全文获取类型
收费全文 | 21900篇 |
免费 | 3294篇 |
国内免费 | 3031篇 |
专业分类
化学 | 13150篇 |
晶体学 | 283篇 |
力学 | 1717篇 |
综合类 | 192篇 |
数学 | 1134篇 |
物理学 | 11749篇 |
出版年
2024年 | 25篇 |
2023年 | 185篇 |
2022年 | 336篇 |
2021年 | 513篇 |
2020年 | 605篇 |
2019年 | 584篇 |
2018年 | 587篇 |
2017年 | 743篇 |
2016年 | 914篇 |
2015年 | 792篇 |
2014年 | 1093篇 |
2013年 | 2073篇 |
2012年 | 1390篇 |
2011年 | 1399篇 |
2010年 | 1104篇 |
2009年 | 1408篇 |
2008年 | 1395篇 |
2007年 | 1525篇 |
2006年 | 1405篇 |
2005年 | 1226篇 |
2004年 | 1149篇 |
2003年 | 990篇 |
2002年 | 962篇 |
2001年 | 746篇 |
2000年 | 756篇 |
1999年 | 664篇 |
1998年 | 529篇 |
1997年 | 427篇 |
1996年 | 365篇 |
1995年 | 363篇 |
1994年 | 277篇 |
1993年 | 243篇 |
1992年 | 263篇 |
1991年 | 181篇 |
1990年 | 130篇 |
1989年 | 113篇 |
1988年 | 143篇 |
1987年 | 100篇 |
1986年 | 71篇 |
1985年 | 72篇 |
1984年 | 62篇 |
1983年 | 32篇 |
1982年 | 53篇 |
1981年 | 48篇 |
1980年 | 24篇 |
1979年 | 27篇 |
1978年 | 32篇 |
1977年 | 21篇 |
1976年 | 27篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 264 毫秒
1.
《Progress in Surface Science》2022,97(3):100663
High-reflective multilayer laser coatings are widely used in advanced optical systems from high power laser facilities to high precision metrology systems. However, the real interface quality and defects will significantly affect absorption/scattering losses and laser induced damage thresholds of multilayer coatings. With the recent advances in the control of coating design and deposition processes, these coating properties can be significantly improved when properly engineered the interface and defects. This paper reviews the recent progress in the physics of laser damage, optical losses and environmental stability involved in multilayer reflective coatings for high power nanosecond near-infrared lasers. We first provide an overview of the layer growth mechanisms, ways to control the microstructures and reduce layer roughness, as well as the nature of defects which are critical to the optical loss and laser induced damage. Then an overview of interface engineering based on the design of coating structure and the regulation of deposition materials reveals their ability to improve the laser induced damage threshold, reduce the backscattering, and realize the desirable properties of environmental stability and exceptional multifunctionality. Moreover, we describe the recent progress in the laser damage and scattering mechanism of nodule defects and give the approaches to suppress the defect-induced damage and scattering of the multilayer laser coatings. Finally, the present challenges and limitations of high-performance multilayer laser coatings are highlighted, along with the comments on likely trends in future. 相似文献
2.
Cavitation erosion is caused in solids exposed to strong pressure waves developing in an adjacent fluid field. The knowledge of the transient distribution of stresses in the solid is important to understand the cause of damaging by comparisons with breaking points of the material. The modeling of this problem requires the coupling of the models for the fluid and the solid. For this purpose, we use a strategy based on the solution of coupled Riemann problems that has been originally developed for the coupling of 2 fluids. This concept is exemplified for the coupling of a linear elastic structure with an ideal gas. The coupling procedure relies on the solution of a nonlinear equation. Existence and uniqueness of the solution is proven. The coupling conditions are validated by means of quasi‐1D problems for which an explicit solution can be determined. For a more realistic scenario, a 2D application is considered where in a compressible single fluid, a hot gas bubble at low pressure collapses in a cold gas at high pressure near an adjacent structure. 相似文献
3.
