全文获取类型
收费全文 | 41076篇 |
免费 | 3012篇 |
国内免费 | 89篇 |
专业分类
电工技术 | 1696篇 |
综合类 | 899篇 |
化学工业 | 14038篇 |
金属工艺 | 759篇 |
机械仪表 | 864篇 |
建筑科学 | 2381篇 |
矿业工程 | 334篇 |
能源动力 | 791篇 |
轻工业 | 3833篇 |
水利工程 | 300篇 |
石油天然气 | 124篇 |
武器工业 | 2篇 |
无线电 | 1825篇 |
一般工业技术 | 7411篇 |
冶金工业 | 2920篇 |
原子能技术 | 170篇 |
自动化技术 | 5830篇 |
出版年
2023年 | 809篇 |
2022年 | 638篇 |
2021年 | 1240篇 |
2020年 | 1005篇 |
2019年 | 923篇 |
2018年 | 1060篇 |
2017年 | 823篇 |
2016年 | 1155篇 |
2015年 | 1270篇 |
2014年 | 1504篇 |
2013年 | 2946篇 |
2012年 | 1625篇 |
2011年 | 1914篇 |
2010年 | 1896篇 |
2009年 | 1972篇 |
2008年 | 1673篇 |
2007年 | 1477篇 |
2006年 | 1207篇 |
2005年 | 1149篇 |
2004年 | 1087篇 |
2003年 | 966篇 |
2002年 | 905篇 |
2001年 | 543篇 |
2000年 | 453篇 |
1999年 | 517篇 |
1998年 | 625篇 |
1997年 | 523篇 |
1996年 | 554篇 |
1995年 | 498篇 |
1994年 | 479篇 |
1993年 | 538篇 |
1992年 | 427篇 |
1991年 | 357篇 |
1990年 | 371篇 |
1989年 | 425篇 |
1988年 | 335篇 |
1987年 | 366篇 |
1986年 | 382篇 |
1985年 | 415篇 |
1984年 | 399篇 |
1983年 | 373篇 |
1982年 | 340篇 |
1981年 | 416篇 |
1980年 | 304篇 |
1979年 | 327篇 |
1977年 | 287篇 |
1976年 | 298篇 |
1975年 | 338篇 |
1974年 | 300篇 |
1973年 | 455篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
Bei der Model Driven Architecture (MDA) bilden Modelle die zentralen Elemente des Softwareentwicklungsprozesses. Ziel ist es, plattformspezifische Modelle möglichst automatisiert aus plattformunabhängigen Modellen abzuleiten. Dadurch soll der Aufwand der Softwareentwicklung verringert und die Adaptierung an neue Technologien erleichtert werden.*Vorschläge an Prof. Dr. Frank Puppe oder Dieter Steinbauer Alle „Aktuellen Schlagwörter“ seit 1988 finden Sie unter: www.ai-wuerzburg.de/as 相似文献
74.
Remote sensing of species mixtures in conifer plantations using LiDAR height and intensity data 总被引:2,自引:0,他引:2
Daniel N.M. Donoghue Peter J. Watt Nicholas J. Cox Jimmy Wilson 《Remote sensing of environment》2007,110(4):509-522
In even-aged, single species conifer plantations LiDAR height data can be modelled to provide accurate estimates of tree height and volume. However, it is apparent that growth models developed for single species stands are not directly transferable to a more general situation of mixed species plantations. This paper evaluates the ability of small footprint, dual-return, pulsed airborne LiDAR data to estimate the proportion of the productive species when mixed with a nurse crop in closed canopy plantations. A study area located in Galloway Forest District in Scotland is used as an example of Lodgepole pine and Sitka spruce mixed plantation; this area contains good examples of a wide range of pure and mixed species plantation types. Three species groups are studied: areas of pure Sitka spruce, areas of pure Lodgepole pine and areas where the two species have been planted together. Two approaches are assessed for detection of plantation mixtures: the first uses LiDAR intensity data to separate spruce and pine species and the second uses LiDAR-derived canopy density measures, coefficient of variation, skewness, percent of ground returns (which provides a measure of canopy openness) and the mean canopy height, which enables areas with height variations to be identified. From analysis of LiDAR data extracted from 54 study plots using logistic regression, the coefficient of variation and LiDAR intensity data provide the most useful predictors of the proportion of spruce in a pine/spruce mixture with coefficients of determination (R2) of 0.914 and 0.930 respectively. The method could be developed as a mapping tool, which in combination with existing inventory data should help to improve timber volume forecasting for mixed species even-aged plantations. 相似文献
75.
Interest in advanced modulation formats for optical communication systems has so far experienced two major waves. The first one was motivated by the potential to enhance receiver sensitivity of thermal noise-limited systems using coherent detection in combination with phase shift keying. It ended with the advent of optical amplification, enabling high sensitivities together with polarization insensitive, simple and stable direct detection. The second wave is still rolling, fueled by the potential of advanced modulation formats to increase robustness of optical transmission systems against signal distortions. Due to performance limitations given by direct detection and nonlinear effects in the transmission fiber, it is not decided yet, whether there will be widespread application in carrier networks. 相似文献
76.
Dr. V. Recina Dr. D. Lundström B. Karlsson 《Metallurgical and Materials Transactions A》2002,33(9):2869-2881
The influence of chemical composition on the microstructure of the γ-titanium aluminide alloy Ti-48Al-2W-0.5Si (at. pct) and the accompanying tensile, low-cycle fatigue, and creep properties
has been evaluated. The study showed that small variations in chemical composition and casting procedures resulted in considerable
variations in the microstructure, yielding vastly different mechanical properties. Low contents of aluminum and tungsten led
to a coarse-grained lamellar (γ/α
2) microstructure with high creep resistance. A composition close to the nominal one produced a duplex (γ+γ/α
2) structure with favorable strength, ductility, and low-cycle fatigue properties. By controlling the solidification and cooling
rates at casting, a pseudoduplex (PS-DP) microstructure with a unique combination of high strength and high fatigue and creep
resistance can be obtained. These unique properties can be explained by the diffuse boundaries between the relatively small
γ grains and the neighboring lamellar colonies, combined with semicoherent interfaces between the γ and α
2 phases. At tensile and low-cycle fatigue loading, these boundaries act like high-angle boundaries, producing a virtually
fine-grained material promoting strength, whereas at creep loading, grain-boundary sliding is hindered in the semicoherent
interfaces leading to high creep resistance. 相似文献
77.
This paper deals with the problem of finding graph layerings restricted to a given maximal width. However, other than previous approaches for width-restricted layering, we take into account the space for dummy nodes, which are introduced by edges crossing a layer. The main result is that the problem of finding a width-restricted layering under consideration of dummy nodes is NP-complete even when all regular nodes have the same constant width and all dummy nodes have the same constant width. 相似文献
78.
Dr. H. -J. Dobner 《Computing》1987,38(3):209-218
This article describes a newly developed and implemented method for computing guaranteed errorbounds for the solution of hyperbolic initial value problems. The basic concepts—modified fixed point theorems and approximated operators—allow an a posteriori error-estimation automatically. Therefore, no a priori knowledge of Lipschitz constants, monotonicity properties or additional error analysis is necessary. 相似文献
79.
80.