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81.
V Gierz J Melomedov C Förster C Deißler F Rominger D Kunz K Heinze 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(34):10677-10688
Coupling of uronium salts with in situ generated N-heterocyclic carbenes provides straightforward access to symmetrical [4](2+) and unsymmetrical bis-imidazolium salts [6](2+) and [9](2+) . As indicated by cyclic and square-wave voltammetry, [6](2+) and [9](2+) can be (irreversibly) reduced by one electron. The initially formed radicals [6](.+) and [9](.+) undergo further reactions, which were probed by EPR spectroscopy and density functional calculations. The final products of the two-electron reduction are the two carbenes. Upon irradiation with UV light both [6](2+) and [9](2+) emit at room temperature in solution but with dramatically different characteristics. The different fluorescence behavior is analyzed by emission spectroscopy and interpreted by using time-dependent density functional calculations as largely due to different excited-state dynamics of [6](2+) and [9](2+) . The geometries of both radicals [6](.+) and [9](.+) and excited states {[6](2+) }* and {[9](2+) }* are substantially different from those of the parent ground-state molecules. 相似文献
82.
M Albrecht Y Shang K Hasui V Gossen G Raabe K Tahara Y Tobe 《Dalton transactions (Cambridge, England : 2003)》2012,41(31):9316-9322
Triangular triscatechol ligands are prepared in facile reaction sequences. The catechol units are either bound to the triangular backbone through their 3- or 4-position. With titanium(IV) ions, the ligands form metallosupramolecular M(4)L(4) tetrahedra which are characterized by ESI MS and proton NMR. Quantum-chemical calculations reveal that connectivity at the catechol in the 3-position results in highly condensed structures while attachment in the 4-position affords container molecules providing huge internal cavities. 相似文献
83.
Böhrsch V Mathew T Zieringer M Vallée MR Artner LM Dernedde J Haag R Hackenberger CP 《Organic & biomolecular chemistry》2012,10(30):6211-6216
In this paper we present the synthesis of glyco-phosphoramidate conjugates as easily accessible analogs of glyco-phosphorous esters via the Staudinger-phosphite reaction. This protocol takes advantage of synthetically accessible symmetrical carbohydrate phosphites in good overall yields, in which ethylene or propylene linkers can be introduced between phosphorous and galactose or lactose moieties. The phosphites were finally applied for the chemoselective reaction with azido-peptides and polyazido(poly)glycerols. 相似文献
84.
Plumeré N Ruff A Speiser B Feldmann V Mayer HA 《Journal of colloid and interface science》2012,368(1):208-219
The synthesis of Stöber silica particles as basis for redox modifications is optimized for desired properties, in particular diameter in a wide sub-micrometer range, spherical shape, monodispersity, the absence of porosity, and aggregation free isolability for characterization and later covalent modification. The materials are characterized by SEM, DLS, nitrogen sorption isotherms, helium as well as Gay-Lussac (water) pycnometry, and DRIFT spectroscopy. Particles with diameters between approximately 50 and 800 nm are obtained by varying the concentrations of the reagents and reactants, the type of solvent as well as the temperature. The use of high water concentrations and post-synthetic calcination at 600 °C results in silica particles that can be considered as nonporous with respect to the size of the active molecules to be immobilized. The effect of reaction temperature on size distribution is identified. Low polydispersity is achieved by performing the reaction in a temperature range in which a change in temperature has only a weak or no effect on the final particle diameter. Upon optimization of the sol–gel process, the shape of the particles is still spherical. The agreement between experimental and geometric data is within the expected precision of the characterization techniques. 相似文献
85.
The reaction rates of muonium with ethylene adsorbed on the surface of amorphous silica powder grains were measured between
6 K and 300 K. kf values characterizing the two-dimensional surface reactions and the 2 1/2 dimensional reactions with muonium in the gas phase
were obtained. 相似文献
86.
87.
L. Asch G. M. Kalvius A. Kratzer F. J. Litterst Ulrike Potzel R. Keitel D. Noakes E. Ansaldo O. Hartmann E. Karlsson R. Wäppling J. Chappert A. Yaouanc 《Hyperfine Interactions》1986,31(1-4):337-338
Two samples of DyAl2 were studied by longitudial μSR in the paramagnetic and ferromagnetic regime. In a region Tc±40 K the samples give different signals although X-ray analysis can not detect any impurity phase in either of them. 相似文献
88.
Brewer JH Ansaldo EJ Carolan JF Chaklader AC Hardy WN Harshman DR Hayden ME Ishikawa M Kaplan N Keitel R Kempton J Kiefl RF Kossler WJ Kreitzman SR Kulpa A Kuno Y Luke GM Miyatake H Nagamine K Nakazawa Y Nishida N Nishiyama K Ohkuma S Riseman TM Roehmer G Schleger P Shimada D Stronach CE Takabatake T Uemura YJ Watanabe Y Williams DL Yamazaki T Yang B 《Physical review letters》1988,60(11):1073-1076
89.
Colourless single crystals of the co‐crystallizate of mercuric chloride and caffeine, HgCl2(Caf), were obtained from an ethanolic solution of mercuric chloride, HgCl2, and caffeine (Caf) and recrystallized from hot water. The crystal structure (monoclinic, P21, Z = 2, a = 398.36(8), b = 1964.5(4), c = 809.6(2) pm, β = 99.24(3)°, Z = 2, R1 = 0.0584 for 1430 Fo > 4σ(Fo)) contains helical chains (parallel to the 21 screw axis) of almost unaffected HgCl2 molecules and caffeine molecules which are very weakly bound to one keto‐oxygen atom (O4) of one and N9 of a second caffeine molecule at distances of 282 and 281 pm, respectively. To the contrary, theoretical calculations show that the molecule HgCl2(Caf)2 is stable (in the gas phase at T = 0 K) with surprisingly strong bonding as indicated by the “tetrahedrization” of the molecule. 相似文献