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41.
Dr. Benedetta Carlotti Dr. Ilijana Kikaš Prof. Irena Škorić Prof. Anna Spalletti Prof. Fausto Elisei 《Chemphyschem》2013,14(5):970-981
Time‐resolved transient absorption and fluorescence spectroscopy with nano‐ and femtosecond time resolution were used to investigate the deactivation pathways of the excited states of distyrylfuran, thiophene and pyridine derivatives in several organic solvents of different polarity in detail. The rate constant of the main decay processes (fluorescence, singlet–triplet intersystem crossing, isomerisation and internal conversion) are strongly affected by the nature [locally excited (LE) or charge transfer (CT)] and selective position of the lowest excited singlet states. In particular, the heteroaromatic central ring significantly enhances the intramolecular charge‐transfer process, which is operative even in a non‐polar solvent. Both the thiophene and pyridine moieties enhance the S1→T1 rate with respect to the furan one. This is due to the heavy‐atom effect (thiophene compounds) and to the 1(π,π)*→3(n,π)* transition (pyridine compounds), which enhance the spin‐orbit coupling. Moreover, the solvent polarity also plays a significant role in the photophysical properties of these push–pull compounds: in fact, a particularly fast 1LE*→1CT* process was found for dimethylamino derivatives in the most polar solvents (time constant, τ≤400 fs), while it takes place in tens of picoseconds in non‐polar solvents. It was also shown that the CT character of the lowest excited singlet state decreased by replacing the dimethylamino side group with a methoxy one. The latter causes a decrease in the emissive decay and an enhancement of triplet‐state formation. The photoisomerisation mechanism (singlet/triplet) is also discussed. 相似文献
42.
Leite Irena Andrianov Victor Zelencova-Gopejenko Diana Loza Einars Kazhoka-Lapsa Iveta Domracheva Ilona Stojak Marta Chlopicki Stefan Kalvins Ivars 《Chemistry of Heterocyclic Compounds》2021,57(12):1235-1235
Chemistry of Heterocyclic Compounds - 相似文献
43.
Bishnu P. Biswal Sreeramulu Valligatla Mingchao Wang Tanmay Banerjee Nabil A. Saad Bala Murali Krishna Mariserla Naisa Chandrasekhar Daniel Becker Matthew Addicoat Irena Senkovska Reinhard Berger D. Narayana Rao Stefan Kaskel Xinliang Feng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(21):6970-6974
Covalent organic frameworks (COFs) have garnered immense scientific interest among porous materials because of their structural tunability and diverse properties. However, the response of such materials toward laser‐induced nonlinear optical (NLO) applications is hardly understood and demands prompt attention. Three novel regioregular porphyrin (Por)‐based porous COFs—Por‐COF‐HH and its dual metalated congeners Por‐COF‐ZnCu and Por‐COF‐ZnNi—have been prepared and present excellent NLO properties. Notably, intensity‐dependent NLO switching behavior was observed for these Por‐COFs, which is highly desirable for optical switching and optical limiting devices. Moreover, the efficient π‐conjugation and charge‐transfer transition in ZnCu‐Por‐COF enabled a high nonlinear absorption coefficient (β=4470 cm/GW) and figure of merit (FOM=σ1/σo, 3565) value compared to other state‐of‐the‐art materials, including molecular porphyrins (β≈100–400 cm/GW), metal–organic frameworks (MOFs; β≈0.3–0.5 cm/GW), and graphene (β=900 cm/GW). 相似文献
44.
Kalina Kostova Vladimir Dimitrov Svetlana Simova Manfred Hesse 《Helvetica chimica acta》1999,82(9):1385-1399
The allylic and homoallylic alcohols 1 – 8 , prepared from (+)-camphor and (−)-fenchone, were ozonized in Et2O at −78° and treated with Et3N or LiAlH4 to give the chiral hydroxy carbonyl compounds 9 – 16 and the diols 17 – 24 , respectively (Scheme 1). In the case of the diols 19 and 24 , the formation of new chiral centers proceeded with high diastereoselectivity. These diols were prepared highly diastereoselectively also by LiAlH4 reduction of the hydroxy carbonyl compounds 11 and 16a , respectively (Scheme 2). The absolute configuration of the new chiral centers in 19 and 24 was determined by X-ray and NMR methods. The ozonization of compounds 2 , 3 , 7 , and 8 provided the relatively stable hydroxy-substituted 1,2,4-trioxolane derivatives (ozonides) 37 – 40 (Scheme 5) which were characterized by 1H- and 13C-NMR spectra, ESI-MS, and natural-abundance 17O-NMR spectra. 相似文献
45.
