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   151843篇
  免费   1584篇
  国内免费   430篇
化学   83882篇
晶体学   2418篇
力学   6215篇
综合类   3篇
数学   14141篇
物理学   47198篇
  2021年   1087篇
  2020年   1260篇
  2019年   1318篇
  2018年   1683篇
  2017年   1740篇
  2016年   2635篇
  2015年   1643篇
  2014年   2435篇
  2013年   6248篇
  2012年   5150篇
  2011年   6313篇
  2010年   4355篇
  2009年   4355篇
  2008年   6041篇
  2007年   5817篇
  2006年   5714篇
  2005年   5302篇
  2004年   4719篇
  2003年   4335篇
  2002年   4244篇
  2001年   5618篇
  2000年   4058篇
  1999年   3127篇
  1998年   2163篇
  1997年   2254篇
  1996年   2148篇
  1995年   1980篇
  1994年   1957篇
  1993年   1768篇
  1992年   2255篇
  1991年   2342篇
  1990年   2161篇
  1989年   2128篇
  1988年   2103篇
  1987年   2114篇
  1986年   1933篇
  1985年   2410篇
  1984年   2436篇
  1983年   1947篇
  1982年   1944篇
  1981年   1795篇
  1980年   1775篇
  1979年   2045篇
  1978年   2136篇
  1977年   2072篇
  1976年   2006篇
  1975年   1902篇
  1974年   1872篇
  1973年   1903篇
  1972年   1256篇
排序方式: 共有10000条查询结果,搜索用时 761 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.
53.
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   
54.
55.
56.
57.
58.
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   
59.
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   
60.
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   
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