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排序方式: 共有792条查询结果,搜索用时 15 毫秒
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Beatriz Pelado Dr. Fawzi Abou‐Chahine Joaquín Calbo Dr. Rubén Caballero Dr. Pilar de la Cruz Dr. José M. Junquera‐Hernández Prof. Enrique Ortí Prof. Nikolai V. Tkachenko Prof. Fernando Langa 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5814-5825
The role of π‐conjugated molecular bridges in through‐space and through‐bond electron transfer is studied by comparing two porphyrin–fullerene donor–acceptor (D–A) dyads. One dyad, ZnP–Ph–C60 (ZnP=zinc porphyrin), incorporates a phenyl bridge between D and A and behaves very similarly to analogous dyads studied previously. The second dyad, ZnP–EDOTV–C60, introduces an additional 3,4‐ethylenedioxythienylvinylene (EDOTV) unit into the conjugated bridge, which increases the distance between D and A, but, at the same time, provides increased electronic communication between them. Two essential outcomes that result from the introduction of the EDOTV unit in the bridge are as follows: 1) faster charge recombination, which indicates enhanced electronic coupling between the charge‐separated and ground electronic states; and 2) the disappearance of the intramolecular exciplex, which mediates photoinduced charge separation in the ZnP–Ph–C60 dyad. The latter can be interpreted as a gradual decrease in electronic coupling between locally excited singlet states of D and A when introducing the EDOTV unit into the D–A bridge. 相似文献
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M. Araceli Snchez-Snchez Cristina Conde Beatriz Gmez-Aylln David Ortega-DelCampo Aristeidis Tsitiridis Daniel Palacios-Alonso Enrique Cabello 《Entropy (Basel, Switzerland)》2020,22(11)
Automated border control systems are the first critical infrastructure point when crossing a border country. Crossing border lines for unauthorized passengers is a high security risk to any country. This paper presents a multispectral analysis of presentation attack detection for facial biometrics using the learned features from a convolutional neural network. Three sensors are considered to design and develop a new database that is composed of visible (VIS), near-infrared (NIR), and thermal images. Most studies are based on laboratory or ideal conditions-controlled environments. However, in a real scenario, a subject’s situation is completely modified due to diverse physiological conditions, such as stress, temperature changes, sweating, and increased blood pressure. For this reason, the added value of this study is that this database was acquired in situ. The attacks considered were printed, masked, and displayed images. In addition, five classifiers were used to detect the presentation attack. Note that thermal sensors provide better performance than other solutions. The results present better outputs when all sensors are used together, regardless of whether classifier or feature-level fusion is considered. Finally, classifiers such as KNN or SVM show high performance and low computational level. 相似文献
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Thais R. Cruz Eliada A. Silva Douglas P. Oliveira Daniele M. Martins Patrik D.S. Gois Antonio E.H. Machado Pedro Ivo S. Maia Beatriz E. Goi Benedito S. Lima-Neto Valdemiro P. Carvalho-Jr 《应用有机金属化学》2020,34(5):e5602
Arene ruthenium(II) complexes bearing the cyclic amines RuCl2(η6-p-cymene)(pyrrolidine)] ( 1 ), [RuCl2(η6-p-cymene)(piperidine)] ( 2 ), and [RuCl2(η6-p-cymene)(peridroazepine)] ( 3 ) were successfully synthesized. Complexes 1 – 3 were fully characterized by means of Fourier transform infrared, UV–visible, and NMR spectroscopy, elemental analysis, cyclic voltammetry, computational methods, and one of the complexes was further studied by single crystal X-ray crystallography. These compounds were evaluated as catalytic precursors for ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and atom-transfer radical polymerization (ATRP) of methyl methacrylate (MMA). NBE polymerization via ROMP was evaluated using complexes 1 – 3 as precatalysts in the presence of ethyl diazoacetate (EDA) under different [NBE]/[EDA]/[Ru] ratios, temperatures (25 and 50°C), and reaction times (5–60 min). The highest yields of polyNBE were obtained with [NBE]/[EDA]/[Ru] = 5000/28/1 for 60 min at 50°C. MMA polymerization via ATRP was conducted using 1 – 3 as catalysts in the presence of ethyl-α-bromoisobutyrate (EBiB) as initiator. The catalytic tests were evaluated as a function of the reaction time using the initial molar ratio of [MMA]/[EBiB]/[Ru] = 1000/2/1 at 95°C. The increase in molecular weight as function of time indicates that complexes 1–3 were able to mediate the MMA polymerization with an acceptable rate and some level of control. Differences in the rate of polymerization were observed in the order 3 > 2 > 1 for the ROMP and ATRP. 相似文献
