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891.
892.
Jorge M Gulaboski R Pereira CM Cordeiro MN 《The journal of physical chemistry. B》2006,110(25):12530-12538
The pure organic liquids nitrobenzene (NB) and 2-nitrophenyl octyl ether (NPOE) have been studied by means of molecular dynamics simulations. Both solvents are extremely important in various interfacial processes, mainly connected with ion transfer taking place across the interface with water. Thermodynamic (mass density, enthalpy of vaporization, isothermal compressibility, dipole moment) and dynamic (viscosities and self-diffusion coefficients) properties of both liquids have been calculated and are in very good agreement with the experimental data. In the case of NB, several potentials have been tested and the obtained results compared and discussed. In most cases, the OPLS all-atom potential gives results that are in better agreement with available experimental values. Atomic radial distribution functions, dihedral and angle distributions, as well as dipole-orientation correlation functions are used to probe the structure and interactions of the bulk molecules of both organic solvents. These were seen to be very similar in terms of structure and thermodynamics, but quite distinct in terms of dynamic behavior, with NPOE showing a much slower dynamic response than NB. A simulation study of the simple Cl- and K+ ions dissolved in both solvents has been also undertaken, revealing details about the diffusion and solvation mechanisms of these ions. It was found that in both liquids the positive potassium ion is solvated by the negative end of the molecular dipole, whereas the negative chloride ion is solvated by the positive end of the dipole. 相似文献
893.
Vyacheslav V. Sushev Yuriy A. Min’ko Natalia V. Belina Yuriy A. Kurskiy Olga V. Kuznetsova Georgy K. Fukin Evgenii V. Baranov Vladimir K. Cherkasov Gleb A. Abakumov 《Journal of organometallic chemistry》2006,691(5):879-889
The reaction of diphosphinohydrazine PhNH-N(PPh2)2 (1) with cobalt(II) silylamide, Co[N(SiMe3)2]2, proceeds via formation of unstable phosphinohydrazide complex Co[NPh-N(PPh2)2]2 followed by rearrangement to a new chelating compound Co(NPh-PPh2N-PPh2)2 (2). Disproportionation of nickel(I) silylamide, (Ph3P)2Ni-N(SiMe3)2, in the presence of 1, yields Ni(0) and Ni(II) phosphinoamide complexes: Ni[(Ph2P)2N-NPhH]2 (3), Ni(NPh-PPh2N-PPh2)2 (4). X-ray analysis reveals tetrahedral environment of the cobalt atom in 2 and square-planar environment of the nickel atom in cis-4. In contrast to the crystalline patterns, the solutions of 2 in THF or toluene have EPR signal which is typical to square-planar low-spin d7 cobalt complex. The reactions of 2 with dioxygen, elemental sulfur and diphenyldiazomethane led to the spirocyclic insertion products Co(NPh-PPh2N-PPh2X)2 (X = O, S, NNCPh2) while the absorption of carbon monoxide is reversible. 相似文献
894.
Shustova NB Kuvychko IV Bolskar RD Seppelt K Strauss SH Popov AA Boltalina OV 《Journal of the American Chemical Society》2006,128(49):15793-15798
Reaction of a mixture of insoluble higher fullerenes with CF3I at 500 degrees C produced a single abundant isomer of C74(CF3)12, C76(CF3)12, and C80(CF3)12, two abundant isomers of C78(CF3)12 and C82(CF3)12, and an indeterminant number of isomers of C84(CF3)12. Using a combination of 19F NMR spectroscopy, DFT calculations, and the structures and spectra of previously reported fullerene(CF3)n compounds, the most-probable structures of six of the seven isolated compounds were determined to be specific isomers of C2-(C74-D3h)(CF3)12, Cs-(C76-Td(2))(CF3)12), C2-(C78-D3h(5))(CF3)12), Cs-(C80-C2v(5))(CF3)12), C2-(C82-C2(5))(CF3)12), and C2-(C82-C2(3))(CF3)12) containing ribbons and/or loops of edge-sharing para-C6(CF3)2 hexagons. The seventh isolated compound is a C1 isomer of C78(CF3)12 containing two such ribbons. This set of compounds represents only the second reported isolable compound with the hollow C74-D3h cage and the first experimental evidence for the existence of the hollow fullerenes C76-Td(2), C78-D3h(5), C80-C2v(5), and C82-C2(5) in arc-discharge soots. 相似文献
895.
