全文获取类型
收费全文 | 3365篇 |
免费 | 483篇 |
国内免费 | 203篇 |
专业分类
化学 | 2082篇 |
晶体学 | 110篇 |
力学 | 110篇 |
综合类 | 17篇 |
数学 | 28篇 |
物理学 | 1704篇 |
出版年
2024年 | 7篇 |
2023年 | 10篇 |
2022年 | 37篇 |
2021年 | 49篇 |
2020年 | 49篇 |
2019年 | 46篇 |
2018年 | 65篇 |
2017年 | 98篇 |
2016年 | 108篇 |
2015年 | 84篇 |
2014年 | 135篇 |
2013年 | 296篇 |
2012年 | 181篇 |
2011年 | 257篇 |
2010年 | 144篇 |
2009年 | 172篇 |
2008年 | 180篇 |
2007年 | 189篇 |
2006年 | 183篇 |
2005年 | 174篇 |
2004年 | 165篇 |
2003年 | 160篇 |
2002年 | 146篇 |
2001年 | 98篇 |
2000年 | 119篇 |
1999年 | 83篇 |
1998年 | 87篇 |
1997年 | 86篇 |
1996年 | 82篇 |
1995年 | 44篇 |
1994年 | 63篇 |
1993年 | 58篇 |
1992年 | 43篇 |
1991年 | 22篇 |
1990年 | 29篇 |
1989年 | 15篇 |
1988年 | 18篇 |
1987年 | 24篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 27篇 |
1981年 | 34篇 |
1980年 | 31篇 |
1979年 | 57篇 |
1978年 | 31篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有4051条查询结果,搜索用时 15 毫秒
101.
Nogami Masayuki Nagakura Takehito Hayakawa Tomokatsu Kasuga Toshihiro 《Journal of Sol-Gel Science and Technology》2000,19(1-3):253-256
Persistent spectral hole burning was studied in Eu3+ ions-doped Al2O3-SiO2 glass prepared by a sol-gel method. The gel synthesized by the hydrolysis of Si- and Al-alkoxides and EuCl3·6H2O was heated in air and hydrogen gas atmospheres. For the glass heated in air to contain OH bonds, the hole was formed by the photoinduced rearrangement of the OH bonds surrounding the Eu3+ ions, and was thermally refilled and erased above 200 K. On the other hand, the glass heated in hydrogen gas showed the hole spectrum above 200 K. It was found that the hole depth was independent of the temperature and was 7% of the total intensity at room temperature. The proposed mechanism was the electron transfer between the Eu3+ ions and the defect centers formed in glass matrix. 相似文献
102.
S. Fakirov Z. Sarac T. Anbar B. Boz I. Bahar M. Evstatiev A. A. Apostolov J. E. Mark A. Kloczkowski 《Colloid and polymer science》1997,275(4):307-314
This second part of a systematic study of the properties of crosslinked-oriented gelatin involves the effects of orientation
and water content on the glass transition temperature T
g and on the melting behavior. The samples were the same as those in the preceding study, and their transition temperatures
were determined by both differential scanning calorimetry and dynamic mechanical thermal analysis. The crosslinked gelatin
which had been room-conditioned showed two transition temperatures: the lower one was attributed to T
g of the water-plasticized gelatin, and the higher one was interpreted as T
g of dried gelatin superimposed by melting. A rather unusual situation arose because of the fact that the T
g and melting temperatures T
m (217 and 230 °C, respectively) are so similar. Using water as plasticizer not only decreases T
g but produces imperfect crystallites which melt below the T
g of the system. The presence of the amorphous phase in the glassy state would presumably make it essentially impossible to
define a melting point or crystallization temperature in the normal manner, as an equilibrium between crystalline and amorphous
phases.
Received: 8 October 1996 Accepted: 2 November 1995 相似文献
103.
Monochrome coloured glass beads of the Merovingians (5th–7th cent. AD) have been examined by different analytical methods. The elemental composition of a large number of mostly unprepared
beads have been measured non-destructively by X-ray fluorescence analysis. After subtracting the content of the colouring
oxides of the glass beads and normalising the residual values to 100% an identical soda-lime-glass matrix was obtained. X-ray
diffraction was used for the identification of the crystalline colouring and opacifying pigments (SnO2, Cu, Cu2O, PbSnO3), and scanning electron microscopy as well as electron probe microanalysis were applied to study the microstructure and the
composition of white, brown, green, orange and yellow coloured glass beads. Oxidised metals, alloys (lead, copper, bronze,
brass and mixtures of them) and iron smelting slag have been identified as raw materials to colour the soda-lime-glass. 相似文献
104.
