全文获取类型
收费全文 | 4567篇 |
免费 | 832篇 |
国内免费 | 500篇 |
专业分类
化学 | 3409篇 |
晶体学 | 41篇 |
力学 | 224篇 |
综合类 | 51篇 |
数学 | 491篇 |
物理学 | 1683篇 |
出版年
2024年 | 13篇 |
2023年 | 82篇 |
2022年 | 170篇 |
2021年 | 131篇 |
2020年 | 186篇 |
2019年 | 207篇 |
2018年 | 162篇 |
2017年 | 134篇 |
2016年 | 250篇 |
2015年 | 210篇 |
2014年 | 274篇 |
2013年 | 307篇 |
2012年 | 379篇 |
2011年 | 373篇 |
2010年 | 271篇 |
2009年 | 293篇 |
2008年 | 314篇 |
2007年 | 274篇 |
2006年 | 258篇 |
2005年 | 226篇 |
2004年 | 163篇 |
2003年 | 144篇 |
2002年 | 181篇 |
2001年 | 152篇 |
2000年 | 93篇 |
1999年 | 103篇 |
1998年 | 68篇 |
1997年 | 60篇 |
1996年 | 71篇 |
1995年 | 45篇 |
1994年 | 56篇 |
1993年 | 36篇 |
1992年 | 22篇 |
1991年 | 43篇 |
1990年 | 38篇 |
1989年 | 29篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 19篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1970年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1959年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有5899条查询结果,搜索用时 0 毫秒
11.
The ρ-T curves in our single phase HgBa2Ca2Cu3O8+δ superconductor were measured as a function of temperature and magnetic field, ρ=ρ0exp(−Ueff/κBT). It can be transformed to another form d(lnρ)/d(1/T)=−Ueff+TdUeff/dT, then this becomes a plot of the activation energy Ueff as a function of temperature. Our data plotted in these ways show a clear crossover from high-temperature two-dimensional vortex-liquid to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents v(z−1)=3.9±1.9 in this system are little different with previous measurements in BSCCO and YBCO systems. 相似文献
12.
Wei-Yan Shao Ying-Nan Cao Wen-Jie Pan Xian-Zhang Bu Lin-Kun An Lian-Quan Gu Albert S.C. Chan 《Tetrahedron letters》2006,47(24):4085-4089
Seventeen unsymmetrical curcumin derivatives were synthesized in good yield and purity by a facile solid phase synthesis strategy. 相似文献
13.
对Sn-C60薄膜进行紫外可见光吸收,X-射线衍射和扫描电镜的测定结果显示,薄膜样品紫外可见光吸收的两个短波段吸收峰比纯C60薄膜的吸收峰显著下降,说明Sn-C60薄膜的电子光吸收跃迁为间接跃迁,能带中有杂质能级的存在;样品的X射线衍射峰则对应于面心立方结构;扫描电镜结果显示薄膜为纳米级颗粒组成。 相似文献
14.
With the advances in pulsed laser systems, microscopic imaging techniques such as multiphoton and pump-probe fluorescence microscopy have developed into effective tools for investigating intensity and time-resolved phenomena inside biological systems. However, pulsed lasers used in these techniques usually are commercial systems with repetition frequencies of around 80 MHz. While these systems have proven to be adequate for multiphoton and pump-probe microscopic imaging applications, the temporal separation of the laser pulse train (around 12.5 ns) is long compared to the fluorescence lifetimes of many common fluorescence species. In this work, we present the designs of repetition rate multipliers based on passive optical components that can be used to increase the efficiency in multiphoton and pump-probe fluorescence microscopy. Depending on the lifetime of fluorescence molecules under investigation, the passive repetition rate multiplier can increase the duty cycle of multiphoton or pump-probe microscopy up to fourfold. 相似文献
15.
16.
利用微分方程的级数求解方法,分析了两端简支的有限长功能梯度圆筒的轴对称稳态热弹性问题,推导出了稳态温度场与应力场的解析解。分析中采用指数函数模型来描述FGM圆筒中材料性能在厚度方向的连续变化,同时忽略温度对材料性能的影响。另外,论文以金属钼和多铝红柱石制成的功能梯度圆筒为例,给出了稳态温度场和应力场的数值结果。 相似文献
18.
19.
设计并镀制了193nm Al2O3/MgF2反射膜,对它们在空气中分别进行了250-400℃的高温退火,测量了样品的透射率光谱曲线和绝对反射率光谱曲线.发现样品在高反射区的总的光学损耗随退火温度的升高而下降,而后趋于饱和.采用总积分散射的方法对样品在不同退火温度下的散射损耗进行了分析,发现随着退火温度的升高散射损耗有所增加.因此,总的光学损耗的下降是由于吸收损耗而不是散射损耗起主导作用.对Al2O3材料的单层膜进行了同等条件的退火处理,由它们光学性能的变化推导出它们的折射率和消光系数的变化,从而解释了相应的多层膜光学性能变化的原因.反射膜的反射率在优化联系、镀膜工艺与退火工艺的基础上达98%以上. 相似文献
20.
Summary Glass formation in nature and materials science is reviewed and the recent recognition of polymorphism within the glassy state,
polyamorphism, is discussed. The process by which the glassy state originates during the continuous cooling or viscous slowdown
process, is examined and the three canonical characteristics of relaxing liquids are correlated through the fragility. The
conversion of strong liquids to fragile liquids by pressure-induced coordination number increases is discussed, and then it
is shown that for the same type of system it is possible to have the same conversion accomplished via a first-order transition
within the liquid state. The systems in which this can happen are of the same type which exhibit polyamorphism, and the whole
phenomenology can be accounted for by a recent simple modification of the van der Waals model for tetrahedrally bonded liquids.
The concept of complex amorphous systems which can lose a significant number of degrees of freedom through weak first-order
transitions is then used to discuss the relation between native and denatured hydrated proteins, since the latter have much
in common with plasticized chain polymer systems. Finally, we close the circle by taking a short-time-scale phenomenon given
much attention by protein physicists,viz., the onset of an anomaly in the Debye-Waller factor with increasing temperature, and showing that for a wide variety of liquids,
including computer-simulated strong and fragile ionic liquids, this phenomenon is closely correlated with the experimental
glass transition temperature. This implies that the latter owes its origin to the onset of strong anharmonicity in certain
components of the vibrational density of states (evidently related to the boson peak) which then permits the system to gain
access to its configurational degrees of freedom. The more anharmonic these vibrational components, the closer to the Kauzmann
temperature will commence the exploration of configuration space and, for a given configurational microstate degeneracy, the
more fragile the liquid will be.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献