全文获取类型
收费全文 | 3147篇 |
免费 | 269篇 |
国内免费 | 309篇 |
专业分类
化学 | 2858篇 |
晶体学 | 49篇 |
力学 | 19篇 |
综合类 | 13篇 |
数学 | 4篇 |
物理学 | 782篇 |
出版年
2024年 | 7篇 |
2023年 | 34篇 |
2022年 | 45篇 |
2021年 | 62篇 |
2020年 | 105篇 |
2019年 | 92篇 |
2018年 | 70篇 |
2017年 | 67篇 |
2016年 | 114篇 |
2015年 | 112篇 |
2014年 | 142篇 |
2013年 | 232篇 |
2012年 | 195篇 |
2011年 | 173篇 |
2010年 | 123篇 |
2009年 | 181篇 |
2008年 | 205篇 |
2007年 | 211篇 |
2006年 | 219篇 |
2005年 | 180篇 |
2004年 | 162篇 |
2003年 | 165篇 |
2002年 | 127篇 |
2001年 | 72篇 |
2000年 | 90篇 |
1999年 | 81篇 |
1998年 | 71篇 |
1997年 | 66篇 |
1996年 | 57篇 |
1995年 | 55篇 |
1994年 | 30篇 |
1993年 | 35篇 |
1992年 | 32篇 |
1991年 | 20篇 |
1990年 | 24篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有3725条查询结果,搜索用时 15 毫秒
91.
本文比较了在标准石墨管,热解涂层和全热解石墨管中钒的吸收信号形状。用全热解石墨管和EDTA铵盐作基体改进剂,直接测定水系沉积物中痕量钒。方法的特征量为61pg/0.0044A。 相似文献
92.
Yu. E. Roginskaya F. Kh. Chibirova T. L. Kulova A. M. Skundin 《Russian Journal of Electrochemistry》2006,42(4):355-362
Products of lithium interaction with thin-film nanostructured SnO2-TiO2 (ST) oxides are studied with the aid of x-ray diffraction analysis and Moessbauer spectroscopy on the 119Sn nuclei. Electrochemical properties of a series of the ST electrodes with different concentrations of TiO2 varied from 0 to 20 mol % are also examined. It is concluded that the specific feature of the charge-discharge mechanism of the ST electrodes is a significant participation of oxygen in reversible reactions during insertion and extraction of lithium as compared with an alloying mechanism of operation of tin-containing anodes. The leading role in this is played by titanium oxide. Remaining stable towards reduction by lithium, it facilitates the holding of the neighboring layers of SnO2 in a nanodisperse state and in an oxidized state. The effect of a decrease in the capacity degradation in modified TiO2 electrodes, which is discovered in this work, is attributed to the hampering of the growth of nanocrystallites of β-Sn by interlayers of tin and titanium oxides mentioned above. 相似文献
93.
O. I. Artyushin E. V. Sharova I. L. Odinets S. V. Lenevich V. P. Morgalyuk I. G. Tananaev G. V. Pribylova G. V. Myasoedova T. A. Mastryukova B. F. Myasoedov 《Russian Chemical Bulletin》2004,53(11):2499-2507
An efficient method for the synthesis of secondary alkylamides of phosphorylacetic acids (APA) was proposed. The method involves amidation of ethyl phosphorylacetates with primary aliphatic amines. The scope of reaction was determined. Reactions with ethylenediamine and 1,4-diaminobutane yield the corresponding bisamides; in the case of 1,3-diaminopropane, N-(3-aminopropyl)diphenylphosphorylacetamide or N,N-propylenebis(diphenylphosphorylacetamide) was obtained, depending on the reaction conditions. The extraction of americium(III) complexes and the sorption of uranium(VI) by sorbents with physically sorbed APA from nitric acid solutions were studied. There is no correlation between the partition coefficient of americium(III) and the structure of APA; in the sorption of uranium(VI), the degree of extraction depends on the complexone structure.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2394–2402, November, 2004. 相似文献
95.
