全文获取类型
收费全文 | 534篇 |
免费 | 13篇 |
国内免费 | 1篇 |
专业分类
化学 | 436篇 |
晶体学 | 10篇 |
力学 | 11篇 |
数学 | 9篇 |
物理学 | 82篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 15篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 5篇 |
2014年 | 14篇 |
2013年 | 40篇 |
2012年 | 40篇 |
2011年 | 49篇 |
2010年 | 13篇 |
2009年 | 12篇 |
2008年 | 16篇 |
2007年 | 26篇 |
2006年 | 25篇 |
2005年 | 22篇 |
2004年 | 17篇 |
2003年 | 18篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有548条查询结果,搜索用时 15 毫秒
101.
Krishna Radhakrishnan Satyajit Gupta Divya Prakash Gnanadhas Praveen C. Ramamurthy Dipshika Chakravortty Ashok M. Raichur 《Particle & Particle Systems Characterization》2014,31(4):449-458
The fabrication of a mesoporous silica nanoparticle (MSN)?protamine hybrid system (MSN?PRM) is reported that selectively releases drugs in the presence of specific enzyme triggers present in the proximity of cancer cells. The enzyme trigger involved is a protease called trypsin, which is overexpressed in certain specific pathological conditions, such as inflammation and cancer. Overexpression of trypsin is known to be associated with invasion, metastasis, and growth in several cancers, such as leukemia, colon cancer, and colorectal cancer. The current system (MSN–PRM) consists of an MSN support in which mesopores are capped with an FDA‐approved peptide drug protamine, which effectively blocks the outward diffusion of the drug molecules from the mesopores of the MSNs. On exposure to the enzyme trigger, the protamine cap disintegrates, opening up the molecular gates and releasing the entrapped drug molecules. The system exhibits minimal premature release in the absence of the trigger and selectively releases the encapsulated drugs in the presence of the proteases secreted by colorectal cancer cells. The ability of the MSN–PRM particles to deliver anticancer drugs to colorectal cancer cells has also been demonstrated. The hydrophobic drug is released into cancer cells subsequent to disintegration of the protamine cap, resulting in cell death. Drug‐induced cell death in colorectal cancer cells is significantly enhanced when the hydrophobic drug that is known to degrade in aqueous environments is encapsulated in the MSN–PRM system in comparison to the free drug (P < 0.05). The system, which shows good biocompatibility and selective drug release, is a promising platform for cancer specific drug delivery. 相似文献
102.
Spectral and photophysical properties of 1,6-naphthyridine derivatives: a new class of compounds for nonlinear optics 总被引:1,自引:0,他引:1
Indirapriyadharshini VK Ramamurthy P Raghukumar V Ramakrishnan VT 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(8):1535-1543
1,6-Naphthyridines are a class of compounds that exhibit second harmonic generation on excitation with a Nd-YAG laser (1064 nm). Solvatochromism has been used to estimate enhancement in the dipole moments on excitation and the values of first-order hyperpolarizability, beta. Photophysical studies on the title compounds show that they have a fluorescence lifetime of about 10 ns and fluorescence quantum yield of approximately 0.05-0.1 in different solvents. Kurtz powder method has been used to find the NLO efficiency of the compounds with reference to urea. 相似文献
103.
M Porel CH Chuang C Burda V Ramamurthy 《Journal of the American Chemical Society》2012,134(36):14718-14721
Supramolecular photoinduced electron transfer dynamics between coumarin 153 (C153) and 4,4'-dimethyl viologen dichloride (MV(2+)) across the molecular barrier of a host molecule, octa acid (OA), has been investigated with femtosecond time resolution. The ultrafast electron transfer from C153 to MV(2+) followed excitation with 150 fs laser pulses at a wavelength of 390 nm despite the fact that C153 was incarcerated within an OA(2) capsule. As a result, the photoexcited coumarin did not show any of the typical relaxation dynamics that is usually observed in free solution. Instead, the excited electron was transferred across the molecular wall of the capsuleplex within 20 ps. Likewise, the lifetime of the charge transfer state was short (724 ps), and electron back-transfer reestablished the ground state of the system within 1 ns, showing strong electronic coupling among the excited electron donor, host, and acceptor. When the donor was encapsulated into the host molecule, the electron transfer process showed significantly accelerated dynamics and essentially no solvent relaxation compared with that in free solution. The study was also extended to N-methylpyridinium iodide as the acceptor with similar results. 相似文献
104.
