全文获取类型
收费全文 | 3764篇 |
免费 | 452篇 |
国内免费 | 174篇 |
专业分类
化学 | 1112篇 |
晶体学 | 24篇 |
力学 | 278篇 |
综合类 | 79篇 |
数学 | 332篇 |
物理学 | 2565篇 |
出版年
2024年 | 8篇 |
2023年 | 26篇 |
2022年 | 97篇 |
2021年 | 105篇 |
2020年 | 126篇 |
2019年 | 85篇 |
2018年 | 64篇 |
2017年 | 133篇 |
2016年 | 178篇 |
2015年 | 143篇 |
2014年 | 214篇 |
2013年 | 303篇 |
2012年 | 164篇 |
2011年 | 173篇 |
2010年 | 177篇 |
2009年 | 207篇 |
2008年 | 213篇 |
2007年 | 233篇 |
2006年 | 175篇 |
2005年 | 165篇 |
2004年 | 152篇 |
2003年 | 174篇 |
2002年 | 138篇 |
2001年 | 92篇 |
2000年 | 116篇 |
1999年 | 89篇 |
1998年 | 94篇 |
1997年 | 79篇 |
1996年 | 64篇 |
1995年 | 77篇 |
1994年 | 59篇 |
1993年 | 55篇 |
1992年 | 43篇 |
1991年 | 17篇 |
1990年 | 31篇 |
1989年 | 21篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有4390条查询结果,搜索用时 20 毫秒
991.
Volha A. Matylitskaya Wolfgang Bock Klaus Thoma Bernd O. Kolbesen 《Mikrochimica acta》2006,156(1-2):33-37
The oxidation and nitridation processes of niobium films in a rapid thermal processing (RTP) – system were investigated. 200
and 500 nm niobium films were deposited via sputtering on sapphire-(1-102)-substrate. At first niobium films were oxidized
in molecular oxygen at temperatures ranging from 350 to 500 °C and for times of 1, 2 and 5 min and then nitridated in ammonia
at 1000 °C for 1 min using an RTP system. For characterisation of the niobium films complementary analytical methods were
used: X-ray diffraction (XRD) for phase analysis, secondary ion mass spectrometry (SIMS) for determining the elemental depth
profiles of the films, scanning electron microscopy (SEM) and atomic force microscopy (AFM) for characterisation of the surface
morphology of the films. The influence of the substrate, single crystalline sapphire, on the reactivity of the niobium films
was studied in dependence of temperature, time of reaction and film thickness. The possibility of existence of niobium oxynitride
phase was investigated. According to XRD and SIMS data, there is evidence that an oxynitride phase is formed after oxidation
and subsequent nitridation in the bulk of some Nb films. In some of the experiments crack formation in the films or even delamination
of the Nb films from the substrates was observed. 相似文献
992.
《Thermochimica Acta》2006,448(1):31-36
In this study, dehydration of sodium carbonate monohydrate (Na2CO3·H2O) (SCM) in microwave (MW) field with silicon carbide (SiC) as an indirect heating medium was investigated. SCM samples containing up to 3% free moisture were placed in the microwave oven. The heating experiments showed that SCM is a poor microwave energy absorber for up to 6 min of irradiation at an 800 W of microwave power. The heat for SCM calcination is provided by SiC which absorbs microwave. The monohydrate is then converted to anhydrous sodium carbonate on the SiC plate by calcining, i.e. by removing the crystal water through heating of the monohydrate temperatures of over 120 °C. The calcination results in a solid phase recrystallization of the monohydrate into anhydrate. In the microwave irradiation process, dehydration of SCM in terms of indirect heating can be accelerated by increasing the microwave field power. 相似文献
993.
A comprehensive computational model has been developed Jbr flowing thermal plasmas in the absence of electromagnetic fields, with particular emphasis on plasma jets. The plasma is represented as a rnulticomponent chemicalh, reacting ideal gas with temperature-dependent thermodynamic and transport properties. The plasma flow is governed by the transient compressible Navier-Stokes equations in two or three space dimensions. Turbulence is represented by subgrid-scale and k- models. Species diffusion is calculated by an effective binary diffusion approximation, generalized to allow /or ambipolar diffusion of charged species. Ionization, dissociation, recombination, and other chemical reactions are computed by general kinetic and equilibrium chemistry algorithms. Radiation heat loss is currently modeled as a temperature-dependent energy sink. Finite-difference approximations to the governing equations are solved on a rectangular spatial mesh using explicit temporal differencing. Computational inefficiency at low Mach number is avoided br reducing the effective sound speed. The overall computational model is embodied in a new computer code called LAVA. Computational results and comparisons with experimental data are presented Jbr LAVA simulations of a steady-stare axisymmetric argon plasma jet flowing into cold argon. 相似文献
994.
