全文获取类型
收费全文 | 1802篇 |
免费 | 251篇 |
国内免费 | 288篇 |
专业分类
化学 | 1370篇 |
晶体学 | 11篇 |
力学 | 232篇 |
综合类 | 31篇 |
数学 | 155篇 |
物理学 | 542篇 |
出版年
2024年 | 2篇 |
2023年 | 31篇 |
2022年 | 53篇 |
2021年 | 90篇 |
2020年 | 97篇 |
2019年 | 61篇 |
2018年 | 59篇 |
2017年 | 57篇 |
2016年 | 81篇 |
2015年 | 71篇 |
2014年 | 80篇 |
2013年 | 139篇 |
2012年 | 81篇 |
2011年 | 107篇 |
2010年 | 86篇 |
2009年 | 81篇 |
2008年 | 83篇 |
2007年 | 103篇 |
2006年 | 99篇 |
2005年 | 100篇 |
2004年 | 103篇 |
2003年 | 88篇 |
2002年 | 79篇 |
2001年 | 58篇 |
2000年 | 65篇 |
1999年 | 61篇 |
1998年 | 55篇 |
1997年 | 32篇 |
1996年 | 37篇 |
1995年 | 29篇 |
1994年 | 28篇 |
1993年 | 39篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 16篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1972年 | 1篇 |
1966年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有2341条查询结果,搜索用时 31 毫秒
1.
Dariusz Marek Adam Domaski Joanna Domaska Jakub Szygua Tadeusz Czachrski Jerzy Klamka 《Entropy (Basel, Switzerland)》2021,23(5)
In this article, a way to employ the diffusion approximation to model interplay between TCP and UDP flows is presented. In order to control traffic congestion, an environment of IP routers applying AQM (Active Queue Management) algorithms has been introduced. Furthermore, the impact of the fractional controller and its parameters on the transport protocols is investigated. The controller has been elaborated in accordance with the control theory. The TCP and UDP flows are transmitted simultaneously and are mutually independent. Only the TCP is controlled by the AQM algorithm. Our diffusion model allows a single TCP or UDP flow to start or end at any time, which distinguishes it from those previously described in the literature. 相似文献
2.
Hideya Sugimoto Masanori Tachikawa Taro Udagawa 《International journal of quantum chemistry》2019,119(10):e25895
The hydrogen transfer reaction in the reaction of HOSO + NO2 with and without H2O have been investigated using multicomponent quantum-mechanics method, which can directly take nuclear quantum effect (NQE) of light nuclei into account. For the case of the reaction without H2O, our calculation reveals that the reaction leading to trans-HONO is preferred. For the reaction with H2O, water-non-mediated and water-mediated (hydrogen-relay) hydrogen transfer mechanism are investigated. The NQE of hydrogen nucleus lowers the relative energy of the stationary point structures and reduces the activation barrier of the reactions. The largest stabilization is found in the transition state structure of the hydrogen-relay type reaction. H/D isotope effects for the reactions are also analyzed. In particular, H/D isotope effect on the activation barrier is analyzed in detail with the aid of the active strain model. 相似文献
3.
Semiconductor materials containing bismuth have attracted the attention of researchers over the past several decades, as a result of their high photocatalytic activity in various reactions and/or high efficiency in their photoelectric conversion of solar energy. This interest originated from the observations that bismuth-containing semiconductors have a sufficiently small bandgap, which makes them sensitive to radiation in the visible spectral range; thus, visible-light-active materials. Among the various bismuth-containing semiconductor materials, the bismuthates of alkaline earth metals are distinguished and describe into separate groups. This article reviews research on the known methods of obtaining bismuthates of various alkaline earth metals (magnesium, calcium, strontium, and barium), and further analyzes their composition, structure, and visible-light-active photocatalytic activity. 相似文献
4.
Wei‐Hong Lai Li‐Fu Zhang Wei‐Bo Hua Sylvio Indris Zi‐Chao Yan Zhe Hu Binwei Zhang Yani Liu Li Wang Min Liu Rong Liu Yun‐Xiao Wang Jia‐Zhao Wang Zhenpeng Hu Hua‐Kun Liu Shu‐Lei Chou Shi‐Xue Dou 《Angewandte Chemie (International ed. in English)》2019,58(34):11868-11873
Both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) are crucial to water splitting, but require alternative active sites. Now, a general π‐electron‐assisted strategy to anchor single‐atom sites (M=Ir, Pt, Ru, Pd, Fe, Ni) on a heterogeneous support is reported. The M atoms can simultaneously anchor on two distinct domains of the hybrid support, four‐fold N/C atoms (M@NC), and centers of Co octahedra (M@Co), which are expected to serve as bifunctional electrocatalysts towards the HER and the OER. The Ir catalyst exhibits the best water‐splitting performance, showing a low applied potential of 1.603 V to achieve 10 mA cm?2 in 1.0 m KOH solution with cycling over 5 h. DFT calculations indicate that the Ir@Co (Ir) sites can accelerate the OER, while the Ir@NC3 sites are responsible for the enhanced HER, clarifying the unprecedented performance of this bifunctional catalyst towards full water splitting. 相似文献
5.
