全文获取类型
收费全文 | 204篇 |
免费 | 28篇 |
国内免费 | 4篇 |
专业分类
化学 | 168篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 40篇 |
物理学 | 23篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 10篇 |
2020年 | 6篇 |
2019年 | 16篇 |
2018年 | 24篇 |
2017年 | 8篇 |
2016年 | 29篇 |
2015年 | 13篇 |
2014年 | 10篇 |
2013年 | 30篇 |
2012年 | 11篇 |
2011年 | 7篇 |
2010年 | 8篇 |
2009年 | 12篇 |
2008年 | 9篇 |
2007年 | 6篇 |
2006年 | 9篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 1篇 |
2002年 | 4篇 |
2001年 | 4篇 |
1998年 | 1篇 |
排序方式: 共有236条查询结果,搜索用时 453 毫秒
141.
Two chaotic indicators namely the correlation dimension and the Lyapunov exponent methods are investigated for the daily river flow of Kizilirmak River. A delay time of 60 days used for the reconstruction is chosen after examining the first minimum of the average mutual information of the data. The sufficient embedding dimension is estimated using the false nearest neighbor algorithm, which has a value of 11. Based on these embedding parameters the correlation dimension of the resulting attractor is calculated, as well as the average divergence rate of nearby orbits given by the largest Lyapunov exponent. The presence of chaos in the examined river flow time series is evident with the low correlation dimension (2.4) and the positive value of the largest Lyapunov exponent (0.0061). 相似文献
142.
Soleimani Ebrahim Torkaman Sara Sepahvand Heshmatollah Ghorbani Somayeh 《Molecular diversity》2019,23(3):739-749
Molecular Diversity - In this research, synthesis and characterization of new surface-functionalized magnetic silica nanoparticles are reported. The magnetic silica nanoparticle was synthesized by... 相似文献
143.
Peiyuan Zuo Abbas Tcharkhtchi Mohammadali Shirinbayan Joseph Fitoussi Farid Bakir 《先进技术聚合物》2019,30(3):584-597
In this paper, the thermo‐oxidation for a short glass fiber–reinforced polyphenylene sulfide (PPS/GF) composite was experimentally and theoretically studied by a wide range of physicochemical and mechanical techniques. The accelerated thermal aging temperatures were fixed at 100°C, 140°C, 160°C, 180°C, and 200°C. Firstly, the results of weight loss under aging indicate the formation of volatile products because of chain scission of end groups. Also, Fourier‐transform infrared spectroscopy (FTIR) results suggest that the formation and accumulation of carbonyl group arising from the formation of hydroperoxides in oxidative propagation process. In all cases of different thermal oxidation temperatures, it is hard to observe some significant change about the concentration of carbonyl group during the induction time. This induction time depends inversely on the oxidation temperature. Moreover, the cross‐linking and chain scissions exist together according to the results of rheological results and it is easier to see the cross‐linking phenomenon at the beginning of oxidation while the chain scissions are more pronounced, with the oxidation process developing further. In aspect of mechanical properties, σmax increases at the beginning of oxidation because of cross‐linking, and subsequently, the σmax always decreases because of thermo‐oxidation of the PPS matrix. In addition, the detailed thermo‐oxidation processes are fully discussed in the end of this study. A mechanistic schema has been proposed to present different oxidation reactions of PPS polymer and then a kinetic model has been extracted from this mechanism. Afterwards, the model has been verified by experimental results at different temperatures. 相似文献
144.
145.
Hossein Hosseinzadeh Soleyman Hosseinzadeh Shahryar Pashaei Naser Ghorbani Rohollah Mazaherpour 《先进技术聚合物》2019,30(11):2860-2871
In this study, a unique magnetic, pH, and thermo‐responsive hydrogel nanocomposite was synthesized via surface reversible addition fragmentation chain transfer (RAFT) copolymerization of acrylic acid (AA) and N‐isopropyl acrylamide (NIPAM) in the presence of magnetic β‐cyclodextrin (β‐CD). The nanocomposite demonstrated a pH‐responsiveness behavior at pHs 3 and 9. Moreover, swelling behaviors of nanocomposite were measured in solutions with various temperatures. Furthermore, the nanocomposites exhibited high swelling capacity by applying an external magnetic field because of the presence of Fe3O4 nanoparticles in the polymer structure. Besides, the doxorubicin (DOX) loading and releasing behaviors of the hydrogel nanocomposites were studied because of the stimuli‐responsive properties of the synthesized carriers. The adsorption of DOX obeyed a pseudo‐second‐order model and fitted well to the Langmuir isotherm model with the maximum adsorption capacity uptake of 291 mg g?1. In conclusion, the hydrogel nanocomposites were found to be as potential nanocarriers for use in controlled release applications. 相似文献
146.
