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   85712篇
  免费   1643篇
  国内免费   1040篇
化学   29421篇
晶体学   868篇
力学   7182篇
综合类   36篇
数学   32819篇
物理学   18069篇
  2023年   163篇
  2022年   285篇
  2021年   296篇
  2020年   365篇
  2019年   304篇
  2018年   10637篇
  2017年   10436篇
  2016年   6429篇
  2015年   1253篇
  2014年   746篇
  2013年   886篇
  2012年   4515篇
  2011年   11164篇
  2010年   6097篇
  2009年   6478篇
  2008年   7088篇
  2007年   9115篇
  2006年   651篇
  2005年   1606篇
  2004年   1767篇
  2003年   2165篇
  2002年   1168篇
  2001年   376篇
  2000年   430篇
  1999年   323篇
  1998年   344篇
  1997年   270篇
  1996年   325篇
  1995年   227篇
  1994年   169篇
  1993年   171篇
  1992年   131篇
  1991年   138篇
  1990年   93篇
  1989年   96篇
  1988年   97篇
  1987年   92篇
  1986年   85篇
  1985年   67篇
  1984年   62篇
  1983年   56篇
  1982年   50篇
  1981年   52篇
  1980年   55篇
  1979年   47篇
  1914年   45篇
  1913年   40篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A novel and simple fluorescence enhancement method for selective pyrophosphate(PPi) sensing was proposed based on a 1:1 metal complex formation between bis(8-hydroxy quinoline-5-solphonat) chloride aluminum(III) (Al(QS)2Cl), (L) and PPi in aqueous solution. The linear response range covers a concentration range of 1.6 × 10−7 to 1.0 × 10−5 mol/L of PPi and the detection limit of 2.3 × 10−8 mol/L. The association constant of L-PPi complex was calculated 2.6 × 105 L/mol. L was found to show selectively and sensitively fluorescence enhancement toward PPi over than I3-, NO3-, CN, CO32−, Br, Cl, F, H2PO4 and SO42−, which was attributed to higher stability of inorganic complex between pyrophosphate and L.  相似文献   
992.
We divide the cross-section for a meson-meson reaction into three parts. The first part is for the quark-interchange process, the second for quark-antiquark annihilation processes and the third for resonant processes. Master rate equations are established to yield time dependence of fugacities of pions, rhos, kaons and vector kaons. The equations include cross-sections for inelastic scattering of pions, rhos, kaons and vector kaons. Cross-sections for quark-interchange-induced reactions, that were obtained in a potential model, are parametrized for convenient use. The number densities of π and ρ (K and K * are altered by quark-interchange processes in equal magnitudes but opposite signs. The master rate equations combined with the hydrodynamic equations for longitudinal and transverse expansion are solved with many sets of initial meson fugacities. Quark-interchange processes are shown to be important in the contribution of the inelastic meson-meson scattering to the evolution of mesonic matter.  相似文献   
993.
We propose a simple target in the form of a miniature torus, in which the heavy shell is used to confine the plasma spread, for a solution of the laser-fusion problem. We achieve a significant decrease of heat losses using an external magnetic field and/or as a result of a self-sustaining magnetic field that is generated in the plasma. We formulate the conditions and determine the energy of the laser pulse (or of a beam of fast charged particles) required to ignite a thermonuclear DD reaction and obtain a positive energy yield. We show that the stopping range of α-particles does not exceed the small radius of the torus within a broad range of the plasma and magnetic-field parameters.  相似文献   
994.
