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排序方式: 共有929条查询结果,搜索用时 78 毫秒
921.
Ralf SchirrmacherPhilippe Lucas Esther SchirrmacherBjörn Wängler Carmen Wängler 《Tetrahedron letters》2011,52(16):1973-1976
Strained tricyclic ring systems such as epoxides are rarely used as precursors for the introduction of anionic fluorine-18 into organic compounds intended for positron emission tomography (PET). Here we report the alpha selective ring opening of epoxides for the introduction of fluorine-18 into small as well as larger biomolecules via 1- and 2-step protocols. [18F]fluoromisonidazole ([18F]MISO), a tracer for hypoxia imaging, and the tumor targeting peptide Tyr3-octreotate (TATE) were radiolabeled using epoxide opening reactions. In the latter case, the new prosthetic labeling synthon 4-(3-[18F]fluoro-2-hydroxypropoxy)benzaldehyde ([18F]FPB) has been used for 18F-introduction. 相似文献
922.
923.
Hua Y Ramabhadran RO Uduehi EO Karty JA Raghavachari K Flood AH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(1):312-321
Triazolophanes are used as the venue to compete an aliphatic propylene CH hydrogen‐bond donor against an aromatic phenylene one. Longer aliphatic C? H ??? Cl? hydrogen bonds were calculated from the location of the chloride within the propylene‐based triazolophane. The gas‐phase energetics of chloride binding (ΔGbind, ΔHbind, ΔSbind) and the configurational entropy (ΔSconfig) were computed by taking all low‐energy conformations into account. Comparison between the phenylene‐ and propylene‐based triazolophanes shows the computed gas‐phase free energy of binding decreased from ΔGbind=?194 to ?182 kJ mol?1, respectively, with a modest enthalpy–entropy compensation. These differences were investigated experimentally. An 1H NMR spectroscopy study on the structure of the propylene triazolophane’s 1:1 chloride complex is consistent with a weaker propylene CH hydrogen bond. To quantify the affinity differences between the two triazolophanes in dichloromethane, it was critical to obtain an accurate binding model. Four equilibria were identified. In addition to 1:1 complexation and 2:1 sandwich formation, ion pairing of the tetrabutylammonium chloride salt (TBA+ ? Cl?) and cation pairing of TBA+ with the 1:1 triazolophane–chloride complex were observed and quantified. Each complex was independently verified by ESI‐MS or diffusion NMR spectroscopy. With ion pairing deconvoluted from the chloride–receptor binding, equilibrium constants were determined by using 1H NMR (500 μM ) and UV/Vis (50 μM ) spectroscopy titrations. The stabilities of the 1:1 complexes for the phenylene and propylene triazolophanes did not differ within experimental error, ΔG=(?38±2) and (?39±1) kJ mol?1, respectively, as verified by an NMR spectroscopy competition experiment. Thus, the aliphatic CH donor only revealed its weaker character when competing with aromatic CH donors within the propylene‐based triazolophane. 相似文献
924.
925.
Esther Amevor Simona Bronco Giambattista Consiglio Silvia Di Benedetto 《Macromolecular Symposia》1995,89(1):443-454
Strictly alternating copolymers between olefins and carbon monoxide are synthesized using cationic palladium catalysts modified by phosphorus or nitrogen ligands. Basic chelate diphosphines as the ligand allow the regioregular copolymerization of aliphatic olefins thus affording, e.g. in the case of propene, poly(1-oxo-2-methyltrimethylene). Steric control of the copolymerization process towards the production of overwhelmingly isotactic copolymers is possible particularly when using atropisomeric ligands. In the case of styrene as the substrate and for all ligands employed the copolymerization process is regioregular. Prevailing syndiotactic structure is obtained with 1,10-phenanthroline or 2,2′-bipyridine as the ligand. Chelate thioether ligands allow the preparation of a completely atactic material. For 4-tert-butylstyrene an isotactic structure became accessible by using chiral bisoxazolidines. The prevailing structure of the copolymers of cyclopentene corresponds to a 1,3-enchainment of the olefin units most probably associated with a prevailing diisotactic structure 相似文献
926.
Emilay B. T. Diogo Dr. Fábio G. Delolo Gabriela A. P. Graça Esther R. S. Paz Ícaro A. O. Bozzi Prof. Dr. Renata Diniz Juliano P. Passos Prof. Dr. Tulio Matencio Dr. Liane K. Soares Prof. Dr. Diego Alves Pedro M. S. Costa Prof. Dr. Claudia Pessoa Prof. Dr. Cynthia L. M. Pereira Prof. Dr. Lutz Ackermann Prof. Dr. Eufrânio N. da Silva Júnior 《European journal of organic chemistry》2023,26(38):e202300506
Undivided electrochemical cells enable economical preparation of sulphur-containing naphthoquinones through electrochemical sulphenylation of quinoidal compounds. The environmentally friendly and efficient protocol eliminates the use of chemical oxidants and facilitates the synthesis of the desired molecules. This approach offers an efficient and versatile method to synthesize quinones that exhibit cytotoxicity against cancer cell lines. 相似文献
927.
928.
Charlotte M. Wentz Kätchen K. Lachmayr Dr. Esther H. R. Tsai Prof. Dr. Lawrence R. Sita 《Angewandte Chemie (International ed. in English)》2023,62(23):e202302739
Experimental results are presented that serve to lower the barrier for developing the science and technology of non-classical thermotropic glycolipid mesophases, which now include dodecagonal quasicrystal (DDQC) and Frank–Kasper (FK) A15 and σ mesophases that can be produced under mild conditions from a versatile class of sugar-polyolefin conjugates. By employing “alloys” comprised of mono- and disaccharide-polyolefin conjugates, and optionally with vitamin E as a small molecule phase modulator, we report the spontaneous formation of stable A15 mesophases at ambient temperature. We further document a rich thermotropic phase map that includes DDQC, A15, and σ mesophases of tunable periodicity that are connected through rapid thermotropic phase transitions as a function of increasing temperature in the order: liquid-like packing (LLP)→DDQC → A15→σ→ disorder. This first direct observation of a rapid thermotropic A15→σ phase transition provides support for a diffusionless martensitic process proceeding through strain-induced introduction of planar defects into the A15 lattice. 相似文献
929.
Esther Oger Nathan R. M. Crawford Rebecca Kelting Patrick Weis Manfred M. Kappes Reinhart Ahlrichs 《ChemInform》2008,39(7):no-no
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献