全文获取类型
收费全文 | 468219篇 |
免费 | 4616篇 |
国内免费 | 1458篇 |
专业分类
化学 | 220547篇 |
晶体学 | 6359篇 |
力学 | 24385篇 |
综合类 | 7篇 |
数学 | 84743篇 |
物理学 | 138252篇 |
出版年
2020年 | 1990篇 |
2019年 | 1965篇 |
2018年 | 18851篇 |
2017年 | 19457篇 |
2016年 | 12472篇 |
2015年 | 4792篇 |
2014年 | 4810篇 |
2013年 | 14380篇 |
2012年 | 17598篇 |
2011年 | 32885篇 |
2010年 | 19519篇 |
2009年 | 19803篇 |
2008年 | 27277篇 |
2007年 | 32290篇 |
2006年 | 12565篇 |
2005年 | 19152篇 |
2004年 | 14705篇 |
2003年 | 13681篇 |
2002年 | 10829篇 |
2001年 | 10446篇 |
2000年 | 8192篇 |
1999年 | 6299篇 |
1998年 | 5106篇 |
1997年 | 4888篇 |
1996年 | 5068篇 |
1995年 | 4563篇 |
1994年 | 4259篇 |
1993年 | 4101篇 |
1992年 | 4551篇 |
1991年 | 4416篇 |
1990年 | 4124篇 |
1989年 | 3953篇 |
1988年 | 4254篇 |
1987年 | 3918篇 |
1986年 | 3791篇 |
1985年 | 5446篇 |
1984年 | 5527篇 |
1983年 | 4495篇 |
1982年 | 4867篇 |
1981年 | 4906篇 |
1980年 | 4665篇 |
1979年 | 4786篇 |
1978年 | 4798篇 |
1977年 | 4703篇 |
1976年 | 4678篇 |
1975年 | 4573篇 |
1974年 | 4414篇 |
1973年 | 4624篇 |
1972年 | 2617篇 |
1971年 | 1907篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
P. W. J. Glover 《Transport in Porous Media》2018,124(1):31-56
In this paper, we have significantly modified an existing model for calculating the zeta potential and streaming potential coefficient of porous media and tested it with a large, recently published, high-quality experimental dataset. The newly modified model does not require the imposition of a zeta potential offset but derives its high salinity zeta potential behaviour from Stern plane saturation considerations. The newly modified model has been implemented as a function of temperature, salinity, pH, and rock microstructure both for facies-specific aggregations of the new data and for individual samples. Since the experimental data include measurements on samples of both detrital and authigenic overgrowth sandstones, it was possible to model and test the effect of widely varying microstructural properties while keeping lithology constant. The results show that the theoretical model represents the experimental data very well when applied to model data for a particular lithofacies over the whole salinity, from 10?5 to 6.3 mol/dm3, and extremely well when modelling individual samples and taking individual sample microstructure into account. The new model reproduces and explains the extreme sensitivity of zeta and streaming potential coefficient to pore fluid pH. The low salinity control of streaming potential coefficient by rock microstructure is described well by the modified model. The model also behaves at high salinities, showing that the constant zeta potential observed at high salinities arises from the development of a maximum charge density in the diffuse layer as it is compressed to the thickness of one hydrated metal ion. 相似文献
62.
63.
Inside Cover: Ru‐Catalysed CH Arylation of Indoles and Pyrroles with Boronic Acids: Scope and Mechanistic Studies (Chem. Eur. J. 14/2015)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
64.
In this work, the effect of various properties of materials on vacuum breakdown initiated by laser radiation is considered. Estimating calculations are performed which show that the material of the target electrode distinctly affects the minimum energy of laser radiation needed for igniting a vacuum spark. The experimental studies carried out confirm the estimating calculations, and a number of materials are revealed which can be arranged in order of increase in the energy needed for the formation of breakdown in vacuum by the impact of a laser pulse. 相似文献
65.
S. Q. Hou W. Wang Z. Y. Wang Z. W. Hu K. Liu 《Journal of Applied Mechanics and Technical Physics》2018,59(1):153-162
In order to investigate the characteristics of force chains in a granular flow system, a parallel plate shear cell is constructed to simulate the shear movement of an infinite parallel plate and observe variations in relevant parameters. The shear dilatancy process is divided into three stages, namely, plastic strain, macroscopic failure, and granular recombination. The stickslip phenomenon is highly connected with the evolution of force chains during the shear dilatancy process. The load–distribution rate curves and patterns of the force chains are utilized to describe the load-carrying behaviors and morphologic changes of force chains separately. Force chains, namely, “diagonal gridding,” “tadpole-shaped,” and “pinnate” are defined according to the form of the force chains in the corresponding three stages. 相似文献
66.
67.
68.
Cover Picture: Coordination Chemistry of N‐Heterocyclic Nitrenium‐Based Ligands (Chem. Eur. J. 19/2015)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
69.
Walter N. Harrington Christina M. Kackos Richard J. Webby 《Experimental & molecular medicine》2021,53(5):737
The influenza virus is a global threat to human health causing unpredictable yet recurring pandemics, the last four emerging over the course of a hundred years. As our knowledge of influenza virus evolution, distribution, and transmission has increased, paths to pandemic preparedness have become apparent. In the 1950s, the World Health Organization (WHO) established a global influenza surveillance network that is now composed of institutions in 122 member states. This and other surveillance networks monitor circulating influenza strains in humans and animal reservoirs and are primed to detect influenza strains with pandemic potential. Both the United States Centers for Disease Control and Prevention and the WHO have also developed pandemic risk assessment tools that evaluate specific aspects of emerging influenza strains to develop a systematic process of determining research and funding priorities according to the risk of emergence and potential impact. Here, we review the history of influenza pandemic preparedness and the current state of preparedness, and we propose additional measures for improvement. We also comment on the intersection between the influenza pandemic preparedness network and the current SARS-CoV-2 crisis. We must continually evaluate and revise our risk assessment and pandemic preparedness plans and incorporate new information gathered from research and global crises.Subject terms: Influenza virus, Infectious diseases 相似文献
70.
Thalia Tsiaka Panagiotis Zoumpoulakis Vassilia J. Sinanoglou Constantinos Makris Georgios A. Heropoulos Antony C. Calokerinos 《Analytica chimica acta》2015
High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE. 相似文献