全文获取类型
收费全文 | 246篇 |
免费 | 110篇 |
国内免费 | 130篇 |
专业分类
化学 | 272篇 |
晶体学 | 6篇 |
力学 | 4篇 |
综合类 | 1篇 |
数学 | 6篇 |
物理学 | 197篇 |
出版年
2024年 | 5篇 |
2023年 | 9篇 |
2022年 | 14篇 |
2021年 | 18篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 18篇 |
2017年 | 23篇 |
2016年 | 13篇 |
2015年 | 21篇 |
2014年 | 26篇 |
2013年 | 57篇 |
2012年 | 32篇 |
2011年 | 58篇 |
2010年 | 54篇 |
2009年 | 31篇 |
2008年 | 32篇 |
2007年 | 23篇 |
2006年 | 16篇 |
2005年 | 5篇 |
2003年 | 1篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1995年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有486条查询结果,搜索用时 0 毫秒
21.
LIU Jing-Jing LUO Zhi-Quan 《理论物理通讯》2008,49(1):239-242
The electron capture of Gamow--Teller transition on iron group nuclei is investigated in a strong magnetic. field at the crusts of neutron stars. The results show that the magnetic field has only a slight effect on the electron capture rates with the range of the magnetic fields (10^9 - 10^13 G) on surfaces of most neutron stars, whereas for some magnetars whose range of the magnetic field is 10^13 - 10^18 G, the electron capture rates of most iron group nuclei would be debased greatly and may be even decreased overrun 3 orders of magnitude by the strong magnetic field. 相似文献
22.
Based on the p-f shell model, the effect of strong magnetic field on neutrino energy loss rates by electron capture is investigated. The calculations show that the magnetic field has only a slight effect on the neutrino energy loss rates in the range of 108—1013G on the surfaces of most neutron stars. But for some magnetars, the range of the magnetic field is 1013—1018G, and the neutrino energy loss rates are greatly reduced, even by more than four orders of magnitude due to the strong magnetic field. 相似文献
23.
The construction of homoclinic and heteroclinic orbitals in asymmetric strongly nonlinear systems based on the Pad'e approximant 下载免费PDF全文
In this paper, the extended Pad'e approximant is used to construct the homoclinic and the heteroclinic trajectories in nonlinear dynamical systems that are asymmetric at origin. Meanwhile, the conservative system, the autonomous system, and the nonautonomous system equations with quadratic and cubic nonlinearities are considered. The disturbance parameter varepsilon is not limited to being small. The ranges of the values of the linear and the nonlinear term parameters, which are variables, can be determined when the boundary values are satisfied. New conditions for the potentiality and the convergence are posed to make it possible to solve the boundary-value problems formulated for the orbitals and to evaluate the initial amplitude values. 相似文献
24.
The quantum fluctuation of photon counting limits the field application of optical time domain reflection. A method of photon counts modulation optics time domain reflection with single photon detection at 1.55 μm is presented. The influence of quantum fluctuation can be effectively controlled by demodulation technology since quantum fluctuation shows a uniform distribution in the frequency domain. Combined with the changing of the integration time of the lock-in amplifier, the signal to noise ratio is significantly enhanced. Accordingly the signal to noise improvement ratio reaches 31.7 dB compared with the direct photon counting measurement. 相似文献
25.
利用实验和能带计算相结合的方法,对介于两种预期的半金属Heusler合金Co2FeSi和Co2MnSi间的四元合金Co50Fe25-xMnxSi25的晶体结构、磁性、能带结构和半金属性进行了研究.采用考虑库仑相互作用的的广义梯度近似方法计算了系列合金的能带结构,通过与实验结果进行对比,揭示了成分变化过程中合金分子磁矩及原子磁矩的变化规律.研究发现,
关键词:
磁性
半金属
Heusler合金 相似文献
26.
Treatment of N-tosyl-1-aryl-1,2,3,4-tetrahydro-isoquinolines or N-tosyl-1-aryl-1,2,3,4-tetrahydro-β-carbolines with a strong base such as NaOH or KOH at 70 °C in dimethylsulfoxide (DMSO) produced 1-aryl-3,4-dihydroisoquinolines or 1-aryl-3,4-dihydro-β-carbolines in good yields via mild and regiospecific β-eliminations. A dramatic solvent effect was observed, DMSO was crucial for the reactions. The temperature is also crucial for the reactions and should be kept between 60 and 80 °C. 相似文献
27.
