全文获取类型
收费全文 | 49060篇 |
免费 | 7776篇 |
国内免费 | 5545篇 |
专业分类
化学 | 26110篇 |
晶体学 | 519篇 |
力学 | 2470篇 |
综合类 | 285篇 |
数学 | 4424篇 |
物理学 | 15171篇 |
无线电 | 13402篇 |
出版年
2024年 | 237篇 |
2023年 | 1190篇 |
2022年 | 1472篇 |
2021年 | 1814篇 |
2020年 | 1873篇 |
2019年 | 1720篇 |
2018年 | 1513篇 |
2017年 | 1483篇 |
2016年 | 2077篇 |
2015年 | 2258篇 |
2014年 | 2672篇 |
2013年 | 3292篇 |
2012年 | 4016篇 |
2011年 | 4090篇 |
2010年 | 2910篇 |
2009年 | 3032篇 |
2008年 | 3197篇 |
2007年 | 2890篇 |
2006年 | 2811篇 |
2005年 | 2213篇 |
2004年 | 1691篇 |
2003年 | 1502篇 |
2002年 | 1394篇 |
2001年 | 1177篇 |
2000年 | 1165篇 |
1999年 | 1121篇 |
1998年 | 1017篇 |
1997年 | 903篇 |
1996年 | 923篇 |
1995年 | 809篇 |
1994年 | 689篇 |
1993年 | 537篇 |
1992年 | 557篇 |
1991年 | 419篇 |
1990年 | 348篇 |
1989年 | 279篇 |
1988年 | 237篇 |
1987年 | 188篇 |
1986年 | 176篇 |
1985年 | 162篇 |
1984年 | 112篇 |
1983年 | 74篇 |
1982年 | 68篇 |
1981年 | 39篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1959年 | 1篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 1 毫秒
921.
[ReO(ppme)X] (where ppme(2-) is 2,5-diazo-N,N'-dimethylhexyl-1,6-bis(phenylphosphinate), X = Br0.3Cl0.7) has been synthesized via a substitution reaction and structurally characterized. The coordination geometry is a distorted octahedron and one phosphinate coordinates cis and the other trans to the oxo O atom. This coordination mode is conserved in all [ReOppmeX] complexes synthesized in this study. [ReO(ppme)Cl] has been prepared by a reduction/complexation reaction from [NH4][ReO4]. [ReO(ppme)Cl] reacts with thiocyanate and benzene thiolate forming [ReO(ppme)X] (X = (-)NCS, (-)SC6H5), but the one-pot synthesis of the respective ternary thiolate complexes from perrhenate was not successful. The reduction/complexation reaction of a thiol, H2ppmeCl4, and perrhenate resulted in the formation of [H3ppme][ReO(SR)4], the reaction of which with [ReO(ppme)Cl] does not lead to [ReO(ppme)SR] in high yields. 相似文献
922.
关于统计学中一个新兴化学分支学科的建立、定义和教育 总被引:1,自引:0,他引:1
本文追溯了统计学发展、建立中的大事, 陈述了它的定义及其化学分支发展、建立的梗概; 鉴于化学界对该新兴化学分支学科的名称长期存在争议, 提出了以化学统计学而不以化学计量学为该学科名称的理由, 把化学统计学定义为一个研究有关数据的收集或产生、描述、分析、综合和解释, 以获得新化学知识或信息的学科; 阐明了许多公认属于统计学的方法, 如显著性检验、方差分析、回归和相关, 以及一些尚未认定属于统计学的方法, 如模型建立、蒙特卡罗方法、傅立叶变换和人工神经网络, 都含有统计学5 个内涵中的一个或多个; 探讨了化学统计学家成长的模式, 认为当务之急是把化学统计学纳入化学专业的教学计划, 以培养懂统计学的化学家。 相似文献
923.
Polysaccharides prepared from Chinese traditional medicine "Ruoye" (Indocalamus tesselatus), a kind of bamboo leaves, were studied. Eight crude polysaccharides were isolated from the dried leaves by successive extraction with 85% ethanol (FE), 0.9% sodium chloride (FS), hot water (FI), 1% ammonium oxalate (FII), 5% NaOH (FIII-a, FIII-b) and 20% NaOH (FIV-a, FIV-b). They were decolorized by hydrogen peroxide treatment and the protein was removed with Savag's method. The polysaccharides were precipitated by three volumes of absolute ethanol. After further purification by gel filtration chromatography on a Sephadex G-200 column, these polysaccharides were lyophilized. Their physicochemical properties and structural feature were elucidated by modern analytical technique such as UV, elemental analysis and high performance gel permeation chromatography. From the results of partial hydrolysis, FE and FIII-b have a main chain comprised solely of glucuronic acid and xylose residues, respectively. 相似文献
924.
We developed a novel on-line preconcentration procedure for microchip gel electrophoresis (MCGE), which enables application of electrokinetic supercharging (EKS) for highly sensitive detection of DNA fragments on a cross-geometry microchip. In comparison with conventional pinched injection using the cross microchip, the present approach allows loading a much larger amount of the sample by taking advantage of a newly developed operational mode. In order to obtain high preconcentration effect and prevent splitting of an enriched sample into subchannels, i.e., off the detector range, effects of the voltage applied on the reservoirs and the time of isotachophoretic preconcentration were examined. The optimal balance between the voltage and time was found for a high-sensitivity analysis of DNA fragments. After experimental optimization the detection limit of a 150 bp fragment was as low as 0.22 mg/L (S/N = 3) that is 10 times better than using the conventional pinched injection. 相似文献
925.
926.
927.
928.
929.
930.