全文获取类型
收费全文 | 16336篇 |
免费 | 2600篇 |
国内免费 | 3592篇 |
专业分类
化学 | 18170篇 |
晶体学 | 313篇 |
力学 | 374篇 |
综合类 | 81篇 |
数学 | 331篇 |
物理学 | 3259篇 |
出版年
2024年 | 53篇 |
2023年 | 267篇 |
2022年 | 591篇 |
2021年 | 737篇 |
2020年 | 975篇 |
2019年 | 771篇 |
2018年 | 681篇 |
2017年 | 756篇 |
2016年 | 918篇 |
2015年 | 879篇 |
2014年 | 1015篇 |
2013年 | 1716篇 |
2012年 | 1202篇 |
2011年 | 1204篇 |
2010年 | 948篇 |
2009年 | 1043篇 |
2008年 | 1090篇 |
2007年 | 1033篇 |
2006年 | 915篇 |
2005年 | 821篇 |
2004年 | 822篇 |
2003年 | 643篇 |
2002年 | 782篇 |
2001年 | 427篇 |
2000年 | 343篇 |
1999年 | 300篇 |
1998年 | 280篇 |
1997年 | 207篇 |
1996年 | 185篇 |
1995年 | 194篇 |
1994年 | 158篇 |
1993年 | 135篇 |
1992年 | 86篇 |
1991年 | 73篇 |
1990年 | 50篇 |
1989年 | 29篇 |
1988年 | 31篇 |
1987年 | 24篇 |
1986年 | 24篇 |
1985年 | 24篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1977年 | 7篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Chunlin Li Yilu Fu Guozhu Bian Tiandou Hu Yaning Xie Jing ZhanDepartment of Chemical Physics University of Science and Technology of China Hefei China Institute of High Energy Physics Chinese Academy of Sciences Beijing China 《天然气化学杂志》2003,12(3)
The Ni/CeO2-ZrO2-Al2O3 catalyst with different Al2O3 and NiO contents were prepared by hydrothermal synthesis method. The catalytic performance for CO2 reforming of CH4 reaction, the interaction among components and the relation between Ni content and catalyst surface basicity were investigated. Results show that the interaction between NiO and Al2O3 is stronger than that between NiO and CeO2-ZrO2.The addition of Al2O3 can prevent the formation of large metallic Ni ensembles, increase the dispersion of Ni, and improve catalytic activity, but excess Al2O3 causes the catalyst to deactivate easily. The interaction between NiO and CeO2 results in more facile reduction of surface CeO2. The existence of a small amount of metallic Ni can increase the number of basic sites. As metallic Ni may preferentially reside on the strong basic sites, increasing Ni content can weaken the catalyst basicity. 相似文献
82.
83.
Multiwalled carbon nanotubes were modified by carboxy groups. Four independent methods for the determination of the degree
of functionalization of the surface were proposed: 13C NMR spectroscopy, thermogravimetry, titrimetry, and fluorimetry. The first two methods show the total content of carboxy
groups in the sample, and the latter two methods give information about the content of the surface groups only.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 291–295, February, 2008. 相似文献
84.
85.
U.Deva Priyakumar 《Tetrahedron letters》2004,45(12):2495-2498
A novel preference for planar tetracoordination was observed over the conventional tetrahedral arrangement in a new series of C5H2, C5H4, C5H41+/2+ and related compounds. The stability of these molecules is assessed with the ring-opening barriers, HOMO-LUMO gap, singlet-triplet energy differences and nucleus independent chemical shift values. 相似文献
86.
A. Filarowski A. Koll A. Kochel J. Kalenik P. E. Hansen 《Journal of Molecular Structure》2004,700(1-3):67-72
The crystal structures of two ortho-hydroxy ketones (5-chloro-2-hydroxyacetophenone (I K) and 3,5-dichloro-2-hydroxyacetophenone (II K)) have been determined with X-ray diffraction at 100 K. A comparison of steric effects on properties of pseudoaromatic hydrogen bonds in ortho-hydroxy acetophenone and ortho-hydroxy ketimines have been carried out with the application of crystallographic data.
Nuclear quadrupole resonance (NQR) spectra have been measured and interpreted. 相似文献
87.
88.
Electrochemical oxidation of thio/carbohydrazide and their hydrazone derivatives Benzaldehyde thiocarbohydrazone [BTCH] diacetylene
thiocarbohydrazone [DATCH] have been studied in Brit-ton Robinson buffer in aqueous and nonaqueous media at a glassy carbon
electrode. The effects of pH, sweep rate, concentration, temperature and surfactants have been studied. The complex bis (carbo/thiocabohydrazide) Zn(II) chloride was also subjected to voltammetric analysis in order to understand the reactivity
both in free and metal bound states. The reaction conditions were optimized for the determination of above compounds in micrograms
quantities by differential pulse voltammetry, analytical utility of this investigation is also highlighted. 相似文献
89.
Xu Zhang Dongfeng Xue Meinan Liu Henryk Ratajczak Dongli Xu 《Journal of Molecular Structure》2005,754(1-3):25-30
On the basis of the crystallographic characteristics of lithium niobate (LN) crystals, Law of Bravais and Pauling's third rule (i.e. Polyhedral Sharing Rule) are employed with the aim to find the relationship between the crystal structure and morphological faces of LN powders. In order to validate our analytical results, we have successfully synthesized LN powders and measured the corresponding X-ray powder diffraction. Our results show that the structural analysis is consistent with the experimental data and is helpful and effective for us to control the single-crystal growth and to design superstructures at the specific plane, starting from the viewpoint of the microscopic behaviors of constituent chemical bonds and polyhedra in the crystallographic frame. 相似文献
90.
ZHU Hai-Xia YAN Shi-Lei 《理论物理通讯》2004,42(11)
We study the ferromagnetic properties of spin-1 system, which is considered in the frame of the bond dilution and random positive or negative anisotropy Blume-Capel model in the effective field theory and a cutting approximation. The investigation of phase diagrams displays some rich properties of the trajectory of tricritical point, reentrant henomena at low temperatures. Under certain both bond concentrations and random negative anisotropy, there are new transition lines of double tricritical points. So special emphasis is placed on the influence of the bond dilution and random anisotropy on phase diagrams. The magnetizations of the system are also discussed. Some results have not been evealed in previous reports. 相似文献