全文获取类型
收费全文 | 10742篇 |
免费 | 1894篇 |
国内免费 | 1253篇 |
专业分类
化学 | 7761篇 |
晶体学 | 65篇 |
力学 | 659篇 |
综合类 | 77篇 |
数学 | 1070篇 |
物理学 | 4257篇 |
出版年
2024年 | 43篇 |
2023年 | 280篇 |
2022年 | 385篇 |
2021年 | 455篇 |
2020年 | 483篇 |
2019年 | 427篇 |
2018年 | 354篇 |
2017年 | 301篇 |
2016年 | 528篇 |
2015年 | 466篇 |
2014年 | 566篇 |
2013年 | 803篇 |
2012年 | 991篇 |
2011年 | 973篇 |
2010年 | 639篇 |
2009年 | 633篇 |
2008年 | 708篇 |
2007年 | 621篇 |
2006年 | 547篇 |
2005年 | 475篇 |
2004年 | 365篇 |
2003年 | 324篇 |
2002年 | 272篇 |
2001年 | 214篇 |
2000年 | 213篇 |
1999年 | 253篇 |
1998年 | 213篇 |
1997年 | 191篇 |
1996年 | 205篇 |
1995年 | 175篇 |
1994年 | 142篇 |
1993年 | 125篇 |
1992年 | 102篇 |
1991年 | 75篇 |
1990年 | 84篇 |
1989年 | 56篇 |
1988年 | 48篇 |
1987年 | 44篇 |
1986年 | 29篇 |
1985年 | 28篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
We investigate the electronic and band structure for the (8; 0) single-wall carbon nanotube (SWCNT) with a europium (Eu) and
a uranium (U) atom outside by using the first-principles method with the density functional theory (DFT). The calculated band
structure (BS), total density of state (TDOS), and projected density of state (PDOS) can elucidate the differences between
the pure (8; 0) SWCNT and the nuclei outside the SWCNT. The indirect band gaps are obtained when Eu and U atom are put outside
the (8; 0) CNT; they are 0.037 eV and 0.036 eV, respectively, which is much smaller than 0.851 eV for pure CNT. Compared with
pure (8; 0) SWCNT, the bottom of the conduction band moves down by 0.383 eV and 0.451 eV with the Eu and U outside, and the
top of valence band moves up by 0.127 eV and 0.162 eV, respectively. More significantly, the top of the valence band has exceeded
the fermi-level. So, a single nucleus changes the semiconductor character of pure nanotube to semi-metal. 相似文献
112.
The morphology and ultrastructure of the alimentary canal in the adult female of the Japanese wax scale, Ceroplastes japonicus Green (Hemiptera: Coccoidea: Coccidae), was investigated using light microscopy, scanning electron microscopy and transmission electron microscopy. The results showed that the foregut was subdivided into a sclerotized pharynx and an oesophagus. A pair of salivary glands attached in the middle of the foregut. The loop-shaped midgut was narrow and longer than the foregut and its inner wall lined with a thick layer of epithelia. The hindgut was divided into a narrower ileum and a broader rectum, with the well-developed filter chamber enclosed in the anterior rectum. Malpighian tubules consisted of two brownish-yellow moniliform tubules with pores, approximately 1 μm in diameter, scattered on the outer surface and many spherical crystals inside the tubules. 相似文献
113.
In0.3Ga0.7N metal-insulator-semiconductor (MIS) and metal-semiconductor (MS) surface barrier photodetectors have been fabricated. The In0.3Ga0.7N epilayers were grown on sapphire by metalorganic chemical vapour deposition (MOCVD). The photoresponse and reverse current-voltage characteristics of the In0.3Ga0.7N MIS and MS photodetectors were measured. A best zero bias responsivity of 0.18 A/W at 450 nm is obtained for the In0.3Ga0.7N MIS photodetector with 10 nm Si3N4 insulator layer, which is more than ten times higher than the In0.3Ga0.7N MS photodetector. The reason is attributed to the decrease of the interface states and increase of surface barrier height by the inserted insulator. The influence of the thickness of the Si3N4 insulator layer on the photoresponsivity of the MIS photodetector is also discussed. 相似文献
114.
115.