The creation of multifunctional nanomaterials by combining organic and inorganic components is a growing trend in nanoscience. The unique size-dependent properties of magnetic nanoparticles (MNPs) make them amenable to numerous applications such as carriers of expensive biological catalysts, in magnetically assisted chemical separation of heavy metals and radionuclides from contaminated water sources. The separation of minor actinides from high-level radionuclide waste requires a sorbent stable in acidic pH, with ease of surface functionalization, and a high capacity for binding the molecules of interest. For the described experiments, the MNPs with 50 nm average size were used (size distribution from 20 to 100 nm and an iron content of 80–90 w/w%). The MNPs that have been double coated with an initial silica coating for protection against iron solubilization and oxidation in nitric acid solution (pH 1) and a second silica/polymer composite coating incorporating partially imbedded poly(allylamine) (PA). The final product is magnetic, highly swelling, containing >95% water, with >0.5 mmol amines g?1 available for functionalization. The amine groups of the magnetic resin were functionalized with the chelating molecules diethylenetriaminepentaacetic acid (DTPA) and N,N-dimethyl-3-oxa-glutaramic acid (DMOGA) for separation of minor actinides from used nuclear fuel.  相似文献   
995.
A fundamental question of human society is the evolution of cooperation. Many previous studies explored this question via setting spatial background, where players obtain their payoffs by playing game with their nearest neighbors. Another undoubted fact is that the environment plays an important role in the individual development. Inspired by these phenomena, we reconsider the definition of individual fitness which integrates the environment, denoted by the average payoff of all individual neighbors, with the traditional individual payoffs by introducing a selection parameter u. Tuning u equal to zero returns the traditional version, while increasing u bears the influence of environment. We find that considering the environment, i.e., integrating neighborhoods in the evaluation of fitness, promotes cooperation. If we enhance the value of u, the invasion of defection could be resisted better. We also provide quantitative explanations and complete phase diagrams presenting the influence of the environment on the evolution of cooperation. Finally, the universality of this mechanism is testified for different neighborhood sizes, different topology structures and different game models. Our work may shed light on the emergence and persistence of cooperation in our life.  相似文献   
996.
贾飞蕾  徐伟  都林 《物理学报》2007,56(10):5640-5647
采用扩阶方法(使响应系统和驱动系统的维数相同),把不同阶数混沌系统的广义同步问题转化为相同阶数混沌系统之间的广义同步,基于Lyapunov稳定性定理和自适应控制方法(用于相同阶数混沌系统的同步),给出了自适应控制器和参数自适应律,进而实现了不同阶数混沌系统的广义同步.将该方法应用于参数未知的超Lü,Lorenz,广义Lorenz和Liu等系统之间的广义混沌同步,理论证明了该方法可以使这些系统达到渐近广义同步,并且可以辨识驱动系统和响应系统的所有参数,数值模拟进一步证明了该方法的有效性.  相似文献   
997.
998.
999.
We explain the (non-)validity of close-to-equilibrium entropy production principles in the context of linear electrical circuits. Both the minimum and the maximum entropy production principles are understood within dynamical fluctuation theory. The starting point are Langevin equations obtained by combining Kirchoff’s laws with a Johnson-Nyquist noise at each dissipative element in the circuit. The main observation is that the fluctuation functional for time averages, that can be read off from the path-space action, is in first order around equilibrium given by an entropy production rate. That allows to understand beyond the schemes of irreversible thermodynamics (1) the validity of the least dissipation, the minimum entropy production, and the maximum entropy production principles close to equilibrium; (2) the role of the observables’ parity under time-reversal and, in particular, the origin of Landauer’s counterexample (1975) from the fact that the fluctuating observable there is odd under time-reversal; (3) the critical remark of Jaynes (1980) concerning the apparent inappropriateness of entropy production principles in temperature-inhomogeneous circuits.  相似文献   
1000.
Critical temperature and condensate fraction of Bose-Einstein condensation in the optical lattice are studied. The results show that the critical temperature in optical lattices can be characterized with an equivalent critical temperature in a single lattice, which provide a fast evaluation of critical temperature and condensate fraction of Bose-Einstein condensation confined with pure optical trap. Critical temperature can be estimated with an equivalent critical temperature. It is predicted that critical temperature is proportional to q in q number lattices for superfluid state and should be equal to that in a single lattic for Mott insulate state. Required potential depth or Rabi frequency and maximum atom number in the lattices both for superfluid state and Mott state are presented based on views of thermal mechanical statistics.  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