全文获取类型
收费全文 | 23151篇 |
免费 | 2635篇 |
国内免费 | 2235篇 |
专业分类
化学 | 10929篇 |
晶体学 | 320篇 |
力学 | 720篇 |
综合类 | 166篇 |
数学 | 1982篇 |
物理学 | 5321篇 |
无线电 | 8583篇 |
出版年
2023年 | 334篇 |
2022年 | 494篇 |
2021年 | 562篇 |
2020年 | 559篇 |
2019年 | 596篇 |
2018年 | 509篇 |
2017年 | 587篇 |
2016年 | 666篇 |
2015年 | 829篇 |
2014年 | 967篇 |
2013年 | 1375篇 |
2012年 | 1617篇 |
2011年 | 1708篇 |
2010年 | 1378篇 |
2009年 | 1454篇 |
2008年 | 1582篇 |
2007年 | 1596篇 |
2006年 | 1430篇 |
2005年 | 1227篇 |
2004年 | 1122篇 |
2003年 | 980篇 |
2002年 | 866篇 |
2001年 | 726篇 |
2000年 | 685篇 |
1999年 | 436篇 |
1998年 | 314篇 |
1997年 | 273篇 |
1996年 | 289篇 |
1995年 | 245篇 |
1994年 | 258篇 |
1993年 | 245篇 |
1992年 | 213篇 |
1991年 | 178篇 |
1990年 | 189篇 |
1989年 | 151篇 |
1988年 | 150篇 |
1987年 | 96篇 |
1986年 | 93篇 |
1985年 | 130篇 |
1984年 | 93篇 |
1983年 | 89篇 |
1982年 | 69篇 |
1981年 | 68篇 |
1980年 | 73篇 |
1979年 | 48篇 |
1978年 | 44篇 |
1977年 | 46篇 |
1976年 | 46篇 |
1974年 | 53篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
Al2O3 incorporated HfO2 films grown by atomic layer deposition (ALD) were investigated by high-resolution X-ray photoelectron spectroscopy (HRXPS). The core level energy state of a 15 Å thick film showed a shift to higher binding energy, as the result of a silicate formation and Al2O3 incorporation. The incorporation of Al2O3 into the HfO2 film had no effect on silicate formation at the interface between the film and Si, while the ionic bonding characteristics and hybridization effects were enhanced compared to a pure HfO2 film. The dissociation of the film in an ultrahigh vacuum (UHV) is effectively suppressed compared to a pure HfO2 film, indicating an enhanced thermal stability of Hf-Al-O. Any dissociated Al2O3 on the film surface was completely removed into the vacuum by vacuum annealing treatment over 850 °C, while HfO2 contributed to Hf silicide formation on the film surface. 相似文献
143.
144.
145.
氩气介质阻挡放电的发光特性 总被引:1,自引:0,他引:1
本文使用水电极介质阻挡放电装置,采用光学方法测量了氩气介质阻挡放电的发光特性。发现在驱动电压处于一定的范围内时,放电处于丝极模式,在驱动电压的每半周期内,无论是放电的总光还是单个微通道的放电发光均只有一次脉冲,单个微放电的时间为2μs,而总放电时间为2.4μs,这表明在氩气的丝极模式中,各单丝产生与熄灭的时间极其接近,各个放电丝之间有着很好的时间相关性。最后将本文的结果与空气中介质阻挡放电丝极模式的发光特性相比较,空气放电在每半周内的总光信号由多个脉冲组成,而每一个脉冲对应多个放电丝,因而氩气中各个放电微通道之间的时间相关性远强于空气的情况。 相似文献
146.
热等离子体裂解天然气制备C2烃 总被引:1,自引:0,他引:1
采用氮气热等离子体来裂解天然气制备乙炔乙烯,着重研究了天然气转化率和乙炔、乙烯收率随氮气流量和天然气流量的变化.结果表明,天然气流量与氮气流量之比为11时,可得到较好的结果.当等离子体功率为15kW、天然气流量为3Nm3*h-1、氮气流量为3Nm3*h-1时得到最好的结果.这时天然气转化率为57%,乙炔、乙烯的收率分别为34%和9%;乙炔在反应气中的体积浓度为7.5%,与部分氧化法相似;扣除不参加反应的氮气,乙炔在气相产品中的体积浓度为13.2%,与热力学平衡计算结果基本符合. 相似文献
147.
Highly ordered composite nanowires with multilayer Ni/Cu and NiFe/Cu have been fabricated by pulsed electrodeposition into
nanoporous alumina membrane. The diameter of wires can be easily varied by pore size of alumina, ranging from 30 to 100 nm.
The applied potential and the duration of each potential square pulse determine the thickness of the metal layers. The nanowires
have been characterized by transmission electron microscopy (TEM), magnetic force microscopy (MFM), and vibrating sample magnetometer
(VSM) measurements. The MFM images indicate that every ferromagnetic layer separated by Cu layer was present as single isolated
domain-like magnet. This technique has potential use in the measurement and application of magnetic nanodevices. 相似文献
148.
The electromagnetic properties of electrically thick rectangular microstrip antennas were investigated experimentally. Antennas were fabricated with different patch sizes and with electrical thicknesses ranging from 0.03 to 0.23 wavelengths in the dielectric substrate. The resonant frequencies were measured and compared to existing formulas. The bandwidth was calculated as a function of electrical thickness and the antenna radiation patterns were measured. 相似文献
149.
In this research, we investigate stopping rules for software testing and propose two stopping rules from the aspect of software reliability testing based on the impartial reliability model. The impartial reliability difference (IRD-MP) rule considers the difference between the impartial transition-probability reliabilities estimated for both software developer and consumers at their predetermined prior information levels. The empirical–impartial reliability difference (EIRD-MP) rule suggests stopping a software test when the computed empirical transition reliability is tending to its estimated impartial transition reliability. To insure the high-standard requirement for safety-critical software, both rules take the maximum probability (MP) of untested paths into account. 相似文献
150.
本文解决了超立方体的Laplace矩阵的谱问题.n维超立方体Q。的Laplace矩阵L(Q)的谱specL(Qn)。[0 2 4…2n Cn^0 Cn^1 Cn^2 … Cn^n],.其中2t(t=0,1,2,…,n)为L(Qn)的n+1个不同的特征值,二项式系数Cn为特征值2t的重数. 相似文献