全文获取类型
收费全文 | 2775篇 |
免费 | 654篇 |
国内免费 | 152篇 |
专业分类
化学 | 306篇 |
晶体学 | 19篇 |
力学 | 15篇 |
综合类 | 1篇 |
数学 | 8篇 |
物理学 | 1829篇 |
无线电 | 1403篇 |
出版年
2024年 | 12篇 |
2023年 | 29篇 |
2022年 | 58篇 |
2021年 | 86篇 |
2020年 | 98篇 |
2019年 | 65篇 |
2018年 | 65篇 |
2017年 | 105篇 |
2016年 | 105篇 |
2015年 | 91篇 |
2014年 | 167篇 |
2013年 | 115篇 |
2012年 | 228篇 |
2011年 | 232篇 |
2010年 | 139篇 |
2009年 | 136篇 |
2008年 | 236篇 |
2007年 | 211篇 |
2006年 | 193篇 |
2005年 | 125篇 |
2004年 | 108篇 |
2003年 | 87篇 |
2002年 | 131篇 |
2001年 | 86篇 |
2000年 | 97篇 |
1999年 | 59篇 |
1998年 | 48篇 |
1997年 | 57篇 |
1996年 | 52篇 |
1995年 | 54篇 |
1994年 | 40篇 |
1993年 | 21篇 |
1992年 | 26篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 24篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 3篇 |
排序方式: 共有3581条查询结果,搜索用时 15 毫秒
51.
《Journal of Polymer Science.Polymer Physics》2018,56(13):965-969
Interchain interactions can play a positive role in reaching amplified spontaneous emission in an interesting core–polymer system where the donor (side chains) and the acceptor (core) are chemically linked together. Different degree of interchain interactions modifies the photophysical characteristics of the polymer. By means of transient absorption spectroscopy we show that the stimulated emission from the core decreases passing from solid state to concentrated solution and it is almost absent in the diluted solution. The conformational rearrangements of the core–polymer chain in solution limits the efficiency of the intrachain Förster energy transfer mechanism. The free chain rotations decrease the exciton hopping along the conjugated chains, the ratio between donor and acceptor moieties in the polymer, and change the relative orientation of the transition dipoles of the donor and acceptor causing a strong decrease of energy transfer efficiency and subsequently of the gain. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 965–969 相似文献
52.
Material growth and device fabrication of terahertz quantum-cascade laser based on bound-to-continuum structure
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The terahertz quantum-cascade laser (THz QCL) based on bound-to-continuum structure is demonstrated. The X-ray diffraction measurement of the material shows a high crystalline quality of the active region. A THz QCL device was fabricated with semi-insulating surface-plasmon waveguide. The test device is lasing at about 3 THz and operating up to 60 K. It shows a single frequency property under different drive currents and temperatures. At 9 K, the maximum output power is greater than 2 mW with a threshold current density of 159 A/cm2. 相似文献
53.
Hao Zhang Dr. Xu Liu Ting-Ting Lu Peng Lv Prof. Wen-Yong Lai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3909-3917
A series of monodisperse six-armed conjugated starbursts ( Tr1F , Tr2F , and Tr3F ) containing a truxene core and multibranched oligofluorene bridges capped with diphenylamine (DPA) units has been designed, synthesized, and investigated as robust gain media for organic semiconductor lasers (OSLs). The influence of electron-rich DPA end groups on their optoelectronic characteristics has been discussed at length. DPA cappers effectively raise HOMO levels of the starbursts, thus enhancing the hole injection and transport ability. Solution-processed electroluminescence devices based on the resulting six-armed starbursts exhibited efficient deep-blue electroluminescence with clear reduced turn-on voltages (3.2–3.5 V). Moreover, the resulting six-armed molecules showed stabilized electroluminescence and amplified spontaneous emission with low thresholds (27.4–63.9 nJ pulse−1), high net gain coefficients (80.1–101.3 cm−1), and small optical loss (2.6–4.4 cm−1). Distributed feedback OSLs made from Tr3F exhibited a low lasing threshold of 0.31 kW cm−2 (at 465 nm). The results suggest that the construction of truxene-centered six-armed conjugated starbursts with the incorporation of DPA units can effectively enhance EL properties by precisely regulating the HOMO energy levels, and further optimizing their optical gain properties. 相似文献
54.
