全文获取类型
收费全文 | 977篇 |
免费 | 54篇 |
国内免费 | 60篇 |
专业分类
化学 | 282篇 |
晶体学 | 3篇 |
力学 | 44篇 |
综合类 | 5篇 |
数学 | 111篇 |
物理学 | 646篇 |
出版年
2024年 | 1篇 |
2023年 | 31篇 |
2022年 | 12篇 |
2021年 | 11篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 16篇 |
2017年 | 18篇 |
2016年 | 20篇 |
2015年 | 26篇 |
2014年 | 54篇 |
2013年 | 83篇 |
2012年 | 45篇 |
2011年 | 73篇 |
2010年 | 59篇 |
2009年 | 79篇 |
2008年 | 60篇 |
2007年 | 67篇 |
2006年 | 57篇 |
2005年 | 45篇 |
2004年 | 31篇 |
2003年 | 41篇 |
2002年 | 27篇 |
2001年 | 21篇 |
2000年 | 16篇 |
1999年 | 22篇 |
1998年 | 22篇 |
1997年 | 16篇 |
1996年 | 12篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 6篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1973年 | 4篇 |
排序方式: 共有1091条查询结果,搜索用时 7 毫秒
991.
992.
993.
研究了使用SC-2000国产色谱仪和手动顶空进样法,对油田水中的苯及其同系物进行分离分析的可行性。优化了实验条件,以苯为测试对象,最小检测限为10ppb,相关系数为0.9997,相对标准偏差(RSD)为1.7%,且所得到的色谱图中苯、甲苯、乙苯分离效果好,具有良好的峰形,方法快速、简便、廉价且准确,可以用于油田水中苯及其同系物的分离分析。 相似文献
994.
995.
The problem of a penny-shaped interface crack between a functionally graded piezoelectric layer and a homogeneous piezoelectric
layer is investigated. The surfaces of the composite structure are subjected to both mechanical and electrical loads. The
crack surfaces are assumed to be electrically impermeable. Integral transform method is employed to reduce the problem to
a Fredholm integral equation of the second kind. The stress intensity factor, electric displacement intensity factor and energy
release rate are derived, some typical numerical results are plotted graphically. The effects of electrical loads, material
nonhomogeneity and crack configuration on the fracture behaviors of the cracked composite structure are analyzed in detail. 相似文献
996.
Awl-shaped diamond-like carbon (DLC) was directly grown on anodic aluminum oxide (AAO) template by using filtered cathodic arc plasma (FCAP) technique at room temperature. The awls of DLC were about 250 nm in the height and the diameters of the awls were ∼100 nm at the top. The awl density was estimated to be ∼108 cm−2. A broad asymmetric band ranging from 1100 to 1800 cm−1 was detected by Raman spectrum. This asymmetric band was characteristic band of DLC. The sp3/(sp3+sp2) ratio of C-C bond of the awl-shaped DLC was measured by X-ray photoelectron spectrum, and it was about 68.3%. Field-emission properties of the awl-shaped DLC were investigated. A low turn-on field of 2.6 V/μm at 10 μA/cm2 with an emission area of 3.14 mm2 was achieved, and the emission current stability was very good. The results indicated that the electrons were emitted under both the effect of enhanced field because of the geometry and the work function of the DLC sample. Based on Fowler-Nordheim plot, the values of work function for the awl-shaped DLC were estimated in ranges of 0.23-1.08 from a linearity plot. 相似文献
997.
We address the problem of determining effective equations of motion for sources in field theories, where finite propagation
speeds lead to radiation reaction and runaway solutions. Acoustics is used to illustrate a solution of this problem: The effective
equation of motion is obtained by reduction to an inertial manifold. This equation can be approximated to any desired accuracy
by expansion (and truncation) in powers of the reciprocal of the wave propagation speed and reduction to a slow manifold of
a singular perturbation problem.
This research is supported by a grant from the National Science Foundation NSF DMS-0604331. 相似文献
998.
The dependence of the spectral distribution of photoelectron emission from gold nano-particles embedded in BaO semiconductor thin film on applied voltage and surface plasmon resonance of gold nano-particles is predicted and investigated theoretically. The photoelectron emission response curves to light wavelength between 0.2 and are given. The dependence of the wavelength threshold on the size of gold nano-particles and external field strength is also shown. The reason that the theoretical photoelectron emission spectra is in the visible region is explained. The probabilities increased for photoexcited electrons to overcome the barrier and escape from the surface are discussed. This could be of importance in designing field-assisted thin film and finding their optimum operation conditions. 相似文献
999.
In this paper the correlation between the kinetic energy of helium atoms and the probability of field ionization is investigated by exploiting the narrow velocity distribution of supersonic molecular beams. Field ionization measurements were carried out on supersonic helium beams at 298 K and 95 K corresponding to energies of about 65 meV and 20 meV, respectively, for the individual atoms. The field ionization was performed with a tungsten tip, radius of curvature 12 nm, kept at room temperature. The ionization probability was found to increase by about a factor 10 when the beam was cooled from 298 K to 95 K. The results presented in this paper are of importance for improving the understanding of field ionization and for the development of a new detector for helium and other molecular beams. 相似文献
1000.
单晶LaB6场发射阵列的电化学腐蚀工艺 总被引:2,自引:0,他引:2
六硼化镧(LaB6)场发射尖锥阵列的刻蚀工艺是制备LaB6场发射阵列阴极的关键。在(111)面单晶LaB6基片上,用等离子体增强化学气相沉积法制备氮化硅层做掩膜,光刻后采用电化学腐蚀方法对基片进行刻蚀,得到具有一定高度的LaB6尖锥场发射阵列。讨论了单晶LaB6的电化学腐蚀机理。改变各种电化学腐蚀参数,包括电解液成分、电解液浓度、阳极所加电压,用电子扫描显微镜观察样品形貌。结果发现H3PO4是刻蚀单晶LaB6的理想电解液,它克服了过去电化学实验中经常遇到的尖锥各向异性问题。随着电解液浓度或阳极电压的增大,尖锥高度增加,但是基底表面变得更为粗糙。另一方面,阳极电压太小时,有横向刻蚀现象产生,不利于提高发射体的场增强因子。此外,在二极管结构中初步测试了LaB6尖锥场发射阵列的电流发射特性,在真空度2×10-4 Pa、极间距离0.1 mm、阳极电压900 V下,发射电流达到13 mA。 相似文献