全文获取类型
收费全文 | 1637篇 |
免费 | 33篇 |
国内免费 | 5篇 |
专业分类
化学 | 981篇 |
晶体学 | 64篇 |
力学 | 32篇 |
数学 | 100篇 |
物理学 | 498篇 |
出版年
2022年 | 24篇 |
2021年 | 28篇 |
2020年 | 26篇 |
2019年 | 27篇 |
2018年 | 21篇 |
2017年 | 29篇 |
2016年 | 40篇 |
2015年 | 33篇 |
2014年 | 57篇 |
2013年 | 123篇 |
2012年 | 84篇 |
2011年 | 102篇 |
2010年 | 47篇 |
2009年 | 49篇 |
2008年 | 63篇 |
2007年 | 63篇 |
2006年 | 72篇 |
2005年 | 48篇 |
2004年 | 53篇 |
2003年 | 32篇 |
2002年 | 45篇 |
2001年 | 28篇 |
2000年 | 22篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 18篇 |
1992年 | 28篇 |
1991年 | 17篇 |
1990年 | 20篇 |
1989年 | 19篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 19篇 |
1985年 | 25篇 |
1984年 | 22篇 |
1983年 | 25篇 |
1982年 | 18篇 |
1981年 | 19篇 |
1980年 | 29篇 |
1979年 | 25篇 |
1978年 | 20篇 |
1977年 | 19篇 |
1976年 | 11篇 |
1975年 | 17篇 |
1973年 | 12篇 |
1971年 | 9篇 |
排序方式: 共有1675条查询结果,搜索用时 390 毫秒
61.
An aqueous aza-Michael reaction is efficiently achieved with excellent conversions without any additives. The method works very well on a molar scale with selectively for aliphatic amines. An intermediate for spermine is also made by this green process. 相似文献
62.
R. M. Joshi 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(8):1309-1383
Abstract The new generalized bond energy scheme has been extended to organic oxygen compounds. About 50 different types of bonds have been identified and their ΔHf°(g) contributions and atomization energies evaluated by a procedure similar to multilinear regression analysis. Recent thermochemical data (1969-1973) on 145 oxygen compounds and about 80 ring compounds have been employed to test the efficiency of the scheme in predicting the gas phase heats of formation. This was found to be about ±0. 8 kcal/mole, which is quite comparable to the group contribution method of Benson and co-workers involving a much larger number of parameters. The typical chemical bonds identified and resolved in respect of their bond energies bear good consistency and correlation with bond lengths and force constants measurable independently. Heats of formation and polymerization on about 47 monomer-polymer systems and enthalpies of other polymeric reactions have been predicted and compared with available experimental data. 相似文献
63.
Conductivity as a Sensor for Monitoring Relative Magnesium Corrosion Rates in Real‐time,in Serum‐containing Media under Cell Culture Conditions 下载免费PDF全文
Kolade Ojo Tracy Hopkins Madhura Joshi Pravahan Salunke Guangqi Zhang Keaton Nahan Zhannping Zhang Daoli Zhao Sarah K. Pixley Vesselin Shanov William R. Heineman 《Electroanalysis》2016,28(12):3000-3008
Because controlling the corrosion rate of magnesium metal will be crucial to the success of biomedical implants containing pure magnesium or magnesium alloys, many ways have been sought to improve in vitro tests to analyze corrosion rates, and also to identify new methods of preparing or post‐processing magnesium. In this work, for an in vitro assay, we explored the use of a commercially available conductivity sensor to study magnesium corrosion under cell culture conditions that duplicate many physiologically appropriate parameters. With this sensor, we studied the corrosion of two previously untested magnesium single crystal samples that differed in surface treatments that could alter corrosion rates. The results show that the relative conductivity changes in (mS/cm) over the total time of immersion were proportional to the corrosion rates in (mm/y) and also to the total magnesium released, as detected by inductively coupled plasma mass spectrometry (ICP‐MS). 相似文献
64.
65.
