全文获取类型
收费全文 | 181篇 |
免费 | 17篇 |
国内免费 | 29篇 |
专业分类
化学 | 127篇 |
晶体学 | 4篇 |
力学 | 3篇 |
综合类 | 1篇 |
数学 | 44篇 |
物理学 | 48篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 10篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 6篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 9篇 |
2013年 | 10篇 |
2012年 | 10篇 |
2011年 | 16篇 |
2010年 | 13篇 |
2009年 | 10篇 |
2008年 | 12篇 |
2007年 | 9篇 |
2006年 | 6篇 |
2005年 | 3篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 7篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有227条查询结果,搜索用时 312 毫秒
41.
We consider the normalized Ricci flow ? t g = (ρ ? R)g with initial condition a complete metric g 0 on an open surface M where M is conformal to a punctured compact Riemann surface and g 0 has ends which are asymptotic to hyperbolic cusps. We prove that when χ(M) < 0 and ρ < 0, the flow g(t) converges exponentially to the unique complete metric of constant Gauss curvature ρ/2 in the conformal class. 相似文献
42.
An easy-to-use fluorescence probe for detecting Sudan I was developed. The probe detects Sudan I because Sudan I and 1,8-diamino naphthalene competitively interact with copper (II). Copper (II) effectively quenches the fluorescence of 1,8-diamino naphthalene because the 1,8-diamino naphthalene interacts with copper (II) and forms a 1,8-diamino naphthalene–copper (II) complex. Adding Sudan I causes the fluorescence of the system to be recovered because the Sudan I removes copper (II) from the 1,8-diamino naphthalene–copper (II) complex, liberating the 1,8-diamino naphthalene. The displacement of 1,8-diamino naphthalene by Sudan I gives a high fluorescence recovery efficiency. Under optimal conditions, the fluorescence intensity F achieved when Sudan I was added had a good linear relationship (R2?=?0.999) with the Sudan I concentration over the range 0–4.6?µM. The Sudan I detection limit was 0.032?µM. The method offers a new way of quantitatively determining Sudan I. 相似文献
43.
Li2FeSiO4/C composites were synthesized via a tartaric-acid-assisted sol–gel method with ethanol and ethylene glycol (EG) as mixed solvents. Effects of solvent composition on the physical properties and electrochemical performances of Li2FeSiO4/C were studied. The materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical performances of Li2FeSiO4/C were evaluated by galvanostatic charge–discharge and electrochemical impedance spectra (EIS) measurements. The results show that the addition of EG to ethanol solvent during preparation has a positive effect on the electrochemical performance of Li2FeSiO4/C. The sample synthesized using EG–ethanol with the volume ratio of 2:7 has the best electrochemical performance. It delivers an initial discharge capacity of 105 mAh g?1 at C/16. AC impendence investigation shows that Li2FeSiO4/C synthesized using the optimal EG/ethanol volume ratio has lower resistance of electrode/electrolyte interface and higher lithium-ion diffusion coefficient than that synthesized using ethanol as solvent. 相似文献
44.
Hao Li Zhoubin Lin Lizhen Zhang Yisheng Huang Guofu Wang 《Journal of luminescence》2012,132(6):1507-1510
This paper reports the spectroscopic properties of Yb3+:Li3Ba2Y3(WO4)8 crystal. The polarized spectral properties of Yb3+:Li3Ba2Y3(WO4)8 crystal were investigated. The laser performance parameters βmin, Isat and Imin of Yb3+:Li3Ba2Y3(WO4)8 crystals have been also established. Yb3+:Li3Ba2Y3(WO4)8 crystal has a broad FWHM of the gain cross-section and larger absorption and emission cross-sections. These results may regard the Yb3+:Li3Ba2Y3(WO4)8 crystal as a tunable laser material. 相似文献
45.
将黑色素纳米颗粒(melanin nanoparticle,MNP)经聚乙二醇(polyethylene glycol,PEG)修饰制备得到PEG-MNP,随后通过与放射性的68Ga3+离子螯合,高标记产率地制备得到68Ga-PEG-MNP,标记产物稳定性良好。进一步将68Ga-PEG-MNP通过雾化方式制备得到68Ga-PEG-MNP PM2.5(particulate matter 2.5,size<2.5μm)模拟颗粒,其经雾化小鼠吸入体内后,通过正电子断层扫描(positron emission tomography,PET)成像对小鼠进行全身显影,结果可见雾化的68Ga-PEG-MNP PM2.5模拟颗粒可由气管向肺部双叶区域扩散,并滞留于肺。体内的PET成像结果与离体放射自显影结果高度一致。 相似文献
46.
介绍了强流重离子加速器装置HIAF(High Intensity heavy-ion Accelerator Facility)项目增强器BRing(Booster Ring)快脉冲二极磁铁的性能指标、测量要求和测量方法,描述了快脉冲二极磁铁稳态磁场测量系统及动态磁场测量系统的构成。在稳态磁场测量中,为提高积分磁场测量精度和测量效率,长线圈测量系统采用了on fly技术;在动态磁场测量中,研制了用于磁场延迟及磁场畸变测量的矩阵线圈。通过样机磁铁的测量,完成了测量系统的性能指标验证和磁铁的稳态磁场测量。实测结果表明,样机磁铁的设计和制造均达到了预期指标,并依据测量数据完成了磁铁的二次削斜。 相似文献
47.
Lizhen Ji 《K-Theory》2007,38(1):35-47
We prove the integral Novikov conjecture for torsion free S-arithmetic subgroups Γ of linear reductive algebraic groups G of rank 0 over a global field k. They form a natural class of groups and are in general not discrete subgroups of Lie groups with finitely many connected
components. Since many natural S-arithmetic subgroups contain torsion elements, we also prove a generalized integral Novikov
conjecture for S-arithmetic subgroups of such algebraic groups, which contain torsion elements. These S-arithmetic subgroups
also provide a natural class of groups with cofinite universal spaces for proper actions.
Partially Supported by NSF grants DMS 0405884 and 0604878. 相似文献
48.
We give new realizations of the maximal Satake compactifications of Riemannian symmetric spaces of noncompact type as orbit closures inside Grassmannians and orthogonal groups. Our constructions are partially motivated by Poisson geometry. 相似文献
49.
50.
The graft copolymerization of acrylamide onto polypropylene (PP) Film was carried out by using a capacitively coupled rf plasma apparatus with external plate electrodes. The relationship between the surface structure of the Ar plasma-treated PP films and the extent of grafting of acrylamide on the films was studied through observing the effects of discharge power and exposure time on the relative content of free-radical on the film surface. Meanwhile, the wettability and surface energy of the PP film were measured. 相似文献