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   839篇
  免费   14篇
  国内免费   4篇
化学   609篇
晶体学   15篇
力学   14篇
数学   59篇
物理学   160篇
  2019年   6篇
  2018年   5篇
  2017年   7篇
  2016年   9篇
  2015年   12篇
  2014年   20篇
  2013年   46篇
  2012年   29篇
  2011年   35篇
  2010年   26篇
  2009年   26篇
  2008年   38篇
  2007年   42篇
  2006年   42篇
  2005年   39篇
  2004年   45篇
  2003年   28篇
  2002年   23篇
  2001年   17篇
  2000年   17篇
  1999年   8篇
  1998年   9篇
  1997年   9篇
  1996年   14篇
  1995年   11篇
  1994年   11篇
  1993年   7篇
  1992年   8篇
  1991年   10篇
  1990年   6篇
  1989年   11篇
  1988年   13篇
  1987年   5篇
  1986年   10篇
  1985年   15篇
  1984年   14篇
  1983年   8篇
  1982年   9篇
  1981年   18篇
  1980年   14篇
  1979年   12篇
  1978年   9篇
  1977年   15篇
  1976年   5篇
  1975年   12篇
  1974年   12篇
  1973年   13篇
  1972年   11篇
  1971年   7篇
  1970年   12篇
排序方式: 共有857条查询结果,搜索用时 265 毫秒
1.
Two experiments were conducted to evaluate the equivalence of noise annoyance scales and questions recommended by Team 6 (Community Response to Noise) of ICBEN for English and Japanese, two strikingly different languages. The first experiment was conducted with bilingual subjects in order to test a key assumption of the method established by ICBEN Team 6 for the development of equivalent noise annoyance scales: subjects who speak different languages interpret the concept of “highest degree” of annoyance similarly. The results indicate that English- and Japanese-speaking subjects do interpret the “highest degree” similarly. The second experiment tested for effects of wording differences. English- and Japanese-speaking subjects were presented with noise annoyance questions of one of three format types. The first type was similar to the question format recommended by ICBEN Team 6. It focused on the degree to which a given noise would “bother, disturb, or annoy” the subject. The second asked subjects to evaluate the “bothersome, annoying, or disturbing” quality of the noise. The third asked how much the noise would “worry, irritate, or concern” the subject. No significant difference was found in responses to the three formats when subjects evaluated noise in laboratory conditions.  相似文献   
2.
Organic dyes such as water soluble porphyrins were incorporated into monodispersed SiO2 particles using the sol-gel technique (the Stober synthesis) and their monomeric and dimeric properties were investigated by aiming at the microcavity effect. Doping efficiencies of dyes into SiO2 particles depended on dye's hydrophilic properties. The doping efficiency of a porphyrin, TTMAPP, decreased with increasing the nominal content in the starting solution and the doping content showed the maximum value of 1.6×10–5 mol/g SiO2. With increasing the TTMAPP content, spectra of doped particles were changed from dimeric to monomeric nature; the absorption peak due to dimers disappeared and halfwidth of absorption at Soret band decreased. This unusual change was caused by the decrease of particle sizes by dye doping. The TTMAPP-doped sample having monomeric spectrum showed the fluorescence life time of 8.5 nsec and photochemical hole burning at about 5 K.  相似文献   
3.
4.
5.
Schotten-Baumann reaction of the amine (X) with 4-benzyloxy-3,4′-oxydiphenylacetyl chloride (XI) gave two amides, (XIIa) and (XIIb), which were cyclized to give the corresponding 3,4-dihydroisoquinolines, respectively. Methylation of the above 3,4-dihydro-isoquinolines, followed by hydrolysis, afforded the compounds having the same composition as berbamine (Ia) and oxyacanthine (Ib), whose structures are under examination.  相似文献   
6.
7.
8.
9.
Thermolysis of a benzocyclobutene derivative (20) prepared from norcamphor produced stereoselectively a tetracyclic compound (2), which was converted to a lactone (21) having correct stereochemistry at C7, C8, C9, C11, C13, and C14 positions of (±)-klaineanone.  相似文献   
10.
The radical copolymerization of diallyl tartrate (DATa) (M1) with diallyl succinate (DASu), diallyl phthalate (DAP), allyl benzoate (ABz), vinyl acetate (VAc), or styrene (St) was investigated in order to disclose in more detail the characteristic hydroxyl group's effect observed in the homopolymerization of DATa. In the copolymerization with DASu or DAP as a typical diallyldicarboxylate, the dependence of the rate of copolymerization on monomer composition was different for different copolymerization systems and unusual values larger than unity for the product of monomer reactivity ratios, r1r2, were obtained. In the copolymerization with ABz or VAc (M2), the r1 and r2 values were estimated to be 1.50 and 0.64 for the DATa/ABz system and 0.76 and 2.34 for the DATa/VAc system, respectively; the product r1r2 for the latter copolymerization system was found again to be larger than unity. In the copolymerization with St, the largest effect due to DATa monomer of high polarity was observed. Solvent effects were tentatively examined to improve the copolymerizability of DATa. These results are discussed in terms of hydrogen-bonding ability of DATa.  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