全文获取类型
收费全文 | 17738篇 |
免费 | 1013篇 |
国内免费 | 1206篇 |
专业分类
化学 | 2549篇 |
晶体学 | 95篇 |
力学 | 485篇 |
综合类 | 143篇 |
数学 | 4583篇 |
物理学 | 2206篇 |
综合类 | 9896篇 |
出版年
2024年 | 33篇 |
2023年 | 126篇 |
2022年 | 299篇 |
2021年 | 322篇 |
2020年 | 393篇 |
2019年 | 341篇 |
2018年 | 336篇 |
2017年 | 389篇 |
2016年 | 448篇 |
2015年 | 463篇 |
2014年 | 821篇 |
2013年 | 1020篇 |
2012年 | 886篇 |
2011年 | 1008篇 |
2010年 | 761篇 |
2009年 | 929篇 |
2008年 | 943篇 |
2007年 | 1211篇 |
2006年 | 1098篇 |
2005年 | 935篇 |
2004年 | 871篇 |
2003年 | 861篇 |
2002年 | 676篇 |
2001年 | 600篇 |
2000年 | 557篇 |
1999年 | 492篇 |
1998年 | 417篇 |
1997年 | 358篇 |
1996年 | 386篇 |
1995年 | 297篇 |
1994年 | 276篇 |
1993年 | 217篇 |
1992年 | 189篇 |
1991年 | 171篇 |
1990年 | 136篇 |
1989年 | 132篇 |
1988年 | 115篇 |
1987年 | 96篇 |
1986年 | 52篇 |
1985年 | 54篇 |
1984年 | 37篇 |
1983年 | 21篇 |
1982年 | 35篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1979年 | 28篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
961.
Pd-catalyzed cross-coupling reactions of various arenediazonium salts with ArSi(OR)3 and KArBF3 have been achieved in good to excellent yields under simple aerobic conditions in water at room temperature. The functional group tolerance makes these transformations as attractive alternatives to the traditional cross-coupling approaches. Furthermore, the sequence can also be performed in a one-pot domino process, omitting the isolation of the intermediate arenediazonium salt. 相似文献
962.
R. Hertz‐Schünemann R. Dorfner C. Yeretzian T. Streibel R. Zimmermann 《Journal of mass spectrometry : JMS》2013,48(12):i-i
Resonance‐enhanced multiphoton ionisation time‐of‐flight mass spectrometry (REMPI‐TOFMS) enables the fast and sensitive on‐line monitoring of volatile organic compounds (VOC) formed during coffee roasting. On the one hand, REMPI‐TOFMS was applied to monitor roasting gases of an industrial roaster (1500 kg/h capacity), with the aim of determining the roast degree in real‐time from the transient chemical signature of VOCs. On the other hand, a previously developed μ‐probe sampling device was used to analyse roasting gases from individual coffee beans. The aim was to explore fundamental processes at the individual bean level and link these to phenomena at the batch level. The pioneering single‐bean experiments were conducted in two configurations: (1) VOCs formed inside a bean were sampled in situ, i.e. via a drilled μ‐hole, from the interior, using a μ‐probe (inside). (2) VOCs were sampled on‐line in close vicinity of a single coffee bean's surface (outside). The focus was on VOCs originating from hydrolysis and pyrolytic degradation of chlorogenic acids, like feruloyl quinic acid and caffeoyl quinic acid. The single bean experiments revealed interesting phenomena. First, differences in time–intensity profiles between inside versus outside (time shift of maximum) were observed and tentatively linked to the permeability of the bean's cell walls material. Second, sharp bursts of some VOCs were observed, while others did exhibit smooth release curves. It is believed that these reflect a direct observation of bean popping during roasting. Finally, discrimination between Coffea arabica and Coffea canephora was demonstrated based on high‐mass volatile markers, exclusively present in spectra of Coffea arabica. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
963.
