全文获取类型
收费全文 | 1756篇 |
免费 | 48篇 |
国内免费 | 3篇 |
专业分类
化学 | 1279篇 |
晶体学 | 32篇 |
力学 | 75篇 |
数学 | 113篇 |
物理学 | 308篇 |
出版年
2023年 | 8篇 |
2022年 | 20篇 |
2021年 | 35篇 |
2020年 | 42篇 |
2019年 | 58篇 |
2018年 | 43篇 |
2017年 | 40篇 |
2016年 | 50篇 |
2015年 | 51篇 |
2014年 | 57篇 |
2013年 | 122篇 |
2012年 | 127篇 |
2011年 | 131篇 |
2010年 | 71篇 |
2009年 | 69篇 |
2008年 | 116篇 |
2007年 | 85篇 |
2006年 | 102篇 |
2005年 | 79篇 |
2004年 | 49篇 |
2003年 | 46篇 |
2002年 | 40篇 |
2001年 | 20篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 17篇 |
1997年 | 10篇 |
1996年 | 16篇 |
1995年 | 15篇 |
1994年 | 14篇 |
1993年 | 10篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 14篇 |
1979年 | 19篇 |
1978年 | 15篇 |
1977年 | 16篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 11篇 |
1973年 | 7篇 |
排序方式: 共有1807条查询结果,搜索用时 62 毫秒
31.
Venkatachalam G Ramesh R 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(9):2081-2087
A series of stable low spin Ru(III) complexes of the type [RuX2(EPh3)2(L)] (where E = P or As; X = Cl or Br; L = mono basic bidentate Schiff bases) have been synthesized and were characterized by analytical, spectral and electrochemical data. A distorted octahedral geometry has been proposed for all the complexes. These complexes catalyze oxidation of primary alcohols and secondary alcohol with high yields in the presence of N-methylmorpholine-N-oxide (NMO). The ruthenium(III) Schiff base complexes show growth inhibitory activity against the bacteria Staphylococcus aureus (209p) and E. coli ESS (2231). 相似文献
32.
An enantioselective total synthesis of the novel natural product (+)-panepophenanthrin has been accomplished in which a biomimetic Diels-Alder dimerisation is a key step. The monomeric precursor 2 was assembled from the readily available Diels-Alder adduct of cyclopentadiene and p-benzoquinone through a short, simple sequence employing chemo- and stereoselective operations. 相似文献
33.
Adsorption of n-hexane in zeolite-5A: a temperature-programmed desorption and IR-spectroscopic study
The adsorption and desorption of n-hexane over Zeolite-5A has been investigated as a function of loading using simultaneous Fourier transform infrared (FTIR)-temperature-programmed desorption (TPD) measurements. The TPD profiles show a second peak developing at lower temperatures when loading exceeds 16 hexane molecules per Zeolite-5A unit cell or two molecules per alpha-cavity of the Zeolite-5A structure. The infrared spectra rule out two types of adsorption sites as the origin of the two peaks in the TPD. Changes in the conformation of the adsorbed hexane as a function of loading and temperature were followed by monitoring the position of the methylene stretching modes in the infrared spectra. With increasing loading, the adsorbed hexane adopts a stretched trans conformation. These changes occur at loading levels below 12 hexane molecules per Zeolite-5A unit cell. No change is observed above this loading, ruling out any conformational change at loadings where the second peak is seen in the TPD. The second peak in the TPD arises, therefore, from a combination of steric repulsion and loss of translational entropy. 相似文献
34.
Ramesh Chitrakar Hirofumi KanohYoshitaka Miyai Kenta Ooi 《Journal of solid state chemistry》2002,163(1):1-4
Microwave irradiation of a suspension of γ-MnOOH in a 4 mol dm−3 LiOH solution brought about a rapid formation of semicrystalline orthorhombic LiMnO2 (o-LiMnO2) within 30 min at 120°C. Cubic Li1.6Mn1.6O4 was obtained by heating o-LiMnO2 at 400°C; lithium could be topotactically extracted from Li1.6Mn1.6O4 with acid to form cubic H1.6Mn1.6O4. 相似文献
35.
A new and convenient synthesis of 2-isopropylfuro-(2,3-b)quinolines () from 3-(3-methylbut-1-enyl)-2-quinolones () is described. A neat synthesis of the alkaloids (±)-lunacrine (), (±)-lunasine () and (±)-demethoxylunacrine () is also reported. 相似文献
36.
