全文获取类型
| 收费全文 | 3104篇 |
| 免费 | 609篇 |
| 国内免费 | 68篇 |
专业分类
| 化学 | 241篇 |
| 晶体学 | 25篇 |
| 力学 | 669篇 |
| 综合类 | 19篇 |
| 数学 | 209篇 |
| 物理学 | 2618篇 |
出版年
| 2025年 | 6篇 |
| 2024年 | 44篇 |
| 2023年 | 49篇 |
| 2022年 | 44篇 |
| 2021年 | 53篇 |
| 2020年 | 70篇 |
| 2019年 | 62篇 |
| 2018年 | 63篇 |
| 2017年 | 76篇 |
| 2016年 | 99篇 |
| 2015年 | 94篇 |
| 2014年 | 202篇 |
| 2013年 | 208篇 |
| 2012年 | 177篇 |
| 2011年 | 188篇 |
| 2010年 | 146篇 |
| 2009年 | 149篇 |
| 2008年 | 180篇 |
| 2007年 | 211篇 |
| 2006年 | 199篇 |
| 2005年 | 203篇 |
| 2004年 | 139篇 |
| 2003年 | 169篇 |
| 2002年 | 113篇 |
| 2001年 | 93篇 |
| 2000年 | 91篇 |
| 1999年 | 89篇 |
| 1998年 | 78篇 |
| 1997年 | 107篇 |
| 1996年 | 57篇 |
| 1995年 | 60篇 |
| 1994年 | 51篇 |
| 1993年 | 28篇 |
| 1992年 | 31篇 |
| 1991年 | 27篇 |
| 1990年 | 29篇 |
| 1989年 | 16篇 |
| 1988年 | 10篇 |
| 1987年 | 19篇 |
| 1986年 | 10篇 |
| 1985年 | 10篇 |
| 1984年 | 10篇 |
| 1982年 | 10篇 |
| 1981年 | 8篇 |
| 1980年 | 1篇 |
| 1978年 | 1篇 |
| 1957年 | 1篇 |
排序方式： 共有3781条查询结果，搜索用时 0 毫秒
91.
Shih‐Chang Syu Chih‐Hsien Cheng Huai‐Yung Wang Yu‐Chieh Chi Gong‐Ru Lin 《Annalen der Physik》2019,531(2)
The carbon‐rich silicon carbide (C‐rich SixC1?x) micro‐ring channel waveguide with asymmetric core aspect is demonstrated for all‐optical cross‐wavelength pulsed return‐to‐zero on‐off keying (PRZ‐OOK) data conversion. Enhanced nonlinear optical Kerr switching enables 12‐Gbit per second data processing with optimized modulation depth. The inverse tapered waveguide at end‐face further enlarges the edge‐coupling efficiency, and the asymmetric channel waveguide distinguishes the polarization modes. To prevent data shape distortion, the bus/ring gap spacing is adjusted to control the quality factor (Q‐factor) of the micro‐ring. Designing the waveguide cross section at 500 × 350 nm2 provides the C‐rich SixC1?x channel waveguide to induce strong transverse electric mode (TE‐mode) confinement with a large Kerr nonlinearity of 2.44 × 10?12 cm2 W?1. Owing to the trade‐off between the Q‐factor and the on/off extinction ratio, the optimized bus/ring gap spacing of 1400 nm is selected to provide a coupling ratio at 5–6% for compromising the modulation depth and the switching throughput. Such a C‐rich SixC1?x micro‐ring with asymmetric channel waveguide greatly enhances the cross‐wavelength data conversion efficiency to favor its on‐chip all‐optical data processing applications for future optoelectronic interconnect circuits. 相似文献
92.
Huizhou Wu Xiangbo Yang Yan Tang Xiaopeng Tang Dongmei Deng Hongzhan Liu Zhongchao Wei 《Annalen der Physik》2019,531(9)
A PT‐symmetric periodic structure with two‐material waveguide networks is constructed. In this study, how changing the number of cells affects the transmission properties is investigated. The results show that the PT‐unbroken (broken) region of the system is only determined by the cell structure, regardless of the number of unit cells. This means that any system has the same exceptional points (EPs), regardless of the number of cells and as long as the cell structure is consistent. In addition, it is confirmed that the coherent perfect absorbers and lasers (CPA lasers) occur in our model. The transfer matrix method is used to derive a sufficient condition for achieving the CPA laser point. A simple, effective formula for predicting the CPA laser state in an N unit cell system is derived. 相似文献
93.
Hongxun Li Yimin Zhang Zhipeng Dong Jialiang Lv Chun Gu Peijun Yao Lixin Xu Rui Zhang Jingqin Su Wei Chen Yonggang Zhu Qiwen Zhan 《Annalen der Physik》2019,531(10)
An all‐fiber laser generating a cylindrical vector beam is proposed and demonstrated using a home‐made ring‐core Yb‐doped fiber (RC‐YDF). In the RC‐YDF, not only annular doping but also ring‐type beam pump is realized. This is believed to be the first report describing the realization of annular doping and ring‐type beam pump in active fiber simultaneously, which can enhance the efficiency for high‐order mode oscillation. This laser operates in the high‐order mode stably with a slope efficiency of as high as 55.7%. Cylindrical vector modes can be obtained easily through adjusting the polarization controller. This work may have great potential for providing high‐efficiency and high‐power cylindrical vector beam and vortex beam sources. 相似文献
94.
