全文获取类型
收费全文 | 8751篇 |
免费 | 1425篇 |
国内免费 | 818篇 |
专业分类
化学 | 4737篇 |
晶体学 | 189篇 |
力学 | 252篇 |
综合类 | 44篇 |
数学 | 321篇 |
物理学 | 5451篇 |
出版年
2024年 | 30篇 |
2023年 | 95篇 |
2022年 | 254篇 |
2021年 | 263篇 |
2020年 | 323篇 |
2019年 | 261篇 |
2018年 | 271篇 |
2017年 | 277篇 |
2016年 | 338篇 |
2015年 | 324篇 |
2014年 | 420篇 |
2013年 | 780篇 |
2012年 | 528篇 |
2011年 | 619篇 |
2010年 | 417篇 |
2009年 | 604篇 |
2008年 | 537篇 |
2007年 | 549篇 |
2006年 | 526篇 |
2005年 | 396篇 |
2004年 | 390篇 |
2003年 | 341篇 |
2002年 | 406篇 |
2001年 | 267篇 |
2000年 | 311篇 |
1999年 | 204篇 |
1998年 | 241篇 |
1997年 | 126篇 |
1996年 | 127篇 |
1995年 | 102篇 |
1994年 | 104篇 |
1993年 | 86篇 |
1992年 | 69篇 |
1991年 | 50篇 |
1990年 | 42篇 |
1989年 | 34篇 |
1988年 | 47篇 |
1987年 | 24篇 |
1986年 | 35篇 |
1985年 | 24篇 |
1984年 | 28篇 |
1983年 | 10篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
S.B. Lisesivdin H. Altuntas A. Yildiz M. Kasap E. Ozbay S. Ozcelik 《Superlattices and Microstructures》2009,45(6):604-611
Experimental Hall data that were carried out as a function of temperature (60–350 K) and magnetic field (0–1.4 T) were presented for Si-doped low Al content (x=0.14) n–AlxGa1−xAs/GaAs heterostructures that were grown by molecular beam epitaxy (MBE). A 2-dimensional electron gas (2DEG) conduction channel and a bulk conduction channel were founded after implementing quantitative mobility spectrum analysis (QMSA) on the magnetic field dependent Hall data. An important decrease in 2DEG carrier density was observed with increasing temperature. The relationship between the bulk carriers and 2DEG carriers was investigated with 1D self consistent Schrödinger–Poisson simulations. The decrement in the 2DEG carrier density was related to the DX-center carrier trapping. With the simulation data that are not included in the effects of DX-centers, 17 meV of effective barrier height between AlGaAs/GaAs layers was found for high temperatures (T>300 K). With the QMSA extracted values that are influenced by DX-centers, 166 meV of the DX-center activation energy value were founded at the same temperatures. 相似文献
993.
采用直流磁控反应溅射方法,通过调节氧分压在玻璃基底上制备了不同载流子浓度的掺Mo的ZnO(ZMO)透明导电薄膜.应用太赫兹电磁波时域光谱技术研究了ZMO导电膜的太赫兹电磁波透射性质及介电响应,得到了与频率相关的电导率、能量吸收和薄膜折射率,实验结果与经典Drude模型相符很好.ZMO导电膜的太赫兹电磁波脉冲透射性质表明,通过调节ZMO薄膜的载流子浓度,该导电膜可作为应用于衬底和光学器件等太赫兹电磁波频率范围的宽带抗反射涂层.
关键词:
太赫兹电磁波光谱
薄膜电导率
宽带抗反射
透明导电薄膜 相似文献
994.
赵万广 《原子与分子物理学报》2013,30(6)
提出了液体夹心法热导率测量技术, 采用CHBr3液体作为夹心材料实现了样品/窗口界面的理想接触, 并将动载荷作用下的夹心法高压热导率实验测量压力下限拓展至40 GPa, 为绝缘介电晶体高温高压热导率测量提供了技术支持. 实验利用平面碰撞和DPS测试技术, 结合液体夹心法实测了LiF单晶高压热导率数据, 对现有热导率理论模型进行了研究和探讨, 结果显示, 在γ/γ0=(ρ0/ρ)2时, 修正后的Roufosse理论公式与实验数据符合较好, 这一研究结果为非透明材料冲击波温度测量中的热传导修正提供了实验数据和理论模型。 相似文献
995.
