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   507461篇
  免费   5529篇
  国内免费   1245篇
化学   255366篇
晶体学   6566篇
力学   24207篇
综合类   13篇
数学   70325篇
物理学   157758篇
  2021年   3724篇
  2020年   4184篇
  2019年   4519篇
  2018年   12402篇
  2017年   12932篇
  2016年   11901篇
  2015年   6201篇
  2014年   8641篇
  2013年   20279篇
  2012年   18924篇
  2011年   28657篇
  2010年   19067篇
  2009年   18979篇
  2008年   25863篇
  2007年   28380篇
  2006年   16405篇
  2005年   19814篇
  2004年   16187篇
  2003年   14598篇
  2002年   12873篇
  2001年   13562篇
  2000年   10333篇
  1999年   7944篇
  1998年   6603篇
  1997年   6332篇
  1996年   6141篇
  1995年   5396篇
  1994年   5360篇
  1993年   5142篇
  1992年   5757篇
  1991年   5862篇
  1990年   5612篇
  1989年   5424篇
  1988年   5454篇
  1987年   5368篇
  1986年   5044篇
  1985年   6556篇
  1984年   6702篇
  1983年   5310篇
  1982年   5400篇
  1981年   5380篇
  1980年   4956篇
  1979年   5395篇
  1978年   5534篇
  1977年   5374篇
  1976年   5354篇
  1975年   4923篇
  1974年   4893篇
  1973年   4932篇
  1972年   3469篇
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
151.
Physics of Atomic Nuclei - A two-stage method is proposed for controlling the regulators in the fuel burnup process during a single operating period. At the first stage, the coefficient of the heat...  相似文献   
152.
Ding  Q.  Yao  M.  Wu  Sh.  Zeng  M.  Xue  N.  Wu  D.  Xu  J. 《Journal of Applied Spectroscopy》2022,89(4):712-718
Journal of Applied Spectroscopy - Based on partial least squares (PLS) analysis, the effects of different smoothing points and different preprocessing methods on the accuracy and precision of the...  相似文献   
153.

The problem of the minimax testing of the Poisson process intensity \({\mathbf{s}}\) is considered. For a given intensity \({\mathbf{p}}\) and a set \(\mathcal{Q}\), the minimax testing of the simple hypothesis \(H_{0}: {\mathbf{s}} = {\mathbf{p}}\) against the composite alternative \(H_{1}: {\mathbf{s}} = {\mathbf{q}},\,{\mathbf{q}} \in \mathcal{Q}\) is investigated. The case, when the 1-st kind error probability \(\alpha \) is fixed and we are interested in the minimal possible 2-nd kind error probability \(\beta ({\mathbf{p}},\mathcal{Q})\), is considered. What is the maximal set \(\mathcal{Q}\), which can be replaced by an intensity \({\mathbf{q}} \in \mathcal{Q}\) without any loss of testing performance? In the asymptotic case (\(T\rightarrow \infty \)) that maximal set \(\mathcal{Q}\) is described.

  相似文献   
154.
In this study, multiwalled carbon nanotube (MWCNT) was modified by the pyridine group using a silane agent and characterized by infrared spectroscopy (IR), thermal analysis (TG/DTA), and elemental analysis (CHN) and scanning electron microscopy (SEM). The application of this sorbent was investigated in determination of lead ions in aqueous samples, using flame atomic absorption spectrometry (FAAS). Through this study, different parameters such as pH and sample flow rate on adsorption process and eluent concentration, volume and flow rate were optimized. The limit of detection (LOD), the relative standard deviation and the recovery of the method were 2 ng mL?1, 1.3% and 99.7%, respectively. Two standard reference materials (NIST 1571 and NIST 1572) were used to verify accuracy of this method. Finally, the sorbent was successfully applied for extraction and determination of low levels of Pb(II) ions in aqueous samples.  相似文献   
155.
Optics and Spectroscopy - The optical absorption spectra of zinc oxide (ZnO) thin films formed by reactive cathode sputtering are studied. The observed absorption of light in the region of photon...  相似文献   
156.
Russian Journal of Organic Chemistry - Selenopheno[2,3-d]pyrimidine- and selenopheno[2,3-d][1,2,3]triazine-containing compounds were synthesized starting from...  相似文献   
157.
The energy per particle BA in nuclear matter is calculated up to high baryon density in the whole isospin asymmetry range from symmetric matter to pure neutron matter.The results,obtained in the framework of the Brueckner-Hartree-Fock approximation with two-and three-body forces,confirm the well-known parabolic dependence on the asymmetry parameterβ=(N?Z)/A(β^2 law)that is valid in a wide density range.To investigate the extent to which this behavior can be traced back to the properties of the underlying interaction,aside from the mean field approximation,the spin-isospin decomposition of BA is performed.Theoretical indications suggest that theβ^2 law could be violated at higher densities as a consequence of the three-body forces.This raises the problem that the symmetry energy,calculated according to theβ^2 law as a difference between BA in pure neutron matter and symmetric nuclear matter,cannot be applied to neutron stars.One should return to the proper definition of the nuclear symmetry energy as a response of the nuclear system to small isospin imbalance from the Z=N nuclei and pure neutron matter.  相似文献   
158.
Journal of Sol-Gel Science and Technology - High temperature stable brookite rich titanium dioxide of average crystallite size 20&;nbsp;nm has been prepared by a novel aqueous sol–gel...  相似文献   
159.
Saleh  Z. M.  Nasser  H.  Özkol  E.  Günöven  M.  Abak  K.  Canli  S.  Bek  A.  Turan  R. 《Journal of nanoparticle research》2015,17(10):1-12
Journal of Nanoparticle Research - Plasmonic interfaces consisting of silver nanoparticles of different sizes (50–100&;nbsp;nm) have been processed by the self-assembled dewetting...  相似文献   
160.
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