全文获取类型
收费全文 | 4128篇 |
免费 | 429篇 |
国内免费 | 248篇 |
专业分类
化学 | 694篇 |
晶体学 | 19篇 |
力学 | 1287篇 |
综合类 | 57篇 |
数学 | 1384篇 |
物理学 | 1364篇 |
出版年
2024年 | 10篇 |
2023年 | 43篇 |
2022年 | 86篇 |
2021年 | 78篇 |
2020年 | 109篇 |
2019年 | 83篇 |
2018年 | 121篇 |
2017年 | 122篇 |
2016年 | 140篇 |
2015年 | 137篇 |
2014年 | 165篇 |
2013年 | 298篇 |
2012年 | 186篇 |
2011年 | 276篇 |
2010年 | 175篇 |
2009年 | 180篇 |
2008年 | 219篇 |
2007年 | 232篇 |
2006年 | 238篇 |
2005年 | 196篇 |
2004年 | 180篇 |
2003年 | 182篇 |
2002年 | 165篇 |
2001年 | 146篇 |
2000年 | 158篇 |
1999年 | 143篇 |
1998年 | 106篇 |
1997年 | 70篇 |
1996年 | 82篇 |
1995年 | 79篇 |
1994年 | 78篇 |
1993年 | 47篇 |
1992年 | 41篇 |
1991年 | 47篇 |
1990年 | 34篇 |
1989年 | 29篇 |
1988年 | 18篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1976年 | 6篇 |
1975年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有4805条查询结果,搜索用时 15 毫秒
101.
S. Zeinali Heris F. Ahmadi Omid Mahian 《Journal of Dispersion Science and Technology》2013,34(10):1368-1375
An experimental study is performed to determine the pressure drop and performance characteristics of Al2O3/water and CuO/water nanofluids in a triangular duct under constant heat flux where the flow is laminar. The effects of adding nanoparticles to the base fluid on the pressure drop and friction factor are investigated at different Reynolds numbers. The results show that at a specified Reynolds number, using the nanofluids can lead to an increase in the pressure drop by 35%. It is also found that with increases in the Reynolds number, the rate of increase in the friction factor with the volume fraction of nanoparticles is reduced. Finally, the performance characteristics of the two nanofluids are investigated using the data of pressure drop and convective heat transfer coefficient. The results show that the use of Al2O3/water nanofluid with volume fractions of 1.5% and 2% is not helpful in the triangular duct. It is also concluded that at the same volume fraction of nanoparticles, using Al2O3 nanoparticles is more beneficial than CuO nanoparticles based on the performance index. 相似文献
102.
A. Sarimeseli 《Journal of Dispersion Science and Technology》2013,34(5):694-697
Measurement of drop sizes play vital role in applications dealing with gas/liquid flow mixtures. In the present work, drop sizes in vertical and horizontal pipe flows were determined using Malvern 2600HSD system that applies laser diffraction method. From the analysis of the experimental data obtained at two different pipe orientations, two separate expressions were developed to determine Sauter mean diameter, d 32. Except for the 20 m/s superficial gas velocity in vertical flow case, a good agreement was found between the developed expressions and the experimental data. 相似文献
103.
Interactions between monolayers of trilaurylamine (TLA) and various water-soluble corrosion, hydrate and scale inhibitors, as well as acetic acid and FeCl2, have been studied by means of the Langmuir technique, The water-soluble compounds were present in the subphase before TLA was spread. Their influence on the monolayer properties were measured by means of surface pressure-area ( k-A) isotherms and constant surface pressure-area relaxation measurements. All the added water soluble species gave rise to monolayer expansion. The monolayer expansion observed for TLA at pH 1, increased when FeCl2 was added to the subphase at the same pH. Polyethyleneglycols with molecular weight higher than 200 destabilized totally the TLA-monolayer, probably due to bending and folding into multilayers. Monolayer expansion and film instability increased with increased acetic acid concentrations. The destabilization mechanism in this case was most likely due to a combination of nucleation and dissolution of film components into the subphase. The corrosion inhibitor Dyno KI 384 had a higher surface activity than TLA. Hence the monolayer 相似文献
104.
Bruce M. Allen Paul K. Predecki Maciej Kumosa 《Journal of computational chemistry》2014,35(9):756-764
Three open‐source applications, NanoEngineer‐1, packmol, and mis2lmp are integrated using an open‐source file format to quickly create molecular dynamics (MD) cells for simulation. The three software applications collectively make up the open‐source software (OSS) suite known as MD Studio (MDS). The software is validated through software engineering practices and is verified through simulation of the diglycidyl ether of bisphenol‐a and isophorone diamine (DGEBA/IPD) system. Multiple simulations are run using the MDS software to create MD cells, and the data generated are used to calculate density, bulk modulus, and glass transition temperature of the DGEBA/IPD system. Simulation results compare well with published experimental and numerical results. The MDS software prototype confirms that OSS applications can be analyzed against real‐world research requirements and integrated to create a new capability. © 2014 Wiley Periodicals, Inc. 相似文献
105.
