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   371篇
  免费   26篇
  国内免费   1篇
化学   288篇
力学   5篇
数学   16篇
物理学   89篇
  2023年   4篇
  2022年   8篇
  2021年   6篇
  2020年   8篇
  2019年   8篇
  2017年   7篇
  2016年   25篇
  2015年   10篇
  2014年   4篇
  2013年   16篇
  2012年   21篇
  2011年   11篇
  2010年   8篇
  2009年   8篇
  2008年   13篇
  2007年   16篇
  2006年   23篇
  2005年   13篇
  2004年   13篇
  2003年   17篇
  2002年   11篇
  2001年   10篇
  2000年   6篇
  1999年   7篇
  1997年   5篇
  1995年   3篇
  1994年   7篇
  1993年   6篇
  1991年   4篇
  1990年   7篇
  1989年   5篇
  1986年   8篇
  1985年   5篇
  1984年   4篇
  1983年   5篇
  1982年   5篇
  1981年   4篇
  1980年   5篇
  1977年   3篇
  1972年   2篇
  1970年   2篇
  1969年   2篇
  1968年   2篇
  1967年   5篇
  1966年   3篇
  1965年   4篇
  1963年   2篇
  1962年   4篇
  1961年   4篇
  1959年   2篇
排序方式: 共有398条查询结果,搜索用时 15 毫秒
151.
A series of new bay region disphospha-functionalised naphthalenes is reported. The reduction of ylidic phosphonium phosphoride NapP(2)Cl(6) (1) (Nap=naphthalene-1,8-diyl) with MeOPCl(2) gives the important synthon Nap(PCl(2))(2) (2) in nearly quantitative yield. Reaction of 1 with magnesium metal affords (NapP(2))(n) (3), which reacts with Br(2) and I(2), yielding Nap(PBr(2))(2) (4) and Nap(PI)(2) (5), respectively. X-ray structure determinations reveal a twisted geometry of the naphthalene ring in sterically strained 2 and 4, whilst the presence of a P-P bond in 5 results in the release of the steric strain and generation of the planar NapP(2) moiety. Although the tetrahedral P environments are severely distorted the sigma(3)P-sigma(3)P bonding in 5 represents a new type of P-P bonding environment in 1,8-diphosphanaphthalenes. Compounds 1, 4 and 5 each represent the highest coordination, achievable by direct halogenation. The new compounds 2-5 were fully characterised by NMR, IR, and Raman spectroscopy, mass spectrometry, and elemental analysis.  相似文献   
152.
Bis(imino)pyridine cobalt(I) n-alkyl complexes react with ethylene by beta-hydrogen transfer, allowing direct study of a termination step commonly encountered in polymerisation and oligomerisation catalysis.  相似文献   
153.
The compressive stress-strain behavior of biaxially oriented polyethylene (PE), obtained by pressing uniaxially oriented samples, is described with the aid of the van der Waals equation of state. Results are discussed in terms of two parameters: the biaxiality (B) and the biaxial draw ratio (), which offer a measure of the strain along the two principal directions and of the average draw ratio on the film plane, respectively. Comparison of experimental and calculated data indicates that after compression up to very large deformations the maximum average strain ( m ), which is proportional to the square root of the chain length of the network, remains constant. This result supports the view that the network of entanglements is not destroyed after compression. Experiments carried out on isotropic melt crystallized PE show the presence of a network having a not very different chain length. Finally, it is shown that the segment length of this network is close to the X-ray long period of the initial structure. This result implies the existence of a high density of entanglements (two entanglements every three adjacent lamellae), which are rejected into the defective layer of the crystals.  相似文献   
154.
155.
We will outline that the sign and magnitude of J(Si,H) coupling constants provide a highly sensitive tool to measure the extent of Si?H bond activation in nonclassical silane complexes. Up to now, this structure–property relationship was obscured by erroneous J(Si,H) sign determinations in the literature. These new findings also help to identify the salient control parameters of the Si?H bond activation process in nonclassical silane complexes.  相似文献   
156.
2,6‐Disubstituted anilines are readily prepared from the direct reaction between amides and diaryliodonium salts. As demonstrated for 24 different examples, the reaction is of unusually broad scope with respect to the sterically congested arene and the nitrogen source, occurs without the requirement for any additional promoter, and proceeds through a direct reductive elimination at the iodine(III) center. The efficiency of the coupling procedure is further demonstrated within the short synthesis of a chemerin binding inhibitor.  相似文献   
157.
Reaction of the triamido stannate MeSi[SiMe(2)N[(R)-CHMePh]](3)SnLi (1) with 0.5 molar equivalent of [RhCl(olefin)(2)](2) (olefin = COE, C(2)H(4)) or [RhCl(P(i)Pr(3))(2)](2) yielded the Rh-Sn complexes [MeSi[SiMe(2)N[(R)-CHMePh]](2)[SiMe(2)N[(R)-CHMe(eta(6)-C(6)H(5))]SnRh(L)] (L = COE: 2a, C(2)H(4): 2b, P(i)Pr(3) 3); their intramolecular eta(6)-coordination, along with the tin-rhodium bond, represents the first "ansa" pi-arene/stannate system.  相似文献   
158.
Annihilation and elastic cross-sections of pp have been measured between 400 and 850 MeV/c. In both cross-sections a resonance is observed at a mass of 1939 ± 3 MeV. For its natural width τ ? 4 MeV is obtained.  相似文献   
159.
Ohne ZusammenfassungHerrn Professor Dr.R. Hosemann zum 60. Geburtstag.  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