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991.
Christine Artner Matthias Czakler Prof. Dr. Ulrich Schubert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(2):493-498
Mixed‐metal clusters have been obtained from the reaction of titanium alkoxides with either strontium or lead acetate and methacrylic acid. The structures of the clusters are derived from the metallacycle Ti8O8(methacrylate)16. The Sr and Pb atoms in Sr2Ti8O8X2(OOCMe)2(methacrylate)16 (X: acetate or OiPr) and Pb2Ti8O8(OBu)2X2(methacrylate)16(BuOH)2 (X: acetate or methacrylate) occupy the central cavity of the Ti8O8 ring. In addition to the crown‐ether‐like coordination of the ring oxygen atoms to the Sr or Pb atoms, bridging carboxylate ligands support the coordination of the latter atoms. In the compound Pb2Ti6O5(OiPr)3X(methacrylate)14 (X: OiPr or methacrylate), the lead atoms are coordinated by a fragment of the Ti8O8(methacrylate)16 metallacycle. 相似文献
992.
Aqueous Self‐Assembly and Cation Selectivity of Cobaltabisdicarbollide Dianionic Dumbbells 下载免费PDF全文
Màrius Tarrés Prof. Clara Viñas Patricia González‐Cardoso Dr. Mikko M. Hänninen Prof. Reijo Sillanpää Vladimír Ďorďovič Dr. Mariusz Uchman Prof. Francesc Teixidor Dr. Pavel Matějíček 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6786-6794
The anion [3,3′‐Co(C2B9H11)2]? ([COSAN]?) produces aggregates in water. These aggregates are interpreted to be the result of C?H???H?B interactions. It is possible to generate aggregates even after the incorporation of additional functional groups into the [COSAN]? units. The approach is to join two [COSAN]? anions by a linker that can adapt itself to act as a crown ether. The linker has been chosen to have six oxygen atoms, which is the ideal number for K+ selectivity in crown ethers. The linker binds the alkaline metal ions with different affinities; thus showing a distinct degree of selectivity. The highest affinity is shown towards K+ from a mixture containing Li+, Na+, K+, Rb+ and Cs+; this can be indicative of pseudo‐crown ether performance of the dumbbell. One interesting possibility is that the [COSAN]? anions at the two ends of the linker can act as a hook‐and‐loop fastener to close the ring. This facet is intriguing and deserves further consideration for possible applications. The distinct affinity towards alkaline metal ions is corroborated by solubility studies and isothermal calorimetry thermograms. Furthermore, cryoTEM micrographs, along with light scattering results, reveal the existence of small self‐assemblies and compact nanostructures ranging from spheres to single‐/multi‐layer vesicles in aqueous solutions. The studies reported herein show that these dumbbells can have different appearances, either as molecules or aggregates, in water or lipophilic phases; this offers a distinct model as drug carriers. 相似文献
993.
Stereochemistry and Conformation of Skyllamycin,a Non‐Ribosomally Synthesized Peptide from Streptomyces sp. Acta 2897 下载免费PDF全文
Dipl.‐Chem. Vivien Schubert Dr. Florent Di Meo Dr. Pierre‐Loïc Saaidi Dr. Stefan Bartoschek Prof. Dr. Hans‐Peter Fiedler Prof. Dr. Patrick Trouillas Prof. Dr. Roderich D. Süssmuth 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4948-4955
Skyllamycin is a non‐ribosomally synthesized cyclic depsipeptide from Streptomyces sp. Acta 2897 that inhibits PDGF‐signaling. The peptide scaffold contains an N‐terminal cinnamoyl moiety, a β‐methylation of aspartic acid, three β‐hydroxylated amino acids and one rarely occurring α‐hydroxy glycine. With the exception of α‐hydroxy glycine, the stereochemistry of the amino acids was assigned by comparison to synthetic reference amino acids applying chiral GC‐MS and Marfey‐HPLC analysis. The stereochemistry of α‐hydroxy glycine, which is unstable under basic and acidic conditions, was determined by conformational analysis, employing a combination of data from NOESY‐NMR spectroscopy, simulated annealing and free MD simulations. The simulation procedures were applied for both R‐ and S‐configured α‐hydroxy glycine of the skyllamycin structure and compared to the NOESY data. Both methods, simulated annealing and free MD simulations independently support S‐configured α‐hydroxy glycine thus enabling the assignment of all stereocenters in the structure of skyllamycin and devising the role of two‐component flavin dependent monooxygenase (Sky39) as S‐selective. 相似文献
994.
