全文获取类型
收费全文 | 355篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
化学 | 285篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 29篇 |
物理学 | 40篇 |
出版年
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 12篇 |
2020年 | 10篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 11篇 |
2013年 | 24篇 |
2012年 | 18篇 |
2011年 | 15篇 |
2010年 | 12篇 |
2009年 | 18篇 |
2008年 | 8篇 |
2007年 | 19篇 |
2006年 | 14篇 |
2005年 | 13篇 |
2004年 | 20篇 |
2003年 | 14篇 |
2002年 | 16篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1993年 | 10篇 |
1992年 | 1篇 |
1991年 | 7篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有359条查询结果,搜索用时 15 毫秒
101.
Giorgio Della Sala Angelo Fontana Aldo Spinella Gianpiero Calabrese Giuliana d'Ippolito Guido Cimino 《Tetrahedron》2007,63(30):7256-7263
Secondary metabolites of the Mediterranean mollusc Scaphander lignarius from different collection sites have been investigated, proving the constant presence of a number of minor metabolites correlated to the already known lignarenones. Complete characterization of the new metabolites has been supported by enantioselective synthesis. The data are consistent with the origin of this unique class of ω-phenyloctanoids from a common polyketide pathway. 相似文献
102.
103.
Federico Berti Cristina Forzato Giada Furlan Patrizia Nitti Giuliana Pitacco Ennio Valentin Ennio Zangrando 《Tetrahedron: Asymmetry》2009,20(3):313-321
The cis- and trans-4-benzylparaconic acids and their ethyl esters were synthesized with high enantiomeric excess by hydrolysis of the corresponding diastereomeric lactonic esters using α-chymotrypsin. Thus, at low conversion values, cis- and trans-4-benzyl-5-oxo-3-tetrahydrofurancarboxylic acids were separately isolated with 99% ee and 92% ee, respectively. Both ethyl ester diastereomers were also obtained in enantiopure form. The absolute configuration of the trans-lactonic acid was assigned by 1H NMR analysis of its ester derivatives with both enantiomers of 1-(9-anthryl)-2,2,2-trifluoroethanol, while that of the cis-lactonic acid was assigned by means of X-ray analysis of a crystalline derivative. The circular dichroism curves of the products obtained are also reported. 相似文献
104.
Giuliana Gervasio Domenica Marabello Claudia Barolo Pierluigi Quagliotto Guido Viscardi 《Journal of heterocyclic chemistry》2003,40(1):129-133
The X‐ray analyses of some neutral and cationic derivatives of 2‐(4‐methylpyridin‐2‐yl)‐1H‐benzimida‐zole are reported and the structural data tentatively correlated to relative UV‐visible properties. A rotation of the γ‐picoline ring with respect to the benzimidazole moiety may be responsible of the spectral behavior. 相似文献
105.
Cardillo G Fabbroni S Gentilucci L Perciaccante R Piccinelli F Tolomelli A 《Organic letters》2005,7(4):533-536
The stereoselective anti SN2' attack of NaN3 to 3-alkenyl-3-bromo-azetidin-2-ones gave a mixture of diastereomeric azides in fast equilibrium. The [3,3]-sigmatropic rearrangement of allylic azides occurred with complete stereocontrol, allowing the equilibrium to be directed preferentially toward the (E)- or (Z)-isomer, useful precursors of 3(2'-amino)-beta-lactams. [reaction: see text] 相似文献
106.
Riassunto In questo lavoro si considerano sottoinsiemi compatti olomorficamente convessi di uno spazio analitico non ridotto e si prova
che questi sono caratterizzati, come nel caso ridotto, dagli analoghi dei teoremiA eB di Cartan. Si dà inoltre una caratterizzazione di certi morfismi in un compatto olomorficamente convesso.
Lavoro eseguito nell'ambito del G.N.S.A.G.A. del C.N.R. 相似文献
Summary In this paper we consider compact holomorphically convex subsets of a non reduced analytic space and we prove that they are characterized, as in the reduced case, by the analogous of Cartan's theoremsA andB. We give also a characterization of some morphisms in a compact holomorphically convex set.
