全文获取类型
收费全文 | 4947篇 |
免费 | 273篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 81篇 |
综合类 | 20篇 |
化学工业 | 861篇 |
金属工艺 | 95篇 |
机械仪表 | 108篇 |
建筑科学 | 234篇 |
矿业工程 | 14篇 |
能源动力 | 148篇 |
轻工业 | 445篇 |
水利工程 | 38篇 |
石油天然气 | 49篇 |
无线电 | 551篇 |
一般工业技术 | 873篇 |
冶金工业 | 931篇 |
原子能技术 | 23篇 |
自动化技术 | 762篇 |
出版年
2023年 | 44篇 |
2022年 | 70篇 |
2021年 | 131篇 |
2020年 | 105篇 |
2019年 | 118篇 |
2018年 | 127篇 |
2017年 | 120篇 |
2016年 | 148篇 |
2015年 | 114篇 |
2014年 | 145篇 |
2013年 | 288篇 |
2012年 | 202篇 |
2011年 | 323篇 |
2010年 | 200篇 |
2009年 | 230篇 |
2008年 | 232篇 |
2007年 | 225篇 |
2006年 | 166篇 |
2005年 | 136篇 |
2004年 | 115篇 |
2003年 | 106篇 |
2002年 | 80篇 |
2001年 | 71篇 |
2000年 | 77篇 |
1999年 | 83篇 |
1998年 | 232篇 |
1997年 | 152篇 |
1996年 | 103篇 |
1995年 | 94篇 |
1994年 | 76篇 |
1993年 | 69篇 |
1992年 | 41篇 |
1991年 | 39篇 |
1990年 | 36篇 |
1989年 | 38篇 |
1988年 | 41篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 44篇 |
1984年 | 39篇 |
1983年 | 32篇 |
1982年 | 48篇 |
1981年 | 40篇 |
1980年 | 28篇 |
1979年 | 36篇 |
1978年 | 29篇 |
1977年 | 51篇 |
1976年 | 61篇 |
1975年 | 21篇 |
1974年 | 32篇 |
排序方式: 共有5233条查询结果,搜索用时 296 毫秒
1.
Tallison O. Abreu Roterdan F. Abreu Felipe F. do Carmo Wellington V. de Sousa Helenilson de O. Barros José E.V. de Morais João P.C. do Nascimento Marcelo A.S. da Silva Sergei Trukhanov Alex Trukhanov Larissa Panina Charanjeet Singh Antonio S.B. Sombra 《Ceramics International》2021,47(11):15424-15432
This work presents the dielectric properties of YNbO4 (YNO)–TiO2 composites in the microwave range. X-ray diffraction analysis demonstrates that the addition of TiO2 to YNO results in the formation of a Y(Nb0.5Ti0.5)2O6 phase. In the microwave range, the values of permittivity and dielectric loss did not present major changes with the increment of TiO2. Moreover, the addition of TiO2 results in an improvement in the thermal stability of YNO, with YNO63 demonstrating a resonant frequency of ?8.96 ppm.°C?1. We utilised numerical simulations to evaluate the behaviour of these materials as dielectric resonator antennae and it is found that they exhibit a reflection coefficient below ?10 dB at the resonant frequency, with a realised gain of 4.94 – 5.76 dBi, a bandwidth of 665–1050 MHz and a radiation efficiency above 84%. Our results indicate that YNO–TiO2 composites are interesting candidates for microwave operating devices. 相似文献
2.
3.
