全文获取类型
收费全文 | 1463篇 |
免费 | 100篇 |
国内免费 | 13篇 |
专业分类
化学 | 934篇 |
晶体学 | 30篇 |
力学 | 82篇 |
数学 | 130篇 |
物理学 | 400篇 |
出版年
2024年 | 8篇 |
2023年 | 18篇 |
2022年 | 93篇 |
2021年 | 88篇 |
2020年 | 60篇 |
2019年 | 58篇 |
2018年 | 49篇 |
2017年 | 44篇 |
2016年 | 71篇 |
2015年 | 62篇 |
2014年 | 75篇 |
2013年 | 117篇 |
2012年 | 98篇 |
2011年 | 124篇 |
2010年 | 72篇 |
2009年 | 51篇 |
2008年 | 55篇 |
2007年 | 47篇 |
2006年 | 45篇 |
2005年 | 39篇 |
2004年 | 40篇 |
2003年 | 25篇 |
2002年 | 16篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 15篇 |
1995年 | 6篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1971年 | 2篇 |
排序方式: 共有1576条查询结果,搜索用时 0 毫秒
101.
M. Aneesuddin P. N. Char M. Raza Hussain E. R. Saxena 《Journal of Thermal Analysis and Calorimetry》1983,26(2):205-215
When chalcopyrite is heated in air, up to 350? there is no marked change. Between 350 and 440?, surface material is oxidised to iron sulphate, CuSO4 and Fe2O3, while in regions not accessible to oxygen the formation of Cu5FeS4, FeS and S takes place. From 440 to 500? oxidation and sulphation phenomena occur. Stable compounds between 500 and 650? are iron sulphate, CuSO4 and Fe4O3, with a minor amount of 6CuO.Cu2O indicated at 650?. After the decomposition of iron sulphate, CuSO4 decomposes, first to CuO.CuSO4 and then to CuO. By 750? the sulphur has been totally lost from all compounds, while the oxides of copper and iron partly react to form CuFe2O4. Final products of oxidation between 800 and 850? are CuO, CuFe2O4 and Fe3O4. 相似文献
102.
Study of various binding materials like potassium bromide, poly(vinyl alcohol), starch, silver and aluminum has been carried out using laser-induced breakdown spectroscopy (LIBS). The role of matrix effects using these five binders on LIBS signal intensity was investigated for better performance of LIBS technique as a quantitative analytical tool. For comparative study of different binders, the signal intensity of different Mg lines at 518.3, 517.2, 383.8 and 279.5 nm wavelengths were recorded for pellets prepared with known concentrations of Mg in these binders. The influence of laser energy on ablated mass under different binding materials and its correlation with LIBS signal intensity has been explored. Optical scanning microscopy images of the ablated crater were studied to understand the laser ablation process. The study revealed that the binding material plays an important role in the generation of LIBS signal. The relative signal intensity measured for a standard Mg line (at 518.3 nm) were 735, 538, 387, 227 and 130 for potassium bromide, starch, poly(vinyl alcohol), silver and aluminum as binders, respectively. This indicates clearly that potassium bromide is better as a binder for LIBS studies of powder samples. 相似文献
103.
104.
Tanveer Hussain Bokhari Muhammad Bilal Butt Saira Hina Munawar Iqbal Muhammad Daud Muhammad Imran 《Journal of Radioanalytical and Nuclear Chemistry》2017,314(3):1487-1496
The field of therapeutic nuclear medicine is emerging rapidly as choice of treatment in oncology and other cellular malignancies. The growth of this branch of nuclear medicine is greatly facilitated by the introduction of a number of new radiopharmaceuticals and radionuclides. 90Y-radiopharmaceuticals have confirmed their worth in medical and clinical areas in a very short span of time. The 90Y is a radioisotope widely used for therapeutic purposes and considerable perfection has been made to understand the chemistry of 90Y-labeled radiopharmaceuticals. The development of these radiopharmaceuticals can be made favorable by using appropriate buffer, incubation period, optimal pH, specific activity and reaction temperature. In this review, we have discussed the preparation of range of 90Y transporting biological molecules such as antibodies radiolabeled peptides, antigens and microsphere with their clinical applications. 相似文献
105.
