全文获取类型
收费全文 | 24068篇 |
免费 | 4130篇 |
国内免费 | 3880篇 |
专业分类
化学 | 18763篇 |
晶体学 | 324篇 |
力学 | 1299篇 |
综合类 | 259篇 |
数学 | 3075篇 |
物理学 | 8358篇 |
出版年
2024年 | 28篇 |
2023年 | 375篇 |
2022年 | 575篇 |
2021年 | 738篇 |
2020年 | 860篇 |
2019年 | 1047篇 |
2018年 | 791篇 |
2017年 | 801篇 |
2016年 | 1117篇 |
2015年 | 1247篇 |
2014年 | 1482篇 |
2013年 | 1855篇 |
2012年 | 2230篇 |
2011年 | 2277篇 |
2010年 | 1639篇 |
2009年 | 1659篇 |
2008年 | 1808篇 |
2007年 | 1540篇 |
2006年 | 1398篇 |
2005年 | 1232篇 |
2004年 | 1062篇 |
2003年 | 817篇 |
2002年 | 937篇 |
2001年 | 734篇 |
2000年 | 588篇 |
1999年 | 507篇 |
1998年 | 413篇 |
1997年 | 350篇 |
1996年 | 306篇 |
1995年 | 251篇 |
1994年 | 227篇 |
1993年 | 209篇 |
1992年 | 152篇 |
1991年 | 143篇 |
1990年 | 132篇 |
1989年 | 106篇 |
1988年 | 104篇 |
1987年 | 55篇 |
1986年 | 57篇 |
1985年 | 61篇 |
1984年 | 34篇 |
1983年 | 25篇 |
1982年 | 28篇 |
1981年 | 14篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1936年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
931.
932.
Huang WL Cui SH Liang KM Gu SR Yuan ZF 《Journal of colloid and interface science》2002,246(1):129-134
Silica xerogels were prepared by thermal drying wet gels in an electric oven (70 degrees C) after certain duration of ambient drying, and the relevant effect is investigated on the mesopore structures and surface fractal dimensions of the resultant xerogels. The silica gels were derived from a hydrochloric acid-catalyzed TEOS (tetraethylorthaosilicate) system, and both magnetic stirring and ultrasonic vibration were adopted during sol preparation. The percentage mesoporosity and surface fractal dimensions are evaluated using image analysis methods, based on FE-SEM (field emission gun-scanning electron microscopy) images. The results show that the mesoporosity of the resultant xerogels decreases with the duration of ambient drying for samples prepared using magnetic stirring and low-intensity ultrasonic vibration, while samples subjected to high-intensity ultrasound show a somewhat reverse trend. Samples prepared with magnetic stirring have almost constant surface fractal dimensions (nearly 3), irrespective of the ambient drying before thermal drying. The surface fractal dimensions of samples prepared using ultrasound increase with the duration of ambient drying. 相似文献
933.
934.
Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure-directing agents (OSDAs), which are chronically hazardous to humans and the environment. It is a growing trend to develop an eco-friendly and nuisanceless OSDA for zeolite synthesis. Herein, choline is employed as a non-toxic and green OSDA to synthesize high silica Y zeolite with SiO2/Al2O3 ratios of 6.5–6.8. The prepared Y zeolite samples exhibited outstanding (hydro)thermal stability at ultrahigh temperature owing to the higher SiO2/Al2O3 ratio. The XRF, SEM, 29Si-NMR and 13Na+ results suggested that choline plays a structure-directing role in the synthesis of Y zeolite, while the feed molar fraction of Na+ is a crucial determinant for the framework SiO2/Al2O3 ratio and the crystal morphology. 相似文献
935.
936.
937.
The title complex, [La(btec)1/2(H2btec)1/2 (H2O)]n (H4btec= 1, 2,4,5‐benzenetetracarboxylic acid) (1) was synthesized by the hydrothermal reaction of 1,2,4,5‐benzenetetracarboxylic dianhydride with La(NO3)3·6H2O in H2O, and crystallizes in the triclinic system, space group P‐1 with a = 0.64403(3) nm, b = 0.94500(4) nm, c = 0.96380(5) nm, a = 88.535(2)°, β = 100.314(2)°, γ = 76.6470(10)°, V = 1.60968(10) nm3, Z = 2, and final R = 0.0274, Rw = 0.0735. In 1, each La(m) ion is coordinated by eight oxygen atoms from six carboxylate groups and one coordinated water molecule. Two different coordination modes of H4btec were present in the structure, one of which contains two protonated carboxylate groups to balance the charge. 相似文献
938.
A new ligand H2L, 1,7-di(1-phenyl-3-methyl-5-pyrazolone-4-benzylidene)diethenetriamine and its three transition metal complexes, ML · nH2O [M=Cu(II), n=2; M=Zn(II), n=0.5; M=Ni(II) (1), n=3] have been synthesized in anhydrous EtOH and characterized on the basis of elemental analyses, molar conductivities, i.r.
spectra, u.v. spectra and thermal analyses. In addition, the DNA-binding properties of the ligand and its complexes have been
investigated by absorption, fluorescence and viscosity measurements. The experimental results indicated that the ligand and
the complex (1) can bind to DNA , but the other two complexes can’t; the binding affinity of the complex (1) is higher than
that of the ligand and the intrinsic binding constant kb of the complex (1) is 7.893×105 m−1. 相似文献
939.
The synthesis, structural characterization, photoluminescence properties, and density functional theory analysis of three Pt(II) diimine complexes, Pt(dbbpy)(C triple bond CR)2 [dbbpy = 4,4'-di(tert-butyl-2,2'-bipyridine; R = -SiMe3, -CC-SiMe3, or -t-Bu], are presented. The Pt(dbbpy)(C triple bond C-tBu)2 complex serves as a carbon-based ligand structure for which the photophysical properties of the two silicon-bearing complexes are compared in dichloromethane. Pt(dbbpy)(C triple bond C-SiMe3)2 and Pt(dbbpy)(C triple bond C-C triple bond C-SiMe3)2 display visible absorptions with strong green emission (lambda(emmax) = 526 and 524 nm, respectively) while Pt(dbbpy)(C triple bond C-t-Bu)2 displays efficient, long-lived yellow emission (lambda(emmax) = 557 nm). Direct side by side comparisons of Pt(dbbpy)(C triple bond C-SiMe3)2 and Pt(dbbpy)(C triple bond C-t-Bu)2 suggest that the difference in excited state energy results from the relative sigma-donor strength of the acetylide ligands. 相似文献
940.
Fang X Li B Petersen E Ji Y Sokolov JC Rafailovich MH 《The journal of physical chemistry. B》2005,109(43):20554-20557
In this paper, we discuss the factors affecting drop evaporation. We found that the droplet morphology at a specific temperature was controlled by the physical properties of the liquid itself, such as the molecular weight, density, diffusion coefficient in air, and heat of vaporization. Two processes are included in drop evaporation: diffusion of liquid molecules into the air (diffusion part) and flow of the liquid molecules from inside the drop to the free outer shell liquid layer within the liquid-vapor interface (evaporation part). The diffusion part remained steady during drying and was not sensitive to the variation of temperature. The evaporation part, however, was an active factor and determined the differences in drop evaporation behaviors. 相似文献