全文获取类型
收费全文 | 333篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
化学 | 262篇 |
晶体学 | 1篇 |
力学 | 3篇 |
综合类 | 1篇 |
数学 | 20篇 |
物理学 | 58篇 |
出版年
2023年 | 5篇 |
2022年 | 20篇 |
2021年 | 25篇 |
2020年 | 11篇 |
2019年 | 14篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 20篇 |
2015年 | 5篇 |
2014年 | 11篇 |
2013年 | 22篇 |
2012年 | 26篇 |
2011年 | 32篇 |
2010年 | 20篇 |
2009年 | 8篇 |
2008年 | 7篇 |
2007年 | 4篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 9篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 6篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1991年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
1903年 | 1篇 |
排序方式: 共有345条查询结果,搜索用时 62 毫秒
71.
Zainab S. Abbas Ghassan M. Sulaiman Majid S. Jabir Salman A. A. Mohammed Riaz A. Khan Hamdoon A. Mohammed Amal Al-Subaiyel 《Molecules (Basel, Switzerland)》2022,27(14)
The purpose of this study was to evaluate the potential of a newly modified cyclodextrin derivative, water-soluble β-cyclodextrin–epichlorohydrin (β-CD), as an effective drug carrier to enhance the poor solubility and bioavailability of galangin (GAL), a poorly water-soluble model drug. In this regard, inclusion complexes of GAL/β-CDP were prepared. UV-VIS spectrophotometry, Fourier-transform infrared spectroscopy (FTIR), X-ray crystallography (XRD), zeta potential analysis, particle size analysis, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) were applied to characterize the synthesized GAL/β-CD. Michigan Cancer Foundation-7 (MCF-7; human breast cancer cells) and rat embryo fibroblast (REF; normal cells) were employed to examine the in vitro cytotoxic effects of GAL/β-CD using various parameters. The dye-based tests of MTT and crystal violet clearly exhibited that GAL/β-CD-treated cells had a reduced proliferation rate, an influence that was not found in the normal cell line. The cells’ death was found to follow apoptotic mechanisms, as revealed by the dye-based test of acridine orange/ethidium bromide (AO/EtBr), with the involvement of the mitochondria via caspase-3-mediated events, as manifested by the Rh 123 test. We also included a mouse model to examine possible in vivo toxic effects of GAL/β-CD. It appears that the inclusion complex does not have a significant influence on normal cells, as indicated by serum levels of kidney and liver enzymatic markers, as well as thymic and splenic mass indices. A similar conclusion was reached on the histological level, as manifested by the absence of pathological alterations in the liver, kidney, thymus, spleen, heart, and lung. 相似文献
72.
Amal Shibli Reem Smoum Israel Goldberg Abraham Rubinstein Morris Srebnik 《应用有机金属化学》2006,20(7):459-462
The first examples of α‐amino boronate complexes stabilized by amino cyanoborane complexation were tested as trypsin and chymotrypsin inhibitors, and they showed moderate inhibition. The structure of compound 1 that contains two different boron atoms reveals that the geometry around the boron atom in the cyano group is tetrahedral, whereas a trigonal planar geometry exists around the boron atom attached to two oxygen atoms and a carbon atom. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
73.
74.
Comparison between single- and double-pulse LIBS at different air pressures on silicon target 总被引:1,自引:0,他引:1
K. Amal S.H. Elnaby V. Palleschi A. Salvetti M.A. Harith 《Applied physics. B, Lasers and optics》2006,83(4):651-657
A comparative study between single- and double-pulse laser-induced breakdown spectroscopy (LIBS) was performed on an n-type silicon(111) target. A new mobile double-pulse instrument for LIBS analysis was used for the measurements. The experiment was carried out at different air pressures of 0.7, 470 and 1000 hPa. It has been found that, in the case of double-pulse LIBS, the emission intensities of atomic and ionic lines are strongly enhanced at higher pressures. Using Stark broadening of the atomic lines of silicon, it was found that the electron number densities for single and double pulses are approximately the same (Ne∼1017 cm-3). Plasma excitation and ionization temperatures were determined from a Boltzmann plot. The double-pulse laser-induced plasma was studied at different interpulse delay times of 1, 2, 5, 10, 15, 25 and 50 μs. The results indicated that the interaction between the laser, plasma and target gives higher atomic and ionic intensities at shorter interpulse delay times. PACS 52.38.Mf; 79.20.Ds; 52.50.Jm 相似文献
75.
Siriwardana AI Kamada M Nakamura I Yamamoto Y 《The Journal of organic chemistry》2005,70(15):5932-5937
The inter- and intramolecular additions of cyclic amides (nitrogen pronucleophiles) to methylenecyclopropanes proceeded smoothly in the presence of catalytic amounts of Pd(PPh(3))(4), affording the corresponding hydroamination products in good to high yields with high regioselectivities. The ring opening of methylenecyclopropanes occurred at the distal position of the cyclopropane ring. 相似文献
76.
Cinchona alkaloids catalyze the enantioselective Mannich reaction of beta-keto esters with acyl aryl imines. The reaction requires 10 mol % of cinchonine or cinchonidine. The reaction products are obtained in good yields (81-99%), high enantioselectivities (80-96% ee), and in diastereoselectivities that range from 1:1 to >95:5. The cinchonine-catalyzed reaction provides access to highly functionalized building blocks used in the asymmetric synthesis of a dihydropyrimidone and beta-amino alcohol. 相似文献
77.
Ibrahim Moustafa Sh. Werida Amal H. Etaiw Safaa El-din H. 《Transition Metal Chemistry》2003,28(5):585-591
Various thiophene compounds have been shown to be encapsulated and partly oxidized within the channels of the three-dimensional (3D) host coordination polymers [(R3Sn)3Fe(CN)6]
n
(R = Me, n-Bu or Ph) to give guest–host encapsulated systems. The structure and physical properties of these systems were studied by X-ray powder diffraction, i.r., u.v.–vis., e.p.r. spectra and magnetic measurements. Thiophene compounds do not polymerize within the channels of the host, but rather give paramagnetic charge-transfer guest–host systems. 相似文献
78.
79.
The impact of constant effort harvesting on the dynamics of a discrete‐time contest competition model
下载免费PDF全文
![点击此处可从《Mathematical Methods in the Applied Sciences》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this paper, we study a general discrete‐time model representing the dynamics of a contest competition species with constant effort exploitation. In particular, we consider the difference equation x n +1=x n f (x n ?k )?h x n where h >0, k ∈{0,1}, and the density dependent function f satisfies certain conditions that are typical of a contest competition. The harvesting parameter h is considered as the main parameter, and its effect on the general dynamics of the model is investigated. In the absence of delay in the recruitment (k =0), we show the effect of h on the stability, the maximum sustainable yield, the persistence of solutions, and how the intraspecific competition change from contest to scramble competition. When the delay in recruitment is 1 (k =1), we show that a Neimark‐Sacker bifurcation occurs, and the obtained invariant curve is supercritical. Furthermore, we give a characterization of the persistent set. 相似文献
80.
Methylthiolation of structurally diverse aryl halides was accomplished under fluoride free conditions using catalytic amounts of CuI, and DMSO as the methylthiolation source. Optimization studies unveiled several varieties of promoters among which Zn(OAc)2 was found ideal. The analogous reaction with DMSO-d6 afforded corresponding deuterated aryl methyl thioether with 99% purity. Mechanistic studies revealed CuSMe as the active methylthiolation agent. 相似文献