全文获取类型
收费全文 | 254篇 |
免费 | 19篇 |
国内免费 | 7篇 |
专业分类
化学 | 188篇 |
晶体学 | 3篇 |
力学 | 11篇 |
数学 | 12篇 |
物理学 | 66篇 |
出版年
2024年 | 3篇 |
2023年 | 2篇 |
2022年 | 12篇 |
2021年 | 33篇 |
2020年 | 18篇 |
2019年 | 20篇 |
2018年 | 19篇 |
2017年 | 16篇 |
2016年 | 19篇 |
2015年 | 12篇 |
2014年 | 12篇 |
2013年 | 19篇 |
2012年 | 21篇 |
2011年 | 14篇 |
2010年 | 13篇 |
2009年 | 8篇 |
2008年 | 9篇 |
2007年 | 11篇 |
2006年 | 8篇 |
2005年 | 3篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2002年 | 1篇 |
1991年 | 1篇 |
1988年 | 2篇 |
1983年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有280条查询结果,搜索用时 187 毫秒
141.
Hassan Abrar Ul Sumrra Sajjad Hussain Zafar Muhammad Nadeem Nazar Muhammad Faizan Mughal Ehsan Ullah Zafar Muhammad Naveed Iqbal Mazhar 《Molecular diversity》2022,26(1):51-72
Molecular Diversity - During the present investigation, two new sulfonamide-based Schiff base ligands, 4-{[(2-hydroxy-3-methoxyphenyl)methylidene]amino}-N-(1,3-thiazol-2-yl)benzene-1-sulfonamide... 相似文献
142.
During the past two decades, the lattice Boltzmann (LB) method has been introduced as a class of computational fluid dynamic methods for fluid flow simulations. In this method, instead of solving the Navier Stocks equation, the Boltzmann equation is solved to simulate the flow of a fluid. This method was originally developed based on uniform grids. However, in order to model complex geometries such as porous media, it can be very slow in comparison with other techniques such as finite differences and finite elements. To eliminate this limitation, a number of studies have aimed to formulate the lattice Boltzmann on the unstructured grids. This paper deals with simulating fluid flow through a synthetic porous medium using the LB method and on the quadtree grid structure. To this end, the LB method was used on nonuniform grids coupled with a technique for image reconstruction which resulted in the quadtree grids for simulation of fluid flow through porous media. Accuracy and efficiency of this algorithm is compared against the conventional LB method based on uniform grids. While the decrease in computational time in the proposed LB method on nonuniform grids is found to be significant regarding the size of the initial and reconstructed images, the same level of accuracy is obtained when compared with the conventional LB method on uniform grids. 相似文献
143.
Sajjad Aslani Khiavi Hamid Khaloozadeh Fahimeh Soltanian 《Mathematical and Computer Modelling of Dynamical Systems: Methods, Tools and Applications in Engineering and Related Sciences》2013,19(5):499-521
ABSTRACTWe study four-echelon supply chains consisting of manufacturer, wholesaler, retailer and customer with recovery center as hybrid recycling channels. In order to gain a larger market share, the retailer often takes the sales as a decision-making variable. For this purpose, in this supply chain, the retailer limits the forecast of market demand in future periods with expected logic. It also manages demand by leveraging prices and choosing market. In this paper, first, we investigate the state-space model of this supply chain system and examine the effect of complex dynamic and stochastic noise on the bullwhip effect. We analytically prove that this factor leads to the bullwhip effect. So, first, we filtered the information between nodes with extended Kalman filter after which we regulated the destructive effects of the bullwhip phenomenon by designing a non-linear quadratic Gaussian optimal controller. Eventually, the simulation results indicate the efficiency of the proposed method. 相似文献
144.
