全文获取类型
收费全文 | 1379篇 |
免费 | 294篇 |
国内免费 | 16篇 |
专业分类
化学 | 143篇 |
晶体学 | 16篇 |
力学 | 15篇 |
综合类 | 1篇 |
数学 | 5篇 |
物理学 | 1509篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 16篇 |
2021年 | 17篇 |
2020年 | 20篇 |
2019年 | 16篇 |
2018年 | 24篇 |
2017年 | 45篇 |
2016年 | 47篇 |
2015年 | 35篇 |
2014年 | 59篇 |
2013年 | 56篇 |
2012年 | 55篇 |
2011年 | 91篇 |
2010年 | 71篇 |
2009年 | 66篇 |
2008年 | 107篇 |
2007年 | 93篇 |
2006年 | 79篇 |
2005年 | 57篇 |
2004年 | 63篇 |
2003年 | 44篇 |
2002年 | 94篇 |
2001年 | 43篇 |
2000年 | 51篇 |
1999年 | 39篇 |
1998年 | 32篇 |
1997年 | 40篇 |
1996年 | 41篇 |
1995年 | 41篇 |
1994年 | 18篇 |
1993年 | 16篇 |
1992年 | 10篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 21篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 22篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1970年 | 1篇 |
排序方式: 共有1689条查询结果,搜索用时 15 毫秒
121.
122.
In modern short-pulse fiber lasers, there is significant pulse breathing over each round trip of the laser loop. Consequently, averaged models cannot be used for quantitative modeling and design. Instead, lumped models, which are obtained by concatenating models for the various components of the laser, are required. As the pulses in lumped models are periodic rather than stationary, their linear stability is evaluated with the aid of the monodromy operator obtained by linearizing the round-trip operator about the periodic pulse. Conditions are given on the smoothness and decay of the periodic pulse that ensure that the monodromy operator exists on an appropriate Lebesgue function space. A formula for the essential spectrum of the monodromy operator is given, which can be used to quantify the growth rate of continuous wave perturbations. This formula is established by showing that the essential spectrum of the monodromy operator equals that of an associated asymptotic operator. Since the asymptotic monodromy operator acts as a multiplication operator in the Fourier domain, it is possible to derive a formula for its spectrum. Although the main results are stated for a particular experimental stretched pulse laser, the analysis shows that they can be readily adapted to a wide range of lumped laser models. 相似文献
123.
Tina Friedenauer Kim Buck Maike Eberwein Anna-Lena Bünte Christoph Rehbock Stephan Barcikowski 《Particle & Particle Systems Characterization》2023,40(12):2300034
One challenge in the development of new drug formulations is overcoming their low solubility in relevant aqueous media. Reducing the particle size of drug powders to a few hundred nanometers is a well-known method that leads to an increase in solubility due to an elevated total surface area. However, state-of-the-art comminution techniques like cryo-milling suffer from degradation and contamination of the drugs, particularly when sub-micrometer diameters are aspired that require long processing times. In this work, picosecond-pulsed laser fragmentation in liquids (LFL) of dispersed drug particles in a liquid-jet passage reactor is used as a wear-free comminution technique using the hydrophobic oral model drugs naproxen, prednisolone, ketoconazole, and megestrol acetate. Particle size and morphology of the drug particles are characterized using scanning electron microscopy (SEM) and changes in particle size distributions upon irradiation are quantified using an analytical centrifuge. The findings highlight the superior fragmentation efficiency of the liquid-jet passage reactor setup, with a 100 times higher fraction of submicrometer particles (SMP) of the drugs compared to the batch control, which enhances solubility and goes along with minimal chemical degradation (<1%), determined by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), high-performance liquid chromatography (HPLC), and X-ray diffraction (XRD). Moreover, the underlying predominantly photo-mechanically induced laser fragmentation mechanisms of organic microparticles (MP) are discussed. 相似文献
124.
Omar Alkhazragi Hang Lu Wenbo Yan Nawal Almaymoni Tae-Yong Park Yue Wang Tien Khee Ng Boon S. Ooi 《Annalen der Physik》2023,535(9):2300289
Random number generation (RNG) is needed for a myriad of applications ranging from secure communication encryption to numerical simulations to sports and games. However, generating truly random numbers can be elusive. Pseudorandom bit generation using computer algorithms provides a high random bit generation rate. Nevertheless, the reliance on predefined algorithms makes it deterministic and predictable once initial conditions are known. Relying on physical phenomena (such as measuring electrical noise or even rolling dice) can achieve a less predictable sequence of bits. Furthermore, if the physical phenomena originate from quantum effects, they can be truly random and completely unpredictable due to quantum indeterminacy. Traditionally, physical RNG is significantly slower than pseudorandom techniques. To meet the demand for high-speed RNG with perfect unpredictability, semiconductor light sources are adopted as parts of the sources of randomness, i.e., entropy sources, in quantum RNG (QRNG) systems. The high speed of their noise, the high efficiency, and the small scale of these devices make them ideal for chip-scale QRNG. Here, the applications and recent advances of QRNG are reviewed using semiconductor emitters. Finally, the performance of these emitters is compared and discuss their potential in future technologies. 相似文献
125.
