全文获取类型
收费全文 | 1104篇 |
免费 | 173篇 |
国内免费 | 149篇 |
专业分类
化学 | 842篇 |
晶体学 | 18篇 |
力学 | 70篇 |
数学 | 81篇 |
物理学 | 415篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 45篇 |
2021年 | 57篇 |
2020年 | 45篇 |
2019年 | 55篇 |
2018年 | 33篇 |
2017年 | 39篇 |
2016年 | 55篇 |
2015年 | 64篇 |
2014年 | 73篇 |
2013年 | 79篇 |
2012年 | 101篇 |
2011年 | 121篇 |
2010年 | 63篇 |
2009年 | 66篇 |
2008年 | 54篇 |
2007年 | 55篇 |
2006年 | 60篇 |
2005年 | 41篇 |
2004年 | 48篇 |
2003年 | 31篇 |
2002年 | 26篇 |
2001年 | 13篇 |
2000年 | 22篇 |
1999年 | 28篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 15篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有1426条查询结果,搜索用时 0 毫秒
251.
252.
Shanshan Guo Rongyuan Lei Xinmiao Liang Jiyan Liu Xueqing Liu Shuyu Gao Xianghong Peng Shilong Bian Yangwei Chen Yi Jin Shaojun Cai Zhihong Liu Jiwen Feng 《化学:亚洲杂志》2019,14(9):1404-1408
Artificial intelligence sensations have aroused scientific interest from electronic conductors to bio‐inspired ionic conductors. The conductivity of electrons decreases with increasing temperature, while the ionic conductivity agrees with an Arrhenius equation or a modified Vogel–Tammann–Fulcher (VTF) equation. Herein, thermo‐responsive poly(N‐isopropyl amide) (PNIPAm) and single‐ion‐conducting poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic lithium salt) (PAMPSLi) were copolymerized via a facile radical polymerization to demonstrate a very intriguing anti‐Arrhenius ionic conductivity behaviour during thermally induced volume‐phase transition. These smart hydrogels presented very promising scaffolds for architecting flexible, wearable or advanced functional ionic devices. 相似文献
253.
利用传输矩阵法设计并优化了用于光催化领域的TiO_2与一维光量子阱的复合结构,并分析了ZnS/SiO_2多层膜量子阱结构的透射特性.通过调节一系列的结构参数,在TiO_2光吸收波段(329.23 nm~482.71 nm)得到一个较宽的高反射率带隙,并且在吸收边附近(380 nm左右)得到了一个反射率高于93%的慢光子效应区.通过增加光线与TiO_2的作用时间和路径来提高光催化效率. 相似文献
254.
This paper develops analytical electromechanical formulas to predict the mechanical deformation of ionic polymer–metal composite(IPMC) cantilever actuators under DC excitation voltages. In this research, IPMC samples with Pt and Ag electrodes were manufactured, and the large nonlinear deformation and the effect of curvature on surface electrode resistance of the IPMC samples were investigated experimentally and theoretically. A distributed electrical model was modified for calculating the distribution of voltage along the bending actuator. Then an irreversible thermodynamic model that could predict the curvature of a unit part of an IPMC actuator is combined with the electrical model so that an analytical electromechanical model is developed. The electromechanical model is then validated against the experimental results obtained from Pt-and Ag-IPMC actuators under various excitation voltages. The good agreement between the electromechanical model and the actuators shows that the analytical electromechanical model can accurately describe the large nonlinear quasi-static deflection behavior of IPMC actuators. 相似文献
255.
Guocheng Zhu Yongning Bian Andrew S. Hursthouse Peng Wan Katarzyna Szymanska Jiangya Ma Xiaofeng Wang Zilong Zhao 《Journal of fluorescence》2017,27(6):2069-2094
Natural organic matter (NOM) found in water sources is broadly defined as a mixture of polyfunctional organic molecules, characterized by its complex structure and paramount influence on water quality. Because the inevitable release of pollutants into aquatic environments due to an ineffective control of industrial and agricultural pollution, the evaluation of the interaction of NOM with heavy metals, nanoparticles, organic pollutants and other pollutants in the aquatic environment, has greatly increased. Three-dimensional (3-D) fluorescence has the potential to reveal the interaction mechanisms between NOM and pollutants as well as the source of NOM pollution. In water purification engineering system, the 3-D fluorescence can indicate the variations of NOM composition and gives an effective prediction of water quality as well as the underline water purification mechanisms. Inadequately treated NOM is a cause of precursors of disinfection byproducts (DBPs), posing a potential threat to human health. Effective control and measurement/evaluation of NOM have long been an important factors in the prevention of water pollution. Overall, 3-D fluorescence allows for a rapid identification of organic components thus indicating possible sources of water pollution, mechanisms of pollutant interactions, and possible DBPs formed during conventional treatment of this water. This article reviews the 3-D fluorescence characteristics of NOM in natural water and typical water purification systems. The 3-D fluorescence was effective for indicating the variabilities in NOM composition and chemistry thus providing a better understanding of NOM in natural water system and water engineering system. 相似文献
256.