6.
Pingping Hu Dr. Manfred Erwin Schuster Dr. Zhiwei Huang Fei Xu Dr. Shifeng Jin Yaxin Chen Prof. Weiming Hua Prof. Dang Sheng Su Prof. Xingfu Tang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9619-9623
The identification of catalytically active sites (CASs) in heterogeneous catalysis is of vital importance to design and develop improved catalysts, but remains a great challenge. The CASs have been identified in the low‐temperature selective catalytic reduction of nitrogen oxides by ammonia (SCR) over a hollandite manganese oxide (HMO) catalyst with a rod‐shaped morphology and one‐dimensional tunnels. Electron microscopy and synchrotron X‐ray diffraction determine the surface and crystal structures of the one‐dimensional HMO rods closed by {100} side facets and {001} top facets. A combination of X‐ray absorption spectra, molecular probes with potassium and nitric oxide, and catalytic tests reveals that the CASs are located on the {100} side facets of the HMO rods rather than on the top facets or in the tunnels, and hence semi‐tunnel structural motifs on the {100} facets are evidenced to be the CASs of the SCR reaction. This work paves the way to further investigate the intrinsic mechanisms of SCR reactions. 相似文献
7.
Direct Estimation of the Surface Location of Immobilized Functional Groups for Concerted Catalysis Using a Probe Molecule 下载免费PDF全文
Hiroto Noda Dr. Ken Motokura Prof. Dr. Yusuke Wakabayashi Kaori Sasaki Dr. Hiroo Tajiri Dr. Akimitsu Miyaji Dr. Sho Yamaguchi Prof. Dr. Toshihide Baba 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(15):5113-5117
The location of active sites during concerted catalysis by a metal complex and tertiary amine on a SiO2 surface is discussed based on the interaction between the functionalized SiO2 surface and a probe molecule, p‐formyl phenylboronic acid. The interactions of the probe molecule with the surface functionalities, diamine ligand, and tertiary amine, were analyzed by FT‐IR and solid‐state 13C and 11B MAS NMR. For the catalyst exhibiting high 1,4‐addition activity, the diamine ligand and tertiary amine base exist in closer proximity than in the catalyst with low activity. 相似文献
8.
目标定位是光电转塔典型功能和任务之一,对其定位精度的考量也是转塔作战技术指标之一,针对该问题,从理论和仿真角度进行了分析。分析目标定位中用到的坐标系及其相互转换关系,给出光电转塔视轴反演、有源目标定位、无源目标定位的算法流程,通过仿真实验加以验证,考虑了定位过程中可能的随机误差来源,并分析是否采用均值滤波及其对定位结果的影响,最后通过Monte-Carlo分析计算了定位精度。分析结果表明:1)有源定位比无源定位的精度高,在仿真假设条件下,精度约提高1倍;2)均值滤波后,定位精度有较大提升(约提高15倍);3)18 km距离时典型无源定位精度在80%置信度条件下约为39.4 m;4)统计直方图反映出80%置信度CEP半径及最大误差距离随载机位置、姿态、转塔视轴等(体现在目标载机距离上)不同参数的变化结果。 相似文献
9.
10.
Dr. Hui Chen Lei Shi Xiao Liang Lina Wang Prof. Tewodros Asefa Prof. Xiaoxin Zou 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(44):19822-19826
Reducing the amount of iridium in oxygen evolution electrocatalysts without compromising their catalytic performances is one of the major requirements in proton-exchange-membrane water electrolyzers. Herein, with the help of theoretical studies, we show that anatase-type TiO2-IrO2 solid solutions possess more active iridium catalytic sites for the oxygen evolution reaction (OER) than IrO2, the benchmark OER catalyst. Note that the same is not observed for their rutile-type counterparts. However, owing to their thermodynamic metastability, anatase-type TiO2-IrO2 solid solutions are generally hard to synthesize. Our theoretical studies demonstrate that such catalytically active anatase-type solid-solution phases can be created in situ on the surfaces of readily available SrTiO3-SrIrO3 solid solutions during electrocatalysis in acidic solution as the solution can etch away Sr atoms. We experimentally show this with porous SrTiO3-SrIrO3 solid-solution nanotubes synthesized by a facile synthetic route that contain 56 % less iridium than IrO2 yet show an order of magnitude higher apparent catalytic activity for OER in acidic solution. 相似文献