The plasma parameters such as electron density, effective electron temperature, plasma potential, and uniformity are investigated in a new dual‐frequency cylindrical inductively coupled plasma (ICP) source operating at two frequencies (2 and 13.56 MHz) and two antennas (a two‐turn high‐frequency antenna and a six‐turn low‐frequency (LF) antenna). It is found that the electron density increases with 2 MHz power, whereas the electron temperature and plasma potential decrease with 2 MHz power at a fixed 13.56 MHz power. Moreover, the plasma uniformity can be improved by adjusting the LF power. These results indicate that a dual‐frequency synergistic discharge in a cylindrical ICP can produce a high‐density, low‐potential, low‐effective‐electron‐temperature, and uniform plasma. 相似文献
95.
《Macromolecular rapid communications》2018,39(7)
A series of polymerization‐induced self‐assembly (PISA) formulations are developed based on reversible addition‐fragmentation chain‐transfer (RAFT) dispersion polymerization of semi‐fluorinated methacrylates. Alcoholic RAFT dispersion polymerization of 2‐(perfluorobutyl)ethyl methacrylate (FBEMA), 2‐(perfluorohexyl)ethyl methacrylate (FHEMA), and 2‐(perfluorooctyl)ethyl methacrylate (FOEMA) is systematically evaluated to extend the general usability of semi‐fluorinated methacrylates to PISA. The nanostructure of the assemblies is correlated to the side‐chain length of the monomer: RAFT dispersion polymerization of FBEMA produces spherical micelles, wormlike micelles, and vesicles depending on its degree of polymerization (DP), while only spheres are generated for the PISA of FHEMA. PISA of FOEMA generates liquid crystalline cylindrical micelles, whose diameter increases with the DP of FOEMA. These results demonstrate the general feasibility of semi‐fluorinated methacrylates to PISA. Besides, PISA of FHEMA is also realized in a variety of solvents, including iso‐propanol, toluene, dioxane, and dimethyl formamide, exhibiting the superior solvent serviceability of the PISA formulations based on semi‐fluorinated methacrylates. 相似文献
96.
针对二维定常可压缩超声速非等熵柱状流,提出一种特征线差分解法,通过在沿马赫线的相容方程中添加沿流线的熵变项以描述非等熵效应,得到等熵流和非等熵流均适用的三族特征线方程组。根据水下爆炸近场特点,建立无限长柱状装药的定常模型,将三族特征线方程组用有限差分法离散求解,通过构造合适的网格保证计算格式可以数值上收敛,由此编制程序并计算几种柱状炸药的水下爆炸近场冲击波。对比有限元模拟结果和实验结果发现,特征线差分法可以比较准确地捕捉冲击波形状并计算冲击波后流场,从而验证了所提出的三族特征线差分法的准确性。 相似文献
97.
采用分离式霍普金森杆实验技术,对表面加工后不同粗糙度的6061铝合金薄壁圆柱管进行动态膨胀断裂冻结回收实验,并对薄壁金属圆柱管动态膨胀断裂过程中裂纹萌生、扩展情况以及最终断裂模式等进行了研究。结果表明：相同冲击压力条件下,薄壁金属圆柱管表面粗糙度越大,材料越容易发生膨胀破裂;裂纹萌生于外壁面,由外向内扩展,并且裂纹的扩展主要受裂纹处应力状态的影响;薄壁金属圆柱管的断裂模式由拉伸和剪切断裂机制起主导作用,其断口为拉剪混合型断口。 相似文献
98.
光学Talbot效应通常是在固体波导中产生的,并且对于一种固体波导结构,只有一种特定的Talbot效应.这种不可调节的缺陷极大地限制了Talbot效应的应用.本文设计了一种液体梯形波导(liquid trapezoidal waveguide),通过光流控技术操纵液体扩散,实现了可调节的Talbot效应.仿真实验结果表明,该液体梯形波导不仅可以实现类似固体波导的特定Talbot效应,还可以通过调节液体流速,实现对干涉焦点所在焦面左漂移和右漂移的调控.这种液体梯形波导有效地解决了传统固体波导中Talbot效应不可调节的问题,可以应用在可调节光学系统设计中. 相似文献
99.
We develop a master equation approach to describe the dynamics of distant resonators coupled through a one-dimensional waveguide. Our method takes into account the back-actions of the reservoirs, and enables us to calculate the exact dynamics of the complete system at all times. We show that such system can cause nonexponential and long-lived photon decay due to the existence of a relaxation effect. The physical origin of non-Markovianity in our model system is the finite propagation speed resulting in time delays in communication between the nodes, and strong decay rate of the emitters into the waveguide. When the distance satisfies the standing wave condition, we find that when the time delay is increased, the dark modes formation is no longer perfect, and the average photon number of dark mode decreases in steady time limit. 相似文献
100.
北极水声学作为水声学研究的一部分,起步要比达·芬奇所描述的声呐雏形晚很多年。第二次世界大战后北极水声学的研究开始受到发达国家(主要是美国)的重视。它的发展和研究重点带有明显的冷战烙印。冷战结束之后,随着北极持续变暖的趋势,北极及其毗邻海域的海洋水声环境受到特别的重视。环北极的8个国家组成排他性的北极理事会。我国政府于2018年1月26日发表北极政策白皮书,声明中国是近北极国家,是北极地区利益攸关方。本文介绍北极水声学研究的新进展,包括我国有关涉海单位近年来所做的科考和学术研究。指出,北极水声学的研究不局限于把传统水声学中的研究内容(如环境噪声、混响、传播等等)并行地在北极环境条件下加以重复探讨,而是要根据北极海洋环境的实际情况,进行有关领域的新研究。其中不乏传统浅海、深海水声学研究中所不具有的特色,如冰-水界面、冰下的半声道效应、冰盖下水下无人载器(UUV)的通信、定位及声呐对冰下环境的适应性研究等课题。 相似文献