全文获取类型
收费全文 | 215017篇 |
免费 | 3655篇 |
国内免费 | 1984篇 |
专业分类
化学 | 109999篇 |
晶体学 | 3420篇 |
力学 | 10128篇 |
综合类 | 100篇 |
数学 | 23882篇 |
物理学 | 73127篇 |
出版年
2021年 | 1935篇 |
2020年 | 2181篇 |
2019年 | 2337篇 |
2018年 | 3004篇 |
2017年 | 2891篇 |
2016年 | 4209篇 |
2015年 | 2727篇 |
2014年 | 4168篇 |
2013年 | 9876篇 |
2012年 | 8108篇 |
2011年 | 9673篇 |
2010年 | 6674篇 |
2009年 | 6600篇 |
2008年 | 8641篇 |
2007年 | 8770篇 |
2006年 | 8383篇 |
2005年 | 7489篇 |
2004年 | 6903篇 |
2003年 | 6028篇 |
2002年 | 5819篇 |
2001年 | 6724篇 |
2000年 | 5199篇 |
1999年 | 4099篇 |
1998年 | 3360篇 |
1997年 | 3305篇 |
1996年 | 3046篇 |
1995年 | 2833篇 |
1994年 | 2705篇 |
1993年 | 2492篇 |
1992年 | 2832篇 |
1991年 | 2799篇 |
1990年 | 2733篇 |
1989年 | 2477篇 |
1988年 | 2529篇 |
1987年 | 2534篇 |
1986年 | 2361篇 |
1985年 | 3030篇 |
1984年 | 3261篇 |
1983年 | 2662篇 |
1982年 | 2829篇 |
1981年 | 2795篇 |
1980年 | 2656篇 |
1979年 | 2742篇 |
1978年 | 2834篇 |
1977年 | 2826篇 |
1976年 | 2893篇 |
1975年 | 2656篇 |
1974年 | 2626篇 |
1973年 | 2765篇 |
1972年 | 1747篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Two new divalent copper (C1) and zinc (C2) chelates having the formulae [M(PIMC)2] (where M = Cu(II), Zn(II) and PIMC = Ligand [(E)-3-(((3-hydroxypyridin-2-yl)imino)methyl)-4H-chromen-4-one] were obtained and characterized by several techniques. Structures and geometries of the synthesized complexes were judged based on the results of alternative analytical and spectral tools supporting the proposed formulae. IR spectral data confirmed the coordination of the ligands to the copper and zinc centers as monobasic tridentate in the enol form. Thermal analysis, UV-Vis spectra and magnetic moment confirmed the geometry around the copper center to be tetrahedral, square pyramidal and octahedral. Study of the binding ability of the synthesized compounds with Circulating tumor DNA (CT-DNA) bas been evaluated applying UV-Vis spectral titration and viscosity measurements. The copper and zinc oxides were achieved from the copper and zinc nano-particles structures Schiff base complexes as the raw material after calcination for 5 hr at 600°C. On the other hand, synthesized of C1 and C2 NPs were used as suitable precursors to the preparation of CuO and ZnO NPs. Finally, the synthesized of the two complexes exhibited enhanced activity against the tested bacterial (Staphylococcus aureus and Escherichia Coli) and fungal strains (Candida albicans and Aspergillus fumigatus) as compared to HPIMC. Among all these synthesized compounds, C1 exhibits good cleaving ability compared to other newly synthesized C2. 相似文献
72.
Martín D. Safe 《Journal of Graph Theory》2020,93(2):268-298
A graph is concave-round if its vertices can be circularly enumerated so that the closed neighborhood of each vertex is an interval in the enumeration. In this study, we give a minimal forbidden induced subgraph characterization for the class of concave-round graphs, solving a problem posed by Bang-Jensen, Huang, and Yeo [SIAM J. Discrete Math., 13 (2000), pp. 179–193]. In addition, we show that it is possible to find one such forbidden induced subgraph in linear time in any given graph that is not concave-round. As part of the analysis, we obtain characterizations by minimal forbidden submatrices for the circular-ones property for rows and for the circular-ones property for rows and columns and show that, also for both variants of the property, one of the corresponding forbidden submatrices can be found (if present) in any given matrix in linear time. We make some final remarks regarding connections to some classes of circular-arc graphs. 相似文献
73.
JETP Letters - The leading role of the bremsstrahlung at resonant Compton scattering of a hard X-ray photon by a multielectron atom has been theoretically predicted. This result can be important in... 相似文献
74.
International Applied Mechanics - Problems of parametric optimization of rod structure stated in terms of the nonlinear programming problem are considered. Use is made of the method of projection... 相似文献
75.
76.
77.
78.
Metabolic profiles of dioscin in rats revealed by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
He Zhu Jin‐Di Xu Qian Mao Hong Shen Ming Kong Jian‐Ping Chen Song‐Lin Li 《Biomedical chromatography : BMC》2015,29(9):1415-1421
Dioscin (DIS), one of the most abundant bioactive steroidal saponins in Dioscorea sp., is used as a complementary medicine to treat coronary disease and angina pectoris in China. Although the pharmacological activities and pharmacokinetics of DIS have been well demonstrated, information regarding the final metabolic fates is very limited. This study investigated the in vivo metabolic profiles of DIS after oral administration by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry method. The structures of the metabolites were identified and tentatively characterized by means of comparing the molecular mass, retention time and fragmentation pattern of the analytes with those of the parent compound. A total of eight metabolites, including seven phase I and one phase II metabolites, were detected and tentatively identified for the first time. Oxidation, deglycosylation and glucuronidation were found to be the major metabolic processes of the compound in rats. In addition, a possible metabolic pathway on the biotransformation of DIS in vivo was proposed. This study provides valuable and new information on the metabolism of DIS, which will be helpful for further understanding its mechanism of action. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
79.
80.
E. A. Andrianova V. D. Davidenko V. F. Tsibulskiy S. V. Tsibulskiy 《Physics of Atomic Nuclei》2015,78(11):1252-1258
Influence of the nuclear energy structure, the conditions of fuel burnup, and accumulation of new fissile isotopes from the raw isotopes on the main parameters of a closed fuel cycle is considered. The effects of the breeding ratio, the cooling time of the spent fuel in the external fuel cycle, and the separation of the breeding area and the fissile isotope burning area on the parameters of the fuel cycle are analyzed. 相似文献