全文获取类型
收费全文 | 5512篇 |
免费 | 597篇 |
国内免费 | 2篇 |
专业分类
系统科学 | 1075篇 |
理论与方法论 | 275篇 |
现状及发展 | 878篇 |
研究方法 | 6篇 |
综合类 | 3875篇 |
自然研究 | 2篇 |
出版年
2024年 | 1篇 |
2020年 | 2篇 |
2018年 | 727篇 |
2017年 | 732篇 |
2016年 | 433篇 |
2015年 | 30篇 |
2014年 | 5篇 |
2013年 | 4篇 |
2012年 | 262篇 |
2011年 | 957篇 |
2010年 | 817篇 |
2009年 | 459篇 |
2008年 | 513篇 |
2007年 | 768篇 |
2006年 | 7篇 |
2005年 | 48篇 |
2004年 | 127篇 |
2003年 | 154篇 |
2002年 | 58篇 |
2000年 | 1篇 |
1994年 | 2篇 |
1991年 | 3篇 |
1967年 | 1篇 |
排序方式: 共有6111条查询结果,搜索用时 23 毫秒
991.
Feng Han 《科学通报(英文版)》2010,55(17):1758-1762
We study the entanglement dynamics for a double Jaynes-Cummings model where two entangled atoms A and B locally interact with independent cavities a and b, respectively, but there are no interactions between locations Aa and Bb. We point out that there exists a parameter range in which simultaneous pairwise entanglement sudden death (ESD) for remote parties, i.e. AB, ab, Ab and Ba, may occur. We show that during this simultaneous ESD period various multipartite entanglement can be created. Our results imply that the pairwise entanglement between two independent locations may be transferred into other multipartite forms which account for the correlations between the two independent locations. 相似文献
992.
The calcifying phytoplankton species,coccolithophores,have their calcified coccoliths around the cells,however,their physio-logical roles are still unknown.Here,we hypothesized that the coccoliths may play a certain role in reducing solar UV radiation(UVR,280-400 nm) and protect the cells from being harmed.Cells of Emiliania huxleyi with different thicknesses of the cocco-liths were obtained by culturing them at different levels of dissolved inorganic carbon and their photophysiological responses to UVR wer... 相似文献
993.
Based on the recent research progress in fractal super fibers,the growth kinematics(or pattern kinematics) of(6+1) -circle fractal super fiber with snowflake-like cross section(abbreviated asfractal super snowflake) is explored.The following results are obtained.(1) The fractal super snowflake obeys simply the straight-line growth mode.(2) At a given movement,the growth speed of the snowflake distributes uniformly in space.At a given point in space,the growth speed decreases along with the time.(3) The grow... 相似文献
994.
Heng Mei ZhiQing Pang Yu Hu Wei Shi HuaFang Wang Jun Deng Tao Guo XinGuo Jiang 《科学通报(英文版)》2010,55(30):3424-3429
In order to examine the effect of EGF1 peptides in directing nanoparticles to thrombi, the synthesized EGF1 peptide was conjugated to poly (ethyleneglycol)-poly (lactide) (PEG-PLA) nanoparticles (NP) to form EGF1-NP. A lipophilic fluorescent dye, coumarin-6, was incorporated into EGF1-NP so as to detect its loading and release capacity. The binding ability of EGF1-NP with TF-expressing cells was shown to be significantly higher than that of the non-conjugated NP. Following an intravenous administration, fluorescence was distributed along the vessel wall of the thrombosis regions in the model rats injected with coumarin-6-loaded EGF1-NP. The in vitro and in vivo results suggest that EGF1-NP is a promising drug delivery system for targeting cerebral thrombi. 相似文献
995.
Effects of typhoon Matsa on ionospheric TEC 总被引:3,自引:0,他引:3
The effects of typhoon Matsa on the ionosphere are studied by using GPS-TEC data observed at about 50 GPS stations.It is shown that the ionosphere has been already influenced and TEC tends to increase before the landing of Matsa,and the difference of TEC from its monthly median over the typhoon area is about 5 TECU.With the landing of Matsa,both the magnitude and the area of increased TEC decrease.One day after the landing of Matsa,TEC reaches its minimum and is lower than the monthly median.In comparison o... 相似文献
996.
