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521.
The [2,3]-Wittig rearrangement of properly designated (E)- and (Z)-crotyl propargyl ether system has been shown to exhibit a remarkably high degree of threo- and erythro -selection, respectively, and the stereochemical outcomes are discussed on mechanistic grounds. Some useful transformations of the rearrangement product are also described within the context of the formal total synthesis of (±)-oudemansin. Further, the high level of diastereoselection is maintained in the reaction of the α-methylcrotyl counterparts, together with the exclusive formation of the (E)-olefinic bond. 相似文献
522.
Miyoko Kamigauchi Yuko Miyamoto Kinuko Iwasa Makiko Sugiura Zjujiro Nishijo Narao Takao Toshimasa Ishida Yasuko In Masatoshi Inoue 《Helvetica chimica acta》1990,73(8):2171-2178
The solid-state and solution conformations of (+)-chelidonine ( 1 ), a biologically active alkaloid, were determined by X-ray diffraction and 1H-NMR spectroscopy, X-Ray diffraction analysis revealed a conformer with B/C ‘anti-type’ cis conjunction, a half-chair of ring B , and a twist half-chair of ring C. One H2O molecule per one alkaloid molecule was cocrystallized and stabilized by H-bonding with OH? C(11). Analysis of the thermal behavior of the crystal showed more thermal stability in the monohydrate than the anhydrate. The NMR measurement of concentration and temperature dependences in CDCl3 and in (CD3)2SO suggested that the OH group of 1 was intramolecularly H -bonded to N(5) in (CD3)2SO and intermolecularly H-bonded to the solvent in CDCl3. Conformational-energy calculations by the MNDO method showed that the intramolecular H -bond was little affected by the conformational stabilization of 1 . 相似文献
523.
[reaction: see text] A novel synthetic approach to N-alkyl-N'-arylimidazolium salts has been developed on the basis of addition of imidazoles to arynes. A variety of N-alkyl-N'-arylimidazolium salts can be synthesized straightforwardly in modest to good yields. Furthermore, utility of the resulting imidazolium salts has been demonstrated by the palladium-catalyzed Suzuki-Miyaura coupling of aryl chlorides. 相似文献
524.
Sequence-specific gene silencing in mammalian cells by alkylating pyrrole-imidazole polyamides 总被引:3,自引:0,他引:3
Shinohara K Narita A Oyoshi T Bando T Teraoka H Sugiyama H 《Journal of the American Chemical Society》2004,126(16):5113-5118
Gene silencing was examined by sequence-specific alkylation of DNA by N-methylpyrrole (Py)-N-methylimidazole (Im) hairpin polyamides. Polyamides ImImPyPygammaImImPyLDu86 (A) and ImImPyPygammaImPyPyLDu86 (B) selectively alkylated the coding regions of the renilla and firefly luciferases, respectively, according to the base pair recognition rule of Py-Im polyamides. Two different plasmids, encoding renilla luciferase and firefly luciferase, were used as vectors to examine the effect of alkylation on gene silencing. Transfection of the alkylated luciferase vectors-by polyamide A or B-into HeLa, 293, and NIH3T3 cells demonstrated that these sequence-specific DNA alkylations lead to selective silencing of gene expression. Next, the vectors were cotransfected into HeLa cells and the cells were treated with polyamide A or B. Selective reduction of luciferase activities was caused by both polyamides. On the basis of this sequence-specific alkylation and gene silencing activity, these alkylating Py-Im polyamides thus have potential as antitumor drugs to target specific gene expression in human cells. 相似文献
525.
Takahashi N Niwa A Sugiura H Nakamura T 《Chemical communications (Cambridge, England)》2003,(3):318-319
Preparation of indium nitride at atmospheric pressure has been examined by means of halide chemical vapour deposition; from the SEM observations of the crystals deposited onto an Si(100) substrate it was found that they showed flower-like structure. 相似文献
526.