Preparation and cycloaddition reaction of novel azulene-substituted N-sulfinylamines 1 and 2 are reported. The influence of the -NSO group on the UV-vis and NMR spectra of the azulene ring to which it is bonded is discussed. X-ray crystal analysis of 1 revealed the syn-configuration and the twisted structure of the N-sulfinylamine moiety. The synthetic utility of 1 and 2 have been explored by the cycloaddition reaction to afford novel azulene-substituted heterocycles under high-pressure conditions. We also described herein the synthesis and some properties of related 2-azulenylisothiocyanate. 相似文献
995.
Bioreactors serve a central role in biotechnological processes by providing the link between starting materials and final
products. In most biological systems, there are complex series of reactions that must be optimized and coordinated in a very
specific environment. Despite the complexity of biocatalytic processes, there is usually a rate-limiting step controlling
the reaction, as well as a few secondary limitations. These limitations provide the basis for process design and bioprocess
equipment specifications. The EIMCO Slurry Bioreactor has been designed to overcome these limitations encountered during the
bio-oxidation of refractory gold ores and concentrates and hazardous waste bioremediation. 相似文献
996.
Flow microcalorimeters are used to determine thermodynamic properties of liquid mixtures, the accuracy of these measures depends
on the right calibration of the instrument. In this work the system is identified by means of the transfer functions of the
two poles, it is proven that the first time constant and the sensitivity change with the value of rc
p
f of the injected liquids (r - density, c
p - heat capacity, f - injection flow), and that the sensitivities obtained in the electrical and chemical calibrations are different for the
same value of rc
p
f because the dissipation in each case does not occur in the same place. As a summary of the calibration carried out, it is
proposed a sensitivity value of 313±4 mV W-1 for rc
p
f<15 mW K-1 that permits to make thermal measures with an uncertainty of 3%.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
997.
小波变换用于二次微分交流示波计时电位信号中有用信息的提取 总被引:14,自引:4,他引:14
小波分析是80年代发展起来的一种新的数学分支。由于小波变换具有许多其它的信号处理手段所不具备的优良特性,如正交性,可变的时-频分辨率和可调节的局部支持等,使它成为信号处理的一种强有力的工具。 相似文献
998.
Yan-zhongZhang Zhi-qiangFan Bai-gengWu Jun-tingXu QiWang 《高分子科学》2004,(3):231-238
Spherical polyethylene/polypropylene (PE/PP) in-reactor blend granules with various ethylene/propylene molar ratios and high porosity were synthesized using a high yield TiCl4/MgCl2 supported catalyst. A solution of benzoyl peroxide (BPO)/maleic anhydride (MAH)/xylene (interfacial reagent) or BPO/MAH/St (comonomer) was absorbed onto the PE/PP inreactor blend granules, and solid phase gratt polymerization of MAH on PE/PP was conducted. The amount of grafted MAH on PE/PP was measured through chemical titration. The results showed that solid phase graft polymerization of MAH in PE/PP in-reactor blend granules produced graft copolymer with high amount of grafted MAH, and the amount of grafted MAH was raised slightly when St was introduced as comonomer. The graft in-reactor blend was fractionated into five fractions through temperature-gradient extraction fractionation (TGEF), and the fractions were analyzed by FTIR. The results revealed that MAH is mainly grafted on the PE segments, whereas MAH was predominantly grafted on the PP segments when St was present in the graft polymerization system. In addition, the final product is still in the form of regular spherical granules, which is beneficial for industrial processing. 相似文献
999.
分析裂解技术在高分子研究中的进展 总被引:7,自引:0,他引:7
介绍了裂解同时衍生化和直接裂解-质谱等分析裂解技术,综述了近年来分析裂解技术在高分子表征、热分解机理、高分子加工等研究领域的主要进展。 相似文献
1000.
The application of image processing in secondary ion mass spectrometry is discussed. The Cameca 4f SIMS uses a single microchannel plate and a highly sensitive camera in combination with an image processor with real time capabilities (Kontron IBAS). An automation procedure with image integration, extended dynamic range image acquisition and retro depth profiling is presented and illustrated with practical applications. 相似文献