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   8464篇
  免费   385篇
  国内免费   1877篇
化学   5041篇
晶体学   8篇
力学   623篇
综合类   85篇
数学   1355篇
物理学   3614篇
  2024年   2篇
  2023年   5篇
  2022年   6篇
  2021年   7篇
  2020年   14篇
  2019年   8篇
  2018年   10篇
  2016年   21篇
  2015年   48篇
  2014年   24篇
  2013年   105篇
  2012年   107篇
  2011年   1373篇
  2010年   691篇
  2009年   687篇
  2008年   113篇
  2007年   120篇
  2006年   197篇
  2005年   428篇
  2004年   1410篇
  2003年   813篇
  2002年   684篇
  2001年   549篇
  2000年   218篇
  1999年   225篇
  1998年   268篇
  1997年   187篇
  1996年   118篇
  1995年   129篇
  1994年   97篇
  1993年   459篇
  1992年   485篇
  1991年   298篇
  1990年   314篇
  1989年   301篇
  1988年   72篇
  1987年   10篇
  1986年   30篇
  1985年   21篇
  1984年   17篇
  1983年   11篇
  1982年   10篇
  1979年   2篇
  1977年   3篇
  1976年   2篇
  1962年   2篇
  1938年   3篇
  1937年   2篇
  1931年   2篇
  1893年   3篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
991.
In this paper, we study the count of head runs up to a fixed time in a two-state stationary Markov chain. We prove that in total variance distance, the negative binomial, Poisson and binomial distributions are appropriate approximations according to the relation of the variance and mean of the count, generalizing earlier results in previous literatures. The proof is based on Stein’s method and coupling.  相似文献   
992.
We consider a modified Markov branching process incorporating with both state-independent immigration-migration and resurrection. The effect of state-independent immigration-migration is firstly in- vestigated in detail. The explicit expressions for the extinction probabilities and mean extinction times are presented. The ergodicity and stability properties of the process incorporating with resurrection structure are then investigated. The conditions for recurrence, ergodicity and exponential ergodicity are...  相似文献   
993.
We investigate birationality of the anti-pluricanonical map Φ-m,the rational map defined by the anti-pluricanonical system |-mKX|,on weak Q-Fano 3-folds.  相似文献   
994.
We propose a unified scheme to implement the optimal 1→ 3economical phase-covariant quantum cloning and optimal 1→3 economical real state cloning with superconducting quantum interference devices (SQUIDs) in a cavity.During this process,no transfer of quantum information between the SQUIDs and cavity is required.The cavity field is only virtually excited.The scheme is insensitive to cavity decay.Therefore,the scheme can be experimentally realized in the range of current cavity QED techniques.  相似文献   
995.
Navigation augmentation technology is one of the most common methods to increase the continuity,reliability and integrity of the global satellite navigation system.The concept of volunteer augmentation navigation (VNA) is proposed and the elements and topological structure of VNA are also analyzed in this paper.The study focuses on the neural network model that volunteers and ordinary users use modern communication information network to exchange self-organizing information.The neural cell model of Voluntee...  相似文献   
996.
Aiming at regional services,the space segment of COMPASS (Phase I) satellite navigation system is a constellation of Geostationary Earth Orbit (GEO),Inclined Geostationary Earth Orbit (IGSO) and Medium Earth Orbit (MEO) satellites.Precise orbit determination (POD) for the satellites is limited by the geographic distribution of regional tracking stations.Independent time synchronization (TS) system is developed to supplement the regional tracking network,and satellite clock errors and orbit data may be obtai...  相似文献   
997.
With the multi-phase field model, the unidirectional solidification with constant velocity growth and variable velocity growth of the CBr4-C2Cl6 eutectic alloy is simulated in three dimensions. The simulated results with constant velocity growth show that with the increase of pulling velocity, the morphology of the CBr4-C2Cl6 alloy evolves in the sequence of lamellar merging →lamellar-rod transition→stable lamellar growth→oscillating growth→lamellar branching. A morphology selection map is established with ...  相似文献   
998.
Lithium isotopes have attracted an intense interest because the abundance of both 6Li and 6Li from big bang nucleosynthesis (BBN) is one of the puzzles in nuclear astrophysics. Many investigations of both astrophysical observation and nucleosynthesis calculation have been carried out to solve the puzzle, but it is not solved yet. Several nuclear reactions involving lithium have been indirectly measured at China Institute of Atomic Energy, Beijing. The Standard BBN (SBBN) network calculations are then perfo...  相似文献   
999.
A new rotational band has been identified and assigned to 188Au for the first time using the 173Yb(19F,4nγ) reaction at the beam energies of 86 and 90 MeV. This band is proposed to be built on the πh9/2  νi13/2 configuration by comparing the band properties with known bands in neighboring nuclei. The prolate-to-oblate shape transition through triaxial shape has been proposed to occur around 188Au for the πh9/2  νi13/2 bands in odd-odd Au isotopes on the basis of total Routhian surface (TRS) calculations.  相似文献   
1000.
High-spin states in 161Er have been studied experimentally via the 150Nd(16O, 5n) reaction at a beam energy of 86 MeV. Three rotational bands built on the 5/2+[642], 3/2-[521], and 11/2-[505] configurations have been extended up to high-spin states, and particularly, the α = -1/2 branch of the ground state 3/2-[521] band has been revised significantly. It is found that signature inversion occurs in the 3/2-[521] band after the band crossing in 161Er. The systematics of the signature inversion associated wit...  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