全文获取类型
收费全文 | 8622篇 |
免费 | 178篇 |
国内免费 | 14篇 |
专业分类
化学 | 4839篇 |
晶体学 | 198篇 |
力学 | 196篇 |
数学 | 1410篇 |
物理学 | 2171篇 |
出版年
2022年 | 150篇 |
2021年 | 173篇 |
2020年 | 120篇 |
2019年 | 153篇 |
2018年 | 167篇 |
2017年 | 153篇 |
2016年 | 279篇 |
2015年 | 212篇 |
2014年 | 294篇 |
2013年 | 665篇 |
2012年 | 432篇 |
2011年 | 487篇 |
2010年 | 394篇 |
2009年 | 354篇 |
2008年 | 403篇 |
2007年 | 387篇 |
2006年 | 328篇 |
2005年 | 287篇 |
2004年 | 271篇 |
2003年 | 262篇 |
2002年 | 218篇 |
2001年 | 167篇 |
2000年 | 150篇 |
1999年 | 116篇 |
1998年 | 120篇 |
1997年 | 95篇 |
1996年 | 96篇 |
1995年 | 120篇 |
1994年 | 75篇 |
1993年 | 60篇 |
1992年 | 80篇 |
1991年 | 54篇 |
1990年 | 76篇 |
1989年 | 72篇 |
1988年 | 72篇 |
1987年 | 62篇 |
1986年 | 70篇 |
1985年 | 106篇 |
1984年 | 121篇 |
1983年 | 70篇 |
1982年 | 71篇 |
1981年 | 80篇 |
1980年 | 86篇 |
1979年 | 58篇 |
1978年 | 66篇 |
1977年 | 72篇 |
1976年 | 64篇 |
1975年 | 59篇 |
1974年 | 50篇 |
1973年 | 43篇 |
排序方式: 共有8814条查询结果,搜索用时 15 毫秒
171.
Grzegorz WojciechowskiMa?gorzata Ratajczak-Sitarz Andrzej KatrusiakBogumil Brzezinski 《Journal of Molecular Structure》2002,612(1):59-64
The crystals of 5,5′-dibromo-3-diethylaminomethyl-2,2′-biphenol N-oxide were studied by X-ray and FT-IR spectroscopy. Within this molecule two short OHO intramolecular hydrogen bonds are formed. The NO?H+?O− bond between the OH and the N-oxide groups is very strong, of 2.419(7) Å between the oxygen atoms. The proton potential of this hydrogen bond is flat, broad and has probably no barrier—consequently it could not be located from X-ray diffraction data. The other hydrogen bond formed between two hydroxyl groups appears asymmetrical from FT-IR spectra, and shows also relatively limited proton polarizability. The molecular conformation is non-planar, due to strong overcrowding effect between the oxygen atoms involved in the hydrogen bonds. 相似文献
172.
Anna Kowalska Zygmunt Kowalski Andrzej Kotarba Andrzej Barański 《Mikrochimica acta》1990,100(5-6):349-353
The analytical procedure of determination of Fe(II) in the presence of Fe(III) in milligram samples is proposed. A solid sample is dissolved in hydrochloric acid in argon atmosphere. Subsequently, the pH-value of the solution is fixed and Fe(III) complexed by phosphoric buffer. At the next step Fe(II) is oxidized by -molybdosilicic acid. Finally, the intensity of colouring caused by the reduced form of the acid is measured at the wavelength 770 nm. The proper treatment of the sample during oxidation, and immediately before, is decisive for the accuracy of the analysis. The method was verified by means of the analysis of synthetic magnetite. The theoretical content of Fe(II) was 24.12%, the determined one was 24.02 ± 0.10%. The method was applied to the determination of the homogeneity of an iron catalyst for ammonia synthesis. 相似文献
173.
Summary
This paper is dedicated to the study of Hilbert functions and Betti numbers of the projective varieties in a flat family. We prove that the Hilbert function H(X
y
,n),y Y-a parameter scheme-is lower semicontinuous for any fixed n. In case Y is integral and noetherian we obtain the well-known fact that the set V Y where H(X
y
,n)is maximal for all n's is open and nonempty. We show also that bi(X
y
)-the i- th Betti number of Xy—is upper semicontinuous for y V. The paper contains also a number of results concerning the relations among the various Betti numbers.Member of G.N.S.A.G.A.-C.N.R. Supported in part by M.P.I. (Italian Minstry of Education). 相似文献
174.
