全文获取类型
收费全文 | 308篇 |
免费 | 38篇 |
国内免费 | 44篇 |
专业分类
化学 | 238篇 |
晶体学 | 3篇 |
力学 | 10篇 |
综合类 | 3篇 |
数学 | 28篇 |
物理学 | 108篇 |
出版年
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 24篇 |
2020年 | 14篇 |
2019年 | 20篇 |
2018年 | 13篇 |
2017年 | 14篇 |
2016年 | 11篇 |
2015年 | 18篇 |
2014年 | 17篇 |
2013年 | 14篇 |
2012年 | 20篇 |
2011年 | 34篇 |
2010年 | 16篇 |
2009年 | 7篇 |
2008年 | 23篇 |
2007年 | 18篇 |
2006年 | 12篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2000年 | 14篇 |
1999年 | 10篇 |
1998年 | 3篇 |
1997年 | 12篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1991年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
排序方式: 共有390条查询结果,搜索用时 31 毫秒
381.
单粒子效应(SEE)加速器地面模拟需要离子束具有较好的均匀度,针对回旋加速器单粒子效应模拟的束流特点,建立了一套以位置灵敏平行板雪崩探测器(Parallel Plate Avalanche Counter,PPAC)为基础的均匀度探测系统并完成了带束测试,对它的结构、工作原理、均匀度获得方法及带束测试结果进行描述。为验证PPAC测量结果准确性,在带束测试过程中,前方同时放置PET膜测量穿过PPAC探测器的粒子分布,与离子径迹测量结果对比,给出PPAC的均匀度的测量误差在5%之内。探测器具有50 mm×50 mm的灵敏面积和小于1 mm的位置分辨,符合单粒子效应实验对束流均匀度测量的要求。 相似文献
382.
A novel three-dimensional cellular automata evacuation model was proposed based on stairs factor for paired effect and variety velocities in pedestrian evacuation. In the model pedestrians' moving probability of target position at the next moment was defined based on distance profit and repulsive force profit, and evacuation strategy was elaborated in detail through analyzing variety velocities and repulsive phenomenon in moving process. At last, experiments with the simulation platform were conducted to study the relationships of evacuation time, average velocity and pedestrian velocity. The results showed that when the ratio of single pedestrian was higher in the system, the shortest route strategy was good for improving evacuation efficiency; in turn, if ratio of paired pedestrians was higher, it is good for improving evacuation efficiency to adopt strategy that avoided conflicts, and priority should be given to scattered evacuation. 相似文献
383.
Study of the interaction between butyl p-hydroxybenzoate (butoben) and human serum albumin (HSA) has been performed by molecular modeling and multi-spectroscopic method. The interaction mechanism was predicted through molecular modeling first, then the binding parameters were confirmed using a series of spectroscopic methods, including fluorescence spectroscopy, UV-visible absorbance spectroscopy, circular dichroism (CD) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The thermodynamic parameters of the reaction, standard enthalpy ΔH0 and entropy ΔS0, have been calculated to be −29.52 kJ mol−1 and −24.23 J mol−1 K−1, respectively, according to the Van’t Hoff equation, which suggests the van der Waals force and hydrogen bonds are the predominant intermolecular forces in stabilizing the butoben-HSA complex. Results obtained by spectroscopic methods are consistent with that of the molecular modeling study. In addition, alteration of secondary structure of HSA in the presence of butoben was evaluated using the data obtained from UV-visible absorbance, CD and FT-IR spectroscopies. 相似文献
384.
在确定天线数值模型的基础上,结合高功率微波天线的真空需要与实验装置情况,设计并加工了X波段基于漏波波导的高功率微波天线,对该天线分别进行低功率和高功率条件下的性能指标测试。在低功率条件下天线测试结果表明:在9.6 GHz下天线增益为26.3 dBi,天线方向图与数值模拟结果一致。在SINUS881加速器上利用返波管进行了天线高功率测试,实验结果表明:天线功率容量大于200 MW,高功率测试方向图、低功率测试方向图和数值模拟取得较为一致的结果。 相似文献
385.
Gang Chen Min Zhang Min Pang Xiao-qing Hou Huijun Su Jie Zhang 《Research on Chemical Intermediates》2013,39(8):3545-3552
Extracts of pomegranate have been investigated, by use of weight loss and potentiodynamic polarization techniques, as green and eco-friendly inhibitors of corrosion of Q235A steel in 1 M hydrochloric acid solution at 60 °C. The efficiency of inhibition by the extracts varied with extract concentration from 10 to 1,000 mg/L; the highest efficiency was 95.0 %. The extracts inhibit corrosion mainly by an adsorption mechanism. In addition, the hydroxyl and ether groups of polyphenols can capture the H+ to reduce the corrosion, and the polyphenols can eliminate dissolved O2 to inhibit oxygen-adsorption corrosion. Potentiodynamic polarization studies show that extracts are mixed-type inhibitors. 相似文献
386.
We study a Cr4+:YAG Q-switched Nd:YAG laser with a thermally-insensitive corner-cube-prism cavity where the corner cube prism is the key element. The corner cube prism is insensitive to misalignment in any direction. We demonstrate experimentally that a laser cavity with such a prism provides stable laser performance under violent changes of ambient temperature and the effect of the laser crystal thermal lens. The laser mode properties are analyzed by numerical simulations. We show that the numerically simulated results agree well with the experimental ones. 相似文献
387.
