全文获取类型
收费全文 | 1029篇 |
免费 | 123篇 |
国内免费 | 17篇 |
专业分类
化学 | 316篇 |
晶体学 | 110篇 |
力学 | 13篇 |
综合类 | 1篇 |
数学 | 8篇 |
物理学 | 721篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 15篇 |
2019年 | 10篇 |
2018年 | 19篇 |
2017年 | 32篇 |
2016年 | 40篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 115篇 |
2012年 | 40篇 |
2011年 | 123篇 |
2010年 | 55篇 |
2009年 | 71篇 |
2008年 | 58篇 |
2007年 | 70篇 |
2006年 | 57篇 |
2005年 | 47篇 |
2004年 | 41篇 |
2003年 | 32篇 |
2002年 | 37篇 |
2001年 | 27篇 |
2000年 | 32篇 |
1999年 | 38篇 |
1998年 | 27篇 |
1997年 | 15篇 |
1996年 | 10篇 |
1995年 | 16篇 |
1994年 | 18篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1169条查询结果,搜索用时 468 毫秒
21.
B. Ritzer M.A. Villegas J.M. Fernández Navarro 《Journal of Sol-Gel Science and Technology》1997,8(1-3):917-921
The darkening of silica sol-gel glasses doped with 0.05 mol% silver was studied. Six sols were prepared from TEOS and silver
nitrate. Different additives were used, to influence the chemical and physical states of silver: oxidizing or reducing agents
(H2O2, As2O5), colloid stabilizer (sodium citrate) and network modifiers (Li2O, CaO). Sols were gelified at 60°C and densified at 600°C. The samples without additives and those prepared with H2O2 at room temperature even if they were protected from light. With increased temperature, the darkening became samples were
heated above, 400°C, reversible bleaching took place. This darkening-bleaching is of thermal nature (“thermochromic effect”)
and seems to be determined by a reversible aggregation-disaggregation of tiny silver particles. The presence of sodium citrate,
as an additive delayed the darkening effect and the presence of CaO delayed it even further. Lithium oxide inhibited it totally. 相似文献
22.
Highly ordered mesoporous bioactive glasses with superior in vitro bone-forming bioactivities 总被引:3,自引:0,他引:3
23.
一种新型铒镱共掺碲硅酸盐玻璃的光谱性质及荧光俘获效应研究 总被引:5,自引:1,他引:5
用高温熔制法制备了系列Er^3+/Yb^3+共掺碲硅酸盐玻璃样品,测试和分析了玻璃样品的吸收光谱、荧光光谱、上转换发光光谱及热稳定性。结果表明:这种玻璃具有较宽的荧光半高宽、较大的受激发射截面,较好的热稳定性。970nm泵浦下该系列玻璃在可见光525,546和658nm这3处存在明显的上转换现象,它们分别由Er^3+离子^2H11/2→^4 I15/2,4S3/2→^4 I15/2和^4 F9/2→^4 I15/2辐射跃迁产生。另外,测试和讨论了在不同样品厚度下玻璃的光谱特性,如荧光光谱、荧光寿命和上转换发光光谱等。结果表明,荧光俘获效应对Er^3+离子1.5μm波段荧光及上转换发光都有着较大的影响,并随着玻璃厚度的增加而增大,导致测量值与实际值产生较大的偏差。 相似文献
24.
Summary The paper deals with the use of controlled-porosity glasses (CPGs) as adsorbents for HPLC. The physicochemical and chromatographic properties of small-pore CPGs are compared to the analogous properties of silica gels. The results show good correlation between them and suggest the possibility of application of CPGs as adsorbents for liquid chromatography. 相似文献
25.
Applications of chalcogenide glass optical fibers 总被引:2,自引:0,他引:2
Chalcogenide-glass fibers based on sulfide, selenide, telluride and their rare-earth-doped compositions are being actively pursued worldwide. Great strides have been made in reducing optical losses using improved chemical purification techniques, but further improvements are needed in both purification and fiberization technology to attain the theoretical optical losses. Despite this, chalcogenide-glass fibers are enabling numerous applications that include laser power delivery, chemical sensing, and imaging, scanning near field microscopy/spectroscopy, IR sources/lasers, amplifiers and optical switches. 相似文献
26.
27.
Artem Malakho Marc Dussauze Bogdan Lazoryak Frederic Adamietz 《Journal of solid state chemistry》2005,178(6):1888-1897
Crystallization of glasses with compositions (1−x)(0.95 NaPO3+0.05 Na2B4O7)+xNb2O5, x=0.4, 0.43, 0.45, 0.48 was investigated by differential scanning calorimetry and X-ray powder diffraction. Crystallization of two phases was observed in the glasses with x=0.43-0.48. First phase is a sodium niobate with the structure of tetragonal tungsten bronze () and second phase is Na4Nb8P4O32 (). The crystallization of sodium niobate is correlated with increasing of nonlinear optical efficiency reported for thermally poled glasses with x>0.4. The results of Raman spectroscopy show the formation of three-dimensional (3D) niobium oxide framework in the glasses with increase of niobium concentration. This framework is supposed to have tetragonal tungsten bronze structure and to be responsible for nonlinear optical properties of the glass. Second harmonic generation signals of as prepared and crystallized glass after thermal poling are compared. The nucleation and crystallization do not improve the NLO properties of the glasses under study. 相似文献
28.
E. Yu. Mikhteeva E. G. Savchuk E. A. Tararako E. B. Merkulov V. K. Goncharuk 《Journal of Structural Chemistry》2005,46(6):1082-1085
Images of cleaved surfaces were obtained for 53ZrF4-20BaF2-4LaF3-3AlF3-20NaF (ZBLAN) glasses and fused quartz using an NTMDT atomic force microscope. It is shown that the scatter of particle size depends on the cooling rate and is 21–48.5 Å for the cleaved surface of ZBLAN glass obtained by very fast cooling and 68–172 Å for the cleaved surface of ZBLAN after slow cooling. For cleaved fused quartz, the range is 25-18 Å. 相似文献
29.
R. Parthasarathy Ravi V. Prasad P. R. Sarode K. J. Rao 《Journal of Chemical Sciences》1982,91(3):201-205
The exafs of Co2+ has been studied in rare earth cobaltites and in sulphate and borate glasses. It has been found that the environment of Co2+ ions is very similar in these cases. It appears feasible to study local structures in glasses using probe ion exafs.
Communication No. 151 from the Solid State and Structural Chemistry Unit. 相似文献
30.
(100-x) mole% SiO2-x mole% P2O5-glasses withx=1–9 have been prepared by the sol-gel process using tetraethylorthosilicate and triethylphosphate as precursors. The gels
were fired at various temperatures up to 950°C and then exposed to γ-ray irradiation to induce paramagnetic centers. CW-EPR
and FT-EPR Spectroscopies were employed at temperatures between 4 and 300 K in order to determine the resulting structures.
The dried gels exhibited four types of O
2
−
-ions trapped in pores of different sizes. The gels fired atT=670°C exhibited theE’
1-center and non-bridging oxygen as a results of the fracture of the Si-O-Si bonds. At higher temperatures, the spectra of
the POHC, POHC
b
,E’, and CH
3
−
-centers have been detected that are a function ofx andT. 相似文献