Mitsuo Ishikawa Ken-Ichi Nakagawa Makoto Kumada 《Journal of organometallic chemistry》1980,190(2):117-128
The photolysis of tris(trimethylsilyl)phenylsilane (I) in the presence of 1-hexyne, 3,3-dimethyl-1-butyne, trimethylsilylacetylene, 3-hexyne, 1-trimethylsilylpropyne, 1,2-bis(trimethylsilyl)acetylene and 2,2,5,5-tetramethyl-3-hexyne afforded the respective silacyclopropenes. The silacyclopropenes produced from monosubstituted acetylenes underwent photochemical isomerization to give disilanylacetylene derivatives, via a 1,2-hydrogen shift in the silacyclopropene ring. Irradiation of I in the presence of 3-hexyne, 1-trimethylsilylpropyne or 2,2,5,5-tetramethyl-3-hexyne, gave the corresponding silacyclopropenes which could be isolated by preparative GLC. The silacyclopropene from 1,2-bis(trimethylsilyl)acetylene, however, readily underwent thermal rearrangement to give [bis(trimethylsilyl)phenylsily] trimethylsilylacetylene via a 1,2-trimethylsilyl shift. This type of rearrangement was also found in the photochemical process. 相似文献
527.
Phosphinated polymer‐incarcerated (PI) Pd catalysts were prepared by immobilization of palladium with phosphinated polymers by using the PI method. The phosphinated PI Pd catalysts showed good catalytic activity without externally added phosphine ligands in the amination of aryl halides for C N bond‐forming reactions, as well as in Suzuki–Miyaura and Sonogashira coupling. No leaching of palladium from the immobilized Pd was observed by fluorescence X‐ray analysis. Furthermore, it was found that immobilization of Pd by the PI process facilitated the suppression of poisoning of the metal by amines. These effects can be ascribed to stabilization of the catalyst by both the phosphine moieties and the benzene rings in the swollen polymer support. The phosphinated PI Pd catalysts could also be recovered by simple filtration and reused several times without leaching of palladium in both the amination and Suzuki–Miyaura coupling reactions. 相似文献
528.
Compound formation in the system PbGeO3? Pb5Ge3O11 was studied by thermal analysis and high-temperature X-ray diffraction. New modifications of PbGeO3 and Pb5Ge3O11 were prepared by the simultaneous hydrolysis of lead and germanium alkoxides, followed by washing and drying; the former has a hexagonal unit cell with a = 15.573 Å and c = 7.240 Å, and the latter has an orthorhombic crystal structure with a = 5.081 Å, b = 7.301 Å and c = 8.817 Å. They are transformed to the known monoclinic and hexagonal modifications at 575 to 610°C and 410 to 450°C, respectively. No compound of Pb3Ge2O7 was confirmed. The structures of germanate groups in the lead germanate compounds are discussed on the basis of the infrared spectral data. 相似文献
529.
K. Ninomiya H. Sugiura T. Nakatsuka Y. Kasamatsu H. Kikunaga W. Sato T. Yoshimura H. Matsumura K. Takamiya M. K. Kubo K. Sueki A. Yokoyama Y. Hamajima T. Miura K. Nishiyama A. Shinohara 《Journal of Radioanalytical and Nuclear Chemistry》2007,272(3):661-664
The electronic X-ray energies of muonic atoms were precisely measured. The atomic number (Z) dependence of the energy difference between electronic X-rays of muonic atoms and Z-1 atoms (energy shift) was systematically investigated. The energy shifts in the low-Z region were compared with those of the high-Z region that had been obtained experimentally and theoretically in previous work. An obvious difference between these two
regions was found in the atomic-number dependence of the energy shift. We also compared the energy shifts of muonic atoms
with those of pionic atoms. 相似文献
530.
Nakamura M Yokono H Tomita K Ouchi M Miki M Dohno R 《The Journal of organic chemistry》2002,67(10):3533-3536
Substitution effect, absorption, and fluorescence behaviors of some benzoaza-15-crown-5 derivatives upon cation complexation in solvent extraction were studied. The introduction of a substituent on the nitrogen atom in benzoaza-15-crown-5 enhanced extractabilities in the solvent extraction of aqueous alkali metal picrates. The nondonating substituents raised the cation selectivity for Na(+) over K(+), but the donating substituents reduced the cation selectivity. The absorption and fluorescence spectral behavior was different with the alkali metal cations. 相似文献