全文获取类型
收费全文 | 20017篇 |
免费 | 2783篇 |
国内免费 | 3136篇 |
专业分类
化学 | 15686篇 |
晶体学 | 316篇 |
力学 | 882篇 |
综合类 | 298篇 |
数学 | 2151篇 |
物理学 | 6603篇 |
出版年
2024年 | 39篇 |
2023年 | 212篇 |
2022年 | 495篇 |
2021年 | 516篇 |
2020年 | 584篇 |
2019年 | 620篇 |
2018年 | 529篇 |
2017年 | 463篇 |
2016年 | 799篇 |
2015年 | 849篇 |
2014年 | 1018篇 |
2013年 | 1438篇 |
2012年 | 1657篇 |
2011年 | 1679篇 |
2010年 | 1280篇 |
2009年 | 1230篇 |
2008年 | 1504篇 |
2007年 | 1384篇 |
2006年 | 1252篇 |
2005年 | 1075篇 |
2004年 | 984篇 |
2003年 | 870篇 |
2002年 | 982篇 |
2001年 | 771篇 |
2000年 | 604篇 |
1999年 | 490篇 |
1998年 | 324篇 |
1997年 | 329篇 |
1996年 | 291篇 |
1995年 | 251篇 |
1994年 | 235篇 |
1993年 | 225篇 |
1992年 | 189篇 |
1991年 | 144篇 |
1990年 | 134篇 |
1989年 | 102篇 |
1988年 | 57篇 |
1987年 | 66篇 |
1986年 | 61篇 |
1985年 | 49篇 |
1984年 | 27篇 |
1983年 | 24篇 |
1982年 | 17篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1978年 | 11篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1974年 | 5篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Hollow particles with interconnected cavities have been prepared by a simple modified suspension polymerization of acrylate monomers in the incorporation of a phase inversion process and polymerizable emulsifier. The morphology of particles has been characterized by scanning electron micrographs (SEMs). Based on observations made using an optical microscope equipped with a digital camera and SEM images of particles obtained under different conditions, the formation mechanisms for multiporous hollow particles are discussed. 相似文献
142.
143.
We have performed total-energy calculations to study theoretical scanning tunneling microscopy (STM) images of the Si(1 1 1)3 × 2 surfaces induced by the adsorption of alkaline-earth metals (AEMs). Previously, in a series of works on Ba/Si(1 1 1) system, we have found that the observed Si(1 1 1)3 × 1-Ba LEED phase indeed has a 3 × 2 periodicity with a Ba coverage of 1/6 ML and the HCC substrate structure. Based on results of the Ba case, we proposed that the HCC structure is also adopted for other AEM atoms, which was confirmed by our recent work. In this paper, we mainly report the STM simulations for different AEM systems to compare with existing experimental data. We discuss the difference in the detailed STM images for different AEM adsorbates. Especially, the difference in filled-state images between Mg and other AEM atoms is attributed to the strong Mg-Si interaction. 相似文献
144.
聚异丁烯高活性端基含量及相对分子质量测定方法的研究 总被引:2,自引:0,他引:2
综合使用核磁,VPO和近红外光谱分析技术对聚异丁烯活性端基含量以及相对分子质量的测定进行了详细研究,分别建立核测定聚异丁烯活性端基含量以及其他烯键含量和近红外光谱快速测量聚异聚丁烯活性端基含量。其他烯键含量和相对分子质量的分析方法。成对t检验结果表明,近红外光谱分析方法测定结果与核磁和VPO方法测定结果之间无显著性差异。 相似文献
145.
联合功率谱的高频成份对相关峰识别具有重要作用,实验中记录的联合功率谱随着频率的增加其强度迅速降低。为增强联合功率谱的高频成分,改善其调制程度,可对功率谱进行对数变换,从而有效保留更多的高频成份,压低零级衍射光斑,提高联合变换相关器的识别能力。 相似文献
146.
In this paper, we consider a time fractional diffusion equation on a finite domain. The equation is obtained from the standard diffusion equation by replacing the first-order time derivative by a fractional derivative (of order 0 < α < 1 ). We propose a computationally effective implicit difference approximation to solve the time fractional diffusion equation. Stability and convergence of the method are discussed. We prove that the implicit difference approximation (IDA) is unconditionally stable, and the IDA is convergent withO(Τ +h 2), where Τ andh are time and space steps, respectively. Some numerical examples are presented to show the application of the present technique. 相似文献
147.
Influence of buffer layer thickness on the structure and optical properties of ZnO thin films 总被引:1,自引:0,他引:1
A series of ZnO thin films were deposited on ZnO buffer layers by DC reactive magnetron sputtering. The buffer layer thickness determination of microstructure and optical properties of ZnO films was investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. XRD results revealed that the stress of ZnO thin films varied with the buffer layer thickness. With the increase of buffer layer thickness, the band gap edge shifted toward longer wavelength. The near-band-edge (NBE) emission intensity of ZnO films deposited on ZnO buffer layer also varied with the increase of thickness due to the spatial confinement increasing the Coulomb interaction between electrons and holes. The PL measurement showed that the optimum thickness of the ZnO buffer layer was around 12 nm. 相似文献
148.
149.
2-Amino-2,4-anhydro-psicofuranose derivative was synthesized starting from d-fructose. 相似文献
150.
LIU Biao BAO Yong-li WEI Zhuang WU Yin MENG Xiang-ying LI Yu-xin YIN Wei-tian 《高等学校化学研究》2006,22(2):217-220
Introduction Activinisamemberofthetransforminggrowth factor(TGF)βsuperfamilyofextracellularsignaling proteins.Themembersofthisfamilyplayacriticalrole duringembryogenesisandinmaintainingtissuehomeo stasisinadultlife[1—3].DeregulatedTGFfamilysigna lingisi… 相似文献