V. Balaram S. L. Ramesh K. V. Anjaiah 《Fresenius' Journal of Analytical Chemistry》1995,353(2):176-182
ICP-MS has been used for the determination of over 30 geochemically significant trace elements (Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Cs, Ba, Hf, Ta, Pb, Th, U and REEs) in anorthosites and related rock reference samples. Open acid digestion, pressure decomposition using HF, HNO3 and HClO4, and a fusion method using lithium metaborate and subsequent dissolution in dil. HNO3 were adopted for the decomposition of these rock samples before analysis. The dissolution problems and interference effects are discussed. Rh and Bi were used as internal standards. The first set of data on several rare earths and other trace elements in the Russian anorthosite reference sample, MO-6 are presented along with data on other samples. The data are compared with the available data. The results obtained with different dissolution methods were found to be in good agreement for the majority of the trace elements. The accuracy and precision achieved (better than 6% RSD in most cases) suggested that the data obtained by ICP-MS for such samples are best suited for geochemical interpretations. 相似文献
37.
Krishnaswamy Vasudevan Sigrid D. Peyerimhoff Robert J. Buenker Wolf E. Kammer Hsiang-lin Hsu 《Chemical physics》1975,7(2):187-209
A series of ab initio calculations is reported for the ground and low-lying valence and Rydberg states of diimide N2H2. Symmetric bending potential curves for both the cis and trans forms of this system have been obtained at the SCF level of treatment. In addition Cl calculations have been carried out for the trans-diimide ground state equilibrium nuclear conformation, using a configuration selection procedure described elsewhere; an associated energy extrapolation scheme is also employed which enables the effective solution of secular equations with orders of up to 40000. The ensuing Cl wavefunctions are interpreted in the discussion and the corresponding calculated energy differences between the various electronic states are compared with experimental transition energy results for both diimide and for related systems such as trans-azomethane. A more detailed analysis of the observed absorption bands in the 1Bg-X1Ag transition in N2H2 is also given, making use of calculated potential curve data as well as the pertinent Cl vertical energy difference. The dipole-forbiddenness of the excitation process is thereupon concluded to result in a distinct non-verticality for this electronic band system, causing its absorption maximum to occur at a position some 0.6 eV to the blue of the so-called vertical transition, i.e., that for which maximum vibrational overlap is obtained. 相似文献
38.
L-histidine substitutes cyano groups of K4Fe (CN)6 at pH 7·0 on irradiation with ultraviolet light. The reaction follows first order kinetics with reference to K4Fe(CN)6 and zero order with reference to histidine. The kinetic data shows the primary process to be aquation of Fe(CN) 6 4? while the final product is formed through a rapid dark reaction of histidine with Fe(CN)4 (H2O) 2 2? to give the product K2Fe(CN)2(histidine)2. The final product has been subjected to chemical and infrared spectral analysis. 相似文献
39.
Ramesh C. Kapoor Raj N. Mehrotra Shared K. Vajpai Purnima Chaudhary 《Transition Metal Chemistry》1991,16(1):65-70
Summary The kinetics of the OsVIII-catalysed oxidation of glycols by alkaline hexacyanoferrate(III) ion exhibits zerothorder dependence in [Fe(CN)
6
3–
] and first-order dependence in [OsO4]. The order with respect to glycols is less than unity, whereas the rate dependence on [OH–] is a combination of two rate constants; one independent of and the other first-order in [OH–]. These observations are commensurate with a mechanism in which two complexes, [OsO4(H2O)G]– and [OsO4(OH)G]2–, are formed either from [OsO4(H2O)(OH)]– or [OsO4(OH)2]2– and the glycol GH, or by [OsO4(H2O)2] and [OsO4(H2O)(OH)]– and the glycolate ion, G–, which is in equilibrium with the glycol GH through the reaction between GH and OH–. Hence there is an ambiguity about the true path for the formation of the two OsVIII-glycol complexes. A reversal in the reactivity order of glycols in the two rate-determining steps, despite the common attack of OH– ion on the two species of OsVIII-complexes, indicates that the two complexes are structurally different because S changes from the negative (corresponding to k11) to positive (related to k2). 相似文献
40.
R. Sathiyamoorthi P. Santhosh P. Shakkthivel T. Vasudevan 《Journal of Solid State Electrochemistry》2007,11(12):1665-1669
Layered Ti-doped lithiated nickel cobaltate, LiNi0.8Co0.2 − xTixO2 (where x = 0.01, 0.03, and 0.05) nanopowders were prepared by wet-chemistry technique. The structural properties of synthesized materials
were characterized by X-ray diffraction (XRD) and thermo-gravimetric/differential thermal analysis (TG/DTA). The morphological
changes brought about by the changes in composition of LiNi0.8Co0.2 − xTixO2 particles were examined through surface examination techniques such as scanning electron microscopy (SEM) and transmission
electron microscopy (TEM) analyses. Electrochemical studies were carried out using 2016-type coin cell in the voltage range
of 3.0–4.5 V (vs carbon) using 1 M LiClO4 in ethylene carbonate and diethyl carbonate as the electrolyte. Among the various concentrations of Ti-doped lithiated nickel
cobaltate materials, C/LiNi0.8Co0.17Ti0.03O2 cell gives stable charge–discharge features. 相似文献