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101.
采用密度泛函理论(DFT)的B3LYP方法,在6-31G*和6-311+G(3df)水平上对CnB(n=1~6)团簇及其阴离子和阳离子的几何构型和电子结构进行了优化和振动频率计算.得到了CnB(n=1~6)团簇的电离能,绝热电子亲合势以及CnBδ(δ=0,±1)团簇的能隙.结果表明CnB-(n=1~6)团簇的基态构型均为线形,这与等电子的Cn簇合物的结构是一致的; CnB(n=1~6)团簇的基态构型中,除C2B为不对称的三角形,C6B为具有C2v对称性的环状结构外,其余均为线形结构.阳离子团簇中n=2、3、6的基态结构具有C2v对称性外,其它几个均为线形结构.从几何参数和振动频率上发现,采用密度泛函B3LYP方法在6-311+G(3df)和6-31G*两种基组上计算得到的键长参数和振动频率非常接近,说明B3LYP方法在计算CnB簇合物结构参数上对于基组的选择是不太敏感的.通过对CnB(n=1~6)的光电子能谱性质的研究发现,C4B容易获得一个电子形成阴离子团簇,但失去一个电子是很困难的,这与实验上观测到的结果非常吻合. 相似文献
102.
K. H. Kim J. H. Lee M. Y. Ko K. S. Shin J. S. Kang W. C. Mar J. R. Youm 《Chromatographia》2002,55(1-2):81-85
Summary A method for the assay of R-(+)- and S-(−)- metoprolol in human urine has been developed using gas chromatography-mass spectrometry.
The method involved purification by liquid-liquid extraction and derivatization with N-methyl-N-(trimethylsilyl)trifluoroacetamide
to form an O-silyl ether, followed by subsequent chiral derivatization with (−)-α-methoxy-α-(trifluoromethyl)phenylacetyl
chloride to form diastereomeric amide. The reaction was rapid and the diastereomeric derivatives were well resolved. Quantitation
was performed by selected-ion monitoring of fragment ions of the diastereomers in electron impact ionization mode. No racemization
was found during the reaction. The detection limit was 0.5 ng·mL−1. The intra-day variation ranged between 0.38 and 7.86% in relation to the measured concentration and inter-day variation
was 2.26–8.06%. The method has been applied to the determination of R-(+)-and S-(−)- metoprolol in human urine from healthy
volunteers dosed with racemic metoprolol tartrate. 相似文献
103.
Ni/γ—Al2O3,Ni/MgO,Ni/SiO2催化剂上甲烷与二氧化碳重整反应的研究 总被引:14,自引:2,他引:14
采用XRD,UV-DRS,XPS,TPR,H2-O2滴定和吡啶吸附-红外光谱等技术,研究了负载于具有不同酸碱性的γ-Al2O3,SiO2,Mgo载体上的镍催化剂表面物理化学性质,及其对甲烷与二氧化碳重整制取合成气反应催化活性的影响。结果表明,在上述负载型镍催化剂上,影响重整反应活性和积炭量的主要原因不是催化剂表面酸碱性,而是金属镍在催化剂表面的分散度。 相似文献
104.
The chiral phosphine‐oxazoline ligands 3 and 4 bearing 4‐alkoxymethyl substituents on the oxazoline ring with (R)‐configuration were prepared from L‐serine methyl ester in 66% and 33% yields, respectively. Along this synthetic pathway, the β‐hydroxylamides derived from L‐serine methyl ester and 2‐halobenzoyl chlorides were expediently converted to the corresponding oxazolines by using diethylaminosulfur trifluoride as the activation agent. Potassium diphenylphosphide was the reagent of choice for replacing the bromine atom on the phenyl ring, giving the desired oxazoline‐phosphine ligands 3 and 4 . Together with [Pd(η3‐allyl)Cl]2, ligands 3 and 4 induced an enantioselective allylic substitution reaction of 1,3‐diphenyl‐2‐pro‐penyl acetate by dimethyl malonate. Although ligands 3 and 4 exhibit the (R)‐configuration, differing from the (S)‐configuration of Pfaltz‐Helmchen‐Williams phosphine‐oxazoline ligands, all these ligands led to the same enantiotopic preference in the allylic substitution reaction. To facilitate the recovery and reuse of the phosphine‐oxazoline ligand, immobilization on Merrifield resin was attempted, albeit in low loading. 相似文献
105.
