全文获取类型
收费全文 | 14480篇 |
免费 | 2591篇 |
国内免费 | 2035篇 |
专业分类
化学 | 11425篇 |
晶体学 | 134篇 |
力学 | 756篇 |
综合类 | 126篇 |
数学 | 1821篇 |
物理学 | 4844篇 |
出版年
2024年 | 35篇 |
2023年 | 297篇 |
2022年 | 374篇 |
2021年 | 457篇 |
2020年 | 679篇 |
2019年 | 647篇 |
2018年 | 564篇 |
2017年 | 445篇 |
2016年 | 678篇 |
2015年 | 721篇 |
2014年 | 843篇 |
2013年 | 1096篇 |
2012年 | 1278篇 |
2011年 | 1318篇 |
2010年 | 958篇 |
2009年 | 898篇 |
2008年 | 911篇 |
2007年 | 846篇 |
2006年 | 836篇 |
2005年 | 689篇 |
2004年 | 588篇 |
2003年 | 515篇 |
2002年 | 627篇 |
2001年 | 383篇 |
2000年 | 354篇 |
1999年 | 369篇 |
1998年 | 251篇 |
1997年 | 230篇 |
1996年 | 211篇 |
1995年 | 166篇 |
1994年 | 155篇 |
1993年 | 97篇 |
1992年 | 103篇 |
1991年 | 99篇 |
1990年 | 76篇 |
1989年 | 64篇 |
1988年 | 54篇 |
1987年 | 29篇 |
1986年 | 43篇 |
1985年 | 41篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1979年 | 4篇 |
1974年 | 2篇 |
1968年 | 3篇 |
1957年 | 3篇 |
1936年 | 2篇 |
1930年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
151.
二氧化碳多相催化加氢的新进展 总被引:4,自引:0,他引:4
就近年来关于CO2活化、几个重要的CO2多相催化加氢反应及廉价氢的供给的研究进展进行综述。参考文献34篇。 相似文献
152.
153.
This is the second part of a paper which deals with the advantages and disadvantages of relative instrumental neutron activation
analysis concerning traceability and uncertainty, and the current scope and possible future extensions of neutron activation
analysis as a primary ratio method. The first part of this paper has been published in this Journal [1].
Received: 19 March 2001 Accepted: 2 October 2001 相似文献
154.
155.
Wei L Yang B Yang R Huang C Wang J Shan X Sheng L Zhang Y Qi F Lam CS Li WK 《The journal of physical chemistry. A》2005,109(19):4231-4241
The photoionization and dissociative photoionization of acetone have been studied at the photon energy range of 8-20 eV. Photoionization efficiency spectra for ions CH3COCH3+, CH3+, C2H3+, C3H3+, C3H5+, CH(2-)CO+, CH3CO+, C3H4O+, and CH3COCH2+ have been measured. In addition, the energetics of the dissociative photoionization has been examined by ab initio Gaussian-3 (G3) calculations. The computational results are useful in establishing the dissociation channels near the ionization thresholds. With the help of G3 results, the dissociation channels for the formation of the fragment ions CH3CO+, CH2CO+, CH3+, C3H3+, and CH3COCH2+ have been established. The G3 results are in fair to excellent agreement with the experimental data. 相似文献
156.
157.
158.
Yong Zhao Xianliang Sheng Jin Zhai Lei Jiang Chunhe Yang Zhongwei Sun Yongfang Li Daoben Zhu 《Chemphyschem》2007,8(6):856-861
Titanium dioxide (TiO(2)) photoelectrodes with micro/nano hierarchical branched inner channels have been prepared by an electrohydrodynamic (EHD) technique and assembled to form dye-sensitized solar cells (DSSCs). Excellent penetration of ionic-liquid electrolytes and enhanced light harvesting in the longer wavelength region are realized within the composite-structure electrode, thus a better fill factor (ff) of 75.3 % and higher conversion efficiency (eta) of 7.1 % are obtained for viscous ionic-liquid electrolytes compared to pure nanostructured films. Hierarchical branched channels in the photoanodes can efficiently improve the transport properties of redox-active species in viscous electrolytes, which is demonstrated by electrical impedance spectroscopy (EIS). The incident monochromatic photon-to-electron conversion efficiency (IPCE) shows that enhanced light scattering in the composite film is of benefit for light harvesting and thus for solar energy conversion efficiency. 相似文献
159.
采用原子吸收光谱法测定了96例精神分裂症患者和101名正常对照组的头发Zn、Cu、Fe、Ca、Mg元素含量。结果发现,精神分裂症患者头发n和Mg元素含量明显低于对照组,而Cu、Fe和Ca元素含量明显高于对照组。提示精神分裂症的发病,可能与Zn和Mg元素含量降低,Cu、Fe和Ca元素含量升高有关。 相似文献
160.
Electroosmotic flow (EOF) is a phenomenon associated with the movement of an aqueous solution induced by the application of an electric field in microchannels. The characteristics of EOF depend on the nature of the surface potential, i.e., whether it is uniform or nonuniform. In this paper, a lattice Boltzmann model (LBM) combined with the Poisson-Boltzmann equation is used to simulate flow field in a rectangular microchannel with nonuniform (step change) surface potentials. The simulation results indicate that local circulations can occur near a heterogeneous region with nonuniform surface potentials, in agreement with those by other authors. Largest circulations, which imply a highest mixing efficiency due to convection and short-range diffusion, were found when the average surface potential is zero, regardless of whether the distribution of the heterogeneous patches is symmetric or asymmetric. In this work, we have illustrated that there is a trade-off between the mixing and liquid transport in EOF microfluidics. One should not simply focus on mixing and neglect liquid transport, as performed in the literature. Excellent mixing could lead to a poor transport of electroosmotic flow in microchannels. 相似文献