全文获取类型
收费全文 | 2257篇 |
免费 | 17篇 |
国内免费 | 8篇 |
专业分类
化学 | 1935篇 |
晶体学 | 5篇 |
力学 | 13篇 |
数学 | 70篇 |
物理学 | 259篇 |
出版年
2023年 | 5篇 |
2022年 | 3篇 |
2021年 | 8篇 |
2020年 | 15篇 |
2019年 | 7篇 |
2018年 | 15篇 |
2017年 | 9篇 |
2016年 | 25篇 |
2015年 | 13篇 |
2014年 | 23篇 |
2013年 | 53篇 |
2012年 | 146篇 |
2011年 | 286篇 |
2010年 | 88篇 |
2009年 | 40篇 |
2008年 | 202篇 |
2007年 | 215篇 |
2006年 | 207篇 |
2005年 | 202篇 |
2004年 | 147篇 |
2003年 | 127篇 |
2002年 | 105篇 |
2001年 | 66篇 |
2000年 | 72篇 |
1999年 | 20篇 |
1998年 | 19篇 |
1997年 | 11篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 18篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1980年 | 3篇 |
1976年 | 3篇 |
1974年 | 4篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1969年 | 3篇 |
1968年 | 2篇 |
1967年 | 5篇 |
1966年 | 5篇 |
排序方式: 共有2282条查询结果,搜索用时 31 毫秒
141.
Different factors affecting the efficiency of the ultrasonic depolymerization of the high-molecular-weight carboxymethylated chitin-glucan prepared from the fungal mycelium of Aspergillus niger have been investigated. The influence of the following parameters was examined: concentration of the chitin-glucan complex, duration of ultrasonic irradiation, reaction temperature and volume of the ultrasonicated solution. The optimized conditions for the efficient ultrasonic depolymerization include: polysaccharide concentration--0.2 mg ml-1; volume of the sonicated solution--25 ml; duration of the sonication--10 min; and constant cooling of the sonicated sample in an ice-water bath. 相似文献
142.
Small amounts of lead in the presence of large amounts of uranium can be determined by complexing the lead with nitrilotriacetic acid in aqueous solution at about pH 6 (adjusted with hexamine)and extracting the uranium into a chloroform solution of diphenylacetic acid. The aqueous phase is then acidified the lead determined polarographically. 相似文献
143.
E.?BrigattiEmail author J. S.?Sá Martins I.?Roditi 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,45(4):529-532
We use a microscopic model of population dynamics, a modified version
of the well known Penna model, to study some aspects of microevolution. This
research is motivated by recent reports on the effect of selective hunting on the
gene pool of bighorn sheep living in the Ram Mountain region, in Canada. Our
model finds a sharp transition in the structure of the gene pool as some
threshold for the number of animals hunted is reached. 相似文献
144.
[reaction: see text] Electrooptical sensors consisting of a conjugated chromophore undergoing a change in color and a redox-active moiety such as quinone fused to the chromophore were synthesized. Strong changes in colorimetric and electrochemical properties were observed in the presence of inorganic anions. A unique anion-specific response was observed for fluoride, pyrophosphate, and acetate. DFT (B3LYP/6-31G) calculations performed for both "on/off" states of a sensor-fluoride model are in good agreement with the observed electrochemical and spectroscopic data. 相似文献
145.
Vanícková M Lehotay J Cizmárik J Labuda J 《Bioelectrochemistry (Amsterdam, Netherlands)》2005,66(1-2):125-127
DNA-drug association interaction at the DNA modified screen-printed electrode for 1-methyl-2-piperidinoethylester of 2-hexoxyphenylcarbamic acid was found leading to an accumulation of the drug within the DNA layer. A procedure for the determination of drug in blood serum matrix using the protein precipitation and voltammetric measurement of the electroactive drug with the DNA biosensor was obtained and an effort was done to apply it for an assay of the drug enzymatic degradation in human and rabbit sera at 37 degrees C. 相似文献
146.
The emission frequency of a diode laser submitted to a frequency-dependent optoelectronic feedback is observed to have more than one stable operation point together with a stable power emission. This is, to our knowledge, the first observation of bistability exclusively in the frequency of an optical system. The experiment was carried out with a semiconductor laser coupled to the cesium D2 line by an orthogonally polarized frequency-sensitive optical feedback. 相似文献
147.
In this paper we compute the line integral of a complex function on a rectifiable cycle homologous to zero obtaining a Green’s
formula with multiplicities that involves the
of the function and the index of the cycle. We consider this formula in several settings and we obtain a sharp version in
terms of the Lebesgue integrability properties of the partial derivatives of the function. This result depends on the proven
fact that the index of a rectifiable cycle is square integrable with respect to the planar Lebesgue measure.
The work of both authors is partially supported by grants 2000SGR-00059, 2001SGR 00172 of Generalitat de Catalunya and BFM
2002-04072-C02-02 of Ministerio de Ciencia y Tecnologia 相似文献
148.
E.?BrigattiEmail author J.?S.?Sá Martins I.?Roditi 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,42(3):431-434
We investigate the scaling properties of the Penna model, which has become a popular tool for the study of population dynamics and evolutionary problems in recent years. We find that the model generates a normalised age distribution for which a simple scaling rule is proposed, that is able to reproduce qualitative features for all genome sizes.Received: 9 October 2004, Published online: 23 December 2004PACS:
87.23.Cc Population dynamics and ecological pattern formation - 89.75.Da Systems obeying scaling laws - 05.10.Ln Monte Carlo methods 相似文献
149.
Dubnicková M Yaradaikin S Lacko I Devínsky F Gordeliy V Balgavý P 《Colloids and surfaces. B, Biointerfaces》2004,34(3):161-164
The influence of 1,4-butanediamonium-N,N'-dialkyl-N,N,N',N'-tetramethyl dibromides (CmA, m = 7-16 is the number of alkyl carbons) on the egg yolk phosphatidylcholine (EYPC) bilayer thickness and lipid surface area at the bilayer-aqueous phase interface is studied using X-ray diffraction on fluid lamellar CmA + EYPC + H2O phases as a function of CmA:EYPC and H2O:EYPC molar ratios and the alkyl chain length m. At the constant CmA:EYPC = 0.4 and H2O:EYPC = 18 molar ratios, the CmA induced bilayer thickness decrease shows a minimum and the lipid surface area increase a maximum at the alkyl chain length m = 9. The obtained results are discussed in the context of a structural perturbation model of the cut-off effect in biological potencies of surfactants which occurs when increasing the alkyl substituent chain length above the critical value. 相似文献
150.
The Kováts retention indices of all 93 acyclic octenes on polydimethylsiloxane and squalane as stationary phases as well as their mass spectra were measured. The means of gas chromatography-mass spectrometry (GC-MS) were used for confirmation of GC identification as well as for mass spectrometric deconvolution of the majority of gas chromatographic unseparated isomeric octene peaks. The distinction between corresponding E and Z acyclic octenes, that is either difficult or even impossible by means of GC-MS, was obtained on the basis of larger temperature coefficients of retention indices for Z isomeric octenes than for corresponding E isomers. The retention data expressed as homomorphy factors were correlated with the degree of branching, position of double bond, and position of alkyl group with respect to the double bond of acyclic octenes, and the structure-retention relationships were formulated. The 81 acyclic octenes were identified in FCC gasoline. 相似文献