全文获取类型
收费全文 | 11032篇 |
免费 | 1478篇 |
国内免费 | 771篇 |
专业分类
化学 | 3110篇 |
晶体学 | 1158篇 |
力学 | 1161篇 |
综合类 | 159篇 |
数学 | 4561篇 |
物理学 | 3132篇 |
出版年
2024年 | 16篇 |
2023年 | 113篇 |
2022年 | 243篇 |
2021年 | 302篇 |
2020年 | 355篇 |
2019年 | 271篇 |
2018年 | 246篇 |
2017年 | 337篇 |
2016年 | 471篇 |
2015年 | 337篇 |
2014年 | 523篇 |
2013年 | 800篇 |
2012年 | 601篇 |
2011年 | 691篇 |
2010年 | 611篇 |
2009年 | 646篇 |
2008年 | 718篇 |
2007年 | 682篇 |
2006年 | 674篇 |
2005年 | 591篇 |
2004年 | 502篇 |
2003年 | 452篇 |
2002年 | 369篇 |
2001年 | 317篇 |
2000年 | 353篇 |
1999年 | 272篇 |
1998年 | 252篇 |
1997年 | 224篇 |
1996年 | 151篇 |
1995年 | 151篇 |
1994年 | 118篇 |
1993年 | 102篇 |
1992年 | 88篇 |
1991年 | 109篇 |
1990年 | 75篇 |
1989年 | 56篇 |
1988年 | 71篇 |
1987年 | 48篇 |
1986年 | 42篇 |
1985年 | 52篇 |
1984年 | 38篇 |
1983年 | 22篇 |
1982年 | 38篇 |
1981年 | 17篇 |
1980年 | 34篇 |
1979年 | 22篇 |
1978年 | 13篇 |
1977年 | 24篇 |
1976年 | 19篇 |
1975年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
The Unexpected Influence of Precursor Conversion Rate in the Synthesis of III–V Quantum Dots 下载免费PDF全文
Daniel Franke Dr. Daniel K. Harris Lisi Xie Prof. Klavs F. Jensen Prof. Moungi G. Bawendi 《Angewandte Chemie (International ed. in English)》2015,54(48):14299-14303
Control of quantum dot (QD) precursor chemistry has been expected to help improve the size control and uniformity of III–V QDs such as indium phosphide and indium arsenide. Indeed, experimental results for other QD systems are consistent with the theoretical prediction that the rate of precursor conversion is an important factor controlling QD size and size distribution. We synthesized and characterized the reactivity of a variety of group‐V precursors in order to determine if precursor chemistry could be used to improve the quality of III–V QDs. Despite slowing down precursor conversion rate by multiple orders of magnitude, the less reactive precursors do not yield the expected increase in size and improvement in size distribution. This result disproves the widely accepted explanation for the shortcoming of current III–V QD syntheses and points to the need for a new generalizable theoretical picture for the mechanism of QD formation and growth. 相似文献
942.
Using cheap n‐butylamine as template, ZSM‐5 zeolites have been successfully synthesized and coated on monolithic interconnected macroporous Al2O3 by the secondary growth method. The use of cheap n‐butylamine could significantly reduce the synthesis cost. Hierarchical monolithic ZSM‐5 zeolites were prepared from synthetic mixtures with different H2O/Na2O or SiO2/Al2O3 ratio. The synthesized samples were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR) and N2 adsorption‐desorption. The results show that the hierarchical monolithic zeolites were obtained with cheap n‐butylamine template as template. During the hydrothermal reaction process, the morphology of the micrometer‐sized support was well maintained. The irregular crystals were formed in a wide range of the H2O/Na2O or SiO2/Al2O3 ratio of synthetic mixtures and coated on monolithic Al2O3. The relative crystallinity of the zeolites was highest at H2O/Na2O=250 or SiO2/Al2O3=160. This type of composites exhibited hierarchical porous structures and relatively high specific surface areas. 相似文献
943.
Perfluoropolyether (PFPE)‐based thermoplastic fluoropolymers are synthesized by A2 + B2 step‐growth polymerization between PFPE‐diyne and fluorinated diazides. This versatile method allows synthesizing PFPE‐based materials with tunable physicochemical properties depending on the exact nature of the fluorinated segment of the diazide precursor. Semicrystalline or amorphous materials endowed with high thermostability (≈300 °C under air) and low glass transition temperature (≈−100 °C) are obtained, as confirmed by differential scanning calorimetry, thermogravimetry, and rheometry. Step‐growth polymerizations can be copper‐catalyzed but also thermally activated in some cases, thus avoiding the presence of copper residues in the final materials. This strategy opens up new opportunities to easily access PFPE‐based materials on an industrial scale. Furthermore, a plethora of developments can be envisioned (e.g., by adding a third trifunctional component to the formulations for the synthesis of PFPE‐based elastomers).
944.
