全文获取类型
收费全文 | 2707篇 |
免费 | 333篇 |
国内免费 | 585篇 |
专业分类
化学 | 2194篇 |
晶体学 | 28篇 |
力学 | 62篇 |
综合类 | 16篇 |
数学 | 2篇 |
物理学 | 275篇 |
综合类 | 1048篇 |
出版年
2024年 | 3篇 |
2023年 | 24篇 |
2022年 | 55篇 |
2021年 | 67篇 |
2020年 | 83篇 |
2019年 | 81篇 |
2018年 | 53篇 |
2017年 | 79篇 |
2016年 | 130篇 |
2015年 | 129篇 |
2014年 | 152篇 |
2013年 | 272篇 |
2012年 | 220篇 |
2011年 | 180篇 |
2010年 | 154篇 |
2009年 | 129篇 |
2008年 | 154篇 |
2007年 | 166篇 |
2006年 | 187篇 |
2005年 | 173篇 |
2004年 | 159篇 |
2003年 | 171篇 |
2002年 | 110篇 |
2001年 | 90篇 |
2000年 | 80篇 |
1999年 | 74篇 |
1998年 | 49篇 |
1997年 | 62篇 |
1996年 | 52篇 |
1995年 | 60篇 |
1994年 | 47篇 |
1993年 | 30篇 |
1992年 | 29篇 |
1991年 | 24篇 |
1990年 | 27篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1955年 | 3篇 |
排序方式: 共有3625条查询结果,搜索用时 140 毫秒
71.
单分散二氧化钛超微粒子的制备 总被引:10,自引:0,他引:10
以四丁氧基钛为原料,采用溶胶-凝胶法制备了超微二氧化钛粉末.改变热处理气氛、升温速率、水与四丁氧基钛的摩尔比以及溶剂,分别得到7nm球形单相锐钛矿以及四方形(40nm×10nm)、球形(44nm)的主相金红石超微粒子. 相似文献
72.
Photocatalytic reactions occurring at semiconductor particles/solution interfaces can be applied to organic syntheses. In this review article, examples of photocatalytic syntheses of cyclic amino acids by suspended semiconductor particles, e.g., titanium(IV) oxide or cadmium(II) sulfide are introduced and interpreted. Different from the photocatalytic decomposition of pollutants under aerobic conditions, selective conversion of organic compounds can be driven by the photocatalytic reactions under deaerated conditions. 相似文献
73.
Aqueous Titanate Sols from Ti Alkoxide-α-Hydroxycarboxylic Acid System and Preparation of Titania Films from the Sols 总被引:1,自引:0,他引:1
Ohya Tomokazu Ito Masamichi Yamada Keiko Ban Takayuki Ohya Yutaka Takahashi Yasutaka 《Journal of Sol-Gel Science and Technology》2004,30(2):71-81
Aqueous titanate sols were prepared by reactions of titanium tetraisopropoxide (TIP) with -hydroxycarboxylic acids in water. IR and Raman spectra, and elemental analyses of the precipitates obtained from the sols revealed that the carboxylates were chelated to titanium but the Ti species were polymerized to form a cluster that had a colloidal nature. Spin-coating of titania (TiO2) thin films from these sols was also examined. Interestingly, it was found that (004) preferentially oriented anatase films with refractive index of 2.54 were obtained from TIP-lactic acid-NH3 (1:1:1, molar ratio) aqueous sol. This crystallographic orientation was characteristic of the TIP-lactic acid-NH3 (1:1:1) system, and was not affected by the kinds of substrates used and the heating rate of the film. TEM observation indicated that small anatase grains had already formed at 200°C. Therefore, the crystallographic orientation might depend strongly on the structure of the chemical species of the precursor solutions. 相似文献
74.
G. S. Zakharova L. Yu. Buldakova V. L. Volkov L. S. Molochnikov E. G. Kovaleva 《Russian Journal of Electrochemistry》2006,42(1):53-58
Complex vanadium and titanium oxides modified by copper ions are studied by the electrochemical and ESR methods. Oxides Cu x V2?y Ti y O5?δ·nH2O (0<y<1.33) have a layered structure and oxides Cu x Ti1?y V y O5+δ·nH2O (0<y<0.25), an anatase structure. The intercalation of cations Cu2+ into the hydrates leads to oxidation of V4+. According to ESR data, V4+ exists in the oxides in the form of VO2+ and an octahedral surround of oxygen (V4+?O6), respectively. The electroreduction of ions of d-elements and chemisorbed oxygen in the oxides is analyzed. The intercalation of cations Cu2+ alters the content of V4+ and the chemisorption ability of the oxides. Possible reasons for this phenomenon are discussed. 相似文献
75.
76.
The
aim of our research was to prepare yellow pigments based on structure of pseudobrookite
Fe2TiO5. Part of Fe was substituted
with Li and Ti from Fe2TiO5
to Li0.05Fe0.07Ti2.44O5.
