全文获取类型
收费全文 | 233篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 142篇 |
力学 | 2篇 |
数学 | 10篇 |
物理学 | 90篇 |
出版年
2023年 | 7篇 |
2022年 | 19篇 |
2021年 | 17篇 |
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 13篇 |
2012年 | 7篇 |
2011年 | 13篇 |
2010年 | 11篇 |
2009年 | 7篇 |
2008年 | 10篇 |
2007年 | 7篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 9篇 |
2003年 | 16篇 |
2002年 | 4篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有244条查询结果,搜索用时 15 毫秒
81.
Chunqiu Zhao Fawad Ur Rehman Hui Jiang Matthias Selke Xuemei Wang Chong-Yang Liu 《中国科学:化学(英文版)》2016,59(5):637-642
Photodynamic therapy (PDT) is one of the latest biomedical technologies used for treatment of various neoplastic and non-neoplastic diseases. However, there still exist some well-known problems regarding its efficacy, e.g. effective concentration of the drug at the desired sites, the irradiation light dosimetry and biocompatibility of the photosensitizer. The introduction of nanotechnology and nanomaterial like biocompatible nano-titania (i.e., nano-TiO2) may facilitate to solve some of these problems. In this study we have explored the possibility of combining tetra sulphonatophenyl porphyrin (TSPP) with nano-titania (PT) for efficient PDT with least adverse effects. The spectroscopic properties of these nano-composites were characterized by using fluorescence and UV-Vis absorption spectroscopic study. The singlet oxygen quantum yield was determined by using 2,5-diphenyl-3,4-benzofuran (DPBF), while the effect of nano TiO2 with TSPP on the synovial fibroblast cells from human (HSC) and rat models (RSC) were investigated by confocal laser microscopy and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Our results suggest that nano TiO2 with TSPP can be readily utilized for effective PDT treatment of Rheumatoid Arthritis (RA). 相似文献
82.
Mohd Nazam Ansari Najeeb Ur Rehman Aman Karim Faisal Imam Abubaker M. Hamad 《Molecules (Basel, Switzerland)》2021,26(5)
The purpose of the research was to examine the protective effect of essential oil from Thymus serrulatus Hochst. ex Benth. (TSA oil) against cadmium (Cd)-induced renal toxicity. The experimental protocol was designed using 30 healthy adult Wistar albino rats allocated into five groups containing six animals in each group. Group 1 was treated as normal control and groups 2, 3, 4, and 5 were treated with cadmium chloride (CdCl2, 3 mg/kg, IP) for 7 days. Group 3 was also treated with silymarin (100 mg/kg, PO) as a standard group, while groups 4 and 5 were administered with TSA oil at doses of 100 and 200 mg/kg PO, respectively. The nephrotoxicity was measured with various parameters such as kidney function markers, oxidative stress markers (glutathione (GSH) and malondialdehyde (MDA)), and messenger ribonucleic acid (mRNA) expression levels of inflammatory factors. The histological studies were also evaluated in the experimental protocol. The CdCl2-treated groups showed a significant increase in the levels of serum kidney function markers along with MDA levels in kidney homogenate. However, renal GSH level was found to be reduced significantly. It was found that CdCl2 significantly upregulated the nuclear factor levels of kappaB (NF-κB p65), inducible nitric oxide synthase (iNOS), and small mothers against decapentaplegic (Smad2) as compared to the normal control group. On the other hand, TSA oil significantly improved the increased levels of serum kidney function markers, non-enzymatic antioxidants, and lipid peroxidation. In addition, TSA oil significantly downregulated the increased expression of NF-κB p65, iNOS, and Smad2 in Cd-intoxicated rats. Moreover, the histological changes in the tissue samples of the kidney of Cd-treated groups were significantly ameliorated in the silymarin- and TSA-oil-treated groups. The present study reveals that TSA oil ameliorates Cd-induced renal injury, and it is also proposed that the observed nephroprotective effect could be due to the antioxidant potential of TSA oil and healing due to its anti-inflammatory action. 相似文献
83.
