全文获取类型
收费全文 | 178681篇 |
免费 | 2533篇 |
国内免费 | 708篇 |
专业分类
电工技术 | 3318篇 |
综合类 | 102篇 |
化学工业 | 28330篇 |
金属工艺 | 7815篇 |
机械仪表 | 5191篇 |
建筑科学 | 4512篇 |
矿业工程 | 875篇 |
能源动力 | 4833篇 |
轻工业 | 16744篇 |
水利工程 | 1716篇 |
石油天然气 | 3135篇 |
武器工业 | 2篇 |
无线电 | 19964篇 |
一般工业技术 | 33728篇 |
冶金工业 | 33176篇 |
原子能技术 | 4304篇 |
自动化技术 | 14177篇 |
出版年
2021年 | 1403篇 |
2019年 | 1338篇 |
2018年 | 2194篇 |
2017年 | 2166篇 |
2016年 | 2307篇 |
2015年 | 1638篇 |
2014年 | 2815篇 |
2013年 | 7970篇 |
2012年 | 4671篇 |
2011年 | 6525篇 |
2010年 | 5148篇 |
2009年 | 6029篇 |
2008年 | 5989篇 |
2007年 | 5942篇 |
2006年 | 5084篇 |
2005年 | 4738篇 |
2004年 | 4527篇 |
2003年 | 4181篇 |
2002年 | 4140篇 |
2001年 | 4137篇 |
2000年 | 3935篇 |
1999年 | 4078篇 |
1998年 | 10402篇 |
1997年 | 7400篇 |
1996年 | 5670篇 |
1995年 | 4287篇 |
1994年 | 3619篇 |
1993年 | 3566篇 |
1992年 | 2609篇 |
1991年 | 2542篇 |
1990年 | 2419篇 |
1989年 | 2437篇 |
1988年 | 2380篇 |
1987年 | 2130篇 |
1986年 | 2070篇 |
1985年 | 2370篇 |
1984年 | 2189篇 |
1983年 | 2012篇 |
1982年 | 1881篇 |
1981年 | 1945篇 |
1980年 | 1796篇 |
1979年 | 1816篇 |
1978年 | 1776篇 |
1977年 | 2108篇 |
1976年 | 2688篇 |
1975年 | 1557篇 |
1974年 | 1550篇 |
1973年 | 1607篇 |
1972年 | 1350篇 |
1971年 | 1262篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
1.
2.
F.T. Munna Vidhya Selvanathan K. Sobayel Ghulam Muhammad Nilofar Asim Nowshad Amin Kamaruzzaman Sopian Md. Akhtaruzzaman 《Ceramics International》2021,47(8):11003-11009
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell. 相似文献
3.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical... 相似文献
4.
Kravchenko V. F. Konovalov Ya. Yu. 《Journal of Communications Technology and Electronics》2022,67(8):952-964
Journal of Communications Technology and Electronics - A new design of wavelets based on the convolution of a compactly supported function with a rectangular pulse is proposed and theoretically... 相似文献
5.
Journal of Communications Technology and Electronics - A statistical study of the effectiveness of the non-threshold search procedure for a noise-like phase-shift keyed signal by the delay time is... 相似文献
6.
Mehmet Dorduncu Junuthula Narasimha Reddy 《Journal of Adhesion Science and Technology》2019,33(2):156-186
This study presents an improved mathematical model to analyse the stress wave propagation in adhesively bonded functionally graded (FG) circular cylinders (butt joint) under an axial impulsive load. The volume fractions of the material constituents in the upper and lower cylinders were functionally tailored through the thickness of each cylinder using a power-law. The effective material properties of both cylinders, which are made of aluminum (Al) and silicon carbide (SiC), at any point were predicted by using the Mori–Tanaka homogenization scheme. In this improved model, the governing equations of the wave propagation include the spatial derivatives of local mechanical properties and were discretized by means of the finite difference method. The influence of these spatial derivatives and the compositional gradient exponent on the displacement and stress distributions of the joint was investigated. The material composition variations of both cylinders affected the displacement and stress fields whereas the compositional gradient exponent had a minor effect. The stress concentrations were alleviated in time, the displacement and stress distributions/variations around/along the upper and lower cylinder-adhesive interfaces were significantly affected by the adhesive layer. The spatial derivatives also affected the temporal histories of the displacement and stress components evaluated at the selected critical points of the upper cylinder, adhesive layer and lower cylinder. The consideration of the spatial local material derivatives provided a more accurate mathematical model of wave propagations through the graded layered structures. 相似文献
7.
Reliable joints of Ti3SiC2 ceramic and TC11 alloy were diffusion bonded with a 50 μm thick Cu interlayer. The typical interfacial structure of the diffusion boned joint, which was dependent on the interdiffusion and chemical reactions between Al, Si and Ti atoms from the base materials and Cu interlayer, was TC11/α-Ti + β-Ti + Ti2Cu + TiCu/Ti5Si4 + TiSiCu/Cu(s, s)/Ti3SiC2. The influence of bonding temperature and time on the interfacial structure and mechanical properties of Ti3SiC2/Cu/TC11 joint was analyzed. With the increase of bonding temperature and time, the joint shear strength was gradually increased due to enhanced atomic diffusion. However, the thickness of Ti5Si4 and TiSiCu layers with high microhardness increased for a long holding time, resulting in the reduction of bonding strength. The maximum shear strength of 251 ± 6 MPa was obtained for the joint diffusion bonded at 850 °C for 60 min, and fracture primarily occurred at the diffusion layer adjacent to the Ti3SiC2 substrate. This work provided an economical and convenient solution for broadening the engineering application of Ti3SiC2 ceramic. 相似文献
8.
Khammatova V. V. Gainutdinov R. F. Khammatova E. A. Titova L. V. 《Fibre Chemistry》2021,53(3):204-207
Fibre Chemistry - An analysis of the aramid fiber market including the range of industrial textile materials containing chemical fibers for specialized protective clothing of metallurgical workers,... 相似文献
9.
Uzun İlhan Orak İkram Yağmur Hatice Karaer Karakaplan Mehmet Yalman Murat 《SILICON》2021,13(12):4703-4713
Silicon - 5-(2,4-dichlorophenyl)-2-furoic acid and anthraquinone-2-carboxylic acid were reacted separately with chitin. The synthesized products were characterized by various spectroscopic methods... 相似文献
10.
Tallison O. Abreu Roterdan F. Abreu Felipe F. do Carmo Wellington V. de Sousa Helenilson de O. Barros José E.V. de Morais João P.C. do Nascimento Marcelo A.S. da Silva Sergei Trukhanov Alex Trukhanov Larissa Panina Charanjeet Singh Antonio S.B. Sombra 《Ceramics International》2021,47(11):15424-15432
This work presents the dielectric properties of YNbO4 (YNO)–TiO2 composites in the microwave range. X-ray diffraction analysis demonstrates that the addition of TiO2 to YNO results in the formation of a Y(Nb0.5Ti0.5)2O6 phase. In the microwave range, the values of permittivity and dielectric loss did not present major changes with the increment of TiO2. Moreover, the addition of TiO2 results in an improvement in the thermal stability of YNO, with YNO63 demonstrating a resonant frequency of ?8.96 ppm.°C?1. We utilised numerical simulations to evaluate the behaviour of these materials as dielectric resonator antennae and it is found that they exhibit a reflection coefficient below ?10 dB at the resonant frequency, with a realised gain of 4.94 – 5.76 dBi, a bandwidth of 665–1050 MHz and a radiation efficiency above 84%. Our results indicate that YNO–TiO2 composites are interesting candidates for microwave operating devices. 相似文献