全文获取类型
收费全文 | 334728篇 |
免费 | 10491篇 |
国内免费 | 3883篇 |
专业分类
电工技术 | 8612篇 |
技术理论 | 9篇 |
综合类 | 4827篇 |
化学工业 | 52227篇 |
金属工艺 | 12456篇 |
机械仪表 | 12407篇 |
建筑科学 | 13668篇 |
矿业工程 | 2501篇 |
能源动力 | 9607篇 |
轻工业 | 33435篇 |
水利工程 | 3535篇 |
石油天然气 | 6274篇 |
武器工业 | 493篇 |
无线电 | 43145篇 |
一般工业技术 | 56716篇 |
冶金工业 | 50837篇 |
原子能技术 | 4178篇 |
自动化技术 | 34175篇 |
出版年
2023年 | 1719篇 |
2022年 | 3230篇 |
2021年 | 4810篇 |
2020年 | 3607篇 |
2019年 | 3627篇 |
2018年 | 4740篇 |
2017年 | 5028篇 |
2016年 | 5155篇 |
2015年 | 5051篇 |
2014年 | 7595篇 |
2013年 | 16874篇 |
2012年 | 11882篇 |
2011年 | 15053篇 |
2010年 | 12200篇 |
2009年 | 12988篇 |
2008年 | 13238篇 |
2007年 | 13178篇 |
2006年 | 12796篇 |
2005年 | 11496篇 |
2004年 | 9863篇 |
2003年 | 9500篇 |
2002年 | 8690篇 |
2001年 | 8974篇 |
2000年 | 8527篇 |
1999年 | 9291篇 |
1998年 | 18651篇 |
1997年 | 13172篇 |
1996年 | 10232篇 |
1995年 | 7927篇 |
1994年 | 6864篇 |
1993年 | 6398篇 |
1992年 | 4607篇 |
1991年 | 4276篇 |
1990年 | 3924篇 |
1989年 | 3700篇 |
1988年 | 3575篇 |
1987年 | 2748篇 |
1986年 | 2631篇 |
1985年 | 3244篇 |
1984年 | 2876篇 |
1983年 | 2611篇 |
1982年 | 2398篇 |
1981年 | 2432篇 |
1980年 | 2237篇 |
1979年 | 2072篇 |
1978年 | 1886篇 |
1977年 | 2202篇 |
1976年 | 2739篇 |
1975年 | 1591篇 |
1973年 | 1564篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
The exfiltration of wastewater from sewer systems in urban areas causes a deterioration of soil and possibly groundwater quality. Beside the simulation of transport and degradation processes in the unsaturated zone and in the aquifer the analysis of the potential impact requires the estimation of quantity and temporal variation of wastewater exfiltration. Exfiltration can be assessed by the application of a leakage model. The hydrological approach was originally developed to simulate the interactions between the groundwater and surface water, it was adapted to allow for modelling of interactions between groundwater and sewer system. In order to approximate the exfiltration specific model parameters infiltration specific parameters were used as a basis. Scenario analysis of the exfiltration in the City of Dresden from 1997 to 1999 and during the flood event in August 2002 shows the variation and the extent of exfiltration rates. 相似文献
992.
RICHARD C. HULA 《Journal of Urban Affairs》1985,7(3):39-56
This paper attempts to measure the effect of a court-ordered desegregation plan on three aspects of the housing market in Dallas County, Texas. The indicators include sale price, number of sales, and proportion of home sales financed by conventional mortgages. Monthly data from 1969 to 1979 are analyzed using Box-Jenkins time series models. After best fit models are determined, various intervention terms are introduced into the models to assess the impact of both a 1975 Circuit Court Order and a 1976 District Court Order. The analysis suggests neither order had a measurable effect on the housing market in Dallas. 相似文献
993.
Analysis and synthesis of on-chip spiral inductors 总被引:3,自引:0,他引:3
This paper presents a physically based compact model for estimating high-frequency performance of spiral inductors. The model accurately accounts for skin and proximity effects in the metal conductors as well as eddy current losses in the substrate. The model shows excellent agreement with measured data mostly within 10% across a variety of inductor geometries and substrate dopings up to 20 GHz. A web-based spiral inductor synthesis and analysis tool COILS, which makes use of the compact models, is presented. An optimization algorithm using binary searches speeds up the synthesis of inductor designs. 相似文献
994.
By combining smart sensors and traversability grids with a JAUS-based component and messaging architecture, DARPA Grand Challenge finalist team CIMAR quickly developed a robust autonomous ground vehicle (AGV), a custom-built off-road vehicle. Key components included six smart sensors for detecting environmental conditions and reporting a priori data, a smart arbiter for fusing data from multiple smart sensors, and a reactive driver for providing real-time navigation planning and obstacle avoidance 相似文献
995.
