全文获取类型
收费全文 | 79352篇 |
免费 | 7918篇 |
国内免费 | 5707篇 |
专业分类
电工技术 | 2438篇 |
技术理论 | 1篇 |
综合类 | 5042篇 |
化学工业 | 20688篇 |
金属工艺 | 7177篇 |
机械仪表 | 4304篇 |
建筑科学 | 2767篇 |
矿业工程 | 2151篇 |
能源动力 | 1944篇 |
轻工业 | 5164篇 |
水利工程 | 1134篇 |
石油天然气 | 3145篇 |
武器工业 | 637篇 |
无线电 | 9607篇 |
一般工业技术 | 11337篇 |
冶金工业 | 3386篇 |
原子能技术 | 1160篇 |
自动化技术 | 10895篇 |
出版年
2024年 | 250篇 |
2023年 | 1398篇 |
2022年 | 2566篇 |
2021年 | 3063篇 |
2020年 | 2529篇 |
2019年 | 2313篇 |
2018年 | 2104篇 |
2017年 | 2649篇 |
2016年 | 2910篇 |
2015年 | 2946篇 |
2014年 | 4233篇 |
2013年 | 4529篇 |
2012年 | 5246篇 |
2011年 | 6618篇 |
2010年 | 4905篇 |
2009年 | 5502篇 |
2008年 | 4811篇 |
2007年 | 5543篇 |
2006年 | 4968篇 |
2005年 | 4179篇 |
2004年 | 3248篇 |
2003年 | 2904篇 |
2002年 | 2350篇 |
2001年 | 1830篇 |
2000年 | 1733篇 |
1999年 | 1404篇 |
1998年 | 1152篇 |
1997年 | 881篇 |
1996年 | 809篇 |
1995年 | 616篇 |
1994年 | 592篇 |
1993年 | 445篇 |
1992年 | 365篇 |
1991年 | 292篇 |
1990年 | 221篇 |
1989年 | 177篇 |
1988年 | 119篇 |
1987年 | 104篇 |
1986年 | 110篇 |
1985年 | 58篇 |
1984年 | 43篇 |
1983年 | 40篇 |
1982年 | 50篇 |
1981年 | 25篇 |
1980年 | 39篇 |
1979年 | 28篇 |
1977年 | 17篇 |
1976年 | 16篇 |
1975年 | 9篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
Yulia Gryaditskya Tania Pouli Erik Reinhard Hans‐Peter Seidel 《Computer Graphics Forum》2014,33(7):61-69
Image calibration requires both linearization of pixel values and scaling so that values in the image correspond to real‐world luminances. In this paper we focus on the latter and rather than rely on camera characterization, we calibrate images by analysing their content and metadata, obviating the need for expensive measuring devices or modeling of lens and camera combinations. Our analysis correlates sky pixel values to luminances that would be expected based on geographical metadata. Combined with high dynamic range (HDR) imaging, which gives us linear pixel data, our algorithm allows us to find absolute luminance values for each pixel—effectively turning digital cameras into absolute light meters. To validate our algorithm we have collected and annotated a calibrated set of HDR images and compared our estimation with several other approaches, showing that our approach is able to more accurately recover absolute luminance. We discuss various applications and demonstrate the utility of our method in the context of calibrated color appearance reproduction and lighting design. 相似文献
993.
Julius Parulek Daniel Jönsson Timo Ropinski Stefan Bruckner Anders Ynnerman Ivan Viola 《Computer Graphics Forum》2014,33(6):276-287
Molecular visualization is often challenged with rendering of large molecular structures in real time. We introduce a novel approach that enables us to show even large protein complexes. Our method is based on the level‐of‐detail concept, where we exploit three different abstractions combined in one visualization. Firstly, molecular surface abstraction exploits three different surfaces, solvent‐excluded surface (SES), Gaussian kernels and van der Waals spheres, combined as one surface by linear interpolation. Secondly, we introduce three shading abstraction levels and a method for creating seamless transitions between these representations. The SES representation with full shading and added contours stands in focus while on the other side a sphere representation of a cluster of atoms with constant shading and without contours provide the context. Thirdly, we propose a hierarchical abstraction based on a set of clusters formed on molecular atoms. All three abstraction models are driven by one importance function classifying the scene into the near‐, mid‐ and far‐field. Moreover, we introduce a methodology to render the entire molecule directly using the A‐buffer technique, which further improves the performance. The rendering performance is evaluated on series of molecules of varying atom counts. 相似文献
994.
We present a data‐driven method for automatically recoloring a photo to enhance its appearance or change a viewer's emotional response to it. A compact representation called a RegionNet summarizes color and geometric features of image regions, and geometric relationships between them. Correlations between color property distributions and geometric features of regions are learned from a database of well‐colored photos. A probabilistic factor graph model is used to summarize distributions of color properties and generate an overall probability distribution for color suggestions. Given a new input image, we can generate multiple recolored results which unlike previous automatic results, are both natural and artistic, and compatible with their spatial arrangements. 相似文献
995.
