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   1738篇
  免费   49篇
  国内免费   1篇
化学   1121篇
晶体学   20篇
力学   43篇
数学   150篇
物理学   454篇
  2023年   6篇
  2022年   31篇
  2021年   62篇
  2020年   39篇
  2019年   42篇
  2018年   45篇
  2017年   47篇
  2016年   82篇
  2015年   52篇
  2014年   86篇
  2013年   96篇
  2012年   108篇
  2011年   143篇
  2010年   85篇
  2009年   85篇
  2008年   98篇
  2007年   109篇
  2006年   82篇
  2005年   72篇
  2004年   64篇
  2003年   27篇
  2002年   36篇
  2001年   18篇
  2000年   32篇
  1999年   11篇
  1998年   20篇
  1997年   12篇
  1996年   14篇
  1995年   21篇
  1994年   18篇
  1993年   11篇
  1992年   11篇
  1991年   21篇
  1990年   16篇
  1989年   10篇
  1988年   10篇
  1987年   10篇
  1986年   9篇
  1985年   9篇
  1984年   3篇
  1983年   3篇
  1982年   2篇
  1981年   5篇
  1980年   6篇
  1979年   2篇
  1977年   4篇
  1975年   4篇
  1963年   1篇
  1957年   1篇
  1955年   1篇
排序方式: 共有1788条查询结果,搜索用时 31 毫秒
91.
This work reports on the photoluminescent properties of three new lanthanide complexes with acetoacetanilide (aaa), a β-diketonate ligand. The complexes have the general molecular formulae [RE(aaa)3(H2O)], they are soluble in organic solvents such as ethanol and chloroform and insoluble in water. The energy of the triplet state was determined at about 4,700 cm?1 higher than the 5D4 emitting level of the Tb(III) ion, leading to an absolute quantum yield of 22 % for the [Tb(aaa)3(H2O)] complex. The photoluminescent properties were studied and the luminescence parameters of the [Eu(aaa)3(H2O)] complex were experimentally determined. The photostabilities of the complexes under continuous UV irradiation were measured and the data indicate low stability of the [Tb(aaa)3(H2O)] complex when the system is excited at the band attributed to energy transfer from the ligand to terbium(III) ion. However, its photostability is significantly improved under inert atmosphere.  相似文献   
92.
Thallium(III)trinitrate trihydrate (TTN) is known to be a useful and extremely versatile reagent in organic synthesis.1-5 Its use has been exploited mainly in oxidation and oxidative rearrangements of chalcones, aromatic ketones and phenols. In this communication, we report an unusual reaction of polyoxygenated methylbenzoates with TTN.  相似文献   
93.
94.
95.
96.
97.
The properties of the wave transmission in the lossy single-negative (SNG) metamaterials are experimentally investigated. The model structure of lossy epsilon-negative (ENG) monolayer and SNG bilayer consisting of a lossy ENG material and a mu-negative (MNG) are considered in this work. Simulation and experimental results show that the transmittance of the lossy SNG materials can be enhanced by two approaches, increasing dissipation coefficient and increasing the thickness of the lossy SNG. The lossy ENG material is physically fabricated by using composite right- and left-handed transmission lines grafted with radiation unit cell. The experimental results are in very good agreement with the previous theoretical analysis.  相似文献   
98.
99.
100.
The composition of sulfated glycosaminoglycans (GAGs) and the tissue distribution of chondroitin sulfate (CS) were analyzed in deeply infiltrating endometriosis (DIE) of rectosigmoid, using metachromatic staining, and biochemical analysis employing electrophoresis before and after specific enzymatic or chemical degradations, and immunostaining with an antibody against CS. The sulfated GAGs were characterized as dermatan sulfate (DS), heparan sulfate (HS) and CS; and DS strongly predominated compared to HS and CS. Immunostaining procedures showed that CS was concentrated in the endometriosis foci, distributed throughout the stroma around the glands. This is the first report describing the composition of sulfated GAGs and the tissue location of CS in DIE by means of histochemical, biochemical and immunohistochemical analyses. These results confirmed that in DIE of rectosigmoid, as in eutopic endometrium [Nasciutti, L.E., Ferrari, R., Berardo, P.T., Souza, M.L.S., Takiya, C.M., Borojevic, R., Abrao, M.S., Silva, L.C.F., 2006. Distribution of chondroitin sulfate in human endometrium. Micron 37, 544–550], CS was the dominant sulfated GAG in stroma of the lesion foci.  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