全文获取类型
收费全文 | 786篇 |
免费 | 36篇 |
国内免费 | 7篇 |
专业分类
化学 | 484篇 |
晶体学 | 2篇 |
力学 | 66篇 |
数学 | 78篇 |
物理学 | 199篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 23篇 |
2021年 | 24篇 |
2020年 | 29篇 |
2019年 | 44篇 |
2018年 | 51篇 |
2017年 | 40篇 |
2016年 | 50篇 |
2015年 | 31篇 |
2014年 | 60篇 |
2013年 | 79篇 |
2012年 | 81篇 |
2011年 | 90篇 |
2010年 | 42篇 |
2009年 | 42篇 |
2008年 | 38篇 |
2007年 | 31篇 |
2006年 | 18篇 |
2005年 | 10篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1996年 | 3篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有829条查询结果,搜索用时 15 毫秒
171.
In this paper we introduce the notion of a von Neumann-Schatten p-frame in separable Banach spaces and obtain some of their characterizations. We show that p-frames and g-frames are a class of von Neumann-Schatten p-frames. 相似文献
172.
Numerical investigation of turbulent free jet flows issuing from rectangular nozzles: the influence of small aspect ratio 总被引:1,自引:0,他引:1
Ehsan Faghani Reza Maddahian Pedram Faghani Bijan Farhanieh 《Archive of Applied Mechanics (Ingenieur Archiv)》2010,80(7):727-745
In this research, the fluid and thermal characteristics of a rectangular turbulent jet flow is studied numerically. The results
of three-dimensional jet issued from a rectangular nozzle are presented. A numerical method employing control volume approach
with collocated grid arrangement was employed. Velocity and pressure fields are coupled with SIMPLEC algorithm. The turbulent
stresses are approximated using k–e{\varepsilon} model with two different inlet conditions. The velocity and temperature fields are presented and the rates of their decay
at the jet centerline are noted. The velocity vectors of the main flow and the secondary flow are illustrated. Also, effect
of aspect ratio on mixing in rectangular cross-section jets is considered. The aspect ratios that were considered for this
work were 1:1 to 1:4. The results showed that the jet entrains more with smaller AR. Special attention has been drawn to the
influence of the Reynolds number (based on hydraulic diameter) as well as the inflow conditions on the evolution of the rectangular
jet. An influence on the jet evolution is found for smaller Re, but the jet is close to a converged state for higher Reynolds numbers. The inflow conditions have considerable influence
on the jet characteristics. 相似文献
173.
Nilofar Mustafa Naveed Iqbal Raja Noshin Ilyas Fozia Abasi Muhammad Sheeraz Ahmad Maria Ehsan Asma Mehak Imran Badshah Jarosaw Prokw 《Molecules (Basel, Switzerland)》2022,27(15)
Agriculture is the backbone of every developing country. Among various crops, wheat (Triticum aestivum L.) belongs to the family Poaceae and is the most important staple food crop of various countries. Different biotic (viruses, bacteria and fungi) and abiotic stresses (water logging, drought and salinity) adversely affect the qualitative and quantitative attributes of wheat. Among these stresses, salinity stress is a very important limiting factor affecting the morphological, physiological, biochemical attributes and grain yield of wheat. This research work was carried out to evaluate the influence of phytosynthesized TiO2 NPs on the germination, physiochemical, and yield attributes of wheat varieties in response to salinity. TiO2 NPs were synthesized using TiO2 salt and a Buddleja asiatica plant extract as a reducing and capping agent. Various concentrations of TiO2 nanoparticles (20, 40, 60 and 80 mg/L) and salt solutions (NaCl) (100 and 150 mM) were used. A total of 20 mg/L and 40 mg/L improve germination attributes, osmotic and water potential, carotenoid, total phenolic, and flavonoid content, soluble sugar and proteins, proline and amino acid content, superoxide dismutase activity, and reduce malondialdhehyde (MDA) content at both levels of salinity. These two concentrations also improved the yield attributes of wheat varieties at both salinity levels. The best results were observed at 40 mg/L of TiO2 NPs at both salinity levels. However, the highest concentrations (60 and 80 mg/L) of TiO2 NPs showed negative effects on germination, physiochemical and yield characteristics and causes stress in both wheat varieties under control irrigation conditions and salinity stress. Therefore, in conclusion, the findings of this research are that the foliar application of TiO2 NPs can help to improve tolerance against salinity stress in plants. 相似文献
174.
