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991.
Despite the general consensus concerning the role played by sodium channels in the molecular mechanism of local anesthetics, the potency of anaesthetic drugs also seems to be related with their solubility in lipid bilayers. In this respect, this work represents a thermodynamic study of benzocaine insertion into lipid bilayers of different compositions by means of molecular dynamics simulation. Thus, the free energy profiles associated with benzocaine insertion into symmetric lipid bilayers composed of different proportions of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylserine were studied. From the simulation results, a maximum in the free energy (ΔG) profile was measured in the region of the lipid/solution interface. This free energy barrier appears to be very much dependent on the lipid composition of the membrane. On the other hand, the minimum free energy (ΔG) within the bilayer remained almost independent of the lipid composition of the bilayer. By repeating the study at different temperatures, it was seen how the spontaneity of benzocaine insertion into the lipid bilayer is due to an increase in the entropy associated with the process. 相似文献
992.
Daiane Cristina Sass Vladimir Constantino Gomes Heleno Jader da Silva Barbosa Gustavo Oliveira Morais Fernando Batista Da Costa Mauricio Gomes Constantino 《Tetrahedron letters》2013,54(7):625-627
The conversion of a germacranolide structure (tagitinin C) into a furanoheliangolide one (diversifolin) was achieved by hydride conjugate addition using Stryker’s reagent. 相似文献
993.
Milena M. Andrade Aneli M. Barbosa Matheus R. Bofinger Robert F. H. Dekker Josana M. Messias Carmen L. B. Guedes Tiago Zaminelli Bruno H. de Oliveira Valéria M. G. de Lima Luiz H. Dall’Antonia 《Applied biochemistry and biotechnology》2013,170(7):1792-1806
The effects of soybean and castorbean meals were evaluated separately, and in combinations at different ratios, as substrates for lipase production by Botryosphaeria ribis EC-01 in submerged fermentation using only distilled water. The addition of glycerol analytical grade (AG) and glycerol crude (CG) to soybean and castorbean meals separately and in combination, were also examined for lipase production. Glycerol-AG increased enzyme production, whereas glycerol-CG decreased it. A 24 factorial design was developed to determine the best concentrations of soybean meal, castorbean meal, glycerol-AG, and KH2PO4 to optimize lipase production by B. ribis EC-01. Soybean meal and glycerol-AG had a significant effect on lipase production, whereas castorbean meal did not. A second treatment (22 factorial design central composite) was developed, and optimal lipase production (4,820 U/g of dry solids content (ds)) was obtained when B. ribis EC-01 was grown on 0.5 % (w/v) soybean meal and 5.2 % (v/v) glycerol in distilled water, which was in agreement with the predicted value (4,892 U/g ds) calculated by the model. The unitary cost of lipase production determined under the optimized conditions developed ranged from US$0.42 to 0.44 based on nutrient costs. The fungal lipase was immobilized onto Celite and showed high thermal stability and was used for transesterification of soybean oil in methanol (1:3) resulting in 36 % of fatty acyl alkyl ester content. The apparent K m and V max were determined and were 1.86 mM and 14.29 μmol min?1 mg?1, respectively. 相似文献
994.
J. A. Souza-Corrêa C. Oliveira L. D. Wolf V. M. Nascimento G. J. M. Rocha J. Amorim 《Applied biochemistry and biotechnology》2013,171(1):104-116
Sugarcane bagasse samples were pretreated with ozone via atmospheric O2 pressure plasma. A delignification efficiency of approximately 80 % was observed within 6 h of treatment. Some hemicelluloses were removed, and the cellulose was not affected by ozonolysis. The quantity of moisture in the bagasse had a large influence on delignification and saccharification after ozonation pretreatment of the bagasse, where 50 % moisture content was found to be best for delignification (65 % of the cellulose was converted into glucose). Optical absorption spectroscopy was applied to determine ozone concentrations in real time. The ozone consumption as a function of the delignification process revealed two main reaction phases, as the ozone molecules cleave the strong carbon–carbon bonds of aromatic rings more slowly than the weak carbon–carbon bonds of aliphatic chains. 相似文献
995.
