全文获取类型
收费全文 | 3308篇 |
免费 | 222篇 |
国内免费 | 19篇 |
专业分类
化学 | 2489篇 |
晶体学 | 35篇 |
力学 | 53篇 |
数学 | 264篇 |
物理学 | 708篇 |
出版年
2023年 | 10篇 |
2022年 | 13篇 |
2021年 | 68篇 |
2020年 | 66篇 |
2019年 | 74篇 |
2018年 | 51篇 |
2017年 | 49篇 |
2016年 | 142篇 |
2015年 | 107篇 |
2014年 | 154篇 |
2013年 | 222篇 |
2012年 | 286篇 |
2011年 | 304篇 |
2010年 | 180篇 |
2009年 | 167篇 |
2008年 | 225篇 |
2007年 | 221篇 |
2006年 | 179篇 |
2005年 | 167篇 |
2004年 | 187篇 |
2003年 | 123篇 |
2002年 | 106篇 |
2001年 | 50篇 |
2000年 | 50篇 |
1999年 | 21篇 |
1998年 | 19篇 |
1997年 | 16篇 |
1996年 | 28篇 |
1995年 | 25篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 36篇 |
1991年 | 19篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 17篇 |
1984年 | 7篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1974年 | 11篇 |
1973年 | 4篇 |
排序方式: 共有3549条查询结果,搜索用时 17 毫秒
41.
Chang-Ho Kang Sang-Hyun Han YuJin Shin Soo Ji Oh Jae-Seong So 《Applied biochemistry and biotechnology》2014,172(6):2907-2915
Contamination by Cd is a significant environmental problem. Therefore, we examined Cd removal from an environmental perspective. Ureolysis-driven calcium carbonate precipitation has been proposed for use in geotechnical engineering for soil remediation applications. In this study, 55 calcite-forming bacterial strains were newly isolated from various environments. Biomineralization of Cd by calcite-forming bacteria was investigated in laboratory-scale experiments. A simple method was developed to determine the effectiveness of microbially induced calcite precipitation (MICP). Using this method, we determined the effectiveness of biomineralization for retarding the flow of crystal violet through a 25-mL column. When the selected bacteria were analyzed using an inductively coupled plasma optical emission spectrometer, high removal rates (99.95 %) of Cd were observed following incubation for 48 h. Samples of solids that formed in the reaction vessels were examined using a scanning electron microscope. The CdCO3 compounds primarily showed a spherical shape. The results of this study demonstrate that MICP-based sequestration of soluble heavy metals via coprecipitation with calcite may be useful for toxic heavy metal bioremediation. 相似文献
42.
43.
Principal component analysis (PCA) is a canonical tool that reduces data dimensionality by finding linear transformations that project the data into a lower dimensional subspace while preserving the variability of the data. Selecting the number of principal components (PC) is essential but challenging for PCA since it represents an unsupervised learning problem without a clear target label at the sample level. In this article, we propose a new method to determine the optimal number of PCs based on the stability of the space spanned by PCs. A series of analyses with both synthetic data and real data demonstrates the superior performance of the proposed method. 相似文献
44.
45.
The polyphenolic profiles and antioxidant effects of Agastache rugosa Kuntze (Banga) flower,leaf, stem and root 下载免费PDF全文
Yun‐Hi Kim Won Sup Lee Soo Jung Lee Jong Sung Jin A. M. Abd El‐Aty Ho‐Chul Shin Jae‐Han Shim Sung Chul Shin 《Biomedical chromatography : BMC》2016,30(2):225-231
Agastache rugosa Kuntze (Korean mint) is used as a spice and in folk medicine in East Asia. The present study identified a total of 18 polyphenols from the flower, leaf, stem and roots of this plant using high‐performance liquid chromatography–tandem mass spectrometry. Fourteen of these compounds had not previously been identified in these plant tissues. Each polyphenol was validated in comparison with external calibration curves constructed using structurally related compounds, with determination coefficients >0.9993. The limits of detection and quantification were 0.092–0.650 and 0.307–2.167 mg/L, respectively. Recoveries of 61.92–116.44% were observed at two spiking levels, with 0.91–11% precision, expressed as relative standard deviation (except anthraquinone spiked at 10 mg/L). Hydroxycinnamic acid was the most abundant compound in the root, while the flowers showed the highest total flavonoid level. Antioxidant activities, determined in terms of reducing power, Fe2+ chelating activity and the radical scavenging activities using α,α‐diphenyl‐β‐picrylhydrazyl and 2‐2?‐azino‐bis‐3‐ethylbenzothiazoline‐6‐sulfonic acid, increased in a concentration‐dependent manner; the highest activity was identified in the stems, followed by leaves > flowers > roots. These findings indicate that A. rugosa is a good source of bioactive compounds and can be used as a functional food. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
46.
47.
48.
49.
50.