全文获取类型
收费全文 | 2742篇 |
免费 | 172篇 |
国内免费 | 271篇 |
专业分类
化学 | 1727篇 |
晶体学 | 5篇 |
力学 | 197篇 |
综合类 | 14篇 |
数学 | 631篇 |
物理学 | 611篇 |
出版年
2024年 | 6篇 |
2023年 | 41篇 |
2022年 | 57篇 |
2021年 | 58篇 |
2020年 | 77篇 |
2019年 | 79篇 |
2018年 | 61篇 |
2017年 | 80篇 |
2016年 | 104篇 |
2015年 | 111篇 |
2014年 | 119篇 |
2013年 | 171篇 |
2012年 | 235篇 |
2011年 | 193篇 |
2010年 | 178篇 |
2009年 | 217篇 |
2008年 | 226篇 |
2007年 | 197篇 |
2006年 | 163篇 |
2005年 | 128篇 |
2004年 | 129篇 |
2003年 | 66篇 |
2002年 | 71篇 |
2001年 | 46篇 |
2000年 | 47篇 |
1999年 | 46篇 |
1998年 | 45篇 |
1997年 | 37篇 |
1996年 | 25篇 |
1995年 | 25篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有3185条查询结果,搜索用时 15 毫秒
991.
A commercial direct laser writing (DLW) system operating at 1070 nm was used to fabricate SiO2 optical waveguides on silicon wafers. A Ti-doped SiO2 Sol-Gel film was deposited on the SiO2/Si substrate by the dip-coating technique, based on which SiO2 optical waveguides were patterned by DLW using a Ytterbium fiber laser and followed by chemical etching. The effects of laser parameters and the preheated temperature of Sol-Gel films on the dimensions of optical waveguides were studied systematically. The differences of etching rate between laser irradiated and non-irradiated areas in Sol-Gel films preheated at various temperatures are characterized by measuring the thickness of the films. Results demonstrate that the available laser power density range for laser densification and the width of the patterned optical waveguides are influenced strongly by the preheated temperature of the Sol-Gel films. The width of the optimized optical waveguide in this work is 25 μm. The minimum propagation loss of the fabricated optical waveguides is 1.7 dB cm−1 at the wavelength of 1550 nm. 相似文献
992.
There is growing interest in developing oxide materials for direct hydrocarbon solid oxide fuel cell anodes. In addition to electronic and ionic conductivities, the electrocatalytic activity of these materials is a critical requirement for a high performance anode. In this paper, we present evidence for the important role of variable lattice oxygen stoichiometry and anode geometry in dictating the activity and reaction mechanism of La0.75Sr0.25Cr1 − xMnxO3 − δ-based anodes for CH4 oxidation. Total oxidation of CH4 is favored by low oxygen vacancy concentration and availability of reducible B-site cations. The non-linear dependence of electrode polarization resistance with current density is attributed to dynamic changes in lattice oxygen vacancy concentration. The relatively high open circuit potential of porous anodes compared with thin films is attributed to an increase in secondary reactions of the fuel within the porous anode. 相似文献
993.
A new Nafion binder solution was prepared using a different organic solvent, dimethylacetamide (DMAc), and applied to a polymer electrolyte membrane-based fuel cell. Wide angle X-ray diffraction (WAXD), electrochemical impedance spectroscopy (EIS), and polarization of the fuel cell were carried out to determine the crystallinity of the Nafion binder film, the cell resistance, and the fuel cell performance. This new Nafion binder film, which was created using a homemade Nafion solution containing DMAc, dissolved slower than a recast Nafion film that was made using a commercial Nafion solution in methanol (2 M). It was found that the slow dissolution of the homemade Nafion binder film was due to a more highly developed crystalline morphology, which can lead to good structural integrity in the catalyst layer for long-term operation of the fuel cell. The micellar structure of Nafion in the commercial Nafion binder solution is broken by new organic solvent, which leads to higher physical chain entanglement between the Nafion membrane and the Nafion binder during preparation of the membrane/electrode assembly (MEA), thereby improving the interfacial stability between the membrane and the electrode and providing long-term stability of the fuel cell. 相似文献
994.
We investigate the stability of a thin liquid film flowing down an inclined wavy plane using a direct numerical solver based on a finite element/arbitrary Lagrangian Eulerian approximation of the free-surface Navier-Stokes equations. We study the dependence of the critical Reynolds number for the onset of surface wave instabilities on the inclination angle, the waviness parameter, and the wavelength parameter, focusing in particular on mild inclinations and relatively large waviness so that the bottom does not fall monotonously. In the present parameter range, shorter wavelengths and higher amplitude for the bottom undulation stabilize the flow. The dependence of the critical Reynolds number evaluated with the Nusselt flow rate on the inclination angle is more complex than the classical relation (5/6 times the cotangent of the inclination angle), but this dependence can be recovered if the actual flow rate at critical conditions is used instead. 相似文献
995.
