全文获取类型
收费全文 | 1443篇 |
免费 | 148篇 |
国内免费 | 140篇 |
专业分类
化学 | 948篇 |
晶体学 | 13篇 |
力学 | 99篇 |
综合类 | 7篇 |
数学 | 208篇 |
物理学 | 456篇 |
出版年
2024年 | 4篇 |
2023年 | 27篇 |
2022年 | 51篇 |
2021年 | 40篇 |
2020年 | 41篇 |
2019年 | 47篇 |
2018年 | 36篇 |
2017年 | 30篇 |
2016年 | 65篇 |
2015年 | 53篇 |
2014年 | 57篇 |
2013年 | 80篇 |
2012年 | 105篇 |
2011年 | 115篇 |
2010年 | 79篇 |
2009年 | 87篇 |
2008年 | 90篇 |
2007年 | 88篇 |
2006年 | 94篇 |
2005年 | 65篇 |
2004年 | 53篇 |
2003年 | 54篇 |
2002年 | 33篇 |
2001年 | 29篇 |
2000年 | 38篇 |
1999年 | 57篇 |
1998年 | 26篇 |
1997年 | 31篇 |
1996年 | 20篇 |
1995年 | 15篇 |
1994年 | 22篇 |
1993年 | 17篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有1731条查询结果,搜索用时 0 毫秒
101.
一个无重复生成所有可逆矩阵的算法 总被引:2,自引:0,他引:2
在本文中,我们给聘个无重复生成所有可逆矩阵的算法,并估计了该算法的计算复杂度。 相似文献
102.
怀柔EAS阵列的Monte Carlo研究 总被引:1,自引:0,他引:1
用GENAS程序包为怀柔阵列产生了36万Monte Carlo模拟EAS事例,用它们研究了怀柔阵列的性能,确定了最佳的事例判造条件,对实验数据进行了正确性检验,得到了怀柔EAS Size(即簇射在观测面的总荷电粒子数)与初级宇宙线能量之间的转换关系.这项研究表明,怀柔阵列的EAS心位和方向测定精度分别好于3m和2.5°;EASSize测定误差典型值约8%;近垂直簇射的Size(N)与初能(E)的关系为E≈1010.64N0.84. 相似文献
103.
长期观测显示,耀变体S5 0716+714具有复杂的光变行为.本文运用混沌理论,研究了S5 0716+714四个较大爆发阶段的射电、光学和X波段的光变曲线.分别计算了它们的关联维和Lyapunov指数.结果表明:1)光变曲线的关联维和Lyapunov指数都介于纯混沌系统与随机噪声之间;2)相轨迹是一个与Rossler吸引子相似的混沌系统,由于受到各种内在或外在因素的影响产生噪声,导致关联维和Lyapunov指数均比Rossler吸引子大,相轨迹出现紊乱.从这两个混沌判据上看,三个波段均表现出很强的混沌特性,因此推断S50714+716的光变是一个混沌现象. 相似文献
104.
105.
N. Guirdjebaye S. Ouédraogo A. Teyou Ngoupo G.L. Mbopda Tcheum J.M.B. Ndjaka 《Opto-Electronics Review》2019,27(1):70-78
One dimension solar cells simulator package (SCAPS) is used to study the possibility of carrying out thin CIGS solar cells with high and stable efficiency. In the first step, we modified the conventional ZnO:B/i-ZnO/CdS/SDL/CIGS/Mo structure by substituting the SDL layer with the P?+?layer, having a wide bandgap from 1 to l.12?eV. Then, we simulated the J-V characteristics of this new structure and showed how the electrical parameters are affected. Conversion efficiency of 18.46% is founded by using 1.1?μm of P?+?layer thickness. Secondly, we analyze the effect of increase thickness and doping density of CIGS, CdS and P?+?layers on the electric parameters of this new structure. We show that only the short-circuit current density (JSC) and efficiency are improved, reaching respectively 34.68?mA/cm2 and 18.85%, with increasing of the acceptors density. Finally, we introduced 10?nm of various electron reflectors at the CIGS/Mo interface in the new structure to reduce the recombination of minority carriers at the back contact. High conversion efficiency of 23.34% and better stability are obtained when wide band-gap BSF is used. 相似文献
106.
Chunxia Ou 《Nonlinear Analysis: Real World Applications》2009,10(5):2652-2658
In this paper, shunting inhibitory cellular neural networks with continuously distributed delays are considered. Without assuming the global Lipschitz conditions of activation functions, some new sufficient conditions for the existence and exponential stability of the almost periodic solutions are established. 相似文献
107.
108.
Xianghua Li Chunsheng Zhao Jun Lin Shenfang Yuan 《Optics and Lasers in Engineering》2007,45(7):819-826
The performance analysis of three-dimensional (3-D) braided composites is made difficult by their complex and interlacing structure, and is still under development. To get complete first-hand data on the material parameters of these composites, co-braided optical fiber sensors (OFS) can be used to measure the internal strain. This information is helpful for subsequent stiffness predictions and failure analysis. This paper introduces a method of incorporating OFS into braided composites, and establishes a constitutive theoretical model for the hybrid material. Experiments are conducted to measure the internal strain of specimens under tension, and the results are compared to theoretical predictions. 相似文献
109.
中学有机化学可称为官能团的化学,知识脉络非常清晰,有人归纳为两句口诀:醇醛酸酯一条线,乙烯辐射一大片.在理科综合的考试形式下,有机化学只剩下一小题、一大题的发挥空间. 相似文献
110.
This paper presents a new standing-wave-type linear ultrasonic motor using combination of the first longitudinal and the second bending modes. Two piezoelectric plates in combination with a metal thin plate are used to construct the stator. The superior point of the stator is its isosceles triangular structure part of the stator, which can amplify the displacement in horizontal direction of the stator in perpendicular direction when the stator is operated in the first longitudinal mode. The influence of the base angle θ of the triangular structure part on the amplitude of the driving foot has been analyzed by numerical analysis. Four prototype stators with different angles θ have been fabricated and the experimental investigation of these stators has validated the numerical simulation. The overall dimensions of the prototype stators are no more than 40 mm (length) × 20 mm (width) × 5 mm (thickness). Driven by an AC signal with the driving frequency of 53.3 kHz, the no-load speed and the maximal thrust of the prototype motor using the stator with base angle 20° were 98 mm/s and 3.2 N, respectively. The effective elliptical motion trajectory of the contact point of the stator can be achieved by the isosceles triangular structure part using only two PZTs, and thus it makes the motor low cost in fabrication, simple in structure and easy to realize miniaturization. 相似文献