全文获取类型
收费全文 | 16381篇 |
免费 | 2569篇 |
国内免费 | 1871篇 |
专业分类
化学 | 11495篇 |
晶体学 | 157篇 |
力学 | 1001篇 |
综合类 | 122篇 |
数学 | 1648篇 |
物理学 | 6398篇 |
出版年
2024年 | 61篇 |
2023年 | 323篇 |
2022年 | 485篇 |
2021年 | 501篇 |
2020年 | 587篇 |
2019年 | 551篇 |
2018年 | 458篇 |
2017年 | 437篇 |
2016年 | 714篇 |
2015年 | 660篇 |
2014年 | 912篇 |
2013年 | 1144篇 |
2012年 | 1322篇 |
2011年 | 1416篇 |
2010年 | 960篇 |
2009年 | 945篇 |
2008年 | 1059篇 |
2007年 | 903篇 |
2006年 | 810篇 |
2005年 | 812篇 |
2004年 | 621篇 |
2003年 | 523篇 |
2002年 | 572篇 |
2001年 | 458篇 |
2000年 | 409篇 |
1999年 | 381篇 |
1998年 | 322篇 |
1997年 | 281篇 |
1996年 | 309篇 |
1995年 | 228篇 |
1994年 | 256篇 |
1993年 | 204篇 |
1992年 | 215篇 |
1991年 | 175篇 |
1990年 | 136篇 |
1989年 | 147篇 |
1988年 | 94篇 |
1987年 | 69篇 |
1986年 | 75篇 |
1985年 | 60篇 |
1984年 | 34篇 |
1983年 | 35篇 |
1982年 | 27篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1976年 | 11篇 |
1974年 | 12篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
用射频磁控溅射结合传统退火的方法制备LiCo0.8M0.2O2 (M=Ni,Zr)阴极薄膜.X射线衍射、拉曼光谱、扫描电子显微镜等手段表征了不同掺杂的LiCo0.8M0.2O2薄膜.结果显示,700℃退火的LiCo0.8M0.2O2薄膜具有类似α-NaFeO2的层状结构.通过对不同掺杂锂钴氧阴极的全固态薄膜锂电池Li/LiPON/LiCo0.8M0.2O2的电化学性能研究表明,电化学活性元素Ni的掺杂使全固态电池具有更大的放电容量(56μAh/cm2μm),而非电化学活性元素Zr的掺杂使全固态电池具有更好的循环稳定性. 相似文献
42.
计算全息图产生的锥面波在激光准直中的应用 总被引:1,自引:0,他引:1
本文提出了用计算全息图产生锥面波的方法.将全息图置于激光光路中,它的衍射图样中心在空间形成了一条准直线.文中对锥面波的传播、准直精度及准直距离作了理论分析,给出了实验结果. 相似文献
43.
Chen-Cheng Sun Shih-Chin Lee Yaw-Shyan Fu Yu-Hwe Lee 《Applied Surface Science》2006,252(23):8295-8300
CrNx thin films have attracted much attention for semiconductor IC packaging molding dies and forming tools due to their excellent hardness, thermal stability and non-sticking properties (low surface free energy). However, few data has been published on the surface free energy (SFE) of CrNx films at temperatures in the range 20-170 °C. In this study CrNx thin films with CrN, Cr(N), Cr2N (and mixture of these phases) were prepared using closed field unbalanced magnetron sputtering at a wide range of Cr+2 emission intensity. The contact angles of water, di-iodomethane and ethylene glycol on the coated surfaces were measured at temperatures in the range 20-170 °C using a Dataphysics OCA-20 contact angle analyzer. The surface free energy of the CrNx films and their components (e.g., dispersion, polar) were calculated using the Owens-Wendt geometric mean approach. The influences of CrNx film surface roughness and microstructure on the surface free energy were investigated by atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. The experimental results showed that the lowest total SFE was obtained corresponding to CrN at temperature in 20 °C. This is lower than that of Cr(N), Cr2N (and mixture of these phases). The total SFE, dispersive SFE and polar SFE of CrNx films decreased with increasing surface temperature. The film roughness has an obvious effect on the SFE and there is tendency for the SFE to increase with increasing film surface roughness. 相似文献
44.
