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1.
A highly selective and efficient oxidative carbocyclization/borylation of enallenols catalyzed by palladium immobilized on amino-functionalized siliceous mesocellular foam (Pd-AmP-MCF) was developed for diastereoselective cyclobutenol synthesis. The heterogeneous palladium catalyst can be recovered and recycled without any observed loss of activity or selectivity. The high diastereoselectivity of the reaction is proposed to originate from a directing effect of the enallenol hydroxyl group. Optically pure cyclobutenol synthesis was achieved by the heterogeneous strategy by using chiral enallenol obtained from kinetic resolution.  相似文献   
2.
唐西林  刘仲奎 《数学杂志》1997,17(3):397-403
本文利用逆半群上的同余扩张,讨论了一类逆半群的亚直可约性,并刻划了这类逆半群的幂等元集的特征。  相似文献   
3.
近年来,羟自由基(^.OH)对DNA氧化损伤已受到广泛关注,但是很少研究^.OH对RNA的氧化损伤。其实,RNA与DNA一样,也是核酸的两大组分之一,也有许多重要功能。所以^.OH攻击RNA也会引起重后果,会造成细胞功能衰退甚至细胞死亡等。为此,我们建立了Vit.C-CuSO4-Phen-H2O2-PNA这一产生和测定^.OH氧化损伤RNA的化学发光体系,以便加强^.OH氧化损伤RNA的研究。通过对本体系测定条件的研究,得出了本体系最佳组方是:Vit.C,CuSO4,Phen,H2O2和RNA,浓度分别为350μmol/L,55μmol/L,350μmol/L,0.2mol/L和20μg/mL,体系pH为5.5,体系终体积为1mL。随后,利用本体系检测了槲皮素,咖啡酸,黄芩甙和芦丁抗^.OH氧化损伤RNA的作用,发现这四种抗氧化剂均能有效抑制^.OH氧化损伤RNA的分子机理,结果发现,^.OH清除剂硫脲几乎抑制全部发光,推测是因硫脲清除了引发剂^.OH所致;O^-.2清除剂SOD只能抑制小部分发光;^1O2清除剂叠氮化钠和苯甲酸都能抑制绝大部分发光。这些事实提示,^.OH是RNA氧化损伤的引发剂;O^-.2只是导致RNA氧化损伤的次要因素,^1O2才是导致RNA氧化损伤的最主要因素。  相似文献   
4.
Dibutyltin-3-hydroxyflavone, Bu2Sn(of), is a new fluorescence probe inhibitor of F1F0-ATPase and oxidative phosphorylation which inhibits by titration of an unidentified component of F0. Its site of action is closely related to that of the trialkyltins and of venturicidin. This F0 component is part of a pool of this component which is present in the heart mitochondrial inner membrane at levels of 5–7 nmol (mg protein)?1 [18 ± 3 Bu2Sn(of) sites per mol F1F0-ATPase]. However, ATPase activity in submitochondrial particles is near maximally inhibited by titration of approx. three Bu2Sn(of) sites per mol F1F0-ATPase. Over 60% (60–80%) of the Bu2Sn(of) interaction sites can be lost during the purification of F1F0-ATPase from submitochondrial particles. The number of Bu2Sn(of) interaction sites in various F1F0-ATPase preparations is variable. The high numbers of Bu2Sn(of) sites per mol F1F0-ATPase for heart mitochondria (18–21) and submitochondrial particles (15–19.5) decline in ATP synthase (11–15) to the low values obtained in Complex V (7–10.5) and the minimal values observed in highly purified F1F0?ATPase (3.5–5.6), thus indicating a variable dissociable component or cofactor of ATP synthase. The Bu2Sn(of) interaction site, a component of ATP synthase, is responsive to the redox status of the respiratory chain and the interaction with Bu2Sn(of) is with the reduced form of this component. Fluorescence titration studies show that this component is in redox equilibrium with the ubiquinone pool of the respiratory chain. It is proposed that this redox component serves as an inhibitor titratable cofactor pool which cycles through an F0 interaction site (or sites) via a system which serves as an energy-transfer link between the respiratory chain and ATP synthase.  相似文献   
5.
