全文获取类型
收费全文 | 735938篇 |
免费 | 10902篇 |
国内免费 | 2606篇 |
专业分类
电工技术 | 14078篇 |
综合类 | 1342篇 |
化学工业 | 114017篇 |
金属工艺 | 27814篇 |
机械仪表 | 21240篇 |
建筑科学 | 18025篇 |
矿业工程 | 3573篇 |
能源动力 | 19655篇 |
轻工业 | 63150篇 |
水利工程 | 7518篇 |
石油天然气 | 13654篇 |
武器工业 | 75篇 |
无线电 | 83037篇 |
一般工业技术 | 143216篇 |
冶金工业 | 140597篇 |
原子能技术 | 15602篇 |
自动化技术 | 62853篇 |
出版年
2021年 | 6936篇 |
2020年 | 5191篇 |
2019年 | 6451篇 |
2018年 | 10612篇 |
2017年 | 10366篇 |
2016年 | 11078篇 |
2015年 | 7896篇 |
2014年 | 12784篇 |
2013年 | 33928篇 |
2012年 | 19740篇 |
2011年 | 27045篇 |
2010年 | 21471篇 |
2009年 | 24398篇 |
2008年 | 24526篇 |
2007年 | 24216篇 |
2006年 | 21054篇 |
2005年 | 19199篇 |
2004年 | 18680篇 |
2003年 | 18403篇 |
2002年 | 17449篇 |
2001年 | 17561篇 |
2000年 | 16274篇 |
1999年 | 17261篇 |
1998年 | 44180篇 |
1997年 | 31040篇 |
1996年 | 23847篇 |
1995年 | 17953篇 |
1994年 | 15750篇 |
1993年 | 15608篇 |
1992年 | 11204篇 |
1991年 | 10594篇 |
1990年 | 10347篇 |
1989年 | 10110篇 |
1988年 | 9357篇 |
1987年 | 8451篇 |
1986年 | 8366篇 |
1985年 | 9192篇 |
1984年 | 8626篇 |
1983年 | 7731篇 |
1982年 | 7284篇 |
1981年 | 7398篇 |
1980年 | 7128篇 |
1979年 | 6860篇 |
1978年 | 6720篇 |
1977年 | 7854篇 |
1976年 | 10354篇 |
1975年 | 5824篇 |
1974年 | 5547篇 |
1973年 | 5835篇 |
1972年 | 4700篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
931.
The quantities of olefins, polyaromatic hydrocarbons and char formed during thermal decomposition in closed systems of alkylbenzenes are substantially reduced if the decomposition takes place in the presence of a good acceptor molecule such as pyrene or adamantane. The chemistry seems to be applicable to the upgrading of whole crude oils by a thermal treatment at 425-450°C in a closed system for 20-25 minutes. 相似文献
932.
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
933.
An asymptotically efficient autoregressive moving-average (ARMA) spectral estimator is presented, based on the sample covariances of observed time series. The estimate of the autoregressive (AR) part is shown to be identical to the optimal instrumental variable (IV) estimator in [7] although derived here using a different approach. The moving-average (MA) spectral parameter estimate is new. 相似文献
934.
935.
M. Kangas J. Villegas N. Kumar T. Salmi D.Yu. Murzin F. Sandelin E. Harlin 《Catalysis Today》2005,100(3-4):363-366
An investigation of the effect of reaction conditions on product distribution in the skeletal isomerisation reaction of linear butenes has been carried out. The main reaction routes over ferrierite have been identified. Beside the main product isobutene, major by-product formation occurs. The unwanted reactions include dimerisation of butene to form octenes, hydrogen transfer yielding small amounts of saturated C3 and C4 hydrocarbons and disproportionation producing propene and pentenes. The most abundant by-products were pentene and propene, though these were not formed in equimolar amounts as could be expected. Oligomerisation experiments of propene over ferrierite produced large amounts of butene and pentene, revealing the presence of adsorbed nonene. The cracking of this surface species to hexene and propene is the most likely reaction route for the excess propene formation. This additional path to propene formation operates mainly at temperatures above 623 K. 相似文献
936.
O Prez‐Camacho S Sepúlveda‐Guzmn M Prez‐lvarez M García‐Zamora G Cadenas‐Pliego 《Polymer International》2005,54(12):1626-1631
New functionalized styrene–maleimide copolymers were prepared by free radical copolymerization of styrene (St) and N‐4‐carboxybutylmaleimide (NBMI) in chloroform, using 2,2′‐azobisisobutyronitrile (AIBN) as initiator. Monomer and copolymer characterization was carried out by 1H‐ and 13C‐NMR. Copolymer composition was determined by elemental analysis and Fourier‐transform infrared (FTIR) spectroscopy. The glass transition temperature (from DSC) and the thermogravimetric analysis (TGA) of the copolymers were consistent with the thermal behavior and stability observed for alternating St–maleimide copolymers. St–NBMI copolymers crosslinked with divinylbenzene (DVB) were also synthesized and their cation exchange properties evaluated in order to assess the capacity of the new copolymers to bind metallic ions. Copyright © 2005 Society of Chemical Industry 相似文献
937.
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
938.
The Metaflow architecture, a unified approach to maximizing the performance of superscalar microprocessors, is introduced. The Metaflow architecture exploits inherent instruction-level parallelism in conventional sequential programs by hardware means, without relying on optimizing compilers. It is based on a unified structure, the DRIS (deferred-scheduling, register-renaming instruction shelf), that manages out-of-order execution and most of the attendant problems. Coupling the DRIS with a speculative-execution mechanism that avoids conditional branch stalls results in performance limited only be inherent instruction-level parallelism and available execution resources. Although presented in the context of superscalar machines, the technique is equally applicable to a superpipelined implementation. Lightning, the first implementation of the Metaflow architecture, which executes the Sparc RISC instruction set is described 相似文献
939.
M. Reza Ziai
Dileep R. Sule
《Computers & Industrial Engineering》1991,21(1-4):385-389The paper describes a computerized facility layout designer, COMLAD II, for plant layout development. Besides developing an efficient layout, COMLAD II has useful features which allow fixing the departments, changing the shape of the departments and changing the length and width dimensions of the overall layout. 相似文献
940.
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