Muhammad Junaid Iqbal Khan Zarfishan Kanwal Masood Yousaf Hamid Ullah Javed Ahmad Abid Latif Yong-Han Shin Ata Ur Rahman Khalid 《理论物理通讯》2021,73(3):35701-147
The development of new materials,having exceptional properties in comparison to existing materials is highly required for bringing advancement in electronic and optoelectronic technologies.Keeping this fact,we investigated structural,electronic,and optical properties of zincblende GaN doped with selected Zn concentrations(6.25%,12.50%,and 18.70%),using the first-principle calculations based on density functional theory with GGA+U.We conducted the entire study using the WIEN2K code.In this study,we calculated various significant parametric quantities such as cohesive energies,formation energies,bulk moduli,and lattice constants along with the study of optical and electronic properties by substituting Ga atoms with Zn atoms in 1×2×2 supercell.The structural stability is confirmed by studying the phonon dispersion curves which suggest that Zn:GaN material is stable against the 6.25%and 18.70%Zn concentrations while for 12.50%,it shows instability.The Hubbard values U=0,2,4,6 eV were added to GGA and the electronic properties were improved with the U=6 eV.Optical absorption was blue shifted while the refractive index and dielectric constant were increased with increasing the Zn concentrations.Electronic properties are enhanced due to the prime contribution of cations(Zn)3ri states.The optical and electronic properties are further discussed in detail in the entire study. 相似文献
84.
We report an efficient and consistent method for the solution of Schrödinger wave equation using the Green's function technique and its successful application to the nonrelativistic radial wave equation of hydrogen atom. For the radial wave equation, the Green's function is worked out analytically by means of Laplace transform method and the wave function is proposed under the boundary conditions. Computationally the product of potential term, the proposed wave function and the Green's function are integrated iteratively to get the nonrelativistic radial wave function. The resultant wave after each iteration is normalized and plotted against the standard nonrelativistic radial wave function. The solution converges to the standard wave with the increasing number of iterations. Results are verified for the first 15 states of hydrogen atom. The method adopted here can be extended to many‐body problem and hope that it can enhance our knowledge about complex systems. 相似文献
85.
Javid Hussain Hidayatullah Khan Liaqat Ali Abdul Latif Khan Najeeb Ur Rehman Sajid Jahangir Ahmed Al‐Harrasi 《Helvetica chimica acta》2015,98(5):719-723
The phytochemical investigations on Cleome droserifolia resulted in the isolation and characterization of a new indole alkaloid, 5‐hydroxy‐2‐methoxy‐1‐methyl‐1H‐indole‐3‐carbaldehyde ( 1 ). The structure elucidation was carried out on the basis of 1D‐ and 2D‐NMR techniques. In addition to 1 , two known aromatic derivatives, veratrol ( 2 ) and 2‐methoxy‐4‐methylacetophenone ( 3 ), were also obtained. All these compounds were purified by repeated column chromatography of the CH2Cl2 fraction obtained from MeOH extract of Cleome droserifolia. The structure of the new compound 1 was finally confirmed by the combined 1D (1H‐ and 13C‐) and 2D (H? C correlations; HMBC and HSQC) NMR and IR spectroscopy, mass spectrometry (MS), and UV absorption spectroscopy techniques. The comparison of the physical and spectroscopic data with those in the literature provided evidence for the structure confirmation of known compounds. All the purified compounds were subjected to urease and α‐glucosidase enzymes inhibition. The results showed that compound 1 was more potent with an IC50 value 11.97±2.067 μg/ml towards urease inhibition, while the activity of α‐glucosidase enzyme was marginal. 相似文献
86.
Being aware of the importance to consider every step in the evaluation of the combined measurement uncertainty of the result,
the purpose of this work was to evaluate the contribution of the radial thermal neutron flux gradient to the uncertainty budget
for trace level uranium determination in biological materials by a radiochemical neutron activation analysis (RNAA). Determination
of uranium via the short-lived nuclide 239U was based on solvent extraction with TBP and measurement of the chemical yield from the gamma-ray spectrum of the isolated
fraction via 235U. It has been shown previously, that radial neutron flux gradient, could have a relevant effect on the final result obtained
by RNAA. In the present work, radial neutron flux gradient within the irradiation assembly generally accepted in our lab (standards
tapped beside the sample), varied between 93 and 108% around the mean value and contributes approximately 20% to the combined
measurement uncertainty of the result. 相似文献
87.