Iman Jafari Mohamadreza Shakiba Fatemeh Khosravi Seeram Ramakrishna Ehsan Abasi Ying Shen Teo Mohammadreza Kalaee Majid Abdouss Ahmad Ramazani S. A Omid Moradi Erfan Rezvani Ghomi 《Molecules (Basel, Switzerland)》2021,26(6)
The incorporation of nanofillers such as graphene into polymers has shown significant improvements in mechanical characteristics, thermal stability, and conductivity of resulting polymeric nanocomposites. To this aim, the influence of incorporation of graphene nanosheets into ultra-high molecular weight polyethylene (UHMWPE) on the thermal behavior and degradation kinetics of UHMWPE/graphene nanocomposites was investigated. Scanning electron microscopy (SEM) analysis revealed that graphene nanosheets were uniformly spread throughout the UHMWPE’s molecular chains. X-Ray Diffraction (XRD) data posited that the morphology of dispersed graphene sheets in UHMWPE was exfoliated. Non-isothermal differential scanning calorimetry (DSC) studies identified a more pronounced increase in melting temperatures and latent heat of fusions in nanocomposites compared to UHMWPE at lower concentrations of graphene. Thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) revealed that UHMWPE’s thermal stability has been improved via incorporating graphene nanosheets. Further, degradation kinetics of neat polymer and nanocomposites have been modeled using equations such as Friedman, Ozawa–Flynn–Wall (OFW), Kissinger, and Augis and Bennett’s. The "Model-Fitting Method” showed that the auto-catalytic nth-order mechanism provided a highly consistent and appropriate fit to describe the degradation mechanism of UHMWPE and its graphene nanocomposites. In addition, the calculated activation energy (Ea) of thermal degradation was enhanced by an increase in graphene concentration up to 2.1 wt.%, followed by a decrease in higher graphene content. 相似文献
175.
Nikooei Niusha Dekamin Mohammad G. Valiey Ehsan 《Research on Chemical Intermediates》2020,46(8):3891-3909
Research on Chemical Intermediates - Benzene-1,3,5-tricarboxylic acid-functionalized MCM-41 (MCM-41-Pr-BTA), as a novel hybrid organosilica, was prepared and properly characterized by the... 相似文献
176.
Hosseini Seyed Ehsan Butler Brayden 《Journal of Thermal Analysis and Calorimetry》2021,144(3):763-778
Journal of Thermal Analysis and Calorimetry - Solar is one of the most promising energy sources because of the abundance of solar radiation in certain parts of the world. One of the main limiting... 相似文献
177.
178.
A triiodide-selective electrode based on copper (II)-Schiff base complex as a membrane carrier is proposed. The electrode
was prepared by incorporating the carrier into a plasticized polyvinylchloride (PVC) membrane and was directly coated on the
surface of a graphite electrode. The obtained electrode showed a near Nernstian slope of 57.0 ± 0.4 mV/decade to I
3
−
ions over an activity range of 1.0 × 10−5−1.0 × 10−1 M with a limit of detection of 4.8 × 10−6 M. The response time of the electrode was fast (5 s) and the electrode could be used for about 2 months without considerable
divergence in response. The potentiometric selectivity coefficients were evaluated and displayed anti-Hofmeister behavior.
The electrode was used as an indicator electrode in the potentiometric titration of the triiodide ion and in the determination
of ascorbic acid in vitamin C tablets.
The text was submitted by the authors in English. 相似文献
179.
M. Sadeghi P. van den Winkel H. Afarideh M. Haji-Saeid 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(3):665-672
The Rh target preparation for production of 103Pd was investigated by using a thick electrodeposition of rhodium metal on a copper backing. The electrodeposition experiments were performed in acidic sulfate media using RhCl3·3H2O, Rh2(SO4)3 (recovered from hydrochloric acid solution) and also in the commercially available Rhodex plating baths. For high current beam irradiation of a Rh target, the qualities of the deposit of the three baths were compared in terms of thermal shock, crack-free and morphology criteria. The quality of the plating obtained from a sulfate bath [Rh2(SO4)3] was comparable with the one obtained from commercially available Rhodex bath. The optimum conditions of the electrodepositions were as follows: 4.8 g rhodium [as Rh2(SO4)3], pH 2, DC current density of ca 8.5 mA·cm–2, 1% sulfamic acid (w/v) and temperature 40–60 °C.The authors would like to thank their colleagues at the VUB-Cyclotron department for help and assistance in preparation of the electrodeposition equipment and taking the SEM photomicrographs and also K. Aardaneh (NRCAM) for his assistance. 相似文献