全文获取类型
收费全文 | 831篇 |
免费 | 51篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 1篇 |
综合类 | 1篇 |
化学工业 | 340篇 |
金属工艺 | 32篇 |
机械仪表 | 19篇 |
建筑科学 | 23篇 |
矿业工程 | 6篇 |
能源动力 | 35篇 |
轻工业 | 54篇 |
无线电 | 46篇 |
一般工业技术 | 133篇 |
冶金工业 | 26篇 |
原子能技术 | 1篇 |
自动化技术 | 167篇 |
出版年
2024年 | 5篇 |
2023年 | 13篇 |
2022年 | 92篇 |
2021年 | 113篇 |
2020年 | 26篇 |
2019年 | 23篇 |
2018年 | 45篇 |
2017年 | 38篇 |
2016年 | 46篇 |
2015年 | 26篇 |
2014年 | 52篇 |
2013年 | 57篇 |
2012年 | 52篇 |
2011年 | 57篇 |
2010年 | 45篇 |
2009年 | 31篇 |
2008年 | 25篇 |
2007年 | 18篇 |
2006年 | 23篇 |
2005年 | 21篇 |
2004年 | 20篇 |
2003年 | 12篇 |
2002年 | 4篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有884条查询结果,搜索用时 15 毫秒
91.
Marcin ?roda Katarzyna Cholewa-KowalskaMarek Ró?ański Marek Nocuń 《Optical Materials》2011,33(3):397-401
Glasses of different matrix (phosphate, borate, silicate and lead-silicate) were studied for their optical properties. The effect of Er dopant on transmittance and luminescence properties was presented. The significant “red shift” and “blue shift” of UV edge absorption were discussed based on the changes in the framework of the borate and phosphate glasses, respectively. It was showed that the integral intensity of the two main optical absorption transitions monotonically increases with the order: phosphate < borate < silicate < lead-silicate. Ellipsometric measurement was applied to obtain the refractive index of the glasses. The correlation between the shift of edge absorption and the change of refractive index was presented. Effect of glassy matrix on luminescence of Er3+ was discussed. 相似文献
92.
93.
In this paper we present results of detailed spectroscopic studies of Tb3+ luminescence from BaF2:0.075 mol% Tb performed at Superlumi station of Hasylab, DESY, Hamburg and at Institute of Physics, N. Copernicus University, Torun, Poland (IF UMK Torun).We have measured UV/VUV excitation spectra of the dominant blue Tb3+ luminescence and emission spectra under excitation into various bands found from the excitation spectra. The excitation spectra are dominated by the two well known broad bands due to the parity and spin-allowed (SA) 4f8 → 4f75d transitions. The higher energy triple t-band and unresolved single e-band at lower energies are widely separated (10 Dq about 16,500 cm−1) reflecting the single d-electron energy in the high symmetry cubic crystal field with a relatively low contribution from the low symmetry component.In addition to these bands we have also detected a number of weaker bands at lower energy sides of both dominant SA bands. While the structured band with components at 252.8, 252.3, 250.4 and 248.4 nm clearly corresponds to the SF (spin-forbidden) band found earlier in LiYF4:Tb, the bands at 183, 178 and 172 nm have been never, to the best of our knowledge, reported before. We present arguments that these new bands are the SF counterparts of the triple SA t-band at about 158 nm. The d-f exchange energies for d(e) and d(t) electrons are different at 7779 and 8245 cm−1, respectively.Although the energy levels corresponding to the identified high and low spin (HS and LS) states of the 4f75d configuration are, in BaF2, well separated, there are no SA nor SF transitions generating d-f emission in BaF2:Tb. This is because the numerous 4f8 energy levels intercept the excitation energy from 4f75d levels leading to the well known blue and green Tb3+ 4f8 emissions. 相似文献
94.
