全文获取类型
收费全文 | 14487篇 |
免费 | 2648篇 |
国内免费 | 2523篇 |
专业分类
化学 | 11686篇 |
晶体学 | 195篇 |
力学 | 646篇 |
综合类 | 258篇 |
数学 | 1573篇 |
物理学 | 5300篇 |
出版年
2024年 | 30篇 |
2023年 | 260篇 |
2022年 | 362篇 |
2021年 | 441篇 |
2020年 | 593篇 |
2019年 | 626篇 |
2018年 | 514篇 |
2017年 | 493篇 |
2016年 | 759篇 |
2015年 | 796篇 |
2014年 | 859篇 |
2013年 | 1142篇 |
2012年 | 1286篇 |
2011年 | 1391篇 |
2010年 | 993篇 |
2009年 | 1011篇 |
2008年 | 1076篇 |
2007年 | 948篇 |
2006年 | 934篇 |
2005年 | 840篇 |
2004年 | 665篇 |
2003年 | 581篇 |
2002年 | 617篇 |
2001年 | 456篇 |
2000年 | 418篇 |
1999年 | 316篇 |
1998年 | 198篇 |
1997年 | 179篇 |
1996年 | 173篇 |
1995年 | 135篇 |
1994年 | 116篇 |
1993年 | 98篇 |
1992年 | 70篇 |
1991年 | 50篇 |
1990年 | 43篇 |
1989年 | 36篇 |
1988年 | 24篇 |
1987年 | 27篇 |
1986年 | 24篇 |
1985年 | 19篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1957年 | 5篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
991.
Guoqing?MiaoEmail author Kai?Huang Yi?Yun Rongjue?Wei 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,40(3):301-304
We present a granular-hydrodynamic model that captures the essence of convection in a fully vibrofluidized granular system. The steady temperature distribution is solved analytically. Numerical simulation shows that the convection always develops through a supercritical bifurcation, with its energy about
of the random (heat) one. A comparison calculation is performed for a normal fluid. The convection roll, or an active roll as we call it, has an angular velocity gradient from its interior to exterior. We conclude that active rolls are universal.Received: 25 March 2004, Published online: 9 September 2004PACS:
45.70.Mg Granular flow: mixing, segregation and stratification - 47.20.Bp Buoyancy-driven instability - 47.27.Te Convection and heat transfer 相似文献
992.
In this communication, we first report the direct synthesis of high-quality carbon nitride nanotubes (CNNTs) with inner diameters of 50-100 nm and wall thicknesses of 20-50 nm with the C(3)N(4) stoichiometry on a high-yield of 40%via a simple benzene-thermal process involving the reaction of C(3)N(3)Cl(3) with NaN(3) in a Teflon-lined autoclave at 220 [degree]C without using any catalyst or template. 相似文献
993.
Aptamer-functionalized Au nanoparticles for the amplified optical detection of thrombin 总被引:7,自引:0,他引:7
Pavlov V Xiao Y Shlyahovsky B Willner I 《Journal of the American Chemical Society》2004,126(38):11768-11769
The catalytic enlargement of aptamer-functionalized Au nanoparticles amplifies the optical detection of aptamer-thrombin complexes in solution and on surfaces. 相似文献
994.
Zinc oxide quantum rods 总被引:5,自引:0,他引:5
Yin M Gu Y Kuskovsky IL Andelman T Zhu Y Neumark GF O'Brien S 《Journal of the American Chemical Society》2004,126(20):6206-6207
Nanoscale zinc oxide (ZnO) rods of diameters close to the Bohr-exciton radius ( approximately 2 nm) can be prepared from a simple acetate precursor, resulting in ligand-capped rods of ZnO, highly dispersible in nonpolar solvents. Zinc oxide, ZnO, is a wide band-gap semiconductor with applications in blue/ultraviolet (UV) optoelectronic devices and piezoelectric devices. We observe self-assembly into uniform stacks of nanorods aligned parallel to each other with respect to the long axis, and photoluminescence measurements provide evidence for one-dimensional quantum confinement. 相似文献
995.
This review describes impulse response techniques with a curve-fitting method to measure thermodynamic properties, such as binary diffusion coefficient, retention factor, and partial molar volume, under supercritical conditions. Theoretical background, parameter sensitivity, sources of experimental error, noise elimination technique, and the correction of apparent binary diffusion coefficients due to column coiling are discussed based on recent studies, together with data sources and predictive correlations for binary diffusion coefficients. 相似文献
996.
The theoretical basis of a Gaussian-like approximate solution was applied to a chromatographic impulse response technique with curve fitting for measuring binary diffusion coefficients and retention factors using a polymer-coated capillary column. The formulae were derived for evaluating both the accuracy of the approximate solution and the sensitivity of the parameters. The validity of the solution also was confirmed experimentally for pulse injection of phenol in acetone into supercritical carbon dioxide flowing at 313.15 K and 11.6-28.6 MPa. Potential sources for experimental errors of the method are discussed. 相似文献
997.
BaWO(4) fishbone-like nanostructures with fourfold structural symmetry have been successfully grown in w/o microemulsion. The BaWO(4) fishbone-like nanostructures have four rows of nanorods, epitaxially grown on the stem and perpendicular to the stem. The obtained samples are characterized by means of XRD, TEM, HRTEM, and SEM. It is found that the water content has a large influence on the size of the product and the molar ratio between cations and anions plays an important role in the morphology of the product. It is assumed that site-selective surfactant adsorption may be responsible for the formation of the BaWO(4) fishbone-like nanostructures. 相似文献
998.
In this paper we have demonstrated that the crystallization method of amorphous colloids is convenient and feasible in the large-scale production of one-dimensional (1D) nanostructures. For the crystals with highly anisotropic structures, such as orthorhombic, trigonal, and hexagonal crystals, the crystallization generally tends to occur along the (001) axis. The preparation of orthorhombic bismuth sulfide (Bi2S3) nanorods and trigonal selenium ( t-Se) nanowires by the crystallization route was used as typical examples to illustrate the process and mechanism of crystallization. The as-prepared products were characterized with transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction, and selected area electron diffraction. Additionally, the detailed crystal growth processes involved in the crystallization of amorphous Bi2S3 colloid were investigated by studying the morphology and structure of intermediates. It demonstrates that the growth of the nanorods is through two key steps: (1) the formation of multiple activated sites on the surface of spherical Bi2S3 colloid and (2) the subsequent preferential growth along these sites. 相似文献
999.
Efficient synthesis of imidazoles from aldehydes and 1,2-diketones using microwave irradiation 总被引:1,自引:0,他引:1
[reaction: see text] A simple, high-yielding synthesis of 2,4,5-trisubstituted imidazoles from 1,2-diketones and aldehydes in the presence of NH(4)OAc is described. Under microwave irradiation, alkyl-, aryl-, and heteroaryl-substituted imidazoles are formed in yields ranging from 80 to 99%. Short syntheses of lepidiline B and trifenagrel illustrate the utility of this approach. 相似文献
1000.
[structure: see text] Tetrabromobutatriene, C(4)Br(4), can be prepared directly from dibromobutadiyne by reaction with Br(2) at -25 degrees C in concentrated hexanes solution. The cumulene precipitates out of the reaction mixture as a yellow powder. Under palladium-catalyzed coupling conditions, C(4)Br(4) can undergo allylic rearrangement, giving a mixture of products, including some with butenyne backbones. However, in furan solution, C(4)Br(4) reacts cleanly at its central double bond to give the furan Diels-Alder adduct. Under Suzuki conditions, this adduct reacts at the furan double bond rather than at bromide. 相似文献