全文获取类型
收费全文 | 1814篇 |
免费 | 281篇 |
国内免费 | 191篇 |
专业分类
电工技术 | 57篇 |
综合类 | 108篇 |
化学工业 | 164篇 |
金属工艺 | 31篇 |
机械仪表 | 172篇 |
建筑科学 | 10篇 |
矿业工程 | 5篇 |
能源动力 | 15篇 |
轻工业 | 27篇 |
水利工程 | 2篇 |
石油天然气 | 17篇 |
武器工业 | 2篇 |
无线电 | 928篇 |
一般工业技术 | 468篇 |
冶金工业 | 30篇 |
原子能技术 | 156篇 |
自动化技术 | 94篇 |
出版年
2024年 | 12篇 |
2023年 | 49篇 |
2022年 | 32篇 |
2021年 | 66篇 |
2020年 | 83篇 |
2019年 | 75篇 |
2018年 | 78篇 |
2017年 | 89篇 |
2016年 | 74篇 |
2015年 | 98篇 |
2014年 | 106篇 |
2013年 | 156篇 |
2012年 | 121篇 |
2011年 | 129篇 |
2010年 | 81篇 |
2009年 | 73篇 |
2008年 | 115篇 |
2007年 | 95篇 |
2006年 | 89篇 |
2005年 | 82篇 |
2004年 | 83篇 |
2003年 | 58篇 |
2002年 | 56篇 |
2001年 | 69篇 |
2000年 | 53篇 |
1999年 | 39篇 |
1998年 | 35篇 |
1997年 | 23篇 |
1996年 | 26篇 |
1995年 | 24篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 16篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 1篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1959年 | 2篇 |
1958年 | 1篇 |
排序方式: 共有2286条查询结果,搜索用时 15 毫秒
131.
Silole‐Based Red Fluorescent Organic Dots for Bright Two‐Photon Fluorescence In vitro Cell and In vivo Blood Vessel Imaging
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Bin Chen Guangxue Feng Bairong He Chiching Goh Shidang Xu Gabriel Ramos‐Ortiz Laura Aparicio‐Ixta Jian Zhou Laiguan Ng Zujin Zhao Bin Liu Ben Zhong Tang 《Small (Weinheim an der Bergstrasse, Germany)》2016,12(6):782-792
Robust luminescent dyes with efficient two‐photon fluorescence are highly desirable for biological imaging applications, but those suitable for organic dots fabrication are still rare because of aggregation‐caused quenching. In this work, a red fluorescent silole, 2,5‐bis[5‐(dimesitylboranyl)thiophen‐2‐yl]‐1‐methyl‐1,3,4‐triphenylsilole ((MesB)2DTTPS), is synthesized and characterized. (MesB)2DTTPS exhibits enhanced fluorescence efficiency in nanoaggregates, indicative of aggregation‐enhanced emission (AEE). The organic dots fabricated by encapsulating (MesB)2DTTPS within lipid‐PEG show red fluorescence peaking at 598 nm and a high fluorescence quantum yield of 32%. Upon excitation at 820 nm, the dots show a large two‐photon absorption cross section of 3.43 × 105 GM, which yields a two‐photon action cross section of 1.09 × 105 GM. These (MesB)2DTTPS dots show good biocompatibility and are successfully applied to one‐photon and two‐photon fluorescence imaging of MCF‐7 cells and two‐photon in vivo visualization of the blood vascular of mouse muscle in a high‐contrast and noninvasive manner. Moreover, the 3D blood vasculature located at the mouse ear skin with a depth of over 100 μm can also be visualized clearly, providing the spatiotemporal information about the whole blood vascular network. 相似文献
132.
Victor Chernomordik Amir H. Gandjbakhche Leonardo Dagdug 《Journal of Modern Optics》2013,60(20):2048-2053
Biomedical applications of near infrared radiation (NIR) techniques (i.e. based on light wavelengths roughly between 400 and 1100?nm) require that a preliminary estimate of the tissue volume being investigated be found. One possible estimate is the depth to which a photon penetrates a tissue before eventually emerging at a separating plane at a given time. A simple model for this problem can be based on a lattice random walk and was initially analyzed when the associated optical coefficients are isotropic with respect to the geometrical configuration. Here we include the effects of anisotropy in the optical coefficients, finding that at long times the statistical properties of the depth of penetration can be accounted for by very simple scaling factors while at short times the anisotropy effects can be quite noticeable. 相似文献
133.
A recurrent stochastic binary network 总被引:1,自引:0,他引:1
赵杰煜 《中国科学F辑(英文版)》2001,44(5):376-388
Stochastic neural networks are usually built by introducing random fluctuations into the network. A natural method is to use stochastic connections rather than stochastic activation functions. We propose a new model in which each neuron has very simple functionality but all the connections are stochastic. It is shown that the stationary distribution of the network uniquely exists and it is approxi-mately a Boltzmann-Gibbs distribution. The relationship between the model and the Markov random field is discussed. New techniques to implement simulated annealing and Boltzmann learning are pro-posed. Simulation results on the graph bisection problem and image recognition show that the network is powerful enough to solve real world problems. 相似文献
134.
