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991.
Yongdong Su Hirofumi Fujii Ekaterina A. Burakova Boris P. Chelobanov Masayuki Fujii Dmitry A. Stetsenko Vyacheslav V. Filichev 《化学:亚洲杂志》2019,14(8):1212-1220
The effect of phosphate group modifications on formation and properties of G‐quadruplexes (G4s) has not been investigated in detail. Here, we evaluated the structural, thermodynamic and kinetic properties of the parallel G‐quadruplexes formed by oligodeoxynucleotides d(G4T), d(TG4T) and d(TG5T), in which all phosphates were replaced with N‐methanesulfonyl (mesyl) phosphoramidate or phosphoryl guanidine groups resulting in either negatively charged or neutral DNA sequences, respectively. We established that all modified sequences were able to form G‐quadruplexes of parallel topology; however, the presence of modifications led to a decrease in thermal stability relative to unmodified G4s. In contrast to negatively charged G4s, assembly of neutral G4 DNA species was faster in the presence of sodium ions than potassium ions, and was independent of the salt concentration used. Formation of mixed G4s composed of both native and neutral G‐rich strands has been detected using native gel electrophoresis, size‐exclusion chromatography and ESI‐MS. In summary, our results indicate that the phosphate modifications studied are compatible with G‐quadruplex formation, which could be used for the design of biologically active compounds. 相似文献
992.
993.
Sergey V. Krivovichev Volker Kahlenberg Ivan G. Tananaev Boris F. Myasoedov 《无机化学与普通化学杂志》2005,631(12):2358-2364
Crystals of four amine‐templated layered uranyl selenates, [C2H10N2][(UO2)(SeO4)2(H2O)](H2O) ( 1 ), [CH6N3]2[(UO2)(SeO4)2(H2O)](H2O)1.5 ( 2 ), [C4H12N]2[(UO2)(SeO4)2(H2O)] ( 3 ), and [CH6N3]3[(UO2)2(SeO4)2(H(SeO4)2)](H2O)2 ( 4 ) were prepared by evaporation from aqueous solution of uranyl nitrate, selenic acid and the respective amine. The structures of all four compounds have been solved by direct methods. The structures of 1 (monoclinic, C2/c, a = 11.787(2), b = 7.7007(10), c = 16.600(3) Å, β = 102.016(14)°, V = 1473.7(4) Å3, R1 = 0.037 for 1743 unique observed reflections), 2 (monoclinic, C2/c, a = 37.314(4), b = 7.1771(6), c = 13.2054(14) Å, β = 109.267(8)°, V = 3338.4(6) Å3, R1 = 0.088 for 3005 unique observed reflections) and 3 (monoclinic, C2/c, a = 27.212(10), b = 7.372(3), c = 23.113(7) Å, β = 117.75(2)°, V = 4103(3) Å3, R1 = 0.073 for 2111 unique observed reflections) are based on sheets of the composition [(UO2)(SeO4)2(H2O)]2? consisting of pentagonal [UO7]8? pentagonal bipyramids linked via [SeO4]2? tetrahedra. The sheets have the same chemical composition but different topologies. The structure of 4 (orthorhombic, P212121, a = 10.7261(9), b = 13.918(2), c = 18.321(2) Å, V = 2735.1(5) Å3, R1 = 0.050 for 5683 unique observed reflections) contains [(UO2)2(SeO4)2(H(SeO4)2)]3? sheets parallel to (001). In all four structures, the layers are connected via protonated amine and H2O molecules. 相似文献
994.
