全文获取类型
收费全文 | 3101篇 |
免费 | 106篇 |
国内免费 | 6篇 |
专业分类
化学 | 1802篇 |
晶体学 | 103篇 |
力学 | 103篇 |
数学 | 301篇 |
物理学 | 904篇 |
出版年
2023年 | 18篇 |
2022年 | 26篇 |
2021年 | 48篇 |
2020年 | 45篇 |
2019年 | 55篇 |
2018年 | 61篇 |
2017年 | 53篇 |
2016年 | 91篇 |
2015年 | 83篇 |
2014年 | 90篇 |
2013年 | 255篇 |
2012年 | 164篇 |
2011年 | 160篇 |
2010年 | 132篇 |
2009年 | 122篇 |
2008年 | 147篇 |
2007年 | 143篇 |
2006年 | 109篇 |
2005年 | 106篇 |
2004年 | 88篇 |
2003年 | 72篇 |
2002年 | 83篇 |
2001年 | 36篇 |
2000年 | 32篇 |
1999年 | 32篇 |
1998年 | 29篇 |
1997年 | 26篇 |
1996年 | 41篇 |
1995年 | 37篇 |
1994年 | 23篇 |
1993年 | 38篇 |
1992年 | 41篇 |
1991年 | 44篇 |
1990年 | 37篇 |
1989年 | 44篇 |
1988年 | 35篇 |
1987年 | 33篇 |
1986年 | 37篇 |
1985年 | 34篇 |
1984年 | 38篇 |
1983年 | 29篇 |
1982年 | 31篇 |
1981年 | 40篇 |
1980年 | 30篇 |
1979年 | 31篇 |
1978年 | 18篇 |
1977年 | 36篇 |
1976年 | 18篇 |
1975年 | 25篇 |
1974年 | 25篇 |
排序方式: 共有3213条查询结果,搜索用时 125 毫秒
61.
62.
The quality of colour changes of the indicators hematoxylin, 4(2-pyridylazo)resorcinol (PAR), xylenol orange, pyrocatechol violet, chromazurolS and eriochrome cyanineR in the complexometric titration of copper(II) with ethylenediaminetetraacetic acid (EDTA) were studied with the help of tristimulus colorimetry, utilising a comparative study of the parameters SCD (specific colour discrimination), CIE La*b* 1976 and LABHNU 1977. Hematoxylin was found to be the best indicator among those studied. A screened indicator, viz. PAR + malachite green (52), was developed to enhance the quality of colour transition at the end-point and the accuracy of the titrimetric determination. 相似文献
63.
Simon G. Bott Duddu Raja Gopal Annavajhula Durga Prasad Alan P. Marchand 《Journal of chemical crystallography》1993,23(12):1013-1017
The structure of a compound derived from a symmetrical cage diketone in which one of the ketone C=O groups has been converted into a ketal is reported. An investigation into reasons for the selective functionalization resulted in the isolation of acis, cisoid, cis linear triquinane derivative in which both ketones are converted to ketals that share a transannular oxygen atom. Crystal data:2, monoclinic,P21/c,a=7.6298(9),b=7.673(3),c=22.125(3)Å,=97.59(1)°,V=1283.9(5)Å3, andR=0.048 (1001 reflections);4, triclinic,P¯1,a=7.3864(9),b=9.6362(9),c=10.3889(9)Å,=75.749(6),=76.300(8), =83.100(8)°,V=694.8(4)Å3, andR=0.088 (1284 reflections). 相似文献
64.
The phosphorescence spectra of naphthalene-octafluoronaphthalene and durene-octafluoronaphthalene at 4.2 K reveal a localized exciton emission from octafluoronaphthalene, a weak intercomponent triplet-states quasi-resonance and a weak exciton-phonon coupling. 相似文献
65.
