全文获取类型
收费全文 | 72490篇 |
免费 | 23099篇 |
国内免费 | 17032篇 |
专业分类
化学 | 45266篇 |
晶体学 | 939篇 |
力学 | 4965篇 |
综合类 | 20篇 |
数学 | 9448篇 |
物理学 | 51983篇 |
出版年
2024年 | 455篇 |
2023年 | 658篇 |
2022年 | 640篇 |
2021年 | 536篇 |
2020年 | 781篇 |
2019年 | 1315篇 |
2018年 | 1307篇 |
2017年 | 1948篇 |
2016年 | 2039篇 |
2015年 | 2252篇 |
2014年 | 2070篇 |
2013年 | 3804篇 |
2012年 | 4087篇 |
2011年 | 5630篇 |
2010年 | 9079篇 |
2009年 | 9330篇 |
2008年 | 3141篇 |
2007年 | 2667篇 |
2006年 | 2356篇 |
2005年 | 2751篇 |
2004年 | 3666篇 |
2003年 | 2944篇 |
2002年 | 2761篇 |
2001年 | 3038篇 |
2000年 | 2247篇 |
1999年 | 2485篇 |
1998年 | 2108篇 |
1997年 | 1915篇 |
1996年 | 2241篇 |
1995年 | 2695篇 |
1994年 | 2765篇 |
1993年 | 2841篇 |
1992年 | 2416篇 |
1991年 | 2076篇 |
1990年 | 1736篇 |
1989年 | 1839篇 |
1988年 | 1829篇 |
1987年 | 1120篇 |
1986年 | 1176篇 |
1985年 | 840篇 |
1984年 | 963篇 |
1982年 | 884篇 |
1981年 | 729篇 |
1980年 | 768篇 |
1979年 | 525篇 |
1978年 | 530篇 |
1977年 | 633篇 |
1976年 | 1041篇 |
1973年 | 436篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
Analysis of the Coaxial Ridge-Loaded Helical Groove Waveguide 总被引:1,自引:0,他引:1
Yonghai Lan Wenxiang Wang Yubin Gong 《International Journal of Infrared and Millimeter Waves》2002,23(3):425-434
The coaxial ridge-loaded helical groove waveguide is proposed in this paper. As an all-metal slow-wave circuit, it has advantages of good heat dissipation and great size, and thus is suitable for use of millimeter TWT. By means of field theory, the expressions of the dispersion equation and the coupling impedance of the coaxial ridge-loaded helical groove waveguide are obtained. The influence of various circuit dimensions on the dispersion relation and the coupling impedance is investigated by the results of numerical computation. 相似文献
182.
183.
The occurrence of charge on recoil56Mn produced by the (n,γ) reaction in polycrystalline potassium permanganate has been examined using the ‘charge plate technique’.
From considerations of capture gamma ray decay schemes and internal conversion it appears that, in a condensed medium, the
recoil atom develops charge after losing much of its initial kinetic energy which allows collection on charged electrodes.
Preliminary findings were presented at the International Symposium on Radiochemistry and Radiation Chemistry, RC-41 BARC,
Bombay, Feb. 4–6 (1991). 相似文献
184.
CLIFFORDMARTINGALESΦ-EQUIVALENCEBETWEENS(f)ANDf¥LONGRULIN;QIANTAO(InstituteofMathematics,AcademiaSinica,Beijing100080,China.)... 相似文献
185.
Hui-Zhen Li Cheng-tian Xue 《International Journal of Infrared and Millimeter Waves》1991,12(12):1437-1449
This paper describes a global optimization design of quasi-optics power combiner of solid-state millimeterwave resonator. It is operated in the frequency range from 50 to 300 GHz using GaAs Gunn diodes. It is shown that sourcearrays containing N2 (N=3,5,...2K+1, where k is positive integer) individual elements. It is very efficient power transfer of energy from the source-array to the fractional power of the fundamental beam mode etc.. The RF output power exceeded the sum of the individual diodes to be threefold to sevenfold. And this data is the global optimization solution. 相似文献
186.
牙齿化石中由辐照产生的陷阱电子的热稳定性研究 总被引:3,自引:1,他引:2
本文对周口店北京猿人遗址的动物牙齿化石进行了辐照产生的陷阱捕获电子的热稳定性研究和釉质样品及牙质样品的热稳定性对比实验。得到釉质样品中g=2.0016 ESR峰的寿命为7.1×106年(20℃)。说明了取该峰进行ESR年代测定的可信性和用釉质样品进行ESR年代测定的必要性。 相似文献
187.
建立了脱镁叶绿素a和脱镁叶绿素b的联合同步荧光分析法。方法简便快速。脱镁叶绿素a和脱镁叶绿素b的线性范围分别为0~400ng/ml和0~200ng/ml,检出限分别为1ng/ml和0.5ng/ml。 相似文献
188.
The Stokes motions of three-dimensional screw-sensed slender particles in a homogeneous shear field are investigated, including the effects of buoyancy. Conclusions are drawn about the possibility of achieving a separation of mixtures of right- and left-handed particles. The linearity of the Stokes equations allows complex flows to be solved by adding the effects of the several terms which describe the flow in which the particle is immersed. The homogeneous shear flow considered here consists of three such terms; solutions for a series of 12 unit motions are sufficient to determine the hydrodynamic resistance tensors. The forces and torques experienced by screw-sensed particles are calculated from these 51 resistance tensors, using slender-filament theory. The results allow an estimate of the range of buoyancy parameters for which gravitational sedimentation can be neglected. The fundamental component of the particle motion is a rotation, at approximately the same angular velocity as that of the fluid. Superimposed on this are variations, of large period, in the particle orientation. A phase plane analysis is used to find the terminal orientations. Very long calculation times are required for the phase portrait. An approximate method based on azimuthally-averaged equations is developed to avoid the requirements for long time integration. 相似文献
189.
Let M be a symplectic manifold with a Hamiltonian circle action with isolated fixed points. We prove that σ (M) = b0(M) − b2(M) + b4(M) − b6(M) + … where σ (M) is the signature of M and bi(M) is the ith Betti number of M. 相似文献
190.
Summary The results of local meteorology, solar radiation and ground-level ozone measurements taken in Antarctica during the second
Italian expedition (December 86–February 87) at Terra Nova Bay are presented. During the summer months the site of the Italian
base camp is characterized by a thin strip of deglaciated ground, along which the temperature measurements close to the ground
and up to 6 m high show a strongly superdiabatic profile. This irregular trend of the temperature in the surface layer is
mainly due to the notable incoming amounts of radiation and to the extreme transparency of the atmosphere. This is also shown
by the low values of the ratio between total radiation and diffuse radiation. The ground is thus subjected to intense heating,
especially in the warmer hours of the day, while the surface layer of the atmosphere will be characterized by strong upward
heat fluxes and by turbulent convective movements. Vertical-temperature-profile measurements show an almost forced persistence
in the superdiabatic trend, which tends towards isothermic values only as a resultof rapid variations in the direction and
intensity of the wind, connected to the downward flux of cold air masses, shown also by the simultaneous increases in ground-level
ozone concentrations which would support the presence of dry-deposition processes in the lower layer. However, the complex
local orography and the horizontal discontinuity (sea, deglaciated coast, snow-covered surfaces) do not permit a correct application
of profile flux relations, normally used in studies on groundlevel dry-deposition.
Paper presented at the IV Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 22–24, 1987, Rome. 相似文献