A combination of "black box" and "calendar-time" methods for the determination of calibration intervals of an analytical
measuring instrument is discussed. Since the methods require information on the distributions of the calibration parameters,
such information is described for an atomic absorption spectrophotometer, as an example. The hypotheses on the normal distribution
of the calibration parameters are tested using the ω2-criterion and accepted at 0.90–0.95 levels of confidence. Corresponding control charts are designed for indication of warning
and action limits of the calibration parameters, and diagnoses of outliers in further calibrations. Control charts indicate
also when the calibration should be done according to the full program of the equipment manufacturer.
Received: 15 April 2000 / Accepted: 24 July 2000 相似文献
46.
Dr. Yaoyu Liang Dr. Irena Efremenko Dr. Yael Diskin-Posner Dr. Liat Avram Prof. Dr. David Milstein 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(21):e202401702
Bond activation and catalysis using s-block metals are of great significance. Herein, a series of calcium pincer complexes with deprotonated side arms have been prepared using pyridine-based PNP and PNN ligands. The complexes were characterized by NMR and X-ray crystal diffraction. Utilizing the obtained calcium complexes, unprecedented N2O activation by metal-ligand cooperation (MLC) involving dearomatization-aromatization of the pyridine ligand was achieved, generating aromatized calcium diazotate complexes as products. Additionally, the dearomatized calcium complexes were able to activate the N−H bond as well as reversibly activate H2, offering an opportunity for the catalytic hydrogenation of various unsaturated molecules. DFT calculations were applied to analyze the electronic structures of the synthesized complexes and explore possible reaction mechanisms. This study is an important complement to the area of MLC and main-group metal chemistry. 相似文献
47.
ABSTRACTHere we report on the synthesis and mesomorphic properties of a series of imino-linked dimeric molecules. In order to improve our understanding of the structure–NTB phase correlations, we have studied the impact of geometric and electronic factors arising from varying mesogenic units, different spacer lengths and from the ratio (n/m) between the lengths of terminal chains (n) and spacer (m). From the perspective of the molecular geometry, the results show that the stability of the NTB phase results from increasing effective molecular bending and with the broadening of the mesogenic unit, in particular near the spacer, and that the n/m ratio plays a substantial role in conjunction with the specific mesogenic unit. A computational study of the electronic properties shows that a broadening of the mesogenic core in the vicinity of the spacer is associated with an increased anisotropy of the electrostatic potential distribution. Within a given series of materials our study suggests that the incidence of the NTB phase and its thermal stability are governed by the synergy of specific geometrical factors and the anisotropy of the electrostatic potential distribution of the mesogenic core. 相似文献
48.
Enhancement of the Efficacy of Photodynamic Inactivation of Candida albicans with the Use of Biogenic Gold Nanoparticles 下载免费PDF全文
Irena Maliszewska Barbara Lisiak Katarzyna Popko Katarzyna Matczyszyn 《Photochemistry and photobiology》2017,93(4):1081-1090
This study reports on successful photodynamic inactivation of planktonic and biofilm cells of Candida albicans using Rose Bengal (RB) in combination with biogenic gold nanoparticles synthesized by the cell‐free filtrate of Penicillium funiculosum BL1 strain. Monodispersed colloidal gold nanoparticles coated with proteins were characterized by a number of techniques including SEM–EDS, TEM, UV–Vis absorption and fluorescence spectroscopy, as well as Fourier transform infrared spectroscopy to be 24 ± 3 nm spheres. A Xe lamp (output power of 20mW, delivering intensity of 53 mW cm?2) was used as a light source to study the effects of RB alone, the gold nanoparticles alone and the RB‐gold nanoparticle mixture on the viability of C. albicans cells. The most effective reduction in the number of planktonic cells was found after 30 min of Xe lamp light irradiation (95.4 J cm?2) and was 4.89 log10 that is 99.99% kill for the mixture of RB with gold nanoparticles compared with 2.19 log10 or 99.37% for RB alone. The biofilm cells were more resistant to photodynamic inactivation, and the highest effective reduction in the number of cells was found after 30 min of irradiation in the presence of the RB–gold nanoparticles mixture and was 1.53 log10, that is 97.04% kill compared with 0.6 log10 or 74.73% for RB. The probable mechanism of enhancement of RB‐mediated photodynamic fungicidal efficacy against C. albicans in the presence of biogenic gold nanoparticles is discussed leading to the conclusion that this process may have a multifaceted character. 相似文献
49.
Kalina Kostova Annalaura Lorenzi-Riatsch Yoshihiko Nakashita Manfred Hesse 《Helvetica chimica acta》1982,65(1):249-251
Synthesis of Macrocyclic Lactones by Ring Enlargement Reaction Treatment of 3-(1-nitro-2-oxocyclohexyl)propanal ( 1 ) prepared by Michael addition of 2-nitrocyclohexanon and acrylaldehyde with methyltri (2-propoxy)tita-nium yielded a mixture of 2 and 3 which was converted into 6-nitro-9-decanolide ( 4 ). 相似文献
50.