全文获取类型
收费全文 | 255篇 |
免费 | 7篇 |
专业分类
化学 | 156篇 |
晶体学 | 2篇 |
力学 | 5篇 |
数学 | 39篇 |
物理学 | 60篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 9篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 11篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 34篇 |
2012年 | 14篇 |
2011年 | 20篇 |
2010年 | 12篇 |
2009年 | 15篇 |
2008年 | 16篇 |
2007年 | 18篇 |
2006年 | 9篇 |
2005年 | 5篇 |
2004年 | 8篇 |
2003年 | 3篇 |
2002年 | 11篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
排序方式: 共有262条查询结果,搜索用时 359 毫秒
171.
It is shown that a general shaped laser beam will eventually approach a Gaussian average intensity profile after propagation in turbulent atmosphere. In our formulation, source field at the exit plane of the laser is taken as the product of arbitrary functions of source transverse coordinates with Gaussian exponential modulations. Following the expansion of the arbitrary functions in terms of Hermite polynomials, the average receiver intensity expression is derived using the extended Huygens-Fresnel principle and the conditions for the intensity profile to assume a Gaussian shape are stated. The results are illustrated by simulating various source field distributions. 相似文献
172.
UV-initiated poly(butyl methacrylate-ethylene glycol dimethacrylate) porous polymer monoliths were prepared in situ in polypropylene-based pipette tips for high-throughput sample preparation. Prior to the in situ polymerization, the surface of the PP tips was modified. In this work, two different surface modification approaches were tested for this purpose. First the photoinitiator benzophenone was used to generate radicals at the surface of PP by hydrogen abstraction. In the second modification approach, a thin layer of a polymer was directly grafted to the surface. The effect of surface modification was measured by contact angle measurements of a drop of water at the surface. As a result of the surface modification, scan electron microscopy images indicate a covalent attachment of the monolith to the wall of the pipette tip. Pipette tips modified with 5% BP in methanol and packed with a plug of monolith were further evaluated for high-throughput sample preparation. Using a liquid handling system, the extraction performance of packed pipette tips was tested for the analysis of ropivacaine in plasma samples. The recovery and reproducibility results were in accordance with internationally accepted criteria for qualitative and quantitative analysis of the test substance, ropivacaine. 相似文献
173.
Dilhan?M.?KalyonEmail author Halil?Gevgilili Rahmi?Yazici Albert?J.?Post Gregory?J.?McFann 《Rheologica Acta》2004,43(4):396-405
Many bar soaps are processed using continuous processing technologies, including single and twin screw extrusion. However, in spite of the industrial importance of the extrusion-based processing of bar soaps the rheological behavior of bar soaps is poorly understood. Here, the shear viscosity and the formation of gross surface irregularities upon extrusion of the bar soap were investigated using steady torsional, rectangular slit, and capillary flows. Furthermore, the structure development aspects were investigated using wide-angle X-ray diffraction and scanning electron microscopy. It is revealed that the flow and deformation behavior of bar soaps is complicated by the ubiquitous presence of wall slip, viscoplasticity, gross surface irregularities, and various structuring aspects. The orientation of crystallites and the shear stress dependent fracture of a crystalline component of the formulation at the wall during flow were identified as some of the contributing effects to the development of the structure of the bar soap during flow and deformation. 相似文献
174.
Gülbanu Koyundereli Çılgı Halil Cetişli Ramazan Donat 《Journal of Thermal Analysis and Calorimetry》2014,115(2):2007-2020
Thermal decomposition of U(C2O4)2·6H2O was studied using TG method in nitrogen, air, and oxygen atmospheres. The decomposition proceeded in five stages. The first three stages were dehydration reactions and corresponded to removal of four, one, and one mole water, respectively. Anhydrous salt decomposed to oxide products in two stages. The decomposition products in nitrogen atmosphere were different from those in air and oxygen atmospheres. In nitrogen atmosphere UO1.5(CO3)0.5 was the first product and U2O5 was the second product, while these in air and oxygen atmospheres were UO(CO3) and UO3, respectively. The second decomposition products were not stable and converted to stable oxides (nitrogen: UO2, air–oxygen: U3O8). The kinetics of each reaction was investigated with using Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa methods. These methods were combined with modeling equations for thermodynamic functions, the effective models were investigated and thermodynamic values were calculated. 相似文献
175.