Khlebtsov NG Melnikov AG Bogatyrev VA Dykman LA Alekseeva AV Trachuk LA Khlebtsov BN 《The journal of physical chemistry. B》2005,109(28):13578-13584
According to the theory of light scattering by small randomly oriented particles, the depolarized ratio of the scattered intensities, I(vh)/I(vv), cannot exceed 1/3. Here we show that this conclusion does not hold for nonspherical plasmon resonant metal particles. Our analysis is based on the Rayleigh approximation and the exact T-matrix method as applied to spheroids and circular cylinders with semispherical ends. For small particles, the condition I(vh)/I(vv) >1/3 can be satisfied within the upper left quadrant of the complex relative dielectric permeability Real(eps) < -2 (rods) and within the upper unit semicircle centered at Real(eps) = -1 (disks). For gold nanorods with the axis ratio exceeding 2, the maximal theoretical values I(vh)/I(vv) lie between 1/3 and 3/4 at wavelengths of 550-650 nm. The extinction and static light scattering spectra (450-850 nm, at 90 degrees degrees) as well as the depolarized ratio of He-Ne laser light scattering were measured with gold nanospheres (the average diameters of 21, 29, and 46 nm) and nanorods (the longitudinal plasmon resonance peak positions at 655, 692, and 900 nm). The measured depolarization ratios of nanospheres (0.07-0.16) and nanorods (0.3-0.48) are in good agreement with theoretical calculations based on estimations of the average particle size and shape. 相似文献
995.
Berry JF Cotton FA Liu CY Lu T Murillo CA Tsukerblat BS Villagrán D Wang X 《Journal of the American Chemical Society》2005,127(13):4895-4902
The X-ray crystallographic structures, the magnetic susceptibilities from 2 to 300 K, and a theoretical analysis of the magnetism for a triangular and a tetranuclear molecule consisting of linked high-spin cobalt(II) centers are described. The interpretation of the magnetic data for the triangular compound [Co(depa)Cl](3) (depa is the anion of 2,2'-(bis-4-ethylpyridyl)amine), which has tetrahedrally coordinated Co(2+) ions, entails isotropic antiferromagnetic exchange interaction and antisymmetric exchange acting within the two low-lying spin doublets. Two strong isotropic ferromagnetic interactions have been modeled in the cuboidal compound Co(4)(DPM)(4)(CH(3)O)(4)(CH(3)OH)(4) (DPM represents the anion of dipivaloylmethane), which has octahedral coordination, and the system can be approximately considered as two weakly coupled S = 3 species. 相似文献
996.
Kulik LV Epel B Lubitz W Messinger J 《Journal of the American Chemical Society》2005,127(8):2392-2393
55Mn pulse ENDOR experiments at 34 GHz (Q-band) are reported for the S0 and S2 states of the oxygen-evolving complex of photosystem II. Their numerical analysis (i) shows that in both states all four Mn ions are magnetically coupled, (ii) allows a refinement of the hyperfine interaction (HFI) parameters obtained earlier for the S2 state at X-band (Peloquin, J. M.; Campbell, K. A.; Randall, D. W.; Evanchik, M. A.; Pecoraro, V. L.; Armstrong, W. H.; Britt, R. D. J. Am. Chem. Soc. 2000, 122, 10926-10942), (iii) provides the first reliable 55Mn HFI tensors for the S0 state, and (iv) leads to the suggestion that the Mn oxidation states in S0 and S2 are Mn4(III, III, III, IV) and Mn4(III, IV, IV, IV), respectively. In addition, a Q-band EPR spectrum is reported for the S0 state, and inversion-recovery experiments at 4.5 K directly show that the electron spin-lattice relaxation for the S0 state is about 2 orders of magnitude faster than that for the S2 state. 相似文献
997.
Resin-bound amines 1a-e condense with isothiocyanates to give thiourea resins 2a-i. Resins 2a-g subsequently react with iodomethane followed by cleavage affording S-methyl isothioureas 4a-g, and resins 2a-b,h-i react with acyl chlorides to afford N-acylated thioureas 6a-d. N-Acylthioureas 8a-f (R(2) = H) were prepared directly from resin-bound amines 1a-d with acyl isothiocyanates. N-Acylthioureas 8a-d,f(R(2) = H) were used for the preparation of S-methyl-N-acylisothioureas 10a-e. Alkylation was performed using methyl iodide. Resin-bound S-methyl-N-acylisothioureas 10a,b,d are converted by an action of hydrazines into 3-amino-1,2,4-triazoles 13a-d. Condensation of resins 8a-e (R(2) = H) with 2-bromoacetophenones in the presence of TEA affords thiazoles 15 a-e. All transformations proceeded in high yields and gave products of good purities. 相似文献
998.