在 pH 4.5 HAc-NaAc缓冲溶液中,钍试剂分别于- 0.36 V、- 0.60 V产生两个灵敏的极谱波。基于钒对溴酸钾氧化钍试剂的催化作用,建立了双极谱波测量的催化动力学极谱法。钒浓度在0.7~15μg/L与△I(△I1+ I2)呈线性关系,检测限为0.5μg/L。研究了极谱波性质及电极反应机理。本法简便、灵敏、准确,已用于直接测定水中痕量钒。 相似文献
96.
97.
LIN Jun-Fan YAN Ya-XieDepartment of ChemistryInstitute of Chemistry Chemical EngineeringNanjing UniversityNanjing Jiangsu 《天然气化学杂志》1995,(2)
A series of perovskite type oxides La_(1-x)A_(x)MnO_3(x=0.1 for A=Li,Na,K;x=0.1~0.5 for A=Li)have been prepared by impregnation.Experimental results showed that the substitution of La~(3 ) by Li~ inLaMnO_(3 ?) greatly increased the selectivity to ethane and ethylene for theoxidative coupling of methane.Temperature-programmed desorption of oxygenproved the presence of oxygen vacancies in the oxide lattice.The higher Mn~(4 )/Mn_t ratio in oxide made the formation of oxygen vacancies easier on the oxidesurface.The general formula of the oxides is La_(1-x)Li_(x)Mn'V'_(y)O_(3-y),V=vacancy. 相似文献
98.
The synthesis, characterization and crystal structure analysis of the ammonium salt of the dioxovanadium(V) complex NH4[VO2(salhyph)] with the tridentate Schiff base ligand derived from salicylaldehyde and benzoic acid hydrazide (H2salhyph) is reported. NH4[VO2(salhyph)] crystallizes in the monoclinic space group Pn with a = 708.8(2), b = 1444.3(3), c = 717.1(2) pm and β = 101.09(2)°. The vanadium atom of the dioxovanadium(V) moiety has a distorted square‐pyramidal coordination geometry. Extensive hydrogen bonding is observed between the ammonium cation and the oxygen atoms coordinated to the vanadium atom yielding to a two‐dimensional network, where the complex anions are arranged in a bilayer. Additional crystal packing within the bilayer appears to be controlled mostly by π stacking between the aromatic rings of the ligand. The reactions of NH4[VO2(salhyph)] with several proton acidic compounds including water, methanol, and proton acids lead to neutral monooxovanadium(V) and dioxovanadium(V) complexes ([VO2(Hsalhyph)], [V2O3(salhyph)2] and [VO(OMe)(salhyph)(HOMe)]). 相似文献
99.
D. V. Tsyganov A. P. Yakubov L. D. Konyushkin S. I. Firgang V. V. Semenov 《Russian Chemical Bulletin》2007,56(12):2460-2465
A series of analogs of the natural mitostatic agent combretastatin were synthesized by the reaction of nitrile oxides with
natural allylbenzenes, such as myristicin, apiol, and dillapiol. The 1,3-dipolar cycloaddition reactions in allylic systems
proceed regiospecifically. The reactions with trans isomers of propenylbenzenes, viz., isomyristicin, isoapiol, and isodillapiol, as dipolarophiles produce regioisomers.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2375–2380, December, 2007. 相似文献
100.
The high-pressure behavior of Li2CO3 is studied up to 25 GPa with synchrotron angle-dispersive powder X-ray diffraction in diamond anvil cells and synthesis using a multi-anvil apparatus. A new non-quenchable hexagonal polymorph (P63/mcm, Z=2) occurs above 10 GPa with carbonate groups in a staggered configuration along the c-axis—a=4.4568(2) Å and c=5.1254(6) Å at 10 GPa. Two columns of face-shared distorted octahedra around the Li atoms are linked through octahedral edges. The oxygen atoms are coordinated to one carbon atom and four lithium atoms to form a distorted square pyramid. Splittings of X-ray reflections for the new polymorph observed above about 22 GPa under non-hydrostatic conditions arise from orthorhombic or monoclinic distortions of the hexagonal lattice. The results of this study are discussed in relation to the structural features found in other Me2CO3 carbonates (Me: Na, K, Rb, Cs) at atmospheric conditions. 相似文献