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131.
The reactions of 1,1-di-p-tolylethane with metalating agents in tetrahydrofuran were examined. With lithio derivatives the nature of the anion formed depended upon the base. The 1H and 13C NMR spectra as well as the products of methylation of the anions are compared with those of p-xylyllithium and 1,1-diphenylethyllithium. Each anion is distinct in spectra and product of methylation. When a deficiency of 1,1-di-p-tolylethane was used, anion equilibration was effected. 相似文献
132.
The lattice dynamics of InAs under variable hydrostatic pressures is investigated on the basis of an ‘11-parameter’ rigid-ion model (RIM). The calculated phonon dispersion curves are in satisfactory agreement with the neutron scattering data (available for the TA modes only) measured at room temperature and atmospheric pressure. The one- and two-phonon densities of states functions and mode Gruneisen parameters have been computed at two arbitrary hydrostatic pressures. The effect of high pressure on the phonon dispersion curves is shown to lead to a typical ‘softening’ in the transverse acoustic modes and eventually to a phase trnasformation of the compound. 相似文献
133.
134.
Valliant-Saunders K Gunn E Shelton GR Hrovat DA Borden WT Mayer JM 《Inorganic chemistry》2007,46(13):5212-5219
In the presence of an excess of pyridine ligand L, osmium tetroxide oxidizes tertiary silanes (Et(3)SiH, (i)Pr(3)SiH, Ph(3)SiH, or PhMe(2)SiH) to the corresponding silanols. With L = 4-tert-butylpyridine ((t)Bupy), OsO(4)((t)Bupy) oxidizes Et(3)SiH and PhMe(2)SiH to yield 100 +/- 2% of silanol and the structurally characterized osmium(VI) mu-oxo dimer [OsO(2)((t)Bupy)(2)](2)(mu-O)(2) (1a). With L = pyridine (py), only 40-60% yields of R(3)SiOH are obtained, apparently because of coprecipitation of osmium(VIII) with [Os(O)(2)py(2)](2)(mu-O)(2) (1b). Excess silane in these reactions causes further reduction of the OsVI products, and similar osmium "over-reduction" is observed with PhSiH(3), Bu(3)SnH, and boranes. The pathway for OsO(4)(L) + R(3)SiH involves an intermediate, which forms rapidly at 200 K and decays more slowly to products. NMR and IR spectra indicate that the intermediate is a monomeric Os(VI)-hydroxo-siloxo complex, trans-cis-cis-Os(O)(2)L(2)(OH)(OSiR(3)). Mechanistic studies and density functional theory calculations indicate that the intermediate is formed by the [3 + 2] addition of an Si-H bond across an O=Os=O fragment. This is the first direct observation of a [3 + 2] intermediate in a sigma-bond oxidation, though such species have previously been implicated in reactions of H-H and C-H bonds with OsO(4)(L) and RuO(4). 相似文献
135.
MPW1K/6-31+G(d,p) calculations which include the effects of small curvature tunneling find that, around room temperature, thermally activated tunneling dominates the 1,5-hydrogen shift reactions of 1,3-cyclopentadiene (2a) and 5-methyl-1,3-cyclopentadiene (2c). The calculated temperature dependence of the H/D kinetic isotope effect (KIE) for the latter rearrangement agrees well with experimental measurements that were published nearly 40 years ago. It is argued that the experimental KIEs provide prima facie evidence for tunneling in this reaction. The calculations also predict that it should be possible, at least in principle, to confirm this conclusion by observing curvature in the Arrhenius plot for the rearrangement of 2c. 相似文献
136.
Jessica D. Posey-Dowty Thelma L. Watterson A. Kent Wilson Kevin J. Edgar Michael C. Shelton Larry R. LingerfeltJr. 《Cellulose (London, England)》2007,14(1):73-83
New carboxymethylcellulose esters were developed with useful properties for oral dosage forms in drug delivery. Normally,
commercial cellulose esters are used as the major excipients in oral dosage forms as a coating or a membrane. In applications
involving compression tablets, cellulose esters are usually mixed with other more hydrophilic matrix components to facilitate
dissolution of the active. In the present study, novel cellulose esters were single component matrix resins. Pharmaceutical
actives were cryogenically ground as a physical blend or an amorphous blend with the polymer. Subsequently, tablets were made
by direct compression using a single tablet press, or capsules were made by filling them with the ground material. Dissolution
tests were completed on the solid dosage forms at pH 1.2, 4.5, 6.8 or 7.4 in a United States Pharmacopeia (USP) II device
to determine the release profiles for up to 24 h. Carboxymethylcellulose esters provide an excellent matrix for controlling
both the rate of release and the pH at which pharmaceutical actives release into the aqueous environment. When used in suitable
quantities, dictated by the active of interest, carboxymethylcellulose acetate butyrate provided zero-order release over sustained
time up to 24 h. 相似文献
137.
Pan D Caruthers SD Hu G Senpan A Scott MJ Gaffney PJ Wickline SA Lanza GM 《Journal of the American Chemical Society》2008,130(29):9186-9187
Although gadolinium has been the dominant paramagnetic metal for MR paramagnetic contrast agents, the recent association of this lanthanide with nephrogenic systemic fibrosis, an untreatable disease, has spawned renewed interest in alternative metals for MR molecular imaging. We have developed a self-assembled, manganese(III)-labeled nanobialys (1), a toroidal-shaped MR theranostic nanoparticle. In this report, Mn(III) nanobialys are characterized as MR molecular imaging agents for targeted detection of fibrin, a major biochemical feature of thrombus. A complementary ability of nanobialys to incorporate chemotherapeutic compounds with greater than 98% efficiency and to retain more than 80% of these drugs after infinite sink dissolution, point to the theranostic potential of this platform technology. 相似文献
138.
139.
140.
L. M. Dennis R. S. Shelton C. Junge E. Conte F. D. Snell M. Speter A. Monsch J. D. Burchard W. Friedel und A. Winstanley 《Fresenius' Journal of Analytical Chemistry》1933,91(1-2):40-43
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