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   1790篇
  免费   71篇
  国内免费   19篇
化学   1405篇
晶体学   28篇
力学   15篇
数学   86篇
物理学   346篇
  2023年   10篇
  2022年   9篇
  2021年   21篇
  2020年   23篇
  2019年   32篇
  2018年   26篇
  2017年   19篇
  2016年   40篇
  2015年   41篇
  2014年   43篇
  2013年   68篇
  2012年   117篇
  2011年   127篇
  2010年   77篇
  2009年   66篇
  2008年   83篇
  2007年   109篇
  2006年   108篇
  2005年   90篇
  2004年   75篇
  2003年   98篇
  2002年   87篇
  2001年   47篇
  2000年   39篇
  1999年   31篇
  1998年   16篇
  1997年   20篇
  1996年   24篇
  1995年   17篇
  1994年   24篇
  1993年   15篇
  1992年   19篇
  1991年   15篇
  1990年   14篇
  1989年   10篇
  1987年   14篇
  1986年   16篇
  1985年   28篇
  1984年   29篇
  1983年   12篇
  1982年   16篇
  1981年   12篇
  1980年   10篇
  1978年   14篇
  1977年   14篇
  1976年   6篇
  1974年   5篇
  1973年   6篇
  1972年   9篇
  1967年   5篇
排序方式: 共有1880条查询结果,搜索用时 15 毫秒
121.
The change of chemical structure of cocaine in the presence of hydrogen peroxide, a main component of hair dye and decolorant treatments, was studied. High-performance liquid chromatography/mass spectrometry (LC/MS) was used for the separation and identification of cocaine derivatives. After a mixture of cocaine and hydrogen peroxide solutions was incubated at 39 degrees C (this temperature is commonly used when the hair is treated with hair dye or decolorant) for 24 h, six reaction products were detected by LC/MS. Two of them were ecgonine methyl ester and benzoylecgonine, which are metabolites of cocaine. The other reaction products were assumed to be ortho-, meta- and para-hydroxycocaines and dihydroxycocaine, in each of which the benzene ring was hydroxylated by the reaction. These five reaction products (except for dihydroxycocaine) were found immediately after mixing cocaine and hydrogen peroxide. Therefore, the above reaction products might be present in the hair of cocaine users that had treated their hair with hair dye or decolorant.  相似文献   
122.
Porphyrin accumulation onto a self-assembled monolayer (SAM) of imidazole-substituted porphyrins by a supramolecular method to form a chain structure leads to significant increase of light absorption in the visible light region and therefore photocurrents.  相似文献   
123.
In view of recent developments in the investigation on cuprate high- T(c) superconductors and the spin-Peierls compound CuGeO3, we study the effect of dilute impurity doping on the spin-Peierls state in quasi-one-dimensional systems. We identify a common origin for the emergence of antiferromagnetic order upon the introduction of static vacancies and superconductivity for mobile holes.  相似文献   
124.
We show that a micropolar fluid model successfully describes collisional granular flows on a slope. A micropolar fluid is the fluid with internal structures in which coupling between the spin of each particle and the macroscopic velocity field is taken into account. It is a hydrodynamical framework suitable for granular systems which consists of particles with macroscopic size. We demonstrate that the model equations can quantitatively reproduce the velocity and the angular velocity profiles obtained from the numerical simulation of the collisional granular flow on a slope using a simple estimate for the parameters in the theory.  相似文献   
125.
Hayakawa R  Shimizu M 《Organic letters》2000,2(25):4079-4081
Methoxyallene oxide was readily prepared in situ by epoxidation of methoxyallene with 3-chloroperbenzoic acid, and the subsequent reaction with aldehydes or acetals was promoted by titanium tetraiodide and additives to give 2,3-dialkoxy- or 3-hydroxy-2-methoxy ketones in good yields.  相似文献   
126.
Novel liquid crystals which have the perfluoropyrrolidino group, a heterocyclic perfluoroalkyl group, and which show smectic phases have been synthesized with perfluoro-(2-pyrrolidinopropionyl fluoride) as one of the starting materials. Analogues with a polymerizable functional group also have been prepared and polymerized to give side chain liquid crystal polymers.  相似文献   
127.
The tricyclic quinone 8 was successfully synthesized from naphthazalin, and the total synthesis of (±)-2-hydroxyaklavinone via 8 was accomplished in an overall yield of about 18% through the regio-controlled route.  相似文献   
128.
The dc component Δn of the electric birefringence of poly(γ-benzyl-L -glutamate) in m-cresol is measured under an ac electric field at frequencies from 0.5 Hz to 200 kHz for solutions covering the dilute and semidilute regions. The dispersion curve indicates that at low frequencies Δn decreases with increasing frequency (low-frequency relaxation). For high-molecular-weight polymers at high concentration, Δn becomes negative at high frequency and its absolute value decreases with further increase in frequency (high-frequency relaxation). A unified theory for the two relaxations is developed on the basis of a model in which, in the semidilute regime, the rodlike polymer is confined in a cage formed by neighboring polymers and the lifetime of the cage lies between relaxation times of the two relaxations. The low-frequency relaxation is ascribed to end-over-end rotation of the polymer and the high-frequency relaxation to the rotation within a limited angle in the cage. The dependences of relaxation parameters on polymer concentration and molecular weight are reasonably explained by the theory.  相似文献   
129.
The decay of 101Ag have been studied using β- and γ-spectrometers in singles and coincidence modes. A half-life of 11.4 ± 0.3 min was obtained and a decay scheme was proposed. The first excited state was established at 80.3 keV and a half-life of 4.8 ± 0.5 ns was suggested. The resultant level structure of 101Pd is compared to a theoretical calculation with strong band mixing.  相似文献   
130.
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