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   146373篇
  免费   1457篇
  国内免费   395篇
化学   79944篇
晶体学   2201篇
力学   6059篇
综合类   3篇
数学   13567篇
物理学   46451篇
  2021年   1022篇
  2020年   1181篇
  2019年   1250篇
  2018年   1639篇
  2017年   1689篇
  2016年   2539篇
  2015年   1559篇
  2014年   2347篇
  2013年   6032篇
  2012年   4844篇
  2011年   5934篇
  2010年   4181篇
  2009年   4207篇
  2008年   5726篇
  2007年   5512篇
  2006年   5383篇
  2005年   4949篇
  2004年   4454篇
  2003年   4121篇
  2002年   4010篇
  2001年   5542篇
  2000年   3972篇
  1999年   3075篇
  1998年   2109篇
  1997年   2210篇
  1996年   2070篇
  1995年   1916篇
  1994年   1914篇
  1993年   1726篇
  1992年   2215篇
  1991年   2301篇
  1990年   2135篇
  1989年   2098篇
  1988年   2054篇
  1987年   2063篇
  1986年   1881篇
  1985年   2336篇
  1984年   2368篇
  1983年   1884篇
  1982年   1894篇
  1981年   1731篇
  1980年   1716篇
  1979年   2003篇
  1978年   2082篇
  1977年   2039篇
  1976年   1971篇
  1975年   1851篇
  1974年   1832篇
  1973年   1866篇
  1972年   1229篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Prostate cancer is a highly prevalent disease and ranks second among malignant neoplasms that affect men around the world, behind lung cancer alone. Trace elements are very important and are involved in many cellular processes. The X-ray microfluorescence technique is an advanced tool of high spatial resolution, sensitivity, multielemental analysis, and nondestructiveness for trace element study. This study aimed to investigate the elemental distribution in spheroids obtained through the following human prostate cell lines using synchrotron X-ray microfluorescence: tumor cell line androgen independent (DU145), tumor cell line androgen dependent (LNCaP), and normal cell line (RWPE-1). The measurements were performed with a standard geometry of 45° of incidence, excited by a white beam using a pixel of 25 μm and an acquisition time of 300 ms/pixel at the X-ray fluorescence beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). The synchrotron X-ray microfluorescence results showed differences between groups in all elements analyzed and suggested that further studies should be performed to understand the relationship of these trace elements with the progression and development of the disease.  相似文献   
52.
Russian Chemical Bulletin - Terminal disaccharide fragment of phenolic glycolipid from Mycobacterium leprae (PGL-I) was synthesized as a glycoside with 4-(2-aminoethoxy)phenyl aglycon. The obtained...  相似文献   
53.
54.
55.
56.
57.
Russian Journal of Applied Chemistry - A spectral-kinetic investigation was carried out to study the fluorescent properties of complexes of molecules of photochromic nitro-substituted spiropyran...  相似文献   
58.
Kim  F. H.  Moylan  S. P.  Phan  T. Q.  Garboczi  E. J. 《Experimental Mechanics》2020,60(7):987-1004
Experimental Mechanics - Insufficient data are available to fully understand the effects of metal additive manufacturing (AM) defects for widespread adoption of the emerging technology....  相似文献   
59.
A model is developed for the formation and propagation of cracks in a material sample that is heated at its top surface, pyrolyses, and then thermally degrades to form char. In this work the sample is heated uniformly over its entire top surface by a hypothetical flame (a heat source). The pyrolysis mechanism is described by a one-step overall reaction that is dependent nonlinearly on the temperature (Arrhenius form). Stresses develop in response to the thermal degradation of the material by means of a shrinkage strain caused by local mass loss during pyrolysis. When the principal stress exceeds a prescribed threshold value, the material forms a local crack. Cracks are found to generally originate at the surface in response to heating, but occasionally they form in the bulk, away from ever-changing material boundaries. The resulting cracks evolve and form patterns whose characteristics are described. Quantities examined in detail are: the crack spacing in the pyrolysis zone; the crack length evolution; the formation and nature of crack loops which are defined as individual cracks that have joined to form loops that are disconnected from the remaining material; the formation of enhanced pyrolysis area; and the impact of all of the former quantities on mass flux. It is determined that the mass flux from the sample can be greatly enhanced over its nominal (non-cracking) counterpart. The mass efflux profile qualitatively resembles those observed in Cone Calorimeter tests.  相似文献   
60.
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