全文获取类型
收费全文 | 62434篇 |
免费 | 1647篇 |
国内免费 | 825篇 |
专业分类
化学 | 29962篇 |
晶体学 | 894篇 |
力学 | 3491篇 |
综合类 | 32篇 |
数学 | 5204篇 |
物理学 | 25323篇 |
出版年
2022年 | 507篇 |
2021年 | 610篇 |
2020年 | 642篇 |
2019年 | 615篇 |
2018年 | 744篇 |
2017年 | 632篇 |
2016年 | 1155篇 |
2015年 | 851篇 |
2014年 | 1238篇 |
2013年 | 2856篇 |
2012年 | 2773篇 |
2011年 | 3439篇 |
2010年 | 2407篇 |
2009年 | 2444篇 |
2008年 | 3037篇 |
2007年 | 2816篇 |
2006年 | 2676篇 |
2005年 | 2372篇 |
2004年 | 2149篇 |
2003年 | 1879篇 |
2002年 | 1673篇 |
2001年 | 3057篇 |
2000年 | 2159篇 |
1999年 | 1577篇 |
1998年 | 1091篇 |
1997年 | 1065篇 |
1996年 | 875篇 |
1995年 | 826篇 |
1994年 | 737篇 |
1993年 | 645篇 |
1992年 | 963篇 |
1991年 | 961篇 |
1990年 | 870篇 |
1989年 | 759篇 |
1988年 | 734篇 |
1987年 | 800篇 |
1986年 | 659篇 |
1985年 | 888篇 |
1984年 | 824篇 |
1983年 | 569篇 |
1982年 | 563篇 |
1981年 | 535篇 |
1980年 | 494篇 |
1979年 | 617篇 |
1978年 | 644篇 |
1977年 | 658篇 |
1976年 | 573篇 |
1975年 | 482篇 |
1974年 | 523篇 |
1973年 | 449篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Two new octahedral [Ni(phen)2(dppz-idzo)]2+ and [Co(phen)2(dppz-idzo)]3+ complexes have been synthesized and characterized by CHN analysis, electrospray ionization-MS, nuclear magnetic resonance, and UV–Vis spectra. The DNA-binding ability of these complexes was spectrophotometrically, hydrodynamically, and electrophoretically evaluated which indicated that they strongly intercalate into the DNA double helix, and that both induced severe DNA damage in the presence of peroxide. The complexes also showed strong antiproliferative effect against HepG2 and MDA-MB-231 cells. By contrast, they were found to be inactive against the MCF-7 cell line. The ligand itself was found to be inactive against the cells tested. 相似文献
22.
A multivariate calibration method was applied to improve the accuracy of the determination of cadmium in the presence of potassium by total reflection X-ray fluorescence (TXRF). Due to TXRF's relatively low resolution, a particular interference caused by potassium at line Kα 3.31 keV as interference can compromise the cadmium determination at line Lα 3.13 keV, respectively. The method is based on the hypothesis that the application of a multivariate calibration method, for example, partial least squares, could reduce variations due to interference and, consequently, improve the selectivity and accuracy in Cd determination. In this work, this strategy was evaluated on the X-ray fluorescence emission signals between 2.50 and 3.90 keV for a set of 26 different synthetic calibration mixtures and eight different mixtures for external calibration. Based on a certified reference material (Clay 2—CRM051) with high potassium levels, a significant improvement of accuracy for cadmium determination was observed, overcoming the problems associated with spectral interferences by potassium. 相似文献
23.
We proposed an electro-optic modulator with two-bus one-ring (TBOR) structure to improve the extinction ratio and reduce insert loss. It has a dual output compared with one-bus one-ring structure. In addition, double-layer graphene makes it possible for the modulation in the visible to mid-infrared wavelength range. It shows that this new electro-optic modulator can present two switching states well with low insertion loss, high absorption and high extinction ratio. At , when the switching states are based on the chemical potential, and , the insertion losses of both output ports are less than 2 dB, the absorption of the output port coupled via a micro-ring reaches 45 dB and the extinction ratio reaches 14 dB. When the refractive index of the dielectric material is 4.2, the applied voltage will be less than 1.2 V, thus can be used in low-voltage CMOS technology. 相似文献
24.
