全文获取类型
收费全文 | 368篇 |
免费 | 8篇 |
国内免费 | 69篇 |
专业分类
化学 | 220篇 |
力学 | 21篇 |
综合类 | 10篇 |
数学 | 60篇 |
物理学 | 134篇 |
出版年
2024年 | 1篇 |
2022年 | 3篇 |
2021年 | 3篇 |
2018年 | 1篇 |
2015年 | 6篇 |
2013年 | 3篇 |
2012年 | 7篇 |
2011年 | 48篇 |
2010年 | 33篇 |
2009年 | 31篇 |
2008年 | 3篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 19篇 |
2004年 | 52篇 |
2003年 | 49篇 |
2002年 | 32篇 |
2001年 | 17篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 18篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
排序方式: 共有445条查询结果,搜索用时 15 毫秒
41.
ZHAO JinYu LI JiaHuang ZHANG Zheng ZHANG ShuYi QU Min FANG JianWen HUA ZiChun 《中国科学:物理学 力学 天文学(英文版)》2013,(7):1301-1309
The enthalpy and conformational volume changes in the photolyses of carboxy-hemoglobin (HbCO) of human, bovine, pig, horse and rabbit are investigated by photoacoustic calorimetry. Considering the time scales of the exciting laser pulse and the receiving ultrasound transducers (PVDF films and PZT ceramics), as well as the reaction lifetimes in the photolysis processes of HbCO, the measured results are related to the geminate recombination and tertiary relaxation in photolyses of HbCO. Moreover, the quantum yields of the five mammals are also measured by laser pump-probe technique. The results show that the dynamic parameters, such as enthalpy and conformational volume changes, differ between the processes of the geminate recombination and tertiary relaxation. Also, the dynamic parameters differ among the five mammals although some of them may be consistent with each other. 相似文献
42.
Ruifang Yang Nanjing Zhao Xue Xiao Shaohui Yu Jianguo Liu Wenqing Liu 《Journal of Chemometrics》2015,29(8):442-447
Sparse non‐negative matrix factorization on right side factor (SNMF/R) has better performance in feature extraction than non‐negative matrix factorization. In this work, SNMF/R was first used to separate the overlapped three‐dimensional fluorescence spectra of polycyclic aromatic hydrocarbons mixtures in pure water, lake water, and river water, respectively. It is found that the similarity coefficients between the acquired three‐dimensional spectra and the corresponding reference spectra with random initials are all above 0.80; the recognition rate of SNMF/R is higher than that of PARAFAC and non‐negative matrix factorization algorithms, especially in the case of lake water and river water samples. In addition, SNMF/R does not need any initialization scheme designing during spectra separation. These results demonstrate that SNMF/R is an appropriate algorithm to separate the overlapped fluorescence spectra of polycyclic aromatic hydrocarbons in aquatic environment accurately and effectively. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
43.
System calibration, which usually involves complicated and time-consuming procedures, is crucial for any three-dimensional (3D) shape measurement system based on vision. A novel improved method is proposed for accurate calibration of such a measurement system. The system accuracy is improved with considering the nonlinear measurement error created by the difference between the system model and real measurement environment. We use Levenberg-Marquardt optimization algorithm to compensate the error and get a good result. The improved method has a 50% improvement of re-projection accuracy compared with our previous method. The measurement accuracy is maintained well within 1.5% of the overall measurement depth range. 相似文献
44.
WANG Wei & ZHU Jun-Jie State Key Laboratory of Analytical Chemistry for Life Science School of Chemistry Chemical Engineering Nanjing University Nanjing China 《中国科学B辑(英文版)》2011,(8)
This review presents a simple introduction on the unique properties and general synthesis of quantum dots (QDs) in which we lay emphasis on the optical applications in the biological system. The detection of biological molecules such as DNA, protein and enzyme, the cell-based analysis and in vivo animal imaging are mainly discussed. 相似文献
45.
In this paper, a new one-step explicit method of fourth order is derived. The new method is proved to be A-stable and L-stable, and it gives exact results when applied to the test equation y'=λy with Re(λ)<0, Also several numerical examples are included. 相似文献
46.
在醋酸/水体系的工业分离中,溶液中的氢键对分离效率有很大影响.本文采用两种第一性原理方法,即从头算分子动力学模拟(AIMD)和量子化学计算(QCC),对由单个醋酸和不同水分子所组成聚合体的氢键相互作用进行了研究,采用极化统一模型和自洽反应场模型计算得到了聚合体在水溶液中的热力学数据.从QCC计算的气相和水溶液中的聚合自由能表明六元环在两种状态下都为最优结构,热力学数据反映出的各种结构的相对稳定性与AIMD模拟的环分布符合得相当一致.研究表明,由于存在醋酸和水分子间的氢键作用,稀醋酸/水溶液中的醋酸分离要比在浓醋酸溶液中困难得多. 相似文献
47.
We create a GaN photocathode based on graded Alx Ga1-x N buffer layers to overcome the influence of buffer-emission layer interface on the photoemission of transmission-mode GaN photocathodes.A gateshaped spectral response with a 260-nm starting wavelength and a 375-nm cut-off wavelength is obtained.Average quantum efficiency is 15% and short wavelength responses are almost equivalent to long wavelength ones.The fitted interface recombination velocity is 5×104 cm/s,with negligible magnitude,proving that the design of the graded buffer layers is efficient in obtaining good interface quality between the buffer and the emission layer. 相似文献
48.
49.
In the framework of the relativistic mean field theory, the effects of the δ meson on the direct Urca (DURCA) processes are investigated. In a neutron star, the DURCA processes involving nucleons, Λ and Ξ- can take place while the process involving the Ξ0 can not. With the inclusion of the δ meson, the threshold densities for the DURCA processes become lower. With the δ included, the threshold neutron star mass for the DURCA process among nucleons and electrons becomes smaller while the threshold masses for the processes involving hyperons become larger. When the δ meson is included, the total neutrino emissivity remarkably increases in the density range of 0.32--0.41 fm-3. The total neutrino luminosity increases with the neutron star mass first and then decreases. The neutrino luminosity gets larger with the inclusion of the δ meson. The cooling of the EXO0748-676 is sensitive to the isovector scalar interaction. 相似文献
50.
SHEN ChangSheng SUN YongZhi SUN DeKun & YANG HongSheng State Key Laboratory of Millimeter Waves School of Electronic Science Engineering Southeast University Nanjing China School of Chemistry Chemical Engineering Nanjing University Nanjing 《中国科学:化学》2010,(1)
By optimizing the microwave chemistry reactor made of the rectangular waveguide resonator,the methane conversion(the maximum 93.7%),the C2 hydrocarbon yield(the maximum 91.0%) and the acetylene yield(the maximum 88.6%) were all greatly increased under the microwave plasma.Furthermore,for the optimal reactor,the change of the methane conversion and the C2 hydrocarbon yield is little within the range of the pressures in the experiments.The C2 hydrocarbon is mainly made up of acetylene,and the selectivity for ... 相似文献