Gu Chaohao 《数学年刊B辑(英文版)》1994,15(4):385-400
COMPLETEEXTREMALSURFACESOFMIXEDTYPEIN3-DIMENSIONALMINKOWSKISPACE¥GUCHAOHAO(InstituteofMathematics,FudanUniversity,Shanghai200... 相似文献
45.
Wei Zhou Ruonong Fu Rongji Dai Zaifu Huang Yanfei Chen 《Journal of separation science》1994,17(10):719-722
A new kind of side chain liquid crystalline polysiloxane containing a crown ether with a longer spacer (PSC-11) has been prepared and coated on a fused silica capillary column. The main chroma-tographic characteristics including efficiency, polarity, and selectivity have been examined. The phase exhibits the retention properties of both liquid crystal and crown ether stationary phases and possesses higher efficiency and better selectivity than PSC-3, which has a shorter spacer between the main polysiloxane chain and liquid crystalline side chain. 相似文献
46.
This paper reports a combined experimental and numerical investigation of three-dimensional steady turbulent flows in inlet manifolds of square cross-section. Predictions and measurements of the flows were carried out using computational fluid dynamics and laser Doppler anemometry techniques respectively. The flow structure was characterized in detail and the effects of flow split ratio and inlet flow rate were studied. These were found to cause significant variations in the size and shape of recirculation regions in the branches, and in the turbulence levels. It was then found that there is a significant difference between the flow rates through different branches. The performance of the code was assessed through a comparison between predictions and measurements. The comparison demonstrates that all important features of the flow are well represented by the predictions. 相似文献
47.
48.
Super-Wavelets and Decomposable Wavelet Frames 总被引:4,自引:0,他引:4
A wavelet frame is called decomposable whenever it is equivalent to a superwavelet frame of length greater than one. Decomposable
wavelet frames are closely related to some problems on super-wavelets. In this article we first obtain some necessary or sufficient
conditions for decomposable Parseval wavelet frames. As an application of these conditions, we prove that for each n > 1 there
exists a Parseval wavelet frame which is m-decomposable for any 1 < m ≤ n, but not k-decomposable for any k > n. Moreover,
there exists a super-wavelet whose components are non-decomposable. Similarly we also prove that for each n > 1, there exists
a Parseval wavelet frame that can be extended to a super-wavelet of length m for any 1 < m ≤ n, but can not be extended to
any super-wavelet of length k with k > n. The connection between decomposable Parseval wavelet frames and super-wavelets is
investigated, and some necessary or sufficient conditions for extendable Parseval wavelet frames are given. 相似文献
49.
R. Silvennoinen K. -E. Peiponen T. Asakura Yan-Fang Zhang Cong Gu K. Ikonen E. J. Morley 《Optics and Lasers in Engineering》1992,17(2)
The specular reflectance of cold-rolled aluminum surface is studied using a fiber optic system. An approximation for the determination of surface roughness is presented. 相似文献
50.
In this article, the linear and nonlinear shear rheological behaviors of polylactide (PLA)/clay (organophilic‐montmorillonite) nanocomposites (PLACNs) were investigated by an Advanced Rheology Expanded System rheometer. The nanocomposites were prepared by master batch method using a twin‐screw extruder with poly(ε‐caprolactone) (PCL) as a compatibilizer. The presence of org‐MMT leads to obvious pseudo‐solid‐like behaviors of nanocomposite melts. The behaviors caused by the formation of a “percolating network” derived from the reciprocity among the strong related sheet particles. Therefore, the storage moduli, loss moduli, and dynamic viscosities of PLACNs show a monotonic increase with MMT content. Nonterminal behaviors exists in PLACNs nanocomposites. Besides the PLACNs melts show a greater shear thinning tendency than pure PLA melt because of the preferential orientation of the MMT layers. Therefore, PLACNs have higher moduli but better processibility compared with pure PLA. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3189–3196, 2007 相似文献