The separation of chlorthalidone enantiomers in capillary electrochromatography on an achiral stationary phase when adding a chiral selector, hydroxypropyl-β-cyclodextrin, to the mobile phase, was optimised. The goal was to investigate the feasibility of modelling retention times and resolution when during the optimisation procedure regular replacement of columns is required due to their fragility. Therefore, it is essential that the packing procedure delivers reproducible columns. The optimisation of an existing chlorthalidone separation was chosen as case study. The influence of two factors, chiral selector concentration and organic modifier content, on the responses was modelled. The experiments performed prior to modelling were defined by a central composite design. Results on different columns, obtained under identical experimental conditions, were found comparable and thus modelling was possible in situations where several columns were required to complete a design. A second-order polynomial model was built for both responses. Optimal separations were also predicted using Derringer’s desirability functions. The optimum was found at 33 mM cyclodextrin and 16% (v/v) acetonitrile on two types of columns (with different packing times) leading to a strong reduction in analysis time for an equally good separation compared to the initial conditions. Measured and predicted responses were found comparable, indicating that acceptable models were obtained. 相似文献
106.
Application of mono (6A-N-ethylenediamine-6A-deoxy) perphenylcarbamoylated β-cyclodextrin (β-CD) bonded stationary phase (CSP) in micro-high performance liquid chromatography (micro-HPLC) and pressurized capillary electrochromatography (p-CEC) was firstly presented. A series of racemic α-amidophosphonates were resolved in reversed- and normal-phase modes on this CSP. The investigated chromatographic parameters include retention factor (k′), separation factor (α) and resolution (Rs) of solutes. In addition, the structural variation of the solutes and the experimental factors affecting chiral separations have been examined, including the percentage of alcohol modifier, the linear velocity (u) of the mobile phase, electrical field strength, etc. Baseline separation was achieved for most of the entities. Hydrophobic interaction, steric effect and π-π interaction contribute to the possible mechanism. Comparative results indicate that higher Rs value up to 3.1 was found in micro-HPLC, higher efficiency up to 29,970 in p-CEC. 相似文献
107.
Mercedes Amat Marta Huguet Oriol Bassas Joan Bosch Josefa Badia Juan Aguilar 《Tetrahedron letters》2004,45(28):5355-5358
Cyclocondensation of (R)-phenylglycinol with appropriately γ-substituted δ-oxo acid derivatives provides bicyclic lactams from which the enantioselective synthesis of 1-deoxy-d-gulonojirimycin has been reported. 相似文献
108.
三菲咯啉合铁手性配合物键合DNA的立体选择性 总被引:2,自引:1,他引:2
应用光谱法研究了手性金属配合物[Fe(phen)3]^2+与小牛胸腺DNA的作用,确定了△型异构体对B型右手螺旋DNA有优先键合的立体选择性。 相似文献
109.
Hans‐Peter Kormann Günter Schmid Katrin Pelzer K. Philippot Bruno Chaudret 《无机化学与普通化学杂志》2004,630(12):1913-1918
Nanoporous alumina membranes, loaded with palladium and ruthenium nanoparticles of various size, were used for gas phase hydrogenation of 1, 3‐butadiene and for oxidation of carbon monoxide, respectively. Those membranes contain 109 ‐ 1011 pores per cm2, all running perpendicular to the surface. Membrane discs of 20 mm in diameter and only 60 μm thick, incorporated in a reactor in which the reactants can be pumped in a closed circuit through the pores, turned out to very actively catalyze hydrogenation of butadiene (Pd) and oxidation of CO (Ru). The activity of the Pd catalysts depends characteristically on the particles size, the gas flow, and of the educts ratio. As could be expected, larger particles are less active than smaller ones, whereas increasing gas flows in case of hydrogenation accelerates the reactions. Excessive hydrogen reduces selectivity with respect to the various butenes, but favours formation of butane. 相似文献