全文获取类型
收费全文 | 1043篇 |
免费 | 237篇 |
国内免费 | 251篇 |
专业分类
化学 | 560篇 |
晶体学 | 25篇 |
力学 | 63篇 |
综合类 | 100篇 |
数学 | 273篇 |
物理学 | 510篇 |
出版年
2024年 | 9篇 |
2023年 | 25篇 |
2022年 | 38篇 |
2021年 | 30篇 |
2020年 | 19篇 |
2019年 | 28篇 |
2018年 | 37篇 |
2017年 | 31篇 |
2016年 | 21篇 |
2015年 | 30篇 |
2014年 | 59篇 |
2013年 | 51篇 |
2012年 | 54篇 |
2011年 | 55篇 |
2010年 | 54篇 |
2009年 | 57篇 |
2008年 | 51篇 |
2007年 | 68篇 |
2006年 | 44篇 |
2005年 | 50篇 |
2004年 | 64篇 |
2003年 | 46篇 |
2002年 | 44篇 |
2001年 | 30篇 |
2000年 | 25篇 |
1999年 | 37篇 |
1998年 | 44篇 |
1997年 | 42篇 |
1996年 | 48篇 |
1995年 | 43篇 |
1994年 | 32篇 |
1993年 | 33篇 |
1992年 | 36篇 |
1991年 | 23篇 |
1990年 | 27篇 |
1989年 | 24篇 |
1988年 | 15篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1959年 | 4篇 |
1958年 | 5篇 |
1957年 | 3篇 |
1955年 | 3篇 |
排序方式: 共有1531条查询结果,搜索用时 15 毫秒
101.
102.
High temperature thermoelectric properties of highly c-axis oriented Bi<sub>2</sub>Sr<sub>2</sub>Co<sub>2</sub>O<sub>y</sub> thin films fabricated by pulsed laser deposition 下载免费PDF全文
High-temperature thermoelectric transport property measurements have been performed on the highly c-axis oriented Bi2Sr2Co2Oy thin films prepared by pulsed laser deposition on LaAlO3(001).Both the electric resistivity ρ and the seebeck coefficient S of the film exhibit an increasing trend with the temperature from 300 K-1000 K and reach up to 4.8 m·Ω· cm and 202 μV/K at 980 K,resulting in a power factor of 0.85 mW/mK which are comparable to those of the single crystalline samples.A small polaron hopping conduction can be responsible for the conduction mechanism of the film at high temperature.The results demonstrate that the Bi2Sr2Co2Oy thin film has potential application in high temperature thin film thermoelectric devices. 相似文献
103.
104.
在切边冲孔机长时间生产中,为了减小菲林形变引起的柔性电路板(FPC)冲切位置误差,利用目标冲切完成后的图像信息,测量金手指与冲切边缘间的距离,计算出系统误差并进行误差补偿。结果显示,经过误差补偿后,系统的冲切位置均方根误差在X与Y方向分别减小了41.6%与17.0%,系统的制程能力指数(CPK)达到1.611 8。利用菲林加大了FPC产品的外围尺寸,提高了产品的可利用面积,降低了生产成本。提出的超分辨率快速测量方法不需要对图像进行配准,可以将边缘位置定位误差由0.5个像素降低为0.25个像素。使用的误差补偿方法能够减小长时间生产所引起的冲切位置误差,设计的系统满足FPC的冲切精度要求。 相似文献
105.
We investigate the activation of living monocytic U937 cells induced by interleukin-6 (IL-6) at the single cell level. We employ home-built Raman tweezers to measure the Raman spectra of living U937 cells with and without IL-6 at the single cell level. Raman peaks of amide III, amide I, DNA backbone, as well as guanine and adenine in U937 cells, change at 1312, 1652, 1090, and 1576 cm ?1 , respectively, shortly after IL-6 is added in the medium. The change is a dynamic temporal process. In the activation process of U937 cells induced by IL-6, the protein signals recover in 20 min, while the nucleic acid signals continue to increase for 20 min. The results reveal that the biochemical cascades of activation in signal transduction induced by IL-6 can be investigated in situ at the single cell level. 相似文献
106.
107.
We measure the half-wave voltage of LiNbO 3 phase modulators in a 26-GHz wideband frequency range, and then analyze it by the phase modulation photonic peak gain linked to the interferometric demodulation. The optical interferometer is constructed with two 50:50 couplers and two fiber arms with a 1-m difference in fiber length. The photonic link gain peaks are frequency dependent, as indicated by the differential time delay in the interferometer. The procedure described is a new and practical half-wave voltage measurement method that can accurately predict the nonlinear frequency characteristics of the phase modulator. Moreover, the method can be applied to various types of LiNbO 3 phase modulators. 相似文献
108.
Two-dimensional particle-in-cell plasma source ion implantation of a prolate spheroid target 下载免费PDF全文
A two-dimensional particle-in-cell simulation is used to
study the time-dependent evolution of the sheath surrounding a
prolate spheroid target during a high voltage pulse in plasma source
ion implantation. Our study shows that the potential contour lines
pack more closely in the plasma sheath near the vertex of the major
axis, i.e. where a thinner sheath is formed, and a non-uniform total
ion dose distribution is incident along the surface of the prolate
spheroid target due to the focusing of ions by the potential
structure. Ion focusing takes place not only at the vertex of the
major axis, where dense potential contour lines exist, but also at
the vertex of the minor axis, where sparse contour lines exist. This
results in two peaks of the received ion dose, locating at the
vertices of the major and minor axes of the prolate spheroid target,
and an ion dose valley, staying always between the vertices, rather
than at the vertex of the minor axis. 相似文献
109.
110.
本文研究了铝(I)与3.5.7,2' ,4,一五轻荃黄烯酮(桑色素,Morin )在非离子表面活性剂Tween 80存在下,pH3. 4-4. 4的HAC-NaAc介质中,Al ( I)与Morin形成稳定的黄绿色配合物,其最大吸收波长在423nm处,表观摩尔吸光系数为7. 2 X 10`L " mol-' " cm ;’配合物组成比Al ( I ) = Morin =1 = 3,其表观不稳定常数为1. 43 X 10-".Al ( I)浓度在0^-15 fig/25m1之间符合比尔定律.以硫脉、抗坏血酸和邻菲罗琳作掩蔽剂,测定了电镀废水中微量铝,结果满意. 相似文献