A new persistent, green emission is reported for europium activated Calcium Zinc Chlorosilicate (CZCS). The phosphor was prepared by the solid state reaction and characterized using XRD, PL and TL techniques. The decay was characterized by admixture of two exponential components with decay constants 20.2 and 101 s. 相似文献
66.
Polymerization of vinyl acetate continues to interest workers in the field as evidenced by recent publications [1–3]. However, little information is available concerning the synthesis of low molecular weight poly(vinyl acetate) (PVAc) despite its industrial importance. 相似文献
67.
Bis-dithianylalkanols and dimers are formed in preparation of 2-lithio-1,3-dithianes due to the presence of oxidising impurity in n-BuLi (perhaps n-BuOOLi). 相似文献
68.
Ghanshyam V. Joshi Bhavesh D. Kevadiya Haresh M. Mody Hari C. Bajaj 《Journal of polymer science. Part A, Polymer chemistry》2012,50(3):423-430
To accomplish the controlled‐release systems based on layered clay minerals, one of the best ways is to intercalate organic molecules into the interlayer gallery of clay minerals. Into a series of chitosan (CS) intercalated montmorillonite (MMT) nanocomposites, prepared via ion‐exchange route, antimalarial drug [quinine (QUI)] was loaded to act as effective drug delivery systems. Among the CS–MMT nanocomposites, higher drug adsorption with decreasing CS concentration was observed. CS–MMT and CS–MMT/QUI intercalated compounds were characterized by powder X‐ray diffraction, Fourier transform infrared spectroscopy, and thermal analysis. The synthesized nanocomposites, filled in the gelatin capsules followed by coating of Eudragit® L 100, were tested for in vitro drug release performance in the sequential buffer environments at 37 ± 0.5 °C. As no drug release (0%) was observed in the gastric fluid, the coating of Eudragit® L 100 to the capsules is highly adequate. However, the drug release rate was comparatively faster from the CS intercalated clay with compare with pure clay. The drug release kinetic data revealed that the release of QUI from the nanocomposites can be explained by modified Freundlich model. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
69.
Balakrishna Kolli Sarada P. Mishra M. P. Joshi S. Raj Mohan T. S. Dhami A. B. Samui 《Journal of polymer science. Part A, Polymer chemistry》2012,50(8):1572-1578
Four linear polymers containing pendant azo moiety were synthesized through click chemistry for second‐order nonlinear optical study. The polymers were found soluble in most of the polar organic solvents such as tetrahydrofuran (THF), chloroform, and dimethyl formamide (DMF). The polymers showed thermal stability up to 300 °C and glass transition temperatures (Tg) in the range of 120–140 °C. The molecular weights (Mw) of these polymers (measured by gel permeation chromatography) were in the range 37,900–55,000 g/mol. The polymers were found to form optically transparent films by solution casting from THF solution. Order parameters were calculated from UV–vis absorption spectra. The morphology changes in the films after poling were characterized by atomic force microscopy. The angular dependence, temperature dependence, and time dependence of second harmonic generation (SHG) intensity were obtained by using 1064 nm Nd:YAG laser. The SHG intensity remained unchanged up to 95 °C. At room temperature, it remained stable up to 8 days after initial drop of about 14%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
70.
Copper(II) complexes of the type [Cu(SPF)(Ln)Cl] (where SPF is sparfloxacin and Ln = substituted terpyridines) were synthesized and found to have a distorted octahedral geometry. Superoxide dismutase‐like activity of the complexes was measured using a nitroblue tetrazolium/reduced nicotinamide adenine dinucleotide/phenazine methosulfate system and expressed in terms of the concentration of complex which terminates the formation of formazan by 50% (IC50 value), which was found to range from 0.572 to 1.522 µm . Interactions of the complexes with herring sperm DNA were studied by absorption titration, viscosity measurement and gel electrophoresis under physiological conditions. The antimicrobial efficiency of the complexes was tested against five different microorganisms and showed good biological activity. All the complexes showed good cytotoxic activity, with LC50 values ranging from 4.01 to 9.64 µg ml?1. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献