Sajjad Shoja Majidabad Heydar Toosian Shandiz Amin Hajizadeh 《Nonlinear dynamics》2014,77(1-2):119-134
This paper presents some novel discussions on fully decentralized and semi-decentralized control of fractional-order large-scale nonlinear systems with two distinctive fractional derivative dynamics. First, two decentralized fractional-order sliding mode controllers with different sliding surfaces are designed. Stability of the closed-loop systems is attained under the assumption that the uncertainties and interconnections among the subsystems are bounded, and the upper bound is known. However, determining the interconnections and uncertainties bound in a large-scale system is troublesome. Therefore in the second step, two different fuzzy systems with adaptive tuning structures are utilized to approximate the interconnections and uncertainties. Since the fuzzy system uses the adjacent subsystem variables as its own input, this strategy is known as semi-decentralized fractional-order sliding mode control. For both fully decentralized and semi-decentralized control schemes, the stability of closed-loop systems has been analyzed depend on the sliding surface dynamics by integer-order or fractional-order stability theorems. Eventually, simulation results are presented to illustrate the effectiveness of the suggested robust controllers. 相似文献
145.
Uzma Khan Bahniman Ghosh Md Waseem Akram Akshaykumar Salimath 《Applied Physics A: Materials Science & Processing》2014,117(4):2281-2288
Analysis of thermal and electrical characteristics of the proposed device, selective buried oxide junctionless transistor (SELBOX-JLT) along with its analog performance, is compared with silicon on insulator junctionless transistor (SOI-JLT). The proposed device shows better thermal efficiency. The maximum device temperature of SELBOX-JLT is 311 K, much less than that of SOI-JLT (445 K). The proposed device has almost no effect of self-heating on output characteristics. SELBOX-JLT exhibits better I ON/I OFF ratio, subthreshold slope, and drain-induced barrier lowering as compared to SOI-JLT for the same channel length. The analog performance parameters as transconductance (G m ), transconductance/drain current ratio (G m /I D), drain conductance (G D), output resistance (R 0), intrinsic gain (G m R 0), and unity-gain frequency (f T ) of the proposed device are found to be better than SOI-JLT. 相似文献
146.
Sohaila Andleeb Imtiaz‐ud‐Din Muhammad Khawar Rauf Syed Sikander Azam Ihsan‐ul Haq Muhammad Nawaz Tahir Sajjad Ahmad 《应用有机金属化学》2019,33(9)
Heteroleptic triorganobismuth (V) complexes of general formula, R3Bi(OOCR')2 ( 1 – 7 ), where R = C6H5 ( 1 – 3 ), p‐CH3C6H4 ( 4 – 7 ) and R' = 3,5‐Cl2C6H3 ( 1 , 5 ); 3,4,5‐(OCH3)3C6H2 ( 2 , 6 ); 3‐CH3C6H4 ( 3 , 7 ); 2‐OH‐3‐OCH3C6H3 ( 4 ) have been synthesized and fully characterized by FT‐IR, 1H &13C NMR spectroscopy, single crystal X‐ray crystallography and elemental analysis. The molecular geometry observed for the compounds is predominantly distorted trigonal bipyramidal, the fact which was subsequently authenticated through X‐ray analyses for ( 1 – 4 ). All the synthesized compounds have been bio‐assayed for antileishmanial (Leishmania tropica KWH23) and Jack beans urease inhibitory activity, and human Lymphocytes were used to measure the general toxicity. Of these, ( 4 ) proved to be highly effective against the target species (Leishmania tropica KWH23), while being non‐toxic towards the mammalian cells at levels below 0.74 μgmL?1, making it highly promising drug candidate. The high activities for ( 2 , 4 , and 6 ) against Jack beans Urease as compared to the reference standard demonstrate their significance in searching of therapeutic agents in future programs. The significant binding score of ( 2 & 4 ) against H. pylori in molecular docking studies further revealed their importance in future drug discovery processes. 相似文献
147.
M. Sajjad Athar M. Honda T. Kajita K. Kasahara S. Midorikawa 《Physics letters. [Part B]》2013,718(4-5):1375-1380
We present the calculation of the atmospheric neutrino fluxes for the neutrino experiments proposed at INO, South Pole and Pyhäsalmi. Neutrino fluxes have been obtained using ATMNC, a simulation code for cosmic ray in the atmosphere. Even using the same primary flux model and the interaction model, the calculated atmospheric neutrino fluxes are different for the different sites due to the geomagnetic field. The prediction of these fluxes in the present Letter would be quite useful in the experimental analysis. 相似文献
148.
149.
150.