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   5712篇
  免费   150篇
  国内免费   19篇
化学   4079篇
晶体学   21篇
力学   71篇
数学   993篇
物理学   717篇
  2020年   50篇
  2019年   54篇
  2018年   40篇
  2016年   93篇
  2015年   94篇
  2014年   104篇
  2013年   167篇
  2012年   161篇
  2011年   229篇
  2010年   115篇
  2009年   106篇
  2008年   217篇
  2007年   214篇
  2006年   218篇
  2005年   252篇
  2004年   190篇
  2003年   171篇
  2002年   168篇
  2001年   88篇
  2000年   81篇
  1999年   70篇
  1998年   53篇
  1997年   76篇
  1996年   76篇
  1995年   79篇
  1994年   54篇
  1993年   53篇
  1992年   71篇
  1991年   54篇
  1990年   75篇
  1989年   45篇
  1988年   66篇
  1987年   70篇
  1986年   45篇
  1985年   105篇
  1984年   61篇
  1983年   67篇
  1982年   74篇
  1981年   67篇
  1980年   56篇
  1979年   69篇
  1978年   74篇
  1977年   54篇
  1976年   81篇
  1975年   80篇
  1974年   54篇
  1973年   49篇
  1972年   42篇
  1970年   48篇
  1966年   42篇
排序方式: 共有5881条查询结果,搜索用时 31 毫秒
51.
Iodine monofluorosulfate has been found to react with fluoroolefins in the absence of a solvent to give the corresponding iodo alkyl fluorosulfates by addition of ?l and ?OSO2F across the double bond. The observed products were ICF2CF2SO3F, CF3CFlCF2SO3F, and the isomer mixture ICF2CFClSO3F and ICFClCF2SO3F. Perfluorocyclobutene was unreactive. The iodine fluorosulfate used for this study was synthesized from the reactions of either I2 or RfI with ClSO3F, with both reactions being new routes to this compound. These iodo fluorocarbon fluorosulfates are novel compounds and were characterized by spectroscopy and by formation of the derivatives CF3CFICFO and ICF2CFO.  相似文献   
52.
Starting from optically active methylferrocene-- and--carboxylic acids (1 a and1 b) of known absolute configuration and enantiomeric purity about 15 chiral ferrocenes (of each isomeric series— and ) were obtained by suitable ligand transformations. Thereby (almost) all possible chiral combinations of the ligands CH3, COOH (COO), COOCH3, CN and NH2 (NH3 +) were accessible which are necessary for a potential test of approximations of chirality functions for compounds with basic symmetry C5v. The chiroptical properties of these disubstituted ferrocenes are recorded.Preliminary tests using a shortened Ansatz revealed large discrepancies between calculated () and found [M]D-values. Possible reasons for this failure are discussed.

61. Mitt. über Ferrocenderivate

39. Mitt.:A. Meyer, H. Neudeck undK. Schlögl, Chem. Ber.110, 1403 (1977).

60. Mitt.:V. Rapi, K. Schlögl undB. Steinitz, J. Organometal. Chem.94, 87 (1975).  相似文献   
53.
54.
Yantasee W  Timchalk C  Weitz KK  Moore DA  Lin Y 《Talanta》2005,67(3):617-624
There is a need to develop reliable portable analytical systems for on-site and real-time biomonitoring of lead (Pb) from both occupational and environmental exposures. Saliva is an appealing matrix since it is easily obtainable, and therefore a potential substitute for blood due to existing reasonably good correlation between Pb levels in blood and saliva. The microanalytical system is based on flow-injection/stripping voltammetry with a wall-jet (flow-onto) microelectrochemical cell. Samples that contain as little as 1% saliva can cause electrode fouling, resulting in significantly reduced responsiveness and irreproducible quantitations. In addition, incomplete Pb release from salivary protein can also yield a lower Pb response than expected. This paper evaluates the extent of in vitro Pb-protein binding and the optimal pretreatment for releasing Pb from the saliva samples. Even in 50% by volume of rat saliva, the electrode fouling was not observed, due to the appropriate sample pretreatment and the constant flow of the sample and acidic carrier that prevented passivation by the protein. The system offered a linear response over a low Pb range of 1-10 ppb, low detection limit of 1 ppb, excellent reproducibility, and reliability. It also yielded the same Pb concentrations in unknown samples as did the ICP-MS. These encouraging results suggest that the microanalytical system represents an important analytical advancement for real-time non-invasive biomonitoring of Pb.  相似文献   
55.
56.
57.
58.
59.
60.
The two diastereoisomeric ferrocenyl‐substituted orvinols 2 and 3 were prepared. The modified alkaloids are still able to interact with opioid receptors (see Table). The ferrocene moiety allows highly selective and sensitive electrochemical detection. The X‐ray crystal structure of the major isomer 2 was determined. The combination of a metallocene and a morphinan alkaloid holds promise for useful antitumor activity.  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