Physical Stability of Octenyl Succinate–Modified Polysaccharides and Whey Proteins for Potential Use as Bioactive Carriers in Food Systems
下载免费PDF全文
![点击此处可从《Journal of food science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The high cost and potential toxicity of biodegradable polymers like poly(lactic‐co‐glycolic)acid (PLGA) has increased the interest in natural and modified biopolymers as bioactive carriers. This study characterized the physical stability (water sorption and state transition behavior) of selected starch and proteins: octenyl succinate–modified depolymerized waxy corn starch (DWxCn), waxy rice starch (DWxRc), phytoglycogen, whey protein concentrate (80%, WPC), whey protein isolate (WPI), and α‐lactalbumin (α‐L) to determine their potential as carriers of bioactive compounds under different environmental conditions. After enzyme modification and particle size characterization, glass transition temperature and moisture isotherms were used to characterize the systems. DWxCn and DWxRc had increased water sorption compared to native starch. The level of octenyl succinate anhydrate (OSA) modification (3% and 7%) did not reduce the water sorption of the DWxCn and phytoglycogen samples. The Guggenheim–Andersen–de Boer model indicated that native waxy corn had significantly (P < 0.05) higher water monolayer capacity followed by 3%‐OSA‐modified DWxCn, WPI, 3%‐OSA‐modified DWxRc, α‐L, and native phytoglycogen. WPC had significantly lower water monolayer capacity. All Tg values matched with the solid‐like appearance of the biopolymers. Native polysaccharides and whey proteins had higher glass transition temperature (Tg) values. On the other hand, depolymerized waxy starches at 7%‐OSA modification had a “melted” appearance when exposed to environments with high relative humidity (above 70%) after 10 days at 23 °C. The use of depolymerized and OSA‐modified polysaccharides blended with proteins created more stable blends of biopolymers. Hence, this biopolymer would be suitable for materials exposed to high humidity environments in food applications. 相似文献
4.
Dr. Li Di Prof. Per Artursson Dr. Alex Avdeef Prof. Leslie Z. Benet Prof. J. Brian Houston Dr. Manfred Kansy Edward H. Kerns Prof. Hans Lennernäs Dr. Dennis A. Smith Prof. Kiyohiko Sugano 《ChemMedChem》2020,15(20):1862-1874
Passive permeability is a key property in drug disposition and delivery. It is critical for gastrointestinal absorption, brain penetration, renal reabsorption, defining clearance mechanisms and drug-drug interactions. Passive diffusion rate is translatable across tissues and animal species, while the extent of absorption is dependent on drug properties, as well as in vivo physiology/pathophysiology. Design principles have been developed to guide medicinal chemistry to enhance absorption, which combine the balance of aqueous solubility, permeability and the sometimes unfavorable compound characteristic demanded by the target. Permeability assays have been implemented that enable rapid development of structure-permeability relationships for absorption improvement. Future advances in assay development to reduce nonspecific binding and improve mass balance will enable more accurately measurement of passive permeability. Design principles that integrate potency, selectivity, passive permeability and other ADMET properties facilitate rapid advancement of successful drug candidates to patients. 相似文献
5.
Hyun‐Cheol Kim Charalampos Z. Patrikakis Nikos Minogiannis Pantelis N. Karamolegkos Alex Lambiris Kyuheon Kim 《ETRI Journal》2006,28(4):411-424
This paper presents a multimedia streaming platform for efficiently transmitting MPEG‐4 content over IP networks. The platform includes an MPEG‐4 compliant streaming server and client, supporting object‐based representation of multimedia scenes, interactivity, and advanced encoding profiles defined by the ISO standard. For scalability purposes, we employ an application‐layer multicast scheme for media transmission using overlay networks. The overlay network, governed by the central entity of the network distribution manager, is dynamically deployed according to a set of pre‐defined criteria. The overlay network supports both broadcast delivery and video‐on‐demand content. The multimedia streaming platform is standards‐compliant and utilizes widespread multimedia protocols such as MPEG‐4, real‐time transport protocol, real‐time transport control protocol, and real‐time streaming protocol. The design of the overlay network was architected with the goal of transparency to both the streaming server and the client. As a result, many commercial implementations that use industry‐standard protocols can be plugged into the architecture relatively painlessly and can enjoy the benefits of the platform. 相似文献
6.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
7.
Decreasing carboxyl retention in deposits from the glow region of an acrylic acid plasma was measured by X-ray photoelectron spectroscopy and chemical derivatisation as the collection distance from the monomer vapour inlet was increased. Volatilisation of plasma polymerised acrylic acid was detected after trifluoroethanol derivatisation; this is correlated with evaporation of low molecular weight components observed previously. 相似文献
8.
9.
Existence conditions are given for maximum likelihood (ML) parameter estimates for several families of 2-parameter software-reliability Poisson-process models. For each such model, the ML equations can be expressed in terms of one equation in one unknown. Bounds are given on solutions to these one equation problems to serve as initial intervals for search algorithms like bisection. Uniqueness of the solutions is established in some cases. Solutions are also tabulated for certain simple cases. Results are given for ungrouped failure data (exact times are available for all failures). ML estimation problems for such a situation are treated as limiting cases of problems based on failure times grouped into intervals of decreasing mesh 相似文献
10.