全文获取类型
收费全文 | 434篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 331篇 |
晶体学 | 9篇 |
力学 | 9篇 |
数学 | 39篇 |
物理学 | 62篇 |
出版年
2023年 | 5篇 |
2022年 | 14篇 |
2021年 | 13篇 |
2020年 | 11篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 16篇 |
2016年 | 13篇 |
2015年 | 3篇 |
2014年 | 10篇 |
2013年 | 37篇 |
2012年 | 14篇 |
2011年 | 43篇 |
2010年 | 14篇 |
2009年 | 10篇 |
2008年 | 26篇 |
2007年 | 19篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 17篇 |
2003年 | 12篇 |
2002年 | 10篇 |
2001年 | 4篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1992年 | 8篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有450条查询结果,搜索用时 15 毫秒
111.
Li G Pandey SK Graham A Dobhal MP Mehta R Chen Y Gryshuk A Rittenhouse-Olson K Oseroff A Pandey RK 《The Journal of organic chemistry》2004,69(1):158-172
meso-(2-Formylvinyl)octaethylporphyrin on reaction with cyanotrimethylsilane in the presence of various catalysts [copper triflate [Cu(OTf)(2)], indium triflate [In(OTf)(3)], or magnesium bromide diethyl etherate (MgBr(2).Et(2)O)] produced a mixture of the intermediate 3-hydroxy-3-cyanopropenoporphyrin, the corresponding trimethylsilyl ether derivative, and the unexpected propenochlorins. The yields of the reaction products were found to depend on the reaction conditions and the catalysts used. The intermediate porphyrins on treatment with concentrated sulfuric acid yielded the free-base cyanobenzochlorins in major quantity along with several other novel benzochlorins as minor products. Reduction of ethyl-3-hydroxy-1-pentenoate-porphyrin with DIBAL-H/NaBH(4) and subsequent acid treatment provided the corresponding free-base 10(3)-(2-hydroxyethyl)benzochlorin, which upon a sequence of reactions gave a free-base benzochlorin bearing a carboxylic acid functionality in good yield. It was then condensed with a variety of carbohydrates (glucosamine, galactosamine, and lactosamine), and the related conjugates were screened using the galectin-binding-ability assay. Among the carbohydrate conjugates investigated, the lactose and galactose analogues displayed the galectin-binding ability with an enhancement of about 300-400-fold compared to lactose. In preliminary studies, all photosensitizers (with or without carbohydrate moieties) were found to be active in vitro [radiation-induced fibrosarcoma (RIF) tumor cells]. However, the cells incubated with lactose (known to bind to beta-galactoside-recognized proteins) prior to the addition of the photosensitizers containing the beta-galactose moiety (e.g., galactose and lactose) produced a 100% decrease in their photosensitizing efficacy. Under similar experimental conditions, benzochlorin without a beta-galactoside moiety or the related glucose conjugate did not show any inhibition in its photosensitizing efficacy. These results in combination with the galectin-binding data indicate a possible beta-galactoside-recognized protein specificity of the galactose- and lactose-benzochlorin conjugates. 相似文献
112.
A simple and high yielding method for the integration of 1,5-benzodiazepines integrated with 5-methyl- 2-oxo-3-phenyl-△^4-1,3,4-oxadiazolines in 75%-90% yield by microwave irradiation is devised. Microwave-accelerated reaction was compared with thermal method. All the compounds were characterized by physical, analytical and spectral (IR, 1^H NMR, MS) data. Title compounds were screened for preliminary pharmacological activities. 相似文献
113.
Vadde Ravinder S. Ashok A. V. S. S. Prasad G. Balaswamy Y. Ravindra Kumar B. Vijaya Bhaskar 《Chromatographia》2008,67(3-4):331-334
A rapid isocratic chiral HPLC method has been developed for the separation of R-galantamine from S-galantamine. Good resolution viz. Rs > 3 between R- and S- forms of galantamine was achieved with chiralpak AD-H (250 × 4.6 mm) column using n-hexane, 20% propionic acid in isopropanol and diethyl amine in the ratio of 80:20:0.2 (v/v) as mobile phase at ambient temperature. Flow rate was kept as 0.8 mL min−1 and the elution was monitored at 289 nm. This method was further used to determine the amount of R-galantamine in pure and pharmaceutical formulations of S-galantamine. This method is capable to detect and quantitate R-galantamine to the levels of 0.21 and 0.84 μg mL−1, respectively. The method was validated as per International Conference on Harmonization (ICH) guidelines in terms of limit
of detection (LOD), limit of quantification (LOQ), linearity, precision, accuracy, specificity, robustness and ruggedness. 相似文献
114.