Progress on gecko-inspired micro/nano-adhesion arrays 总被引:2,自引:0,他引:2
Gecko’s excellent adhesion ability is thought to derive from van der Waals force generated between the millions of keratinous hairs/setae and the contact surface. Fabricating highly gecko-inspired foot-hair becomes one of the key technologies to realize the three-dimensional-obstacle-free motion of robot. Researchers have fabricated various gecko-like foot-hair arrays which have leaning, large end, and hierarchical structures. Those significant works are summarized and suggestions for future work are proposed in this paper. 相似文献
997.
Dynamics of phytoplankton and picoplankton over a tidal cycle in a subtropical lagoon 总被引:1,自引:0,他引:1
Kwee Siong Tew Pei-Jie Meng Hung-Jen Lee Yi-Xiu Ye Jimmy Kuo Lee-Shing Fang Wei-Rung Chou 《科学通报(英文版)》2010,55(23):2522-2528
The influences of a tidal cycle on the distribution of autotrophic plankton were investigated in a hyper-eutrophic lagoon designated as a scenic area. Results showed that the highest concentrations of picoplankton and phytoplankton were found in the middle and inner part of the lagoon, irrespective of the tides. The MDS result also revealed that phytoplankton communities, dominated by Ceratium furca, were similar among stations in the inner bay during both flood tides and ebb tides. The time series sampling results at the inlet-outlet channel revealed that almost the same amounts of phytoplankton and picoplankton were carried through the channel during flood and ebb tides, with no trend in nutrient fluctuations except for phosphate which had a net loss from the lagoon. The results showed that tidal cycles do not effectively flush away phytoplankton and picoplankton from the lagoon, and the blooming of phyto- and picoplankton is inevitable should the situation stay the same. Steps are needed to alleviate the eutrophication condition instead of depending on the natural process such as tidal cycle. 相似文献
998.
I-doping of anodized TiO<Subscript>2</Subscript> nanotubes using an electrochemical method 总被引:1,自引:0,他引:1
In order to obtain TiO2 with high photocatalytic activity, a cathode reduction was used to dope I7+ and I5+ into TiO2 nanotubes of anodized Ti in C2H2O4•2H2O + NH4F electrolyte. SEM images show that the anodization method integrated the preparation with the doping process, which for nonmetals-doping is advantageous to maintain the morphological integrity of TiO2 nanotubes. I7+-I5+-doping enhances the UV response of TiO2 and result in a red-shift. Under UV/visible irradiation, a I7+-I5+-doped sample (400°C) showed the highest Iph and photocatalytic efficiency. A part of I– in the I7+-I5+-doped sample is involved in the UV response, the red-shift and the higher Iph. 相似文献
999.
Perfluorinated compounds in milk,milk powder and yoghurt purchased from markets in China 总被引:1,自引:0,他引:1
The exposure to perfluorinated compounds (PFCs) through the diet for humans is of great concern. Among the diet, dairy products are in great demand. This paper reports the study on the levels of 9 perfluorinated acids and 2 fluorotelomer acids in milk, milk powder and yoghurt purchased from Chinese markets from 2008 to 2009. The analytes were quantitated by high performance liquid chromatography/electrospray tandem mass spectrometry (HPLC-ESI-MS/MS). In milk samples, perfluoroheptanoic acid (PFHpA) and perf... 相似文献
1000.
YaoMing Xiao JiHuai Wu QingHua Li GuiXiang Xie GenTian Yue HaiFeng Ye Zhang Lan MiaoLiang Huang JianMing Lin 《科学通报(英文版)》2010,55(10):980-985
A TiO2 slurry was prepared by hydrothermal treating mixture of commercial TiO2 (P25),ethanol and distilled water in an autoclave.A flexible photoanode and dye-sensitized solar cell (DSSC) was fabricated on an ITO-coated poly (ethylene naphthalate) sheet (ITO/PEN) substrate by a doctor-blade technique.The sample was characterized with SEM,UV-vis,FTIR,and the photoelectric properties of the DSSC were measured.The influence of preparation conditions on the properties of the flexible DSSC was investigated.It is... 相似文献