全文获取类型
收费全文 | 9789篇 |
免费 | 621篇 |
国内免费 | 2976篇 |
专业分类
化学 | 6866篇 |
晶体学 | 13篇 |
力学 | 705篇 |
综合类 | 83篇 |
数学 | 1464篇 |
物理学 | 4255篇 |
出版年
2023年 | 7篇 |
2022年 | 9篇 |
2021年 | 17篇 |
2020年 | 22篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 7篇 |
2016年 | 47篇 |
2015年 | 91篇 |
2014年 | 39篇 |
2013年 | 385篇 |
2012年 | 370篇 |
2011年 | 1516篇 |
2010年 | 759篇 |
2009年 | 762篇 |
2008年 | 178篇 |
2007年 | 147篇 |
2006年 | 232篇 |
2005年 | 541篇 |
2004年 | 1824篇 |
2003年 | 1121篇 |
2002年 | 948篇 |
2001年 | 649篇 |
2000年 | 259篇 |
1999年 | 271篇 |
1998年 | 338篇 |
1997年 | 230篇 |
1996年 | 150篇 |
1995年 | 135篇 |
1994年 | 104篇 |
1993年 | 448篇 |
1992年 | 493篇 |
1991年 | 304篇 |
1990年 | 323篇 |
1989年 | 303篇 |
1988年 | 73篇 |
1987年 | 16篇 |
1986年 | 33篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1970年 | 6篇 |
1931年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
The current and the voltage of an X-pinch were measured. The inductance of the X-pinch was assumed to be a constant and estimated by the calculation of the magnetic field based on the well-known Biot-Savart's Law. The voltage of the inductance was calculated with L · di/dt and subtracted from the measured voltage of the X-pinch. Then, the resistance of the X-pinch was determined and the following results were obtained. At the start of the current flow the resistance of the exploding wires is several tens of Ohms, one order of magnitude, higher than the metallic resistance of the wires at room temperature, and then it falls quickly to about 1 , which reflects the physical processes occurring in the electrically exploding wires, i.e., a current transition from the highly resistive wire core to the highly conductive plasma. It was shown that the inductive contribution to the voltage of the X-pinch is less than the resistive contribution. For the wires we used, the wires' material and diameter have no strong influence on the resistance of the X-pinch, which may be explained by the fact that the current flows through the plasma rather than through the metallic wire itself. As a result, the current is almost equally divided between two parallel X-pinches even though the diameter and material of the wires used for these two X-pinches are significantly different. 相似文献
993.
通过对40例疤痕组织和正常皮肤组织的ETIR光谱比较分析发现,由于个体差异,其光谱均可分为三种不同类型。此外,疤痕组织中的胶原、蛋白质、核酸和脂类等生物大分子的吸收峰强度均在不同程度上高于正常皮肤组织,但两者的A_(1083)/A_(1548)并无明显差异。提示疤痕组织中的细胞仍属正常生长,治疗中不应损伤。 相似文献
994.
利用G98及GAMESS从头计算程序的RHF/6-31方法,对β-榄香烯的全部振动基频作了计算,并与实测红外光谱做了对比,归属了它们的振动模式,讨论了它们的特征基频,并对理论计算的振动频率进行了标度校正。 相似文献
995.
A high detection efficiency calorimeter which is used to detect γ-rays with energies from 1 MeV up to 10 MeV as well as light charged particles has been proposed. Design of the geometry, results of the crystal tests and Monte Carlo simulations are presented in this paper. The simulation results confirm that the calorimeter can obtain high detection efficiency and good energy resolution with the current designed geometry. And the calorimeter is competent for the future External Target Facility (ETF) experiments. 相似文献
996.
997.
A theoretical and experimental study on all-normal-dispersion Yb-doped mode-locked fiber lasers
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)
We report on a theoretical and experimental study of an all-normal-dispersion (ANDi) Yb-doped mode-locked fiber laser, in which nonlinear polarization rotation (NPR) is used to realize mode-locking without any dispersion compensation. Based on the coupled nonlinear Schrdinger (CNLS) equation, a model simulating the mode-locked process of an allnormal-dispersion ring fiber laser is developed, which shows that the achievement of stable mode-locking depends on the alignment of the polarization controller (PC) along the fast-polarization axis of the fiber, the birefringence intensity, and the net cavity dispersion. According to the theoretical analysis, stable mode-locked pulses with pulse duration 300 ps and average output power 33.9mW at repetition rate 36MHz are obtained. 相似文献
998.
The theoretical analysis and experimental results of the wavelength tunability of a tandem optical parametric oscillator (TOPO) based on a single nonlinear crystal are presented.TOPO is a configuration wherein the signal laser is used as a pump laser to generate secondary optical parametric oscillator (OPO).The cascaded parametric interactions are achieved synchronously in a single-grating-period MgO doped periodically poled lithium niobate (PPMgOLN).Tunable multiple-wavelength mid-infrared (mid-IR) lasers are obtained by changing the temperature of the crystal.When the PPMgOLN crystal with a grating period of 31.2 μm is operated at 148 ℃,the dual OPOs generate an identical mid-IR laser of 2.83 μm.The secondary OPO transforms into an optical parametric amplifier,in which different frequency mixing from the signal laser results in the amplification of the idler laser in the first OPO.TOPO is a useful configuration for multiple laser output,broad tuning range,and high-efficiency mid-IR lasers. 相似文献
999.
LIU HaiFeng LIU HaiYan & SONG WeiDong State Key Laboratory of Explosion Science Technology Beijing Institute of Technology Beijing China School of Civil Hydraulic Engineering Ningxia University Yinchuan School of Science 《中国科学:物理学 力学 天文学(英文版)》2010,(2)
This paper takes concrete as a four-phase composite made of the intact matrix and three mutually perpendicular groups of penny-shaped micro-cracks. The intact matrix is assumed to be elastic,homogeneous and isotropic,and the micro-cracks are penny-shaped. Combined with the failure mechanism of concrete subjected to impact loading,a dynamic constitutive model for concrete is developed based on Mori-Tanaka's average stress concept and Eshelby's equivalent inclusion theory. Experimental results show that concr... 相似文献
1000.