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71.
OH and HO(2) radicals, atmospheric detergents, and the reservoir thereof, play central roles in tropospheric chemistry. In spite of their importance, we had no choice but to trust their concentrations predicted by modeling studies based on known chemical processes. However, recent direct measurements of these radicals have enabled us to test and revise our knowledge of the processes by comparing the predicted and observed values of the radical concentrations. We developed a laser-induced fluorescence (LIF) instrument and successfully observed OH and HO(2) at three remote islands of Japan (Oki Island, Okinawa Island, and Rishiri Island). At Okinawa Island, the observed daytime level of HO(2) agreed closely with the model estimates, suggesting that the photochemistry at Okinawa is well described by the current chemistry mechanism. At Rishiri Island, in contrast, the observed daytime level of HO(2) was consistently much lower than the calculated values. We proposed that iodine chemistry, usually not incorporated into the mechanism, is at least partly responsible for the discrepancy in the results. At night, HO(2) was detected at levels greater than 1 pptv at all three islands, suggesting the presence of processes in the dark that produce radicals. We showed that ozone reactions with unsaturated hydrocarbons, including monoterpenes, could significantly contribute to radical production. 相似文献
72.
Bi-Sr-Ca-Cu-O超导材料中存在110K和80K2个超导相。其组成是Bi_2Sr_2Ca_2Cu_3O_y和Bi_2Sr_2CaCu_2O。但迄今为止,在按2223组成比合成的未掺杂Bi系超导材料中从未得到过纯的110K相,也未见过组成为2223,零电阻温度在100K以上材料的报道。为了探索形成110K相的最佳条件,本文以2223组成比为参考,合成了5个系列材料:Bi_xSr_2Ca_2Cu_3O_y,Bi_2Sr_xCa_2Cu_3O_y,Bi_2Sr_2Ca_xCu_3O_y,Bi_2Sr_2Ca_2Cu_xO_y,Bi_i Sr_uCa_yCu_wO_s。 相似文献
73.
聚醚聚酯嵌段共聚物共混物表面组成的ESCA研究 总被引:1,自引:0,他引:1
<正> 关于生物医用材料的微多相分离结构和适宜的亲、疏水性同它血液相容性间关系的研究已有不少文献报道。由于材料在使用时真正同血液相接触的只是材料的表面部分,因此材料的表面组成、结构和性质对它的血液相容性就具有更为直接的关系。对聚醚 相似文献
74.
The thermal degradation characteristics of head-to-head poly(styrene) [HHPS] should provide insight with respect to the impact
of head-to-head placement on the thermal stability of traditional atactic head-to-tail polymer [HTPS]. The synthesis of head-to-head
poly(styrene) must be accomplished indirectly. The head-to-head polymer is most satisfactorily obtained by dissolving metal
reduction of poly(2,3-diphenyl-1,3-butadiene) [PDBD] generated by radical polymerization of the corresponding diene monomer.
Full saturation of the polymer mainchain requires several iterations of the reduction procedure. Since the decomposition of
poly(2,3-diphenyl-1,3-butadiene) is prominent at 374°C and that for head-to-head poly(styrene) is similarly facile at 406°C,
it seemed feasible that TG of partially hydrogenated PDBD might be utilized as a convenient means of monitoring the extent
of hydrogenation. This has been demonstrated for various levels of unsaturation remaining - from approximately 90 to less
than 10%. Within this range the peak areas from the DTG plots of the partially hydrogenated polymer provide a good reflection
of the ratio of unsaturated to saturated units in the polymer. Even low levels of unsaturation in the polymer may be detected
by the asymmetry of the decomposition peak for the polymer.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
75.
Bromide and iodide ions were determined simultaneously by capillary isotachophoresis using an aqueous electrolyte system; the separation principle was based on the ion-pairing equilibria between tetradecyldimethylbenzylammonium ion and these anions in the leading electrolyte. The interaction between iodide ion and tetradecyldimethylbenzylammonium ion was stronger than that for bromide ion. Thus complete separation of bromide and iodide ions could be obtained by using a leading electrolyte containing 1.5 mM tetradecyldimethylbenzylammonium ion. The pH of the leading electrolyte was adjusted to 5.0. The relative standard deviations of the zone length for bromide and iodide ions were 1.1 and 1.2%, respectively, when mixture of 3.0 mM of these ions was analysed. A 150-μl volume could be injected for the simultaneous determination of low concentrations of bromide and iodide ions. 相似文献
76.
