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   3129篇
  免费   129篇
  国内免费   576篇
化学   3545篇
晶体学   32篇
力学   14篇
综合类   24篇
数学   1篇
物理学   218篇
  2024年   1篇
  2023年   18篇
  2022年   71篇
  2021年   44篇
  2020年   61篇
  2019年   83篇
  2018年   72篇
  2017年   83篇
  2016年   98篇
  2015年   94篇
  2014年   110篇
  2013年   352篇
  2012年   177篇
  2011年   163篇
  2010年   154篇
  2009年   154篇
  2008年   150篇
  2007年   216篇
  2006年   178篇
  2005年   179篇
  2004年   189篇
  2003年   165篇
  2002年   126篇
  2001年   122篇
  2000年   116篇
  1999年   110篇
  1998年   76篇
  1997年   68篇
  1996年   80篇
  1995年   44篇
  1994年   53篇
  1993年   58篇
  1992年   40篇
  1991年   30篇
  1990年   15篇
  1989年   9篇
  1988年   10篇
  1987年   7篇
  1986年   11篇
  1985年   3篇
  1984年   10篇
  1983年   3篇
  1982年   8篇
  1981年   5篇
  1980年   7篇
  1979年   4篇
  1978年   3篇
  1977年   2篇
  1975年   1篇
  1973年   1篇
排序方式: 共有3834条查询结果,搜索用时 0 毫秒
91.
《Analytical letters》2012,45(4):537-552
Abstract

The formation and extraction of copper (II) in the form of benzyl bismuthiol and naphthyl bismuthiol chelates has been studied. The reagents' solvation in butanone is investigated and optimum conditions for extraction are established. Both chelates have been studied in solution and in solid form. After studying the influence of 14 possible interferences, an atomic absorption spectrometric determination of copper using both reagents was carried out in tap water samples.  相似文献   
92.
许国强  黄雪红 《应用化学》2001,18(3):200-203
甲基丙烯酸三丁基锡酯与甲基丙烯酸甲酯共聚物的分子量测定和K、α值的订定  相似文献   
93.
二甲基十三醇;甲基溴辛烷;戊酮;松树叶蜂性信息素的合成  相似文献   
94.
乙基二茂铁与乙酰丙酸甲酯的缩合反应   总被引:2,自引:0,他引:2  
以多聚磷酸-浓硫酸-甲醇为催化剂和环已烷为溶剂,由乙基二茂铁与乙酰丙酸甲酯缩合合成4,4-双(乙基二茂铁基)成酸甲酯,转化率73%,产率84%。正交实验法获得的适宜反应条件:乙基二茂铁55mmol,乙酰丙酸甲酯75mmol,浓硫酸3.0mL,环已烷20mL,甲醇11mL。通过元素分析、IR、^1H NMR和^13C NMR确证了缩合产物的结构。  相似文献   
95.
硒(Ⅳ)-硫氰酸钾-甲基紫萃取光度法测定痕量硒   总被引:6,自引:0,他引:6  
研究了硒(Ⅳ)与硫氰酸钾和甲基紫(MV)的显色反应,发现在pH=1.85的HCl介质中,[Se(SCN)_6)~(2-)与MV形成不溶解于水的三元离子缔合物,该缔合物可溶解于苯等有机溶剂,在苯溶液中,该缔合物的最大吸收峰位于600nm处,其摩尔吸光系数为1.18×10~5L/(mol·cm),硒(Ⅳ)浓度在0.0~6.0μg/25mL范围内符合比耳定律。该方法应用于合成水样和环境水样中硒的测定,结果准确、可靠。  相似文献   
96.
Two-photon ionization and recombination processes of an aromatic chromophore doped in polymer films werestudied and the features of these processes were discussed in relation to photofunctional polymers, An aromatic moleculehaving low ionization potential, e.g., N,N,N',N'-tetramethyl-p-phenylene diamine doped in poly(methyl methacrylate)(PMMA) film was easily photoionized by intense laser ligh excitation, giving a colored radical cation (photochromism) anda trapped electron in PMMA matrix. As a reversed process, the radical cation recombined with the trapped electron, showingdiscoloration and emitting luminescence, either isothermal luminescence (ITL), or thermoluminescence (TL). In this report,ITL and TL through the charge recombination process were studied and the luminescence was suggested as a mean of the read-out of photorecording.  相似文献   
97.
Hexane-2,5-dione or 1,1,1,10,10,10-hexafluorodecane-2,4,7,9-tetrone react with methyl trifluoroacetate in the presence of LiH to give, upon treatment with diluted acid, 6-hydroxy-9-oxo-2,4,10-tris(trifluoromethyl)-3,11,12-trioxatetracyclo[5,2,1,02,6,04,10]dodecane. The structure of this compound was determined by X-ray diffraction study.  相似文献   
98.
Hydrophobic association hydrogels were fabricated via micellar copolymerization of acrylamide and hydrophobic monomers lauryl (meth)acrylate (LA or LMA) in an aqueous solution of sodium dodecyl sulfate. The effect of methyl groups of hydrophobic monomers on the crosslinking network structure and mechanical behavior of the gels was investigated on the basis of rubber elastic theory. It was found that the LMA-gel exhibited higher effective crosslink density and elastic modulus. The methyl groups of hydrophobic monomers limited the flexibility of the methacrylate backbone in the association domain, which resulted in the increment of chains constraints. With the increase of stretch rate, the dissipated energy of LMA-gel increased more highly than that of LA-gel. In addition, the methyl group hindered the movement of polymer chains, leading to the lower recovery efficiency of dissipated energy for LMA-gel. In contract, the LA-gel exhibited a rapid response to external force, and possessed better elasticity and self-recovery property. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1505–1512  相似文献   
99.
A high‐activity AgBr/Ag3PO4 heterojunction photocatalyst was synthesized based on hexadecyltrimethylammonium bromide. Its microspheres were characterized using X‐ray diffractometry, transmission electron microscopy and ultraviolet–visible diffuse reflectance spectroscopy. The new photocatalyst with high photocatalytic activity exceptionally outperforms pure Ag3PO4 and AgBr in methyl orange degradation. The enhancement of photocatalytic activity is attributed to the efficient separation of electron–hole pairs. In this photocatalytic reaction, h+ and ?O2? are the main reactive species that induce visible‐light‐driven degradation.  相似文献   
100.
Gas phase decompositions of protonated methyl benzoate and its conjugates have been studied by using electrospray ionization‐collision induced dissociation‐tandem mass spectrometry. Loss of CO2 molecule, thus transfer of methyl group, has been observed. In order to better understand this process, the theoretical calculations have been performed. For methyl benzoate conjugates, it has been found that position of substituent affects the loss of CO2 molecule, not the electron donor/withdrawing properties of the substituent. Therefore, electrospray ionization‐mass spectrometry in positive ion mode may be useful for differentiation of isomers of methyl benzoate conjugates.  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