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   823篇
  免费   20篇
  国内免费   4篇
化学   620篇
晶体学   2篇
力学   3篇
数学   26篇
物理学   196篇
  2021年   6篇
  2020年   6篇
  2019年   6篇
  2018年   4篇
  2017年   7篇
  2016年   9篇
  2015年   5篇
  2014年   18篇
  2013年   34篇
  2012年   35篇
  2011年   47篇
  2010年   22篇
  2009年   24篇
  2008年   60篇
  2007年   42篇
  2006年   63篇
  2005年   49篇
  2004年   48篇
  2003年   21篇
  2002年   25篇
  2001年   28篇
  2000年   16篇
  1999年   18篇
  1998年   7篇
  1997年   5篇
  1996年   10篇
  1995年   10篇
  1994年   6篇
  1993年   9篇
  1992年   5篇
  1991年   14篇
  1990年   9篇
  1989年   8篇
  1988年   8篇
  1987年   8篇
  1986年   7篇
  1985年   15篇
  1984年   22篇
  1983年   7篇
  1982年   9篇
  1981年   4篇
  1980年   7篇
  1979年   12篇
  1978年   11篇
  1977年   7篇
  1976年   15篇
  1975年   7篇
  1974年   12篇
  1973年   8篇
  1968年   3篇
排序方式: 共有847条查询结果,搜索用时 31 毫秒
51.
The temperature dependence of 207Pb chemical shift in magic angle spinning (MAS) NMR spectrum of Pb(NO3)2 provides a sensitive method to calibrate sample temperatures in MAS NMR. The temperature dependence is uniform in the temperature range between 30 degrees C and 400 degrees C. The NMR sensitivity and the line width are also favorable.  相似文献   
52.
53.
54.
55.
Then th,α)-reaction spectroscopical data are reported on95Mo,123Te and145Nd (target nuclei). The95Mo(n, α)92Zr and123Te(n, α)120Sn reactions showed up two lines each corresponding to the ground state and the 1st excited state with a total cross section of 32 ub and 52 μb respectively. In the case of145Nd(n, α)142Ce, a transition only to the 1st excited state of142Ce is present. It is shown that in the case of95Mo,145Nd and probably123Te, most of the cross-section comes respectively from the 2+ possibly 4?, and 0 bound levels whose widths are determined to beΓ α=0.5 × 10?6 eV,Γ α=1.6×10?8 eV andΓ α=1.6 × 10?6 eV. The present results on these three nuclei, when combined with the existing data, are consistent with the calculated statistical model values.  相似文献   
56.
1,1-Dialkylethenes are readily prepared in good yields from vinyltrialkylborates derived from trialkylboranes and trisylhydrazones of methyl ketones by treatment with iodine.  相似文献   
57.
The electronic absorption spectra of four monosubstituted naphthalenes, α-, β-naphthols, and α-, β-naphthylamines have been investigated by means of configuration analysis with particular attention to the dependence of spectra on the position of substitution and on the electron-donating power of the substituent. The results of molecular orbital calculations based on the Pariser-Parr-Pople method are analyzed in terms of locally excited states and intramolecular charge-transfer configurations. The characteristic changes in location and polarization of the Lb, La, and Bb bands caused by substitution at the α- or β-position are adequately explained by the analysis. Two strong absorption bands of α-substituted naphthalenes, which appear in place of the Bb band of naphthalene, are shown to result from a mixing of the B3u+(Bb) and Ag? states. The amino group exerts a great influence on the electronic structure of the parent molecule, so that the Bb band cannot be identified in the spectrum of β-naphthylamine.  相似文献   
58.
Experimental observation of optical Ramsey interference in saturated absorption of methane in a low-pressure gas cell with three spacially separated laser beams at 3.39 μm is reported.  相似文献   
59.
This paper describes a novel, sensitive detection system for biomolecules (DNA and proteins etc.) that is integrated in a lab-on-a-chip utilizing optical compact discs (CDs) and bio-nanofibers. The new method comprises a microchannel containing CD grating that confines fragments of unique bacterial cellulose fibrils (BC), which have nanometre scale fibers and holes. A maximum of six times higher sensitivity to detect DNA was obtained with this CD and BC system compared to a conventional method. We also demonstrate an effective light-confining effect for biological application with the new method.  相似文献   
60.
We demonstrate the generation of up to the 63rd harmonic (lambda = 12.6 nm) of a Ti:sapphire laser pulse (150 fs, 10 mJ), using a prepulse- (210-ps,24-mJ) produced boron plasma as the nonlinear medium. The influence of various parameters on the harmonic conversion efficiency was analyzed. The steep decrease in intensity for low-order harmonics (up to 19th order) was followed by a plateau. Typical conversion efficiencies were evaluated to be 10(-4) (for a 3rd harmonic) to 10(-7) (within the plateau region). Harmonic generation appeared to be efficient for the plasma that comprised neutral atoms and singly ionized boron.  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