Sn基合金负极材料具有高达990 mAh·g-1的理论比容量,但其也存在因脱嵌锂过程发生巨大的体积变化而导致循环性能较差的问题. 本文以Sn、Fe、石墨为原料利用简易的高能球磨法成功制备了具有核壳结构的FeSn2-C复合物,系统研究了球磨时间、FeSn2相含量对材料物相结构及电化学性能的影响,并分析了电极的失效机理. 研究表明,球磨时间的增加有利于FeSn2金属间化合物相的形成及材料颗粒的细化,进而有利于材料比容量的增加及循环性能的提升;FeSn2相含量的增加能够提高FeSn2-C材料的比容量,但会降低FeSn2-C电极的循环稳定性. 经工艺优化及组分调节,球磨24 h合成的Sn20Fe10C70材料具有最优的电化学性能,材料的比容量在540 mAh·g-1左右,并能稳定循环100次,是一种非常有发展前途的锂离子电池高比容量负极材料. 相似文献
77.
The multilayer adsorption on the solid/liquid interface in binary mixtures was studied by adsorption space filling with constant
and variable layer thickness. Adsorption from benzene/n-heptane mixtures was examined on hydrophilic and hydro-phobic surfaces.
The free enthalpy of adsorption, Δ21
G=f (x
1), was calculated from the adsorption excess isotherm by integration of the Gibbs equation. Supposing that the free enthalpy
is mainly due to adsorption in the first layer, the composition of this layer can be calculated from the Δ21
G=f (x
1) function. It was established that the adsorption layer thickness in benzene/heptane mixtures increases significantly with
increasing benzene content. This statement was supported by X-ray diffraction on hydrophobic clay minerals.
Received: 2 April 1997 Accepted: 10 June 1997 相似文献
78.
Optical resolution of new quinolone drugs by capillary electrophoresis with ligand-exchange and host-guest interactions 总被引:3,自引:0,他引:3
A method for the optical resolution of new quinolone drugs (NQs) by capillary electrophoresis has been investigated. The NQs were adequately resolved using a γ-cyclodextrin (γ-CD)-Zn(II)-
-phenylalanine (
-Phe) solution as the running solution. The resolution depended on the components of the running solution and their concentrations. When
-Phe was used instead of
-Phe, inversion of the migration order of the enantiomers was observed. The resolution mechanism is considered to be due to a ligand-exchange interaction of the NQs with Zn(II) and
-Phe, in combination with a host-guest interaction of those with γ-CD. 相似文献
79.
On the basis of the data on the distribution of various neutral solutes between sodium dodecyl sulfate (SDS) micelles and water, the control of separation selectivity in micellar electrokinetic chromatography (MEKC) by modification of the micellar phase with organic additives has been proposed and applied to the separation of simple model compounds. It was found that the distribution constants between the micelles and water (Kd,mc), which were determined by means of MEKC, of the solutes possessing hydrophilic functional groups are much larger than those between heptane and water (Kd,hep), whereas the Kd,mc values of the solutes possessing no hydropholic groups are comparable to their Kd,hep values. This indicates that the former solutes are preferentially solubilized in the Stern layer of the micelles and that the latter are located in the hydrocarbon core. In MEKC separations of aromatic compounds and metal acetylacetonates, considerable changes in separation selectivity were caused by the addition of compounds possessing both hydrophilic functional groups such as alcohols, phenol and ketones to the SDS micellar solution. The variations of the retention factors of the analytes could be explained in terms of saturation of the solubilization sites in the Stern layer with the modifiers, specific interaction of the modifiers with the analytes via hydrogen bonding in the micelles, and expansion of the core volume with the hydrocarbon parts of the modifiers. Such effects of the micellar modification could improve the resolution as well as the selectivity of MEKC separations. 相似文献
80.
Henning Henke 《无机化学与普通化学杂志》1993,619(2):311-317
Crystal Structure and Pseudosymmetry of a New Modification of Potassium Hexachloroniobate(V), KNbCl6. Comments on the Cubic Phase Long needles of KNbCl6 – invariably twinned around [100] – are obtained if the material is crystallized from SOCl2 solution. The structure has been determined from X-ray data collected with a single-crystal diffractometer at room temperature [space group P21/n, Z = 16, a = 6.894(1), b = 22.073(4), c = 23.337(3) Å, β = 91.00(1)°, R = 0.032 for 2 909 unique reflexions, 290 structural parameters]. Distorted NbCl6? octahedra and ?interstitial’? K+ ions are found to form similar arrangements, each of them corresponding to a closest packing of spheres with the layer sequence ACAB (stacking symbol hc). The resulting asymmetry in coordination by potassium is coupled with a strong off-centre displacement of the Nb atoms in any of the four independent chlorine polyhedra (0.14 Å on average). A pronounced pseudosymmetry accounts for the twinning. Since P21/m21/n21/b (no. 62) is already a good approximation of the real structure, only one formal step of symmetry reduction (index t2) is needed to create both, the observed twin law and the actual space group P1 21/n1. Above 180°C a reconstructive phase transition leads to the ‘face-centred cubic’ modification with ~ 10% lower density. 相似文献