Muhammad Yaseen Muhammad Shakirullah Imtiaz Ahmad Ata Ur Rahman Faiz Ur Rahman Muhammad Usman Rauf Razzaq 《燃料化学学报》2012,40(6):714-720
In the current study simultaneous reactions of hydrodesulfurization(HDS) of dibenzothiophene(DBT) and reforming of methanol in a micro-autoclave reactor were studied over bi-metallic(Co-Mo/Al2O3 and Ni-Mo/Al2O3) and tri-metallic(Pd-Co-Mo/Al2O3 and Pd-Ni-Mo/Al2O3) catalyst systems which were prepared by incipient impregnation method.In situ hydrogen utilization and low Pd loadings were the major targets of this study.For comparison purpose,catalytic activity was separately determined for both the methanol reforming and HDS of DBT reactions as well.Ni based catalysts were confirmed with better activity than Co ones for both the reactions with Pd promoted ones ranking at the top i.e.Pd-Ni-Mo/Al2O3 > Ni-Mo/Al2O3 > Pd-Co-Mo/Al2O3 > Co-Mo/Al2O3 where Pd-Ni-Mo/Al2O3 showed 91% DBT conversion at 380 ℃ and 12 h reaction time.Some of the selected organic additives on catalytic activity were tested for their effect toward HDS reaction which was unique with close relation to their chemical nature.Reaction products were quantitatively and qualitatively analyzed via HPLC and GC-MS techniques respectively which helped in elucidating reaction mechanism. 相似文献
88.
Ather Farooq Khan Muhammad Awais Abdul Samad Khan Sobia Tabassum Aqif Anwar Chaudhry Ihtesham Ur Rehman 《应用光谱学评论》2013,48(4):329-355
Abstract Raman spectroscopy of natural bones and hydroxyapatites is described. In addition, how Raman spectroscopy has proved crucial in providing baseline data for the modification of synthetic apatite powders that are routinely used now as bone replacement materials is explained. It is important to understand the chemical structural properties of natural bone. Bone consists of two primary components: an inorganic or mineral phase, which is mainly a carbonated form of a nanoscale crystalline calcium phosphate, closely resembling hydroxyapatite, and an organic phase, which is composed largely of type I collagen fibers. Other constituents of bone tissue include water and organic molecules such as glycosaminoglycans, glycoproteins, lipids, and peptides. Ions such as sodium, magnesium, fluoride, and citrate are also present, as well as hydrogenophosphate. Hence, the mineral phase in bone may be characterized essentially as nonstoichiometric substituted apatite. Such a distinction is important in the development of synthetic calcium phosphates for application as skeletal implants. An understanding of bone function and its interfacial relationship to an implant clearly depends on the associated structure and composition. Therefore, it is essential to fully understand the chemical composition of bone, and Raman spectroscopy is an excellent technique for such an analysis. 相似文献
89.
Gadea A Lenzi SM Lunardi S Mărginean N Zuker AP de Angelis G Axiotis M Martínez T Napoli DR Farnea E Menegazzo R Pavan P Ur CA Bazzacco D Venturelli R Kleinheinz P Bednarczyk P Curien D Dorvaux O Nyberg J Grawe H Górska M Palacz M Lagergren K Milechina L Ekman J Rudolph D Andreoiu C Bentley MA Gelletly W Rubio B Algora A Nacher E Caballero L Trotta M Moszyński M 《Physical review letters》2006,97(15):152501
Gamma decays from excited states up to Jpi=6+ in the N=Z-2 nucleus 54Ni have been identified for the first time. Level energies are compared with those of the isobars 54Co and 54Fe and of the cross-conjugate nuclei of mass A=42. The good but puzzling f7/ cross-conjugate symmetry in mirror and triplet energy differences is analyzed. Shell model calculations reproduce the new data but the necessary nuclear charge-dependent phenomenology is not fully explained by modern nucleon-nucleon potentials. 相似文献
90.
SU Siyi LI Xiaoyu GUO Xu ZHOU Ruiming LI Manman MING Pengfei HUANG Yingying Sajid Ur RAHMAN DING Hongyan FENG Shibin LI Jinchun WANG Xichun LI Yu WU Jinjie 《高等学校化学研究》2019,35(6):1105-1110
The anti-inflammatory activity of tea polyphenols(TPs) in RAW264.7 macrophages stimulated by lipopolysaccharide(LPS) was investigated in this paper. RAW264.7 macrophages were treated with different concentrations of TP(0, 12.5, 25, 50, 100, and 200 μg/mL) and then stimulated by LPS. Another blank control group was set up. The expression of pro-inflammatory cytokines associated with the nuclear factor-kappa B(NF-κB) signaling pathway was investigated before and after TP treatment. Pretreatment of RAW264.7 cells with TP decreased the expression of tumor necrosis factor-α(TNF-α), interleukin-6(IL-6) and interleukin 1 beta(IL-1β) pro-inflammatory cytokines. In addition, TP inhibited the phosphorylation of p65 and IκB by blocking the phosphorylation and the degradation of NF-κB inhibitor protein. In conclusion, TP exerts anti-inflammatory effects by regulating the release of inflammatory mediators via the NF-κB signaling pathway. 相似文献