SR Samanta R Kulasekharan R Choudhury P Jagadesan N Jayaraj V Ramamurthy 《Langmuir : the ACS journal of surfaces and colloids》2012,28(32):11920-11928
In this report, we present methods of functionalization of AuNP's with deep-cavity cavitands that can include organic molecules. Two types of deep-cavity cavitand-functionalized AuNP's have been synthesized and characterized, one soluble in organic solvents and the other in water. Functionalized AuNP soluble in organic solvents forms a 1:1 host-guest complex where the guest is exposed to the exterior solvents. The one soluble in water forms a 2:1 host-guest complex where the guest is protected from solvent water. Phosphorescence from thiones and benzil included within heterocapsules attached to AuNP was quenched by gold atoms present closer to the guests included within deep-cavity cavitands. During this investigation, we have synthesized four new deep-cavity cavitands. Of these, two thiol-functionalized hosts allowed us to make stable AuNP's. However, AuNP's protected with two amine-functionalized cavitands tended to aggregate within a day. 相似文献
105.
Some novel Y-shaped imidazole derivatives were developed and characterized by NMR and mass spectral techniques. The photophysical
properties of these imidazole derivatives were studied in several solvents. The Kamlet-Taft and Catalan’s solvent scales were
found to be the most suitable for describing the solvatochromic shifts of the absorption and fluorescence emission. The adjusted
coefficient representing the electron releasing ability or basicity of the solvent, C
β
or C
SB has a negative value, suggesting that the absorption and fluorescence bands shift to lower energies with the increasing electron-donating
ability of the solvent. This effect can be interpreted in terms of the stabilization of the resonance structures of the chromophore.
The observed lower fluorescence quantum yield may be due to an increase in the non-radiative deactivation rate constant. This
is attributed to the loss of planarity in the excited state provided by the non co-planarity of the cinnamaldehyde ring attached
to C(2) atom of the imidazole ring. Such a geometrical change in the excited state leads to an important Stokes shift, reducing
the reabsorption and reemission effects in the detected emission in highly concentrated solutions. 相似文献
106.
Porel M Jockusch S Parthasarathy A Rao VJ Turro NJ Ramamurthy V 《Chemical communications (Cambridge, England)》2012,48(21):2710-2712
The efficient photoinduced electron transfer from a stilbene derivative incarcerated within a negatively charged organic nanocapsule to positively charged acceptors (methyl viologen and a pyridinium salt) adsorbed outside and the back electron transfer were controlled by supramolecular effects. 相似文献
107.
Jayaraman Jayabharathi Venugopal Thanikachalam Marimuthu Venkatesh Perumal 《Journal of luminescence》2012,132(3):707-712
The interaction between the imidazole derivative 2-(2,4-difluorophenyl)-1-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline (dfppip) and bovine serum albumin (BSA) was investigated by fluorescence and UV–vis absorbance spectroscopy. From the experimental results, it was found that the imidazole derivative has strong ability to quench the intrinsic fluorescence of BSA by forming complexes. Electrostatic interactions play an important role to stabilize the complex. The binding constants and the number of binding sites have been determined in detail. The distance (r) between the donor and the acceptor was obtained according to fluorescence resonance energy transfer (FRET). Conformational changes of BSA were observed from synchronous fluorescence spectroscopy. The effect of metal ions such as Cu2+, Zn2+, Ca2+, Mg2+, Ni2+, Co2+ and Fe2+ on the binding constants between the imidazole derivative and BSA were also studied. 相似文献
108.
Selvarangam E. Kiruthika Rangarajan Amritha Paramasivan T. Perumal 《Tetrahedron letters》2012,53(26):3268-3273
A facile strategy for the synthesis of functionalized spirolactones from isatin, primary amines, and activated alkynes through Huisgen dipolar additions are discussed. A novel route for the formation of dispirodihydrofuranyl oxindoles from activated cyclic electrophiles, amines, and DMAD has also been developed. This method offers several advantages like high yield, readily available starting materials, and involves less hazardous chemical techniques. 相似文献
109.
110.
Hoong‐Kun Fun R. Sankaranarayanan D. Velmurugan S. Shanmuga Sundara Raj G. Babu P. T. Perumal 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(4):475-476
In the title compound, C26H22N2O2S, the tetrahydropyridine ring has a conformation intermediate between half‐chair and sofa. The tetrahydroquinoline mean plane makes a dihedral angle of 73.3 (1)° with the cyclopentene ring, which adopts an envelope conformation, and an angle of 45.45 (4)° with the indole best plane. The dihedral angle between the benzene and pyrrole rings is 2.6 (1)°. The orientations of the phenyl ring on the sulfonyl group and of the indole are governed by weak C—H?O interactions. The packing of the molecule in the solid state is stabilized by C—H?O and C—H?N hydrogen bonds. 相似文献