全文获取类型
收费全文 | 2560篇 |
免费 | 223篇 |
国内免费 | 196篇 |
专业分类
化学 | 1562篇 |
晶体学 | 59篇 |
力学 | 81篇 |
综合类 | 26篇 |
数学 | 340篇 |
物理学 | 911篇 |
出版年
2023年 | 46篇 |
2022年 | 60篇 |
2021年 | 61篇 |
2020年 | 68篇 |
2019年 | 67篇 |
2018年 | 71篇 |
2017年 | 74篇 |
2016年 | 94篇 |
2015年 | 76篇 |
2014年 | 99篇 |
2013年 | 135篇 |
2012年 | 173篇 |
2011年 | 160篇 |
2010年 | 118篇 |
2009年 | 135篇 |
2008年 | 139篇 |
2007年 | 120篇 |
2006年 | 99篇 |
2005年 | 96篇 |
2004年 | 71篇 |
2003年 | 72篇 |
2002年 | 72篇 |
2001年 | 44篇 |
2000年 | 29篇 |
1999年 | 34篇 |
1998年 | 26篇 |
1997年 | 20篇 |
1996年 | 30篇 |
1995年 | 36篇 |
1994年 | 28篇 |
1993年 | 33篇 |
1992年 | 40篇 |
1991年 | 26篇 |
1990年 | 29篇 |
1989年 | 31篇 |
1988年 | 22篇 |
1987年 | 23篇 |
1986年 | 23篇 |
1985年 | 30篇 |
1984年 | 33篇 |
1983年 | 25篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 19篇 |
1978年 | 14篇 |
1976年 | 18篇 |
1974年 | 17篇 |
1973年 | 25篇 |
1972年 | 14篇 |
排序方式: 共有2979条查询结果,搜索用时 15 毫秒
41.
环戊二烯热聚产物及二聚环戊二烯加氢产物的质谱 总被引:1,自引:0,他引:1
本实验用色谱-质谱-计算机联用仪测定了环戊二烯热聚产物及双环戊二烯加氢产物的质谱,讨论了环状化合物的开裂规律,有开环断裂反应及骨架重排等问题。 相似文献
42.
K. D. Sen T. V. Gayatri R. Krishnaveni M. Kakkar Helge Toufar Geert O. A. Janssens Bart G. Baekelandt Robert A. Schoonheydt Wilfried J. Mortier 《International journal of quantum chemistry》1995,56(4):399-408
The average local electrostatic potential function, V(r)/ ρ(r), is calculated for 87 atoms, Li-Ac, in the ground state using the nonrelativistic average-over-configuration numerical Hartree-Fock density. It is found empirically that in a given atom the shell boundaries are expressed as the successively increasing maxima in V(r)/ ρ(r) and the outermost maximum presents good approximate estimates of the core-valence separation in atoms. The likeness in behavior of V(r)/ ρ(r) at each shell boundary with the maximum hardness principle is discussed. The single-exponent-fit parameters for the electron density in the valency region are provided for all atoms. © 1995 John Wiley & Sons, Inc. 相似文献
43.
44.
45.
[formula: see text] The biological relevance and irresistible synthetic challenge of compounds containing the diaryl ether linkage encourages the development of new methodologies targeted toward this structural subunit. The syntheses of diaryl ethers 2 using a benzannulation strategy that formally involves a [3 + 2 + 1] cycloaddition between aryloxy-substituted Fischer carbenes 1 and alkynes are described. This methodology provides a neutral near ambient temperature formation of diaryl ethers. 相似文献
46.
Yuyin Wang Yan Wang Li Zhang Prof. Dr. Chun‐Sen Liu Prof. Dr. Huan Pang 《化学:亚洲杂志》2019,14(16):2790-2795
To realize the effective conversion of renewable energy through water decomposition, efficient electrocatalysts for the oxygen evolution reaction (OER) are essential. In this article, PBA@POM was successfully prepared with a Prussian blue analogue (PBA) as the initial structure. A facile hydrothermal process is reported for obtaining PBA@POM by etching the cubic PBA with a strong Brønsted acid, H3PMo12O40 (HPMo). The hollow cube structure not only exposes more active sites but also promotes electron transport, which results in excellent electrocatalytic activity for the OER. Compared with the PBA, which initially simply adhered to POM, the optimum PBA@POM hybrids display remarkably enhanced OER catalytic activity, with an almost constant overpotential of 440 mV at a current density of 10 mA cm?2 and a small Tafel slope (23.45 mV dec?1). The facilely prepared PBA@POM with good electrochemical activity and stability promises great potential for the OER. 相似文献
47.
Peng CY Nam WJ Fonash SJ Gu B Sen A Strawhecker K Natarajan S Foley HC Kim SH 《Journal of the American Chemical Society》2003,125(31):9298-9299
We describe the use of hard etching methods to create nanodimensional channels and their use as templates for the formation of polymer filament arrays with precise dimensional and orientational control in a single integrated step. The procedure is general as illustrated by the radical, coordination, and photochemical polymerizations that were performed in these nanochannels. The nanochannel templates (20 nm high, 20-200 nm wide, and 100 mum long) were fabricated by the combined use of electron-beam lithography and a sacrificial metal line etching technique. Radical polymerization of acrylates, metal-catalyzed polymerization of norbornene, and photochemical polymerization of 1,4-diiodothiophene were carried out in these nanochannels. The polymers grown follow the dimensions and orientation of the channels, and the polymer filaments can be released without breaking. The approach opens up the possibility of just-in-place manufacturing and processing of patterns and devices from nanostructured polymers using well-established polymer chemistry. 相似文献
48.
Summary Thorium and zirconium can be quantitatively precipitated by quinaldinic acid atph 2.7 and 3, respectively. As the precipitates are of nonstoichiometric composition they are to be ignited to oxides. By this reagent thorium can be quantitatively separated from arsenic (As3+), mercury (Hg2+), rare earths, manganese, magnesium and alkaline earths and zirconium from all the aforesaid ions excepting rare earths which contaminate to a slight extent. 相似文献
49.
XinYingZHANG XueSenFAN JianJiWANG YanZhenLI 《中国化学快报》2004,15(10):1170-1172
Quinoline derivatives were efficiently prepared through acid-catalyzed Friedlander reaction in ionic liquid ([bmim] [BF4]). It is shown that the proposed method is operationally simple and environmentally benign in that the reaction media and the catalyst can be recovered and be reused effectively for at least four times. 相似文献
50.
The reactivity of the fluorescent reagent calcein with the trivalent cations of the rare earths has been spectrofluorimetrically studied in aqueous solution. Optimum excitation and emission wavelengths were 492-497 and 519-522 nm, respectively. Optimum pH was in the range 6.0-9.2. The stoichiometry of the complexes was 1:1. A direct, rapid and sensitive method for the determination of rare earth mixtures has been proposed with a detection limit of 4.49x10(-8) M and a coefficient of variation of 0.82%. 相似文献