全文获取类型
收费全文 | 4236篇 |
免费 | 190篇 |
国内免费 | 9篇 |
专业分类
化学 | 2591篇 |
晶体学 | 38篇 |
力学 | 134篇 |
数学 | 729篇 |
物理学 | 943篇 |
出版年
2023年 | 30篇 |
2022年 | 106篇 |
2021年 | 89篇 |
2020年 | 95篇 |
2019年 | 114篇 |
2018年 | 133篇 |
2017年 | 111篇 |
2016年 | 200篇 |
2015年 | 131篇 |
2014年 | 178篇 |
2013年 | 312篇 |
2012年 | 225篇 |
2011年 | 241篇 |
2010年 | 163篇 |
2009年 | 158篇 |
2008年 | 165篇 |
2007年 | 189篇 |
2006年 | 152篇 |
2005年 | 94篇 |
2004年 | 92篇 |
2003年 | 76篇 |
2002年 | 94篇 |
2001年 | 77篇 |
2000年 | 61篇 |
1999年 | 53篇 |
1998年 | 40篇 |
1997年 | 33篇 |
1996年 | 36篇 |
1995年 | 28篇 |
1994年 | 33篇 |
1992年 | 23篇 |
1991年 | 24篇 |
1990年 | 32篇 |
1988年 | 29篇 |
1987年 | 28篇 |
1986年 | 25篇 |
1985年 | 34篇 |
1984年 | 32篇 |
1983年 | 28篇 |
1982年 | 24篇 |
1981年 | 29篇 |
1980年 | 42篇 |
1979年 | 28篇 |
1978年 | 44篇 |
1977年 | 40篇 |
1976年 | 44篇 |
1975年 | 34篇 |
1974年 | 29篇 |
1971年 | 24篇 |
1968年 | 25篇 |
排序方式: 共有4435条查询结果,搜索用时 15 毫秒
31.
Zusammenfassung Die Reaktion von 1-Nitroso-2-naphthol mit 1-und 2-Naphthol sowie die Reaktion von 2-Nitroso-1-naphthol mit 2-Naphthol in Äthanol und in Äther bei Anwesenheit von HNO3 gibt 5H-Dibenzo[a,j]phenoxazon-(5) (I), 5H-Dibenzo[a,j]phenoxazon-(5)-14-oxid (II), 5H-Dibenzo[a,h]phenoxazon-(5) (III) sowie 5H-Dibenzo[a,h]phenoxazon-(5)-14-oxid (IV). Es wurde ein Reaktionsmechanismus vorgeschlagen und die Konstitution der hergestellten Verbindungen spektrophotometrisch und potentiometrisch bestimmt.
Mit 4 Abbildungen 相似文献
The reaction of 1-nitroso-2-naphthol with 2-and 2-naphthol and the reaction of 2-nitroso-1-naphthol with 2-naphthol in ethanol or ether in the presence of nitric acid have been studied. The main reaction products isolated were the dibenzophenoxazones I–IV. The reaction mechanism for their formation is proposed.
Mit 4 Abbildungen 相似文献
32.
The oxidation of iron(II) with tert-butyl hydroperoxide was investigated in the absence of oxygen in water, methanol, and the dichloromethane—methanol solvent
mixture (φr = 2:1). The oxidation rate depends on solvent polarity; measured in the presence of SCN− at constant 0.8 mmol dm−3 HCl, the rate constant increases with the polarity decrease passing from water and methanol to the dichloromethane—methanol
solvent mixture. Further, in non-aqueous solutions at this acid concentration the rate constant was higher than the rate constant
in the presence of Cl− only. The oxidation rate measured in the [FeCl]2+ complex in dichloromethane—methanol was slow in acidic medium and increased by decreasing the acid concentration. Approaching
the physiological pH conditions the rate constant attained the value of an order of magnitude of 103 dm3 mol−1 s−1, while very little alteration of stoichiometry of the oxidation reaction was observed. The rate constant measured in the
presence of Cl− strongly depends on electrolyte concentration at concentrations less than 0.5 mmol dm−3 HCl, both in MeOH and the solvent mixture. Based on these results, a possible mechanism of the influence of solvent, acidity,
and ligand type on the rate constant is discussed. We assume that the oxidation proceeds by an inner-sphere mechanism considering
that the breakdown of the successor inner-sphere complex forming reactive alkoxyl radicals is probably the rate-limiting step.