Transformation thermodynamics as a major extension of transformation optics has recently received considerable attention. In this paper, we present two-dimensional (2D) and three-dimensional (3D) diamond-shaped transient thermal cloaks with non-singular homogeneous material parameters. The absence of singularity in the parameters results from the fact that the linear coordinate transformation is performed by expanding a line segment rather than a point into a region, while the mechanism behind the homogeneity is the homogeneous stretching and compression along orthogonal directions during the transformation. Although the derived parameters remain anisotropic, we further show that this can be circumvented by considering a layered structure composed of only four types of isotropic materials based on the effective medium theory. Numerical simulation results confirm the good performance of the proposed cloaks. 相似文献
28.
Jing-Jing Zhu Chao-Feng Zhang Mian Zhang S.W. Annie Bligh Li Yang Zhi-Min Wang Zheng-Tao Wang 《Journal of chromatography. A》2010,1217(33):5384-5388
Six C-glucosyl anthrones were characterized as three pairs of epimers by on-line high performance liquid chromatography–circular dichroism (HPLC–CD) analysis and isolated from the roots of Rumex dentatus by column chromatography. Their structures were elucidated by mass spectrometry, nuclear magnetic spectroscopy and HPLC–CD analysis. They are 10R-C-β-d-glucosyl-10-hydroxyemodin-9-anthrone (rumejaposide E, 1) and 10S-C-β-d-glucosyl-10-hydroxyemodin-9-anthrone (rumejaposide F, 2), 10R-C-β-d-glucosylemodin-9-anthrone (rumejaposide G, 3) and 10S-C-β-d-glucosylemodin-9-anthrone (rumejaposide H, 4), 10S-C-β-d-glucosyl-10-hydroxychrysophanol-9-anthrone (cassialoin, 5) and 10R-C-β-d-glucosyl-10-hydroxychrysophanol-9-anthrone (rumejaposide I, 6). Rumejaposides F–I (2–4 and 6) were new C-glucosyl anthrones. Rumejaposide E (1) and cassialoin (5) were isolated for the first time in Rumex plants. On-line HPLC–UV–CD analysis was a useful tool for structure elucidating epimeric C-glycosides anthrones 3–6 because of the poor stability of the pure isomers (3 and 4) and the minute quantity of 5 and 6 in the mixture. 相似文献
29.
Chen HB Chen L Zhang Y Zhang JJ Wang YZ 《Physical chemistry chemical physics : PCCP》2011,13(23):11067-11075
A novel phosphorus-containing copolyester (PTTP), poly(trimethylene terephthalate) (PTT) copolyester with a bulky linking pendent group of 9,10-dihydro-10-[2,3-di(hydroxycarbonyl) propyl]-10-phosphaphenanthrene-10-oxide (DDP) was prepared, and its crystallization, crystal morphology and interference color were investigated in this article for the first time. Differential scanning calorimeter (DSC) results showed that with the increase of DDP content, the melting point (T(m)) and crystallization ability of PTTP decreased. WAXD results suggests that the three samples share one crystal structure, however the crystallinity decreases with increasing DDP content. Polarized optical microscope (POM) observation indicated that the samples showed non-banded spherulites at a lower and higher temperature, and banded spherulites at the middle temperature range. From the micrographs obtained from scanning electronic microscopy (SEM) and atomic force microscopy (AFM), ringed patterns with many defects could be found for samples with higher DDP contents, which crystallized at a lower temperature, and a transformation from square-shaped spherulites to circular spherulites was noted for samples with higher DDP contents, which crystallized at a higher temperature. The interference color of the spherulites was also studied and it was shown that with the increase of film thickness or decrease of DDP content, the spherulites became more colorful under POM observation, indicating that the hindering effect and randomness caused by incorporating the DDP monomer with a bulky pendent group into the PTT molecular chain exhibited a negative influence on the molecular mobility and crystallization ability of the copolyester, and led to the formation of the defective band morphology and the less colorful interference color of the PTTP spherulites. 相似文献
30.