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   512567篇
  免费   4314篇
  国内免费   1202篇
化学   260235篇
晶体学   7992篇
力学   24778篇
综合类   13篇
数学   68067篇
物理学   156998篇
  2018年   11688篇
  2017年   12439篇
  2016年   9913篇
  2015年   4848篇
  2014年   6451篇
  2013年   17494篇
  2012年   16128篇
  2011年   25852篇
  2010年   16969篇
  2009年   16789篇
  2008年   23154篇
  2007年   26310篇
  2006年   13916篇
  2005年   18056篇
  2004年   14305篇
  2003年   13252篇
  2002年   11354篇
  2001年   12164篇
  2000年   9539篇
  1999年   7311篇
  1998年   6149篇
  1997年   6154篇
  1996年   6000篇
  1995年   5530篇
  1994年   5529篇
  1993年   5174篇
  1992年   6057篇
  1991年   5934篇
  1990年   5841篇
  1989年   5733篇
  1988年   5811篇
  1987年   5688篇
  1986年   5360篇
  1985年   7127篇
  1984年   7384篇
  1983年   6147篇
  1982年   6451篇
  1981年   6345篇
  1980年   6210篇
  1979年   6401篇
  1978年   6865篇
  1977年   6560篇
  1976年   6592篇
  1975年   6158篇
  1974年   6198篇
  1973年   6347篇
  1972年   4400篇
  1971年   3662篇
  1968年   3840篇
  1967年   4001篇
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
21.
Chemistry of Heterocyclic Compounds - 2-Imino-2,5-dihydrofurans are a highly valuable class of heterocyclic compounds that show versatile biological activity and are used in diverse fields of...  相似文献   
22.
Siberian Mathematical Journal - Let $ \{(A_{i},B_{i})\}_{i=1}^{m} $ be a set pair system. Füredi, Gyárfás, and Király called it $ 1 $ -cross intersecting if $...  相似文献   
23.
The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R−BF3). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R−BF3, by cyanostar macrocycles that are size-complementary to the inorganic BF4 progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K+ salts of R−BF3 anions.  相似文献   
24.
25.
Sun  J.  Yuan  H. 《Experimental Mechanics》2021,61(3):565-580
Experimental Mechanics - Temperature gradients significantly affect the material fatigue process. A reliable and robust test procedure is needed for quantifying the effects of temperature gradients...  相似文献   
26.
Kobayashi  M.  Zhang  Y.  Ishikawa  H.  Sun  J.  Oddershede  J.  Juul Jensen  D.  Miura  H. 《Experimental Mechanics》2021,61(5):817-828
Experimental Mechanics - The internal strain distribution developing during plastic deformation is important for understanding the mechanical properties of polycrystalline materials. Such...  相似文献   
27.
Journal of Applied Spectroscopy - Detailed measurements of nonlinear optical properties and optical limiting for four phthalocyanine (Pc) derivatives (PcCo, PcCu, PcMn, and PcSi) are reported. The...  相似文献   
28.
Russian Physics Journal - The specific features of the sorption activity of silver nanoparticles (AgNPs) on biodegradable polymers of natural (collagen) and artificial (polyamide 6.6) origin have...  相似文献   
29.
A formal computation proving a new operator identity from known ones is, in principle, restricted by domains and codomains of linear operators involved, since not any two operators can be added or composed. Algebraically, identities can be modelled by noncommutative polynomials and such a formal computation proves that the polynomial corresponding to the new identity lies in the ideal generated by the polynomials corresponding to the known identities. In order to prove an operator identity, however, just proving membership of the polynomial in the ideal is not enough, since the ring of noncommutative polynomials ignores domains and codomains. We show that it suffices to additionally verify compatibility of this polynomial and of the generators of the ideal with the labelled quiver that encodes which polynomials can be realized as linear operators. Then, for every consistent representation of such a quiver in a linear category, there exists a computation in the category that proves the corresponding instance of the identity. Moreover, by assigning the same label to several edges of the quiver, the algebraic framework developed allows to model different versions of an operator by the same indeterminate in the noncommutative polynomials.  相似文献   
30.
Crystallography Reports - The crystal and molecular structures of Cl–C6H4–O–C16H33 (I) have been studied, and its differential scanning calorimetry (DSC) study is performed....  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