全文获取类型
收费全文 | 1096篇 |
免费 | 51篇 |
专业分类
化学 | 706篇 |
晶体学 | 2篇 |
力学 | 46篇 |
数学 | 155篇 |
物理学 | 238篇 |
出版年
2023年 | 5篇 |
2022年 | 26篇 |
2021年 | 27篇 |
2020年 | 20篇 |
2019年 | 16篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 37篇 |
2015年 | 33篇 |
2014年 | 35篇 |
2013年 | 47篇 |
2012年 | 56篇 |
2011年 | 72篇 |
2010年 | 21篇 |
2009年 | 45篇 |
2008年 | 66篇 |
2007年 | 62篇 |
2006年 | 47篇 |
2005年 | 40篇 |
2004年 | 39篇 |
2003年 | 27篇 |
2002年 | 45篇 |
2001年 | 18篇 |
2000年 | 13篇 |
1999年 | 17篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1989年 | 13篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 5篇 |
1973年 | 8篇 |
1970年 | 4篇 |
1905年 | 4篇 |
排序方式: 共有1147条查询结果,搜索用时 15 毫秒
31.
Summary White crystalline complexes of general formula Cu2L4X2 (where X = Cl, Br and L = 1, 3-oxazolidine-2-thione, pyrrolidine-2-thione,N-methyl-1,3-imidazolidine-2-thione andN-ethyl-1,3-imidazolidine-2-thione) and CuLX (where L = 1,3-imidazolidine-2-thione) were prepared by reduction of copper(II) halides and studied by i.r. spectroscopy in the 4000–200 cm– range. Evidence for ligand coordination to the metal through sulphur was found in each case. The(CuCI) vibration in all the chloro derivatives falls atca. 240 cm–. 相似文献
32.
The protolysis equilibria of 2-hydroxybenzohydroxamic acid, H2SAX, have been studied at 25 degrees C in different ionic media by potentiometric titration with a glass electrode. The media were 0.513, 1.05, 2.21 and 3.5 mol/kg NaClO4. The constants beta(-p)(H2SAX<==>H(2-p)SAX(-p)+pH+), combined with salting effects of NaClO4 on H2SAX deduced from solubility determinations, were processed by the specific interaction theory, SIT, to give equilibrium constants at infinite dilution, log beta(-1)(o) = -7.655 +/- 0.013 and log beta(-2)(o) = -17.94 +/- 0.04, as well as specific interaction coefficients b(HSAX-,Na+) = 0.12 +/- 0.01 and b(SAX2-,Na+) = 0.17 +/- 0.02, molal(-1). 相似文献
33.
Lorenzo MalavasiPaolo Ghigna Gaetano ChiodelliGiorgio Maggi Giorgio Flor 《Journal of solid state chemistry》2002,166(1):171-176
The synthesis and structural properties of Mg1−xMn2+xO4, for 0≤x≤1 are described. Complete miscibility in the solid state exists for this system. For the material with the correct stoichiometry, i.e. MgMn2O4, the effect of temperature on the cation distribution was investigated= above 600°C the inversion degree (m) starts increasing. The electrical conductivity shows a small dependence on P(O2) which is consistent with the small oxygen non-stoichiometry determined by means of thermogravimetry. The main contribution to the transport properties arises from the inversion equilibrium. Two distinct conductivity regimes, below and above the inversion threshold, can be assumed to explain the electrical conductivity and thermoelectric power results. 相似文献
34.
Gaetano Dattolo Girolamo Cirrincione Anna Maria Almerico Enrico Aiello Isabella D'Asdia 《Journal of heterocyclic chemistry》1986,23(5):1371-1373
Pyrrolo[1,2-f]phenanthridines were prepared in good yields by the diazotization in acetic acid of the amines la,b and subsequent treatment with hypophosphorous acid. The necessity for hypophosphorous acid in the reaction was demonstrated. 相似文献
35.
