全文获取类型
收费全文 | 10667篇 |
免费 | 347篇 |
国内免费 | 361篇 |
专业分类
电工技术 | 367篇 |
综合类 | 290篇 |
化学工业 | 1338篇 |
金属工艺 | 411篇 |
机械仪表 | 769篇 |
建筑科学 | 115篇 |
矿业工程 | 34篇 |
能源动力 | 432篇 |
轻工业 | 101篇 |
水利工程 | 40篇 |
石油天然气 | 38篇 |
武器工业 | 42篇 |
无线电 | 2905篇 |
一般工业技术 | 3262篇 |
冶金工业 | 63篇 |
原子能技术 | 154篇 |
自动化技术 | 1014篇 |
出版年
2024年 | 8篇 |
2023年 | 111篇 |
2022年 | 178篇 |
2021年 | 202篇 |
2020年 | 171篇 |
2019年 | 177篇 |
2018年 | 170篇 |
2017年 | 266篇 |
2016年 | 294篇 |
2015年 | 303篇 |
2014年 | 559篇 |
2013年 | 481篇 |
2012年 | 552篇 |
2011年 | 1011篇 |
2010年 | 584篇 |
2009年 | 664篇 |
2008年 | 628篇 |
2007年 | 577篇 |
2006年 | 585篇 |
2005年 | 447篇 |
2004年 | 392篇 |
2003年 | 373篇 |
2002年 | 331篇 |
2001年 | 216篇 |
2000年 | 216篇 |
1999年 | 270篇 |
1998年 | 254篇 |
1997年 | 246篇 |
1996年 | 262篇 |
1995年 | 156篇 |
1994年 | 153篇 |
1993年 | 100篇 |
1992年 | 93篇 |
1991年 | 90篇 |
1990年 | 73篇 |
1989年 | 74篇 |
1988年 | 43篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
11.
《International Journal of Hydrogen Energy》2022,47(64):27608-27616
The vanadium hydrides have better hydrogen storage capacity in comparison to the other metal hydrides. Although the structure of VH2 hydride has been reported, the structural stability, electronic and optical properties of VH2 hydride are unclear. To solve these problems, we apply the first-principles method to study the structural stability, electronic and optical properties of VH2 hydrides. Similar to the metal dihydrides, four possible VH2 hydrides such as the cubic (Fm-3m), tetragonal (I4/mmm), tetragonal (P42/mnm) and orthorhombic (Pnma) are designed. The result shows that the cubic VH2 hydride is a thermodynamic and dynamical stability. In particular, the tetragonal (I4/mmm) and the orthorhombic (Pnma) VH2 hydrides are firstly predicted. It is found that these VH2 hydrides show metallic behavior. The electronic interaction of V (d-state)-H (s-state) is beneficial to improve the hydrogen storage in VH2 hydride. In addition, the formation of V–H bond can improve the structural stability of VH2 hydride. Based on the analysis of optical properties, it is found that all VH2 hydrides show the ultraviolet response. Compared to the tetragonal and orthorhombic VH2 hydrides, the cubic VH2 hydride has better storage optical properties. Therefore, we believe that the VH2 hydride is a promising hydrogen storage material. 相似文献
12.
Application-specific optical glass properties are achieved by utilizing complex material compositions. This can be problematic in reactive plasma-assisted deterministic surface processing since a non-volatile surface layer may form depending on the glass composition, which affects the etch rate and thereby the local etching depth. In this investigation, a model algorithm is proposed to tackle some restrictions in applying fluorine-based plasma jet as etching tool utilized for freeform surface machining of optics made of complex glass composition, like borosilicate crown glass (e.g., N-BK7®). In this regard, firstly an analytical model is proposed for estimating the depth-dependent etch rate function. Subsequently, a recursive simulation algorithm is introduced for convolving the derived depth-dependent etch rate function with the given dwell time matrix to simulate a deterministic freeform generation process. By the proposed simulation algorithm, the impeding influence of the residual layer on the reduction of etching depth is computed prior to a real experiment in order to scale the local dwell time to ensure the targeted local removal. Finally, the simulated freeform shape is compared with the corresponding result of an etching experiment to validate the feasibility of the proposed approach. 相似文献
13.
This paper reports an investigation on the structure-properties correlation of trivalent metal oxide (Al2O3)-doped V2O5 ceramics synthesized by the melt-quench technique. XRD patterns confirmed a single orthorhombic V2O5 phase formation with increasing strain on the doping of Al2O3 in place of V2O5 in the samples estimated by Williamson-Hall analysis. FTIR and Raman investigations revealed a structural change as [VO5] polyhedra converts into [VO4] polyhedra on the doping of Al2O3 into V2O5. The optical band gap was found in a wide semiconductor range as confirmed by UV–visible spectroscopy analysis. The thermal and conductivity behavior of the prepared samples were studied using thermal gravimetric analysis (TGA) and impedance analyzer, respectively. All the prepared ceramics exhibit good DC conductivity (0.22–0.36 Sm-1) at 400 ?C. These materials can be considered for intermediate temperature solid oxide fuel cell (IT-SOFC)/battery applications due to their good conductivity and good thermal stability. 相似文献
14.
