全文获取类型
收费全文 | 253716篇 |
免费 | 6383篇 |
国内免费 | 4856篇 |
专业分类
化学 | 132767篇 |
晶体学 | 3591篇 |
力学 | 13948篇 |
综合类 | 329篇 |
数学 | 31317篇 |
物理学 | 83003篇 |
出版年
2021年 | 3390篇 |
2020年 | 3795篇 |
2019年 | 4346篇 |
2018年 | 5572篇 |
2017年 | 5577篇 |
2016年 | 6806篇 |
2015年 | 3900篇 |
2014年 | 6449篇 |
2013年 | 11059篇 |
2012年 | 9794篇 |
2011年 | 11002篇 |
2010年 | 8936篇 |
2009年 | 9043篇 |
2008年 | 9977篇 |
2007年 | 9643篇 |
2006年 | 8652篇 |
2005年 | 7655篇 |
2004年 | 7198篇 |
2003年 | 6504篇 |
2002年 | 6705篇 |
2001年 | 6977篇 |
2000年 | 5243篇 |
1999年 | 4141篇 |
1998年 | 3819篇 |
1997年 | 3501篇 |
1996年 | 3273篇 |
1995年 | 2915篇 |
1994年 | 2914篇 |
1993年 | 2892篇 |
1992年 | 2887篇 |
1991年 | 3204篇 |
1990年 | 3117篇 |
1989年 | 3112篇 |
1988年 | 2891篇 |
1987年 | 2903篇 |
1986年 | 2717篇 |
1985年 | 3252篇 |
1984年 | 3287篇 |
1983年 | 2870篇 |
1982年 | 2905篇 |
1981年 | 2733篇 |
1980年 | 2511篇 |
1979年 | 2913篇 |
1978年 | 3059篇 |
1977年 | 3146篇 |
1976年 | 3325篇 |
1975年 | 3030篇 |
1974年 | 2995篇 |
1973年 | 3173篇 |
1972年 | 2625篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Yu Wang Xin-jing Zhao Rong-Jing Wei Gui-jie Liang Kang Wang Yuan-zhi Tan Ye Yang 《化学物理学报(中文版)》2021,34(5):591-597
The intermolecular interaction determines the photophysical properties of the organic aggregates, which are critical to the performance of organic photovoltaics. Here, excitonic coupling, an important intermolecular interaction in organic aggregates, between the π-stacking graphene quantum dots is studied by using transient absorption spectroscopy. We find that the spectral evolution of the ground state bleach arises from the dynamic variation of the excitonic coupling in the excited π-stacks. According to the spectral simulations, we demonstrate that the kinetics of the vibronic peak can be exploited as a probe to measure the dynamics of excitonic coupling in the excited π-stacks. 相似文献
182.
A zinc coordination polymer derived from pyridine-2,6-dicarboxylate (PDC), {[Zn2(PDC)2]}n, was successfully prepared via conventional, sonication and microwave-irradiation methods. The composition and characteristics of the obtained coordination polymers (CPs) were investigated by elemental analysis, TGA/DTA, X-ray diffraction and spectroscopic techniques. The so obtained CPs were heat-treated in the air at 600 °C for 2 h to produce ZnO of nanosized particles (NPs). It is of interest to note that the synthesis approach of the precursor greatly affects both the nanoparticle size and the structure of the resulting ZnO NPs. Moreover, the smallest particle size was associated with the sample derived from the ultrasonically prepared precursor. TEM analysis revealed that all samples have sphere-like morphologies. Structural analysis of the prepared ZnO samples was conducted and compared using Rietveld analysis of their PXRD patterns. Optical band gap calculations based on analysis of the UV–vis spectra of ZnO samples using Tauc's power law were achieved. The highest band gap of 3.63 eV was observed for ZnO sample obtained from the ultrasonically prepared precursor. Furthermore, the photocatalytic activity of ZnO NPs for the removal of Eosin Y color was monitored. The highest removal efficiency was recorded for ZnO originated from the ultrasonically synthesized precursor. Enhancement of removal efficiency that reached 98% was attained in only a period of 8 min. Its recycling test showed that it can be reused without structural changes over four cycling experiments. 相似文献
183.
Xiao Sun Li Zhang Yu Cao Jinhua Li Atanas G. Atanasov Linfang Huang 《Biomedical chromatography : BMC》2020,34(12):e4949
Balanophora involucrata J. D. Hooker has been known to possess potential anti-inflammatory and antibacterial activities; however, its antiviral activity has not been evaluated so far. In order to find new neuraminidase inhibitors (NAIs), the neuraminidase (NA) inhibition activity of different B. involucrata extracts was evaluated. In this study, an in vitro NA inhibition assay was performed to identify which extract of B. involucrata exhibits (maximal) inhibitory activity against NA. Ultra high performance liquid chromatography/quadrupole time-of-flight–tandem mass spectroscopy (MS/MS) and molecular docking techniques were used to identify the specific compounds responsible for the anti-influenza activity of the extract, and to explore the potential natural NAIs. The ethyl acetate extract of B. involucrata exhibited significant inhibitory activity against NA with 50% inhibitory concentration (IC50) value of 159.5 μg/mL. Twenty compounds were identified according to the MS/MS spectra; among them two compounds (quercitrin and phloridzin) showed obvious inhibitory activity against NA, with IC50 of 311.76 and 347.32 μmol/L, respectively. This study suggested that B. involucrata can be a potential natural source of NAIs and may be useful in the fight against ferocious influenza viruses. 相似文献
184.
185.
Galia Pozina Elizaveta I. Girshova Konstantin M. Morozov Konstantin A. Ivanov Anton Yu. Egorov Mikhail A. Kaliteevski 《Annalen der Physik》2019,531(6)
Enhancement of spontaneous emission in a resonant Bragg quantum well (QW) structure with 60 periods of triple InAs monolayers embedded in a GaAs matrix is studied experimentally and theoretically. From measurements of the time‐resolved photoluminescence, besides the QW exciton at 1.47 eV, a specific super‐radiant (SR) emission demonstrating nonlinear properties is found. The SR mode shows a near‐quadratic dependence of intensity on excitation power, while its energy position follows the Bragg condition. It is revealed that the SR mode shows a peculiar non‐monotonic dependence of intensity on direction, with a maximum observed at approximately 40°. The enhancement in the SR emission at a specific direction is correlated well with suggested theoretical consideration of the modal Purcell factor for periodic quantum well structures. 相似文献
186.
Tereshchenko E. D. Cherniakov S. M. Yurik R. Yu. Rietveld M. T. Häggström I. 《Radiophysics and Quantum Electronics》2020,62(10):667-676
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar... 相似文献
187.
Doklady Mathematics - In this paper, for the first time, we provide a quasi-polynomial time approximation scheme for the well-known capacitated vehicle routing problem formulated in metric spaces... 相似文献
188.
Radiophysics and Quantum Electronics - We consider whether it is possible in principle to retrieve the key parameters of the mixed layer in the upper ocean (its thickness, bulk eddy viscosity and... 相似文献
189.
Siberian Mathematical Journal - Under study are the right-symmetric algebras over a field $ F $ which possess a “unital” matrix subalgebra $... 相似文献
190.
N. I. Golovina G. N. Nechiporenko G. G. Nemtsev G. P. Dolganova V. P. Roshchupkin D. B. Lempert G. B. Manelis 《Russian Journal of Applied Chemistry》2007,80(1):24-30
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined. 相似文献