Reference analysis is one of the most successful general methods to derive noninformative prior distributions. In practice, however, reference priors are often difficult to obtain. Recently developed theory for conditionally reducible natural exponential families identifies an attractive reparameterization which allows one, among other things, to construct an enriched conjugate prior. In this paper, under the assumption that the variance function is simple quadratic, the order-invariant group reference prior for the above parameter is found. Furthermore, group reference priors for the mean- and natural parameter of the families are obtained. A brief discussion of the frequentist coverage properties is also presented. The theory is illustrated for the multinomial and negative-multinomial family. Posterior computations are especially straightforward due to the fact that the resulting reference distributions belong to the corresponding enriched conjugate family. A substantive application of the theory relates to the construction of reference priors for the Bayesian analysis of two-way contingency tables with respect to two alternative parameterizations.  相似文献   
6.
Total syntheses of the peptide enamide natural products terpeptin and aspergillamides A and B are reported. An oxidative decarboxylation-elimination protocol is employed to construct the indolic enamide moiety. Unambiguous stereochemical assignment of (−)-terpeptin is accomplished by synthesis of all possible stereochemical analogues. Select compounds have been evaluated in cell cycle inhibitor assays which show that the natural amino acid configuration of terpeptin has the most potent inhibitory activity.  相似文献   
7.
Novel catalytic systems, prepared in situ by the oxidative addition of 8‐hydroxyquinoline ligands to bis(1,5‐cyclooctadiene)nickel(0) and activated by methylaluminoxane, were studied in ethylene polymerization. When 8‐hydroxyquinoline was employed, only oligomeric products were obtained. On the contrary, 5,7‐dinitro‐8‐hydroxyquinoline gave linear polyethylene (PE), but with a modest activity. For the catalyst based on 5‐nitro‐8‐hydroxyquinoline, the productivity was largely dependent on the content of free trimethylaluminum (TMA) present in the commercial aluminoxane. The progressive optimization of the TMA/oligomeric methylaluminoxane ratio increased the productivity, which reached 700 kg of PE/(mol of Ni × h), by an order of magnitude. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 200–206, 2006  相似文献   
8.
Well‐defined polystyrene‐ (PSt) or poly(ε‐caprolactone) (PCL)‐based polymers containing mid‐ or end‐chain 2,5 or 3,5‐ dibromobenzene moieties were prepared by controlled polymerization methods, such as atom transfer radical polymerization (ATRP) or ring opening polymerization (ROP). 1,4‐Dibromo‐2‐(bromomethyl)benzene, 1,3‐dibromo‐5‐(bromomethyl)benzene, and 1,4‐dibromo‐2,5‐di(bromomethyl)benzene were used as initiators in ATRP of styrene (St) in conjunction with CuBr/2,2′‐bipyridine as catalyst. 2,5‐Dibromo‐1,4‐(dihydroxymethyl)benzene initiated the ROP of ε‐caprolactone (CL) in the presence of stannous octoate (Sn(Oct)2) catalyst. The reaction of these polymers with amino‐ or aldehyde‐functionalized monoboronic acids, in Suzuki‐type couplings, afforded the corresponding telechelics. Further functionalization with oxidable groups such as 2‐pyrrolyl or 1‐naphthyl was attained by condensation reactions of the amino or aldehyde groups with low molecular weight aldehydes or amines, respectively, with the formation of azomethine linkages. Preliminary attempts for the synthesis of fully conjugated poly(Schiff base) with polymeric segments as substituents, by oxidative polymerization of the macromonomers, are presented. All the starting, intermediate, or final polymers were structurally analyzed by spectral methods (1H NMR, 13C NMR, and IR). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 727–743, 2006  相似文献   
9.
在添加了15%Li_2O的NdMO_3(M=Cr、Mn、Fe、Co、Ni)上进行了甲烷氧化偶联(OCM)反应研究.通过改变反应气中CH_4:O_2浓度比,在氧化态和“脱氧态”催化剂上的CH_4脉冲反应,探讨了表面吸附氧和晶格氧在OCM反应中的作用以及NdMO_3中不同金属离子(M)对OCM反应活性的影响等.  相似文献   
10.
徐法强  侯瑞玲 《分子催化》1997,11(4):247-252
以碳酸锶为甲烷吸附活化的模型催化剂,用切换变应答、CH4(CO2)-TPD等技术,对甲烷的吸附、碱性对催化剂性能的影响进行了研究,结果表明,甲烷在碳酸锶上的活化显示出明显的酸碱活化机理特征,瞬变应答及TPD结果均证明,甲烷在碳酸锶表面有较强的吸附,其脱附温度约310℃,关联结果表明,甲烷转化率及C2烃收率与催化剂表面SrO碱性中心浓度有非常一致的顺变关系,因此催化剂表面的酸碱中心可能是甲烷的选择活  相似文献   
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