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排序方式: 共有402条查询结果,搜索用时 31 毫秒
241.
Konstantin N. Gavrilov Alexei A. Shiryaev Sergey V. Zheglov Vladislav K. Gavrilov Nikolay N. Groshkin Marina G. Maksimova Alexandr N. Volov Ilya A. Zamilatskov 《Tetrahedron》2014
A small family of P,P∗-bidentate C1-symmetric ligands containing 1,3,2-diazaphospholidine rings with stereogenic phosphorus atoms has been prepared. Palladium catalytic systems with these phosphine-diamidophosphites afforded 95% and 63% ees in asymmetric allylic substitution and desymmetrization processes, respectively. The influence of the nature of both the phosphine and diamidophosphite moieties of these compounds on the enantioselectivity is discussed. The ‘mixed-ligand approach’ in Pd-catalyzed asymmetric allylation with participation of some new P∗-monodentate diamidophosphites and PPh3 is also considered. 相似文献
242.
Jan ejka Bohumil Kratochvíl Ivana Císaov Alexandr Jegorov 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(8):o428-o430
Simvastatin, or (1S,3R,7S,8S,8aR)‐8‐{2‐[(2R,4R)‐4‐hydroxy‐6‐oxo‐3,4,5,6‐tetrahydro‐2H‐pyran‐2‐yl]ethyl}‐3,7‐dimethyl‐1,2,3,7,8,8a‐hexahydronaphthalen‐1‐yl 2,2‐dimethylbutanoate, C25H38O5, is almost isostructural with lovastatin, and the general conformational features are closely related to those of other reported crystal structures of statins. The only hydrogen bond present facilitates the formation of infinite chains of molecules along the b axis. 相似文献
243.
Galina Leonidovna Starova Maxim Sergeevitch Egorov Evgenija Sergeevna Vasiljeva Alexandr Grigorievitch Shavva 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(8):o451-o453
The conformation of the crystal of 17β‐ethoxy‐3‐methoxy‐8‐isoestra‐1,3,5(10)‐triene, C21H30O2, (I), has been established and compared with the molecular structure of a typical steroid estrogen 8‐iso‐analogue, (II). Calculations of distances separating some of the H‐atom pairs in (I) and (II) by molecular‐mechanical and semi‐empirical methods revealed the similarity of the values to the H⃛H distances obtained from X‐ray analysis. 相似文献
244.
Konstantin V. Savateev Victor V. Fedotov Vladimir L. Rusinov Svetlana K. Kotovskaya Alexandr A. Spasov Aida F. Kucheryavenko Pavel M. Vasiliev Vadim A. Kosolapov Victor S. Sirotenko Kseniya A. Gaidukova Georgiy M. Uskov 《Molecules (Basel, Switzerland)》2022,27(1)
Hypercytokinemia, or cytokine storm, is one of the severe complications of viral and bacterial infections, involving the release of abnormal amounts of cytokines, resulting in a massive inflammatory response. Cytokine storm is associated with COVID-19 and sepsis high mortality rate by developing epithelial dysfunction and coagulopathy, leading to thromboembolism and multiple organ dysfunction syndrome. Anticoagulant therapy is an important tactic to prevent thrombosis in sepsis and COVID-19, but recent data show the incompatibility of modern direct oral anticoagulants and antiviral agents. It seems relevant to develop dual-action drugs with antiviral and anticoagulant properties. At the same time, it was shown that azolo[1,5-a]pyrimidines are heterocycles with a broad spectrum of antiviral activity. We have synthesized a new family of azolo[1,5-a]pyrimidines and their condensed polycyclic analogs by cyclocondensation reactions and direct CH-functionalization and studied their anticoagulant properties. Five compounds among 1,2,4-triazolo[1,5-a]pyrimidin-7-ones and 5-alkyl-1,3,4-thiadiazolo[3,2-a]purin-8-ones demonstrated higher anticoagulant activity than the reference drug, dabigatran etexilate. Antithrombin activity of most active compounds was confirmed using lipopolysaccharide (LPS)-treated blood to mimic the conditions of cytokine release syndrome. The studied compounds affected only the thrombin time value, reliably increasing it 6.5–15.2 times as compared to LPS-treated blood. 相似文献
245.
