全文获取类型
收费全文 | 215060篇 |
免费 | 2037篇 |
国内免费 | 478篇 |
专业分类
化学 | 113948篇 |
晶体学 | 3472篇 |
力学 | 10450篇 |
综合类 | 10篇 |
数学 | 23506篇 |
物理学 | 66189篇 |
出版年
2021年 | 2324篇 |
2020年 | 2310篇 |
2019年 | 2831篇 |
2018年 | 3922篇 |
2017年 | 3909篇 |
2016年 | 5274篇 |
2015年 | 2762篇 |
2014年 | 4743篇 |
2013年 | 9400篇 |
2012年 | 7713篇 |
2011年 | 8986篇 |
2010年 | 7068篇 |
2009年 | 7263篇 |
2008年 | 8458篇 |
2007年 | 8363篇 |
2006年 | 7344篇 |
2005年 | 6538篇 |
2004年 | 6125篇 |
2003年 | 5564篇 |
2002年 | 5528篇 |
2001年 | 5802篇 |
2000年 | 4323篇 |
1999年 | 3258篇 |
1998年 | 2817篇 |
1997年 | 2872篇 |
1996年 | 2676篇 |
1995年 | 2300篇 |
1994年 | 2409篇 |
1993年 | 2293篇 |
1992年 | 2593篇 |
1991年 | 2707篇 |
1990年 | 2596篇 |
1989年 | 2657篇 |
1988年 | 2557篇 |
1987年 | 2582篇 |
1986年 | 2440篇 |
1985年 | 3076篇 |
1984年 | 3137篇 |
1983年 | 2619篇 |
1982年 | 2592篇 |
1981年 | 2549篇 |
1980年 | 2355篇 |
1979年 | 2720篇 |
1978年 | 2685篇 |
1977年 | 2881篇 |
1976年 | 2876篇 |
1975年 | 2673篇 |
1974年 | 2608篇 |
1973年 | 2722篇 |
1972年 | 2088篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
331.
332.
Alexander N Shivanyuk Dmitry M Rudkevich David N Reinhoudt 《Tetrahedron letters》1996,37(52):9341-9344
An assembly of cation receptor 1 and anion receptor 2 via the hydrogen bonding melamine-barbiturate structural motif complexes sodium thiocyanate, sodium iodide, and sodium azide in apolar solvents. 相似文献
333.
M. U. Belyi N. E. Bartnitskaya I. F. Mel'nik B. A. Okhrimenko S. M. Yablochkov 《Journal of Applied Spectroscopy》1995,62(3):564-567
T. Shevchenko Kiev University, 252022 Kiev, Pr. Akad. Glushakova, 6, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 62, No. 3, pp. 192–196, May–June, 1995. 相似文献
334.
335.
M. N. Vidyakin Yu. N. Lazareva Yu. P. Yampolskii A. Yu. Alentiev D. Yu. Likhachev A. L. Rusanov O. V. Kozlova 《Polymer Science Series A》2006,48(6):596-600
The correlation between chemical structure and gas transport properties is considered for a new class of membrane materials based on structurally similar polyphenylquinoxalines that are characterized by different numbers of flexible-O-ether bonds in the repeating unit and different chain rigidities. Permeability, diffusion, and solubility coefficients have been estimated for the gases H2, He, O2, N2, CO, CO2, and CH4; separation factors for various gas pairs have been determined. For the materials with a similar level of cohesive energy density, which characterizes interchain interactions, permeability decreases with a decrease in chain rigidity, whereas selectivity of gas separation increases. 相似文献
336.
This study has investigated the effect of shelf aging, for up to one year in air, on the properties of gamma-irradiated ultra-high molecular weight polyethylene (UHMWPE). A variety of techniques were used to characterize the properties of treated samples. Differential scanning calorimetery (DSC) was used to characterize the morphology. The extent of cross-linking in a polymer network was detected by swelling measurements. The durometer hardness test was used to measure the relative hardness of this material, and changes in density were also measured. Results from all these measurements were combined to explain the changes in the microstructure of the aged, irradiated UHMWPE. This study shows that crystallinity is increased with radiation dose and with aging due to chain scission, which leads to a reduction in the molecular weight of the material. This allows the chains to rearrange to form crystalline regions. Positron annihilation lifetime spectroscopy confirms these conclusions. Fractional free volumes have been deduced from lifetime parameters, which correlate with the data obtained by the other techniques. 相似文献
337.
338.
E. D. Mishina N. É. Sherstyuk V. O. Val’dner A. V. Mishina K. A. Vorotilov V. A. Vasil’ev A. S. Sigov M. P. De Santo E. Cazzanelli R. Barberi Th. Rasing 《Physics of the Solid State》2006,48(6):1210-1213
Ferroelectric composite two-dimensional ferroelectric/aluminum oxide nanostructures were studied. A porous aluminum oxide matrix was used as a template into which a ferroelectric precursor was introduced, followed by annealing. The prepared nanostructures were studied using optical second harmonic generation and micro-Raman scattering. 相似文献
339.
L. I. Bryukvina E. A. Ermolaeva S. N. Pidgurskiĭ L. F. Suvorova V. M. Khulugurov 《Physics of the Solid State》2006,48(1):68-72
It was detected for the first time that films consisting of a transition-metal-based structure form (via thermal diffusion
of intracrystalline impurities) on the surface of alkali-halide (LiF, NaF) crystals activated by transition metals Co, Ni,
or Mn. The thickness, density, and composition of the films are shown to be different, depending on the heat treatment conditions.
The crystals were annealed at temperatures varying from 473 to 1073 K in vacuum and air. The surface structures forming upon
annealing in vacuum exhibit magnetic properties. The films were studied by optical, x-ray fluorescence, and electron spectroscopy
to reveal the mechanisms of transition-metal film formation during thermal annealing. 相似文献
340.