全文获取类型
收费全文 | 129429篇 |
免费 | 2199篇 |
国内免费 | 1133篇 |
专业分类
化学 | 71962篇 |
晶体学 | 2074篇 |
力学 | 5331篇 |
综合类 | 33篇 |
数学 | 12585篇 |
物理学 | 40776篇 |
出版年
2016年 | 1461篇 |
2015年 | 1173篇 |
2014年 | 1542篇 |
2013年 | 5107篇 |
2012年 | 3759篇 |
2011年 | 4791篇 |
2010年 | 3002篇 |
2009年 | 2748篇 |
2008年 | 4216篇 |
2007年 | 4210篇 |
2006年 | 4264篇 |
2005年 | 4170篇 |
2004年 | 3624篇 |
2003年 | 3318篇 |
2002年 | 3213篇 |
2001年 | 3699篇 |
2000年 | 2790篇 |
1999年 | 2322篇 |
1998年 | 1962篇 |
1997年 | 1950篇 |
1996年 | 1885篇 |
1995年 | 1843篇 |
1994年 | 1595篇 |
1993年 | 1595篇 |
1992年 | 1800篇 |
1991年 | 1793篇 |
1990年 | 1717篇 |
1989年 | 1718篇 |
1988年 | 1704篇 |
1987年 | 1691篇 |
1986年 | 1604篇 |
1985年 | 2150篇 |
1984年 | 2274篇 |
1983年 | 1900篇 |
1982年 | 2223篇 |
1981年 | 2035篇 |
1980年 | 2078篇 |
1979年 | 2061篇 |
1978年 | 2189篇 |
1977年 | 2092篇 |
1976年 | 2123篇 |
1975年 | 2059篇 |
1974年 | 1897篇 |
1973年 | 2108篇 |
1972年 | 1287篇 |
1971年 | 978篇 |
1970年 | 915篇 |
1969年 | 923篇 |
1968年 | 1050篇 |
1967年 | 1101篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
201.
202.
The Dantzig-Wolfe reformulation principle is presented based on the concept of generating sets. The use of generating sets allows for an easy extension to mixed integer programming. Moreover, it provides a unifying framework for viewing various column generation practices, such as relaxing or tightening the column generation subproblem and introducing stabilization techniques. 相似文献
203.
Raman scattering studies were performed on hot-wall chemical vapor deposited (heteroepitaxial) silicon carbide (SiC) films grown on Si substrates with orientations of (1 0 0), (1 1 1), (1 1 0) and (2 1 1), respectively. Raman spectra suggested that good quality cubic SiC single crystals could be obtained on the Si substrate, independent of its crystallographic orientation. Average residual stresses in the epitaxially grown 3C-SiC films were measured with the laser waist focused on the epilayer surface. Tensile and compressive residual stresses were found to be stored within the SiC film and in the Si substrate, respectively. The residual stress exhibited a marked dependence on the orientation of the substrate. The measured stresses were comparable to the thermal stress deduced from elastic deformation theory, which demonstrates that the large lattice mismatch between cubic SiC and Si is effectively relieved by initial carbonization. The confocal configuration of the optical probe enabled a stress evaluation along the cross-section of the sample, which showed maximum tensile stress magnitude at the SiC/Si interface from the SiC side, decreasing away from the interface in varied rate for different crystallographic orientations. Defocusing experiments were used to precisely characterize the geometry of the laser probe in 3C-SiC single crystal. Based on this knowledge, a theoretical convolution of the in-depth stress distribution could be obtained, which showed a satisfactory agreement with stress values obtained by experiments performed on the 3C-SiC surface. 相似文献
204.
The dry etching characteristics of transparent and conductive indium-zinc oxide (IZO) films have been investigated using an inductively coupled high-density plasma. While the Cl2-based plasma mixture showed little enhancement over physical sputtering in a pure argon atmosphere, the CH4/H2/Ar chemistry produced an increase of the IZO etch rate. On the other hand, the surface morphology of IZO films after etching in Ar and Ar/Cl2 discharges is smooth, whereas that after etching in CH4/H2/Ar presents particle-like features resulting from the preferential desorption of In- and O-containing products. Etching in CH4/H2/Ar also produces formation of a Zn-rich surface layer, whose thickness (∼40 nm) is well-above the expected range of incident ions in the material (∼1 nm). Such alteration of the IZO layer after etching in CH4/H2/Ar plasmas is expected to have a significant impact on the transparent electrode properties in optoelectronic device fabrication. 相似文献
205.
206.
M. Mayr K. -H. Speidel M. Knopp W. Karle T. Faestermann F. Hagelberg H. -J. Simonis P. N. Tandon J. Gerber 《Zeitschrift für Physik A Hadrons and Nuclei》1987,327(2):157-161
[Theg-factor ratio of the first excited 3? and 5? states in40Ca was measured to beg 3/g 5=1.01(10) employing the implantation perturbed angular correlation technique. The static hyperfine fields (SF) in Fe and Gd hosts were used. In addition the lifetime of the 5? state was measured to be τ=426(7)ps. The values of the SF in Gd and Fe hosts were deduced and compared with systematics in this element region. 相似文献
207.
208.
The authors give a consistent affirmative response to a question of Juhász, Soukup and Szentmiklóssy: If GCH fails, there are (many) extraresolvable, not maximally resolvable Tychonoff spaces. They show also in ZFC that for ω<λ?κ, no maximal λ-independent family of λ-partitions of κ is ω-resolvable. In topological language, that theorem translates to this: A dense, ω-resolvable subset of a space of the form (DI(λ)) is λ-resolvable. 相似文献
209.
We introduce a new technique for imaging oxygen concentrations in fuel/air mixtures that takes advantage of the different
responses of toluene and 3-pentanone to collisional quenching by molecular oxygen. Since laser-induced fluorescence signals
from both tracers upon excitation at 248 nm are spectrally well separated, simultaneous detection is possible. The technique
is first applied to instantaneous imaging in turbulent mixing processes of interacting seeded air and nitrogen flows.
Received: 1 August 2001 / Revised version: 29 October 2001 / Published online: 29 November 2001 相似文献
210.
Si衬底上ZnSe外延膜的低压MOCVD生长 总被引:2,自引:2,他引:0
以硒化氢(H2Se)和二甲基锌为源材料,生长温度是300℃时,用低压金属有机化学气相沉积(LP-MOCVD)系统在Si(111)衬底上外延生长了ZnSe薄膜。通过X射线衍射(XRD)、扫描电子显微镜的能量色散(EDS)以及光致发光(PL)实验验证ZnSe外延膜的质量,在X射线衍射谱中只有一个强的ZnSe(111)面衍射峰,这说明外延膜是(111)取向的单晶薄膜,在能量色散谱中除了Si,Zn和Se原子外,没有观测到其他原子,说明ZnSe外延膜中杂质含量较少。ZnSe外延膜中Zn/Se原子比接近1,有较好的化学配比。在ZnSe外延膜的77K光致发光谱中没有观测到与深中心发射相关的发光峰,表明ZnSe外延膜的晶格缺陷密度较小。77K时的近带边发射峰447nm在室温时移至465nm附近。 相似文献