全文获取类型
收费全文 | 9716篇 |
免费 | 969篇 |
国内免费 | 629篇 |
专业分类
化学 | 7204篇 |
晶体学 | 30篇 |
力学 | 223篇 |
综合类 | 103篇 |
数学 | 303篇 |
物理学 | 3451篇 |
出版年
2024年 | 27篇 |
2023年 | 120篇 |
2022年 | 268篇 |
2021年 | 382篇 |
2020年 | 339篇 |
2019年 | 298篇 |
2018年 | 222篇 |
2017年 | 401篇 |
2016年 | 435篇 |
2015年 | 442篇 |
2014年 | 599篇 |
2013年 | 604篇 |
2012年 | 726篇 |
2011年 | 560篇 |
2010年 | 514篇 |
2009年 | 619篇 |
2008年 | 563篇 |
2007年 | 589篇 |
2006年 | 525篇 |
2005年 | 519篇 |
2004年 | 488篇 |
2003年 | 299篇 |
2002年 | 220篇 |
2001年 | 159篇 |
2000年 | 153篇 |
1999年 | 149篇 |
1998年 | 115篇 |
1997年 | 117篇 |
1996年 | 100篇 |
1995年 | 109篇 |
1994年 | 80篇 |
1993年 | 80篇 |
1992年 | 75篇 |
1991年 | 53篇 |
1990年 | 56篇 |
1989年 | 50篇 |
1988年 | 55篇 |
1987年 | 40篇 |
1986年 | 29篇 |
1985年 | 29篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1982年 | 30篇 |
1981年 | 14篇 |
1980年 | 5篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 484 毫秒
61.
62.
63.
Summary This paper reports the results of a study on the use of a new polymer-based, strong anion-exchange, stationary phase for rapid
and selective separation of carbohydrates and related compounds by high-pH, anion-exchange chromatography with pulsed amperometric
detection. The new adsorbent has been obtained by direct nitration of 2.8 μm, spherical non-porous highly cross-linked, styrene-divinylbenzene
copolymer beads, followed by reduction of superficially introduced nitro groups with nascent hydrogen and quaternization of
the resultant amino groups with iodomethane. It is reported that by optimizing the ionic strength of the mobile phase, columns
packed with the new anion-exchanger can be successfully employed to separate, either in isocratic or gradient elution mode,
oligosaccharides, positional isomers of gluco-disaccharides, as well as uronic acids and sugar monophosphates. 相似文献
64.
Summary Four different techniques to quantify unresolved chromatographic peaks with known spectral features combined with photodiode array detection, are investigated as regards their efficiency for the accurate and precise determination of drugs in the low g-range. The comparison includes peak suppression utilising difference chromatograms, first-order derivative chromatograms, selective chromatograms, generated by the calculation of orthogonal polynomial shares, and the powerful least-squares multicomponent analysis approach. Each of these methods uses UV-spectra taken throughout, the peak. The results presented and conclusions reached should enable the chromatographer to come to a decision about the reasonable use of these options now provided by multichannel detection in HPLC. 相似文献
65.
66.
Omar El Tall Nicole Jaffrezic‐Renault Monique Sigaud Olivier Vittori 《Electroanalysis》2007,19(11):1152-1159
Boron‐doped Diamond (BDD) electrode has become one of the important tools for heavy metal detection. By studying some analytical parameters of DPASV method, like deposition time and potential in different electrolyte concentrations (acetate buffer), the conditions for detecting very low metal ion levels (Zn, Cd, Pb, and Cu) could be chosen. Diluted electrolyte (0.01 M buffer) was one of the factors favoring low detection and quantification limits, but its quantification range is short in comparison to more concentrated media. For ?1.7 V deposition potential, the detection of single metal at ppb levels was reached in 60 s deposition time. Understanding different metal‐metal interactions shows the limits to the simultaneous determination of heavy metals at BDD. Quantification was possible for the simultaneous determination of Zn, Cd and Pb despite the overlapping of Zn and Cd peaks. The performance of the BDD was compared with that of another C‐based solid electrode: the glassy carbon electrode (without mercury plating). A lower base line current, wider potential range, higher sensitivity (3 to 5 times higher than GC) and longevity of the material were noticed for the BDD. 相似文献
67.
Kinetics of chemiluminescence reactions of 2-methyl-6-phenylimidazo[1,2-a]pyrazin-3(7H)-one (1c, Cypridina luciferin analogue) and substituent effects of the 6-aryl group of derivatives 1 strongly suggest that the rate-determining step is a single electron transfer from an anion derived from 1 to a triplet molecular oxygen (O2) in the oxygenation process. 相似文献
68.
研究开发的一种新型的元素光度检测器主要用于锗、砷、锡和锑的氢化物气相色谱检测,具有高灵敏,高选择性。它是在普通火焰光度检测器的基础上加装了特制的滤光片改制而成的。对锗、砷、锡和锑的检测限分别为3.0×10 ̄(-11)g、7.0×10 ̄(-11)g、7.0×10 ̄(-10)g和1.1×10 ̄(-8)g,相对标准偏差分别为1.8%、2.4%、2.6%和3.0%。 相似文献
69.
O157∶H7大肠埃希菌是一种致病力非常强的微生物.近年来,陆续有其引起食物中毒事件的报道.1996年日本发生O157∶H7大肠埃希菌食物中毒的爆发流行,感染病例逾万人,死亡9例.2001年我国江苏及安徽等地也发生了肠出血性O157∶H7大肠埃希菌所引发的感染性腹泻事件.目前O157∶H7大肠埃希菌实验室常规检测方法为分离培养计数法,此法费时费力,需要几天的时间才能得到检测结果[1,2],缺乏应对突发事件的能力,因此亟需开发快速检测技术.近年来,多种微生物快速检测技术如ELISA法[3]、热解质谱测定法[4]、多聚酶链反应[5]、荧光成像技术[6]、生物发… 相似文献
70.