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991.
The stability constants of several divalent first row transition and trivalent lanthanide metal complexes were determined by capillary electrophoresis (CE) methods. Four different approaches, i.e. direct formation, ligand exchange, metal exchange and metal-ligand double exchange were developed. To verify if these CE methods are indeed applicable, the stability constant of CuHEDTA was re-determined to be 17.47 ± 0.20 (consistent with the published 17.50) using the CuEDTA and ZnHEDTA metal-ligand double exchange approach. The stability constants of lanthanide (Ce3+ and Eu3+) and transition metal (Ni2+ and Zn2+) complexes of an aminopolycarboxylate ligand, DO2A (1,7-dicarboxymethyl-1,4,7,10-tetraazacyclododecane) were measured under the direct complex formation condition. The stability constant of the NiDO2A complex was determined by the ligand exchange method using 1,4,8,11-tetraazaundecane (2,3,2-tet) as the competing ligand. The stability constant of CuDO2A complex was determined by the metal exchange method using Zn2+ ion as the competing metal ion, and complex formation competitions of Ni2+ and Cu2+ between DO2A and 2,3,2-tet were studied by the metal-ligand double exchange method. Effects of experimental conditions and the advantages and limitations of these CE methods are discussed. 相似文献
992.
We report ab initio calculations of the indirect nuclear spin–spin coupling constants of PbH4 using a basis set which was specially optimized for correlated calculations of spin–spin coupling constants. All nonrelativistic
contributions and the most important part of the spin–orbit correction were evaluated at the level of the random phase approximation.
Electron correlation corrections to the coupling constants were calculated with the multiconfigurational linear-response method
using extended complete and restricted active space wavefunctions as well as with the second-order polarization propagator
approximation and the second-order polarization propagator approximation with coupled-cluster singles and doubles amplitudes.
The effects of nuclear motion were investigated by calculating the coupling constants as a function of the totally symmetric
stretching coordinate. We find that the Fermi contact term dominates the Pb‐H coupling, whereas for the H‐H coupling it is
not more important than the orbital paramagnetic and diamagnetic contributions. Correlation affects mainly the Fermi contact
term. Its contribution to the one-bond coupling constant is reduced by correlation, independent of the method used; however,
the different correlated methods give ambiguous results for the Fermi contact contribution to the H‐H couplings. The dependence
of both coupling constants on the Pb‐H bond length is dominated by the change in the Fermi contact term. The geometry dependence
is, however, overestimated in the random phase approximation.
Received: 16 November 1998 / Accepted: 30 March 1999 / Published online: 14 July 1999 相似文献
993.
采用电位滴定法在DMSO/H2O(质量比80:20)混合体系中测定了磺酰脲和三唑并嘧啶磺酰胺类除草剂的酸离解常数,进而采用回归分析方法探讨了测得的pKa值与化合物的前沿轨道能级以及取代基效应之间的相关性,结果较为满意,从而证明从该体系测得的pKa值用于构效关系分析是完全可行的. 相似文献
994.
用从头算的方法在6-31G水平上研究了3-羟基-3-甲基-2-丁酮(1)和苯甲酰甲酸甲酯(2)热分解反应的机理。结果是:前一反应是经历五元环过渡态到达氢键中间体,它接着直接分解成乙醛的异构体和丙酮,最后乙醛的异构体异构化成乙醛;后一反应经历六元环过渡态形成中间体1(INT1),中间体1(INT1)直接分解成中间体2(INT2)和甲醛,中间体2(INT2)经过第二个过渡态分解成苯甲醛的异构体和一氧化碳,最后苯甲醛异构体异构化成苯甲醛。其中氢迁过程是反应的速控步骤。在MP~2/6-31G//HF/6-31G+ZPE水平上,对应于这两个反应速控步骤的活化位垒分别是251.42kJ/moL和247.94kJ/mol。采用传统过渡态理论计算了两反应的热反应速率常数,理论的计算结果与实验值吻合较好。 相似文献
995.
V. A. Tolkachev 《Journal of Applied Spectroscopy》1999,66(6):874-881
The sensitivity of the delay time of the molecular rotational quantum echo to change in the rotational constants of molecules
was investigated with a model of the rotational quantum echo considered as an optically induced quantum synchronization of
the Fourier rotational modes of an asymmetric molecular top. The J-echo and the K-echo were investigated for the A- and C-configurations
of rotation of a top molecule. The contour maps of the dependence of the sensitivity of the delay time of these types of echo
to changes in the rotational constants on the parameters of the molecular tops have been obtained for all the rotational constants.
They show that the delay time of the rotational quantum echo is greatly dependent on the configuration of rotation of the
top molecule and on the rotational constants. It is shown that the optical probing of the rotational quantum echo can also
be performed by the optical rotation of the investigated molecule, and in this case the rotational force is dependent on the
intramolecular orientation of the magnetic dipole moment. It was determined that a high sensitivity of the delay time of the
echo to changes in the rotational constants can be responsible for the broadening of the echo pulse and even for its disappearance.
Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70 F. Skorina Ave., Minsk, 220072, Belarus;
e-mail: lssm@imaph.bas-net.by. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 758–764, November–December,
1999. 相似文献
996.