Christian Krnkel Daniel‐Timo Marzahl Francesca Moglia Günter Huber Philip Werner Metz 《Laser \u0026amp; Photonics Reviews》2016,10(4):548-568
The rise of semiconductor‐based pump sources such as InxGa1‐xN‐laser diodes or frequency‐doubled optically pumped semiconductor lasers with emission wavelengths in the blue encourages a revisitation of the rare‐earth ions Pr3+, Sm3+, Tb3+, Dy3+, Ho3+ and Er3+ with respect to their properties as active ions in crystalline solid‐state laser materials with direct emission in the visible spectral range. Nowadays, some of these blue‐pumped visible lasers compete with Nd3+‐lasers in terms of efficiency and direct lasing at various colors from the cyan‐blue to the deep red can be addressed in very simple and compact laser setups. This paper highlights the spectroscopic properties of suitable rare‐earth ions for visible lasing and reviews the latest progress in the field of blue‐pumped visible rare‐earth doped solid‐state lasers.
126.
127.
128.
提出了一种利用半导体环形激光器(SRLs)的新型高速双向、双信道混沌保密通信系统. 在该系统中, 首先利用交叉双光反馈对驱动激光器的顺时针模式和逆时针模式的混沌延时特征进行抑制. 然后将此混沌信号注入到一对响应激光器对应的顺时针模和逆时针模中, 以实现带宽的增强及混沌同步. 最后基于响应激光器之间的混沌同步, 实现高速率、双向、双信道的混沌保密通信. 通过对驱动激光器在交叉双光反馈作用下的混沌特性、以及响应激光器在不同条件下的同步特性进行了相关理论和仿真研究, 结果表明: 驱动激光器在合适的交叉双光反馈作用下可以产生延时特性被良好隐藏的顺时针模式和逆时针模式混沌信号; 在该混沌信号的注入下, 响应激光器输出的混沌信号带宽可以得到明显增强; 通过设置合适注入强度值和频率失谐值, 响应激光器之间可实现高质量的等时混沌同步. 最后, 对系统的双向、双信道混沌保密通信特性进行了讨论. 当10 Gbit/s信号传输距离为10 km时, 解调信息Q因子值仍可保持在6以上. 相似文献
129.
基于氧化限制型内腔接触垂直腔面发射激光器(VCSEL) 结构设计, 研究了VCSEL的多横模分布及其模式波长分裂特性与氧化孔径尺寸、形状的关系. 在实验基础上, 通过建立有效折射率模型, 并利用标量亥姆霍兹方程的迭代算法理论, 分别对椭圆形氧化孔径和圆形氧化孔径VCSEL的横向模式特性进行模拟研究, 计算得到不同形状孔径的多横模光场分布情况, 同时测量得到高阶横模多频输出光谱. 研究发现, 椭圆氧化孔形状不仅影响横模分布特性, 还会导致每个模式的波长产生分裂, 分裂值可达0.037 nm. 同时, 随着氧化孔径的增大, 波长分裂影响会逐渐减小, 直至趋近于圆形氧化孔径的分布特性. 研究结果为进一步实现氧化限制型VCSEL的多横模锁定提供了有益参考和借鉴. 相似文献
130.
There is enormous interest in visualizing the chemical composition of organic material that comprises our world. A convenient method to obtain molecular information with high spatial resolution is imaging mass spectrometry. However, the internal energy deposited within molecules upon transfer to the gas phase from a surface can lead to increased fragmentation and to complications in analysis of mass spectra. Here it is shown that in laser desorption with postionization by tunable vacuum ultraviolet (VUV) radiation, the internal energy gained during laser desorption leads to minimal fragmentation of DNA bases. The internal temperature of laser‐desorbed triacontane molecules approaches 670 K, whereas the internal temperature of thymine is 800 K. A synchrotron‐based VUV postionization technique for determining translational temperatures reveals that biomolecules have translational temperatures in the range of 216–346 K. The observed low translational temperatures as well as their decrease with increased desorption laser power is explained by collisional cooling. An example of imaging mass spectrometry on an organic polymer by using laser‐desorption VUV postionization shows 5 μm feature details while using a 30 μm laser spot size and 7 ns pulse duration. Applications of laser‐desorption postionization to the analysis of cellulose, lignin, and humic acids are briefly discussed. 相似文献