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861.
Ko YH Kim K Kang JK Chun H Lee JW Sakamoto S Yamaguchi K Fettinger JC Kim K 《Journal of the American Chemical Society》2004,126(7):1932-1933
A novel approach to the noncovalent synthesis of molecular necklaces successfully led to the first quantitative self-assembly of a molecular necklace [6]MN, in which five small rings are threaded on a large ring, from 10 components. Our strategy involves the host-guest complex formation between the molecular host cucurbit[8]uril (CB[8]) and a guest molecule in which an electron donor and an electron acceptor unit are connected by a rigid linker with a proper angle, to form a cyclic oligomer through the host-stabilized intermolecular charge-transfer (CT) complex formation. In the structure of the molecular necklace [6]MN, five molecules of the guest form a cyclic framework by the intermolecular CT interactions, on which five CB[8] molecules are threaded with an arrangement reminiscent of a five-fold propeller. The molecular necklace measures approximately 3.7 nm in diameter and approximately 1.8 nm in thickness. 相似文献
862.
Eietsu Hasegawa Kentaro Okamoto Momoe Nakamura Takashi Hoshi 《Tetrahedron letters》2006,47(44):7715-7718
The reaction of samarium diiodide with some cyclic and acyclic ketones tethering acyloxyalkyl side chains produced 2-hydroxy cyclic hemiacetals in moderate to good yields, in which an intramolecular addition of samarium ketyl radicals to distant ester carbonyls would be involved. 相似文献
863.
Shuying Wang Kentaro Teramura Takashi Hisatomi Kazunari Domen Hiroyuki Asakura Saburo Hosokawa Tsunehiro Tanaka 《Chemical science》2021,12(13):4940
Loading Ag and Co dual cocatalysts on Al-doped SrTiO3 (AgCo/Al-SrTiO3) led to a significantly improved CO-formation rate and extremely high selectivity toward CO evolution (99.8%) using H2O as an electron donor when irradiated with light at wavelengths above 300 nm. Furthermore, the CO-formation rate over AgCo/Al-SrTiO3 (52.7 μmol h−1) was a dozen times higher than that over Ag/Al-SrTiO3 (4.7 μmol h−1). The apparent quantum efficiency for CO evolution over AgCo/Al-SrTiO3 was about 0.03% when photoirradiated at a wavelength at 365 nm, with a CO-evolution selectivity of 98.6% (7.4 μmol h−1). The Ag and Co cocatalysts were found to function as reduction and oxidation sites for promoting the generation of CO and O2, respectively, on the Al-SrTiO3 surface.Deposition Ag and Co dual cocatalysts onto Al-SrTiO3 significantly improves its activity for photoreduction of CO2 by H2O, with extremely high selectivity to CO evolution (99.8%), in which Ag and Co enable CO2 reduction and H2O oxidation, respectively. 相似文献
864.
Hu W Haddad PR Tanaka K Mori M Tekura K Hasebe K Ohno M Kamo N 《Journal of chromatography. A》2003,997(1-2):237-242
New stationary phases for chromatographic separation of anions, obtained by loading liposomes made from dimyristolyphosphatidylcholine (DMPC) onto reversed-phase packed columns (C18 and C30) are reported. Mono- and divalent anions were used as model analyte ions and retention data for these species were obtained using the DMPC stationary phases and used to elucidate the separation mechanisms involved in this chromatographic system. The DMPC stationary phases can separate anions by either a solvation-dependent mechanism or an electrostatic ion-exchange mechanism, depending upon the relative magnitudes of the negative electrostatic potential (Psi(-)) of the phosphate moiety (P-) and the positive electrostatic potential (Psi(+)) of the quaternary ammonium groups (N+) on the headgroup of DMPC. If Psi(+) > Psi(-), such as in case where Psi(-) has been reduced either by binding of eluent cations (e.g., H+ or divalent cations) onto the P- group of DMPC or by steric screening when a C30 reversed-phase material was used to support the DMPC, then the overall electrostatic surface potential (and hence also the effective anion-exchange capacity) was generally large and the anions were separated on the basis of an electrostatic mechanism. However, if Psi(+) was similar to Psi(-), such as in the case of using a C18 reversed-phase support and monovalent cations as eluent cations, then the overall electrostatic surface potential and the effective anion-exchange capacity were very small and the analyte anions were separated on the basis of a solvation-dependent mechanism. The DMPC stationary phases were found to be suitable for the direct determination of iodide and thiocyanate in highly saline water samples, such as seawater samples. 相似文献
865.
