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   403篇
  免费   7篇
  国内免费   1篇
化学   308篇
晶体学   4篇
力学   10篇
数学   34篇
物理学   55篇
  2022年   5篇
  2021年   4篇
  2020年   4篇
  2019年   8篇
  2018年   6篇
  2017年   5篇
  2016年   7篇
  2015年   4篇
  2014年   12篇
  2013年   33篇
  2012年   18篇
  2011年   18篇
  2010年   5篇
  2009年   21篇
  2008年   25篇
  2007年   26篇
  2006年   16篇
  2005年   14篇
  2004年   11篇
  2003年   15篇
  2002年   15篇
  2001年   7篇
  2000年   8篇
  1999年   3篇
  1998年   5篇
  1997年   3篇
  1996年   7篇
  1994年   3篇
  1993年   2篇
  1992年   2篇
  1991年   3篇
  1990年   4篇
  1988年   5篇
  1987年   2篇
  1986年   6篇
  1985年   5篇
  1984年   7篇
  1981年   4篇
  1980年   5篇
  1979年   8篇
  1978年   4篇
  1975年   6篇
  1974年   4篇
  1973年   8篇
  1972年   6篇
  1971年   3篇
  1970年   6篇
  1964年   2篇
  1957年   1篇
  1937年   1篇
排序方式: 共有411条查询结果,搜索用时 31 毫秒
91.
Journal of Radioanalytical and Nuclear Chemistry - Particle induced X-ray emission technique was used to obtain the serum elemental profile of healthy subjects and breast cancer patients (BCPs)...  相似文献   
92.
Journal of Analytical Chemistry - A water-compatible molecularly imprinted polymer (MIP) was prepared for specific extraction of HIV-1 integrase inhibitor elvitegravir (EVG). It was prepared by a...  相似文献   
93.
A radiochemical method for the determination of fluoride has been developed. The effect of fluoride on the extraction of the Fe/III/ thiocyanate complex into TBP in nitrobenzene has been utilized. Microgram quantities of F have been determined. Effect of diverse ions has also been reported. The method is applied for the determination of F in a natural sample of apetite.  相似文献   
94.
95.
Highly ordered mesoporous C60 with a well‐ordered porous structure and a high crystallinity is prepared through the nanohard templating method using a saturated solution of C60 in 1‐chloronaphthalene (51 mg mL?1) as a C60 precursor and SBA‐15 as a hard template. The high solubility of C60 in 1‐chloronaphthalene helps not only to encapsulate a huge amount of the C60 into the mesopores of the template but also supports the oligomerization of C60 and the formation of crystalline walls made of C60. The obtained mesoporous C60 exhibits a rod‐shaped morphology, a high specific surface area (680 m2 g?1), tuneable pores, and a highly crystalline wall structure. This exciting ordered mesoporous C60 offers high supercapacitive performance and a high selectivity to H2O2 production and methanol tolerance for ORR. This simple strategy could be adopted to make a series of mesoporous fullerenes with different structures and carbon atoms as a new class of energy materials.  相似文献   
96.
A short and practical enantioselective synthesis of (+)-negamycin has been achieved in high enantio- and diastereomeric excess using an iterative Jacobsen’s hydrolytic kinetic resolution as the key step.  相似文献   
97.
Nitroaminoguanidine (NAG) has been investigated as regards its thermal decomposition characteristics using simultaneous thermal analysis, infrared spectroscopy, X-ray diffraction and polarising microscopy. XRD studies show thatNAG crystal belongs to the tetragonal system. The crystal structure parameters are found to be:a=17.063±0.005Å,b=17.063±0.005Å,c=5.155±0.005Å andc/a axial ratio=0.302. Under non-isothermal conditions,NAG decomposed apparently in one stage with a loss in weight of 80%. But the thermal decomposition ofNAG in the solid phase under isothermal conditions proceeded through three stages. Both the first and the second stages obeyed theA-E (Avrami Erofee'v) equation forn=1. The 3rd stage is too slow and kinetics has not been attempted. The rate parameters for the first and second stages have been evaluated. Gaseous decomposition products detected using the IR gas cell are NH3, NO2, HCN, N2O, CO and CO2. High temperature IR studies indicate preferential deamination reaction initially indicating breaking of N?NH2 and C?NH2 bonds leading to NH2 radical formation. Addition of diphenylamine, a known chain inhibitor, decelerated the thermal decomposition, supporting a radical chain reaction.  相似文献   
98.
On-column complexation of metal ions with 2,6-pyridinedicarboxylate (2,6-PDC) to form anionic complexes enabled their separation by capillary zone electrophoresis with direct UV detection at 214 nm. Nine metal ions, Cu2+, Zn2+, Ni2+, Cd2+ Mn2+, Pb2+, Fe3+, Al3+ and Ca2+, were determined in less than 7 min using 10 mM 2.6-PDC solution containing 0.75 mM tetradecyltrimethylammonium bromide at pH 4.0. Satisfactory working ranges (20-300 microM), detection limits (3-10 microM) and good repeatability of the peak areas (RSD 2.1-4.2%, n=5) were obtained using hydrodynamic injection (30 s). The proposed method was used successfully for the determination of Mn2+, Fe3+, Al3+ and Ca2+ in groundwaters.  相似文献   
99.
The kinetics of oxidation of aliphatic ketones (acetone, ethyl methyl ketone and diethyl ketone) by chloramine-T in presence of hydrochloric acid (0.1 to 0.3M) have been investigated at 30 °C. The rate of disappearance of chloramine-T has been found to be first order each with respect to oxidant, ketone and [H+], in the range of the acid concentrations studied. The thermodynamic and kinetic parameters have been evaluated by determining the rate constants at different temperatures. The products of the reaction have been identified as chloroketones by their NMR spectra. The solvent isotope effect has been studied in the case of the oxidation of acetone and ethyl methyl ketone. A mechanism has been proposed.  相似文献   
100.
An investigations of the optical absorption and fluorescence spectra of 0.2 mol% Er2O3 in mixed alkali borate glasses of the type 67.8B2O3 x xLi2O(32-x)Na2O, 67.8B2O3 x xLi2O(32-x)K2O and 67.8B2O3 x xNa2O(32-x)K2O (where x = 8, 12, 16, 20 and 24) are presented. The glasses were obtained by quenching melts consisting of H3BO3, Li2CO3, Na2CO3, K2CO3 and Er2O3 (950-1100 degrees C, 1.5-2 h) between two brass plates. Spectroscopic parameters like Racah (E1, E2 and E3), spin-orbit (xi(4f)) and configuration interaction (alpha) parameters are deduced as function of x. Using Judd-Ofelt theory, Judd-Ofelt intensity parameters (omega2, omega4 and omega6) are obtained. Radiative and non-radiative transition rates (A(T) and W(MPR)), radiative lifetimes (tauR), branching ratios (beta) and integrated absorption cross-sections (sigma) have been computed for certain excited states of Er3+ in these mixed alkali borate glasses. Emission spectra have been studied for all the three Er3+ doped mixed alkali borate glasses. The present paper throws light on the trends observed in the intensity parameters, radiative lifetimes, branching ratios and emission cross-sections as a function of x in these borate glasses, keeping in view the effect of mixed alkalies in borate glasses.  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