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   558篇
  免费   27篇
  国内免费   1篇
化学   469篇
晶体学   2篇
力学   5篇
数学   52篇
物理学   58篇
  2023年   4篇
  2022年   7篇
  2021年   9篇
  2020年   9篇
  2019年   5篇
  2018年   2篇
  2017年   3篇
  2016年   27篇
  2015年   19篇
  2014年   15篇
  2013年   35篇
  2012年   36篇
  2011年   37篇
  2010年   37篇
  2009年   26篇
  2008年   31篇
  2007年   34篇
  2006年   42篇
  2005年   23篇
  2004年   34篇
  2003年   19篇
  2002年   11篇
  2001年   12篇
  2000年   11篇
  1999年   6篇
  1998年   5篇
  1997年   12篇
  1996年   12篇
  1995年   8篇
  1994年   9篇
  1993年   6篇
  1992年   7篇
  1991年   2篇
  1990年   1篇
  1989年   3篇
  1988年   4篇
  1987年   2篇
  1986年   1篇
  1984年   3篇
  1983年   1篇
  1982年   3篇
  1980年   2篇
  1979年   3篇
  1978年   1篇
  1977年   2篇
  1976年   3篇
  1975年   1篇
  1973年   1篇
排序方式: 共有586条查询结果,搜索用时 31 毫秒
51.
52.
Power-dependent Overhauser dynamic nuclear polarization (DNP) enhancements and continuous-wave electron paramagnetic resonance (EPR) spectra of nitroxide radicals were measured in the magnetic field of a mobile Halbach-array permanent magnet and compared with results from a commercially available electromagnet. DNP saturation factors for varying microwave power were obtained from both measurement series and used to investigate how the increased magnetic field inhomogeneity present in the Halbach magnet affects the saturation efficiency. An EPR detection system was designed to allow continuous-wave EPR measurements at microwave power up to 20?W. Our results show that despite the lower magnetic field homogeneity, a Halbach-array magnet can be used for EPR and DNP-enhanced nuclear magnetic resonance of high quality providing almost the same performance as a more homogeneous electromagnet.  相似文献   
53.
The synthesis of block copolymers via polymer conjugation of well‐defined building blocks offers excellent control over the structures obtained, but often several coupling strategies need to be explored to find an efficient one depending on the building blocks. To facilitate the synthesis of polymers with adjustable functional end‐groups for polymer conjugation, we report on the combination of activated ester chemistry with RAFT polymerization using a chain transfer agent (CTA) with a pentafluorophenyl ester (PFP‐CTA), which allows for flexible functionalization of either the CTA prior to polymerization or the obtained polymer after polymerization. Different polymethacrylates, namely PMMA, P(t‐BuMA) and PDEGMEMA, were synthesized with an alkyne‐CTA obtained from the aminolysis of the PFP‐CTA with propargylamine, and the successful incorporation of the alkyne moiety could be shown via 1H and 13C NMR spectroscopy and MALDI TOF MS. Further, the reactive α‐end‐groups of polymers synthesized using the unmodified PFP‐CTA could be converted into azide and alkyne end‐groups after polymerization, and the high functionalization efficiencies could be demonstrated via successful coupling of the resulting polymers via CuAAC. Thus, the PFP‐CTA allows for high combinatory flexibility in polymer synthesis facilitating polymer conjugation as useful method for the synthesis of block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010  相似文献   
54.
55.
56.
PDE-constrained optimization problems under the influence of perturbation parameters are considered. A quantitative stability analysis for local optimal solutions is performed. The perturbation directions of greatest impact on an observed quantity are characterized using the singular value decomposition of a certain linear operator. An efficient numerical method is proposed to compute a partial singular value decomposition for discretized problems, with an emphasis on infinite-dimensional parameter and observation spaces. Numerical examples are provided.  相似文献   
57.
58.
Methods for estimation of dispersion effects in two‐level unreplicated factorial designs are studied. The consequences of non‐constant variance are discussed. A natural assumption concerning the form of the covariance of location effects leads to a particular normal model. Some linear combinations of the response variables are constructed in order to make a simple structure for inference. The precision of point estimators of dispersion effects, where one is based on experiments with replicates, are compared. A numerical example is given as an illustration of a test. Finally, estimations in fractional designs are described and discussed. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
59.
Feeding of (2,3,4,5,6‐13C5)mevalonolactone to the fungus Hypomyces odoratus resulted in a completely labeled sesquiterpene ether. The connectivity of the carbon atoms was easily deduced from a 13C,13C COSY spectrum, revealing a structure that was different from the previously reported structure of hypodoratoxide, even though the reported 13C NMR data matched. A structural revision of hypodoratoxide is thus presented. Its absolute configuration was tentatively assigned from its co‐metabolite cis‐dihydroagarofuran. Its biosynthesis was investigated by feeding of (3‐13C)‐ and (4,6‐13C2)mevalonolactone, which gave insights into the complex rearrangement of the carbon skeleton during terpene cyclization by analysis of the 13C,13C couplings.  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