A new algorithm for parallel calculation of the second derivatives (Hessian) of the conformational energy function of biomolecules in internal coordinates is proposed. The basic scheme of this algorithm is the division of the entire calculation of the Hessian matrix (called "task") into subtasks and the optimization of the assignment of processors to each subtask by considering both the load balancing and reduction of the communication cost. A genetic algorithm is used for this optimization considering the dependencies between subtasks. We applied this method to a glutaminyl transfer RNA (Gln-tRNA) molecule for which the scalability of our previously developed parallel algorithm was significantly decreased when the large number of processors was used. The speedup for the calculation was 32.6 times with 60 processors, which is considerably better than the speedup for our previously reported parallel algorithm. The elapsed time for the calculation of subtasks, data sending, and data receiving was analyzed, and the effect of the optimization using the genetic algorithm is discussed. 相似文献
866.
Yoshiyuki Sato Hajime HashiguchiKenzo Inohara Shigeki TakishimaHirokatsu Masuoka 《Fluid Phase Equilibria》2007
PVT properties of four polyethylene random copolymers (ethylene-propylene, ethylene-1-butene, ethylene-1-hexene, and ethylene-1-octene) and linear polyethylene were measured at temperatures from 313 to 493 K and pressures up to 200 MPa. Dependence of properties such as specific volume, thermal expansion coefficient, isothermal compressibility, and characteristic parameter of equations of state on the length of the polymer branched chains were examined. It was found that the length of the branched chain did not affect the thermal expansion coefficient and isothermal compressibility. The specific volume of copolymers having longer branched chains were slightly larger than those copolymers with short branched chains. 相似文献
867.
Park SJ Shin DM Sakamoto S Yamaguchi K Chung YK Lah MS Hong JI 《Chemical communications (Cambridge, England)》2003,(8):998-999
Bowl-shaped superstructures have been constructed by intra-clipping of resorcin[4]arene derivatives with two equivalents of (en)Pd(NO3)2 in water. The binding phenomena of the aromatic carboxylates were proven to be both enthalpically and entropically favoured. 相似文献
868.
Rapid and sensitive HPLC method for the simultaneous determination of paraquat and diquat in human serum. 总被引:1,自引:0,他引:1
Shuuji Hara Noriaki Sasaki Daizi Takase Shouichi Shiotsuka Kentaro Ogata Koujiro Futagami Kazuo Tamura 《Analytical sciences》2007,23(5):523-526
A rapid and sensitive HPLC method for the simultaneous determination of paraquat and diquat in human serum has been developed. After deproteinization of the serum with 10% trichloroacetic acid, the samples were separated on a reversed-phase column, and subsequently reduced to their radicals with alkaline sodium hydrosulfite solution. These radicals were monitored with a UV detector at 391 nm. This method permitted the reliable quantification of paraquat over linear ranges of 50 ng - 10 microg/ml and 100 ng - 10 microg/ml for diquat in human serum. The within- and between-day variations are lower than 2.3 and 2.2%, respectively. This technique was also utilized to determine the paraquat and diquat serum levels in a patient who had ingested herbicide (Prigrox L) containing paraquat and diquat. 相似文献
869.
[reactions: see text] The reaction of delta-silyl-gamma,delta-epoxypentanenitrile derivatives 9-12 with a base and an alkylating agent affords (Z)-delta-siloxy-gamma,delta-unsaturated pentanenitrile derivatives via a tandem process that involves the formation of a cyclopropane derivative by epoxy nitrile cyclization followed by Brook rearrangement and an anion-induced cleavage of the cyclopropane ring. Exclusive formation of a (Z)-derivative from trans-epoxides is explained by the reaction pathway that involves a backside displacement of the epoxide by the alpha-nitrile carbanion and the O-Si bond formation followed by concerted processes involving Brook rearrangement and the anti-mode of eliminative ring fission of the cyclopropane from the rotamer 19. The fact that (E)-isomers are exclusively obtained from cis-epoxides and alpha-cyclopropyl-alpha-silylcarbinol derivative 26 provides experimental support for the proposed pathway. 相似文献
870.
Herbert Eichenberger Kentaro Tsutsumi Guy de Weck Hans Richard Wolf 《Helvetica chimica acta》1980,63(6):1499-1519
Photochemistry of Conjugated δ-Keto-enones and β,γ,δ,?-Unsaturated Ketones On 1π,π*-excitation the δ-keto-enones 5–8 are isomerized to compounds B ( 18 , 22 , 26 , 28 ) via 1,3-acyl shift and to compounds C ( 19 , 23 , 27 , 29 ) via 1,2-acyl shift, whereas the β,γ,δ,?-unsaturated ketone 9 gives the isomers 32 and 33 by 1,2-and 1,5-acyl shift, respectively. Furthermore, isomerization of 6 to 24 , dimerization of 8 to 30 and addition of methanol to 8 ( 8 → 31 ) is observed. Unlike 7 and 8 the acyclic ketones 5 , 6 and 9 undergo photodecarbonylation on 1π,π*-excitation ( 5 → 20 , 21 ; 6 → 20 , 25 ; (E)- 9 → 35–38 ). Evidence is given, that the conversion to B as well as the photodecarbonylation of 5,6 and 9 arise from an excited singulet state, but the conversion to C as well as the dimerization of 8 from the T1-state. 相似文献