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Beatriz F. dos Santos Caroline F. Pereira Mikaela P. Pinz Aline R. de Oliveira George Brand Ramesh Katla Ethel A. Wilhelm Cristiane Luchese Nelson L.C. Domingues 《应用有机金属化学》2020,34(7):e5650
Functionalization of 2,1,3-benzothiadiazole (BTD) with thiols at C-5 position remains low explored. Moreover, the arylthiol-substitutions at this position are also unexplored and can not be found by a SN2 or SN1 reaction. In this sense, herein we present a new palladium-catalyzed methodology for a wide variety of unpublished 5-arylsulfanyl-benzo-2,1,3-thiadiazole derivatives synthesis with moderate to high yields using a low catalytic loading of Pd(L-Pro)2 as low-coast, and efficient catalyst in low reaction time. Besides, we concluded that the pKa of thiol species has an important role in this catalysis, mainly in the CMD like catalytic cyclo process, which strongly interferes in the reaction yields. Furthermore, arylsulfanyl-benzo-2,1,3-thiadiazoles derivatives have been assessed (in vitro) as potential acetylcholinesterase inhibitors. 相似文献
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Dr. Beatriz Feringán Jesús Cerdá Dr. Beatriz Diosdado Dr. Juan Aragó Prof. Dr. Enrique Ortí Dr. Raquel Giménez Dr. Teresa Sierra 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(66):15313-15322
The ability of a star-shaped tris(triazolyl)triazine derivative to hierarchically build supramolecular chiral columnar organizations through the formation of H-bonded complexes with benzoic acids was studied from a theoretical and experimental point of view. The combined study has been done at three different levels including the study of the structure of the triazine core, the association with benzoic acids in stoichiometry 1:3, and the assembly of 1:3 complexes in helical aggregates. Although the star-shaped triazine core crystallizes in a non-C3 conformation, the C3-symmetric conformation is theoretically predicted to be more stable and gives rise to a favorable C3 supramolecular 1:3 complex upon the interaction with three benzoic acids in their voids. In addition, calculations at different levels (DFT, PM7, and MM3) for the 1:3 host-guest complex predict the formation of large stable columnar helical aggregates stabilized by the compact packing of the interstitial acids by π–π and CH⋅⋅⋅π interactions. The acids restrict the movement of the the star-shaped triazine cores along the stacking axis causing a template effect in the self-assembly of the complex. Theoretical predictions correlate with experimental results, since the interaction with achiral or chiral 3,4,5-(4-alkoxybenzyloxy)benzoic acids gives rise to supramolecular complexes that organize in bulk hexagonal columnar mesophases stable at room temperature with intracolumnar order. The existence of supramolecular chirality in the mesophase was determined for complexes formed by acids derived from (S)-2-octanol. Chiral aggregation was also evidenced for complexes formed in dodecane. 相似文献
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Micelle‐Triggered β‐Hairpin to α‐Helix Transition in a 14‐Residue Peptide from a Choline‐Binding Repeat of the Pneumococcal Autolysin LytA 下载免费PDF全文
Héctor Zamora‐Carreras Dr. Beatriz Maestro Dr. Erik Strandberg Prof. Anne S. Ulrich Dr. Jesús M. Sanz Dr. M. Ángeles Jiménez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8076-8089
Choline‐binding modules (CBMs) have a ββ‐solenoid structure composed of choline‐binding repeats (CBR), which consist of a β‐hairpin followed by a short linker. To find minimal peptides that are able to maintain the CBR native structure and to evaluate their remaining choline‐binding ability, we have analysed the third β‐hairpin of the CBM from the pneumococcal LytA autolysin. Circular dichroism and NMR data reveal that this peptide forms a highly stable native‐like β‐hairpin both in aqueous solution and in the presence of trifluoroethanol, but, strikingly, the peptide structure is a stable amphipathic α‐helix in both zwitterionic (dodecylphosphocholine) and anionic (sodium dodecylsulfate) detergent micelles, as well as in small unilamellar vesicles. This β‐hairpin to α‐helix conversion is reversible. Given that the β‐hairpin and α‐helix differ greatly in the distribution of hydrophobic and hydrophilic side chains, we propose that the amphipathicity is a requirement for a peptide structure to interact and to be stable in micelles or lipid vesicles. To our knowledge, this “chameleonic” behaviour is the only described case of a micelle‐induced structural transition between two ordered peptide structures. 相似文献