Jesús Ibarz M Ferreira V Hernández-Orte P Loscos N Cacho J 《Journal of chromatography. A》2006,1116(1-2):217-229
A procedure has been developed for the GC-MS analysis of the aromas released in fast acid hydrolysis of precursor fractions from grape musts and skins. Different sorbents for the extraction of the precursors were compared. The best results were obtained with LiChrolut EN polymeric resins which displayed two and six-fold more extraction capacity than Amberlite XAD-2 resins and C18 sorbents, respectively. C18 sorbents are more suitable for selective extraction of less polar precursors. The initial version of the method was imprecise and so the imprecision of the different steps was assessed. The maceration of the solid parts and the liquid-liquid extraction of the aromas released in the acid hydrolysis proved to be the critical steps. Greater crushing of the solid parts and solid-phase extraction (SPE) instead of liquid-liquid extraction (LLE) improved reproducibility. In the method finally proposed about 100 aromatic components belonging to four large groups (lipid derivatives, shikimic acid derivatives, norisoprenoids and terpenes) were determined with good reproducibility. Important aroma compounds, such as cis-rose oxide or wine lactone were detected in non-Muscat grapes. 相似文献
896.
This forum article outlines some of the major challenges in present day biomarker discovery research. Notably the dilemma of reaching sufficient concentration sensitivity versus the required analysis time per sample is highlighted using a model calculation. A number of possible developments and recent research findings are considered to show possible ways out of this dilemma. Finally, the challenge of processing large, megavariate datasets prior to statistical analysis is presented. 相似文献
897.
898.
Koryagina NL Savelieva EI Khlebnikova NS Goncharov NV Jenkins RO Radilov AS 《Analytical and bioanalytical chemistry》2006,386(5):1395-1400
A novel procedure has been developed for determination of fluoroacetic acid (FAA) in water and biological samples. It involves
ethylation of FAA with ethanol in the presence of sulfuric acid, solid-phase microextraction of the ethyl fluoroacetate formed,
and subsequent analysis by GC-FID or by GC-MS in selected-ion-monitoring mode. The detection limits for FAA in water, blood
plasma, and organ homogenates are 0.001 μg mL−1, 0.01 μg mL−1, and 0.01 μg g−1, respectively. The determination error at concentrations close to the detection limit was less than 50%. For analysis of
biological samples, the approach has the advantages of overcoming the matrix effect and protecting the GC and GC-MS systems
from contamination. Application of the approach to determination of FAA in blood plasma and organ tissues of animals poisoned
with sodium fluoroacetate reveals substantial differences between the dynamics of FAA accumulation and clearance in rabbits
and rats. 相似文献
899.
Poór B Michniewicz N Kallay M Buma WJ Kubinyi M Szemik-Hojniak A Deperasiñska I Puszko A Zhang H 《The journal of physical chemistry. A》2006,110(22):7086-7091
We have unraveled the effects of an amino substituent in the ortho position on the excited-state dynamics of 4-nitropyridine N-oxide by studying the picosecond fluorescence kinetics and femtosecond transient absorption of a newly synthesized compound, 2-butylamino-6-methyl-4-nitropyridine N-oxide, and by quantum chemical calculations. Similar to the parent compound, the S(1) state of the target molecule has significant charge-transfer character and shows a large (approximately 8000 cm(-1)) static Stokes shift in acetonitrile. Analysis of the experimental and the theoretical results leads, however, to a new scenario in which this intramolecular charge transfer triggers in polar, aprotic solvents an ultrafast (around 100 fs) intramolecular proton transfer between the amino and the N-O group. The electronically excited N-OH tautomer is subsequently subject to solvent relaxation and decays with a lifetime of approximately 150 ps to the ground state. 相似文献
900.
Amelichev SA Konstantinova LS Obruchnikova NV Rakitin OA Rees CW 《Organic letters》2006,8(20):4529-4532
Fused aromatic and heterocyclic 1,2,3,4,5-pentathiepins react with triphenylphosphine and alkynes bearing electron-withdrawing groups to give the corresponding 1,4-dithiins in high yields. Unsymmetrical alkynes add regioselectively to afford products in agreement with the electron distribution in a proposed reaction intermediate. A mechanism for these reactions is proposed. 相似文献