The complex formation equilibria between iron(II) and sulfate ions have been studied at 25 degrees C in 3 M NaClO4 ionic medium by measuring with a glass electrode the competition of Fe2+ and H+ ions for the sulfate ion. The concentrations of the metal and of the ligand were varied in the ranges 0.01 to 0.125 and 0.01 to 0.250 M, respectively. The analytical concentration of strong acid was chosen to be 0.01 or 0.03 M. The potentials of the glass electrode, corrected for the effect of replacement of medium ions with reagent species, have been interpreted with the equilibria [formula: see text] Stability constants valid in the infinite dilution reference state, logK zero = 1.98 +/- 0.16, log beta 1 zero = 2.1(5) +/- 0.2 and log beta 2 = 2.5 +/- 0.2, have been estimated by assuming the validity of the specific interaction theory. 相似文献
36.
Franco Cristiani Francesco A. Devillanova Gaetano Verani 《Transition Metal Chemistry》1977,2(1):50-52
Summary White crystalline complexes of general formula ML2X2, where M = Zn, Cd, Hg; X = Cl, 13r, I and L = pyrrolidine-2-thione, were prepared and studied by i.r. spectroscopy in the 4000-200 cm–1 range. Evidence for coordination of the ligand to the metal through sulphur was found in each case. The previous assignment of the band present in the ligand at 1110 cm–1 to the(CS) fundamental is discussed.This work was supported by the National Research Council (C.N.R.) of Italy. 相似文献
37.
Abstract –The individual tryptophanyl contributions to the near-ultraviolet dichroic activity of apomyoglobin in its native conformation have been resolved. This was accomplished by comparing the spectra of two classes of apomyoglobin with different aromatic residue contents and observing the effect of a specific modification of indole residues. The circular dichroism (CD) spectra of apomyoglobins containing two tryptophanyl residues, i.e. Trp A-5 and A-12, show the presence of a positive peak centered at 292 nm, attributable to indolic chromophore, which is missing in the CD spectrum of tuna apomyoglobin possessing only Trp A-12. Moreover, the specific modification of Trp A-5 by 2-hydroxy-5-nitrobenzyl bromide is shown by the lack of the 292 nm peak and the appearance of a positive band at longer wavelength. The pH dependence of the position of this band suggests that it arises from the 2-hydroxy-5-nitrobenzyl moiety. The results suggest that Trp A-12 does not substantially contribute to the optical activity in the near ultraviolet. 相似文献
38.
Summary The retention, selectivity and elution order of fluorescent 1,N6-etheno derivatives of diadenosine polyphosphates and their enzymatic degradation products on octadecyl and phenyl-bonded
silica columns have been studied as a function of mobile phase pH, ionic strength and organic modifier content. Good separations
of the compounds of interest were achieved using mobile phases of around 0.1M potassium phosphate buffers at neutral pH containing
approximately 10% methanol or 4% acetonitrile for C18 columns and 5% methanol or 1.5% acetonitrile for phenyl columns. The data obtained were used to establish isocratic assays
for diadenosine polyphosphate cleaving activities from chromaffin cells using Di(1,N6-ethenoadenosine) polyphosphates as fluorogenic substrate analogues followed by fluorescence detection. 相似文献
39.
Senthilkumar K Grozema FC Guerra CF Bickelhaupt FM Siebbeles LD 《Journal of the American Chemical Society》2003,125(45):13658-13659
The effective energy of a positive charge when it is localized at a specific guanine nucleobase in DNA was calculated using density functional theory. The results demonstrate that the efficiency of a guanine to act as a hole-trap in DNA strongly depends on the nature of the flanking nucleobases. The presence of a pyrimidine base at the 3' position adjacent to a guanine significantly increases the localization energy of the positive charge. The calculated distributions of a positive charge in sequences of two or three adjacent guanines, flanked by other nucleobases, provide an explanation for experimental literature data on the site-selective oxidation of DNA. 相似文献
40.
Francesco A. Devillanova Gaetano Verani D. N. Sathyanarayana 《Journal of heterocyclic chemistry》1978,15(6):945-947
An infrared investigation cm N-methyl-1,3-thiazolidine-2-thione and -2-selone in the range 4000-200 cm?1 is reported. The v CS and v CSe vibrations give contributions to the absorptions around 1000 cm?1 and below 600 cm?1. The assignments are supported by comparison of their ir spectra with those of S- and Se-methiodides. The π-bond orders of the thio- and seleno-ketonic links in these compounds are higher than those found for 1,3-imidazolidine-2-thione and -2-selone. 相似文献