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   1725篇
  免费   567篇
  国内免费   118篇
化学   286篇
晶体学   29篇
力学   158篇
综合类   63篇
数学   478篇
物理学   1396篇
  2024年   3篇
  2023年   20篇
  2022年   42篇
  2021年   48篇
  2020年   51篇
  2019年   46篇
  2018年   56篇
  2017年   92篇
  2016年   100篇
  2015年   88篇
  2014年   137篇
  2013年   138篇
  2012年   120篇
  2011年   105篇
  2010年   103篇
  2009年   106篇
  2008年   125篇
  2007年   139篇
  2006年   109篇
  2005年   110篇
  2004年   78篇
  2003年   72篇
  2002年   79篇
  2001年   48篇
  2000年   55篇
  1999年   49篇
  1998年   40篇
  1997年   38篇
  1996年   30篇
  1995年   30篇
  1994年   24篇
  1993年   28篇
  1992年   12篇
  1991年   14篇
  1990年   10篇
  1989年   7篇
  1988年   8篇
  1987年   10篇
  1986年   4篇
  1985年   6篇
  1984年   9篇
  1982年   5篇
  1981年   3篇
  1979年   4篇
  1978年   1篇
  1977年   1篇
  1976年   2篇
  1975年   1篇
  1973年   1篇
  1959年   1篇
排序方式: 共有2410条查询结果,搜索用时 31 毫秒
91.
This paper proposes a circular threshold quantum secret sharing (TQSS) scheme with polarized single photons. A polarized single photon sequence runs circularly among any t or more of n parties and any t or more of n parties can reconstruct the secret key when they collaborate. It shows that entanglement is not necessary for quantum secret sharing. Moreover, the theoretic efficiency is improved to approach 100% as the single photons carrying the secret key are deterministically forwarded among any t or more of n parties, and each photon can carry one bit of information without quantum storage. This protocol is feasible with current technology.  相似文献   
92.
报道在脉宽50fs—22ps,波长800nm脉冲激光作用下的空气电离阈值的研究结果.利用探测等离子体发光信号的方法,实验测量了激发空气电离所需的阈值激光强度.结果表明,当激光脉冲宽度从50fs增加到22ps时,阈值光强Ith从8.7×1014W/cm2下降到2.7×1013W/cm2Ith经历了由迅速降低逐渐发展为缓慢降低的过程.在50fs—1p  相似文献   
93.
In order to improve the optical properties of the Ⅲ-Ⅴ laser diodes(LDs) by means of H2S plasma passivation technology,H2S plasma passivation treatment is performed on the GaAs(110) surface.The optimum passivation conditions obtained are 60-W radio frequency(RF)power and 20-min duration.So the laser cavity surfaces axe treated under the optimum passivation conditions.Consequently,compared with unpassivated lasers with only AR/HR-coatings,the catastrophic optical damage (COD) threshold value of the passivated lasers by H2S plasma treatment is increased by 33%,which is almost the same as that of (NH4)2Sx treatment.And the life-test experiment has demonstrated that this passivation method is more stable than(NH4)2Sx solution wet-passivated treatment.  相似文献   
94.
A method for automatically identifying the order of fringe pattern traces is presented. It uses the simplified Otsu algorithm for obtaining the threshold, the angular scan in the range of 45~ for searching the trace positions, and the zone search technique for identifying different traces. Experimental results show that the proposed method may reliably obtain the order of fringe pattern traces orientating from almost 45° to 90°.  相似文献   
95.
A new charge measurement method, time over threshold (TOT), has been used in some gas detectors lately. Here TOT is studied for TOF system, made of plastic scintillator counter, which can simplify the electronics of the system. The signal characteristics are measured and analyzed with a high quality oscilloscope, including noise, pedestal, signal amplitude, total charge, rise time and the correlation between them. The TOT and charge are related and can be fitted by some empirical formula. The charge measurement resolution by TOT is given and this will help the design of TOF electronics.  相似文献   
96.
The interband transitions in a narrow-band InSb quantum spherical layer are studied theoretically within the framework of the spherical rotator model. The electron and light-hole dispersions are described using the two-band Kane approximation, while for heavy holes the standard dispersion is considered. The absorption coefficients for transitions between conduction and lighthole, heavy-hole bands are calculated. The selection rules and threshold absorption frequencies are determined. It is shown that in the presence of a weak electric field the selection rules and threshold absorption frequencies for dipole transitions are modified.  相似文献   
97.
We extend the range of observed behaviour among length functionsof optimal asynchronously automatic structures. We do so bymeans of a construction that yields asynchronously automaticgroups with finite aspherical presentations where the Dehn functionof the group is polynomial of arbitrary degree. Many of thesegroups can be embedded in the automorphism group of a free group.Moreover, the fact that the groups have aspherical presentationsmakes them useful tools in the search to determine the spectrumof exponents for second order Dehn functions. We contributeto this search by giving the first exact calculations of groupswith quadratic and superquadratic exponents. 2000 Mathematical Subject Classification: 20F06, 20F65, 20F69.  相似文献   
98.

In this paper properties and construction of designs under a centered version of the -discrepancy are analyzed. The theoretic expectation and variance of this discrepancy are derived for random designs and Latin hypercube designs. The expectation and variance of Latin hypercube designs are significantly lower than that of random designs. While in dimension one the unique uniform design is also a set of equidistant points, low-discrepancy designs in higher dimension have to be generated by explicit optimization. Optimization is performed using the threshold accepting heuristic which produces low discrepancy designs compared to theoretic expectation and variance.

  相似文献   

99.
100.
In this paper the calculation of resonance frequencies and threshold gains of distributed feedback (DFB) lasers with strong modulations is discussed. The theory is based on the Floquet solutions of a complex Hill differential equation. The dispersion relation of the above solutions is shown to be of importance for the behaviour of the resonances of the DFB laser.  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