全文获取类型
收费全文 | 7435篇 |
免费 | 974篇 |
国内免费 | 1381篇 |
专业分类
化学 | 5457篇 |
晶体学 | 66篇 |
力学 | 885篇 |
综合类 | 65篇 |
数学 | 345篇 |
物理学 | 2972篇 |
出版年
2024年 | 13篇 |
2023年 | 70篇 |
2022年 | 141篇 |
2021年 | 196篇 |
2020年 | 194篇 |
2019年 | 202篇 |
2018年 | 232篇 |
2017年 | 265篇 |
2016年 | 312篇 |
2015年 | 307篇 |
2014年 | 397篇 |
2013年 | 720篇 |
2012年 | 456篇 |
2011年 | 519篇 |
2010年 | 409篇 |
2009年 | 467篇 |
2008年 | 459篇 |
2007年 | 474篇 |
2006年 | 442篇 |
2005年 | 432篇 |
2004年 | 378篇 |
2003年 | 336篇 |
2002年 | 292篇 |
2001年 | 237篇 |
2000年 | 230篇 |
1999年 | 210篇 |
1998年 | 191篇 |
1997年 | 177篇 |
1996年 | 122篇 |
1995年 | 129篇 |
1994年 | 123篇 |
1993年 | 71篇 |
1992年 | 63篇 |
1991年 | 47篇 |
1990年 | 38篇 |
1989年 | 43篇 |
1988年 | 36篇 |
1987年 | 47篇 |
1986年 | 44篇 |
1985年 | 71篇 |
1984年 | 34篇 |
1983年 | 25篇 |
1982年 | 52篇 |
1981年 | 37篇 |
1980年 | 20篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有9790条查询结果,搜索用时 15 毫秒
91.
V. B. Vol'eva A. I. Prokofev A. Yu. Karmilov N. L. Komissarova I. S. Belostotskaya T. I. Prokofeva V. V. Ershov 《Russian Chemical Bulletin》1998,47(10):1920-1923
The formation of semiquinone and phenoxazyl radicals and metallocomplexes with semiquinone ligands was observed by ESR during
the interaction of di-tert-butylpyrocatechol with Al2O3, ZnO, SiO2, and TiO2. In the case of different modifications of SiO2, admixtures of TiO2 exhibit a higher reactivity in complex formation with the organic substrate.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1975–1978, October, 1998. 相似文献
92.
93.
Georgi E. Chernev Bisserka I. Samuneva Petar R. Djambaski Isabel M. M. Salvado Helena V. Fernandes 《Central European Journal of Chemistry》2006,4(1):81-91
In this work we present experimental results about the formation, properties and structure of sol — gel silica based biocomposite
containing Calcium alginate as an organic compound. Two different types of silicon precursors have been used in the synthesis:
tetramethylortosilicate (TMOS) and ethyltrimethoxysilane (ETMS). The samples have been prepared at room temperature. The hybrids
have been synthesized by replacing different quantitis of the inorganic precursor with alginate. The structure of the obtained
hybrid materials has been studied by XRD, IR Spectroscopy, EDS, BET and AFM. The results proved that all samples are amorphous
possessing a surface area from 70 to 290 m2/g. It has also been established by FT IR spectra that the hybrids containing TMOS display Van der Walls and Hydrogen bonding
or electrostatic interactions between the organic and inorganic components. Strong chemical bonds between the inorganic and
organic components in the samples with ETMS are present. A self-organized nanostructure has been observed by AFM. In the obtained
hybrids the nanobuilding blocks average in size at about 8–14 nm for the particles. 相似文献
94.
95.
96.
碳酸氢铵沉淀法制备氧化钇粉体时反应条件对产物粒度的影响 总被引:7,自引:1,他引:7
研究了碳酸氢铵沉淀法的反应条件对氧化钇粒度的影响,探讨了粒度变化规律。发现在沉淀反应中,晶型碳酸钇铵的形成与否是影响氧化钇粒度的关键因素。在较低的反应温度下,当碳酸氢铵和氯化钇的浓度大于0.25mol·L-1,摩尔比大于5,陈化时间大于60min时得到碳酸钇铵沉淀,经煅烧可获得粒度(D50)大于1μm的氧化钇。当反应物浓度较低、摩尔比小,陈化时间较短时得到无定型碳酸钇沉淀,煅烧沉淀可获得粒度(D50)小于0.5μm的氧化钇。实验证明选择适当的沉淀反应条件,可制备D50在0.3~10μm范围内的不同粒度级别的氧化钇粉体。 相似文献
97.
Hideki Nishimori Masahiro Tatsumisago Tsutomu Minami 《Journal of Sol-Gel Science and Technology》1997,9(1):25-31
Monodispersed silica particles up to ca. 1.2 μm in diameter were prepared by hydrolysis of tetraethoxysilane in the presence
of sodium dodecyl sulfate (SDS). The particle size was increased with an increase of SDS added. The geometrical standard deviation
of the particles was decreased with an increase of SDS. In the earlier reaction stage, double spherical particles by the coalescence
of the particles were frequently observed when large amounts of SDS were added. Particle size was gradually increased after
the coalescence occurred and spherical particles were finally obtained. The results of Nielsen’s chronomal analysis suggest
that the polynuclear layer growth took place after the coalescence of the particles in the presence of larger amount of SDS. 相似文献
98.
Nicole Fietkau Fran?ois G Chevallier Li Jiang Timothy G J Jones Richard G Compton 《Chemphyschem》2006,7(10):2162-2167
The size of a glass sphere positioned in the center of a microdisk electrode is determined by using a simple electrochemical procedure and is confirmed, additionally, by a microscopical measurement of the sphere at the time of the electrochemical measurement. The cyclic voltammetric response of the naked electrode and of the electrode with the sphere positioned in its center is recorded over a wide range of scan rates (0.002-1.5 V s(-1)). The size of the sphere is then determined by comparison of the experimental voltammogram with simulations for each individual scan rate. 相似文献
99.
Dynamic light scattering experiments in acid-catalyzed silica sols are discussed. It is shown that in spite of limited parameter accuracy and limited absolute knowledge of the particle sizes, the scattering data from various experiments are comparable with one another and give information about structural differences. Measurements at various angles indicate changes between non-spherical and nearly spherical particles and allow the estimation of gelling times before gelation. 相似文献
100.
Hae‐Jeong Lee Christopher L. Soles Da‐Wei Liu Barry J. Bauer Wen‐Li Wu 《Journal of Polymer Science.Polymer Physics》2002,40(19):2170-2177
X‐ray reflectivity has been used to determine the mass uptake of probe molecules in porous thin films supported on thick silicon wafers. The adsorption occurs by capillary condensation when the films are exposed to probe vapor at controlled partial vapor pressures. The probe solvent partial pressure was varied by mixing saturated air and dry air at constant temperature or by changing sample temperature at a constant vapor concentration. Pore size distribution in the films can be calculated from the probe uptake with typical porosimetric approaches such as the application of the Kelvin equation to convert partial pressure into pore size. For illustration, the pore size distribution of three different nanoporous thin films, the primary candidate of ultra‐low‐k interlevel dielectrics in the next generation of integrated circuit chips, was determined with this technique. These samples represent different generations of low‐k dielectrics developed by industry. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2170–2177, 2002 相似文献