Kocan Marcin Wagner Lothar Rack H. J. 《Journal of Materials Engineering and Performance》2005,14(6):765-772
This investigation examined the role of microstructure and surface finish on the high cycle fatigue (HCF) performance of TIMETAL
LCB (Ti-6.8Mo-4.5Fe-1.5Al). The as-received microstructure of LCB consisted of elongated β grains with a semicontinuous grain
boundary α layer. In contrast, a fine equiaxed β + spheroidized α LCB microstructure was achieved by hot swaging and solution
(recrystallization) anneal. The latter modification of the prior β grain structure, together with the size, morphology, and
distribution of the primary α phase, resulted in a significant enhancement in the tensile and HCF properties. Furthermore,
prestraining (PS), as would be expected during the fabrication of an automotive coil spring, and prior to aging for 30 min
at temperatures between 500 and 550 °C, led to additional increases in tensile strength. In contrast, the HCF performance
was always reduced when PS prior to aging was included in the overall processing procedure. Finally, shot-peening and roller-burnishing
both resulted in an increased fatigue life in the finite life regimen; however, significant reductions in the 107 cycle fatigue strengths were observed when these procedures were used. These observations have been explained by including
the effect of process-induced residual tensile stresses in the fatigue analysis, resulting in subsurface fatigue crack nucleation.
This paper was presented at the Beta Titanium Alloys of the 00’s Symposium sponsored by the Titanium Committee of TMS, held
during the 2005 TMS Annual Meeting & Exhibition, February 13–16, 2005 in San Francisco, CA. 相似文献
95.
Wochna A Niemczyk E Kurono C Masaoka M Majczak A Kedzior J Slominska E Lipinski M Wakabayashi T 《Journal of electron microscopy》2005,54(2):127-138
Detailed mechanisms of the switch of the cell death mode from apoptosis to necrosis remain to be solved, although the intracellular level of ATP and that of free radicals have been postulated to be the major factors involved in the mechanisms. In the present study menadione (MEN)-induced cell injury processes were studied using rho0 cells derived from human osteosarcoma 143B cells and parental rho+ cells co-treated with inhibitors of electron transfer chain of mitochondria or oligomycin, an inhibitor of ATP synthesis. Treatment of rho+ cells with 100 microM MEN induced apoptosis, which reached the maximum at 6 h, and was followed by an abrupt decrease thereafter, while necrotic cells (NC) increased continuously when they were judged by Annexin V and PI double staining. On the other hand, MEN induced apoptotic and necrotic changes much faster in rho0 cells compared to rho+ cells. The frequency to find apoptotic cells (AP) in the former cells was distinctly smaller than that to find NC judged by Annexin V and PI double staining. Electron microscopically, a major population of rho0 cells treated with MEN for 6 h consisted of intermediate cells, and a small number of AP co-existed. At 9 h of the treatment intermediate cells were exclusively seen, and AP were hardly detected. When parental rho+ cells were treated with MEN in the presence of oligomycin or oligomycin plus antimycin A both apoptotic and necrotic changes of the cells were distinctly accelerated. The intracellular level of superoxide in rho0 cells continuously increased after the MEN treatment, whereas that of ATP remained distinctly low before and after the MEN treatment compared to that in rho+ cells. These data suggest that the intracellular level of superoxide may be a key factor controlling the switch from apoptosis to necrosis. 相似文献
96.