The use of a carbon rod atomizer for the analysis of lead in petroleum and petroleum products is described. Variables affecting sensitivity studied include: type of lead salt and type of solvent for standard and sample preparation, hydrogen diffusion flame, choice of analytical wavelength and interferences. For the 217.00-nm line, a sensitivity of 1·10-11 g (absolute) and for the 283.31-nm line, a detection limit of 2·10-12 g (absolute) are reported. Results of analysis of gasoline, used bunker heating oil, used jet engine lubricating oil, and crude oil for lead content are presented. An organic-to-aqueous solvent extraction system for lead is described. 相似文献
66.
Raman phonon spectroscopy has been used to study photodimerization reaction inp-chloro cinnamic acid (pCCA) crystal. The β-form of the crystal yields the 4,4′-dichloro-β-truxinic acid dimer. Six distinct low frequency phonon
bands are observed in thepCCA monomer crystal. On reaction progress, these bands show a monotonic shift to lower frequencies and broaden out. Finally,
in the dimer crystal the phonon spectrum shows two weak broad bands. These results suggest that the reaction is homogeneous
in the initial stages and, as the product concentration increases, the lattice becomes highly disordered. The reactant and
the product were characterised by infrared and Raman spectroscopy. The disappearance of aliphatic C=C bond stretching vibration
and appearance of cyclobutane ring deformation and cyclobutane ring-breathing vibrations on reaction confirm photodimerization
by cyclobutane ring formation. The large Stoke's shift between the absorption and emission band suggest strong exciton-phonon
coupling in the monomer lattice. This reaction seems to be phonon-mediated. 相似文献
67.
Telluiium can be determined by atomic absorption spetroscopy at 2143, 2359, and 2386 A The sensitivities for these lines are in the ratio of 1.9.9 187 With aqueous solutions, a Beckman triple-buiner (air-hydrogen) and a 5-pass optical system, the line 2143 Å has a sensitivity of 0.23 p.p.m , and a detection limit ot 0.076 p.p.m The sensitivities for this line in acqueous and organic solvents, and in air-hydrogen and air-acetylene flames were studied and the optimum conditions determined Where necessary, preconcentration of tellurium by coprecipitation with elemental arsenic, 01 by extraction of K2Tel6 or tellurium diethyldithiocarbomate with MIBK can be applied, the latter gives a two-fold enhancement in sensitivity compared with aqueous solutions. 相似文献
68.
Masahiro Kono Krishnagopal Mandal Bireswar Chakrabarti 《Photochemistry and photobiology》1988,47(4):593-597
Abstract— Irradiation of γ-crystallins with 300 nm light or with the photosensitizers riboflavin or methylene blue (MB) leads to intermolecular cross-linking and insolubilization. Sodium dodecyl sulfate polyacrylamide gel electrophoresis studies reveal that these cross-links are composed of nondisulfide covalent bonds. The water-insoluble phase is stabilized by noncovalent forces, as denaturants readily dissolve it. High-performance liquid chromatography and electrophoresis results further indicate that the higher multimers are part of this water-insoluble fraction only, with the exception of MB-sensitized reactions, which are also able to produce a water-soluble, high-molecular-weight protein of at least 1 million. Labeling the external sulfhydryl groups with iodoacetamide does not prevent the photoreac-tions; however, a reducing agent such as dithiothreitol does. A mechanism involving initial oxidation and interaction of sulfhydryl groups (forming an intramolecular disulfide) buried within the protein as a necessary precursor to polymerization and precipitation has been proposed in the preceding paper. The present study provides support for this mechanism. 相似文献
69.
70.
K. Nagarajan M. Bhupathy Rajendra Prasad Ziley Singh V. Venugopal D.D. Sood 《Thermochimica Acta》1980,36(1):85-89
The thermal decomposition kinetics of Pr2(SO4)3 to Pr2O2SO4 have been studied by isothermal weight change determination. The reaction was found to obey a linear law up to α = 0.5; beyond α = 0.5 it could be described as a phase-boundary controlled process. A dependence of the activation energy upon the sample weight was observed. The changes in surface area and density which occur during the decomposition are also given. 相似文献