Dr. Alexey S. Kiryutin Dr. Grit Sauer Dr. Daniel Tietze Martin Brodrecht Stephan Knecht Prof. Dr. Alexandra V. Yurkovskaya Prof. Dr. Konstantin L. Ivanov Dr. Olga Avrutina Prof. Dr. Harald Kolmar Prof. Dr. Gerd Buntkowsky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(16):4025-4030
Two-dimensional NMR spectroscopy is one of the most important spectroscopic tools for the investigation of biological macromolecules. However, due to the low sensitivity of NMR spectroscopy, it takes usually from several minutes to many hours to record such spectra. Here, the possibility of detecting a bioactive derivative of the sunflower trypsin inhibitor-1 (SFTI-1), a tetradecapeptide, by combining parahydrogen-induced polarization (PHIP) and ultrafast 2D NMR spectroscopy is shown. The PHIP activity of the inhibitor was achieved by labeling with O-propargyl-l -tyrosine. In 1D PHIP experiments a signal enhancement of a factor of approximately 1200 compared to standard NMR was found. This enhancement permits measurement of 2D NMR correlation spectra of low-concentrated SFTI-1 in less than 10 seconds, employing ultrafast single-scan 2D NMR detection. As experimental examples PHIP-assisted ultrafast single-scan TOCSY spectra of SFTI-1 are shown. 相似文献
55.
Detailed gas-phase chemical kinetic models are widely used in combustion research, and many new mechanisms for different fuels and reacting conditions are developed each year. Recent works have highlighted the need for error checking when preparing such models, but a useful community tool to perform such analysis is missing. In this work, we present a simple online tool to screen chemical kinetic mechanisms for bimolecular reactions exceeding collision limits. The tool is implemented on a user-friendly website, cloudflame.kaust.edu.sa, and checks three different classes of bimolecular reactions; (ie, pressure independent, pressure-dependent falloff, and pressure-dependent PLOG). In addition, two other online modules are provided to check thermodynamic properties and transport parameters to help kinetic model developers determine the sources of errors for reactions that are not collision limit compliant. Furthermore, issues related to unphysically fast timescales can remain an issue even if all bimolecular reactions are within collision limits. Therefore, we also present a procedure to screen ultrafast reaction timescales using computational singular perturbation. For demonstration purposes only, three versions of the rigorously developed AramcoMech are screened for collision limit compliance and ultrafast timescales, and recommendations are made for improving the models. Larger models for biodiesel surrogates, tetrahydropyran, and gasoline surrogates are also analyzed for exemplary purposes. Numerical simulations with updated kinetic parameters are presented to show improvements in wall-clock time when resolving ultrafast timescales. 相似文献
56.
Phase separation dynamics of a poly(vinyl methyl ether)/polystyrene (PVME/PS) blend studied by ultrafast differential scanning calorimetry
下载免费PDF全文
![点击此处可从《Journal of Polymer Science.Polymer Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Shaochuan Luo Lai Wei Jing Jiang Ye Sha Gi Xue Xiaoliang Wang Dongshan Zhou 《Journal of Polymer Science.Polymer Physics》2017,55(18):1357-1364
In this work, ultrafast differential scanning calorimetry (UFDSC) is used to study the dynamics of phase separation. Taking poly(vinyl methyl ether)/polystyrene (PVME/PS) blend as the example, we firstly obtained the phase diagram that has lower critical solution temperature (LCST), together with the glass transition temperature (Tg) of the homogeneous blend with different composition. Then, the dynamics of the phase separation of the PVME/PS blend with a mass ratio of 7:3 was studied in the time range from milliseconds to hours, by the virtue of small time and spatial resolution that UFDSC offers. The time dependence of the glass transition temperature (Tg) of PVME‐rich phase, shows a distinct change when the annealing temperature (Ta) changes from below to above 385 K. This corresponds to the transition from the nucleation and growth (NG) mechanism to the spinodal decomposition (SD) mechanism, as was verified by morphological and rheometric investigations. For the SD mechanism, the temperature‐dependent composition evolution in PVME‐rich domain was found to follow the Williams–Landel–Ferry (WLF) laws. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1357–1364 相似文献
57.
Black phosphorus saturable absorber for ultrafast mode‐locked pulse laser via evanescent field interaction
下载免费PDF全文
![点击此处可从《Annalen der Physik》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Kichul Park Junsu Lee Young Tack Lee Won‐Kook Choi Ju Han Lee Yong‐Won Song 《Annalen der Physik》2015,527(11-12):770-776
Black phosphorus, or BP, has found a lot of applications in recent years including photonics. The most recent studies have shown that the material has an excellent optical nonlinearity useful in many areas, one of which is in saturable absorption for passive mode‐locking. A direct interaction scheme for mode‐locking, however, has a potential to optically cause permanent damage to the already delicate material. Evanescent field interaction scheme has already been proven to be a useful method to prevent such danger for other 2‐dimensional nanomaterials. In this report, we have utilized the evanescent field interaction to demonstrate that the optical nonlinear characteristics of BP is sufficiently strong to use in such an indirect interaction method. The successful demonstration of the passive mode‐locking operation has generated pulses with the pulse duration, repetition rate, and time bandwidth product of 2.18 ps, 15.59 MHz, and 0.336, respectively. 相似文献
58.
59.
60.