WU Liting XIN Yujia GUO Zhaoyang GAO Wei ZHU Yanpeng br WANG Yinsong RAN Ruixue YANG Xiaoying 《高等学校化学研究》2022,38(2):562-571
Combining photothermal therapy and radiotherapy(PTT-RT) with reducing tumor hypoxia acts as an important antitumor modality. However, it is a great challenge to realize photothermal therapy, radiotherapy and exogenous oxygen supply in one nanosystem. To realize a combination of the three functions, we fabricated a red blood cell membrane(RBCm)-camouflaged, red blood cell content(RBCc) and the copper sulfide(CuS) co-loaded dendritic large pore mesoporous silica nanoparticle(DLMSN/CuS/RBCc/ RBCm). The cell membrane coating endowed the nanoparticles with good stability in the physiological environment, and CuS allowed the nanoparticle exhibiting good photothermal and radiosensitization properties. RBCc loaded nanoparticle DLMSN/CuS/RBCc enhanced superior anti-tumor effect than DLMSN/CuS during combined PTT-RT therapy because the introduction of RBCc increased the exogenous oxygen supply. The in vitro study further demonstrated that the combination of photothermal therapy and radiotherapy induced superior antitumor efficacy than single therapy. Our work thus presents a unique multifunctional nanoscale platform favorable for combined PTT and RT. 相似文献
106.
Multiphase flow metering with operationally robust, low-cost real-time systems that provide accuracy across a broad range of produced volumes and fluid properties, is a requirement across a range of process industries, particularly those concerning petroleum. Especially the wide variety of multiphase flow profiles that can be encountered in the field provides challenges in terms of metering accuracy. Recently, low-field magnetic resonance (MR) measurement technology has been introduced as a feasible solution for the petroleum industry. In this work, we study two phase air-water horizontal flows using MR technology. We show that low-field MR technology applied to multiphase flow has the capability to measure the instantaneous liquid holdup and liquid flow velocity using a constant gradient low flip angle CPMG (LFA-CPMG) pulse sequence. LFA-CPMG allows representative sampling of the correlations between liquid holdup and liquid flow velocity, which allows multiphase flow profiles to be characterized. Flow measurements based on this method allow liquid flow rate determination with an accuracy that is independent of the multiphase flow profile observed in horizontal pipe flow for a wide dynamic range in terms of the average gas and liquid flow rates. 相似文献
107.
Ionic liquids (ILs) are considered to be one of the steppingstones to fabricate next generation electrochemical devices given their unique physical and chemical properties. The addition of water to ILs significantly impact electrochemical related properties including viscosity, density, conductivity, and electrochemical window. Herein we utilize ambient pressure X-ray photoelectron spectroscopy (APXPS) to examine the impact of water on values of the electrochemical shift (S), which is determined by measuring changes in binding energy shifts as a function of an external bias. APXPS spectra of C 1s, O 1s and N 1s regions are examined for the IL 1-butyl-3-methylimidazolium acetate, [C4mim][OAc], at the IL/gas interface as a function of both water vapor pressure and external bias. Results reveal that in the absence of water vapor there is an IL ohmic drop between the working electrode and quasi reference electrode, giving rise to chemical specific S values of less than one. Upon introducing water vapor, S values approach one as a function of increasing water vapor pressure, indicating a decrease in the IL ohmic drop as the IL/water mixture becomes more conductive and the potential drop is driven by the electric double layer at the electrode/IL interface. 相似文献
108.
针对大口径离轴凸非球面面形检测的困难,本文将光学系统波像差检验技术与子孔径拼接干涉技术相结合,提出了凸非球面系统拼接检测方法。对该方法的基本原理和具体实现过程进行了分析和研究,并建立了合理的子孔径拼接数学模型。当离轴三反光学系统的主镜和三镜加工完成以后,对整个系统进行装调和测试,并依次测定光学系统各视场的波像差分布,通过综合优化子孔径拼接算法和全口径面形数据插值可以求解得到大口径非球面全口径的面形信息,从而为非球面后续加工和系统的装调提供了依据和保障。结合工程实例,对一口径为287 mm×115 mm的离轴非球面次镜进行了系统拼接测试和加工,经过两个周期的加工和测试,其面形分布的RMS值接近1/30λ(λ=632.8 nm)。 相似文献
109.
《印度化学会志》2021,98(12):100235
India has abundance of biomass such as rice husk, bagasse, wheat straw, sawdust etc. which is used as a main or auxiliary fuel in the fluidized bed combustor, gasifier and pyrolizer. Design of such fluidized bed equipments require the knowledge of minimum fluidization velocity (Umf), complete fluidization velocity (Ucf) and transport disengagement height (TDH). The present work reports the fluidization characteristic, Umf, Ucf and TDH of the individual size groups of sawdust and mixture thereof. The results indicate that the Umf and Ucf have a tendency to increase with increase in particle diameter, however the TDH shows the reverse trend. The sawdust particle size of 925 and 1200 μm showed significant difference between their Umf and Ucf, an essential parameter for controlled fluidization. Based on the experimental work new correlations for the prediction of Umf, Ucf and TDH for sawdust sample are proposed. The proposed correlations of Umf, Ucf and TDH are in good agreement with experimental values and the deviations found within the range of nearly ±10% for all the samples. 相似文献
110.
Threshold switching is a phenomenon where the resistivity of an insulating material changes and the insulator exhibits metallic behavior. This could be explained by phase transformation in oxide materials; however, this behavior is also seen in amorphous insulators. In this study, through an ex-situ experiment using transmission electron microscopy (TEM), we proved that threshold switching of amorphous NbO2 accompanies local crystallization. The change in I–V characteristics after electroforming was examined by evaluating the concentration profile. Atom probe tomography (APT) combined with in-situ TEM probing technique was performed to understand the threshold switching in amorphous NbO2. The local crystallization in amorphous NbO2 was validated by the observed difference in time-of-flight (ToF) between amorphous and crystalline NbO2. We concluded that the slower ToF of amorphous NbO2 (a-NbO2) compared with crystalline NbO2 (c-NbO2) is due to the resistivity difference and trap-assisted recombination. 相似文献