全文获取类型
收费全文 | 1302篇 |
免费 | 196篇 |
国内免费 | 124篇 |
专业分类
化学 | 541篇 |
晶体学 | 3篇 |
力学 | 241篇 |
综合类 | 12篇 |
数学 | 53篇 |
物理学 | 772篇 |
出版年
2024年 | 1篇 |
2023年 | 19篇 |
2022年 | 32篇 |
2021年 | 37篇 |
2020年 | 24篇 |
2019年 | 29篇 |
2018年 | 35篇 |
2017年 | 29篇 |
2016年 | 36篇 |
2015年 | 53篇 |
2014年 | 49篇 |
2013年 | 108篇 |
2012年 | 73篇 |
2011年 | 121篇 |
2010年 | 91篇 |
2009年 | 93篇 |
2008年 | 94篇 |
2007年 | 73篇 |
2006年 | 87篇 |
2005年 | 67篇 |
2004年 | 77篇 |
2003年 | 53篇 |
2002年 | 43篇 |
2001年 | 45篇 |
2000年 | 42篇 |
1999年 | 36篇 |
1998年 | 32篇 |
1997年 | 21篇 |
1996年 | 21篇 |
1995年 | 15篇 |
1994年 | 16篇 |
1993年 | 9篇 |
1992年 | 17篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有1622条查询结果,搜索用时 312 毫秒
991.
In this paper we calculate the contributions to the branching ratio of Bs→γγ from charged pseudo-Goldstone bosons appearing in the one generation Technicolor model. We find that the theoretical value of the branching ratio, BR(Bs→γγ), including the contributions of PGBs, P± and P±8, is very different from the standard model (SM) prediction. The new physical effects can provide a one to two order of magnitude enhancement of the SM results. It is shown that the decay Bs→γγ can test new physical signals from the technicolor model. 相似文献
992.
CHENBao-Qiu MAZhong-Yu 《理论物理通讯》2004,42(4):594-598
The macroscopic deformed potential energies for super-heavy elements Z = 110,112,114,116,118 arc determined within a generalized liquid drop model (GLDM). A quasi-molecular mechanism is introduced to describe the deformation of a nucleus in the GLDM and the shell model simultaneously. The macroscopic energy of a twocenter nuclear system in the GLDM includes the volume-, surface-, and Coulomb-energies, the proximity effect at each mass asymmetry, and accurate nuclear radius. The shell correction is calculated by the Strutinsky method and the microscopic single particle energies are derived from a shell model in an axially deformed Woods-Saxon potential with the quasi-molecular shape. The total potential energy of a nucleus can be calculated by the macro-microscopic method as the summation of the liquid-drop energy and the Strutinsky shell correction. The theory is applied to predict the fusion barriers of the cold reactions ^64Ni ^208 spb → ^272 110*, ^70Zn ^208pb → ^278 112*, ^76Ge ^208seb → ^284 114*,^82Se ^208pb → ^29 116*, ^86Kr ^208pb → ^294 118*. It is found that the neck in the quasi-molecular shape is responsible for the deep valley of the fusion barrier. In the cold fusion path, double-hump fusion barriers could be predicted by the shell corrections and complete fusion events may occur. 相似文献
993.
微滴溶剂萃取/低温电热蒸发ICP-AES联用新技术用于超痕量元素分析 总被引:2,自引:0,他引:2
Liu等[1] 首先提出了微滴溶剂萃取的新概念 ,并设计了微滴萃取装置 .Jeannot等[2 ] 用微升级的正辛烷对蛋白质溶液中键合 /未键合的黄体酮进行了萃取分离 .随后 ,文献 [3 ]报道了富集倍数超过 1 0 0 0的连续流动微滴溶剂萃取技术 .针对生物样品量少且昂贵这一情况 ,Kellert等 [4 ]提出纳升级溶剂超微滴萃取技术 .电热蒸发 (ETV)作为一种有效的微量试样 (固体、液体 )引入技术备受人们的关注[5,6 ] .微滴萃取技术与高灵敏度的 ETV-ICP-AES/ MS联用必将在微量试样的超痕量分析 /形态分析中发挥重要作用 .我们基于微滴溶剂萃取原理 ,设… 相似文献
994.
