全文获取类型
收费全文 | 233166篇 |
免费 | 17193篇 |
国内免费 | 9629篇 |
学科分类
工业技术 | 259988篇 |
出版年
2024年 | 878篇 |
2023年 | 2836篇 |
2022年 | 5744篇 |
2021年 | 7855篇 |
2020年 | 5750篇 |
2019年 | 4464篇 |
2018年 | 18753篇 |
2017年 | 18345篇 |
2016年 | 14515篇 |
2015年 | 7554篇 |
2014年 | 8659篇 |
2013年 | 10018篇 |
2012年 | 14280篇 |
2011年 | 20961篇 |
2010年 | 18698篇 |
2009年 | 15544篇 |
2008年 | 16449篇 |
2007年 | 16858篇 |
2006年 | 8491篇 |
2005年 | 8383篇 |
2004年 | 5932篇 |
2003年 | 5258篇 |
2002年 | 4458篇 |
2001年 | 3524篇 |
2000年 | 3017篇 |
1999年 | 2609篇 |
1998年 | 1773篇 |
1997年 | 1528篇 |
1996年 | 1410篇 |
1995年 | 1095篇 |
1994年 | 886篇 |
1993年 | 618篇 |
1992年 | 509篇 |
1991年 | 413篇 |
1990年 | 312篇 |
1989年 | 256篇 |
1988年 | 211篇 |
1987年 | 126篇 |
1986年 | 116篇 |
1985年 | 52篇 |
1984年 | 47篇 |
1982年 | 42篇 |
1968年 | 43篇 |
1966年 | 42篇 |
1965年 | 45篇 |
1959年 | 49篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Hao Li Pengcheng Zhang Shengquan Yu Hongyu Yang Bin Tang Fuhai Li Shuren Zhang 《Ceramics International》2019,45(9):11639-11647
Mg2(Ti1-xSnx)O4 (x?=?0–1) ceramics were prepared through conventional solid-state method. This paper focused on the dependence of microwave dielectric properties on crystal structural characteristics via crystal structure refinement, Raman spectra study and complex chemical bond theory. XRD spectrums delineated the phase information of a spinel structure, and structural characteristic of these compositions were achieved with the help of Rietveld refinements. Raman spectrums were used to depict the correlations between vibrational phonon modes and dielectric properties. The variation of permittivity is ascribed to the Mg2(Ti1-xSnx)O4 average bond covalency. The relationship among the B-site octahedral bond energy, tetrahedral bond energy and temperature coefficient are discussed by defining on the change rate of bond energy and the contribution rate of octahedral bond energy. The quality factor is affected by systematic total lattice energy, and the research of XPS patterns illustrated that oxygen vacancies can be effectively restrained in rich oxygen sintering process. Obviously, the microwave dielectric properties of Mg2(Ti1-xSnx)O4 compounds were obtained (= 12.18, ?=?170,130?GHz, ?=??53.1?ppm/°C, x?=?0.2). 相似文献
2.
3.
Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted
calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical
composition (CaO)0.75(La203)0.20(Fe2O3)6 was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO3)2 and (NH4)2HPO4 maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX
and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite
particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies
by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give
clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse
to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites
could be useful for hyperthermia. 相似文献
4.
5.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
6.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method
in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer.
But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results
showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that,
the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic
whereas chloride doped polyaniline films were found to be highly hygroscopic. 相似文献
7.
基于进化算法的常减压装置模拟 总被引:1,自引:0,他引:1
提出了基于优选优生进化算法(Select—best and prepotency evolution algorithm,SPEA)的常减压装置模拟方法。以各塔的温度分布为目标,基于生产过程和分析数据,采用SPEA确定各塔板Murphree效率,从而精确描述各塔板平衡偏离程度。在实际应用中,获得具有良好精度的常减压装置模型。系统分析了SPEA算法的关键参数——优选领域大小与计算复杂性及寻优性能之间的关系,结果显示其取值为群体规模的10%最为合适。 相似文献
8.
9.
10.