Rajiv Kumar Marcin Nyk Tymish Y. Ohulchanskyy Christopher A. Flask Paras N. Prasad 《Advanced functional materials》2009,19(6):853-859
Here, novel nanoprobes for combined optical and magnetic resonance (MR) bioimaging are reported. Fluoride (NaYF4) nanocrystals (20–30 nm size) co‐doped with the rare earth ions Gd3+ and Er3+/Yb3+/Eu3+ are synthesized and dispersed in water. An efficient up‐ and downconverted photoluminescence from the rare‐earth ions (Er3+ and Yb3+ or Eu3+) doped into fluoride nanomatrix allows optical imaging modality for the nanoprobes. Upconversion nanophosphors (UCNPs) show nearly quadratic dependence of the photoluminescence intensity on the excitation light power, confirming a two‐photon induced process and allowing two‐photon imaging with UCNPs with low power continuous wave laser diodes due to the sequential nature of the two‐photon process. Furthermore, both UCNPs and downconversion nanophosphors (DCNPs) are modified with biorecognition biomolecules such as anti‐claudin‐4 and anti‐mesothelin, and show in vitro targeted delivery to cancer cells using confocal microscopy. The possibility of using nanoprobes for optical imaging in vivo is also demonstrated. It is also shown that Gd3+ co‐doped within the nanophosphors imparts strong T1 (Spin‐lattice relaxation time) and T2 (spin‐spin relaxation time) for high contrast MR imaging. Thus, nanoprobes based on fluoride nanophosphors doped with rare earth ions are shown to provide the dual modality of optical and magnetic resonance imaging. 相似文献
97.
The domestic goat (Capra aegagrus hircus), a mammalian species with high genetic merit for production of milk and meat, can be a tremendously valuable tool for transgenic research. This research is focused on the production and multiplication of genetically engineered or genome-edited cloned specimens by applying somatic cell nuclear transfer (SCNT), which is a dynamically developing assisted reproductive technology (ART). The efficiency of generating the SCNT-derived embryos, conceptuses, and progeny in goats was found to be determined by a variety of factors controlling the biological, molecular, and epigenetic events. On the one hand, the pivotal objective of our paper was to demonstrate the progress and the state-of-the-art achievements related to the innovative and highly efficient solutions used for the creation of transgenic cloned does and bucks. On the other hand, this review seeks to highlight not only current goals and obstacles but also future challenges to be faced by the approaches applied to propagate genetically modified SCNT-derived goats for the purposes of pharmacology, biomedicine, nutritional biotechnology, the agri-food industry, and modern livestock breeding. 相似文献
98.
In recent years there has been a fast grow of various electronic services.Each service requires specif-ic credentials for authenticating and authorizing user ac-cess or specific subset of user's personal information for transactions the service offers.Such a situation causes problems with remembering multiple,service-specific authentication data,with controlling user's personal data spread across different services-problems with managing user's identities.This paper is an overview on Identity Management(IdM... 相似文献
99.
Marcin Kozak Christine H Scaman 《Journal of the science of food and agriculture》2008,88(7):1115-1127
This paper reviews three unsupervised multivariate classification methods: principal component analysis, principal component similarity analysis and heuristic cluster analysis. The theoretical basis of each method is presented in brief, and assumptions inherent to the methods are highlighted. A literature review shows that these methods have sometimes been used inappropriately or without referencing all essential parameters. The paper also brings to the attention of the reader a relatively unknown method: probabilistic or model‐based cluster analysis. The goal of this method is to uncover the true classification of objects rather than a convenient classification provided by the other methods. For this reason it is felt that model‐based cluster analysis will have broad application in the future. Copyright © 2008 Society of Chemical Industry 相似文献
100.
Mariusz Andrzejczuk Marcin Rasiski Agata Roguska Marcin Pisarek Malgorzata Lewandowska 《Microscopy research and technique》2019,82(3):173-177
To characterize complex, three‐dimensional nanostructures, modern microscopy techniques are needed, such as electron tomography and focused ion beam (FIB) sectioning. The aim of this study was to apply these two techniques to characterize TiO2 nanotubes in terms of their size, shape, volume, porosity, geometric surface area, and specific surface area (SSA). For these experiments, titania nanotubes were fabricated by means of the electrochemical oxidation of titanium at a voltage of 20 V for 2 hr followed by heat treatment at 450°C for 3 hr to change the amorphous structure into a crystalline anatase structure. The quantitative data obtained from the FIB and electron tomography reconstructions show a high similarity in porosity and some differences in SSA. These might be the result of differences in resolution between the two reconstruction techniques. 相似文献