Presented at the 20th International Conference on the Coordination and Bioinorganic Chemistry organized by the Slovak Chemical
Society, Slovak University of Technology, Comenius University, and the Slovak Academy of Sciences, Smolenice Castle, 5–10
June 2005. 相似文献
33.
The method reported for the determination of calcium in silicate rocks involves titration with ethyleneglycol-bis(2-aminoethylether)tetraacetic acid (EGTA) to a potentiometric end-point. A Crytur calcium-selective electrode is used; the selectivity constants (Kca,x) are less than 10-3 for Mg, Ba, Sr, K and Na. The method can be used for calcium contents of 2% or higher (and exceptionally for lower contents), in the presence of up to 60% Mg, 33% AI, 17% Fe, 5% Ba, 5% Ti, and 2.5% Mn. Al, Fe and Ti are masked with sulphosalicylic acid, barium is precipitated as its sulphate, and manganese is bound as its cyanide complex. If the magnesium content is less than that of calcium, EDTA can be used as titrant, magnesium being masked with acetylacetone. 相似文献
34.
A series ofc-axis oriented YBa2Cu3O
x
-films with different oxygen content were prepared by laser deposition. The oxygen contentx was determined by X-ray diffraction and by resonant Rutherford-back-scattering (RRBS) measurements. Thec-axis length in these films of YBa2Cu3O
x
is about 0.5% larger compared to bulk values. We describe transport measurements in magnetic fields up to 7 Tesla between room temperature andT
c
in samples with an oxygen content between the orthorhombic-to-tetragonal transition (x6.4) and full oxygenation (x7). The ratio /R
H
was investigated with respect to the two-dimensional Luttinger liquid theory and the model of the two-dimensional ionic metal. We report on deviations from the expected quadratic temperature behaviour of /R
H
, especially in films with high oxygen content. 相似文献
35.
Precise values of energies and widths of low-lying resonances in some rare-gas atom systems (Ar-Ar, Ne-Kr, Ne-Xe) are reported. 相似文献
36.
An analytical scheme is proposed which combines three speciation techniques for determination of particular Al species in soil extracts and percolating waters. A cation-exchange fast protein liquid chromatography — inductively coupled plasma atomic emission spectrometry (FPLC-ICP-AES) procedure, a microcolumn chelating ion-exchange chromatography- atomic absorption spectrometry (MCC-ETAAS) technique and the 8-hydroxyquinoline spectrophotometric method (8HQ-spectrophotometry) were employed. The FPLC-ICP-AES procedure offers determination of Al3+ (retention time 4.5 min) and Al(OH)2+ species (retention time 4.0 min) which are separated from Al(OH)+
2 (retention time 1.5min). AlF2+ coelutes with Al(OH)2+ species, while Al(SO4)+, AlF+
2 and negatively charged Al organic complexes coelute with Al(OH)+
2 species. The MCC-ETAAS technique enables determination of the sum of positively charged monomeric aqua- and hydroxy-Al species plus sulphate- and fluoro-Al complexes. Employing the 8HQ-spectrophotometry the sum of positively charged monomeric aqua- and hydroxy-Al species plus sulphato- and most of the labile organic Al species are determined. The sensitivities of these selected techniques were adequate for speciation of Al in the samples analyzed. On the basis of the specific selectivity of a particular technique various groups of Al species may be determined. Thus, the comparison of analytical data from complementary procedures provides more comprehensive information on Al species present in soil extracts and percolating waters. 相似文献
37.
