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991.
Though liquid chromatography electrospray tandem mass spectrometry (LC-ESI-MS2) has been widely used in the structural elucidation of triacylglycerols (TAG) in vegetable oils, its potentiality for the identification of TAG molecules in omega-3 rich oils remains unexplored till date. Hence, this article investigates the applicability of LC-ESI-MS2 for the structural characterization of naturally occurring TAG in cod liver oil without the TAG fractionation during the sample preparation. A computational algorithm was developed to automatically interpret the mass spectra and elucidate the TAG structures respectively. The results were compared against the lipase benchmark method. A principal component analysis study revealed that it is possible to discriminate genuine from adulterated cod liver oil. 相似文献
992.
Davydov R Osborne RL Shanmugam M Du J Dawson JH Hoffman BM 《Journal of the American Chemical Society》2010,132(42):14995-15004
Dehaloperoxidase (DHP) from Amphitrite ornata is a heme protein that can function both as a hemoglobin and as a peroxidase. This report describes the use of 77 K cryoreduction EPR/ENDOR techniques to study both functions of DHP. Cryoreduced oxyferrous [Fe(II)-O(2)] DHP exhibits two EPR signals characteristic of a peroxoferric [Fe(III)-O(2)(2-)] heme species, reflecting the presence of conformational substates in the oxyferrous precursor. (1)H ENDOR spectroscopy of the cryogenerated substates shows that H-bonding interactions between His N(ε)H and heme-bound O(2) in these conformers are similar to those in the β-chain of oxyferrous hemoglobin A (HbA) and oxyferrous myoglobin, respectively. Decay of cryogenerated peroxoferric heme DHP intermediates upon annealing at temperatures above 180 K is accompanied by the appearance of a new paramagnetic species with an axial EPR signal with g(⊥) = 3.75 and g(∥) = 1.96, characteristic of an S = 3/2 spin state. This species is assigned to Compound I (Cpd I), in which a porphyrin π-cation radical is ferromagnetically coupled with an S = 1 ferryl [Fe(IV)═O] ion. This species was also trapped by rapid freeze-quench of the ambient-temperature reaction mixture of ferric [Fe(III)] DHP and H(2)O(2). However, in the latter case Cpd I is reduced very rapidly by a nearby tyrosine to form Cpd ES [(Fe(IV)═O)(porphyrin)/Tyr(?)]. Addition of the substrate analogue 2,4,6-trifluorophenol (F(3)PhOH) suppresses formation of the Cpd I intermediate during annealing of cryoreduced oxyferrous DHP at 190 K but has no effect on the spectroscopic properties of the remaining cryoreduced oxyferrous DHP intermediates and kinetics of their decay. These observations indicate that substrate (i) binds to oxyferrous DHP outside of the distal pocket and (ii) can reduce Cpd I to Cpd II [Fe(IV)═O]. These assumptions are also supported by the observation that F(3)PhOH has only a small effect on the EPR properties of radiolytically cryooxidized and cryoreduced ferrous [Fe(II)] DHP. EPR spectra of cryoreduced ferrous DHP disclose the multiconformational nature of the ferrous DHP precursor. The observation and characterization of Cpds I, II, and ES in the absence and in the presence of F(3)PhOH provides definitive evidence of a mechanism involving consecutive one-electron steps and clarifies the role of all intermediates formed during turnover. 相似文献
993.
The physical swelling effect-induced shape recovery is studied in a thermo-responsive styrene-based shape memory polymer (SMP). Fourier transform-infrared (FTIR) test reveals no apparent change in the characteristic polar bonds of CO and O-H after immersing the SMP into toluene solvent. Based on the rubber elastic and relaxation theory, the decrease in internal energy is identified as the driving force for the shape recovery. Subsequently, the rubber elastic theory is further applied to investigate the swelling-induced free/constraint shape recovery in this SMP, and the free-energy function is utilized to analyze the swelling-induced homogenous/inhomogeneous deformation. This study provides a framework to study both the swelling effect-induced shape recovery and complex shape memory behavior in solvent-responsive SMPs. 相似文献
994.
