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41.
Phytochemistry of genus Gentiana XXV: Study of the flavonic and xanthonic compounds in leaves of Gentiana X marcailhouana RY . New cinnamoyl-C-glucosyl-flavones Nine flavonic compounds: isoorientin ( 1 ), isovitexin ( 2 ), isoorientin-4′-O-β-D -glucoside ( 3 ), isovitexin-4′-O-β-D -glucoside ( 4 ), luteolin-7-O-β-D -glucoside ( 5 ), trans-cafeoyl-2′′-isoorientin ( 6 ), trans-feruloyl-2′′-isoorientin ( 7 ), trans-p-coumaroyl-2′′-isoorientin ( 8 ), p-O-β-D -glucosyl-trans-cafeoyl-2′′-isoorientin ( 9 ) and three xanthones: gentioside ( 10 ), isogentisine ( 11 ), mangiferin ( 12 ), have been identified from leaves of Gentiana X marcailhouana RY . Compounds 8 and 9 were described for the first time. The cyclitol L -(+)-bornesitol ( 13 ) has been also isolated. 相似文献
42.
43.
Par F. Soriano 《Abhandlungen aus dem Mathematischen Seminar der Universit?t Hamburg》1998,68(1):329-338
Zusammenfassung Wir verallgemeinern den Begriff der logarithmischen Klassen und wir geben eine Formel für Fixpunkte.
In this paper we generalize the concept of logarithmic class group and give a point fix formula.
Résumé Nous généralisons la notion de classes logarithmiques et donnons une formule de point fixe. 相似文献
44.
If (, M)is a factorization system on a category C, we define new classes of maps as follows: a map f:AB is in if each of its pullbacks lies in (that is, if it is stably in ), and is in M
* if some pullback of it along an effective descent map lies in M(that is, if it is locally in M). We find necessary and sufficient conditions for (, M
*) to be another factorization system, and show that a number of interesting factorization systems arise in this way. We further make the connexion with Galois theory, where M
*is the class of coverings; and include self-contained modern accounts of factorization systems, descent theory, and Galois theory. 相似文献
45.
Leeuwenburgh MA Litjens RE Codee JD Overkleeft HS van der Marel GA van Boom JH 《Organic letters》2000,2(9):1275-1277
[formula: see text] Tributyltin radical mediated cyclization of carbohydrate-derived beta-(alkynyloxy)acrylates leading to highly functionalized cis- and trans-fused bicyclic ethers of various ring sizes is described. The efficacy of the radical cyclization is nicely illustrated in the iterative construction of a trans-fused tricyclic tetrahydropyran. 相似文献
46.
García Ruano JL Gamboa AE Gutiérrez LG Martín Castro AM Rodríguez Ramos JH Yuste F 《Organic letters》2000,2(6):733-736
A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group. 相似文献
47.
Augusto Colombo Jordi Frigola Juan Parés Blas Andaluz 《Journal of heterocyclic chemistry》1989,26(4):949-955
The synthesis and structure elucidation of new pyrazolo[3,4-b][1,4]diazepines and pyrazolo[3,4-b]pyrazines are reported and the characterisation of isomers and tautomers by proton and carbon-13 nmr are discussed. In some case only NOE experiments allow us to identify the isomeric structure. 相似文献
48.
Structural sites occupied by lithium in the rhombohedral LiTi2-xZrx(PO4)3 series (0 < or = x < or = 2) have been investigated by 7Li NMR spectroscopy. At room temperature, the XRD patterns of the end-members of the series display rhombohedral R3c symmetry in LiTi2(PO4)3 and triclinic C in LiZr2(PO4)3. In the first compound, Li ions occupy M1 sites; however, in the second one Li occupy intermediate M1/2 sites. As the temperature increases, a first-order displacive transformation is detected in the triclinic phase, but a second-order/disorder transition is detected in the rhombohedral phase. From the temperature dependence of the 7Li NMR quadrupole constant (CQ) of the two compounds, the evolution of M1 and M1/2 sites occupancy in the Nasicon conduction network has been deduced. At high temperatures, analyzed phases tend toward a disordered rhombohedral phase, in which both M1 and M1/2 sites are equally populated and in which lithium mobility is favored by the existence of vacant M1 sites. According to this study, this phase can also be obtained by substituting Ti by Zr in the LiTi2-xZrx(PO4)3 series. 相似文献
49.
Juan Alfonso Redondo Rodrigo Navarro Enrique Martínez‐Campos Mónica Pérez‐Perrino Rodrigo París José Luis López‐Lacomba Carlos Elvira Helmut Reinecke Alberto Gallardo 《Journal of polymer science. Part A, Polymer chemistry》2014,52(16):2297-2305
A new synthetic strategy for the preparation of methacrylic monomers and polymers carrying acyl β‐amino groups is presented. The approach is based on the Michael addition of aliphatic amines onto asymmetric acrylic/methacrylic compounds, reacting the amine highly selectively with the acrylic unit while leaving the methacrylic moiety unreacted. The corresponding polymers are then obtained by conventional radical polymerization. The use of N,N,N′,N′‐tetraethyldiethylenetriamine (TEDETA) as the secondary amine leads to TEDETA moieties supported on polymeric chains. The new aminopolymers are sensitive to pH and to temperature exhibiting a lower critical solution temperature of between 50 and 90 °C. A further interesting feature of the new approach is that the stability toward hydrolysis of the side β‐amino acyl compounds was found to be dependent on whether an acrylamide or an acrylate is employed as the acrylic group of the asymmetric starting material. The esters exhibit an enhanced sensitivity to hydrolysis, compared to standard aliphatic esters, and decompose releasing a derivative of the amine precursor, within hours or weeks, depending on the pH and temperature conditions. The use of the amides leads to stable polymers when the same experimental conditions are applied. The novel dendronic polyamines have been proven to interact with DNA and to transfect cells with efficiency close to that obtained with polyethyleneimine vectors used as positive controls. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2297–2305 相似文献
50.
Dr. Xiaoyan Shi Felix León Ying Sim Shina Quek Gavin Hum Yi Xin Joycelyn Khoo Zi Xuan Ng Mian Yang Par How Chee Ong Varun K. Singh Dr. Rakesh Ganguly Assoc. Prof. Jack K. Clegg Dr. Jesús Díaz Felipe García 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(49):22284-22292
We have synthesized a completely new family of acyclic trimeric cyclodiphosphazane compounds comprising NH, NiPr, NtBu and NPh bridging groups. In addition, the first NH-bridged acyclic dimeric cyclophosphazane has been produced. The trimeric species display highly tuneable characteristics so that the distance between the terminal N(H)R moieties can be readily modulated by the steric bulk present in the bridging groups (ranging from ≈6 to ≈10 Å). Moreover, these species exhibit pronounced topological changes when a weak non-bonding NH⋅⋅⋅π aryl interaction is introduced. Finally, the NH-bridged chloride binding affinities have been calculated and benchmarked along with the existing experimental data available for monomeric cyclodiphosphazanes. Our results underscore these species as promising hydrogen bond donors for supramolecular host–guest applications. 相似文献