S.F. Mansour S. Wageh Maged F. Alotaibi M.A. Abdo M.S. Sadeq 《Ceramics International》2021,47(15):21443-21449
Understanding the impact of bismuth cations on the optical properties of borosilicate glass is significant for manipulating borate glass applications. In this paper, the influence of bismuth cations on both structural and optical properties of borosilicate glass doped with NiO was investigated. Different glass samples, containing different amounts of Bi2O3 and a constant amount of NiO, were prepared and studied. Infrared (IR) analysis was carried out to study the internal structure within the investigated glass samples. Optical absorption studies were performed to investigate the impact of Bi2O3 content on optical properties of the BiBaNiB-glasses. Astonishingly, with Bi2O3 addition, an absorption band at 380 nm has appeared. Moreover, this band is overlapped with the Urbach edge; which regularly produced an artificial edge-like feature at ~450 nm. A detailed deconvolution protocol has been implemented for an appropriate understanding of these spectra and unraveling the hidden Urbach edge. Optical band gap energy, linear and nonlinear refractive index for each BiBaNiB sample were calculated. Furthermore, the metallization criterion was calculated to examine the metallic or insulating nature of the BiBaNiB-glasses. The values of the nonlinear third-order susceptibility and nonlinear refractive index were increased with Bi2O3 doping. The BiBaNiB-glasses exhibited outstanding stability and optical band gap than the pristine glass sample, which makes it possible for practical applications. 相似文献
15.
Engineering new glass compositions have experienced a sturdy tendency to move forward from (educated) trial-and-error to data- and simulation-driven strategies. In this work, we developed a computer program that combines data-driven predictive models (in this case, neural networks) with a genetic algorithm to design glass compositions with desired combinations of properties. First, we induced predictive models for the glass transition temperature (Tg) using a dataset of 45,302 compositions with 39 different chemical elements, and for the refractive index (nd) using a dataset of 41,225 compositions with 38 different chemical elements. Then, we searched for relevant glass compositions using a genetic algorithm informed by a design trend of glasses having high nd (1.7 or more) and low Tg (500 °C or less). Two candidate compositions suggested by the combined algorithms were selected and produced in the laboratory. These compositions are significantly different from those in the datasets used to induce the predictive models, showing that the used method is indeed capable of exploration. Both glasses met the constraints of the work, which supports the proposed framework. Therefore, this new tool can be immediately used for accelerating the design of new glasses. These results are a stepping stone in the pathway of machine learning-guided design of novel glasses. 相似文献
16.
Alireza Ramezani Hossein Abdizadeh Mohammad Reza Golobostanfard 《Ceramics International》2021,47(13):17895-17906
In this work, the BaTiO3 and SrTiO3 thin films as well as BaTiO3/SrTiO3 lamellar composites are synthesized via sol-gel spin-coating method. The formation of corresponding phases from their sols is investigated by virtue of X-ray diffraction on their powders, which confirms the formation of tetragonal structure for BaTiO3, but cubic structure for SrTiO3. The field emission scanning electron microscopy images show that crack-free films with different morphologies are formed in each sample. Likewise, by changing periodicity of the samples, the morphology of the composite samples is changed. As the number of layers increases from 1 to 20, the band gap reduces from 4.38 eV to 4.10 eV for BaTiO3 samples and from 4.13 eV to 3.80 eV for SrTiO3 samples confirmed by UV–Vis spectra. The band gap of periodicity = 1 sample is higher than that of BaTiO3, while band gaps of periodicity = 2 and 5 composites mount between those of BaTiO3 and SrTiO3. In addition, the refractive indices of multi-stacked composites are about 0.2 lesser than refractive indices of BaTiO3 sample in high wavelengths. The periodicity dependence of optical frequency dielectric constant, dielectric loss, impedance, Urbach tail, extinction coefficient, and electric modulus of multi-stacked composites are also studied. 相似文献
17.
G. Stanciu L. Gheorghe F. Voicu S. Hau C. Gheorghe G. Croitoru M. Enculescu R.P. Yavetskiy 《Ceramics International》2019,45(3):3217-3222
(Y0.87-xLa0.1Zr0.03Ybx)2O3 (x?=?0.02, 0.04, 0.05) transparent ceramics were obtained by solid-state reaction and combined sintering procedures with La2O3 and ZrO2 as sintering additives. A method based on two-step intermediate sintering in air followed by vacuum sintering was applied in order to control the densification and grain growth of the samples during the final sintering process. The results indicate that La2O3 and ZrO2 co-additives can improve the microstructure and optical properties of Yb:Y2O3 ceramics at relatively low sintering temperature. On the other hand, the addition of Zr4+ ions leads to the formation of dispersed scattering volumes in the ceramic bodies. Transmittance of 78.8% was measured for the 2.0?at% Yb:Y2O3 ceramic sample at the wavelength of 1100?nm. The spectroscopic properties of Yb:Y2O3 ceramics were investigated at room temperature. The obtained results show that the absorption cross-section at 978?nm is in the range of 2.08?×?10–20 to 2.36?×?10–20 cm2, whereas the emission cross-section at 1032?nm is ~1.0?×?10–20 cm2. 相似文献
18.
