全文获取类型
收费全文 | 4586篇 |
免费 | 1397篇 |
国内免费 | 906篇 |
专业分类
化学 | 2996篇 |
晶体学 | 106篇 |
力学 | 66篇 |
综合类 | 42篇 |
数学 | 649篇 |
物理学 | 3030篇 |
出版年
2024年 | 29篇 |
2023年 | 73篇 |
2022年 | 160篇 |
2021年 | 157篇 |
2020年 | 236篇 |
2019年 | 198篇 |
2018年 | 161篇 |
2017年 | 191篇 |
2016年 | 271篇 |
2015年 | 229篇 |
2014年 | 234篇 |
2013年 | 642篇 |
2012年 | 341篇 |
2011年 | 331篇 |
2010年 | 244篇 |
2009年 | 351篇 |
2008年 | 343篇 |
2007年 | 305篇 |
2006年 | 318篇 |
2005年 | 255篇 |
2004年 | 256篇 |
2003年 | 225篇 |
2002年 | 195篇 |
2001年 | 206篇 |
2000年 | 166篇 |
1999年 | 140篇 |
1998年 | 122篇 |
1997年 | 85篇 |
1996年 | 82篇 |
1995年 | 56篇 |
1994年 | 48篇 |
1993年 | 38篇 |
1992年 | 38篇 |
1991年 | 24篇 |
1990年 | 22篇 |
1989年 | 16篇 |
1988年 | 10篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 13篇 |
1984年 | 16篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有6889条查询结果,搜索用时 15 毫秒
41.
Experiments employing photoreflectance spectroscopy have uncovered band bending due to electrically active defects at the Si(1 1 1)–SiO2 interface after sub-keV Ar+ ion bombardment. The band bending of about 0.5 eV resembles that for Si(1 0 0)–SiO2, and both interfaces exhibit two kinetic regimes for the evolution of band bending upon annealing due to defects healing. The healing takes place about an order of magnitude more quickly at the (1 1 1) interface, however, probably because of less fully saturated bonding and higher compressive stress. 相似文献
42.
有序分组资料的线性趋势检验主要用于检验几个二项总体反应率的线性趋势;在医学与生物学中最典型的用途是研究剂量和反应的关系. 如果用Z检验来代替通常在本检验中所用的卡方检验,就可容易地导出本检验的确切概率计算方法,和其他2×C有序列联表有着相同的形式.本文给出了该检验的确切概率计算方法. 相似文献
43.
本文把代数结构与分析体系结合起来,运用同调的方法,较系统地确定了A上C^*-模的部分理论,这里A为复数域C上的交换C^*-代数。即不仅定义了与C^*-模有关的某些新概念,而且还得到了有关C^*-模的若干结果。 相似文献
44.
Michelle J. S. Spencer Andrew Hung Ian K. Snook Irene Yarovsky 《Surface science》2003,540(2-3):420-430
The adsorption of atomic S on the Fe(1 1 0) surface is examined using density functional theory (DFT). Three different adsorption sites are considered, including the atop, hollow and bridge sites and the S is adsorbed at a quarter monolayer coverage in a p(2 × 2) arrangement. The hollow site is found to be the most stable, followed by the bridge and atop sites. At all three sites, S adsorption results in relatively minor surface reconstruction, with the most significant being that for the hollow site, with lateral displacements of 0.09 Å. Comparisons between S-adsorbed and pure Fe surfaces revealed reductions in the magnetic moments of surface-layer Fe atoms in the vicinity of the S. At the hollow site, the presence of S causes an increase in the surface Fe d-orbital density of states between 4 and 5 eV. However, S adsorption has no significant effect on the structure and magnetic properties of the lower substrate layers. 相似文献
45.
In this paper, we study the electronic band structure and the ferromagnetic properties of the organic radicalp-NPNN by employing density-functional theory with generalized gradient approximation (GGA) and local-spin densityapproximation (LSDA). The density of states, the total energy, and the spin magnetic moment are calculated. Thecalculations reveal that the δ-phase of p-NPNN has a stable ferromagnetic ground state. It is found that an unpairedelectron in this compound is localized in a single occupied molecular orbital (SOMO) constituted primarily of π* (NO)orbitals, and the main contribution of the spin magnetic moment comes from the π* (NO) orbitals. By comparison, wefind that the GGA is more suitable to describe free radical systems than LSDA. 相似文献
46.
47.
Stereoselectivity in the intermolecular Pauson-Khand reaction of electron-deficient terminal alkynes
A family of terminal alkyne dicobalthexacarbonyl complexes bearing groups with a range of electron-withdrawing abilities has been synthesized. After submitting these complexes to the intermolecular Pauson-Khand reaction with norbornadiene, electron-deficient substrates afforded up to 26% of the unexpected endo-cyclopentenone. 相似文献
48.
Image potential resonances on the Sn/Ge(1 1 1) α-phase are investigated by two closely related methods: specular electron reflection and so-called selective electron scattering. Electrons from image resonances are detected on this surface at 120 and 300 K, i.e. below and above the phase transition at about 200 K. The dispersion of the image resonances reveals at these two temperatures equivalent effective electron masses, which are characteristic for this type of electronic surface states. The results of the two methods are consistent according to the similarity of the scattering processes. Changes in the loss peak intensity with the annealing temperature are assigned to the surface quality and are reflected by characteristic photoemission intensities. 相似文献
49.
A. A. Kuznetsova V. I. Mikhailenko A. Yu. Popovskii 《Journal of Applied Spectroscopy》2004,71(5):648-653
Two types of absorption centers, one being related to monomers and the other to dimers, have been revealed by the method of statistical analysis of the normalized absorption spectra of a superthin interlayer of nitrobenzene of variable thickness formed on activated surfaces of quartz and barium fluoride and measured for different thicknesses of the interlayer. On a decrease in the interlayer thickness the concentration of dimers increases. 相似文献
50.