全文获取类型
收费全文 | 58070篇 |
免费 | 4310篇 |
国内免费 | 3003篇 |
专业分类
化学 | 30499篇 |
晶体学 | 536篇 |
力学 | 3295篇 |
综合类 | 285篇 |
数学 | 12165篇 |
物理学 | 18603篇 |
出版年
2024年 | 105篇 |
2023年 | 592篇 |
2022年 | 915篇 |
2021年 | 975篇 |
2020年 | 1129篇 |
2019年 | 1091篇 |
2018年 | 2071篇 |
2017年 | 2234篇 |
2016年 | 1960篇 |
2015年 | 1804篇 |
2014年 | 1985篇 |
2013年 | 2661篇 |
2012年 | 5706篇 |
2011年 | 4916篇 |
2010年 | 3421篇 |
2009年 | 3142篇 |
2008年 | 2258篇 |
2007年 | 2233篇 |
2006年 | 2058篇 |
2005年 | 5594篇 |
2004年 | 4803篇 |
2003年 | 3046篇 |
2002年 | 1217篇 |
2001年 | 838篇 |
2000年 | 645篇 |
1999年 | 818篇 |
1998年 | 687篇 |
1997年 | 639篇 |
1996年 | 700篇 |
1995年 | 547篇 |
1994年 | 504篇 |
1993年 | 408篇 |
1992年 | 539篇 |
1991年 | 474篇 |
1990年 | 388篇 |
1989年 | 308篇 |
1988年 | 255篇 |
1987年 | 192篇 |
1986年 | 168篇 |
1985年 | 154篇 |
1984年 | 116篇 |
1983年 | 87篇 |
1982年 | 59篇 |
1981年 | 54篇 |
1979年 | 47篇 |
1976年 | 99篇 |
1975年 | 65篇 |
1974年 | 68篇 |
1973年 | 59篇 |
1972年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
We study linear dynamical systems with multidimensional time in Banach spaces. Using Taylor functional calculus we prove that under additional assumptions hyperbolic systems have shadowing property. 相似文献
192.
Jiangen Huang Guiqin Zhang Yuanhe Huang Decai Fang Deqing Zhang 《Journal of magnetism and magnetic materials》2006
A one-dimensional (1D) silver (I) complex of nitronyl nitroxide with fairly strong antiferromagnetic interaction, in which the metal ions are diamagnetic, is investigated by means of the ab initio crystal orbital method based on the density functional theory. The calculated values of the magnetic coupling constant (J) are close to the experimental measured J value in the periodic system. The magneto-structural correlation reveals that the existence of an antiferromagnetic coupling pathway along nitronyl nitroxide units via silver (I) ion in this system. The spin population distribution also shows the existence of spin delocalization along the ONCNO–Ag–ONCNO, which affords a rational interpretation for the antiferromagnetic interaction mechanism. 相似文献
193.
对不同组分的掺FeⅢ-Ⅴ族混晶GaAs1-xPx,测量了Fe深受主中心空穴热发射的非指数恒温暗电容瞬态及DLTS谱。用混晶无序使Fe深能级展宽的模型理论拟合实验结果,得到Fe能级Gauss型展宽的半宽和中心能级的热发射率,并确定出基态空穴跃迁的中心能级的焓变与组分的关系:先是减少,而后增大,与由光电容方法得到的Gibbs自由能变量与组分x的关系明显不同。 进一步讨论表明,上述两种测量方法得到的Fe中心的激活能不同,可能反映Fe中心的键合状态和混晶无序诱导的品格弛豫的影响。 相似文献
194.
S?awomir Solecki 《Topology and its Applications》2007,154(12):2462-2464
Let I0 be the σ-ideal of subsets of a Polish group generated by Borel sets which have perfectly many pairwise disjoint translates. We prove that a Fubini-type theorem holds between I0 and the σ-ideals of Haar measure zero sets and of meager sets. We use this result to give a simple proof of a generalization of a theorem of Balcerzak-Ros?anowski-Shelah stating that I0 on N2 strongly violates the countable chain condition. 相似文献
195.
196.
R. Knizikevi?ius 《Applied Surface Science》2006,253(3):1581-1583
The ion-beam-assisted etching of silicon in Cl2 environment is considered. The theoretically calculated dependences of silicon etching rate on the flux of Cl2 molecules at different ion current densities are compared with experimentally measured. The composition of the adsorbed layer is determined. It is found that SiCl2 molecules prevail in the adsorbed layer. The reciprocal of relative concentration of SiCl2 molecules in the adsorbed layer linearly depends on the ion-to-neutral flux ratio. 相似文献
197.
Highly ordered composite nanowires with multilayer Ni/Cu and NiFe/Cu have been fabricated by pulsed electrodeposition into
nanoporous alumina membrane. The diameter of wires can be easily varied by pore size of alumina, ranging from 30 to 100 nm.
The applied potential and the duration of each potential square pulse determine the thickness of the metal layers. The nanowires
have been characterized by transmission electron microscopy (TEM), magnetic force microscopy (MFM), and vibrating sample magnetometer
(VSM) measurements. The MFM images indicate that every ferromagnetic layer separated by Cu layer was present as single isolated
domain-like magnet. This technique has potential use in the measurement and application of magnetic nanodevices. 相似文献
198.
199.
SnO2 was added to high-permeability MnZn ferrites and MnZn ferrites for high-frequency power supplies. The effects of the SnO2 addition were studied. Sn4+ ions can dissolve into the spinel lattice and form stable Fe2+–Sn4+ pairs and hence can compensate the magneto-crystalline anisotropy constant K1 and improve the initial permeability effectively. The initial permeability of ferrites is also improved as abnormal grain growth caused by ion vacancy is controlled with SnO2 doping. In addition, the SnO2 doping also leads to a decrease in the relative loss factor and an increase in density. The power loss and minimum power loss temperature decrease with SnO2 doping. 相似文献
200.