This letter describes an original freezing process that yields homogeneous solid films at ambient temperature with preservation of the layered structure of the chiral smectic phase. One of the most remarkable features of the process is its ability to provide complexly bent films with arbitrary three-dimensional shapes. Their optical homogeneity is observed in the planar as well as in the bent films. The method is very simple. After forming the films by spreading the liquid crystal above a hole in a glass slice placed over a hot stage, the film is heated from below. The hot film is exposed to ambient temperature. Then, a solid object at room temperature with a specifically adapted shape is immersed in the liquid film. The mechanical constraints imposed by the object curves the film and stabilises various solid two- and three-dimensional structures. Their homogeneous optical properties are due to long-range organisation of the molecular orientation (tilt), which combines with a complex helical arrangement of the frozen smectic layers. 相似文献
964.
S. Fournanty K. El Omari J.-P. Dejean 《Journal of Dispersion Science and Technology》2013,34(10):1355-1366
The formation of heavy crude oil in water (O/W) emulsion by a low energy laminar controlled flow has been investigated. The emulsion was prepared in an eccentric cylinder mixer. Its geometry allows the existence of chaotic flows that are able to mix well highly viscous fluids. This new mixer design is used to produce high internal phase ratio emulsions for three oils: castor oil and two heavy crude oils of different initial viscosity (Zuata and Athabasca crude oils). The influence of the stirring conditions, geometrical parameters, and water volume fraction on the rheological properties of the resulting O/W emulsion is studied. 相似文献
965.
Shi‐Zhao Kang Zhizhen Xu Yixin Song 《Journal of Dispersion Science and Technology》2013,34(6):857-859
In this article, TiO2 nanorods (aspect ratio >20) were prepared through a polyol process and doped with metal ions (Cu2+, Ni2+, Fe3+, and Cr3+). Compared with TiO2 nanoparticles, the TiO2 nanorods displayed relatively higher photocatalytic activity for the degradation of copper sulfophthalocyanine. Moreover, the photocatalytic activity was greatly enhanced when the metal ions were doped in the TiO2 nanorods. 相似文献
966.
967.
968.
一种基于流动注射梯度技术识别异常峰及校正的方法 总被引:1,自引:0,他引:1
基于流动注射梯度信息提出了一种利用梯度比均值进行定量的校正方法。方法具有在线自动判别和修复异常峰并自行校正的功能,和通用的标准系列定量方法相比,两者测定精度相当。但本文提出的方法抗干扰能力明显优于后者,可适用于在线过程监测。 相似文献
969.
将化工流程模拟Aspen Plus软件与环境影响评估领域常用的生命周期评价(LCA)进行集成应用,围绕环境工程原理教学中有关化工过程质量能量衡算与环境污染防治内容的协同应用与拓展,构建化工流程模拟-环境风险评估科研案例“苯酐生产流程模拟及环境风险研究”,并将其作为环境工程原理的综合教学案例。教学实践经验表明,通过引入工程相关综合教学案例,不仅使得抽象的理论知识更加生动具体,而且在深化学生对课程理论知识理解的同时,提高学生应用专业知识分析和解决化工生产环境污染工程问题的综合能力和素质,为学生将来步入相关领域工作奠定扎实的基础。 相似文献
970.
Simultaneous application of multiple sinusoidal waveforms perturbations superimposed onto DC staircase step significantly enriches current response. The measured current is characterized by a matrix of data rather than a conventional voltammetric output in a form of a vector. This increase of the dimensionality of the current response and therefore the wealth of analytical information is achieved without compromising the time of analysis. The natural approach for compression of such data and extraction of relevant information is by utilizing multi-way chemometric decomposition techniques. An electroplating solution presents a very challenging analyte for electroanalysis as its constituents interact synergistically with each other during both the plating process and its simulation during electroanalysis. For some components the mechanism is not entirely understood. Therefore, the only way to benefit from the analytical data is by employing soft modeling. The electrode processes involving additives rely heavily on adsorption and, indirectly, on electron transfer kinetics for which AC voltammetry is an analytical technique capable of delivering informative signals. This paper presents a rigorous universal method for calculating and validating an exemplary multi-way calibration of a leveler component in a copper electroplating bath used in the semiconductor industry. The method presented employs comparatively Parallel Factor Analysis coupled with Inverse Least Squares Regression and multi-linear Partial Least Squares. The calibration training set consists of multi-frequency AC voltammetric data subjected to pretreatments aiming to select informative independent variables and exclude outliers. 相似文献