全文获取类型
收费全文 | 35026篇 |
免费 | 4814篇 |
国内免费 | 4944篇 |
专业分类
化学 | 26884篇 |
晶体学 | 552篇 |
力学 | 1707篇 |
综合类 | 448篇 |
数学 | 3645篇 |
物理学 | 11548篇 |
出版年
2024年 | 67篇 |
2023年 | 429篇 |
2022年 | 924篇 |
2021年 | 1003篇 |
2020年 | 1078篇 |
2019年 | 1134篇 |
2018年 | 925篇 |
2017年 | 897篇 |
2016年 | 1478篇 |
2015年 | 1530篇 |
2014年 | 1828篇 |
2013年 | 2528篇 |
2012年 | 2961篇 |
2011年 | 3047篇 |
2010年 | 2242篇 |
2009年 | 2079篇 |
2008年 | 2470篇 |
2007年 | 2186篇 |
2006年 | 2098篇 |
2005年 | 1840篇 |
2004年 | 1597篇 |
2003年 | 1436篇 |
2002年 | 1600篇 |
2001年 | 1189篇 |
2000年 | 993篇 |
1999年 | 819篇 |
1998年 | 554篇 |
1997年 | 537篇 |
1996年 | 479篇 |
1995年 | 439篇 |
1994年 | 371篇 |
1993年 | 341篇 |
1992年 | 317篇 |
1991年 | 249篇 |
1990年 | 223篇 |
1989年 | 184篇 |
1988年 | 135篇 |
1987年 | 108篇 |
1986年 | 101篇 |
1985年 | 99篇 |
1984年 | 58篇 |
1983年 | 47篇 |
1982年 | 33篇 |
1981年 | 33篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1976年 | 8篇 |
1974年 | 7篇 |
1973年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Hong Ming ZHANG Xian Hong WANG Xiao Jiang ZHAO Ji LI Fo Song WANG 《中国化学快报》2006,17(4):437-440
A novel method for the preparation of oligothiophene molecular wires is described via a bi-directional solid-phase synthesis. Using an alternating sequence of bromination and Stille coupling reactions, oligomers were obtained up to the heptamer in excellent yield and purity. 相似文献
72.
In this talk, the interaction of a single photon injected to a single atom is studied, for which initially the photon is uncorrelated with the atom. The spontaneous emitted photon will then evolve to be entangled with the atom on their continuous kinetic variables (momentum) in the process of resonant scattering. We find the relations between the entanglement and their physical control parameters (such as the linewidth of the injected photon wave packet, and that of the atomic wave packet, etc. ), which indicates that high entanglement can be reached by broadening the scale of the atomic wave or squeezing the linewidth of the incident single-photon pulse. 相似文献
73.
沿直线的垂直方向匀速直线运动的带电直线的电场 总被引:1,自引:1,他引:0
本文利用相对论变换关系计算了沿直线的垂直方向匀速运动的带电直线的电场. 相似文献
74.
The feature selection consists of obtaining a subset of these features to optimally realize the task without the irrelevant
ones. Since it can provide faster and cost-effective learning machines and also improve the prediction performance of the
predictors, it is a crucial step in machine learning. The feature selection methods using support machines have obtained satisfactory
results, but the noises and outliers often reduce the performance. In this paper, we propose a feature selection approach
using fuzzy support vector machines and compare it with the previous work, the results of experiments on the UCI data sets
show that feature selection using fuzzy SVM obtains better results than using SVM. 相似文献
75.
76.
Kyung Hwa Hong Jong Lyoul Park In Hwan Sul Ji Ho Youk Tae Jin Kang 《Journal of Polymer Science.Polymer Physics》2006,44(17):2468-2474
Polyvinyl alcohol (PVA) nanofibers containing Ag nanoparticles were prepared by electrospinning PVA/silver nitrate (AgNO3) aqueous solutions, followed by short heat treatment, and their antimicrobial activity was investigated for wound dressing applications. Since PVA is a water soluble and biocompatible polymer, it is one of the best materials for the preparation of wound dressing nanofibers. After heat treatment at 155 °C for 3 min, the PVA/AgNO3 nanofibers became insoluble, while the Ag+ ions therein were reduced so as to produce a large number of Ag nanoparticles situated preferentially on their surface. The residual Ag+ ions were reduced by subsequent UV irradiation for 3 h. The average diameter of the Ag nanoparticles after the heat treatment was 5.9 nm and this value increased slightly to 6.3 nm after UV irradiation. It was found that most of the Ag+ ions were reduced by the simple heat treatment. The PVA nanofibers containing Ag nanoparticles showed very strong antimicrobial activity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2468–2474, 2006 相似文献
77.
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
78.
79.
2-Amino-2,4-anhydro-psicofuranose derivative was synthesized starting from d-fructose. 相似文献
80.
标的股价服从混合过程的期权定价公式及有限元算法 总被引:2,自引:0,他引:2
本文将马尔科夫跳跃过程叠加于 Ito过程 ,形成混合过程 ,并用该过程来刻画股价走势情况。而后在标的股价服从混合过程的基础上 ,推导出了欧式看涨期权的定价公式 ,并对美式看跌期权定价给出了有限元算法。 相似文献