全文获取类型
收费全文 | 608篇 |
免费 | 35篇 |
国内免费 | 17篇 |
专业分类
化学 | 445篇 |
晶体学 | 1篇 |
力学 | 39篇 |
数学 | 83篇 |
物理学 | 92篇 |
出版年
2023年 | 1篇 |
2022年 | 16篇 |
2021年 | 22篇 |
2020年 | 26篇 |
2019年 | 38篇 |
2018年 | 35篇 |
2017年 | 29篇 |
2016年 | 62篇 |
2015年 | 36篇 |
2014年 | 36篇 |
2013年 | 99篇 |
2012年 | 50篇 |
2011年 | 42篇 |
2010年 | 40篇 |
2009年 | 26篇 |
2008年 | 23篇 |
2007年 | 29篇 |
2006年 | 7篇 |
2005年 | 11篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有660条查询结果,搜索用时 18 毫秒
91.
Effects of substrate on crystallinity, surface morphology, and luminescence properties of radio frequency sputtered zinc oxide (ZnO) thin films were investigated. A variety of materials such as Si (100), Si (111), Al2O3, quartz, and silicon carbide (SiC) wafers were examined as substrates for deposition of ZnO thin films. The results showed smooth and uniform growth of c-axis orientation films. The thickness of the layers was about 50 nm. The average grain sizes of films were about 10, 13, and 12 nm for Si (111), quartz, and SiC samples, respectively. The deposited film on Al2O3 showed the largest grain size, about 500 nm. Grazing incidence x-ray diffraction patterns of the samples revealed that sputtered layers on Al2O3 and quartz had better crystallinity with higher peak at (002) orientation compared to Si and SiC substrates. Moreover, the Al2O3 sample exhibited a weak peak at position of (100) planes of ZnO too. The photoluminescence spectra of the samples showed a typical luminescence behavior with a broad UV band, including a main peak at around 388 nm and a weak shoulder peak at around 381 nm, corresponding with bound excitonic recombination and free excitonic recombination, respectively. The luminescence peak revealed that the intensity of UV emission is not necessarily dependent on the grain sizes and the micro-structural quality of ZnO films. 相似文献
92.
This paper presents an output-feedback adaptive controller for a class of linear systems with unknown time-varying state delay
and in the presence of actuator failures. We consider a common type of actuator failure in which some unknown system inputs
may be stuck at some unknown fixed values and at unknown time instants. The adaptive controller is designed based on SPR–Lyapunov
approach for relative degree one and two cases. Closed-loop system stability and asymptotic output tracking are proved using
suitable Lyapunov–Krasovskii functional for each case. Simulation results are provided to demonstrate the effectiveness of
the proposed results. 相似文献
93.
Nonlinear Dynamics - The aim of this paper is to tackle the problem of adaptive fuzzy voltage-based tracking control for uncertain electrically driven robotic manipulators subject to input delay... 相似文献
94.
95.
Using Auslander’s G-dimension, we assign a numerical invariant to any group Γ. It provides a refinement of the cohomological dimension and fits well into the well-known hierarchy of dimensions assigned already to Γ. We study this dimension and show its power in reflecting the properties of the underlying group. We also discuss its connections to relative and Tate cohomology of groups. 相似文献
96.
97.
Abedini-Torghabeh Javad Eshghi Hossein Bakavoli Mehdi Rahimizadeh Mohammad 《Research on Chemical Intermediates》2015,41(6):3649-3658
Research on Chemical Intermediates - PPh3 was used as an efficient catalyst for the one-pot three-component Mannich reactions of acetophenone with different aromatic amines and aromatic aldehydes... 相似文献
98.
Javad Jamalzadeh 《代数通讯》2017,45(3):1187-1188
99.
Let T be a Wakamatsu tilting module. A module M is called (n, T)-copure injective (resp. (n, T)-copure flat) if ɛ
T
1 (N, M) = 0 (resp. Γ1
T
(N, M) = 0) for any module N with T-injective dimension at most n (see Definition 2.2). In this paper, it is shown that M is (n, T)-copure injective if and only if M is the kernel of an I
n
(T)-precover f: A → B with A ∈ Prod T. Also, some results on Prod T-syzygies are presented. For instance, it is shown that every nth Prod T-syzygy of every module, generated by T, is (n, T)-copure injective. 相似文献
100.
Lei Yang Mohammad Javad Afshari Jianxian Ge Dandan Kou Lei Chen Dandan Zhou Cang Li Shuwang Wu Leshuai Zhang Jianfeng Zeng Jian Zhong Roland H. Stauber Mingyuan Gao 《Molecules (Basel, Switzerland)》2022,27(20)
Hypoxia is a common biological condition in many malignant solid tumors that plays an imperative role in regulating tumor growth and impacting the treatment’s therapeutic effect. Therefore, the hypoxia assessment is of great significance in predicting tumor development and evaluating its prognosis. Among the plenty of existing tumor diagnosis techniques, magnetic resonance imaging (MRI) offers certain distinctive features, such as being free of ionizing radiation and providing images with a high spatial resolution. In this study, we develop a fluorescent traceable and hypoxia-sensitive T1-weighted MRI probe (Fe3O4-Met-Cy5.5) via conjugating notable hypoxia-sensitive metronidazole moiety and Cy5.5 dye with ultrasmall iron oxide (Fe3O4) nanoparticles. The results of in vitro and in vivo experiments show that Fe3O4-Met-Cy5.5 has excellent performance in relaxivity, biocompatibility, and hypoxia specificity. More importantly, the obvious signal enhancement in hypoxic areas indicates that the probe has great feasibility for sensing tumor hypoxia via T1-weighted MRI. These promising results may unlock the potential of Fe3O4 nanoparticles as T1-weighted contrast agents for the development of clinical hypoxia probes. 相似文献