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   6133篇
  免费   141篇
  国内免费   22篇
化学   4336篇
晶体学   71篇
力学   79篇
数学   298篇
物理学   1512篇
  2022年   32篇
  2021年   35篇
  2020年   61篇
  2019年   71篇
  2018年   58篇
  2017年   43篇
  2016年   99篇
  2015年   101篇
  2014年   131篇
  2013年   282篇
  2012年   286篇
  2011年   318篇
  2010年   178篇
  2009年   183篇
  2008年   325篇
  2007年   293篇
  2006年   309篇
  2005年   279篇
  2004年   284篇
  2003年   232篇
  2002年   237篇
  2001年   155篇
  2000年   172篇
  1999年   94篇
  1998年   73篇
  1997年   69篇
  1996年   80篇
  1995年   46篇
  1994年   80篇
  1993年   99篇
  1992年   101篇
  1991年   81篇
  1990年   66篇
  1989年   57篇
  1988年   77篇
  1987年   77篇
  1986年   80篇
  1985年   119篇
  1984年   106篇
  1983年   43篇
  1982年   77篇
  1981年   84篇
  1980年   75篇
  1979年   70篇
  1978年   63篇
  1977年   67篇
  1976年   55篇
  1975年   41篇
  1974年   50篇
  1973年   34篇
排序方式: 共有6296条查询结果,搜索用时 15 毫秒
61.
Photoelectron angular distributions in the laboratory frame (LF-PADs) from the A((2)sigma(+)) state of NO molecule were measured by femtosecond time-resolved photoelectron imaging with (1 + 1(')) resonance enhanced multiphoton ionization via the A state. High-precision measurements of the anisotropy parameters of LF-PADs were performed for the photoelectron kinetic energy from 0.03 to 1.05 eV as a function of the pump-probe delay time. The revival feature of the rotational wave packet on the A state was clearly observed in the time dependence of the photoelectron anisotropy parameters. By approximating the phase shifts of the photoelectron partial waves by the quantum defects in the high-lying Rydberg states using the multichannel quantum defect theory, the energy-dependent photoionization transition dipole moments were determined, for the first time, from time-dependent LF-PADs measured by time-resolved photoelectron spectroscopy.  相似文献   
62.
Let be a distance regular graph with diameterd, and d () the set of vertices at distanced from. is said to be thin if the induced subgraph on d () is a union of cliques for every vertex. We show that the diameterd is bounded above by a function depending only onk d, which is the cardinality of d (), if is not thin. We also investigate thin distance regular graphs witha d 0.  相似文献   
63.
64.
65.
66.
67.
The mechanism of 201Tl chloride accumulation is unclear in thyroid gland and thyroid tumor. This report examines 108 patients that received thyroid scintigraphy examinations with both 201Tl chloride and sodium 131I. The patients were diagnosed clinically and histologically whenever possible. The ROI were obtained by subtraction imaging with both isotopes and by subtraction positive and negative areas of imaging. Dynamic curves were obtained for 201Tl chloride per square unit of each ROI. The dynamic curve in the radioiodide-accumulated area was examined. The data indicate that the clearance rate of 201Tl chloride (T15) was correlated with the sodium 131I uptake rate at 24 h (r = 0.70).  相似文献   
68.
69.
An alternative original approach to achieve single-transverse-mode laser emissions from multimode (MM) active fibers is demonstrated. The fiber cavity is constructed by simply splicing a conventional passive single-mode fiber (SMF-28) onto a few centimeters-long active MM fiber section whose length is precisely controlled. Owing to the self-imaging property of multimode interference (MMI) in the MM fiber, diffraction-limited laser output is obtained from the end of the SMF-28, and the MMI fiber laser is nearly as efficient as the corresponding MM fiber laser. Moreover, because of the spectral filtering effect during in-phase MMI, the bandwidth of the MMI fiber laser is below 0.5 nm.  相似文献   
70.
The time course of Mg uptake and release using intact rice plants and 28Mg as a tracer is presented. Since there is no conventional Mg tracer available, 28Mg was produced via 27Al(α, 3p)28Mg reaction using a cyclotron. Using the purified 28Mg tracer, it was found that the uptake amount of 28Mg by the rice plants increased linearly during 30 min of application. After 28Mg treatment for 90 min, the roots were sequentially washed with iced solution for 120 min. Within about 10 min, almost all of the 28Mg, that was thought to be weakly bound to the apoplast, was washed away.  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