首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   8830篇
  免费   360篇
  国内免费   127篇
化学   6614篇
晶体学   48篇
力学   441篇
综合类   3篇
数学   830篇
物理学   1381篇
  2024年   24篇
  2023年   68篇
  2022年   317篇
  2021年   414篇
  2020年   403篇
  2019年   413篇
  2018年   408篇
  2017年   389篇
  2016年   551篇
  2015年   395篇
  2014年   510篇
  2013年   952篇
  2012年   729篇
  2011年   664篇
  2010年   414篇
  2009年   403篇
  2008年   407篇
  2007年   345篇
  2006年   262篇
  2005年   220篇
  2004年   161篇
  2003年   155篇
  2002年   125篇
  2001年   49篇
  2000年   32篇
  1999年   39篇
  1998年   28篇
  1997年   32篇
  1996年   29篇
  1995年   15篇
  1994年   22篇
  1993年   21篇
  1992年   21篇
  1991年   18篇
  1990年   18篇
  1989年   14篇
  1988年   12篇
  1987年   21篇
  1986年   17篇
  1985年   23篇
  1984年   23篇
  1983年   9篇
  1982年   28篇
  1981年   16篇
  1980年   21篇
  1979年   12篇
  1978年   12篇
  1977年   14篇
  1976年   11篇
  1975年   5篇
排序方式: 共有9317条查询结果,搜索用时 0 毫秒
91.
The output energy of photovoltaic (PV) modules is influenced by the spectral irradiance distribution of the solar spectrum under outdoor conditions. To rate the precise output energy of PV modules, the correction of short circuit current (ISC) based on actual environmental conditions is needed, because ISC significantly depends on the shape of the spectral irradiance distribution. The average photon energy (APE) is a zero-dimensional index for spectral irradiance distribution, and APE value uniquely describes the shape of a solar spectrum. Thus, APE has an impact on ISC of PV modules. In this contribution, the relationship between APE coefficient and ISC of the multi-crystalline silicon, single-crystalline silicon, heterojunction intrinsic thin-layer, back contact, copper indium selenide and cadmium telluride PV modules has explored. It is revealed that APE value changes the ISC of PV modules which appeared to have immense possibilities of ISC correction using APE coefficient. This new approach can be very effective for precise rating the output energy of PV modules under actual outdoor conditions.  相似文献   
92.
Ionics - A novel carbon paste electrode (CPE) modified with 2,2′-[1,7–heptanediylbis(nitrilomethylidene)]-bis(4-hydroxyphenol) (DHB) and carbon nanotubes (CNTs) was prepared. At first,...  相似文献   
93.
94.
95.
Short and long distance contributions to the exclusive B-decays into various K-resonances and dileptons, i.e. $B \to K^i \ell \bar \ell (\ell = e,\mu ,\nu )$ , are examined. The heavy quark effective theory has been used to calculate the hadronic matrix elements. Substantial branching fractions are obtained for the dileptonic B-decays into some higher excited states of K-mesons. The long distance (resonance) contributions to these exclusive rare B-decay modes dominate the short distance contributions mostly by two orders of magnitude. It is pointed out that, excluding the resonance contributions, the P-wave channels are dominant, accounting for about 50% of the inclusiveB??X s ? + ? ? branching fraction.  相似文献   
96.
Kim MS  Scharf T  Haq MT  Nakagawa W  Herzig HP 《Optics letters》2011,36(19):3930-3932
We report on the fabrication and characterization of nanoscale solid immersion lenses (nano-SILs) with sizes down to a subwavelength range. Submicrometer-scale cylinders fabricated by electron-beam lithography are thermally reflowed to form a spherical shape. Subsequent soft lithography leads to nano-SILs on transparent substrates for optical characterization. The optical characterization is performed using a high-resolution interference microscope with illumination at 642 nm wavelength. The focal spots produced by the nano-SILs show both spot-size reduction and enhanced optical intensity, which are consistent with the immersion effect.  相似文献   
97.
We consider the tachyon-brane inflationary universe model in the context of a polytropic gas equation of state. In slow-roll approximation, we discuss general conditions of this model. For exponential potential, in high-energy limit the characteristics of the model are presented. By using the seven-year Wilkinson Microwave Anisotropy Probe (WMAP7) observational data, we constrain the cosmological parameters of the model.  相似文献   
98.
The holographic model for a two-dimensional superconductor has been investigated by considering the three-dimensional gravity in the bulk. To find the critical temperature, we used the Sturm–Liouville variational method. Where as the same method is applied for calculating the condensation of the dual operators on the boundary. We included the back reactions on the metric by a combination of the perturbation method of the fields with respect to the small parameter and then applying the variational integrals on the resulting equations of the motion. The critical temperature has been successfully obtained on the backreaction effects, and we showed that it dropped with a rise in the backreaction of the fields, and it makes the condensation harder. We can use our analytical results to support the numerical data which was reported previously.  相似文献   
99.
Spin-flip (paramagnetic) scattering and neutron depolarization studies were performed on Ce2Fe17 in its paramagnetic phase on the Dhruva neutron polarization analysis spectrometer. The absence of normalQ dependence of the scattered spin flip intensity shows that Ce2Fe17 is not a normal paramagnetic and there exist superparamagnetic clusters of sufficiently large dimensions (~100Å). The observed neutron depolarization gives an indication of the dynamics of these Ce2Fe17 superparamagnetic clusters.  相似文献   
100.
Isotactic polypropylene (iPP) film was melt-crystallized in a temperature gradient. The iPP film showed well oriented α- and β-crystalline textures along the gradient. The crystalline structure, phase transition boundary and lamellar twisting were examined by X-ray diffraction and laser light diffraction (LLD). On the α-β boundary, LLD shows a sharp streak perpendicular to the boundary, where the a-axis of the β-crystal is oriented perpendicular to the temperature gradient. Apart from the boundary, the a-axis of the β-crystal becomes parallel to the gradient. The β-crystal shows lamellar twisting with a pitch of 200 μm at room temperature. When heated the β-crystal, the lamellar distance of 295Å at room temperature decreases to 285Å at 80–100°C and then increases to more than 300Å above 120°C. During the heating, the value of the twist period increases from 200 to 210 μm at 90–100°C, and then to above 224 μm at 140°C. The increase of the twist period is related to the increasing crystalline thickness of the β-lamellae.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号