全文获取类型
收费全文 | 1938篇 |
免费 | 47篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 33篇 |
化学工业 | 373篇 |
金属工艺 | 78篇 |
机械仪表 | 33篇 |
建筑科学 | 31篇 |
能源动力 | 77篇 |
轻工业 | 66篇 |
水利工程 | 6篇 |
石油天然气 | 7篇 |
无线电 | 293篇 |
一般工业技术 | 407篇 |
冶金工业 | 296篇 |
原子能技术 | 14篇 |
自动化技术 | 278篇 |
出版年
2023年 | 15篇 |
2022年 | 31篇 |
2021年 | 51篇 |
2020年 | 43篇 |
2019年 | 41篇 |
2018年 | 65篇 |
2017年 | 38篇 |
2016年 | 51篇 |
2015年 | 42篇 |
2014年 | 32篇 |
2013年 | 115篇 |
2012年 | 68篇 |
2011年 | 102篇 |
2010年 | 71篇 |
2009年 | 80篇 |
2008年 | 99篇 |
2007年 | 96篇 |
2006年 | 58篇 |
2005年 | 53篇 |
2004年 | 33篇 |
2003年 | 34篇 |
2002年 | 29篇 |
2001年 | 23篇 |
2000年 | 24篇 |
1999年 | 35篇 |
1998年 | 63篇 |
1997年 | 67篇 |
1996年 | 43篇 |
1995年 | 40篇 |
1994年 | 40篇 |
1993年 | 35篇 |
1992年 | 18篇 |
1991年 | 25篇 |
1990年 | 23篇 |
1989年 | 13篇 |
1988年 | 24篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 26篇 |
1984年 | 22篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 14篇 |
1978年 | 18篇 |
1977年 | 12篇 |
1976年 | 22篇 |
1975年 | 6篇 |
1974年 | 15篇 |
排序方式: 共有1992条查询结果,搜索用时 15 毫秒
21.
An unsteady state heat conduction model with a convective boundary condition is proposed for the drying of low-rank, high-porosity coals, such as lignites, during fluidized-bed combustion. The drying front is assumed to be the receding surface of a wet core. The solution technique for this moving boundary problem is based on the heat balance integral approach with immobilization of the moving boundary by a change in space variable. The governing cubic equation describing the drying curve in dimensionless form may be solved easily by the Newton—Raphson method. The model predictions are compared with experimental data for Mississippi lignite with excellent agreement. A correlation for estimation of total drying time is proposed. The temperature profiles obtained may be used for the study of the coupled drying and devolatilization in fluidized-bed combustors. The profiles could also be of importance in the study of formation of fissures/cracks in lignites subjected to intense heating conditions encountered during fluidized-bed combustion. 相似文献
22.
A differentiation between free carboxyl and various lactone groups in different types of oxycelluloses was carried out based on the variation in their reaction rate with KI/KIO3 solution. For oxycelluloses prepared under acidic conditions, a large proportion of carboxyl groups are present in free form. Each oxycellulose was also studied after cation freeing as well as after blocking the free carboxyl groups by treatment with sodium chloride. Cation freeing was found to cause considerable lactonization of carboxyl groups; sodium chloride treatment blocked them only partially. 相似文献
23.
24.
Self-recoverable fragile watermarking is meant for accurate tamper localization as well as image recovery with superior visual quality. However, most of the existing state of art approaches perform authentication and recovery on block basis owing to which the entire block is categorized as tampered in case of alteration of one or more pixels of it. This, results in staircase formation of tamper detected regions, hence lacking in accuracy. Furthermore, the visual quality of the recovered image also deteriorates as an approximate value is assigned to all the block pixels corresponding to the altered region. The proposed watermarking scheme performs both authentication and recovery pixelwise. The authentication of each pixel is done via multi level tamper detection(MLTD) through three authentication bits based on value, location and neighbourhood information. The domain for image recovery is chosen dynamically based on the content of the block, may it be in spatial domain for smooth blocks or frequency domain for the rough ones. This provides high accuracy in recovery. As the embedding of recovery information is done in the frequency domain, the imperceptibility of the watermarked image scheme remains high. Also, embedding of authentication information in the spatial domain maintains its fragile nature. Even for higher tampering ratios, the lost content is rebuilt with high peak signal to noise ratio(PSNR) of the recovered image. The probabilities of false rejection and false acceptance head towards the ideal value for most of the empirical analysis. Comparative study via metric evaluation of probability of false rejection (PFR), probability of false acceptance (PFA) and PSNR of recovered image for different standard test cover images demonstrate the efficacy of the proposed scheme over other existing state of art approaches. Further, the security of the proposed scheme remains high due to usage of multi-layered secret keys and chaos based random mapping handling worst tamper scenarios. 相似文献
25.