通过光学显微镜、拉曼光谱确定了CVD(化学气相沉积法)制备的不同厚度MoS2的层数,采用拉曼分析结合原子力显微镜观测分析了由HIRFL提供的高能209Bi离子辐照CVD制备的单层MoS2样品随辐照注量的损伤规律。随辐照注量增加,E2g1和A1g两种声子振动模式对应的拉曼峰逐渐蓝移,且拉曼特征峰强度减弱,这是由于带正电荷的209Bi辐照产生潜径迹型晶格缺陷吸附空气中氧分子而引入p型掺杂引起的。同时,在辐照注量为5×1010 ions/cm2的单层MoS2的AFM图像中观察到潜径迹主要以凹坑形式出现,与机械剥离法观测到的凸起径迹明显不同,分析了不同制备工艺对径迹形貌的影响。比较了机械剥离法制备MoS2样品的拉曼光谱和AFM成像的实验数据和结果,认为不同制备方法会影响单层或少层MoS2的电子密度。The layer number of MoS2 with different thickness was determined by the optical microscope and Raman spectra. And the damage effect of the CVD (chemical vapor deposition) prepared single-layer MoS2 sample irradiated by 209Bi ions was analyzed by the combination of Raman analysis and AFM observations. With the increase of irradiation fluence, the Raman characteristic peaks of E2g1 and A1g corresponding to both phonon vibration modes gradually bluely shift, and the intensity of the peaks obviously decreased. This is due to the fact that the 209Bi ion irradiation results in the latent track type lattice defects and they adsorb the oxygen molecules in the air ended with the p-type doping. Meanwhile, from the AFM image of the mono-layer of irradiated MoS2 under the 5×1010 ions/cm2, it can been seen that latent tracks mainly occur in the form of pits, which different from the hillock tracks observed by mechanical stripping method. The influence of different preparation technology to the track morphology is analyzed. Compared with the Raman and AFM results of MoS2 prepared by mechanical stripping, it is considered that different preparation methods will affect the electron density in single or few layers of MoS2. 相似文献
388.
Low-dimensional materials have excellent properties which are closely related to their dimensionality. However, the growth mechanism underlying tunable dimensionality from 2D triangles to 1D ribbons of such materials is still unrevealed. Here, we establish a general kinetic Monte Carlo model for transition metal dichalcogenides (TMDs) growth to address such an issue. Our model is able to reproduce several key findings in experiments, and reveals that the dimensionality is determined by the lattice mismatch and the interaction strength between TMDs and the substrate. We predict that the dimensionality can be well tuned by the interaction strength and the geometry of the substrate. Our work deepens the understanding of tunable dimensionality of low-dimensional materials and may inspire new concepts for the design of such materials with expected dimensionality. 相似文献
389.
Chong Wang Chang-Yi Tian Ya Zhao Shuai Jiang Tiantong Wang Huijun Zheng Wenhui Yan Prof. Dr. Gang Li Prof. Dr. Hua Xie Prof. Dr. Jun Li Prof. Dr. Han-Shi Hu Prof. Dr. Xueming Yang Prof. Dr. Ling Jiang 《Angewandte Chemie (International ed. in English)》2023,62(32):e202305490
Spectroscopic characterization of neutral highly-coordinated compounds is essential in fundamental and applied research, but has been proven to be a challenging experimental target because of the difficulty in mass selection. Here, we report the preparation and size-specific infrared-vacuum ultraviolet (IR-VUV) spectroscopic identification of group-3 transition metal carbonyls Sc(CO)7 and TM(CO)8 (TM=Y, La) in the gas phase, which are the first confinement-free neutral heptacarbonyl and octacarbonyl complexes. The results indicate that Sc(CO)7 has a C2v structure and TM(CO)8 (TM=Y, La) have a D4h structure. Theoretical calculations predict that the formation of Sc(CO)7 and TM(CO)8 (TM=Y, La) is both thermodynamically exothermic and kinetically facile in the gas phase. These highly-coordinated carbonyls are 17-electron complexes when only those valence electrons that occupy metal−CO bonding orbitals are considered, in which the ligand-only 4b1u molecular orbital is ignored. This work opens new avenues toward the design and chemical control of a large variety of compounds with unique structures and properties. 相似文献
390.
Weidong Ao Huijun Ren Changgen Cheng Zhishuai Fan Prof. Qing Qin Prof. Peiqun Yin Prof. Qi Zhang Prof. Lei Dai 《Angewandte Chemie (International ed. in English)》2023,62(42):e202307924
Rational design of electrocatalysts is essential to achieve desirable performance of electrochemical synthesis process. Heterostructured catalysts have thus attracted widespread attention due to their multifunctional intrinsic properties, and diverse catalytic applications with corresponding outstanding activities. Here, we report an in situ restoration strategy for the synthesis of ultrathin Pd-Ni(OH)2 nanosheets. Such Pd-Ni(OH)2 nanosheets exhibit excellent activity and selectivity towards reversible electrochemical reforming of ethylamine and acetonitrile. In the acetonitrile reduction process, Pd acts as reaction center, while Ni(OH)2 provide proton hydrogen through promoting the dissociation of water. Also ethylamine oxidation process can be achieved on the surface of the heterostructured nanosheets with abundant Ni(II) defects. More importantly, an electrolytic cell driven by solar cells was successfully constructed to realize ethylamine-acetonitrile reversible reforming. This work demonstrates the importance of heterostructure engineering in the rational synthesis of multifunctional catalysts towards electrochemical synthesis of fine chemicals. 相似文献