全文获取类型
收费全文 | 5432篇 |
免费 | 634篇 |
国内免费 | 328篇 |
专业分类
电工技术 | 60篇 |
综合类 | 246篇 |
化学工业 | 163篇 |
金属工艺 | 22篇 |
机械仪表 | 447篇 |
建筑科学 | 11篇 |
矿业工程 | 5篇 |
能源动力 | 28篇 |
轻工业 | 12篇 |
水利工程 | 3篇 |
石油天然气 | 5篇 |
武器工业 | 82篇 |
无线电 | 4136篇 |
一般工业技术 | 856篇 |
冶金工业 | 66篇 |
原子能技术 | 51篇 |
自动化技术 | 201篇 |
出版年
2024年 | 10篇 |
2023年 | 30篇 |
2022年 | 48篇 |
2021年 | 81篇 |
2020年 | 97篇 |
2019年 | 80篇 |
2018年 | 109篇 |
2017年 | 195篇 |
2016年 | 151篇 |
2015年 | 191篇 |
2014年 | 354篇 |
2013年 | 360篇 |
2012年 | 511篇 |
2011年 | 398篇 |
2010年 | 336篇 |
2009年 | 331篇 |
2008年 | 486篇 |
2007年 | 418篇 |
2006年 | 481篇 |
2005年 | 375篇 |
2004年 | 317篇 |
2003年 | 192篇 |
2002年 | 113篇 |
2001年 | 116篇 |
2000年 | 74篇 |
1999年 | 83篇 |
1998年 | 61篇 |
1997年 | 52篇 |
1996年 | 52篇 |
1995年 | 37篇 |
1994年 | 47篇 |
1993年 | 39篇 |
1992年 | 29篇 |
1991年 | 30篇 |
1990年 | 33篇 |
1989年 | 28篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有6394条查询结果,搜索用时 15 毫秒
101.
Gd2 O3∶Eu3+ isanefficientredemittinglumines centmaterial ,whichcanbeappliedindisplays[1,2 ] .TheconventionalcommercialGd2 O3∶Eu3+ ismainlysynthesizedbyhightemperaturesolid statereactionandchemicalco precipitationmethods .Anadvancedperformanceofdisplaysrequireshighqualityphospho rssuchashighbrightnessandefficiency ,monodisper sityandfinegrainsize .Muchresearchhasanticipatedthatsubmicrometer sizedandnanometerluminescentmaterialswillhavethesepotentialadvantages[3~ 8] ,sosubmicrometer sizedan… 相似文献
102.
Pure and rare earth doped gadolinium oxide (Gd2O3) waveguide films were prepared by a simple sol-gel process and dip-coating method. Structure of Gd2O3 films annealed at different temperature was investigated by X-ray diffraction and transmission electron microscopy. Oriented growth of (400) face of Gd2O3 has been observed when the films were deposited on amorphous substrate. The refractive index and thickness of films were determined by m-lines spectroscopy. The laser beam (λ= 632.8 nm) was coupled into the film by a prism coupler and the propagation length is about 3.5 cm. Luminescence properties of europium ions doped films were measured by waveguide fluorescence spectroscopy, which shows disordered environment for Eu^3 at 400℃. 相似文献
103.
The green phosphor for white LED, Ca8Mg(SiO4)4Cl2∶Eu2+, Mn2+, was synthesized by high temperature solid state reaction under reducing atmosphere. During the process of the phosphor prepared, the excess CaCl2 can improve the intensity of emission. The experimental results indicate that there is an effective energy transfer from Eu2+ to Mn2+in Ca8Mg(SiO4)4Cl2 host. This kind of energy transfer may be due to resonance transfer, and this energy transfer is limited. 相似文献
104.
A new europium (Ⅲ)complex Eu(HFNH)3Phen (HFNH: 4, 4, 5, 5, 6, 6, 6-heptafluoro-l-(2-naphthyl)hexane-1,3-dione ; phen : 1, 10-phenanthroline) was synthesized and its tribolumineseent phenomenon was observed. Photoluminescence and tfiboluminescence spectra were successfidly determined. The most intense tfiboluminescent emission originates from the transition of the central Eu^3 ion from ^5D0 level to ^7F2 level. The tribolunlinescent spectrum is basically similar to that of photoluminescence, which correlates with the disorders of F atoms. 相似文献
105.