Matiss Pals Maris Lauberts Douwe S. Zijlstra Jevgenija Ponomarenko Alexandr Arshanitsa Peter J. Deuss 《Molecules (Basel, Switzerland)》2022,27(10)
European aspen (Populus tremula (L.) (Salicaceae)) bark is a promising raw material in multi-step biorefinery schemes due to its wide availability and higher content of secondary metabolites in comparison to stem wood biomass. The main objective of this study was to investigate the major cell wall component-enriched fractions that were obtained from aspen bark residue after extractives isolation, primarily focusing on integration of separated lignin fractions and cellulose-enriched bark residue into complex valorization pathways. The “lignin first” biorefinery approach was applied using mild organosolv delignification. The varying solvent systems and process conditions for optimal delignification of residual aspen bark biomass were studied using a response surface methodology approach. The conditions for maximum process desirability at which the highest amount of lignin-enriched fraction was separated were as follows: 20-h treatment time at 117 °C, butanol/water 4:1 (v/v) solvent system with solid to liquid ratio of 1 to 10. At optimal separation conditions, lignin-enriched fraction exhibited a higher content of β–O–4 linkages vs. C–C linkages content in its structure as well as a high amount of hydroxyl groups, being attractive for its further valorization. At the same time, the content of glucose in products of cellulose-enriched residue hydrolysis was 52.1%, increased from 10.3% in untreated aspen bark. This indicates that this fraction is a promising raw material for obtaining cellulose and fermentable glucose. These results show that mild organosolv delignification of extracted tree bark can be proposed as a novel biorefinery approach for isolation of renewable value-added products with various application potentials. 相似文献
246.
Alexandr Oshchepkov Antoine Bonnefont Gaël Maranzana Elena R. Savinova Marian Chatenet 《Current Opinion in Electrochemistry》2022
Direct borohydride fuel cells (DBFC) oxidize an easily-stored energy-dense borohydride fuel (sodium borohydride: NaBH4), that in theory reacts ca. 400 mV below H2 and produces 8 electrons per BH4- anion. However, the borohydride oxidation reaction (BOR) does not fully meet these promises in practice: the electrocatalyst nature, structure and state-of-surface, and the operating conditions (pH, BH4- concentration, temperature, fluxes) noticeably influence the BOR kinetics and mechanism. Nickel and platinum-based catalysts both have assets for the BOR. DBFCs can only yield decent performance if their separator combines high ion-conductivity and efficient separation of the reactants; cation-exchange membranes, anion-exchange membranes, bipolar membranes and porous separators all have their own advantages and drawbacks. Besides the anode, the choice of separator must consider the DBFC cathode reaction, where oxygen (usually from air) or hydrogen peroxide are reduced, provided adapted catalysts are used. All these aspects drive the DBFC performance and stability/durability. 相似文献
247.
248.
Wei W. Chen Dr. Anton Cunillera Dandan Chen Dr. Sébastien Lethu Albert López de Moragas Prof. Dr. Jun Zhu Prof. Dr. Miquel Solà Dr. Ana B. Cuenca Dr. Alexandr Shafir 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):20376-20382
A metal-free C−H allylation strategy is described to access diverse functionalized ortho-allyl-iodoarenes. The method employs hypervalent (diacetoxy)iodoarenes and proceeds through the iodane-guided “iodonio-Claisen” allyl transfer. The use of allylsilanes bearing electron-withdrawing functional groups unlocks the functionalization of a broad range of substrates, including electron-neutral and electron-poor rings. The resulting ortho-allylated iodoarenes are versatile building blocks, with examples of downstream transformation including a concise synthesis of the experimental antimitotic core of Dosabulin. DFT calculations shed additional light on the reaction mechanism, with notable aspects including the aromatic character of the transition-state structure for the [3,3] sigmatropic rearrangement, as well as the highly stereoconvergent nature of the trans-product formation. 相似文献
249.
250.
Natalia E. Sedyakina Nataliya B. Feldman Oksana I. Gudkova Alexandr L. Rozofarov Vladimir N. Kuryakov Sergey V. Lutsenko 《Mendeleev Communications》2021,31(3):312-314
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