The wetting of well-characterized heterogeneous surfaces of block copolymers has been studied by low-rate dynamic contact
angle measurements using axisymmetric drop-shape analysis. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy
(XPS) were used to investigate the roughness, the heterogeneity and the chemical composition of the surfaces. By changing
the block length of polysulfone and semifluorinated polyester segments in the block copolymers, the surface heterogeneity
of thin films prepared on silicon wafers could be controlled. Tapping-mode AFM measurements showed that soft, hydrophobic
domains of varying size on the submicrometer length scale were obtained on these surfaces (60–250 nm). The mean roughness
was of the order of several nanometers. The results of the contact angle measurements showed that neither roughness nor heterogeneity
had a significant effect on the advancing contact angle of water, at the scale of the features present; however, the contact
angle hysteresis increased with increasing percentage of the soft domains. We assume that liquid retention by the solid upon
retraction of the three-phase line is the main cause for the observed increase in contact angle hysteresis. Concerning the
molecular composition of these block copolymer surfaces, angle-resolved XPS analysis showed a surface segregation of fluorine
within the surface region. A direct correlation was found between the fluorine content of the block copolymer surfaces and
the advancing contact angle of water.
Received: 26 May 2000 Accepted: 3 January 2001 相似文献
995.
M. Lintuluoto 《Journal of Molecular Structure》2001,540(1-3):177-192
The structures of alkali halide clusters NanFn, LinFn and NanCln, and their metal-excess clusters NanFn−1+, LinFn−1+ and NanCln−1+ were investigated by the ab initio molecular orbital method for cluster sizes from 1 to 14. The magic numbers for the neutral clusters NanFn, LinFn and NanCln are 4, 6, and 8. The most stable structure for these cluster sizes is a perfect crystallite for NanFn and NanCln, and a double ring for LinFn. The magic numbers for the metal-excess clusters are 5 and 8, which are near ideal cuboids with (100) facets. 相似文献
996.
The paper presents the results of an experimental study that was carried out to determine turbulent friction and heat transfer characteristics of four spirally corrugated tubes, which have various geometrical parameters, with water and oil as the working fluids. Experiments were performed under conditions of Reynolds number varying from 6000 to 93,000 for water, and from 3200 to 19,000 for oil, respectively. The results show that the thermal performance of these tubes was superior compared to a smooth tube, but the heat transfer enhancements were not as large as the friction factor increases. Friction factors and heat transfer coefficient in these rough tubes were analyzed on the basis of momentum and heat transfer analogy, and the correlations obtained were compared with the present data and also the results of previous investigators. A mathematical model to evaluate the performance of spirally corrugated tube, which takes account of the large variation of fluid Prandtl number with temperature, was developed by the extension of previous work of Bergles and Webb. The results reported enable practical designs with standard products and optimization of tube geometry for specific conditions. 相似文献
997.
This paper presents crack shapes development of 3D surface semielliptical cracks which are always found at the weld toe of
non-load-carrying cruciform welded joints. The alternating current potential drop technique has been used to measure the eight
crack depths along the weld toe where probes are placed at 10-mm intervals. 3D crack shapes can be obtained at any particular
cycle during the fatigue test. Subregion boundary element methods incorporating the transition and quarter-point elements
along the crack front are used to validate the experimental stress intensity factors along the crack front. A method for evaluating
the effective stress intensity factors is proposed. It is found that the numerical results generally agree with the experimental
results. 相似文献
998.
The CP-violating effects to the subprocess gg → H H- are studied in the mSUGRA scenario at the CERN large hadron collider, by taking into account the experimental bounds of electron and neutron electric dipole moments.The CP-violating effects in this process are related to the complex phases ofμ and Af in the mSUGRA scenario. In our calculation we consider smallCP phases ofμ and Af and neglect the effects of neutral Higgs boson mixing. In this case the CP effects to the process mainly come from the complex couplings of Higgs-squark-squark. We find a strong dependence of charged Higgs boson pair production rate on the complex couplings in the parameter space of minimal supersymmetric standard model`` 相似文献
999.
The CP-violating effects to the subprocess gg→H+H- are studied in the mSUGRA scenario at the CERN large hadron collider, by taking into account the
experimental bounds of electron and neutron electric dipole moments.
The CP-violating effects in this process are related to the complex phases of μ and Af in
the mSUGRA scenario. In our calculation we consider small CP phases of
μ and Af and neglect the effects of neutral Higgs boson mixing.
In this case the CP effects to the process mainly come from the complex
couplings of Higgs-squark-squark. We find a strong dependence of
charged Higgs boson pair production rate on the complex couplings
in the parameter space of minimal supersymmetric standard model. 相似文献
1000.
滴体积法测定了十六烷基溴化吡啶溶液的动态表面张力。考察了浓度、温度对动态表面张力的影响。讨论了十六烷基溴化吡啶分子在气/液界面上的吸附动力学,发现吸附遵从扩散-动力学控制机理.从表观扩散系数计算了吸附能垒,分析了吸附能垒存在的原因。 相似文献