Summary Novel hyperbranched copolymers were successfully synthesized by the controlled charge transfer complex inimer and living radical copolymerization of p-(chloromethyl)styrene (PCMS) and acrylonitrile (AN). The resulting copolymers were characterized by SEC, NMR, FTIR, DSC and elemental analysis etc.. The influences of reaction conditions, such as the polymerization temperature, the catalyst (CuBr) concentration and the monomer ratio, on the resulting copolymers were investigated in detail. The monomer reactivity ratios were evaluated to be rPCMS=0.937 and rAN=0.088 respectively by the Fineman-Ross method. The higher are the polymerization temperature and the ratio of catalyst to monomer, the higher is the branching degree of the resulting copolymer. When the amount of monomer AN was used in excess than that of the monomer PCMS in the raw feed, the hyperbranched predominantly alternating copolymers HP[PCMS-co-AN] could be obtained. These hyperbranched copolymers were successfully used as functional macroinitiators to synthesize the star-shaped poly(PCMS-co-AN)/poly(MMA) block copolymers. 相似文献
996.
This paper presents the main current theoretical issues in Information Retrieval. The principles of conceptual modelling, as they have emerged in the database area, are presented and their application to document modelling in order to enhance document retrieval is discussed. Finally, the main features of the MULTOS project are presented and critically reviewed confronting them with the requirements which have been identified during the general discussion on document conceptual modelling for information retrieval. 相似文献
997.
P. C. Campbell E. B. Hawbolt J. K. Brimacombe 《Metallurgical and Materials Transactions A》1991,22(11):2769-2778
The goal of this study was to develop a mathematical model which incorporates heat flow, phase transformation kinetics, and
property-structure-composition relationships to predict the mechanical properties of steel rod being control cooled under
industrial conditions. Thus, the principles of microstructural engineering have been brought to bear on this interdisciplinary
problem by combining computer modeling with laboratory measurements of heat flow, austenite decomposition kinetics, microstructure
and mechanical properties, and industrial trials to determine heat transfer and obtain rod samples under known conditions.
Owing to the length and diversity of the study, it is reported in three parts,[8191]the first of which is concerned with the heat flow measurements. A relatively simple and reliable technique, involving a preheated
steel rod instrumented with a thermocouple secured at its centerline, has been devised to determine the cooling rate in different
regions of the moving bed of rod loops on an operating Stelmor line. The measured thermal response of the rod has been analyzed
by two transient conduction models (lumped and distributed parameter, respectively) to yield overall heat-transfer coefficients
for radiation and convection. The adequacy of the technique has been checked by cooling instrumented rods under well-defined,
air crossflow conditions in the laboratory and comparing measured heat-transfer coefficients to values predicted from well-established
equations. The industrial thermal measurements have permitted the characterization of a coefficient to account for radiative
interaction among adjacent rod loops near the edge and at the center of the bed.
Formerly Graduate Student, The University of British Columbia. 相似文献
998.
The strengths of two graphite/epoxy notched laminate systems with a softening strip were investigated. The softening strip was created by replacing the 0°-graphite/epoxy plies by a glass/epoxy composite. Experimental results indicated that the use of softening strips could significantly increase the laminate strength. Analysis was performed with finite elements developed using the classical laminated plate theory and was shown to be adequate. A simple point-stress failure criterion was used to predict the strength of notched laminates with softening strips and the result was found to be satisfactory. 相似文献
999.
1000.
Plastic deformation and fracture of binary TiAl-base alloys 总被引:4,自引:0,他引:4
The mechanical behavior of binary TiAl alloys containing 46 to 60 at. pct Al has been studied in bulk materials preparedvia rapid solidification processing. Bending and tensile tests were carried out at room temperature as a function of Al concentration.
A few alloys were also tested from liquid nitrogen temperature to ∼ 1000°C. Deformation substructures were studied by analytical
transmission electron microscopy and fracture modes by scanning electron microscopy (SEM). It was found that both microstructure
and composition strongly affect the mechanical behavior of TiAl-base alloys. A duplex structure, which contains both primary
y grains and transformedγ/α
2 lamellar grains, is more deformable than a single-phase or a fully transformed structure. The highest plasticities are observed
in duplex alloys containing 48–50 at. pct Al after heat treatment in the center of theγ + α phase field. The deformation of these duplex alloys is facilitated by 1/2[110] slip and {111} twinning, but very limited
superdislocation slip occurs. The twin deformation is suggested to result from a lowered stacking fault energy due to oxygen
depletion or an intrinsic change in chemical bonding. Other factors, such as grain size and grain boundary chemistry and structure,
are important from a fracture point of view. The results on the deformation and fracture modes as a function of test temperature
are also discussed. 相似文献