全文获取类型
收费全文 | 216篇 |
免费 | 3篇 |
专业分类
化学 | 158篇 |
晶体学 | 2篇 |
力学 | 6篇 |
数学 | 9篇 |
物理学 | 44篇 |
出版年
2024年 | 4篇 |
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 10篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 11篇 |
2015年 | 6篇 |
2014年 | 9篇 |
2013年 | 18篇 |
2012年 | 16篇 |
2011年 | 17篇 |
2010年 | 12篇 |
2009年 | 2篇 |
2008年 | 12篇 |
2007年 | 12篇 |
2006年 | 13篇 |
2005年 | 10篇 |
2004年 | 7篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1948年 | 1篇 |
1943年 | 2篇 |
1941年 | 1篇 |
排序方式: 共有219条查询结果,搜索用时 31 毫秒
91.
In the present study also a superparamagnetic nanocomposite of Poly (vinyl- alcohol-g-acrylonitrile) has been designed by homogeneous impregnation of iron oxide nanoparticles into the graft polymer matrix. The so prepared nanocomposite was characterized by FT-IR, TEM and XRD techniques and studied for water sorption behavior and magnetization properties. The superparamagnetic nanocomposite was loaded with an antibiotic drug, ciprofloxacin (CFx), and its release behavior was investigated under varying experimental conditions such as chemical composition of the matrix, pH of the release media, applied magnetic field and percent loading of the drug. The drug transport mechanism was also analyzed using Ficks power law. The drug loaded magnetic nanocomposite was also studied for antibacterial and in-vitro blood compatible properties. 相似文献
92.
93.
Kulkarni RV Boppana R Krishna Mohan G Mutalik S Kalyane NV 《Journal of colloid and interface science》2012,367(1):509-517
In the present work, we synthesized pH-responsive interpenetrating network (IPN) hydrogel beads of polyacrylamide grafted κ-carrageenan (PAAm-g-CG) and sodium alginate (SA) for targeting ketoprofen to the intestine. The PAAm-g-CG was synthesized by free radical polymerization followed by alkaline hydrolysis under nitrogen gas. The PAAm-g-CG was characterized by elemental analysis, FTIR spectroscopy and thermogravimetric analysis (TGA). The drug-loaded IPN hydrogel beads were prepared by simple ionotropic gelation/covalent crosslinking method. The amorphous nature of drug in the beads was confirmed by differential scanning calorimetry and X-ray diffraction studies. The spherical shape of the beads was confirmed by scanning electron microscopic analysis. The beads exhibited ample pH-responsive behavior in the pulsatile swelling study. The ketoprofen release was significantly increased when pH of the medium was changed from acidic to alkaline. The beads showed maximum of 10% drug release in acidic medium of pH 1.2, and about 90% drug release was recorded in alkaline medium of pH 7.4. Stomach histopathology of albino rats indicated that the prepared beads were able to retard the drug release in stomach leading to the reduced ulceration, hemorrhage and erosion of gastric mucosa. 相似文献
94.
Tsai YF Shih CH Su YT Yao CH Lian JF Liao CC Hsia CW Shui HA Rani R 《Organic & biomolecular chemistry》2012,10(5):931-934
The total synthesis of ganglioside 2, an analogue of the ganglioside Hp-s1 (1) which displays neuritogenic activity toward the rat pheochromocytoma cell line PC-12 cell in the presence of nerve growth factor (NGF) with an effect (34.0%) greater than that of the mammalian ganglioside GM 1 (25.4%), was accomplished by applying a chemoselective-activation glycosylation strategy. Moreover, we also demonstrate that the synthesized ganglioside 2 exhibited neuritogenic activity toward the human neuroblastoma cell line SH-SY5Y without the presence of NGF. 相似文献
95.
Krishnan MM Venkatraghavan V Acharya UR Pal M Paul RR Min LC Ray AK Chatterjee J Chakraborty C 《Micron (Oxford, England : 1993)》2012,43(2-3):352-364
Oral cancer (OC) is the sixth most common cancer in the world. In India it is the most common malignant neoplasm. Histopathological images have widely been used in the differential diagnosis of normal, oral precancerous (oral sub-mucous fibrosis (OSF)) and cancer lesions. However, this technique is limited by subjective interpretations and less accurate diagnosis. The objective of this work is to improve the classification accuracy based on textural features in the development of a computer assisted screening of OSF. The approach introduced here is to grade the histopathological tissue sections into normal, OSF without Dysplasia (OSFWD) and OSF with Dysplasia (OSFD), which would help the oral onco-pathologists to screen the subjects rapidly. The biopsy sections are stained with H&E. The optical density of the pixels in the light microscopic images is recorded and represented as matrix quantized as integers from 0 to 255 for each fundamental color (Red, Green, Blue), resulting in a M×N×3 matrix of integers. Depending on either normal or OSF condition, the image has various granular structures which are self similar patterns at different scales termed "texture". We have extracted these textural changes using Higher Order Spectra (HOS), Local Binary Pattern (LBP), and Laws Texture Energy (LTE) from the histopathological images (normal, OSFWD and OSFD). These feature vectors were fed to five different classifiers: Decision Tree (DT), Sugeno Fuzzy, Gaussian Mixture Model (GMM), K-Nearest Neighbor (K-NN), Radial Basis Probabilistic Neural Network (RBPNN) to select the best classifier. Our results show that combination of texture and HOS features coupled with Fuzzy classifier resulted in 95.7% accuracy, sensitivity and specificity of 94.5% and 98.8% respectively. Finally, we have proposed a novel integrated index called Oral Malignancy Index (OMI) using the HOS, LBP, LTE features, to diagnose benign or malignant tissues using just one number. We hope that this OMI can help the clinicians in making a faster and more objective detection of benign/malignant oral lesions. 相似文献
96.