Structural,compositional and hardness properties of hydrogenated amorphous carbon nitride thin films synthesized by dense plasma focus device 下载免费PDF全文
Z. A. Umar R. S. Rawat R. Ahmad Z. Chen Z. Zhang J. Siddiqui A. Hussnain T. Hussain M. A. Baig 《Surface and interface analysis : SIA》2017,49(6):548-553
The hydrogenated amorphous carbon nitride (a‐CNx:H) thin films were synthesized on the SS‐304 substrates using a dense plasma focus device. The a‐CNx:H thin films were synthesized using CH4/N2 admixture gas and 20 focus deposition shots on substrates placed at different distances from the anode top. X‐ray photoelectron spectroscopy and Raman analysis confirmed different C–N bonding in the a‐CNx:H thin films. A decrease in the N/C ratio as well as the sp3/sp2 ratio with an increase in the substrate distance has been observed. The higher amount of C–N formation for the film synthesized at 10 cm is observed which decreases with increasing distance. The X‐ray photoelectron spectroscopy and Raman analysis affirmed the C ≡ N presence in all the thin films synthesized at different distances. The morphology of the synthesized a‐CNx:H thin films showed nanoparticles and nanoparticle clusters formation at the surface. The hardness results showed comparatively lower hardness of the a‐CNx:H thin films due to the presence of C ≡ N. The C–N formation with lower amount of C ≡ N and a higher N/C ratio as well as a higher sp3/sp2 ratio for the films synthesized at 10 cm show reasonably higher hardness. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
106.
Fabrication of Sensitive Potentiometric Cholesterol Biosensor Based on Co3O4 Interconnected Nanowires 下载免费PDF全文
Highly sensitive, selective, reliable and inexpensive cholesterol biosensors are highly demanded for the routine monitoring of cholesterol molecules in order to prevent heart failure incidents. In this study, Co3O4 nanostructures are synthesized using polyvinyl pyrrolidone surfactant as growth template by a low temperature aqueous chemical growth method. The morphology of nanostructures was investigated by scanning electron microscopy and X‐ray diffraction techniques. The nanostructures exhibit interconnected nanowires like morphology with interconnected network of nanowires. The nanostructures of Co3O4 are polycrystalline. The cholesterol oxidase was physically adsorbed on the interconnected nanowires of Co3O4 for the chemical sensing of cholesterol molecules. The sensor device detected a wide range of cholesterol from 1×10?7 M to 1×10?3 M concentrations with sensitivity of ?94.031 mV/decade. A detection limit of 0.035×10?7 M cholesterol concentration was observed and a fast response time of 10 s was also noticed. The fabricated device is highly stable, selective, sensitive, reproducible and repeatable. All the collected information about presented cholesterol biosensor indicates its potential application for the monitoring of cholesterol concentrations from human blood serum and real‐life samples. 相似文献
107.
108.
109.
High bit-rate (>10 Gb/s) signals are composed of very short pulses and propagation of such pulses through a semiconductor
optical amplifier (SOA) requires consideration of intraband phenomena. Due to the intraband effects, the propagating pulse
sees a fast recovering nonlinear gain which introduces less distortion in the pulse shape and spectrum of the output pulse
but introduces a positive chirping at the trailing edge of the pulse. 相似文献
110.
J. O’Hara A. K. Azad A. J. Taylor 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,58(2):243-247
Metamaterials’ properties may be quantified through the assignment of bulk material parameters such as magnetic permeability
and electric permittivity. These assignments rely on the assumption that metamaterials are effective media, in this context
meaning that their electromagnetic properties are independent of the sample size. This assumption is not always valid, particularly
for metafilms, the surface equivalents of metamaterials. However, metamaterials comprised of numerous metafilm and dielectric
layers can be uniquely characterized in the effective medium approximation when all aspects of the metamaterial are properly
integrated. We present a simple model based on stratified systems to illustrate this fact. The model further assists in the
interpretation of novel metamaterial behaviors and offers a rapid and accurate method to determine the functionality of bulk
metamaterial-based devices. 相似文献