Luke Gordon Joel B. Varley John L. Lyons Anderson Janotti Chris G. Van de Walle 《固体物理学:研究快报》2015,9(8):462-465
Achieving high levels of n‐type conductivity in AlN and high Al‐content nitride alloys is a long standing problem; significant decreases in conductivity are observed as the Al content is increased, a phenomenon that has been attributed to donors such as oxygen or silicon forming DX centers. We address this problem through a comprehensive first‐principles hybrid density functional study of potential n‐type dopants, identifying SN and SeN as two elements which are potential shallow donors because they do not undergo a DX transition. In particular, SN is highly promising as an n‐type dopant because it also has a low formation energy and hence a high solubility. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
996.
W. Hanke O. Schmitt H. Endres R. Kleiner P. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):465-471
A quantitative analysis of a microscopic model for the intrinsic Josephson effect in high-temperature superconductors based
on interlayer tunneling is presented both within a mean-field BCS evaluation and a numerically essentially exact Quantum Monte-Carlo
study. The pairing correlations in the CuO2-planes are modelled by a 2D Hubbard model with attractive interaction, a model which accounts well for some of the observed
features such as the short planar coherence length. The stack of Hubbard planes is arranged on a torus, which is threaded
by a magnetic flux. The current perpendicular to the planes is calculated as a function of applied flux (i.e. the phase), and - after careful elimination of finite-size effects due to single-particle tunneling - found to display a
sinusoidal field dependence in accordance with interlayer Josephson tunneling. Studies of the temperature dependence of the
supercurrent reveal at best a mild elevation of the Josephson transition temperature compared to the planar Kosterlitz-Thouless
temperature. These and other results on the dependence of the model parameters are compared with a standard BCS evaluation.
Received: 24 February 1998 / Revised: 28 April 1998 / Accepted: 23 June 1998 相似文献
997.
A Li hexagonal boron nitride (hBN) intercalation compound (Li-hBNIC) was successfully synthesized by the annealing of powder or bulk hBN and Li at 1523 K. By an XRD analysis, a strong peak indicating the expansion of BN interlayer distance due to Li-intercalation was observed at an angle lower than that of hBN (0 0 2). In the sample, the interlayer distance and its expansion ratio were 3.76 Å and 12.6%, respectively, and these values were similar to those of a first stage Li-graphite intercalation compound (Li-GIC), LiC6. The electrical conductivity of the sample was increased by several orders of magnitude, from 10−15 to 10−7 Ω−1 cm−1 at room temperature. Li de-intercalation was confirmed by the dispersion of the sample in purified water. 相似文献
998.
Frank-Michael Matysik 《Mikrochimica acta》2008,160(1-2):1-14
Amperometric and conductometric detection are currently the two major electrochemical detection modes in capillary and chip
electrophoresis. The ease of miniaturization and integration of electrochemical detection elements offers a high potential
for the development of portable analytical devices based on electromigrative separations. The challenges and basic concepts
of both detection principles in the context of capillary/chip electrophoresis are shortly introduced and milestones of the
methodical developments are summarized from a historical perspective. Recent advances and applications are discussed with
more detail. Particular attention is paid to new trends in this area of research such as measurements in short capillaries
and the enormous progress and increased popularity of contactless conductivity detection.
Correspondence: Frank-Michael Matysik, Institute of Analytical Chemistry, University of Leipzig, Linnéstr. 3, D-04103 Leipzig,
Germany 相似文献
999.
含有不同的链长的w-吡咯烷基二甲基氯硅烷作为粘合剂通过自组装(SAMs)吸附于二氧化硅表面,然后聚吡咯膜化学沉积于该粘合剂修饰的表面。化学沉积的聚吡咯膜的表面形貌用扫描电镜(SEM)及原子力显微镜(AFM)表征。除短链外不同链长的粘合剂对聚吡咯膜的厚度影响不大。聚吡咯膜的电特性用电流-电压表征。结果显示电流与粘合剂的链长无关。电特性表明载流子迁移率为1.4 ´ 10-4 cm2×V-1.s –1。 相似文献
1000.
Chitrakara Hegde Arun M. Isloor Mahesh Padaki Hoong-Kun Fun 《Arabian Journal of Chemistry》2013,6(3):319-326
The present work describes about the synthesis and characterization of Polysulfone blend nanoporous membrane with nonwoven support. This Nonwoven support provides mechanical strength to membrane while filtration process and minimizes membrane fouling. Hence it helps in better membrane performance in terms of salt rejection, improved flux, thermal stability and fairly increases in proton conductivity. In this work we have used K.C.270 nonwoven material consisting of fine polyester fibers and has a thickness of below 110 μm. 相似文献