全文获取类型
收费全文 | 181篇 |
免费 | 8篇 |
专业分类
化学 | 153篇 |
力学 | 9篇 |
数学 | 8篇 |
物理学 | 19篇 |
出版年
2023年 | 1篇 |
2022年 | 10篇 |
2021年 | 9篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 3篇 |
2015年 | 4篇 |
2014年 | 10篇 |
2013年 | 5篇 |
2012年 | 11篇 |
2011年 | 7篇 |
2010年 | 8篇 |
2009年 | 6篇 |
2008年 | 14篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 7篇 |
2004年 | 6篇 |
2003年 | 11篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 4篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1973年 | 1篇 |
1933年 | 1篇 |
1923年 | 1篇 |
排序方式: 共有189条查询结果,搜索用时 15 毫秒
71.
Alessandra Barbanente Rosa Maria Iacobazzi Amalia Azzariti James D. Hoeschele Nunzio Denora Paride Papadia Concetta Pacifico Giovanni Natile Nicola Margiotta 《Molecules (Basel, Switzerland)》2021,26(11)
Two new Pt(II)-pyrophosphato complexes containing the carrier ligands cis-1,3-diaminocyclohexane (cis-1,3-DACH) and trans-1,2-diamine-4-cyclohexene (1,2-DACHEX), variants of the 1R,2R-diaminocyclohexane ligand present in the clinically used Pt-drug oxaliplatin, have been synthesized with the aim of developing new potential antitumor drugs with high bone tropism. The complexes are more stable at physiological pH than in acid conditions, with Na2[Pt(pyrophosphato)(cis-1,3-DACH)] (1) slightly more stable than [Pt(dihydrogenpyrophosphato)(1,2-DACHEX)] (2). The greater reactivity at acidic pH ensures a greater efficacy at the tumor site. Preliminary NMR studies indicate that 1 and 2 react slowly with 5’-GMP (used as a model of nucleic acids), releasing the pyrophosphate ligand and affording the bis 5’-GMP adduct. In vitro cytotoxicity assays performed against a panel of four human cancer cell lines have shown that both compounds are more active than oxaliplatin. Flow cytometry studies on HCT116 cells showed that the pyrophosphato compounds with the non-classical 1,3- and 1,4-diaminocyclohexane ligands (1 and 4) are the most capable to induce cells’ death by apoptosis and necrosis. 相似文献
72.
Romain Pertschi Elodie Brun Adiran de Aguirre Laure Guénée Amalia I. Poblador-Bahamonde Jérôme Lacour 《Helvetica chimica acta》2021,104(10):e2100122
The synthesis of spirocyclic amide acetals (33–93 %) has been achieved through Ru(II)-catalyzed condensations of N-carbamate protected pyrrolidinones with metal carbenes derived from α-diazo-β-ketoesters. Thanks to the mildness of the diazo decomposition conditions induced by a 1 : 1 combination of [CpRu(MeCN)3][BArF] and 1,10-phenanthroline, the formation of the sensitive products is possible. Full characterization of this carbonyl-ylide mediated process is provided by DFT calculations. 相似文献
73.
Hyperpolarization of cationic liposomes improves their stability in the presence of human serum albumin. 相似文献
74.
The dehydrobromination reaction 2-(p-nitrophenyl)ethyl bromide + OH? was investigated in several alkanediyl-α-ω-bis(dodecyldimethylammonium) bromide, 12-s-12,2Br? (with s = 2, 3, 4, 5, 6, 8, 10, 12) micellar solutions, in the presence of NaOH 5 × 10?3 M. The kinetic data were quantitatively rationalized within the whole surfactant concentration range by using an equation based on the pseudophase ion-exchange model and taking the variations in the micellar ionization degree caused by the morphological transitions into account. The agreement between the theoretical and the experimental data was good in all the dimeric micellar media studied, except for the 12-2-12,2Br? micellar solutions. In this case, the strong tendency to micellar growth shown by the 12-2-12,2Br? micelles could be responsible for the lack of accordance. Results showed that the dimeric micelles accelerate the reaction more than two orders of magnitude as compared to water. 相似文献
75.