This paper proposes a new approach for color transfer between two images. Our method is unique in its consideration of the scene illumination and the constraint that the mapped image must be within the color gamut of the target image. Specifically, our approach first performs a white‐balance step on both images to remove color casts caused by different illuminations in the source and target image. We then align each image to share the same ‘white axis’ and perform a gradient preserving histogram matching technique along this axis to match the tone distribution between the two images. We show that this illuminant‐aware strategy gives a better result than directly working with the original source and target image's luminance channel as done by many previous methods. Afterwards, our method performs a full gamut‐based mapping technique rather than processing each channel separately. This guarantees that the colors of our transferred image lie within the target gamut. Our experimental results show that this combined illuminant‐aware and gamut‐based strategy produces more compelling results than previous methods. We detail our approach and demonstrate its effectiveness on a number of examples. 相似文献
996.
George Ting-Kuo Fey P. Muralidharan Cheng-Zhang Lu Yung-Da Cho 《Electrochimica acta》2006,51(23):4850-4858
An enhanced electrochemical performance LiCoO2 cathode was synthesized by coating with various wt.% of La2O3 to the LiCoO2 particle surfaces by a polymeric method, followed by calcination at 923 K for 4 h in air. The surface-coated materials were characterized by XRD, TGA, SEM, TEM, BET and XPS/ESCA techniques. XRD patterns of La2O3-coated LiCoO2 revealed that the coating did not affect the crystal structure, α-NaFeO2, of the cathode material compared to pristine LiCoO2. TEM images showed a compact coating layer on the surface of the core material that had an average thickness of about ∼15 nm. XPS data illustrated that the presence of two different environmental O 1s ions corresponds to the surface-coated La2O3 and core material. The electrochemical performance of the coated materials by galvanostatic cycling studies suggest that 2.0 wt.% coated La2O3 on LiCoO2 improved cycle stability (284 cycles) by a factor of ∼7 times over the pristine LiCoO2 cathode material and also demonstrated excellent cell cycle stability when charged at high voltages (4.4, 4.5 and 4.6 V). Impedance spectroscopy demonstrated that the enhanced performance of the coated materials is attributed to slower impedance growth during the charge-discharge processes. The DSC curve revealed that the exothermic peak corresponding to the release of oxygen at ∼464 K was significantly smaller for the La2O3-coated cathode material and recognized its high thermal stability. 相似文献
997.
Ultrafine lithium ion conducting La2/3−xLi3xTiO3 (x = 0.11, LLT) powder was synthesized by a simple polymerizable complex method based on the Pechini-type process. The formation mechanism, homogeneity and microstructure of the samples were investigated by thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). XRD analysis indicated the formation of pure perovskite-type phase. The powder synthesized at a temperature as low as 900 °C in a much shorter time than solid-state reaction method was well crystallized. The lithium ion conductivity of the LLT ceramics sintered at 1200 °C was found to be 9 × 10−4 S/cm at room temperature. 相似文献
998.
E. A. Levashov A. S. Rogachev V. V. Kurbatkina Yu. K. Epishko N. A. Kochetov 《International Journal of Self-Propagating High-Temperature Synthesis》2007,16(4):218-224
Biocompatible composites (Ti, Ta)C
x
+ Ca3(PO4)2 for deposition of nanofilms onto load-bearing implants by ion-plasma sputtering were prepared from Ti + Ta + C + Ca3(PO4)2 mixtures by forced SHS compaction. The effect of Ta + C addition to green mixtures (characterized by parameter z) on the structure/phase formation in combustion products was explored. The addition of tantalum and carbon was found to have
little or no influence on the burning velocity U and combustion temperature T
c. Two thermal spikes exhibited by thermograms were associated with the occurrence of two consecutive reactions leading to
formation of titanium and tantalum carbides. With increasing z, the grain size of (Ti, Ta)C was found to diminish, its relative density to decrease, while the hardness to markedly grow.
相似文献
999.
Electrochromic properties of electrochemically deposited and etched (EDE) WO3−x films have been investigated using voltammetry and nanogravimetry to elucidate the amount of residual stress associated with lattice polarization and deformation in WO3−x nanoparticles. The cathodic WO3−x deposition from pertungstic acid solution and unusual properties of the cathodic electroetching of the oxide in tetraethyl ammonium chloride solution are reported and elucidated on the basis of Electrochemical Quartz Crystal Nanogravimetry (EQCN) measurements. The stress enhanced resonant frequency shift was observed upon WO3−x film coloration. However, the stress enhancement appeared to be much lower (up to 4-6 times) than that measured for films synthesized by other methods. The stress reduction in WO3−x films under study has been attributed to the stress relaxing propensity of EDE film to suppress the compressive stress wave. A considerable isotopic effect has been observed in nanogravimetry of the H+ and D+ ion intercalation into WO3−x films. We have found that the isotopic effect is primarily due to the true mass loading difference between hydrogen and deuterium ions, for the same concentration of color centers (2.65 × 1021 cm−3), since EQCN frequency shifts associated with stress in the film for H+ and D+ are very close to each other. 相似文献
1000.
以固体超强酸SO2-4/TiO2 WO3为催化剂,通过丁酮和1,2 丙二醇反应合成了丁酮1,2 丙二醇缩酮。探讨了SO2-4/TiO2 WO3对缩酮反应的催化活性,研究了酮醇摩尔比、催化剂用量、反应时间对产品收率的影响。实验表明,在n(丁酮)∶n(1,2 丙二醇)=1∶1 5,催化剂用量为反应物料总质量的0 7%,环己烷为带水剂,反应时间1 0h的优化条件下,丁酮1,2 丙二醇缩酮的收率可达85 7%。 相似文献