Wenwen Zhao Kuibao Zhang Weiwei Li Baozhu Luo Haibin Zhang Kai Xu 《Ceramics International》2019,45(9):11717-11722
In this study, transparent LaErZr2O7 ceramic with high excess La and Er contents (nominally La1.28Er1.28Zr2O7.84) was successfully prepared by vacuum sintering at 1850?°C for 6?h using nanosized powder. The XRD, SEM, EDX and TEM results reveal that the single pyrochlore phase in the powder sample transforms to the coexistence of La-rich pyrochlore phase and Er-rich defect fluorite phase after high temperature sintering. The high excess amounts of La and Er favor the formation of pyrochlore structure. Despite the coexistence of two phases, the sample with 1?mm thickness shows excellent in-line transmittance in the visible to mid-infrared region (as high as 81% at 1100?nm). The upconversion and infrared emission under 980?nm exciting were measured and discussed as well. 相似文献
19.
Efficient hydrogen evolution by liquid phase plasma irradiation over Sn doped ZnO/CNTs photocatalyst
《International Journal of Hydrogen Energy》2021,46(58):30019-30030
In this study, the liquid phase plasma (LPP) was irradiated over pure zinc oxide (ZnO), strontium (Sn) doped ZnO, and Sn doped ZnO/CNTs photocatalysts for hydrogen evolution from pure water and from aqueous solution of water-methanol. The possible relationship between hydrogen evolution and optical emissions from LPP for activation of ZnO based photocatalysts was revealed. The role of carbon nanotubes (CNTs) as a support material for improved photocatalytic hydrogen evolution was also investigated in this study. The photocatalytic hydrogen evolution from water mixed methanol under LPP irradiation was compared with pure water splitting. The photolysis produced negligible amount of hydrogen due to minimal photodecomposition of water molecules under LPP irradiation. The plasma born reactive species also played crucial role in photolysis. However, the hydrogen evolution rate increased significantly in the presence of ZnO photocatalyst. Further improvement in hydrogen evolution rate was noticed on Sn doping of ZnO and compositing with CNTs. The highest hydrogen evolution rate of 11.46 mmh−1g−1 from water mixed methanol was achieved with Sn doped ZnO/CNTs photocatalyst. This hydrogen evolution rate from water-methanol solution was 9 times higher than from the splitting of pure water. This hydrogen evolution rate is attributed to excessive production of hydroxyl radicals, red shift in optical band gap of Sn doped ZnO/CNTs photocatalyst, slow electron-hole recombination and fast decomposition of methanol as sacrificial reagent. 相似文献
20.
《Contact lens & anterior eye》2021,44(6):101388
PurposeTo investigate the relationship between the real contact lens imprint into the conjunctival tissue, observed by optical coherence tomography (OCT) and conjunctival staining and contact lens wearing comfort.Methods17 participants (mean age = 26.6 SD ± 3.6 years; 7 females) were fitted with three different contact lenses base curves of the same silicone hydrogel custom lens type (Visell 50; Hecht Contactlinsen, Au, Germany) in a randomised order. One lens was optimally fitted according to the manufacturer's recommendation, one fitted 0.4 mm flatter and one fitted 0.4 mm steeper. After 4 h of lens wear the contact lens edge in the area of the conjunctiva was imaged nasally and temporally using OCT (Optovue iVue SD-OCT). To correct the artefact due to optical distortion with OCT, the imprint of all worn lenses was measured on a glass plate afterwards. Conjunctival staining in the limbal region after 4 h of lens wear was classified using the CCLRU Grading Scale. Comfort scoring was based on visual analog scales from 0 (very poor) to 100 (excellent).ResultsThe mean conjunctival imprint of all contact lens edges was 32.0 ± 8.1 μm before and 7.3 ± 6.5 μm after distortion correction of the OCT images. The distortion corrected conjunctival imprint with the 0.4 mm steeper lens (11.5 ± 6.2 μm) was statistically significantly greater compared to the optimally fitted lens (6.5 ± 5.9 μm) (One-way ANOVA followed Tukey-test; p = 0.017) and greater compared to the 0.4 mm flatter lens (3.9 ± 5.3 μm) (p < 0.001). There was no statistically significant difference between the optimally fitted lens and the 0.4 mm flatter lens (p = 0.209). The nasally measured imprint (11.4 ± 9.0 μm) was significantly greater than the temporally measured (3.3 ± 7.6 μm) (p < 0.001). There was no statistically significant correlation between the amount of conjunctival imprint and the graded conjunctival staining (p = 0.346) or the wearer’s comfort (p = 0.735).ConclusionsContact lens edges imaged by OCT exhibited displacement artefacts. The observed conjunctival imprints are a combination of real conjunctival compression and artefacts. A deeper imprint of the contact lens into the conjunctiva caused by a steeper base curve was not related to clinically significant staining or changes in comfort after 4 h of lens wear. The observed differences between nasal and temporal imprint are likely to be caused by variations of conjunctival thickness and the shape of the underlying sclera. 相似文献