全文获取类型
收费全文 | 29871篇 |
免费 | 5137篇 |
国内免费 | 3866篇 |
专业分类
化学 | 21419篇 |
晶体学 | 417篇 |
力学 | 2066篇 |
综合类 | 282篇 |
数学 | 3357篇 |
物理学 | 11333篇 |
出版年
2024年 | 108篇 |
2023年 | 653篇 |
2022年 | 1175篇 |
2021年 | 1245篇 |
2020年 | 1323篇 |
2019年 | 1278篇 |
2018年 | 1066篇 |
2017年 | 956篇 |
2016年 | 1436篇 |
2015年 | 1538篇 |
2014年 | 1704篇 |
2013年 | 2244篇 |
2012年 | 2603篇 |
2011年 | 2719篇 |
2010年 | 1802篇 |
2009年 | 1702篇 |
2008年 | 1796篇 |
2007年 | 1636篇 |
2006年 | 1568篇 |
2005年 | 1357篇 |
2004年 | 1133篇 |
2003年 | 871篇 |
2002年 | 847篇 |
2001年 | 773篇 |
2000年 | 657篇 |
1999年 | 612篇 |
1998年 | 496篇 |
1997年 | 424篇 |
1996年 | 448篇 |
1995年 | 402篇 |
1994年 | 375篇 |
1993年 | 296篇 |
1992年 | 299篇 |
1991年 | 245篇 |
1990年 | 230篇 |
1989年 | 175篇 |
1988年 | 109篇 |
1987年 | 106篇 |
1986年 | 96篇 |
1985年 | 93篇 |
1984年 | 56篇 |
1983年 | 59篇 |
1982年 | 45篇 |
1981年 | 26篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1977年 | 6篇 |
1975年 | 6篇 |
1973年 | 6篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
光电直读光谱法测定稀土铝合金中La,Ce,Pr,Nd,Sm ,Si,Fe,Cu 总被引:3,自引:0,他引:3
李跃平 《光谱学与光谱分析》2002,22(2):317-319
本文报道了稀土铝合金中La,Ce,Pr,Nd,Sm,Si,Fe,Cu的光电直读光谱测定,对光源的激发方式及最佳工作条件进行了选择,应用KH-5高能预火花光源,采用单向全功率放电,先冲洗3秒,然后预燃5秒,曝光10秒。各元素谱线间无干扰,。使用固体试样,样品处理简单。经试验验证该法简便快速,精密度准确度高,含量在0.001%-0.002%之间RSD<6%,0.02%-0.3%之间RSD<3%,标准样品的测定值与准确值吻合较好,结果令人满意。 相似文献
994.
Two multivariate hazard rate stochastic orders are introduced and studied. Their meaning, properties, and relationship to other common stochastic orders are examined and investigated. Some examples that illustrate the theory are detailed. Finally, some applications of the new orders in reliability theory and in actuarial science are described. 相似文献
995.
996.
The problem of generating a matrix A with specified eigen‐pair, where A is a symmetric and anti‐persymmetric matrix, is presented. An existence theorem is given and proved. A general expression of such a matrix is provided. We denote the set of such matrices by ??????En. The optimal approximation problem associated with ??????En is discussed, that is: to find the nearest matrix to a given matrix A* by A∈??????En. The existence and uniqueness of the optimal approximation problem is proved and the expression is provided for this nearest matrix. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
997.
A stable single longitudinal mode (SLM) fiber ring laser that incorporates polarization maintaining erbium doped fiber (PM EDF) acting as gain medium and saturable absorber is proposed and demonstrated. Both theoretical deviation and experimental result prove that optical intensity is time invariant when the laser operates in single longitudinal mode, the SLM operation can be approximately verified by optical intensity analysis, which is practical to analyze longitudinal mode in the application of engineering. The linewidth of the fiber ring laser is measured by the delayed self-heterodyne interferometery, and an acousto-optic frequency shifter is employed to shift the lasing frequency and eliminate zero frequency interfere. The SLM operation is verified by the scanning Fabry–Perot interferometer, whereas the lasing frequency drift slowly during a period of 2 h, PM EDF is proved to be effective on suppressing mode hopping and selecting longitudinal mode. 相似文献
998.
The fringe pattern phase analysis method is proposed for the leveling of mask and wafer in proximity lithography. The tilt between mask and wafer in the space is reflected in the tilted fringe pattern. The method combining the 2-D Fourier transform and 2-D Hanning window is proposed for processing the tilted fringe pattern. The offset and angle of tilt are extracted through phase analysis. Computer simulation and experiment are both performed to verify this method. The results indicate that the tilt of the mask and wafer in the space can be extracted with high accuracy through this method. 相似文献
999.
X.S. Zhou C. Zhao R. Hou J. Zhang K.J. Kirk D. Hutson Y.J. Guo P.A. Hu S.M. Peng X.T. Zu Y.Q. Fu 《Ultrasonics》2014
Nanocrystalline ZnO films with both C-axis vertical grown and inclined angled grown were sputter-deposited onto aluminium foils (50 μm thick) and characterised for using as flexible ultrasonic transducers. As-deposited C-axis grown ZnO films were annealed at different temperatures up to 600 °C to enhance film crystallinity and reduce film stress. The C-axis grown ZnO film on the Al foil were bonded onto steel plates, and the pulse-echo tests verified a good performance (with dominant longitudinal waves) of the ultrasonic transducers made from both as-deposited and post-annealed films. Inclined angled ZnO films on the Al foil glued onto steel plates generated mixed shear and longitudinal waves in the pulse-echo test. 相似文献
1000.
Quantum entanglement between two field modes can be achieved through the collective squeezing of the two respective modes. If single-mode squeezing is performed prior to such a two-mode squeezing, an enhancement of entanglement production can happen. Interestingly, the occurrence of this enhancement can be implicitly linked to the local classical dynamical behavior via the paradigm of quantum–classical correspondence. In particular, the entanglement generated through quantum chaos is found to be hardly enhanced by prior squeezing, since it is bounded by the saturation value of the maximally entangled Schmidt state with fixed energy. These results illustrate that entanglement enhancement via initial squeezing can serve as a useful indicator of quantum chaotic behaviour. 相似文献