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   107974篇
  免费   1525篇
  国内免费   565篇
化学   44637篇
晶体学   1066篇
力学   7660篇
综合类   1篇
数学   34472篇
物理学   22228篇
  2023年   155篇
  2022年   329篇
  2021年   546篇
  2020年   484篇
  2019年   515篇
  2018年   10705篇
  2017年   10527篇
  2016年   6821篇
  2015年   1556篇
  2014年   1216篇
  2013年   2036篇
  2012年   5912篇
  2011年   12787篇
  2010年   7030篇
  2009年   7233篇
  2008年   8489篇
  2007年   10504篇
  2006年   2003篇
  2005年   2913篇
  2004年   2931篇
  2003年   3092篇
  2002年   2112篇
  2001年   1003篇
  2000年   936篇
  1999年   546篇
  1998年   481篇
  1997年   470篇
  1996年   580篇
  1995年   416篇
  1994年   399篇
  1993年   400篇
  1992年   354篇
  1991年   293篇
  1990年   243篇
  1989年   232篇
  1988年   224篇
  1987年   204篇
  1986年   176篇
  1985年   262篇
  1984年   181篇
  1983年   158篇
  1982年   188篇
  1981年   156篇
  1980年   149篇
  1979年   136篇
  1978年   134篇
  1977年   129篇
  1976年   135篇
  1975年   136篇
  1973年   156篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
71.
The fuzzification of convex sets in median algebras is considered, and some of their properties are investigated. A characterization of finite valued fuzzy convex set is given.  相似文献   
72.
It is explicitly shown that if phase transition occurs at the core of a newborn neutron star with moderately strong magnetic field strength, which populates only the electron’s Landau levels, then in the β -equilibrium condition, the quark core is energetically much more unstable than the neutron matter of identical physical condition.  相似文献   
73.
We describe the pulse forming of pulsed CO2 laser using multi-pulse superposition technique. Various pulse shapes, high duty cycle pulse forming network (PFN) are constructed by time sequence. This study shows a technology that makes it possible to make various long pulse shapes by activating SCRs of three PFN modules consecutively at a desirable delay time with the aid of a PIC one-chip microprocessor. The power supply for this experiment consists of three PFN modules. Each PFN module uses a capacitor, a pulse forming inductor, a SCR, a high voltage pulse transformer, and a bridge rectifier on each transformer secondary. The PFN modules operate at low voltage by driving the primary of HV pulse transformer. The secondary of the transformer has a full-wave rectifier, which passes the pulse energy to the load in a continuous sequence.We investigated various long pulse shapes as different trigger time intervals of SCRs among three PFN modules. As a result, we could obtain laser beam with various pulse shapes and durations from about 250 to 1000 μs.  相似文献   
74.
75.
For more than 25 years production has helped to sharpen our understanding of QCD. In proton induced reaction some observations are rather well understood while others are still unclear. The current status of the theory of production will be sketched, paying special attention to the issues of formation time and re-interaction in a nuclear medium.  相似文献   
76.
During the course of our investigation of the electron transfer properties of some redox species through highly hydrophobic long chain alkanethiol molecules on gold in aqueous and non-aqueous solvents, we obtained some intriguing results such as unusually low interfacial capacitance, very high values of impedance and film resistance, all of which pointed to the possible existence of a nanometer size interfacial gap between the hydrophobic monolayer and aqueous electrolyte. We explain this phenomenon by a model for the alkanethiol monolayer—aqueous electrolyte interface, in which the extremely hydrophobic alkanethiol film repels water molecules adjacent to it and in the process creates a shield between the monolayer film and water. This effectively increases the overall thickness of the dielectric layer that is manifested as an abnormally low value of interfacial capacitance. This behaviour is very much akin to the ‘drying transition’ proposed by Lum, Chandler and Weeks in their theory of length scale dependent hydrophobicity. For small hydrophobic units consisting of apolar solutes, the water molecules can reorganize around them without sacrificing their hydrogen bonds. Since for an extended hydrophobic unit, the existence of hydrogen bonded water structure close to it is geometrically unfavourable, there is a net depletion of water molecules in the vicinity leading to the possible creation of a hydrophobic interfacial gap.  相似文献   
77.
Basic ideas and results which characterize quantum diffusion of defects in quantum crystals like solid helium as a new phenomenon are presented. Quantum effects in such media lead to a delocalization of point defects (vacancies, impurities etc.) and they turn into quasiparticles of a new type—defectons, which are characterized not by their position in the crystal lattice but by their quasimomentum and dispersion law. Defecton-defecton and defecton-phonon scattering are considered and an interpolation formula for the diffusion coefficient valid in all interesting temperature and concentration regions is presented. A comparison with the experimental data is made. Some alternative points of view are discussed in detail and the inconsistency of the Kisvarsanyi-Sullivan theory is shown.  相似文献   
78.
This paper describes a compulsorily phase locked differential interferometer using an orthogonally polarized light source of a modulated LD with high extinction ratio to reduce non-linearity of the interferometer caused by polarization cross-talk. The current modulated LD is used as a light source to make the interferometer compact and for the scanning phase of the interferometer. The interferometer is operated compulsorily at the maximum inclination point of the fringe intensity curve by fringe scanning and an electric system. A Wollaston prism of high extinction ratio (50 dB) is used to combine the polarizing beams and to make the polarization cross-talk very small. In one light source the polarized output beams are on the same propagation axis; in the other they have a small crossing angle (2.5 mrad ∼ 10 mrad) to completely exclude non-linearity of the interferometer causded by polarization cross-talk. Using jets of a gas mixture of nitrogen and ethylene, this interferometer was demonstrated to be useful in detecting the photothermal effect of a photothermal velocimeter under phase fluctuation in a turbulent flow.  相似文献   
79.
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described.  相似文献   
80.
In this paper we obtain a number of Maharam-type slice integral representations, with respect to scalar measures, for positive projections in Dedekind complete vector lattices and f-algebras. AMS Classification: 47B65, 46A40, 06F25  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