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   7070篇
  免费   219篇
  国内免费   27篇
化学   5306篇
晶体学   80篇
力学   120篇
数学   529篇
物理学   1281篇
  2022年   46篇
  2021年   57篇
  2020年   81篇
  2019年   102篇
  2018年   60篇
  2017年   47篇
  2016年   119篇
  2015年   117篇
  2014年   156篇
  2013年   339篇
  2012年   381篇
  2011年   420篇
  2010年   225篇
  2009年   219篇
  2008年   437篇
  2007年   456篇
  2006年   466篇
  2005年   401篇
  2004年   359篇
  2003年   326篇
  2002年   289篇
  2001年   108篇
  2000年   93篇
  1999年   90篇
  1998年   59篇
  1997年   94篇
  1996年   94篇
  1995年   51篇
  1994年   73篇
  1993年   63篇
  1992年   60篇
  1991年   64篇
  1990年   40篇
  1989年   38篇
  1988年   53篇
  1987年   47篇
  1986年   46篇
  1985年   99篇
  1984年   105篇
  1983年   44篇
  1982年   91篇
  1981年   93篇
  1980年   83篇
  1979年   80篇
  1978年   75篇
  1977年   56篇
  1976年   68篇
  1975年   49篇
  1974年   46篇
  1973年   70篇
排序方式: 共有7316条查询结果,搜索用时 15 毫秒
11.
12.
In a graph, a cluster is a set of vertices, and two clusters are said to be non-intersecting if they are disjoint or one of them is contained in the other. A clustered graph C consists of a graph G and a set of non-intersecting clusters. In this paper, we assume that C has a compound planar drawing and each cluster induces a biconnected subgraph. Then we show that such a clustered graph admits a drawing in the plane such that (i) edges are drawn as straight-line segments with no edge crossing and (ii) the boundary of the biconnected subgraph induced by each cluster is a convex polygon.  相似文献   
13.
14.
Nonlinear susceptibility of a quantum dot (QD) embedded in a two-sided cavity, is studied theoretically from a weak-coupling to a strong-coupling regime. In the relevance of a quantum logic gate, the corresponding nonlinear phase shifts (Kerr effect) are estimated for coherent wavepackets including one photon on average. In the weak-coupling regime, the phase shift enhances strongly as a function of a coupling constant between the cavity photon and QD, and eventually saturates in the strong-coupling regime. We also show transmission spectra to evaluate the efficiency of the phase shift. Although the efficiency decreases monotonically in the weak-coupling regime, it rises in the strong-coupling regime.  相似文献   
15.
Frequency dependence of ac conductivity from 1 to 105 Hz and time series of the conductivity at 2 kHz were measured along c-axis of thulium nitrate crystal, Tm(NO3)36H2O at temperatures from 203.15 to 293.15 K. The meta-stability was observed. The frequency spectra of the conductivity were similar to those in disorder system. Aging effect was observed. Non-periodic instability (burst) was found. Non-linear dynamical property was characterized by 1/f noise spectrum, limit cycle in return map and dependence of correlation exponent on embedding dimension.  相似文献   
16.
We deal with the q-numerical radius of weighted unilateral and bilateral shift operators. In particular, the q-numerical radius of weighted shift operators with periodic weights is discussed and computed.  相似文献   
17.
The oxygen storage capacity of CeO2, Ce0.9Pr0.1O2, Pt?Rh/CeO2 and Pt?Rh/Ce0.9Pr0.1O2 was investigated by conventional GC pulse method and transient pulse techniques. It is shown that incorporation of PrOy into CeO2 matrix strongly promotes oxygen storage capacity (OSC) measured using the transient pulse technique. The improvement of OSC at low temperature is observed in Pt?Rh loaded onto CeO2 and Ce?Pr catalysts.  相似文献   
18.
19.
We calculated the intake of each chemical species of dietary arsenic by typical Japanese, and determined urinary and blood levels of each chemical species of arsenic. The mean total arsenic intake by 35 volunteers was 195±235 (15.8-1039) μg As day?1, composed of 76% trimethylated arsenic (TMA), 17.3% inorganic arsenic (Asi), 5.8% dimethylated arsenic (DMA), and 0.8% monomethylated arsenic (MA): the intake of TMA was the largest of all the measured species. Intake of Asi characteristically and invariably occurred in each meal. Of the intake of Asi, 45-75% was methylated in vivo to form MA and DMA, and excreted in these forms into urine. The mean measured urinary total arsenic level in 56 healthy volunteers was 129±92.0 μg As dm?3, composed of 64.6% TMA, 26.7% DMA, 6.7% Asi and 2.2% MA. The mean blood total arsenic level in the 56 volunteers was 0.73±0.57 μg dl?1, composed of 73% TMA, 14% DMA and 9.6% Asi. The urinary TMA levels proved to be significantly correlated with the whole-blood TMA levels (r = 0.376; P<0.01).  相似文献   
20.
Photonic sensing technologies are an integral part of Remote Fiber Test Systems used for maintaining optical fiber networks. Optical components used for this purpose such as branching components, filters, switches, water sensors and fiber identifiers are overviewed.  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