We used Moiré interferometry to evaluate the strains induced on a specimen subjected to a steady tensile load. The strains were evaluated by differentiating the whole-field phase values obtained by a phase-shifting algorithm. Because the direct differentiation of even slightly noisy data may lead to unacceptable derivative errors, the strain evaluation procedure included the application of a low-pass filter, which allowed us to smooth out local fluctuations in the phase data. In addition to the noise, the strain values were also affected by systematic errors in the phase values rendered by the phase-shifting algorithm as well as uncertainties in the determination of both the interferometer sensitivity and the magnification of the imaging system. In this paper, the influence of these error sources was assessed by applying a Monte Carlo-based uncertainty propagation technique; the strain uncertainty evaluation was based on simulating a large number of times, both the phase-shifting procedure and the post-image processing (which included the filter application). We found that the strain uncertainty strongly depends on the low-pass filter used to counteract the noise effect. Although we obtained the phase data from a Moiré pattern, the procedure presented to evaluate the strain uncertainty is valid independently of the techniques used to generate the fringe pattern or the algorithm applied to exploit the phase-shifting procedure. 相似文献
76.
Karolina Strakova Dr. Amalia I. Poblador-Bahamonde Dr. Naomi Sakai Prof. Stefan Matile 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(65):14935-14942
To image the membrane tension in living cells, planarizable push–pull probes have been introduced. The first operational probe is built around two dithieno[3,2-b:2′,3′-d]thiophenes (DTTs) that are twisted out of co-planarity and polarized with donors and acceptors at either end. In this report, the chemical space available for the twisting of “flipper probes” is assessed comprehensively. The result is, not surprisingly, that every atom matters: Removal of one methyl group in the twist region yields probes that planarize already in solution and are thus less sensitive to membrane tension. Addition of one or more carbons in the same region hinders non-interfering probe alignment along lipid tails and thus partitioning into lipid bilayer membranes as well as mechanosensitivity. However, substitution of one methyl by an isosteric trifluoromethyl group in the twist region, achieved by quite substantial multistep organic synthesis, yields excitation maxima that shift over +100 nm to the red in response to increasing order of the surrounding membrane. This record redshift comes with record changes in fluorescence intensity and lifetime, high push–pull transition dipoles and higher rotational barriers. Supported by distinct dependence on viscosity and twist of the push–pull probes, kinetic competition between dark, fully twisted and bright, fully planarized relaxed excited states emerges as unifying origin of fluorescence quantum yields. 相似文献
77.
78.
Ernestina Múoz María Del Mar Graciani Rafael Jimnez Amalia Rodríguez María Luisa Moy Francisco Snchez 《国际化学动力学杂志》1994,26(2):299-307
Salt effects on the oxidation of the iron(II) complexes Fe(CN)4(bpy)2?, cis-(CN)2(bpy)2 and Fe(bpy)32+ by S2O82? as well as on the reaction Fe2+ + Co(NH3)5Cl2+ have been studied in concentrated electrolyte solutions at 298.2 K. We have gone from anion–anion to cation–cation reaction with the intermediate cases of anion–neutral and cation–anion reactions. Results show that the main cause of the kinetic salt effects observed is the interaction between supporting electrolytes and the solvent. © 1994 John Wiley & Sons, Inc. 相似文献
79.
Amalia Rodríguez Pilar Prez-tejeda Rafael Jimnez Francisco Snchez Pilar Lpez Juan Jos Calvente Marí Luisa Moy 《国际化学动力学杂志》1995,27(8):807-815
The reaction between Co(en)2(2?pzCO2)2+ (bis-ethylenediamine (2-pyrazinecarboxylato)cobalt(III)) and Fe(CN)5H2O3? (aquopentacyanoferrate(II)) to form the binuclear complex [(en)2Co( μ-pzCO2)Fe(CN)5]? has been studied in several isodielectric binary mixtures at 298.2 K (cosolvents: methanol, ethanol, tertbutyl alcohol, ethyleneglycol, and glycerol). Results were rationalized by using a free energy relationship. The importance of correcting the rate constants obtained in the different mixtures from the ionic strength influence has been shown. © 1995 John Wiley & Sons, Inc. 相似文献
80.