Mehmet Somer 《无机化学与普通化学杂志》2000,626(12):2478-2480
The vibrational spectra of the cluster anions [E4]4– (E = Si, Ge) in the metallic compounds Ba2E4 and Na4E4 have been measured and assigned based on the Td symmetry of the discrete tetrahedranide anion. Due to the lower site‐symmetries in the respective crystals all degenerate modes are split, but to different extends. The characteristic breathing frequency ν(E–E) of the [E4]4– cluster appears exclusively in the Raman spectrum and is almost unaffected by the nature of counterions: ν(E–E) = 486 cm–1 (E = Si) and 276 and 278 (Ge), respectively. The calculated valence force constants fd (Si–Si) = 1.17 Ncm–1 ( Na ); 1.15 Ncm–1 ( Ba ) and fd (Ge–Ge) = 0.98 Ncm–1 ( Na ); 0.94 Ncm–1 ( Ba ) are in good agreement with those previously reported. 相似文献
997.
Aubrey D. Jenkins Koichi Hatada Tatsuki Kitayama Takafumi Nishiura 《Journal of polymer science. Part A, Polymer chemistry》2000,38(24):4336-4342
The electron density on a carbon atom determines the 13C chemical shift observed in the NMR spectrum. In a vinyl monomer, the same electron density must contribute strongly to polar effects involved in the addition of a radical to that monomer and possibly in the addition (to a double bond) of a radical terminated by a unit derived from that monomer. It is shown that the expected correlation exists when the polar effects in polymerization reactions are represented by the parameters of the revised patterns scheme. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4336–4342, 2000 相似文献
998.
Peter G. Sutton Christopher F. Harrington Ben Fairman E. Hywel Evans Les Ebdon Tim Catterick 《应用有机金属化学》2000,14(11):691-700
Synthetic methods for the small‐scale laboratory preparation of isotopically enriched dibutyltin dichloride, dibutyltin di‐iodide, tributyltin chloride, tributyltin iodide, diphenyltin dichloride, triphenyltin chloride and triphenyltin iodide have been successfully established. Organotin iodides were prepared from redistribution reactions between tin(IV) iodide and the corresponding tetraorganotin, with the exception of dibutyltin di‐iodide, which was prepared directly from the reaction between tin metal and iodobutane. The development of novel procedures for the dealkylation/dearylation of tetraorganotins by acid hydrolysis produced superior yields of tributyltin chloride and diphenyltin dichloride in comparison with redistribution reactions. Organotin iodide redistribution reaction products were converted to their chloride analogues via the fluoride salts using an aqueous ethanolic solution of potassium fluoride. The insolubility of organotin fluoride salts was exploited to isolate and purify the isotopically enriched compounds, and to prevent losses during the purification procedure. The nuclear magnetic resonance (NMR) spectroscopic study of ‘natural abundance’ and isotopically enriched organotin compounds gave proton (1H) and carbon‐13 (13C) spectra for butyltins, Bu4−nSnXn, and phenyltins, Ph4−nSnXn (X = I, Cl), allowing the assignment of 1H and 13C chemical shifts, and 119Sn–13C and 117Sn–13C coupling constants. The 13C NMR spectroscopic analysis of 117Sn‐enriched organotin compounds has allowed the assignment of certain resonances and tin–carbon coupling constants which were previously unobservable. The spectral patterns show that Δ(1H) and Δ(13C) values are sensitive to structural changes, and that 13C shielding decreases with an increase in the electronegativity of the substituent. The tin–carbon coupling constants are also sensitive to structural changes, and for alkyl and aryl compounds the couplings decrease in the order 1J > 3J > 2J > 4J. The 13C chemical shift values and the magnitude of tin–carbon coupling constants are shown to be solvent‐dependent. The 13C spectra of the isotopically enriched compounds show that the degree of isotopic enrichment and the nature of the isotope used (magnetic or non‐magnetic) are reflected in the spectral pattern obtained. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
999.
双核钴簇合物(C6H5C2R)Co2(CO)6的合成 总被引:1,自引:0,他引:1
羰基钴簇合物Co2(CO)8可用于有机合成的催化剂。但Co2(CO)8本身不稳定,易被氧化。因此,研究不向CO2簇合物的稳定性及其催化性能具有一定的意义。 相似文献
1000.
Complexation reactions in a binary metal/phosphate system were studied. Protolytic equilibria of phosphate in the presence
of cobalt, nickel, iron, copper, chromium and silver metal ions were investigated by potentiometric titrations in the pH range
of 2–11. Stability constants of the metal/phosphate complexes were determined by computer analysis of the potentiometric titration.
Potentiometric titrations suggest that the presence of metal phosphate and metal hydrogen phosphate provides the solutions
with stability constants logK
c 2.21, 2.11, 2.23, 2.34, 1.96, and 2.14 of Co, Ni, Fe, Ag, Cr, and Cu/phosphate, respectively. The results of infrared spectroscopy,
X-ray powder diffraction and equilibrium studies were used to reveal the mode of interaction between the metal ions and phosphate.
Metal phosphates with a hydrogen phosphate anion and fully nonprotonated phosphate could be isolated under the reaction conditions. 相似文献