M.C. Maccarone O. CatalanoS. Giarrusso G. La RosaA. Segreto G. AgnettaB. Biondo A. ManganoF. Russo S. Billotta 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2011,659(1):569-578
UVscope is a portable multi-pixels photon detector developed at IASF-Pa to support experimental activities in the high-energy astrophysics and cosmic rays field. The instrument, working in single photon counting mode, is designed to directly measure light flux in the wavelengths range 300-650 nm. Thanks to its features and operational flexibility, the instrument can be used in a wide field of applications where the knowledge of the environmental luminosity is required, as in the characterization of sites for ground-based Cherenkov and fluorescence telescopes, and for cross-calibration of their cameras.The present version of UVscope is based on a Multi Anode Photo Multiplier Tube and it is completed by a motorized mount and a filter wheel which allow to make low-light measurements, at programmed pointing directions and at different filter wavelengths. In this paper, the instrument is firstly presented in all its components; then the procedures adopted for its absolute and relative calibration are detailed. The performance of UVscope is evaluated and, finally, current and planned scientific applications are described. 相似文献
135.
In this paper, we demonstrate how the confinement and enhancement of optical fields by surface plasmon resonance can allow non‐linear microscopy to be performed in a simple, cost‐effective widefield configuration, rather than the more usual laser‐scanning arrangement. We present second harmonic and two‐photon luminescence widefield images of dielectric and gold samples obtained with both prism‐based and high numerical aperture objective (‘prismless’) microscope arrangements. 相似文献
136.
K. Somaiah K. Ravi Kanth V. Dayakar K. Radhakrishna Rao P. Veeresham 《Materials Chemistry and Physics》2001,70(3):259-262
Thermally stimulated luminescence (TSL) of Na2ZnCl4 single crystals showed three glow peaks having their peak maxima at 343, 425 and 475 K. Optical absorption (OA) data of unirradiated samples revealed an absorption band at 272 nm while X-irradiation caused additional bands at 462 and 723 nm. Growth and room temperature annealing studies of TSL and OA supported the idea of attribution of 425 K glow peak and 462 nm absorption band to F-centres. The 272 nm OA band is due to Zn2+ centres whereas the 723 nm absorption band and 475 K glow peak have been assigned to Zn+ centres. 相似文献
137.
LIAO Chang-jun~ WANG Jin-dong~ L Hua~ PENG Xiao-dong~ GUO Jian-ping~ LI Ri-hao~ ZHAO Feng~ WEI Zheng-jun~ ZHOU Jin-yun~ FENG Jin-yuan~ LIU Wei-ping~ LIU Song-hao~ 《半导体光子学与技术》2005,11(2):73-77
Based on the commercially available avalanche photodiodes, the basic needs of gated-mode operation for single photon are discussed. Gated-mode technique based on the experimental data for detection of single photon is analyzed at communication wavelengths so that the basic operation parameters can decide properly for efficient detection of single photon. The bias voltage has related to the punch-through voltage in combining the cooling technique with synchronization to decrease the dark counts. 相似文献
138.
Subpixel position measurement using 1D, 2D and 3D centroid algorithms with emphasis on applications in confocal microscopy 总被引:1,自引:0,他引:1
A. Patwardhan 《Journal of microscopy》1997,186(3):246-257
The accuracy with which centroid algorithms in 1D, 2D and 3D can estimate an object's position has been investigated. Three factors that can influence the method's accuracy have been investigated: systematic error of the algorithm, influence of photon noise and the influence of perturbations such as scanning nonlinearity. The variation of the accuracy with parameters that are relevant for confocal microscopy, such as object diameter and photon noise/pixel, has been considered. Theory and simulations presented show that the variation of the accuracy with respect to such parameters can differ drastically between the 1D, 2D and 3D cases. Experiments performed using microspheres show that the magnitudes of the three types of error can be approximately the same under normal operating conditions and that it is therefore necessary to take all three into account when assessing the total error. 相似文献
139.
Compositional and structural information were obtained from an ancient 1600-year old Indian iron using microprobe techniques
(EDS, μXRD and μPIXE). Several different local locations in the iron matrix and in the entrapped slag inclusions were analyzed.
The P content of the metallic iron matrix was very heterogeneous. Lower P contents were observed in the regions near slag
inclusions. This was correlated to the dephosphorization capacity of the slag. The crystallized phases identified in the slag
inclusions were wüstite and fayalite. The compositions of the slag inclusions were relatively homogeneous. 相似文献
140.
The dipolar relaxation in poly(vinyl alcohol) (PVA), sodium carboxy methyl cellulose (NaCMCs), and their blends were studied using a thermally stimulated depolarization current (TSDC) technique. The mutual effects of polarization conditions such as heating rate, poling temperature, time, and field on the properties of TSDC were investigated. Quantitative analysis of the experimental data is given in terms of dipolar and space charge polarization. A thermal sampling (TS) technique was applied to decompose the complex relaxations in individual polymers and their blend of 0.5/0.5 wt/wt into its normal distribution components. The activation energy of TS‐formed electrets was determined by fitting the experimental curve to Bucci and Fieschi equations. Peak parameters such as activation energy and preexponential factor τ0 were obtained. A linear relationship between the activation energy and logarithm of the preexponential factor was found, thus confirming operation of the compensation law. In addition, by using the Eyring equation of the rate theory, the activation enthalpy ΔH≠ and the activation entropy ΔS≠ were calculated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1342–1353, 2005 相似文献