High pressure can effectively control the phase transition of MoTe2 in experiment, but the mechanism is still unclear. In this work, we show by first-principles calculations that the phase transition is suppressed and phase becomes more stable under high pressure, which originates from the pressure-induced change of the interlayer band occupancies near the Fermi energy. Specifically, the interlayer states of phase tend to be fully occupied under high pressure, while they keep partially occupied for the phase. The increase of the band occupancies makes the phase more favorable in energy and prevents the structure changing from to phase. Moreover, we also analyze the superconductivity under high pressure based on BCS theory by calculating the density of states and phonon spectra. Our results may shed some light on understanding the relationship between the interlayer band occupancy and crystal stability of MoTe2 under high pressures. 相似文献
25.
26.
Experimental Mechanics - Simulating the deformations of soft tissues has gained importance in recent years due to the development of 3D patient-specific biomechanical models in the context of... 相似文献
27.
Yongtao Bai Lihua Song Yongheng Zhang Guoliang Dai Weidong Zhang Shanshan Song Hong Sun Wen Jing Meijuan Xu Wenzheng Ju 《Biomedical chromatography : BMC》2019,33(9)
A highly selective and efficient LC–MS/MS method was developed to determine the plasma concentration of magnolol, hesperidin, neohesperidin and geniposide following oral administration of Zhi‐Zi‐Hou‐Po decoction in normal and depressed rats. Plasma samples were pretreated by protein precipitation with methanol. Chromatographic separation was performed on an XTerra® MS C18 column using a gradient elution with a mobile phase composed of acetonitrile–0.1% aqueous formic acid. The proposed method was validated to be specific, accurate and precise for the analytes determination in plasma samples. The calibration curves displayed good linearity over definite concentration ranges for the analytes. The intra‐ and inter‐day precision of the proposed method at three different levels were all within <11.13% and the relative errors ranged from ?8.46 to 8.93%. The recovery of the four compounds ranged from 82.72 to 89.08% and no apparent matrix effect was observed during sample analysis. After full validation, the established method was successfully applied for comparing the pharmacokinetics of four components between normal and depressed rats. The results showed that the AUC and Cmax of four analytes in depressed rats were significantly different from those in normal rats and might provide helpful information to guide the clinical use of Zhi‐Zi‐Hou‐Po to treat depression. 相似文献
28.
Tyrosine nitration of human ERK1 introduces an intra-hydrogen bond by molecular dynamics simulations
Xu Wu Zhang Yuanya Achi Oliver Y. Knierim Kathleen D. Hanks Justin G. Wang Yingchun 《Structural chemistry》2019,30(4):1459-1470
Structural Chemistry - ERK1 is an important kinase in Ras–Raf–MEK signaling. We have recently demonstrated by mass spectrometry that Tyr210 of ERK1 can be nitrated, and the nitration... 相似文献
29.
Guo J. Dadashi S. Bender M. Paruchuri S. T. Powell N. Sharma Y. Kurdila H. McGlothlin J. W. Kurdila A. J. 《Nonlinear dynamics》2019,98(1):195-213
Nonlinear Dynamics - In contrast to many systems studied in the field of classical mechanics, models of animal motion are often distinguished in that they are both highly uncertain and evolve in a... 相似文献
30.
Zhu Hong Zeng Xiangbing Han Tianli Li Xuexue Zhu Shuguang Sun Bai Zhou Ping Liu Jinyun 《Journal of Solid State Electrochemistry》2019,23(7):2173-2180
Journal of Solid State Electrochemistry - Since conventional graphite-based anode possesses a low capacity, seeking for high-capacity anode candidates becomes significant for constructing emerging... 相似文献