全文获取类型
收费全文 | 24184篇 |
免费 | 3921篇 |
国内免费 | 2628篇 |
专业分类
化学 | 16929篇 |
晶体学 | 296篇 |
力学 | 1443篇 |
综合类 | 240篇 |
数学 | 2664篇 |
物理学 | 9161篇 |
出版年
2024年 | 78篇 |
2023年 | 504篇 |
2022年 | 819篇 |
2021年 | 829篇 |
2020年 | 989篇 |
2019年 | 904篇 |
2018年 | 753篇 |
2017年 | 727篇 |
2016年 | 1101篇 |
2015年 | 1041篇 |
2014年 | 1300篇 |
2013年 | 1675篇 |
2012年 | 2082篇 |
2011年 | 2083篇 |
2010年 | 1431篇 |
2009年 | 1369篇 |
2008年 | 1531篇 |
2007年 | 1405篇 |
2006年 | 1344篇 |
2005年 | 1085篇 |
2004年 | 870篇 |
2003年 | 721篇 |
2002年 | 623篇 |
2001年 | 520篇 |
2000年 | 516篇 |
1999年 | 594篇 |
1998年 | 490篇 |
1997年 | 430篇 |
1996年 | 436篇 |
1995年 | 387篇 |
1994年 | 357篇 |
1993年 | 326篇 |
1992年 | 269篇 |
1991年 | 230篇 |
1990年 | 236篇 |
1989年 | 159篇 |
1988年 | 119篇 |
1987年 | 84篇 |
1986年 | 97篇 |
1985年 | 66篇 |
1984年 | 37篇 |
1983年 | 39篇 |
1982年 | 37篇 |
1981年 | 21篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1976年 | 1篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
81.
82.
83.
Zhu Da xin 《数学年刊B辑(英文版)》1994,15(3):293-298
ACOMPLETEMETRICOFPOSITIVECURVATUREONR~nANDEXISTENCEOFCLOSEDGEODESICS¥ZHUDAXIN(DepartmentofMathematics,TianjinUniversitylTianj?.. 相似文献
84.
The impact of fabrication errors on a planar waveguide demultiplexer is analyzed based on an analytical method. The explicit
expression of the transfer function taking into account phase and amplitude errors is presented in order to analyze the loss
and crosstalk of the demultiplexer caused by fabrication errors. A basic requirement for the demultiplexer with a certain
crosstalk criterion can be easily obtained. Using an etched diffraction grating demultiplexer as an example, it is shown that
the analytical results have a good agreement with results from a numerical method. 相似文献
85.
86.
The new phenylpropanoid diglycoside ligusinenoside A ( 1 ), and the two new 8,4′‐oxyneolignan(‘8‐O‐4′‐neolignan’) diglycosides ligusinenosides B ( 2 ) and C ( 3 ), together with nine known compounds, were isolated from the rhizomes of Ligusticum sinensis Oliv. The structures of 1 – 3 were elucidated on the basis of spectroscopic analyses. 相似文献
87.
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
88.
89.
Jie Xue Liang Chen Li Zhou Zhifeng Jia Yanping Wang Xinyuan Zhu Deyue Yan 《Journal of Polymer Science.Polymer Physics》2006,44(15):2050-2057
α‐Cyclodextrin (α‐CD) has been complexed with various poly(ethylene glycol) (PEG) derivatives in aqueous solution. It has been found that the end groups of PEG derivatives affect the complexation kinetics greatly, but have only a little influence on the thermodynamic behavior. By increasing the hydrophobicity of end groups, the complexation speeds up rapidly. On the other hand, the bulky end groups slow down the threading of polymeric guests into the cavity of CD. By changing the hydrophobicity and the size of end groups, the complexation rate can be adjusted in the range of several orders of magnitudes, which should be quite useful in the design of new supramolecular systems. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2050–2057, 2006 相似文献
90.