Nanocrystalline Zn1?xMnxS (x = 0.00, 0.01, 0.02, 0.03, 0.05, and 0.1) thin films having different Mn content were grown by the sol–gel dip coating process. The effect of Mn content on the structural, optical and magnetic properties of Zn1?xMnxS nanocrystalline thin films were investigated. X-ray diffraction results showed the presence of single hexagonal phase corresponding to ZnS with a preferred orientation along the ZnS (002) hexagonal plane direction without any detectable secondary phase, suggesting the incorporation of Mn ions into the ZnS lattice. Scanning electron microscope revealed the surface of the nanocrystalline films to be homogeneous and dense and the grains of the film surface were randomly scattered. In ultraviolet–visible measurements, the band gap energy corresponding to the absorption edge estimated were found to be 3.59–3.23 eV depending on the Mn doping ratio. Magnetic measurements showed that a paramagnetic behavior at 5 K and ferromagnetic behavior at 300 K. 相似文献
176.
The Photolyase/Cryptochrome Family of Proteins as DNA Repair Enzymes and Transcriptional Repressors 下载免费PDF全文
177.
A series of rigid and chiral C2-symmetric 18-crown-6 type macrocycles (S,S)-4, (S,S)-5, (S,S)-6 and (R,R)-2 bearing diamide–ester groups were synthesized. The binding properties of these macrocycles were examined for α-(1-naphthyl)ethylammonium perchlorates salts by an 1H NMR titration method. Taking into account the host employed, important differences were observed in the Ka values of (R)- and (S)-enantiomers of guests for macrocycles (S,S)-4 and (S,S)-6, KS/KR = 3.6, and KS/KR = 0.1 (KR/KS = 10.3) ΔΔG = 3.19 and ΔΔG = ?5.77 kJ mol?1, respectively. The results indicated excellent enantioselectivity of macrocyclic (S,S)-6 towards the enantiomers of α-(1-naphthyl)ethylammonium perchlorate salts. 相似文献
178.
Halil İbrahim Ulusoy 《Journal of Radioanalytical and Nuclear Chemistry》2014,302(1):497-504
Determination of trace uranyl ions was performed by using mixed micellar system and spectrophotometric determination. The method is based on cloud point extraction of uranyl ions after formation of an ion-association complex in the presence of Celestine Blue and sodium dodecyl sulfate. Then, the formed complex was extracted to non-ionic surfactant phase of Triton X-114 at pH 8.0. The optimal extraction and reaction conditions (e.g. concentrations and types of surfactants, concentration of complex forming agent, incubation conditions) were studied and analytical characteristics of the method (e.g. limit of detection, linear range, pre-concentration factor) were obtained by experimental studies. Linearity was obeyed in the range of 50–1,500 ng mL?1 for uranium(VI) ion and the detection limit of is 14.20 ng mL?1. The interference effects of common ions were also tested and validation studies were performed by using recovery test. The method was applied to the determination of uranium(VI) in several real samples. 相似文献
179.
Mustafa Halil 《International Journal of Theoretical Physics》1981,20(12):911-919
We solve the geodesies equation for a charged particle in Bell-Szekeres spacetime. In the same geometry we give the test particle solution of Dirac's equation.Supported by the Scientific and Technical Research Council of Turkey (T.B.T.A.K). 相似文献
180.
The key criteria for assessing the success of bone tissue engineering are the quality and quantity of the produced minerals within the cultured constructs. The accumulation of calcium ions and inorganic phosphates in culture medium serves as nucleating agents for the formation of hydroxyapatite, which is the main inorganic component of bone. Bone nodule formation is one of the hallmarks of mineralization in such cell cultures. In this study, we developed a new two-step procedure to accelerate bone formation in which mouse bone cell aggregates were produced first on various chemically treated non-adhesive substrates. After this step, the bone cells' growth and mineralization were followed in conventional culture plates. The number and size of cell aggregates were studied with light microscopy. The minerals' formation in the form of nodules produced by the cell aggregates and the bone crystal quality were studied with Fourier Transform Infrared (FTIR) spectroscopy. The FTIR spectra of the ash specimens (mineral phase only) from thermal gravimetric analysis (TGA) provided valuable information of the quality of the minerals. The υ(4) PO(4) region (550-650 cm(-1)), which reveals apatitic and non-apatitic HPO(4) or PO(4) environments, and phosphate region (910-1180 cm(-1)) were examined for the minerals produced in the form of nodules. The peak position and intensity of the spectra demonstrate that the quality of the bone produced by cell aggregates, especially from the bigger ones, which were formed on Plunoric treated substrates, exhibit a composition more similar to that of native bone. This work establishes a new protocol for high quality bone formation and characterization, with the potential to be applied to bone tissue engineering. 相似文献