The effects of introducing nitrogen atoms in the fjord regions and chalcogen bridges on the conformations of overcrowded bistricyclic aromatic enes (1, X not equal to Y) (BAEs) were studied. 9-(9'H-1',8'-Diazafluoren-9'-ylidene)-9H-thioxanthene (12), 9-(9H-1',8'-diazafluoren-9'-ylidene)-9H-selenoxanthene (13), 9-(9'H-1',8'-diazafluoren-9'-ylidene)-9H-telluroxanthene (14), 9-(9' H-1',8'-fluoren-9-ylidene)-9H-xanthene (15) and 9-(9' H-1',8'-fluoren-9'-ylidene)-9H-fluorene (16) were synthesized by two-fold extrusion coupling reactions of 1,8-diaza-9H-fluoren-9-one (19)/chalcoxanthenthiones (24-27) (or /9H-fluorene-9-thione (30)). The 1',8'-diazafluoren-9-ylidene-chalcoxanthenes (11) were compared with the respective fluoren-9-ylidene-chalcoxanthenes (10). The structures of 12-16 were established by 1H, 13C, 77Se, and 125Te NMR spectroscopies. The crystal and molecular structures of 12-14 were determined by X-ray analysis. The yellow molecules of 12-14 adopted mono-folded conformations with folding dihedrals in the chalocoxanthylidene moieties of 62.7 degrees (12), 62.4 degrees (13) and 59.9 degrees (14). The folding dihedrals in the respective 1',8'-diazafluorenylidene moieties were very small, ca. 2 degrees, compared with 10.2/8.0 degrees in (9'H-fluoren-9'-ylidene)-9H-selenoxanthene (7). A 5 degree pure twist of C9=C9' in 14 is noted. The degrees of overcrowding in the fjord regions of 12-14 (intramolecular non-bonding distances) were relatively small. The degrees of pyramidalization of C9 and C9' were 17.0/3.0 degrees (12), 17.4/2.4 degrees (13) and 2.2/2.2 degrees (14). These high values in 12 and 13 stem from the resistance of the 1.8-diazafluorenylidene moiety to fold and from the limits in the degrees of folding of the thioxanthylidene and selenoxanthylidene moieties (due to shorter S10-C4a/S10-C10a and Se10-C4a/Se10-C10a bonds, as compared with the respective Te-C bonds in 14). The molecules of 15 and 16 adopt twisted conformations, a conclusion drawn from the 1H NMR chemical shifts of the fjord regions protons (H1 and H8) at 8.70 (15) and 9.00 ppm (16) and from their colors and UV/VIS spectra: 15 is purple (lambdamax = 521 nm) and 16 is orange-red. A comparison of the NMR spectra of 11 and 10 (deltadelta = delta(11) -delta(10)) showed substantial downfield shifts of 0.56-0.62 ppm of the fjord regions protons of twisted 15 and 16: deltadelta (C9) were negative (upfield): -4.0 (12), -3.7 (13), -3.4 (14), -7.1 (15), -5.0 ppm (16), while deltadelta (C9') were positive (downfield) = +6.8 (12), +6.5 (13), +5.8 (14), + 11.7 (15), +7.7 ppm (16). In 15, deltadelta (C9) - deltadelta (C9') = + 18.8 ppm, attributed to a push-pull character and significant contributions of zwitterionic structures in the twisted conformation. The 77Se and 125Te NMR signals of 13 and 14 were shifted upfield relative to the respective fluorenylidene-chalcoxanthene derivatives: deltadelta77Se = 17.2 ppm and deltadelta125Te = 22.0 ppm. The presence of the nitrogen atoms (N1' and N8') in 13 and 14 causes shielding of the selenium and tellurium nuclei. 相似文献