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401.
Wang tiles are square tiles with colored edges. We construct an aperiodic set of Wang tiles that is strongly deterministic
in the sense that any two adjacent edges of a tile determine the tile uniquely. Consequently, the tiling group of this set
is not hyperbolic and it acts discretely and co-compactly on a CAT(0) space.
Submitted: February 1998, revised: October 1998. 相似文献
402.
The FTIR spectra of solid resin-free samples of chemically modified Norway spruce wood were recorded. Correlations were noted between spectral and hydrogen bond structure, chemical modification, fibre crystallinity and macroscopic softening point. 相似文献
403.
404.
High‐throughput method for simultaneous quantification of N,C and S stable isotopes and contents in organics and soils 下载免费PDF全文
405.
Toni Mäkelä Anniina Kiesilä Dr. Elina Kalenius Prof. Kari Rissanen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14264-14272
Synthesis and ion‐pair complexation properties of novel ditopic bis‐urea receptors based on dibenzo[21]crown‐7 ( R1 ) and dibenzo[24]crown‐8 ( R2 ) scaffolds have been studied in the solid state, solution, and gas phase. In a 4:1 CDCl3/[D6]DMSO solution, both receptors clearly show positive heterotropic cooperativity toward halide anions when complexed with Rb+ or Cs+, with the halide affinity increasing in order I?<Br?<Cl?. In solution, the rubidium complexes of both receptors have higher halide affinities compared to the caesium complexes. However, Rb+ and Cs+ complexes of R2 show stronger affinities toward all the studied anions compared to the corresponding cationic complexes of R1 . Similar selectivity of the receptors toward the studied ion pairs was also observed also in the gas phase by competition experiments with mass spectrometry. A total of eight crystal structures with different rubidium and caesium halides and oxyanions were obtained in addition to the crystal structure of R2?BaCl2 . The selectivity observed in solution and in the gas phase is explainable by the conformational differences observed in the crystal structures of ion‐pair complexes with R1 and R2 . In the solid state, R1 has an open conformation due to the asymmetric crown‐ether scaffold, whereas R2 has a compact, folded conformation. Computational studies of the ion‐pair complexes of R2 show that the interaction energies of the complexes increase in the order CsI<CsBr<CsCl<RbCl, supporting the selectivity observed in solution and the gas‐phase. 相似文献
406.
407.
CF3: An Electron‐Withdrawing Substituent for Aromatic Anion Acceptors? “Side‐On” versus “On‐Top” Binding of Halides 下载免费PDF全文
Prof. Dr. Markus Albrecht Dr. Hai Yi Okan Köksal Prof. Dr. Gerhard Raabe Dr. Fangfang Pan Dr. Arto Valkonen Prof. Dr. Kari Rissanen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(20):6956-6963
The ability of multiple CF3‐substituted arenes to act as acceptors for anions is investigated. The results of quantum‐chemical calculations show that a high degree of trifluoromethyl substitution at the aromatic ring results in a positive quadrupole moment. However, depending on the polarizability of the anion and on the substitution at the arene, three different modes of interaction, namely Meisenheimer complex, side‐on hydrogen bonding, or anion–π interaction, can occur. Experimentally, the side‐on as well as a η2‐type π‐complex are observed in the crystal, whereas in solution only side‐on binding is found. 相似文献
408.
Kristen Lewis Kari Copeland Glake Hill 《International journal of quantum chemistry》2014,114(24):1678-1684
The redox properties of DNA play an influential role in several important processes such as DNA mutation and the interaction of DNA with drugs. Structural changes in DNA nucleobases from its canonical form to its tautomeric forms can alter these properties and may lead to DNA mutation due to altered base‐pairing properties. Experimental results for the standard value of DNA redox properties vary due to choice of methodology and solvent. Theoretical determination of these properties is helpful in pinpointing standard values but still vary depending on methodology and chosen experimental benchmark. However, it is of importance to identify the overall trend of electron mobility within DNA while providing reliable standard values for redox reactions. In this work, we present the results of theoretical calculations for redox properties. Using the thermodynamic cycle, we can approximate reliable values. We report the electron affinities, ionization potentials, and redox potential for the canonical DNA nucleobases and their rare tautomers. For each of these properties, we evaluate its overall trend to gain a greater understanding of the role that electron attachment and electron mobility have within the DNA strand. All calculations are computed at the M06‐2X/6–31++G(d,p) level of theory. © 2014 Wiley Periodicals, Inc. 相似文献
409.
410.
Single‐Shell Carbon‐Encapsulated Iron Nanoparticles: Synthesis and High Electrocatalytic Activity for Hydrogen Evolution Reaction 下载免费PDF全文
Mohammad Tavakkoli Dr. Tanja Kallio Olivier Reynaud Prof. Albert G. Nasibulin Dr. Christoffer Johans Dr. Jani Sainio Dr. Hua Jiang Prof. Esko I. Kauppinen Prof. Kari Laasonen 《Angewandte Chemie (International ed. in English)》2015,54(15):4535-4538
Efficient hydrogen evolution reaction (HER) through effective and inexpensive electrocatalysts is a valuable approach for clean and renewable energy systems. Here, single‐shell carbon‐encapsulated iron nanoparticles (SCEINs) decorated on single‐walled carbon nanotubes (SWNTs) are introduced as a novel highly active and durable non‐noble‐metal catalyst for the HER. This catalyst exhibits catalytic properties superior to previously studied nonprecious materials and comparable to those of platinum. The SCEIN/SWNT is synthesized by a novel fast and low‐cost aerosol chemical vapor deposition method in a one‐step synthesis. In SCEINs the single carbon layer does not prevent desired access of the reactants to the vicinity of the iron nanoparticles but protects the active metallic core from oxidation. This finding opens new avenues for utilizing active transition metals such as iron in a wide range of applications. 相似文献