全文获取类型
收费全文 | 6077篇 |
免费 | 620篇 |
国内免费 | 3篇 |
专业分类
系统科学 | 1080篇 |
教育与普及 | 2篇 |
理论与方法论 | 279篇 |
现状及发展 | 1020篇 |
研究方法 | 87篇 |
综合类 | 4216篇 |
自然研究 | 16篇 |
出版年
2018年 | 728篇 |
2017年 | 733篇 |
2016年 | 434篇 |
2015年 | 31篇 |
2014年 | 3篇 |
2013年 | 12篇 |
2012年 | 292篇 |
2011年 | 997篇 |
2010年 | 818篇 |
2009年 | 458篇 |
2008年 | 531篇 |
2007年 | 785篇 |
2006年 | 25篇 |
2005年 | 74篇 |
2004年 | 143篇 |
2003年 | 167篇 |
2002年 | 71篇 |
2001年 | 25篇 |
2000年 | 26篇 |
1999年 | 14篇 |
1998年 | 3篇 |
1994年 | 5篇 |
1992年 | 6篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1974年 | 15篇 |
1973年 | 14篇 |
1972年 | 4篇 |
1971年 | 8篇 |
1970年 | 13篇 |
1969年 | 12篇 |
1968年 | 11篇 |
1967年 | 13篇 |
1966年 | 15篇 |
1965年 | 12篇 |
排序方式: 共有6700条查询结果,搜索用时 46 毫秒
991.
Precise orbit determination for geostationary satellites with multiple tracking techniques 总被引:5,自引:0,他引:5
A new precise orbit determination (POD) strategy based on the combination of satellite laser ranging (SLR) and C-band transfer ranging for geostationary satellites (GEO) is presented.Two approaches to calibrate ranging biases of the C-band ranging system are proposed,namely the two tracking system co-location comparison and the combined POD method,with calibration accuracies estimated to be 0.5 ns and 1 ns respectively.Using data from a C-band tracking network in China,POD experiments indicate that meter-le... 相似文献
992.
XiShuang Li YueXia Zhao BaoHua Liu ChenGuang Liu YanLiang Pei GuoZhong Han QingFeng Hua 《科学通报(英文版)》2010,55(18):1908-1916
The Tan-Lu Fault zone (TLFZ) is a significant fractural zone in eastern China and also a seismicity belt in North China. Based on total 4000-km-long shallow penetrated single seismic data with high-resolution, structural deformation and fault activity of the TLFZ in the Bohai Sea since the late Pleistocene are discussed in detail. The results show that the TLFZ with a discontinuous distribution and a general NNE-trending consists of 14 active subfaults with an NNE or NE strike in the Bohai Sea. Seismic data reveal that de-formation zones along the subfaults in the central Bohai Sea and the Laizhou Bay are wider and more complex than those in the Liaodong Gulf. Related folds and lots of secondary normal faults which are characterized by nearly vertical fault planes and a same or reverse dip construct the fractural zone in the Laizhou Bay and the central Bohai Sea. Usually, micro symmetrical grabens develop on the top of anticlines. In the Liaodong Gulf, subfault fractural zones usually consist of secondary normal faults with the same inclination or opposite inclination. Ages of seismic sequences and cutting relation between subfaults and seismic sequences suggest that the latest faulting age of the TLFZ is the end of the late Pleistocene in the Liaodong Gulf and the early Holocene in the Laizhou Bay and the central Bohai Sea. There is a good match between distribution of earthquakes and that of the subfaults in the Laizhou Bay and the central Bohai. Statistical result shows that total vertical offset of the TLFZ since the late Pleistocene ranges from 6 to 11 m. On the basis of offsets of the subfaults, the vertical slip rate is calculated and results show that average vertical slip rates in the central Bohai Sea are larger than those in the Liaodong Gulf and the Laizhou Bay. Slip rates more than 0.06 mm/a during 23–10 ka B.P. and 85–65 ka B.P. are larger than those in other stages. The TLFZ was mainly dominated by tensional normal component since the late Pleistocene. Synthesizing shallow deformation, activity and distribution of earthquakes, the TLFZ in the Bohai Sea can be divided into three segments: the Laizhou-Bay segment, the Bozhong segment, and the Liaodong-Gulf segment. 相似文献
993.
The volume-surface integral equation(VSIE) ,the surface integral equation(SIE) and the volume integral equation(VIE) of EM scattering problem are converted into linear equations with the method of moment,then the precorrected-FFT method is used to solve the linear equations.To overcome the drawback of conventional stencil topology,two kinds of improved stencil topology,stencil topology B and stencil topology C,are presented,and the construction and actual performance of the three kinds of stencil topology a... 相似文献
994.
Phoshpine (PH3), a volatile and toxic gas, has been proved to commonly exist in the environment. The determination of gaseous phosphine and its emission fluxes in Ny-Ålesund is reported in this paper. Results showed that gaseous phosphine exist in Arctic atmosphere commonly and the concentration of phosphine ranged from 16.3–600.2 ng/m3, with the maximum concentration of phosphine in tundra areas and the minimum in surface air of ocean. The concentration of phosphine ranged from 65.79–1259 ng/m3 in colliery atmosphere at different altitudes and the maximum was found in the center of colliery. Emission fluxes of phosphine were different in various Arctic areas. Emission fluxes of phosphine from protected areas, with average concentration of 32.13±5.353 ng m–2 h–1, were higher than from other areas. And the flux of phosphine from ocean was lower. 相似文献
995.
Easily accessible (1R,2S)-1,2-diphenyl-2-formamidoethanol has been developed as an effective Lewis base catalyst in the enanti-oselective hydrosilylation of ketimines, affording high isolated yields (up to 94%) and moderate to high enantioselectivities (up to 82% ee) for a broad range of ketimines. 相似文献
996.
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
997.
Randomly oriented ZnO microsheets were successfully self-assembled on TiO2 nanoparticle (TN) film to act as the scattering layer via a cathodic electrodeposition process. The light scattering properties of ZnO microsheets were studied by UV-Vis spectrometer in the 400–800 nm wavelength range. It was found that ZnO microsheets exhibited excellent ability to scatter the incident light for ZnO microsheet-TiO2 nanoparticle (ZT) composite films. The results showed that dye-sensitized solar cells (DSSCs) fabricated with ZT composite films showed higher short-circuit density (Jsc) and conversion efficiency than TN-based DSSCs, due to the light scattering properties of ZnO microsheets. 相似文献
998.
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
999.
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
1000.
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