New thermoelectric materials, n-type Bi6Cu2Se4O6 oxyselenides, composed of well-known BiCuSeO and Bi2O2Se oxyselenides, are synthesized with a simple solid-state reaction. Electrical transport properties, microstructures, and elastic properties are investigated with an emphasis on thermal transport properties. Similar to Bi2O2Se, it is found that the halogen-doped Bi6Cu2Se4O6 possesses n-type conducting transports, which can be improved via Br/Cl doping. Compared with BiCuSeO and Bi2O2Se, an extremely low thermal conductivity can be observed in Bi6Cu2Se4O6. To reveal the origin of low thermal conductivity, elastic properties, sound velocity, Grüneisen parameter, and Debye temperature are evaluated. Importantly, the calculated phonon mean free path of Bi6Cu2Se4O6 is comparable to the interlayer distance for BiO─CuSe and BiO─Se layers, which is ascribed to the strong interlayer phonon scattering. Contributing from the outstanding low thermal conductivity and improved electrical transport properties, the maximum ZT ≈0.15 at 823 K and ≈0.11 at 873K are realized in n-type Bi6Cu2Se3.2Br0.8O6 and Bi6Cu2Se3.6Cl0.4O6, respectively, indicating the promising thermoelectric performance in n-type Bi6Cu2Se4O6 oxyselenides. 相似文献
4.
5.
6.
A 1.5-μm eye-safe, 3-D scanning, and compact Mie LIght Detection and Ranging (LIDAR) is presented. The transmitter of the LIDAR is based on a KTA optical parameter oscillator (OPO) resonator. For detecting return signals, an InGaAs APD is used. The all solid-state OPO laser transmitter has the feature of small volume and lightweight, which allows a 165-lb compact eye-safe scanning LIDAR to be constructed. A system simulation using our own model was conducted to direct the system development. A method to solve the problem with small active area APD detectors was developed and described. The preliminary field-test measurement results indicated that the LIDAR has the capability to detect aerosols and clouds in lower atmospheres up to three dimensions. 相似文献
7.
The paper discusses the applicability of quasi-crystalline approximation to describing the thermal motion of water molecules in their normal and supercooled states. The problem is subjected to the critical analysis of experimental data on incoherent scattering of slow neutrons based on theories developed by Singwi-Sjolander [1] and Oskotsky [2] modified to duly take into account the limited applicability range of diffusion approximation. The applicability conditions of quasi-crystalline approximation are shown to be consistently satisfied only when water is in supercooled state and within a narrow temperature range above the melting temperature. 相似文献
8.
本文研究了胆绿素的表面增强拉曼光谱。结果表明,在溶液酸度不同时,拉曼光谱特征频率的变化表现出胆绿素的质子化。铜离子与胆绿素的相互作用实验结果说明金属铜离子可与胆绿素生成金属配合物。 相似文献
9.
Chien-Hsin Cheng 《中国化学会会志》1994,41(1):33-38
Dynamic and static scattering of light was employed to investigate mixed micelles of two homologous anionic surfactants-sodium octyl sulfate and sodium hexadecyl sulfate, above the phase boundary temperature and critical micelle concentrations (cmc). The results indicate that the mixed micelles change from prolate to sphcrical as the molar ratio SOS/SHS increases from 1 to 8. Below 1 or above 8, the formation of micelles is due to one surfactant dissolving the other. 相似文献
10.
Phase Relations and Sodium Ion Conductivity within the Quasi-binary System Na2SiF6/Na2AIF6 . The phase diagram of the Na2SiF6/Na3AlF6 system has been determined by means of x-ray powder diffraction, thermal analysis and conductivity measurements in the sub-solidus region. Na3AlF6 accomodates up to 73 mol.-% Na2SiF6 maintaining the crystal structure type. The sodium ion conductivity increases by about five orders of magnitude upon doping Na3AlF6 with Na2SiF6. 相似文献