Changes in molecular mobility are important in defining the stability and quality of amorphous solid foods, pharmaceuticals,
and other solid biomaterials. Predictions of stability must consider matrix mobility below and above Tg (the glass transition temperature); measurement of molecular mobility in amorphous solids over time scales ranging from <10−9 s to >108 s requires specialized methods. This research investigated how the steady-state and time-resolved emission and intensity
of phosphorescence from vanillin (4-hydroxy-3-methoxy benzaldehyde), a common flavor compound, can be used to probe molecular
mobility when dispersed within amorphous pure sucrose films. Phosphorescence emission spectra and time-resolved intensity
decays, measured in sucrose as a function of temperature in the absence of oxygen, were strongly modulated by matrix molecular
mobility. Temperature had a significant effect on vanillin phosphorescence peak frequency and bandwidth, intensity, and lifetime
both in the glass and in the melt. Time-resolved phosphorescence intensity decays from vanillin were multiexponential both
below and above the glass transition temperature, indicating that the pure (single component) amorphous matrix was dynamically
heterogeneous on the molecular level. These data show that vanillin is a promising intrinsic probe of molecular mobility and
dynamic heterogeneity in amorphous solid foods and perhaps pharmaceuticals. 相似文献
97.
Mandavi Singh Mohammad SaquibShyam Babu Singh Swastika SinghPreyas Ankit Shahin FatmaJagdamba Singh 《Tetrahedron letters》2014
A new environmentally friendly methodology for the efficient synthesis of biologically significant triazole thiazolidinone hybrids in aqueous medium, using acetic acid as an organocatalyst in the presence of cetyltrimethylammonium bromide (CTAB) surfactant has been developed for the first time. The effect of several surfactants on the yield and completion time of the reaction was investigated and it was found that the use of CTAB at 60 °C gave the best results (79–96% in 20 min–35 min) for the synthesis of the target compounds. 相似文献
98.
99.
Kuppuswamy Nagarajan Vunnam R. Rao Rashmi K. Shah Sharada J. Shenoy Hans Fritz Wilhelm J. Richter Dieter Muller 《Helvetica chimica acta》1988,71(1):77-92
Homophthalic acid ( 1 ) undergoes reaction with 1,2-, 1,3-, and 1,4-diamines to give condensed 1(2H)-isoquinolinones like 2 , 4 , 13 , and 25 , which exhibit marked enamine character. These are attacked by electrophiles at the N or C terminus. Some notable reactions of imidazoisoquinolone 2 are those with maleic and acrylic acids to form the tetracycles 48 and 51 , respectively. With propiolic acid, 5 underwent an interesting reaction to form the benzimidazonaphthyridine 53 . An equally interesting behaviour was elicited from 2 in its reaction with formaldehyde, when in addition to the expected methylene-bridged molecule 59 , the novel spiro derivative 60 was formed by the dimerisation of a presumed azadiene intermediate 63 . 相似文献
100.
Kalagouda B. Gudasi Rashmi V. Shenoy Ramesh S. Vadavi Manjula S. Patil Siddappa A. Patil 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(1-2):93-101
Reaction of Ln(NO3)3 with 2,6-bis[(3-methoxysalicylidene)hydrazino carbonyl]pyridine (BMSPD) afforded binuclear complexes of the type [Ln2(BMSPD)(NO3)2(H2O)5]·3H2O in case of La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III) and Dy(III), and [Ln2(BMSPD)(NO3)2(H2O)5] in case of Y(III). The mode of coordination of ligand and the conformational changes on complexation with lanthanides was studied based on elemental analysis, magnetic studies, TG/DTA, IR, 1H-NMR, Electronic, EPR and Fluorescence spectral studies. The ligand coordinates to one metal centre through enolized deprotonated carbonyls and pyridine nitrogen whereas doubly deprotonated phenolate oxygens and two hydrazonic nitrogens ligate to another lanthanide centre. Both the metal ions are in eight-coordination environments. The ligand and complexes were further tested for antifungal and antibacterial activities. 相似文献