It is assumed from the energy level that ultraviolet (UV) photons may have intensifying effect on BaFBr: Eu^2 .In this paper, effect of UV photons (220-290 nm) on the PSL intensity of X-ray irradiated BaFBr:Eu^2 was measured and compared to that on the PSL intensity of 220 nm photons irradiated BaFBr: Eu^2 . It was found that after the excitation of UV photons the PSL intensity of X-ray irradiated samples decreases least at 250 nm and that of 220 nm photons irradiated samples increases most at 250 nm. When the irradiation sources are X-rays and 220 nm photons the excited electrons are photoelectron and thermal-electrons, respectively, and they have different possibility of being captured by electron traps or combined with luminescent centers. And the peak at 250 nm can be explained with the model of electrons tunneling. It is assumed that the electrons excited by 250 nm have the most possibility of tunneling. 相似文献
106.
Nanocrystalline monoclinic and cubic Gd2O3∶Eu with different Eu3 concentration were prepared using glycine-nitrate combustion synthesis. By changing the ratio of glycine to nitrate and proper heat treatment, pure monoclinic and cubic Gd2O3∶Eu with particle size less than 40 nm can be easily formed. Under ultraviolet excitation, main emission of Eu3 (5D0→7F2) locates at 624 nm in monoclinic Gd2O3∶Eu and 611 nm in cubic sample. In excitation spectrum two broad bands corresponding to the host absorption and charge transfer state(CTS) and f-f transitions of Gd3 and Eu3 were observed and discussed. The quenching concentration of monoclinic and cubic Gd2O3∶Eu is 10% and 15%, respectively, both of which are much higher than that of bulk Gd2O3∶Eu. 相似文献
107.
A new kind of doped rare earth free phosphor Y2O2S∶xTi(0<x≤0.10) with doped Ti as activative center was synthesized by solid state reaction and sintered at 1200 ℃ for 2.5 h under reducing atmosphere. XRD patterns, photoluminescence spectra, time-resolved phosphorescence spectra and decay curves of the phosphor were investigated. XRD results reveal that a single Y2O2S phase exists with Ti content up to 6%(mol fraction). Yellow long lasting phosphorescence for present materials was observed in the dark with naked eye after the removal of the excitation light. From the time-resolved phosphorescence spectra the broad emission band centered at 565 nm was confirmed to be responsible for the long lasting phosphorescence which could maintain above 1 h. The possible mechanism responsible for the long lasting phosphorescence of the Y2O2S∶Ti phosphor was proposed. 相似文献
108.
Luminescence and defect properties of novel phosphor β-Zn3(PO4)2:Zr4 were systematically investigated. Corresponding to its lowest optical absorption transition at 240 nm, phosphor emits a bluish-green light at 485 nm, which yields the Stokes shift about 20000 cm-1. The unusual optical properties of Zr4 ion are ascribed to its uncommon coordination environment. In addition it shows intensive bluish-green long lasting phosphorescence(LLP) due to the existence of electron trap, which is generated by aliovalent substitution of Zr4 ion for the cation site in the matrix as shown in thermoluminescence(TL) spectrum. 相似文献
109.
Measurement of cell volume in living epithelial cells has become an important technique in studies of membrane transport processes that function in cell volume regulation. Planimetry of video images of optical sections enables the measurement of the cross sectional area of each section. Cell volume is calculated from the measured area of each section and the known focus displacements. In the past the measurement of cross section area has been done by manual positioning of a cursor superimposed on the video image. Each experiment generates approximately 200 images in which two or more cells may be analysed. We have developed a computer-based method that uses one image as a template, and allows automated area determination of successive images by template matching and digital image processing. This new method is comparable to the older method in speed and accuracy, but requires much less effort from the experimenter. 相似文献
110.
We present a simple and versatile scheme for characterising amplitude and phase modulation by an active element, such as a deformable mirror, in the pupil plane of a high NA microscope. By placing a mirror in the vicinity of the focal plane of the objective and recording images of the reflected focal spot on a camera, we show that reliable measurements of the influence function of the mirror actuators in the pupil plane of the objective can be obtained using an iterative electric field retrieval algorithm. Compared to direct wavefront sensors, the proposed method allows characterisation for a variety of objectives with different NA and pupil sizes without modification of the setup, requires minimal space inside the microscope, and can be used with pulsed sources such as used for multiphoton microscopy. In order to validate our method, we compare our data to the results obtained with a Shack-Hartmann wavefront sensor, and show that comparable precision is achieved. 相似文献