全文获取类型
收费全文 | 232篇 |
免费 | 11篇 |
国内免费 | 4篇 |
专业分类
化学 | 142篇 |
晶体学 | 1篇 |
力学 | 11篇 |
数学 | 44篇 |
物理学 | 49篇 |
出版年
2022年 | 7篇 |
2021年 | 5篇 |
2020年 | 16篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 16篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2014年 | 24篇 |
2013年 | 29篇 |
2012年 | 17篇 |
2011年 | 19篇 |
2010年 | 9篇 |
2009年 | 5篇 |
2008年 | 13篇 |
2007年 | 7篇 |
2006年 | 4篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2000年 | 2篇 |
1998年 | 1篇 |
1993年 | 1篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有247条查询结果,搜索用时 15 毫秒
71.
Firouzeh Nemati Ali Ghorbani Gharjeh Ghiyaei Behrouz Notash Mojtaba Hajiloo Shayegan Vahid Amani 《Tetrahedron letters》2014
An efficient route for the synthesis of gem-bis(dithiocarbamate) derivatives is developed using dithiocarbamic acid salts generated from primary aliphatic amines and CS2. The method offers high yields, employs mild reaction conditions, and demonstrates excellent functional group compatibility. The structures of the products were confirmed spectroscopically and by X-ray analysis. 相似文献
72.
Vatmurge NS Hazra BG Pore VS Shirazi F Deshpande MV Kadreppa S Chattopadhyay S Gonnade RG 《Organic & biomolecular chemistry》2008,6(20):3823-3830
We report herein the synthesis and biological evaluation of bile acid dimers linked through 1,2,3-triazole and bis-beta-lactam. The dimers were synthesized using 1,3-dipolar cycloaddition reaction of diazido bis-beta-lactams , and terminal alkynes derived from cholic acid/deoxycholic acid in the presence of Cu(i) catalyst (click chemistry). These novel molecules were evaluated in vitro for their antifungal and antibacterial activity. Most of the compounds exhibited significant antifungal as well as antibacterial activity against all the tested fungal and bacterial strains. Moreover, their in vitro cytotoxicities towards HEK-293 and MCF-7 cells were also established. 相似文献
73.
Leal C Ewert KK Shirazi RS Bouxsein NF Safinya CR 《Langmuir : the ACS journal of surfaces and colloids》2011,27(12):7691-7697
The self-assembly of a custom-synthesized pentavalent cationic lipid (MVL5) and glycerol monooleate (GMO) with small interfering RNA (siRNA) results in the formation of a double-gyroid bicontinuous inverted cubic phase with colocalized lipid/siRNA domains as shown by synchrotron X-ray scattering and fluorescence microscopy. The high charge density (due to MVL5) and positive Gaussian modulus of the GMO-containing membranes confer optimal electrostatic and elastic properties for endosomal escape, enabling efficient siRNA delivery and effective, specific gene silencing. 相似文献
74.
The one-pot four-component synthesis of highly functionalized fused hydroxyl dihydropyrroles and dihydropyrazines from readily available diamines, 1,1-bis (methylsulfanyl)-2-nitroethene, phenylglyoxal monohydrates, and C-H acids have been developed. This strategy provides an efficient, catalyst-free approach for easy access to various new hydroxyl-dihydropyrrole and dihydropyrazine rings in good to high yields. The products were confirmed by 1H and 13C NMR, IR, mass, and X-ray crystal structure analyses. 相似文献
75.
In this study, the effect of Ru and Gd promoters on 15Co/\(\gamma\)-Al2O3 catalyst in the Fischer–Tropsch synthesis is investigated. The catalysts were synthesized by dry impregnation method and characterized by XRD, adsorption/desorption of nitrogen, TPR, TEM, ICP and XPS analyses. Activity and selectivity of the catalysts were examined in a fixed bed reactor at 210–230 °C with a H2/CO ratio of 2 and atmospheric pressure. The results showed that the Ru-promoted catalyst has the highest activity and methane selectivity which reduce the chain growth probability. The Gd-promoted catalyst was shown smaller particle size and higher dispersion of cobalt particles in compared with unpromoted catalyst. The smaller particles have more interaction and thus show the lower catalyst reducibility. The presence of Gd in the catalyst cause higher chain growth probability compared to the unpromoted one. The Ru–Gd-promoted catalysts were shown a synergic effect in the catalyst reducibility. Based on the screening of the catalysts in the atmospheric pressure; the unpromoted, 0.1Ru/15Co/Al2O3, and 0.1Ru1Gd/15Co/Al2O3 catalysts were selected to test at high pressure conditions, which the 0.1Ru1Gd/15Co catalyst showed the highest C5 + selectivity (75%) compared with the 0.1Ru/15Co/Al2O3 and the unpromoted one. 相似文献
76.
77.
We have constructed a collaboration network for physicists based in Iran working in different disciplines. By discussing properties like collaborators per author, shortest path, betweenness, and the concept of power in networks for this local model, and comparing with the global model, we understand how a developing country in the Middle East is contributing to the scientific growth in the world statistically. In this comparison, we found some properties of the local model which were not in accordance with the standard global society of science, which should be considered in developing the future policies. Our results show significant differences in factors like the degree and the diameter of the networks. Even though the diversity of disciplines is low in contrast with the rest of the world according to the diameter of networks, people are reluctant to collaborate as their degree shows. 相似文献
78.
Seyed Behrouz Khodadadi Fariborz Jolai 《Central European Journal of Operations Research》2012,20(2):281-297
In this paper we deal with a single server retrial queue with vacations. The server serves the customers until the system becomes empty, then it takes a vacation. The system consists of two types of costs. The blocking cost is considered whenever a customer is blocked either because of the server is busy or off. There is also a cost each time the server is turned on. The problem is to find an effective policy for turning on the dormant server. We propose a Fuzzy Based Threshold Policy (FBTP) to control the server, substitute for conventional threshold policies. The FBTP is based on four input parameters, an inference stage and it is tuned up using a stochastic List Based Threshold Accepting (LBTA) algorithm. Simulation models are developed to validate the fuzzy controller. Numerical experiments are provided to show that the proposed method is superior to crisp threshold policies. 相似文献
79.
Hamed Soleimani Mirmehdi Seyyed-Esfahani Mohsen Akbarpour Shirazi 《Annals of Operations Research》2016,242(2):399-421
Analyzing current trends in supply chain management, lead to find unavoidable steps toward closing the loop of supply chain. In order to expect best performance of Closed-Loop Supply Chain (CLSC) network, an integrated approach in considering design and planning decision levels is necessary. Further, real markets usually contain uncertain parameters such as demands and prices of products. Therefore, the next important step is considering uncertain parameters. 相似文献
80.
Arash Ghorbani-Choghamarani Ali Naghipour Heshmatollah Babaee Hayedeh Heidarnezhad Behrouz Notash 《Journal of the Iranian Chemical Society》2018,15(9):2123-2134
In this study, palladium (II) chloride reacted with the phosphonium salt [PhCH2COOCH2P(Ph)3]Br to give [PhCH2COOCH2P(Ph)3]2[Pd2Br6] (1). The characterization of synthesized compound was performed by elemental analysis, FT-IR, 1H, 31P, 13C NMR and also X-ray crystallography. It was found that this compound works as an efficient catalyst for the amination of aryl halides to afford primary amines, the results of which were satisfactory. Furthermore, it was found that the catalyst showed a high activity for Suzuki carbon–carbon cross-coupling of aryl halides and phenylboronic acid. Interestingly, the catalyst can be recovered from the reaction mixture and recycled four consecutive runs without any significant loss in activity. 相似文献