Kevin P. Nolan Akshat Agarwal Shenghui Lei Robin Shields 《Microfluidics and nanofluidics》2016,20(7):101
Detailed measurements of the flow instability of dilute shear-thinning viscoelastic aqueous solutions, with relatively low zero-shear viscosities, in an obstructed microchannel flow are reported. We examine the flow behaviour resulting from a 100 μm post placed in the channel centreline over a range of Reynolds numbers (\(5<Re<300\)) and Weissenberg numbers (\(20<Wi<10^3\)). Micro-particle image velocimetry measurements show the onset of an upstream instability within a Reynolds number range and at a critical elasticity number corresponding to polymer concentrations above 25 ppm of long-chain polyacrylamide. The instability results in significant local fluctuations in the flow field approaching 30 % of the mean velocity. The magnitude of the local viscosity ratio in the region upstream of the post is proposed as a driving mechanism for the instability which resembles a buckling flow. Additionally, the classical instability owing to separation and vortex formation downstream of the post in Newtonian flow is suppressed and a very long stable wake is observed extending over 10 post-diameters downstream. 相似文献
26.
27.
Wireless Personal Communications - Finding the best path between a given source and a destination in a road network is an important problem. It has its applications in various map services and... 相似文献
28.
29.
Let There be Light: Polymeric Micelles with Upper Critical Solution Temperature as Light‐Triggered Heat Nanogenerators for Combating Drug‐Resistant Cancer 下载免费PDF全文
Yongyan Deng Florian Käfer Tingting Chen Qiao Jin Jian Ji Seema Agarwal 《Small (Weinheim an der Bergstrasse, Germany)》2018,14(37)
Complete drug release and efficient drug retention are two critical factors in reversing drug resistance in cancer therapy. In this regard, polymeric micelles with an upper critical solution temperature (UCST) are designed as a new exploration to reverse drug resistance. The amphiphilic UCST‐type block copolymers are used to encapsulate photothermal agent IR780 and doxorubicin (DOX) simultaneously. The integrated UCST‐type drug nanocarriers show light‐triggered multiple synergistic effects to reverse drug resistance and are expected to kill three birds with one stone: First, owing to the photothermal effect of IR780, the nanocarriers will be dissociated upon exposure to laser irradiation, leading to complete drug release. Second, the photothermal effect‐induced hyperthermia is expected to avoid the efflux of DOX and realize efficient drug retention. Last but not least, photothermal ablation of cancer cells can be achieved after laser irradiation. Therefore, the UCST‐type drug nanocarriers provide a new strategy in reversing drug resistance in cancer therapy. 相似文献
30.
Alpana Agarwal C.F. Tai J.N. Chung 《Computer Methods in Applied Mechanics and Engineering》2010,199(17-20):1080-1090
An accurate finite-volume based numerical method for the simulation of an isothermal two-phase flow, consisting of a rising deformable bubble translating in a quiescent, unbounded liquid, is presented. This direct simulation method is built on a sharp interface concept and developed on an Eulerian, Cartesian fixed-grid with a cut-cell scheme and marker points to track the moving interface. The unsteady Navier–Stokes equations in both liquid and gas phases are solved separately. The mass continuity and momentum flux conditions are explicitly matched at the true surface phase boundary to determine the evolving interface shape and movement of the bubble. The highlights of this method are that it utilizes a combined Eulerian–Lagrangian approach, and is capable of treating the interface as a sharp discontinuity. A fixed underlying grid is used to represent the control volume. The interface, however, is denoted by a separate set of marker particles which move along with the interface. A quadratic curve fitting algorithm with marker points is used to yield smooth and accurate information of the interface curvatures. This numerical scheme can handle a wide range of density and viscosity ratios. The bubble is assumed to be spherical and at rest initially, but deforms as it rises through the liquid pool due to buoyancy. Additionally, the flow is assumed to be axisymmetric and incompressible. The bubble deformation and dynamic motion are characterized by the Reynolds number, the Weber number, the density ratio and the viscosity ratio. The effects of these parameters on the translational bubble dynamics and shape are given and the physical mechanisms are explained and discussed. Results for the shape, velocity profile and various forces acting on the bubble are presented here as a function of time until the bubble reaches terminal velocity. The range of Reynolds numbers investigated is 1 < Re < 100, and that of Weber number is 1 < We < 10. 相似文献