Energy Transfer in Aminonaphthalimide‐Boron‐Dipyrromethene (BODIPY) Dyads upon One‐ and Two‐Photon Excitation: Applications for Cellular Imaging 下载免费PDF全文
Dr. Daniel Collado Patricia Remón Dr. Yolanda Vida Dr. Francisco Najera Dr. Pratik Sen Dr. Uwe Pischel Prof. Ezequiel Perez‐Inestrosa 《化学:亚洲杂志》2014,9(3):797-804
Aminonaphthalimide–BODIPY energy transfer cassettes were found to show very fast (kEET≈1010–1011 s?1) and efficient BODIPY fluorescence sensitization. This was observed upon one‐ and two‐photon excitation, which extends the application range of the investigated bichromophoric dyads in terms of accessible excitation wavelengths. In comparison with the direct excitation of the BODIPY chromophore, the two‐photon absorption cross‐section δ of the dyads is significantly incremented by the presence of the aminonaphthalimide donor [δ≈10 GM for the BODIPY versus 19–26 GM in the dyad at λexc=840 nm; 1 GM (Goeppert–Mayer unit)=10?50 cm4 s molecule?1 photon?1]. The electronic decoupling of the donor and acceptor, which is a precondition for the energy transfer cassette concept, was demonstrated by time‐dependent density functional theory calculations. The applicability of the new probes in the one‐ and two‐photon excitation mode was demonstrated in a proof‐of‐principle approach in the fluorescence imaging of HeLa cells. To the best of our knowledge, this is the first demonstration of the merging of multiphoton excitation with the energy transfer cassette concept for a BODIPY‐containing dyad. 相似文献
995.
Patricia Gramming Johan Sundberg Sten Ternstrm Rolf Leanderson William H. Perkins 《Journal of voice》1988,2(2)
Changes in mean fundamental frequency accompanying changes in loudness of phonation are analyzed in 9 professional singers, 9 nonsingers, and 10 male and 10 female patients suffering from vocal functional dysfunction. The subjects read discursive texts with noise in earphones, and some also at voluntarily varied vocal loudness. The healthy subjects phonated as softly and as loudly as possible at various fundamental frequencies throughout their pitch ranges, and the resulting mean phonetograms are compared. Mean pitch was found to increase by about half-semitones per decibel sound level. Grossly, the subject groups gave similar results, although the singers changed voice pitch more than the nonsingers. The voice pitch changes may be explained as passive results of changes of subglottal pressure required for the sound level variation. 相似文献
996.
Veronica Armendariz Isaac Herrera Jose R. peralta-videa Miguel Jose-yacaman Horacio Troiani Patricia Santiago Jorge L. Gardea-Torresdey 《Journal of nanoparticle research》2004,6(4):377-382
Oat (Avena sativa) biomass was studied as an alternative to recover Au(III) ions from aqueous solutions and for its capacity to reduce Au(III) to Au(0) forming Au nanoparticles. To study the binding trend of Au(III) to oat and the possible formation of Au nanoparticles, the biomass and a solution of Au(III) were reacted for a period of 1 h at pH values ranging from 2 to 6. The results demonstrated that Au(III) ions were bound to oat biomass in a pH-dependent manner, with the highest adsorption (about 80%) at pH 3. HRTEM studies showed that oat biomass reacted with Au(III) ions formed Au nanoparticles of fcc tetrahedral, decahedral, hexagonal, icosahedral multitwinned, irregular, and rod shape. To our knowledge, this is the second report about the production of nanorods as a product of the reaction of a Au(III) solution with a biological material. These studies also showed that the pH of the reaction influenced the nanoparticle size. The smaller nanoparticles and the higher occurrence of these were observed at pH values of 3 and 4, whereas the larger nanoparticles were observed at pH 2. 相似文献
997.
Hydrosilylation of alkenes catalysed by rhodium complexes immobilized on silica via a pyridine group
2-(2-Trimethoxysilylethyl)pyridine, together with 3-methcryloxypropyltrimethoxysilane, was used to prepare a series of rhodium carbonyl complexes bound to silica via a pyridine group. The rhodium complex Rh2(CO)4Cl2 (Rh2) was used as the starting compound, and the immobilized complexes were prepared by four different routes which yielded both surface-bonded complexes and complexes bonded within the silicate matrix. These complexes were efficient catalysts of hydrosilylation of octene by triethxysilane. All the immobilized complexes were more than their homogeneous analogues and some could be re-used. 相似文献
998.
999.
T. Bauer M. Schubert R. Lange R. Sh. Abiev 《Russian Journal of Applied Chemistry》2006,79(7):1047-1056
The review discusses the present-day state of research, industrial experience, and prospects for application of reactors with a multichannel catalyst for gas-fluid catalytic reactions. 相似文献
1000.
Helmut Fric Michael Puchberger Ulrich Schubert 《Journal of Sol-Gel Science and Technology》2006,40(2-3):155-162
The structural chemistry of crystalline adducts M2(OR)8(amine)2 (M = Ti: OR = OiPr, amine = NH2CH2Ph, NH2Bu; M = Ti: OR = OEt, amine = piperidine; M = Zr: OR = OiPr, amine = NH2CH2Ph, NH2C6H11) is discussed. The adducts were obtained by reaction of Ti(OEt)4 or M(OiPr)4 with primary or secondary amines. The monoamine adducts are centrosymmetric dimers in which the amines are coordinated axially
to the M2μ-OR)2 ring and hydrogen-bonded to neighboring alkoxo ligands. The adducts are sufficiently stable if the hydrogen bond is strong.
15N NMR studies revealed that the amines are also coordinated in solution. Coordination polymers were obtained when diamines
with two terminal NH2 groups are reacted with Ti(OiPr)4. The general structure is the same as that of Ti2(OiPr)8(RNH2)2. However, the diamines bridge the Ti2(OiPr)8 units. When Zr(OiPr)4 was reacted with NH2CH2CH2NHMe, the adduct Zr2(OiPr)8[NH2CH2CH2NHMe]2 was obtained where only the NH2 group is coordinated. 相似文献