Petit de Peña Y Paredes B Rondón W Burguera M Burguera JL Rondón C Carrero P Capote T 《Talanta》2004,64(5):1351-1358
A continuous flow system for the determination of lead in home made spirituous beverages was developed. The determination was based on the formation of a neutral chelate of the element with ammonium pyrrolidine dithiocarbamate, its adsorption onto a minicolumn packed with sodium faujasite type Y synthetic zeolite, followed by elution with methyl isobutyl ketone and determination by flame atomic absorption spectrometry. Ethanol and copper interfere strongly in the determination and therefore, must be separated prior to the analysis. Copper is removed by precipitation with rubeanic acid, while ethanol is eliminated by rotaevaporation. Sample solutions containing Pb2+ in the concentration range from 5 to 120 μg l−1 at pH 2.5 could be analyzed, by using a preconcentration time of 3 min. Preconcentration factors from 80 to 140 were achieved for a sample volume of 6 ml and the detection limit varied from 1.4 to 3.5 μg l−1, depending on the matrix composition. The relative standard deviations for 60 μg l−1 Pb was 3.2% (n = 10) and the recovery of spikes (20, 40, 60 and 80 μg l−1) added to the samples was estimated within 92–105% range, suggesting that lead can be quantitatively determined in such samples. Determining lead in several samples by an alternative technique further checked the accuracy. Finally, the concentrations of Pb2+ determined in 28 samples of Venezuelan spirituous beverages were in 12.6–370.0 μg l−1 range, depending on the fermenting material based on different mixtures of agave, raw sugar cane and white sugar. 相似文献
999.
Boris Minaev Oleksandr Loboda Olav Vahtras Kenneth Ruud Hans Ågren 《Theoretical chemistry accounts》2004,111(2-6):168-175
We have calculated solvent effects on the zero-field splitting (ZFS) constants induced by electron spin–spin coupling (SSC) in the low-lying triplet states of azaaromatic molecules in solutions using multiconfiguration self-consistent-field wave functions and the polarizable continuum model. The second-order spin–orbit coupling (SOC) contribution to the splitting of the 3* states is found to be almost negligible, and the calculations therefore provide a good estimate of the ZFS parameters and their solvent dependence based only on the electron spin–spin coupling expectation values. The correlation between the shift in the ZFS and the phosphorescence frequency that has been observed in optically detected magnetic resonance experiments in low-temperature glasses is supported by our direct SSC calculations without taking SOC into account. This makes it possible to distinguish between the two theories that earlier were proposed to explain the inhomogeneous broadening of triplet state spectra, and discard the one that is exclusively based on the SOC-induced mixing of the singlet and triplet states.Contribution to the Jacopo Tomasi Honorary IssueAcknowledgments. This work was supported (B. M.) by the Swedish Royal Academy of Science (KVA). This work was also supported by the Norwegian Research Council through a grant of computer time from the Program for Supercomputing. We are grateful to B. Schimmelpfenning for his valuable assistance in the computations. 相似文献
1000.
Pavel . Volkov Nina I. Ivanova Nina K. Gusarova Boris G. Sukhov Kseniya O. Khrapova Lev E. Zelenkov Vladimir I. Smirnov Tatyana N. Borodina Tamara I. Vakul'skaya Spartak S. Khutsishvili Boris A. Trofimov 《Heteroatom Chemistry》2015,26(5):329-334
Secondary phosphine chalcogenides react with diacetone‐d‐glucose (DAG) in the system CCl4/Et3N (70°C, 4–24 h) to afford DAG chalcogenophosphinates in up to 79% yield, thus paving a short way to optically active chalcogenophosphinates with glucose moieties. As an example, a mild regioselective hydrolysis (70°C, aqueous MeCOOH) of DAG bis(2‐phenylethyl)selenophosphinate) obtained leads to monoacetone‐d‐glucose bis(2‐phenylethyl)selenophosphinate. 相似文献