Jiří Kohout Mária Kabešová Prof. Dipl.-Ing. Dr. Ján Gažo 《Monatshefte für Chemie / Chemical Monthly》1977,108(5):1011-1018
The infrared spectra of thiocyanato-copper(II) complexes of the type Cu(NCS)2
L
2 with all isomeric picolines and lutidines (L) as well as those of the type Cu(NCS)2
L
3 withL=3- and 4-picoline, 3,4- and 3,5-lutidine were measured. The behaviour of the (CN) stretching vibrations of the Cu(NCS)2
L
2 complexes led to conclusions on the different kind of coordination of the NCS groups in dependence on the ligandL. The mutually conditioned strength of the Cu–NCS and Cu–N(L) bonds in the equatorial plane, especially in the presence of ligandsL with the steric effect, was determined from the frequency shift of the Cu–NCS and Cu–N(L) stretching vibrations with regard to the vibrations for Cu(NCS)2(pyridine)2.
Mit 1 Abbildung 相似文献
Mit 1 Abbildung 相似文献
38.
The extraction of Am, Eu, Ce(III), Zr(IV), and Sr from aqueous nitric acid— nitrate media by dibutyl N,N-diethylcarbamylphosphonate
and dibutyl N,N-diethylcar-bamylmethylenephosphonate dissolved in carbon tetrachloride was studied. The trivalent actinide
and lanthanide elements may be separated in certain aqueous phase acidity regions from Fe(III), Zr(IV), and Sr, whereas the
separation of actinide elements from the lanthanide elements is poor. The extractant to metal ratio in the extracted complexes
of Am, Eu, and Ce(III) is 3. The interferences in the extraction due to acidic impurities in the extracting agent are discussed. 相似文献
39.
A correction method is proposed for the quantitative determination of stoichiometric ratios in porous materials by electron microprobe analysis. Analysis of this kind of material is complicated by an imperfect surface that can only be improved to some extent. The correction is based on a linear dependence (different for each element) of the analyses on a sum of weight concentrations of oxides. With this correction it is possible to use analyses affected by the imperfection of the surface with much better confidence compared to common normalisation. An example is presented for a series of ceramic superconductors Bi2.1(SrCa)2.9Cu2O8+. 相似文献
40.
J. Kohout M. Quastlerová-Hvastijová J. Gažo 《Monatshefte für Chemie / Chemical Monthly》1973,104(3):779-783
Zusammenfassung Die Ligandenfeldspektren der Komplexe des Typs Cu(NCO)2
L
2 (L=Ligand der Chinolin- bzw. Isochinolingruppe) im festen Zustand wurden aufgenommen. Das Spektrum des Komplexes Cu(NCO)2(Chin)2 weist eine einzige Bande auf und deutet auf eine pseudooktaedrische Struktur. Die Spektren der übrigen Komplexe enthalten hingegen neben den Hauptbanden auch Schultern bzw. ist die anwesende Bande zusammengesetzt, so daß diese Spektren mit einer planaren Struktur im Einklang sind. Die annähernden Werte für den Parameter 10Dq wurden berechnet; sie liegen im Bereich von 7,1 bis 7,8 kK.
Mit 1 Abbildung
6. Mitt.:M. Quastlerová-Hvastijová, J. Kohout undJ. Gao, Z. anorg. allgem. Chem., im Druck. 相似文献
Ligand field spectra of some cyanato-copper(II) complexes with ligands from the quinoline- and isoquinoline group
The ligand field spectra of complexes of the type Cu(NCO)2 L 2 (L=ligand from the quinoline or isoquinoline group) in the solid state were recorded. Only the spectrum of Cu(NCO)2(Quin)2 exhibits a single band and indicates a pseudooctahedral structure, while the spectra of the remaining complexes also contain shoulders in addition to the main band, or this band is composite, thus being in accordance with a planar structure. The approximate values of the parameter 10Dq were calculated and found to be in the range of 7.1 to 7.8 kK.
Mit 1 Abbildung
6. Mitt.:M. Quastlerová-Hvastijová, J. Kohout undJ. Gao, Z. anorg. allgem. Chem., im Druck. 相似文献