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971.
Peroxisomicine A1 is a potentially antineoplastic compound isolated from the seeds of Karwinskia parvifolia. It is considered as a useful chemotype for the preparation of topoisomerase II targeted anticancer cells. Stereochemically, it is characterized by the presence of two stereocenters and a rotationally hindered and thus likewise stereogenic biaryl axis. In this contribution, the absolute configuration of peroxisomicine A1 and its epimer, peroxisomicine A2, was established by means of a five-step degradative procedure giving the respective R- and S-configured methyl 2-(2′-methyl-5′-oxotetrahydrofuryl)acetates. The configuration of the degradation product was obtained by means of optical rotation, 1H NMR analysis using a chiral displacement reagent, and by experimental and quantum chemical circular dichroism (CD) investigations. Based on the results obtained here and considering our previous work on the relative configuration at centers versus axis of these compounds, peroxisomicine A1 resulted to be the P,3S,3′S-isomer and peroxisomicine A2 the P,3R,3′S-isomer. 相似文献
972.
酞菁,酞菁铁及酞菁镍电子性质的理论研究 总被引:1,自引:0,他引:1
以双片层分子为晶体单胞模型,用量子化学具有晶体轨道的EHMO方法研究了酞菁、酞菁铁及酞菁镍的导电性能,讨论了碘掺杂对它的影响。计算结果表明:由于碘掺杂后,系体构型发生了较大的变化,层间作用加强,从而前述几种晶体的能隙均显著降低,电导率大幅度提高。 相似文献
973.
A white substance was got by directly heating TiSi powder on Ti foil, under Ar+O
2 atmosphere. ED, EDX, SEM and HRTEM studies reveal that the white substance consists of amorphous SiO
2 nanowires of smooth surface and uniform diameter (40-90 nm). X-ray-induced luminescent emission experiment shows that two
broad peaks are at 430 and 570 nm. A one-dimensional growth mechanism, on the basis of the one-dimensional thermal flow during
nanowire formation, is discussed. 相似文献
974.
Parameterization of OPLS-AA force field for the conformational analysis of macrocyclic polyketides 总被引:1,自引:0,他引:1
The parameters for the OPLS-AA potential energy function have been extended to include some functional groups that are present in macrocyclic polyketides. Existing OPLS-AA torsional parameters for alkanes, alcohols, ethers, hemiacetals, esters, and ketoamides were improved based on MP2/aug-cc-pVTZ and MP2/aug-cc-pVDZ calculations. Nonbonded parameters for the sp(3) carbon and oxygen atoms were refined using Monte Carlo simulations of bulk liquids. The resulting force field predicts conformer energies and torsional barriers of alkanes, alcohols, ethers, and hemiacetals with an overall RMS deviation of 0.40 kcal/mol as compared to reference data. Densities of 19 bulk liquids are predicted with an average error of 1.1%, and heats of vaporization are reproduced within 2.4% of experimental values. The force field was used to perform conformational analysis of smaller analogs of the macrocyclic polyketide drug FK506. Structures that adopted low-energy conformations similar to that of bound FK506 were identified. The results show that a linker of four ketide units constitutes the shortest effector domain that allows binding of the ketide drugs to FKBP proteins. It is proposed that the exact chemical makeup of the effector domain has little influence on the conformational preference of tetraketides. 相似文献
975.
976.
977.
某些分子光谱分析法测定核酸的进展 总被引:36,自引:3,他引:36
对近年来利用分光光度法、荧光法和共振光散射法定量测定核酸的现状进行了评述,表中列出了重要的反应体系及分析特征,引用文献77篇。 相似文献
978.
A. V. Sinitsky M. B. Darhovskii A. L. Tchougreff I. A. Misurkin 《International journal of quantum chemistry》2002,88(4):370-379
In the present work the semiempirical effective crystal field (ECF) method previously designed for electronic structure calculations of transition metal complexes and utilizing non‐Hartree–Fock trial wave function and parameterized for complexes of doubly charged Cr2+, V2+, Mn2+, Fe2+, Co2+, and Ni2+ cations is extended to complexes of triply charged cations of 3d‐elements. With the parameters adjusted the ECF method is applied to calculations of ground states and low‐energy spectra of the d‐shells of fluoro‐, chloro‐, aqua‐, amino‐, and cyano‐complexes of the triply charged cations. Obtained total spin and symmetry of the ground states match the experimentally observed ones. Satisfactory agreement between the calculated and experimental d‐shell electronic transition energies is achieved as well. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
979.
利用纯电化学手段获得了具有较强表面增强拉曼活性的镍电极, 改进了原有的镍电极表面预处理方法. 结果表明, 在0.5 mol/L的NaClO4溶液中, 结合电化学阶跃技术和循环伏安技术, 可以得到合适的粗糙镍电极; 同时, 还得到了探针分子吡啶在该粗糙镍电极表面随电极电位变化的表面增强拉曼光谱(SERS), 此时谱峰强度获得了极大的增强; 还研究了粗糙镍电极的扫描电子显微镜(SEM)图像, 并估算出其SERS增强因子约为104, 此结果比以前的镍电极表面粗糙方法所能达到的增强因子高一个数量级. 相似文献
980.
A rapid and reliable high performance liquid chromatographic (HPLC) method for the simultaneous determination of heterocyclic
compounds, namely nicotinic acid, nicotinamide, and 3-cyanopyridine, in industrial effluent is described. A Φ4.6 mm × 150
mm, 5 μm C-18 reversed phase stationery phase, and a methanol-acetonitrile-water tertiary mobile phase (20:20:60 v/v) were
used for separation. The detection wavelength of a diode array (DAD) was set at 216 nm with a bandwidth of 16 nm. Phenol was
used as an internal standard. The regression equations revealed a linear relationship between the concentration of the analytes
injected and the peak area detected by DAD. The limits of detection (S/N = 3) ranged from 0.70 to 1.18 mg L−1, the recoveries ranged from 87% to 102% and the precision expressed as % RSD intra-day and inter-day varied from 0.9 to 3.9
and 1.2 to 5.6, respectively. This method is rapid, sensitive and suitable for the monitoring of nicotinic acid, nicotinamide,
and 3-cyanopyridine in effluent of related pharmaceutical manufacturing plants. 相似文献