Cardiac glycosides are used for treatment of irregular heartbeats, cardiac arrhythmia and congestive heart failures. In this research, digitoxin as a cardiac glycoside was identified and isolated for the first time in the world from Adonis aestivalis and investigated for its cytotoxic activity against cervical cancer cell (HeLa) lines and human lymphocytes by MTT test. Digitoxin extracted from the aerial parts of the plant collected from west of Iran and purified by column and thin layer chromatographic techniques. The structure of isolated cardiac glycoside was identified by IR, 1H NMR and 13C NMR methods and so the presence of digitoxin was established. The half maximal inhibitory concentration values for cervical cancer and lymphocyte cells were obtained to be 5.62 and 412.94 μg/mL. The results of this study introduced the new resource of digitoxin which has considerable cytotoxic effects against HeLa cancer cells but did not damage normal human lymphocyte cells. 相似文献
147.
Guido Mann Rüdiger Preuß Mohammadali Zoheidi Jörg Krüger 《Applied Surface Science》2007,254(4):1096-1100
Optical multimode fibers are applied in materials processing (e.g. automotive industry), defense, aviation technology, medicine and biotechnology. One challenging task concerning the production of multimode fibers is the enhancement of laser-induced damage thresholds. A higher damage threshold enables a higher transmitted average power at a given fiber diameter or the same power inside a thinner fiber to obtain smaller focus spots.In principle, different material parameters affect the damage threshold. Besides the quality of the preform bulk material itself, the drawing process during the production of the fiber and the preparation of the fiber end surfaces influence the resistance. Therefore, the change of the laser-induced damage threshold of preform materials was investigated in dependence on a varying thermal treatment and preparation procedure.Single and multi-pulse laser-induced damage thresholds of preforms (F300, Heraeus) were measured using a Q-switched Nd:YAG laser at 1064 nm wavelength emitting pulses with a duration of 15 ns, a pulse energy of 12 mJ and a repetition rate of 10 Hz. The temporal and spatial shape of the laser pulses were controlled accurately.Laser-induced damage thresholds in a range from 150 J cm−2 to 350 J cm−2 were determined depending on the number of pulses applied to the same spot, the thermal history and the polishing quality of the samples, respectively. 相似文献
148.
Ebrahimi Armin Ghorbani Bahram Ziabasharhagh Masoud Rahimi Mohammad Javad 《Journal of Thermal Analysis and Calorimetry》2021,146(3):1283-1296
Journal of Thermal Analysis and Calorimetry - Isothermal titration calorimetry (ITC) has been used to characterize inclusion complex formation of natural (α-, β-, γ-)cyclodextrins... 相似文献
149.
Leila Tajik Abdulrahman Bahrami Alireza Ghiasvand Farshid Ghorbani Shahna 《Chemical Papers》2017,71(10):1829-1838
Excessive and uncontrolled exposures of the workers to benzene, toluene, ethylbenzene and xylene (BTEX) have currently raised great concerns among industrial hygienist all over the world. Therefore, the effective monitoring of such exposures is assumed to be of prime importance. A cold fiber solid-phase microextraction device based on a cooling capsule as a cooling unit and CO2 as a coolant was applied to quantitatively analyze BTEX in aqueous samples. A gas chromatography with flame ionization detection was recruited to analyze the target analytes, which had been identified according to their retention times. Several factors such as coating temperature, extraction time and temperature, sample volume and sodium content were optimized. Two modes of extraction, i.e., headspace (HS) and headspace cold fiber (HS-CF) in SPME, were investigated and compared under optimized conditions. The results revealed that HS-CF-SPME has the most appropriate outcome for the extraction of BTEX from aqueous samples. Under the optimized conditions, the calibration curves were linear within the range of 0.2–500 ng ml?1 and the detection limits were between 0.02 and 0.07 ng ml?1.The intraday relative standard deviations was lower than about 10%. The method was successfully applied to the determination of BTEX in urine samples with good recovery. 相似文献
150.
Magnetic ion-imprinted polymer nanospheres, which have core–shell structures, have been synthesized as an adsorbent for extraction of Pb2+ from real samples prior to its flame atomic absorption spectrometric determination. The prepared adsorbent has been characterized using XRD, VSM, TEM, and FTIR measurements. The optimization results revealed that the adsorbent exhibited high selectivity toward Pb2+ over other cations such as Cu2+ and Zn2+. In addition, the removal efficiency of synthesized adsorbent was considerable (qm?=?171.42?mg g?1), its calibration curve was linear (0.5?850.0?ng mL?1), and detection limit was 0.01?ng mL?1. These results suggested that the prepared nanoadsorbent is an ideal candidate for solid-phase extraction of Pb2+ ions. 相似文献