Juan MaYigang Ji Hanjun SunYu Chen Yawen TangTianhong Lu Junwei Zheng 《Applied Surface Science》2011,257(24):10483-10488
A highly dispersed and ultrafine carbon supported Pd nanoparticles (Pd/C) catalyst is synthesized by a facile homogeneous precipitation-reduction reaction method. Under the appropriate pH conditions, [PdCl4]2− species in PdCl2 solution are slowly transformed into the insoluble palladium oxide hydrate (PdO·H2O) precipitation by heat treatment due to a slow hydrolysis reaction, which results in the generation of carbon supported PdO·H2O nanoparticles (PdO·H2O/C) sample with the high dispersion and small particle size. Consequently, a highly dispersed and ultrafine Pd/C catalyst can be synthesized by PdO·H2O → Pd0 in situ reduction reaction path in the presence of NaBH4. As a result, the resulting Pd/C catalyst possesses a significantly electrocatalytic performance for formic acid electrooxidation, which is attributed to the uniformly sized and highly dispersed nanostructure. 相似文献
996.
997.
Kyung-In JangByung-Kwon Min Jongwon Seok 《Journal of magnetism and magnetic materials》2011,323(10):1324-1329
A model that considers the mutual interaction between particles and the external field in a magnetorheological (MR) fluid is proposed. The model predicts the magnetization, interaction energy density, and shear stress against an imposed strain along the planar direction under a uniform magnetic field. Using the Lekner summation method, slowly convergent magnetization functions are transformed into rapidly convergent ones. By applying the proposed model to an application suitable for commercial clutches and dampers working in direct shear mode, it is revealed that the mean magnetization vector and the associated functional quantities of the MR fluid behave harmonically with respect to the imposed shear strain. 相似文献
998.
The microscopic transport model UrQMD and a micro + macro hybrid model are used to calculate direct photon spectra from U+U-collisions at Elab=35 A GeV as will be measured by the CBM Collaboration at FAIR. In the hybrid model, the intermediate high-density part of the nuclear interaction is described with ideal 3+1-dimensional hydrodynamics. Different equations of state of the matter created in the heavy-ion collisions are investigated and the resulting spectra of direct photons are predicted. The emission patterns of direct photons in space and time are discussed. 相似文献
999.
A Highly Sensitive and Selective Enzymatic Biosensor Based on Direct Electrochemistry of Hemoglobin at Zinc Oxide Nanoparticles Modified Activated Screen Printed Carbon Electrode 下载免费PDF全文
Selvakumar Palanisamy Chelladurai Karuppiah Shen‐Ming Chen Prakash Periakaruppan 《Electroanalysis》2014,26(9):1984-1993
A sensitive enzymatic biosensor has been developed for the detection of hydrogen peroxide (H2O2), nitrite ( ) and trichloroacetic acid (TCA) by using hemoglobin (Hb) immobilized on activated screen printed carbon electrode (ASPCE) and zinc oxide (ZnO) composite. A pair of well defined redox peaks is observed with a heterogeneous electron transfer rate constant (Ks) of 5.27 s?1 for Hb at ASPCE/ZnO. The biosensor exhibits the detection of H2O2, TCA and in the concentration range of 0.5–129.5 µmol L?1, 2.5–72.5 mmol L?1 and 0.2–674 µmol L?1 with the detection limit of 0.083 µmol L?1, 0.12 mmol L?1 and 0.069 µmol L?1, respectively. 相似文献
1000.
Multiple detection of proteins by SERS-based immunoassay with core shell magnetic gold nanoparticles
A highly selective and sensitive surface-enhanced Raman scattering (SERS)-based immunoassay for the multiple detection of proteins has been developed. The proposed core shell magnetic gold (Au) nanoparticles allow for successful protein separation and high SERS enhancement for protein detection. To selectively detect a specific protein in a mixed protein solution, we employed the sandwich type SERS immunoassay with core shell magnetic Au nanoparticles utilizing specific antigen–antibody interactions. Based on this proposed SERS immunoassay, we can successfully detect proteins in very low concentrations (∼800 ag/mL of mouse IgG and ∼5 fg/mL of human IgG) with high reproducibility. Magnetically assisted protein separation and detection by this proposed SERS immunoassay would provide great potential for effective and sensitive multiple protein detection. This technique allows for the straightforward SERS-based bioassays for quantitative protein detections. 相似文献