In‐Sik Kim In‐Bok Kim Dong‐Yu Kim Seong‐Hoon Kwon Do‐Kyeong Ko 《Macromolecular rapid communications》2016,37(15):1242-1248
The femtosecond transient absorption (TA) characterization of a new benzothiadiazole (BT)‐based donor–acceptor conjugated copolymer, poly[(2,6‐dithieno[3,2‐b:2′,3′‐d]thiophene)‐alt‐(4,7‐di(4‐octyldodecylthiopen‐2‐yl)‐2,1,3‐benzo[c][1,2,5]thiadiazole (PBT), as well as its fluorinated derivatives, PFBT and PDFBT, is carried out. Additionally, bulk heterojunction (BHJ) films consisting of the copolymers and [6,6]‐phenyl‐C71‐butylic acid methyl ester (PC70BM) are examined using TA spectroscopy. Both the singlet excited state dynamics in the copolymers and the charge transfer state dynamics in the BHJs are investigated in terms of fluorination dependency; the fluorinated copolymers exhibit less singlet exciton recombination rate than the fluorine‐free copolymer, and the BHJs including the fluorinated copolymers display slower monomolecular recombination than the fluorine‐free analogue. Furthermore, the excitation‐intensity‐dependent TA dynamics of the copolymers and BHJs is investigated, revealing that, when sufficiently high excitation intensity is used to induce annihilation processes, the fluorinated copolymers and BHJs incorporating the fluorinated copolymers show more rapid TA decay ascribable to morphological enhancement. These TA spectroscopic findings are found to correlate with the device characteristics with respect to fluorinated content in the polymer solar cells. In particular, both the short‐circuit current density and fill factor of BHJ solar cells correspond closely with the fast decay parameters of the BHJ films under high excitation intensity.
945.
946.
V. A. Petushkov 《Fluid Dynamics》2005,40(3):413-425
A mathematical model and a numerical method are developed for studying nonlinear wave processes in two-phase liquids with gas or vapor bubbles under conditions of impact interaction with deformable media. On the basis of the proposed approach to the numerical modeling of the dynamics of the transient processes in the two-phase vapor-liquid and deformable media, the basic features of the phase behavior, the phase transitions, and the interphase heat and mass transfer, typical of liquids containing vapor bubbles, are analyzed. The results of solving problems of the dynamics of different vapor-liquid media are presented.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, 2005, pp. 88–102.Original Russian Text Copyright © 2005 by Petushkov. 相似文献
947.
QixiangWang GuoqingNing FeiWei GuohuaLuo 《中国颗粒学报》2003,1(6):253-257
Multi-walled carbon nanotubes (MWNTs) with 20 nm outer diameter were prepared by chemical vapor deposition of ethylene using ultrafine surface-modified acicular α-Fe catalyst particles.The growth mechanism of MWNTs on the larger catalyst particles are attributed to the interaction between the Fe nanoparticles with the surface-modified silica layer.This interaction-mediated growth mechanism is illustrated by studying the electronic,atomic and crystal properties of surface-modified catalysts and MWNTs products by characterization with X-ray diffraction (XRD),transmission electron microscopy (TEM),high resolution transmission electron microscopy (HRTEM),thermal gravimetric analysis (TGA) and Raman spectra. 相似文献
948.
Thermocapillary- and buoyancy-driven convection in open cavities with differentially heated endwalls is investigated by numerical
solutions of the two-dimensional Navier-Stokes equations coupled with the energy equation. We studied the thermocapillary
and buoyancy convection in the cavities, filled with low-Prandtl-number fluids, with two aspect-ratiosA=1 and 4, Grashof number up to 105 and Reynolds number ⋎Re⋎≤104. Our results show that thermocapillary can have a quite significant effect on the stability of a primarily buoyancy-driven
flow, as well as on the flow structures and dynamic behavior for both additive effect (i.e., positiveRe) and opposing effect (i.e., negativeRe). 相似文献
949.
Federico Poujol Jorge Rojas Eduardo Ramos 《International Journal of Heat and Fluid Flow》1993,14(4):357-365
The transient natural convection of a fluid with Prandtl number of order 200 in a two-dimensional square cavity has been numerically studied. One of the vertical walls of the cavity is kept at a constant (ambient) temperature and a constant heat flux is applied on the opposite wall. The other walls are adiabatic. Initially, a boundary layer is formed near the heated wall; subsequently, a large vortical structure is generated, together with an upper intrusion layer. As time progresses, the average temperature in the cavity increases, and a descending boundary layer is formed near the constant temperature wall. During the transition to the steady-state regime, a thermal stratification pattern is formed. The results are compared with the scale analysis presented by Patterson and Imberger (1980). 相似文献
950.
Special fractal dendrite Cu nanostructures have been synthesized through a simple hydrothermal method, and the effects of the volume ratio between glycerol and water and the concentration of H3PO3 on the morphologies of dendrite Cu have been studied in detail. The Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and X-ray diffraction (XRD) have been used to characterize these Cu products. The results indicate that rhombic diamond and different morphologies of fractal dendrite were prepared because of the accumulation of Cu nuclei based on the diffusion-limited aggregation (DLA) and the nucleation-limited aggregation (NLA) model. Fortunately, symmetrical leaf-like dendrite Cu nanostructures different from Cu dendrites reported before have been obtained. Additionally, an explanation for the growth of fractal dendrite Cu has been discussed carefully. 相似文献