玻璃载体表面脱氧核糖核酸的固定及其化学发光检测 总被引:2,自引:0,他引:2
用硅烷化偶联剂把DNA直接共价固定在载玻片表面,将辣根过氧化物酶标记的探针与之进行核酸杂交,杂交后用增强的化学发光检测。方法的检出限为75pg。研究了DNA分子固定在玻璃载体表面的各种条件,并建立了在玻璃载体表面进行核酸杂交的体系,为研究光纤DNA生物传感器打下了基础。 相似文献
105.
A method is described for the gas-chromatographic determination of the diastereomers of vitamin K1 (phylloquinone) in the form of their dihydro dimethyl ethers. The reported method of derivatization and chromatographic analysis in conjunction with optical rotation measurements are useful approaches for characterization of vitamin K1 samples with respect to their origin. 相似文献
106.
Two published procedures for glass capillary column production are applied to produce capillaries for chromatography of polar natural compounds. Soda lime glass capillaries, after leaching with aqueous HCL, are either treated with colloidal silicic acid or with barium carbonate and coated with either Silar 7CP or SE 52. A test mixture as well as polar carbohydrate and peptide mixtures are chromatographed on the different columns and their chromatographic properties are evaluated. Combined capillary gas chromatography-electron impact and chemical ionization mass spectrometry are used for identification of the peptide sequence. 相似文献
107.
108.
Ahmed Abd El-Fattah Mohamad Nageeb Hassan Ahmad Rashad Mona Marei Sherif Kandil 《International Journal of Polymer Analysis and Characterization》2020,25(5):362-373
Abstract An injectable composite hydrogel composed of polyvinyl alcohol (PVA) and bioactive glass (BG) particles were synthesized by a physical crosslinking approach. The morphology, mechanical properties, and viscoelasticity of the PVA/BG composite hydrogel were characterized. Scanning electronic microscopy (SEM) showed uniform and homogeneous distribution of BG particles throughout the composite hydrogel. The incorporation of 2.5?wt% of BG particles in the composite hydrogel formulations, enhanced the static compressive strength and static elastic modulus by 325% and 150%, respectively. The storage molds (G′) was greater than the loss modules (G′′) at all the frequency range studied, which revealed a self-standing elastic composite hydrogel with a smooth injectability. The PVA/BG composite hydrogel was also implanted subcutaneously in the dorsal region of adult male rats. After 4?weeks of implantation, no inflammatory cells were seen within and around the implant, which indicated that the composite hydrogel was biocompatible. The properties of the synthesized injectable PVA/BG composite hydrogel demonstrate its capability toward bone regeneration. 相似文献
109.
A.A. Ahmed I.M. Youssof A.F. Abbas O. Abou Eleinen 《Journal of Sol-Gel Science and Technology》1998,13(1-3):753-756
The chemical durability of lead glass tumblers (24% PbO) in a 4% (v/v) acetic acid solution before and after coating with sol-gel derived SiO2 films was assessed to determine the extent of reduction in Pb-leaching that can be achieved. It was found that by coating the internal surface of the glass tumblers with 1 ml of 10% TEOS solutions at 100°C and densifying the coating formed at 500°C for 1 h, it was possible to reduce Pb-leaching to about one quarter of that of the uncoated glass. 相似文献
110.
Two types of commercial glass fibers were subjected to attack in strongly basic KOH solutions. The resulting leach solutions were analysed for Na, Ca, and Si. This showed that the corrosion process attacks the fibers incongruently. Although there are some distinct differences in the performance of these fibers, to a first approximation both types behave similarly. Further, the fibers were depth profiled using a recently developed SNMS technique for fiber in-depth analysis. This showed that both types of fibers behave in a quite dissimilar manner. The fibers were weathered already without any treatment. Although both fibers show alkali ion exchange and network splitting processes, on one of the fiber layers enriched in SiO2, Fe2O3, and CaO are formed by a redeposition process from the leach solution.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献