Time synchronization and carrier frequency control of CAPS navigation signals generated on the ground 总被引:2,自引:2,他引:0
The Chinese Area Positioning System (CAPS) works without atomic clocks on the satellite, and the CAPS navigation signals transmitted
on the ground may achieve the same effect as that with high-performance atomic clocks on the satellite. The primary means
of achieving that effect is through the time synchronization and carrier frequency control of the CAPS navigation signals
generated on the ground. In this paper the synchronization requirements of different time signals are analyzed by the formation
of navigation signals, and the theories and methods of the time synchronization of the CAPS navigation signals generated on
the ground are also introduced. According to the conditions of the high-precision satellite velocity-measurement signal source,
the carrier frequency and its chains of the navigation signals are constructed. CAPS velocity measurement is realized by the
expected deviation of real time control to the carrier frequency, and the precision degree of this method is also analyzed.
The experimental results show that the time synchronization precision of CAPS generating signals is about 0.3 ns and the precision
of the velocity measurement signal source is about 4 cm/s. This proves that the theories and methods of the generating time
synchronization and carrier frequency control are workable.
Supported by the Major Knowledge Innovation Programs of the Chinese Academy of Sciences (Grant No. KGCX1-21), the National
High Technology Research and Development Program of China (Grant Nos. 2004AA105030 and 2006AA12Z314), the National Natural
Science Foundation of China (Grant No. 10453001), and the Major State Basic Research Development Program of China (Grant No.
2007CB815502) 相似文献
257.
Guo‐Qing Bian Takayoshi Kuroda‐Sowa Hisashi Konaka Masahiko Maekawa Megumu Munakata 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(7):m338-m340
The title compound, [Mn2(μ‐O)(C6H3NO3)2(C5H5N)4]·H2O, was isolated from the reaction of 2,6‐pyridinedicarboxylic acid with [Mn12O12(CH3COO)16(H2O)4] in pyridine. The dimanganese complex has twofold symmetry; the MnIII atoms are bridged by one oxo and two amidate ligands and show compressed octahedral Jahn–Teller distortion. The molecular packing comprises a three‐dimensional structure constructed by means of extensive intermolecular interactions, including three kinds of hydrogen bonds and π–π interactions. 相似文献
258.
中介尺度Au纳米团簇熔化的分子动力学模拟 总被引:2,自引:0,他引:2
采用分子动力学模拟技术,研究了原子个数为16~8628的 Au纳米团簇的熔化过程.采用 Johnson的EAM (embedded atom method) 模型,模拟结果表明,金属纳米团簇存在一中介尺度区域.对Au纳米团簇而言,当原子个数N >456时,团簇的热力学性质与团簇尺寸呈线性关系,熔化首先从表面开始,逐步向中心区域推进,且满足Tmb-Tmc(N)=aN(-1/3)的关系.另外,计算了中介区域的团簇的尺寸、熔化温度、表面能、熵、焓等热力学量以及均方根位移(RMSD)等动力学量,为研究纳米团簇提供定量数据. 相似文献
259.
A fundamental problem in communication networks is wavelength assignment (WA): given a set of routing paths on a network, assign a wavelength to each path such that the paths with the same wavelength are edge-disjoint, using the minimum number of wavelengths. The WA problem is NP-hard for a tree of rings network which is well used in practice. In this paper, we give an efficient algorithm which solves the WA problem on a tree of rings with an arbitrary (node) degree using at most 3L wavelengths and achieves an approximation ratio of 2.75 asymptotically, where L is the maximum number of paths on any link in the network. The 3L upper bound is tight since there are instances of the WA problem that require 3L wavelengths even on a tree of rings with degree four. We also give a 3L and 2-approximation (resp. 2.5-approximation) algorithm for the WA problem on a tree of rings with degree at most six (resp. eight). Previous results include: 4L (resp. 3L) wavelengths for trees of rings with arbitrary degrees (resp. degree at most eight), and 2-approximation (resp. 2.5-approximation) algorithm for trees of rings with degree four (resp. six). 相似文献
260.
We introduce the setwise homotopy relation and prove that two chain maps induce the same cohomology map if and only if they
are setwise homotopic. 相似文献