Lavoro eseguito nell'ambito del G.N.S.A.G.A. del C.N.R. 相似文献
107.
The authors consider product rules of Gauss type for the numerical approximation of certain two-dimensional Cauchy principal value integrals with respect to generalized smooth Jacobi weight functions.Convergence results for these rules are given, and some asymptotic estimates of the remainder are established.Work sponsored by Italian Research Council and by the Ministero della Pubblica Istruzione of Italy. 相似文献
108.
Stefania Balzamo Remo Bucci Vincenzo Carunchio Giuliana Vinci 《Transition Metal Chemistry》1986,11(8):316-319
Summary The complexes between cobalt(III) and aminoacids such as glutamine, asparagine, glutamic acid, aspartic acid and proline were studied.Cobalt(III)-aminoacid systems were investigated by spectrophotometry after oxidizing the cobalt(II) complexes by sodium peroxide. The variation of the absorption spectra shows the pH dependence of the process and it is clear that the formation of the complexes occurs through oxo-intermediates.Complexation ratios, molar absorptivity values and the concentration quotients at equilibrium were determined at pH 2.2 to avoid the formation of binuclear dioxygen-cobalt complexes. 相似文献
109.
Reddi E Ceccon M Valduga G Jori G Bommer JC Elisei F Latterini L Mazzucato U 《Photochemistry and photobiology》2002,75(5):462-470
A series of derivatives of 5,10,15,20-tetrakis-(4-N-methylpyridyl)-porphine, where one N-methyl group was replaced by a hydrocarbon chain ranging from C6 to C22, were characterized for their photophysical and photosensitizing properties. The absorption and fluorescence features of the various compounds in neutral aqueous solutions were typical of largely monomeric porphyrins, with the exception of the C22 derivative, which appeared to be extensively aggregated. This was confirmed by the very low triplet quantum yield and lifetime of the C22 derivative as compared with 0.2-0.7 quantum yields and 88-167 micros lifetimes for the other porphyrins. The photophysical properties and photosensitizing activity toward N-acetyl-L-tryptophanamide of the C22 porphyrin became comparable to those typical of the other derivatives in 2% aqueous sodium dodecyl sulfate, where the C22 compound is fully monomerized. All the porphyrin derivatives exhibited at micromolar concentrations photoinactivation activity against both Staphylococcus aureus and Escherichia coli, even though the gram-negative bacteria were markedly less photosensitive. The photosensitizing efficiency was influenced by (1) the amount of cell-bound porphyrin, which increased with increasing length of the hydrocarbon chain; and (2) the tendency to undergo partial aggregation in the cell, which seems to be especially important for the C22 derivative. 相似文献
110.
Andrea Luigi Cavalot Dr. Francesca Palonta Giuliana Preti Giuseppe Nazionale Eugenia Ricci Nicola Vione Roberto Albera Giorgio Cortesina 《Journal of voice》2001,15(4):587-591
The insertion of a prosthesis and restoration with pectoralis major myocutaneous flaps for patients subjected to total pharyngolaryngectomy is a technique now universally accepted; however the literature on the subject is lacking. Our study considers 10 patients subjected to total pharyngolaryngecto-my and restoration with pectoralis major myocutaneous flaps who were fitted with vocal function prostheses and a control group of 50 subjects treated with a total laryngectomy without pectoralis major myocutaneous flaps and who were fitted with vocal function prostheses. Specific qualitative and quantitative parameters were compared. The quantitative measurement of the levels of voice intensity and the evaluation of the harmonics-to-noise ratio were not statistically significant (p > 0.05) between the two study groups at either high- or low-volume speech. On the contrary, statistically significant differences were found (p < 0.05) for the basic frequency of both the low and the high volume voice. For the qualitative analysis seven parameters were established for evaluation by trained and untrained listeners; on the basis of these parameters the control group had statistically better voices. 相似文献