Franz Weitzer Masaaki Naka Nataliya Krendelsberger Frank Stein Cuiyun He Yong Du Julius C. Schuster Prof. Dr. 《无机化学与普通化学杂志》2010,636(6):982-990
The constitution of the ternary system Ni/Si/Ti is investigated over the entire composition range using X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDS), differential thermal analysis (DTA), and metallography. The solid state phase equilibria are determined for 900 °C. Eight ternary phases are found to be stable. The crystal structures for the phases τ1NiSiTi, τ2Ni4Si7Ti4, τ3Ni40Si31Ti13, τ4Ni17Si7Ti6, and τ5Ni3SiTi2 are corroborated. For the remaining phases the compositions are determined as Ni6Si41Ti53 (τ6), Ni16Si42Ti42(τ7), and Ni12Si45Ti43 (τ8). The reaction scheme linking the solid state equilibria with the liquidus surface is amended to account for these newly observed phases. The discrepancies between previous experimental conclusions and modeling results are addressed. The liquidus surface is dominated by the primary crystallisation field of τ1NiSiTi, the only congruently melting phase. 相似文献
995.
The novel efficient procedure has been developed for the conjugate addition of amines to electron deficient alkenes using
the novel SO3H functionalized ionic liquid as catalyst. The results showed that the novel catalyst owned high activities for the reactions
with excellent yields within several minutes. Various amines and electron deficient alkenes were successfully transformed
to the corresponding products in the catalytic system. Operational simplicity, without need of any solvent, low cost of the
catalyst used, room temperature, high yields, reusability, excellent chemoselectivity and wide applicability are the key features
of this methodology. 相似文献
996.
The general sum-connectivity index of a graph G is defined as χ
α
(G) = ∑edges (d
u
+ d
v
)
α
, where d
u
denotes the degree of vertex u in G and α is a real number. In this report, we determine the minimum and the second minimum values of the general sum-connectivity
indices of n-vertex unicyclic graphs for non-zero α ≥ −1, and characterize the corresponding extremal graphs. 相似文献
997.
Guang-jin Wang Yun-zhi Gao Zhen-bo Wang Chun-yu Du Ge-ping Yin 《Electrochemistry communications》2010,12(8):1070-1073
Here, we report the development of a new membrane electrode assembly (MEA) structure for passive direct borohydride fuel cells (DBFCs). The anode of this type of MEA includes upper and lower parts for the electro-oxidation of borohydride and hydrogen, respectively. In comparison to conventional MEAs, the maximum power of this MEA is increased by 28.1%, and the anode polarization is decreased due to the current contribution of hydrogen electro-oxidation. The hydrogen generated from borohydride hydrolysis can be oxidized inside the cell, and the fuel coulombic efficiency reaches 100%. Therefore, high fuel utilization and cell safety can be obtained by employing this novel MEA in DBFCs. 相似文献
998.
Dr. Sylvain Antoniotti Prof. Dr. Vincent Dalla Dr. Elisabet Duñach 《Angewandte Chemie (International ed. in English)》2010,49(43):7860-7888
The continuously increasing need for novel and selective methods in organic synthesis to aid drug discovery and to address environmental concerns is a constant source of stimulation to develop novel and more efficient reaction systems. This has often resulted in a focus on transition metals, ligands, and additives, with much less attention paid to the counterion(s) of the metal cation. Recently, metal salts with one or more triflimidate counterion(s) have appeared as a unique class of catalysts that display outstanding σ‐ and π‐Lewis acid character. The highly delocalized nature of the triflimidate counterion, combined with its high steric hindrance results in virtually no nucleophilic behavior and an extremely high positive charge density on the metal cation, thus enhancing its Lewis acid character. Consequently, these metal triflimidates often outperform their metal halide or triflate analogues. This Review describes general methods for the preparation of metal triflimidate salts and their use as catalysts. 相似文献
999.
1000.
Wei Zhang Yongzhai Du Zhili Feng Jun Xu 《International Journal for Ion Mobility Spectrometry》2010,13(2):65-71
Membrane-extraction Ion Mobility Spectrometry (ME-IMS) is a feasible technique for the continuous monitoring of chlorinated hydrocarbons in water. This work studies theoretically the time-dependent characteristics of sampling and detection of trichloroethylene (TCE). The sampling is configured so that aqueous contaminants permeate through a hollow polydimethylsiloxane (PDMS) membrane and are carried away by a transport gas flowing through the membrane tube into IMS analyzer. The theoretical study is based on a two-dimensional transient fluid flow and mass transport model. The model describes the TCE mixing in the water, permeation through the membrane layer, and convective diffusion in the air flow inside membrane tube. The effect of various transport gas flow rates on temporal profiles of IMS signal intensity is investigated. The results show that fast time response and high transport yield can be achieved for ME-IMS by controlling the flow rate in the extraction membrane tube. These modeled time-response profiles are important for determining duty cycles of field-deployable sensors for monitoring chlorinated hydrocarbons in water. 相似文献