M. Ježabek J. Karczmarczuk M. Rożańska 《Zeitschrift fur Physik C Particles and Fields》1985,29(1):55-60
In the framework of the dual parton model we calculate the spectra of secondary antibaryons in \(\bar p\) -nucleus non-annihilation inelastic interactions. We find that the number of antibaryons in the backward hemisphere in the \(\bar p\) -nucleon centre-of-mass frame can grow with the atomic number of the nucleus. 相似文献
175.
The anomalous temperature dependence of the elastic constantsc
11 andc
66 and the elastic instability temperatureT
c are obtained in the two-dimensional microscopic model of the alkali cyanides crystals. It has been found, by means of the Michel and Naudts' theory of the translation rotation coupling, that the orientational disorder in the high-temperature phase leads to the critical softening of the shear elastic constantc
66. 相似文献
176.
Teresa Borowiak Maciej Kubicki Grzegorz Dutkiewicz Marek Pietraszkiewicz Oksana Pietraszkiewicz 《Journal of inclusion phenomena and macrocyclic chemistry》2005,51(3-4):181-189
Two newly identified supramolecular structures arise from self-assembly of the macrocyclic 1,5,9,18,22,26- hexaaza[11.11]-p-cyclophane salts with o-nitrophenol (C28H50N6)4+·4(C6H4NO2O)− (1) and with HCl (C28H52N6)6+·6Cl-·4H2O (2). In both cases two-dimensional supramolecular sheets are formed. 相似文献
177.
An HPLC procedure for determination of phenoxyalkanoic acid herbicides in water samples is proposed. The analytical column Phenomenex C18(2) Luna 5 µm and UV detection at 225 nm were applied. Baseline resolution was achieved in isocratic mode with a mobile phase consisting of acetonitrile/acetic acid (40/60, v/v), adjusted to pH 2.5. SPE sorbents – C18 BondElut, phenyl-silica, LiChrolut SAX and polymeric sorbents – were compared for isolation and preconcentration of 6 phenoxyalkanoic acid herbicides. Higher (above 95%) and more reproducible recoveries were obtained with polymeric and phenyl-silica sorbents using pure methanol for elution. The method was tested for river water samples with the limit of detection in the range of 2–3 µg L−1 (for 50 mL sample) and a reproducibility of 5% RSD. 相似文献
178.
The strategy to identify cadmium deactivation mechanism in Arabidopsis thaliana has been developed using selective and sensitive hyphenated techniques. Cadmium concentrations, in main parts of the plant, were determined by ICP-MS and total amount was found as 0.43-0.44 μg g−1 in leaves and 3.3-3.4 μg g−1 in roots. Speciation of the metal complexes in cells was investigated by SEC-ICP-MS in order to estimate the accumulation process. Phytochelatins, desglycyl-phytochelatins and phytochelatins homologues lacking the N-terminal γ-linked glutamic acid were extracted from plant and were identified by RPLC-ESI-MS. Two-dimensional chromatography allowed to link the metal complexes separated by SEC with isoforms of phytochelatins analyzed by high resolution RPLC and confirm their significant responsibility for metal accumulation. The potential of the cadmium complexes speciation indicates that obtained results could be reliable source of knowledge to confirm the information coming from the well-known genomic sequence of Arabidopsis and to estimate the role of γ-glutamyl transpeptidase in metabolism of glutathione. 相似文献
179.
W. Bocian J. Jaźwiński O. Staszewska J. W. Wiench L. Stefaniak G. A. Webb 《Chemistry of Heterocyclic Compounds》1996,32(11-12):1358-1366
Multinuclear1H,13C,14N,15N, and17O NMR data are presented for some sydnones, isosydnones and isothiosydnones. The type of valence tautomerism shown in (Fig. 1) is not observed for the compounds studied. At high pH compounds2 and12 are found to undergo transformations. The more suitable NMR parameters are reported for establishing the structures of mesoionic compounds containing three heteroatoms in the five-membered conjugated ring. Someab initio GIAO calculations on a model structure of sydnones and related compounds have been performed. 相似文献
180.
Andrzej Czerwiński Iwona Kiersztyn Michał Grdeń 《Journal of Solid State Electrochemistry》2003,7(6):321-326
The effect of temperature on hydrogen and deuterium electrosorption into a palladium LVE (limited-volume electrode) has been
investigated. A decrease in hydrogen capacity (H/Pd ratio) with increasing temperature has been observed. Temperature strongly
influences the plots of measured H(D)/Pd values vs. potential scan rate. In addition, hydrogen absorption was found to be
dependent on the composition of the surrounding electrolyte solution. These results have confirmed the hypothesis that two
different mechanisms of hydrogen desorption from the palladium electrode take place, namely electrochemical oxidation and
non-electrochemical recombination. Further, the ratio between the rate constants for these two processes has been found to
change with temperature.
Electronic Publication 相似文献