Mahesh Kulkarni Ravindra Potrekar R. A. Kulkarni S. P. Vernekar 《Journal of polymer science. Part A, Polymer chemistry》2008,46(17):5776-5793
A novel aromatic diacid, 3, 5‐dicarboxyl‐4′‐amino diphenyl ether, containing pendant phenoxy amine group was synthesized. Homo‐ and co‐polybenzimidazoles containing different content of pendant phenoxyamine groups were synthesized by condensation of 3,3′‐diaminobenzidine with this acid and a mixture of this acid and isophthalic acid in different ratio in polyphosphoric acid. Copolybenzimidazoles with structural variations were also synthesized based on this acid and pyridine dicarboxylic acid, terephthalic acid, adipic acid, or sebacic acid. The polymers have good solubility in polar aprotic solvents and strong acids and they form tough flexible films by solution casting. The polymers were characterized by different instrumental techniques (FTIR, TGA, DSC, XRD, etc.) and for solvent solubility, mechanical properties, inherent viscosity, and proton conductivity. The inherent viscosities of the polymers vary in the range of 0.62–1.52 dL/g. They have high thermal stability up to 475–506 °C (IDT) in nitrogen, high glass transition temperatures (Tg) ranging from 313 to 435 °C and good tensile strength ranging from 58 to 125 MPa. Proton conductivity of homo polymer is 3.72 × 10?3 S/cm at 25 °C and 2.45 × 10?2 S/cm at 200 °C © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5776–5793, 2008 相似文献
115.
Ravindra P. Singh Sanjoy Roychowdhury Virendra K. Jaiswal 《Optics Communications》2007,274(2):281-285
Before we use an optical vortex for any application, it is important to know if the vortex is axial or non-axial, since properties of one type of the vortex are quite different from another. We show that the Wigner distribution can provide a solution, being different for axial and non-axial vortex. We use transport properties of the Wigner function to study the propagation of an axial as well as non-axial vortex and find them different. 相似文献
116.
Bhatt PM Ravindra NV Banerjee R Desiraju GR 《Chemical communications (Cambridge, England)》2005,(8):1073-1075
Saccharin, acting as a weak acid, forms salts with basic APIs and these salts have the desirable property of enhanced water solubility. 相似文献
117.
Rawal RK Solomon VR Prabhakar YS Katti SB De Clercq E 《Combinatorial chemistry & high throughput screening》2005,8(5):439-443
Selected 4-thiazolidinone have been synthesized and tested as anti-HIV activity. The results of the in vitro tests showed that one of the compounds, 5, inhibited the enzyme at 0.204 microM concentration with minimal toxicity to MT-4 cell. Furthermore, the QSAR studies indicated the role of PMIZ, Ovality and Total energy content of the compounds in rationalizing the activity. 相似文献
118.
V.P. Gupta N.M. Ravindra V.K. Srivastava 《Journal of Physics and Chemistry of Solids》1980,41(2):145-148
It is well known that Pyrite associated with Black Ore induces the severest difficulty among other constituents in the flotation process in mineral dressing. One of the possible reasons for this difficulty is related to its semiconducting properties which may affect surface conditions. We present here a study of the semiconducting properties of pyrite. Our calculations of the energy gap at various temperatures are shown to be in very good agreement with the experimental data. The Penn gap calculated using the Grimes-Cowley modification [1] of the Penn model has been shown to agree very well with the reflectivity data of Horita [2]. Using the Clausius-Mossotti relation, we calculate the electronic polarizability for pyrite. Also evaluated are the pressure and lattice parameter dependence of the energy gap. We predict the temperature of decomposition of natural pyrite in inert atmosphere from Mössbauer studies. 相似文献
119.
Ravindra Kumar 《Applied Scientific Research》1965,14(1):396-404
Summary Steady flow of Bingham material between two concentric rotating spheres has been investigated taking into account the constitutive equations given by Oldroyd. Motions in the elastic as well as in the flow region have been discussed. A critical value of the Bingham number has been found below which the flow takes place in the whole region and above which the elastic and flow regions occur side by side.Nomenclature
r, ,
space co-ordinates
-
u
r
,u
,u
velocity components
-
density
-
modulus of rigidity (constant)
-
bulk modulus
-
e
ii
, the dilatation
-
1
coefficient of viscosity (constant)
-
e
ik
strain tensor
-
d
ik
rate of strain tensor
-
p
ik
stress tensor primes denote deviatoric components of tensors, e.g.
-
p
ik
p
ik
+p
k
i
, p=–1/3p
ii
-
yield value (constant)
- D/Dt
materiaal derivative with regard to time following the particle
-
R
1
radius of the inner sphere
-
R
2
radius of the outer sphere
-
R
radius of the yield surface (spherical)
-
1
velocity of the inner sphere
-
B
Bingham number 相似文献
120.
C. S. Barnes R. J. Goldsack Ravindra Pratap Rao 《Journal of mass spectrometry : JMS》1971,5(3):317-324
The low resolution mass spectra of a number of homologous 5-alkylthio-1,3,4-thiadiazolyl-2-amines have been determined. With the methylthio compound the only significant loss from the molecular ion is the sulphydryl radical. As the homologous series is ascended this reaction becomes less important and is insignificant with the butylthio isomers. The ethylthio compound suffers extensive loss of ethylene and when the alkyl group contains three or more carbon atoms the main reaction is always loss of the olefin coresponding to the alkyl group.All of the n-alkylthio compounds showed in addition loss of methylthio radical from the molecular ion. A mechanism is proposed and comparisons made with alkyl phenyl thioethers and alkylthio substituted heterocycles. 相似文献