考虑了在非平衡凝固条件下球晶生长过程中界面动力学系数随界面温度的变化,利用渐近分析方法求出了在过冷熔体中球晶生长温度场和界面的近似解析解,研究了非线性界面动力学过冷对于过冷熔体中球晶界面形态和生长速度的影响.研究表明,界面动力学系数越大,球晶的生长速度越快; 反之,表明界面动力学系数越小,球晶的生长速度越慢.与忽略界面动力学的情形比较,在球晶生长过程中依赖于界面温度变化的界面动力学显著地减缓了晶体生长的速度.
关键词:
球晶
界面形态
渐近分析 相似文献
116.
Wenyu Ji Letian Zhang Mo Liu Jing Wang Guoqiang Liu Wenfa Xie Hanzhuang Zhang 《Current Applied Physics》2011,11(6):1410-1413
White top-emitting organic light-emitting devices (TEOLEDs) were fabricated on a glass substrate with metal/organic multilayer of (Ag/Alq3)2 (Alq3 is tris-(8-hydroxyquinoline) aluminum) as cathode. White TEOLEDs with high efficiency were obtained due to the microcavity effects. And the (Ag/Alq3)2 cathode, which adjusted the optical characteristics of the devices, played an important role. In addition, Alq3–Ag–Alq3 multilayer could work as a buffer layer, which would simplify the process of encapsulation for devices. We also calculated the electroluminescence spectrum of devices encapsulated with Al2O3 (150 nm) and Al2O3(75 nm)/ZrO2(75 nm). And the results indicated that the CIE coordinates is almost the same between with and without encapsulating. 相似文献
117.
以丝阵内爆零维模型为基础,采用Pspice模拟行为建模方法,建立了丝阵内爆动态电感与Z箍缩驱动器耦合的全电路模型,实现驱动器放电过程与丝阵内爆过程的自洽求解,并研究了丝阵参数、电路参数对内爆过程的影响.结果表明:丝阵负载与驱动器存在强耦合关系,丝阵参数、电路参数对丝阵峰值箍缩电流、内爆时间、内爆动能影响很大;在驱动器参数不变,内爆时间不超过电路固有放电周期1/4的前提下,峰值箍缩电流、内爆时间、内爆动能随丝阵质量的增加而增大,内爆时间随丝阵初始半径的增加而增大;在丝阵参数不变时,随着驱动器等效电容的增大,内爆时间减小,丝阵内爆动能增大,但驱动器储能转化为内爆动能的效率却先增大后减小.对于特定的驱动器,优化的丝阵参数应使内爆过程充分利用驱动器固有放电周期的上升沿,使丝阵快速收缩的时间起点接近电路固有放电周期的四分之一,以获得最大的动能效率.
关键词:
Z箍缩驱动器
零维内爆模型
模拟行为建模
耦合特性 相似文献
118.
119.
In this paper, we investigate the problem of synchronization for the time varying delayed complex dynamical networks via impulsive control method, several sufficient synchronization conditions are given, and we consider the impulsive control matrices are time varying delayed matrices. Furthermore, we found impulsive control does not always play an active role in synchronization although impulsive control strategy is cheaper and simpler than other control strategy. Finally, numerical simulations are also given to demonstrate the effectiveness of the proposed schemes. 相似文献
120.
C. Chen D.J. Chen Z.L. Xie P. Han R. Zhang Y.D. Zheng Z.H. Li G. Jiao T.S. Chen 《Applied Physics A: Materials Science & Processing》2008,90(3):447-449
Effects of an AlN passivation layer on the microstructure and electronic properties of AlGaN/GaN heterostructures were investigated
by X-ray diffraction and Hall effect measurements. AlN passivation induced an additional compressive stress in an AlGaN barrier
layer instead of an additional tensile stress induced by Si3N4 passivation. The change of strain after passivation contributes in a relatively small proportion to the variation of the
carrier concentration in AlGaN/GaN heterostructures compared with the contribution from passivation of surface traps. The
results from Hall effect measurements show that the AlN passivation layer has a better effect on passivation of deep levels
than the Si3N4 film and also results in a remarkable increase in mobility of the two-dimensional electron gas.
PACS 73.40.Kp; 71.55.Eq; 81.65.Rv; 81.05.Ea; 61.05.cp 相似文献