Synthesis and pigmentary-application properties in the Li2O–Fe2O3–TiO2 system were studied for 800 and 900°C using classical ceramic
method of preparation. The main attention was aimed to usage of four different
sources of titanium compounds as raw materials. We studied the influence of
different sources of titanium compounds on the structural and the colour properties
of the prepared pigments. The thermal analysis was used for characterization
of titanium compounds and determination of their thermal stability. 相似文献
77.
Abarca A Galakhov MV Gracia J Martín A Mena M Poblet JM Sarasa JP Yélamos C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(10):2337-2346
Treatment of [[Ti(eta(5)-C(5)Me(5))(micro-NH)](3)(micro(3)-N)] (1) with the imido complexes [Ti(NAr)Cl(2)(py)(3)] (Ar=2,4,6-C(6)H(2)Me(3)) and [Ti(NtBu)Cl(2)(py)(3)] in toluene affords the single azatitanocubanes [[Cl(2)(ArN)Ti]( micro(3)-NH)(3)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]].(C(7)H(8)) (2.C(7)H(8)) and [[Cl(2)Ti](micro(3)-N)(2)(micro(3)-NH)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]] (3), respectively. Similar reactions of complex 1 with the niobium and tantalum imido derivatives [[M(NtBu)(NHtBu)Cl(2)(NH(2)tBu)](2)] (M=Nb, Ta) in toluene give the single azaheterometallocubanes [[Cl(2)(tBuN)M](micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]] (M=Nb (4), Ta (5)), both complexes react with 2,4,6-trimethylaniline to yield the analogous species [[Cl(2)(ArN)M](micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]].(C(7)H(8)) (Ar=2,4,6-C(6)H(2)Me(3), M=Nb (6.C(7)H(8)), Ta (7.C(7)H(8))). Also the azaheterodicubanes [M[micro(3)-N)(2)(micro(3)-NH)](2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)](2)].2C(7)H(8) [M=Ti (8.2C(7)H(8)), Zr (9.2C(7)H(8))], and [M[(micro(3)-N)(5)(micro(3)-NH)][Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)](2)].2 C(7)H(8) (Nb (10.2C(7)H(8)), Ta (11.2C(7)H(8))) were prepared from 1 and the homoleptic dimethylamido complex [M(NMe(2))(x)] (x=4, M=Ti, Zr; x=5, M=Nb, Ta) in toluene at 150 degrees C. X-ray crystal structure determinations were performed for 6 and 10, which revealed a cube- and double-cube-type core, respectively. For complexes 2 and 4-7 we observed and studied by DNMR a rotation or trigonal-twist of the organometallic ligands [[Ti(eta(5)-C(5)Me(5))(micro-NH)](3)(micro(3)-N)] (1) and [(micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]](1-). Density functional theory calculations were carried out on model complexes of 2, 3, and 8 to establish and understand their structures. 相似文献
78.
A new glass electrolyte formed by constant amounts of titanium oxide (TiO2) and various amount of phosphotungstic acid (PWA) doped P2O5-SiO2 is prepared using the sol-gel process. The structural formation is confirmed by Fourier infrared spectroscopy (FTIR) and from thermogravimetric and differential thermal analysis (TG/DTA) measurements, the glasses display good thermal stability. Further characterisation is undertaken by N2 adsorption/desorption measurements, proton conductivity and hydrogen permeability analyses and a H2/O2 fuel cell test is also performed. The glass materials with large pores and specific surface area are suitable for use as the electrolyte in H2/O2 fuel cells. The effect of TiO2 processing with constant amount of PWA in phosphosilicate glasses, is investigated and discussed. The hydrogen permeability is 1.57x10(-11) mol cm(-1) s(-1) Pa(-1) at 110 degrees C for 0.8 mm thick glass; a power density of 46.3 mW cm(-2) at 125 mA cm(-2) and a current density of 175 mA cm(-2) is obtained (T=28 degrees C, relative humidity). 相似文献
79.
Summary Mesoporous TiO2-CeO2mixed oxides (m-TiO2-CeO2) were synthesized under easy-operating neutral conditions. The structure was characterized by means of FT-IR, XRD, and N2adsorption methods. For methanol decomposition to CO and H2, the catalytic activity of the Ru/ m-TiO2-CeO2 catalyst was higher than that of the Ru/ m-TiO2.</o:p> 相似文献
80.
通过原子力显微镜研究了二氧化钛纤维表面担载Pt的表面形貌及其结构.结果表明,TiO2纤维表面担载的Pt具有微米尺度的近似六边形或者近似长方形的结构,与在单晶TiO2(110)表面的Pt纳米簇形貌相似,但尺度较大.TiO2纤维担载的Pt表面明显存在不同高度的台阶结构,台阶高度以2~4倍Pt(111)晶面面间距的高度为主.由Pt在TiO2纤维表面的形貌与纤维的纳米晶粒排布有序性推测可知,Pt与TiO2纤维存在强的相互作用,可能正是这种强相互作用和表面台阶结构才使TiO2表面担载的Pt虽是微米尺寸但仍具有高光催化活性. 相似文献