Graciele de Oliveira Kuhn Clarissa Dalla Rosa Marceli Fernandes Silva Helen Treichel Débora de Oliveira J. Vladimir Oliveira 《Applied biochemistry and biotechnology》2013,169(3):750-760
Commercial inulinase from Aspergillus niger was immobilized in montmorillonite and then treated in pressurized propane and liquefied petroleum gas (LPG). Firstly, the effects of system pressure, exposure time, and depressurization rate, using propane and LPG, on enzymatic activity were evaluated through central composite design 23. Residual activities of 145.1 and 148.5 % were observed for LPG (30 bar, 6 h, and depressurization rate of 20 bar?min?1) and propane (270 bar, 1 h, and depressurization rate of 100 bar?min?1), respectively. The catalysts treated at these conditions in both fluids were then used for the production of fructooligosaccharides (FOS) using sucrose and inulin as substrates in aqueous and organic systems. The main objective of this step was to evaluate the yield and productivity in FOS, using alternatives for enhancing enzyme activity by means of pressurized fluids and also using low-cost supports for enzyme immobilization, aiming at obtaining a stable biocatalyst to be used for synthesis reactions. Yields of 18 % were achieved using sucrose as substrate in aqueous medium, showing the potential of this procedure, hence suggesting a further optimization step to increase the process yield. 相似文献
996.
Thermal 1,3‐dipolar cycloaddition of ethyl 4‐azido‐2,3,4‐trideoxy‐α‐D‐erythro‐hex‐2‐enopyranosides with diethyl acetylenedicarboxylate or copper‐catalyzed reaction with various functionalized alkynes gave the corresponding 1‐(ethyl 2,3,4‐trideoxy‐α‐D‐erythro‐hex‐2‐enopyranosid‐4‐yl)‐1H‐1,2,3‐triazole derivatives in quite good yields. These unsaturated compounds could be transformed into 1‐(ethyl 2,3‐di‐O‐acetyl‐4‐deoxy‐α‐D‐mannopyranosid‐4‐yl)‐1H‐1,2,3‐triazoles by a simple dihydroxylation reaction. Copper‐catalyzed condensation of ethyl 6‐O‐acetyl‐4‐azido‐2,3,4‐trideoxy‐α‐D‐erythro‐hex‐2‐enopyranoside with 1,3,5‐triethynylbenzene or 1,3,5‐tris(prop‐2‐ynyloxy)benzene afforded the corresponding trivalent glycoconjugate clusters. 相似文献
997.
Dr. Luciana M. Ramos Bruna C. Guido Catharine C. Nobrega Dr. José R. Corrêa Dr. Rafael G. Silva Dr. Heibbe C. B. de Oliveira Alexandre F. Gomes Prof. Fábio C. Gozzo Prof. Brenno A. D. Neto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(13):4156-4168
The present work describes the synthesis, characterization, and application of a new ion‐tagged iron catalyst. The catalyst was employed in the Biginelli reaction with impressive performance. High yields have been achieved when the reaction was carried out in imidazolium‐based ionic liquids (BMI ? PF6, BMI ? NTf2, and BMI ? BF4), thus showing that the ionic‐liquid effects play a role in the reaction. Moreover, the ion‐tagged catalyst could be recovered and reused up to eight times without any noticeable loss in activity. Mechanistic studies performed by using high‐resolution electrospray‐ionization quadrupole‐time‐of‐flight mass (HR‐EI‐QTOF) spectrometry and kinetic experiments indicate only one reaction pathway and rule out the other two possibilities under the development conditions. The theoretical calculations are in accordance with the proposed mechanism of action of the iron catalyst. Finally, the 37 dihydropyrimidinone derivatives, products of the Biginelli reaction, had their cytotoxicity evaluated in assays against MCF‐7 cancer cell linages with encouraging results of some derivatives, which were virtually non‐toxic against healthy cell linages (fibroblasts). 相似文献
998.
Several low molecular weight alkanes have been polymerized (polycondensed) over HSO3 F-SbF5 to yield a highly branched oily oligomer with a molecular weight range from the molecular weight of the monomer to around 700. The order of reactivity for butane and lower molecular alkanes is isobutane > n-butane > propane > ethane > methane. The reactivity is explained by the ease of attack of an acid proton derived from the acid on the alkane sigma bonds as well as the relative stability of the resulting cation formed. A cationic mechanism for this reaction is proposed. 相似文献
999.
1000.
S. A. Liebman D. H. Ahlstrom W. H. Starnes JR. F. C. Schilling 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):935-950
This study compares the use of pyrolysis hydrogenation gas chromatography (PHGC) and 13C Fourier transform nuclear magnetic resonance (FTNMR) methods for the analysis of reference polyethylene (PE) samples, ethylene-α-olefin copolymers, and specially prepared poly(vinyl chloride) (PVC) samples which were reduced to their PE skeletal structures. The nature and relative quantities of the short branches along the polymer chains were determined using both techniques. Improved high-resolution PHGC data, obtained with a fused silica capillary separation column, gave results which were in satisfactory agreement with the 13C FTNMR data. This approach confirms that detailed microstructural information can be obtained with these methods by using carefully controlled experimental conditions and appropriate reference systems. 相似文献