全文获取类型
收费全文 | 4419篇 |
免费 | 353篇 |
国内免费 | 761篇 |
专业分类
化学 | 3143篇 |
晶体学 | 63篇 |
力学 | 404篇 |
综合类 | 28篇 |
数学 | 265篇 |
物理学 | 1630篇 |
出版年
2024年 | 22篇 |
2023年 | 217篇 |
2022年 | 185篇 |
2021年 | 186篇 |
2020年 | 166篇 |
2019年 | 128篇 |
2018年 | 143篇 |
2017年 | 163篇 |
2016年 | 168篇 |
2015年 | 150篇 |
2014年 | 199篇 |
2013年 | 332篇 |
2012年 | 217篇 |
2011年 | 317篇 |
2010年 | 192篇 |
2009年 | 274篇 |
2008年 | 252篇 |
2007年 | 254篇 |
2006年 | 285篇 |
2005年 | 217篇 |
2004年 | 204篇 |
2003年 | 182篇 |
2002年 | 108篇 |
2001年 | 108篇 |
2000年 | 88篇 |
1999年 | 96篇 |
1998年 | 99篇 |
1997年 | 93篇 |
1996年 | 77篇 |
1995年 | 64篇 |
1994年 | 49篇 |
1993年 | 52篇 |
1992年 | 33篇 |
1991年 | 22篇 |
1990年 | 25篇 |
1989年 | 27篇 |
1988年 | 24篇 |
1987年 | 14篇 |
1986年 | 14篇 |
1985年 | 22篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 2篇 |
排序方式: 共有5533条查询结果,搜索用时 0 毫秒
101.
Commercial WO3 powder was annealed in air at four different temperatures and characterized by XRD and BET. The samples were used for the photooxidation of H2O to O2 under visible light irradiation (λ > 420 nm) in the presence of IO3− and the evolved gases were analyzed by gas chromatography. The results showed that the WO3 photocatalyst of monoclinic phase, which was obtained by annealing at 750 °C for 4 h, displayed the best activity in terms of O2 evolution among all the samples. Moreover, the activity was also found to be slightly affected by the grain size of the WO3 samples. 相似文献
102.
This paper reports that monitoring the composition of the c(0 0 0 1), a(11–20) and m(10–10) sapphire surfaces is essential for a proper interpretation of the surface morphologies obtained after annealing at 1253 and 1473 K in ArH2 or ArO2 atmospheres. Our experimental investigations, which have used Auger electron spectroscopy (AES) and atomic force microscopy (AFM) on the surfaces of 99.99% pure sapphire wafers, have led to the following original conclusions: (i) Calcium segregates at the c-surface of sapphire both under ArO2 and ArH2. (ii) Potassium adsorption enhances the kinetics of step-bunching on the c-surface under ArO2. (iii) The step edges on the a-surface may develop a comb-like morphology made of parallel strips along the [10–10] direction. (iv) At 1253 K, clean m-surfaces may be stable. (v) Under ArH2, alumina surface diffusion is much slower than under ArO2 for all surface orientations, the surface concentration of impurities is low, and the Al–O ratio of the AES signals at the surface is significantly larger. 相似文献
103.
104.
Macrì MA Garreffa G Giove F Guardati M Ambrosini A Colonnese C Maraviglia B 《Magnetic resonance imaging》2004,22(10):1385-1393
A quantitative analysis of cerebellar metabolites in normal subjects has been performed by proton MR spectroscopy (MRS) with relaxation time correction. Quantitation was carried out in seven healthy human subjects with the well-established LCModel program. The prior knowledge utilized for quantitation was obtained from solutions containing the major brain metabolites and MRS investigated under the same experimental conditions. The tissue water signal was used as an internal standard for the in vivo studies. Both in vitro (for the prior knowledge template) and in vivo data were acquired separately at 1.5 T by PRESS sequence (TR, 1500 ms; TE, 30 ms). The absolute concentration of main cerebellar metabolites was corrected for relaxation time effects. Different noise and line broadening conditions were considered and simulated in the spectral processing in order to evaluate the effect of spectral quality on the concentration estimates. 相似文献
105.
106.
107.
Hongrui Zhang Mingju Chao Mingyi Gao Liwen Zhang Jianquan Yao 《Optics & Laser Technology》2003,35(6):573-449
A fiber-coupled diode-single-end-pumped Nd:YVO4 laser with an Nd:YVO4 crystal of 0.3 at% doping concentration and 3×3×10 mm3 dimensions was reported. 14.850 W of continuous-wave output power in an M2 factor of 1.12 was obtained under pump power of 27.365 W, with an optical conversion efficiency of 60.49%, and a slope efficiency of 64.5%. 相似文献
108.
M.A. Muñoz-Márquez 《Surface science》2004,565(1):1-13
The oxidation of Ni(1 0 0) and Ni(1 1 1) at elevated temperatures and large oxygen exposures, typical of the methods used in the preparation of NiO(1 0 0) films for surface studies, has been investigated by medium energy ion scattering (MEIS) using 100 keV H+ incident ions. Oxide film growth proceeds significantly faster on Ni(1 1 1) than on Ni(1 0 0), but on both surfaces oxide penetration occurs to depths significantly greater than 100 Å with total exposures of 1200 and 6000 L respectively. The metal/oxide interface is extremely rough, with metallic Ni extending to the surface, even for much thicker oxide films on Ni(1 1 1). On Ni(1 1 1), NiO growth occurs with the (1 0 0) face parallel to the Ni(1 1 1) surface and the close-packed 〈1 1 0〉 directions parallel. On Ni(1 0 0) the MEIS blocking curves cannot be reconciled with a single orientation of NiO(1 0 0) (with the 〈1 1 0〉 directions parallel) on the surface, but is consistent with the substantial orientational disorder (including tilt) previously identified by spot-profile analysis LEED. 相似文献
109.
A.?F.?ZatsepinEmail author D.?Yu.?Biryukov V.?S.?Kortov 《Journal of Applied Spectroscopy》2005,72(3):407-412
The methodological aspects of PSEE spectroscopy of the surface of irradiated dielectrics have been considered. A generalized
method for processing the nonselective photostimulated electron emission (PSEE) spectra taking into account the effects of
radiation electrification and structural disordering is proposed and has been substantiated. The procedure of separation of
the emission contribution of discrete radiation centers providing, in the stationary approach, estimation of a number of parameters
and the concentration of emission-active defects of the surface layer of the material has been described. The potentialities
of the method have been demonstrated with the example of Be2SiO4 phenacite crystals and crystalline and glassy SiO2. Diamagnetic oxygen-deficient centers, body and surface E'-centers, as well as hole O
1
0
-centers on nonbridging oxygen atoms have been registered.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 381–385, May–June, 2005. 相似文献
110.
以金镍复合膜作催化剂,在96%的高氢气浓度下实现了碳纳米管的定向生长,并对其生长过 程进行了深入探讨.结果表明,高氢气浓度下碳纳米管生长的实现与本实验所选用的催化剂 ——金镍复合膜有密切关系.催化剂中金的参与,促进了碳在催化剂中的扩散,提高了碳在 催化剂中的活度.与催化剂中没有金的情况相比较,金的参与有利于镍吸收气氛中的碳,从 而使镍更容易达到碳饱和,有利于在高的氢气浓度下实现碳纳米管的定向生长.
关键词:
金镍复合膜
高氢气浓度
原子氢
碳活度 相似文献