als ungenügend in der Berechnung der Stickoxid- und Hydroxylkonzentrationen
heraus. Eine deutlich bessere Vorhersage wird durch Einführen einer Reaktionsfortschrittsvariablen für das chemische Modell
erreicht. 相似文献
28.
29.
Cis-1,4-polybutadiene (PB) in a 0.5% solution of a solvent mixture of dichloromethane and 1,2-dibromoethane or tetrahydrofuran was quantitatively brominated with elemental bromine at 0°C under careful exclusion of oxygen to head-to-head poly(vinyl bromide). Partially brominated PB has a structure of random or block sequences of butadiene units in the polymer depending on the bromination solvent but shows no stereospecificity in the CHBrCHBr-dyads. Partially brominated PB with block structure showed a microphase-separated morphology over a wide range of composition. Microphase separation is less pronounced for the more random structure of butadiene units. I.r and 13C n.m.r. spectroscopy of the partially brominated PB was used to follow the progress of the bromination. 相似文献
30.
Many new speciality polymers have been developed in the last few years. In this paper polymeric stabilizers (antioxidants, flame retardants and ultraviolet stabilizers) will be discussed. Polymeric antioxidants of the hindered-phenol type, copolymers of 2,6-ditertiarybutyl-4-vinyl(or isopropenyl)phenol with styrene, methyl methacrylate, or more importantly butadiene or isoprene have been prepared; hydrogenation of the latter copolymers gave copolymers of the two polymerizable phenolic antioxidants with ethylene or ethylene/propylene. The polymeric antioxidants have been blended with diene polymers and selected polyolefins and have improved the long-term oxidative stability of these polymers. Polymeric flame retardants have been prepared by copolymerizing styrene and/or acrylonitrile with acrylates and methacrylates of aliphatic bromine-containing alcohols or bromine-containing phenols. Polymers with polymer-bound flame retardants have a higher limiting oxygen index compared with the original polymer. A new class of polymerizable ultraviolet stabilizers has also been developed; these stabilizers are styryl, α-methylstyryl, acryloyl and methacryloyl derivatives of 2(2-hydroxyphenyl)2H-benzotriazoles. These monomers have been copolymerized with styrene, acrylates and methacrylates. 2(2-Hydroxyphenyl)2H-benzotriazoles substituted in the 4 position of the benzotriazole ring with hydroxyl, acetoxy or carboxyl groups suitable for incorporation into polyesters, polycarbonates, polyamides and epoxy resins have also been synthesized. All 2(2-hydroxyphenyl)2H-benzotriazole ultraviolet absorbers and the polymers into which they are incorporated have high light absorbency with γmax between 330 and 350 nm and extinction coefficients in some cases as high as 4.5 × 104 1 mol?1 cm?1. 相似文献