全文获取类型
收费全文 | 542篇 |
免费 | 75篇 |
国内免费 | 98篇 |
专业分类
化学 | 361篇 |
晶体学 | 3篇 |
力学 | 54篇 |
综合类 | 9篇 |
数学 | 76篇 |
物理学 | 212篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 41篇 |
2012年 | 33篇 |
2011年 | 39篇 |
2010年 | 41篇 |
2009年 | 25篇 |
2008年 | 44篇 |
2007年 | 38篇 |
2006年 | 34篇 |
2005年 | 37篇 |
2004年 | 31篇 |
2003年 | 16篇 |
2002年 | 25篇 |
2001年 | 24篇 |
2000年 | 21篇 |
1999年 | 25篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 11篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1884年 | 2篇 |
1877年 | 1篇 |
1875年 | 1篇 |
1874年 | 1篇 |
1872年 | 2篇 |
1871年 | 1篇 |
排序方式: 共有715条查询结果,搜索用时 31 毫秒
701.
702.
Pål A. Olsvik Kai K. Lie Anne-Kristin Stavrum Sonnich Meier 《International journal of environmental analytical chemistry》2013,93(3):195-210
The effects of produced water (a by-product of oil and gas extraction) on gene expression were studied in gills and liver tissues of zebrafish. Adult, non-breeding zebrafish were exposed to control (freshwater mixed with 5% seawater) or produced water (freshwater mixed with 5% of produced water from the Oceberg C Oil Platform in the North Sea). A zebrafish library was used to make a microarray that consisted of 15,806 unique genes. The results indicate that 27 genes in the gills and 55 genes in the liver show significantly altered expression (greater than two-fold change). More than 70% of these gene sequences have not been annotated in the Gene Ontology (GO) database, making it difficult to characterize the affected genes. CYP1A displayed the greatest upregulation in the gills (eightfold, verified with quantitative real-time PCR). This study illustrates the utility of microarray approaches in investigations of environmental effects of toxicants. 相似文献
703.
Cheng‐Qin Liang Jing Hu Yi‐Ming Shi Shan‐Zhai Shang Xue Du Rui Zhan Wei‐Guang Wang Wen‐Yong Xiong Wei‐Lie Xiao Hong‐Bin Zhang Han‐Dong Sun 《Helvetica chimica acta》2013,96(7):1376-1385
Five new nortriterpenoids, schicagenins D–F ( 1 – 3 , resp.) and negleschidilactones A and B ( 4 and 5 , resp.), together with eleven known ones, were isolated from the stems of Schisandra neglecta. Their structures were established on the basis of extensive spectroscopic analyses. All the compounds were evaluated for their activities regarding insulin sensitivity in 3T3‐L1 differentiated adipocytes. None of them showed a significant bioactivity at 10 μM concentration. 相似文献
704.
Ling‐Zhi Wang Win‐Lwin Thuya Dorothy Su‐Lin Toh Michael George‐Limenta Lie Jie‐Ying Amelia Lau Li‐Ren Kong Seow‐Ching Wan Kian‐Ngiap Chua Edmund Jon‐Deoon Lee Boon‐Cher Goh 《Journal of mass spectrometry : JMS》2013,48(3):406-412
A sensitive analytical method has been developed and validated for the quantification of L‐ergothioneine in human plasma and erythrocytes by liquid chromatography‐tandem mass spectrometry. A commercially available isotope‐labeled L‐ergothioneine‐d9 is used as the internal standard. A simple protein precipitation with acetonitrile is utilized for bio‐sample preparation prior to analysis. Chromatographic separation of L‐ergothioneine is conducted using gradient elution on Alltime C18 (150 mm × 2.1 mm, 5 µ). The run time is 6 min at a constant flow rate of 0.45 ml/min. The mass spectrometer is operated under a positive electrospray ionization condition with multiple reaction monitoring mode. The mass transitions of L‐ergothioneine and L‐ergothioneine‐d9 are m/z 230 > 127 and m/z 239 > 127, respectively. Excellent linearity [coefficient of determination (r2) ≥ 0.9998] can be achieved for L‐ergothioneine quantification at the ranges of 10 to 10 000 ng/ml, with the intra‐day and inter‐day precisions at 0.9–3.9% and 1.3–5.7%, respectively, and the accuracies for all quality control samples between 94.5 and 101.0%. This validated analytical method is suitable for pharmacokinetic monitoring of L‐ergothioneine in human and erythrocytes. Based on the determination of bio‐samples from five healthy subjects, the mean concentrations of L‐ergothioneine in plasma and erythrocytes are 107.4 ± 20.5 ng/ml and 1285.0 ± 1363.0 ng/ml, respectively. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
705.
A new phenylethanoid glycoside,seulponisidc(1) was isolated from the aerial parts of Isodon sculponeatus(Vaniot) Kudo, along with six known compounds martynoside(2),verbascoside(3),(+)-hydroxypinoresinol-8-O- β-D-glucoside(4),cedrusin(5), 7-megastigmene-3S,5R,6R,7E,9S-tetrol(6) and 4-oxo- β-ionol- β-D-glucopyranoside(7).Their chemical structures were elucidated from physieochemical data and by acidic hydrolysis. 相似文献
706.
郑列 《纯粹数学与应用数学》2004,20(4):308-316
研究了一类离散的非线性爆炸方程.证明了在爆炸占优的条件下,方程解的ω极限集只含有平衡点. 相似文献
707.
提出当对无磁液氮玻璃钢杜瓦抽真空时 ,向无磁液氮玻璃钢杜瓦的真空夹层充注微量的二氧化碳气体 ,所充入的二氧化碳气体就会和玻璃钢表面的氢气、一氧化碳、二氧化碳、甲烷等气体发生协同交换反应 ,使玻璃钢表面的氢气、一氧化碳、二氧化碳、甲烷等气体的脱附速度大大增加 ,减少了抽真空时间。由于无磁液氮玻璃钢杜瓦内使用的活性炭吸附剂对二氧化碳的吸附性能远远大于对玻璃钢材料所放出的氢气、一氧化碳和甲烷等主要气体的吸附性能 ,从而使得抽好真空的无磁液氮玻璃钢杜瓦的真空保持时间大大增加 ,延长了无磁液氮玻璃钢杜瓦的使用寿命 相似文献
708.
709.
710.
Mehdi Jafari Jamnani Bjarte Holmelid Anni Vedeler Hoda Houshiar Parsian Heidi Lie Andersen Torgils Fossen 《Molecules (Basel, Switzerland)》2023,28(1)
For several millennia, leaves of Echium amoenum Fisch. & C. A. Mey., an important Iranian medicinal plant with nutritional value as nutraceutical, have been used as tea for the treatment of several conditions, including inflammation. The nutritional value of intake of E. amoenum tea has mainly been correlated to its rich content of mainly water-soluble antioxidants. Although the entire plant is utilized, only natural products of the flowers have previously been thoroughly investigated. The rare natural products bis(3-(3,4-dihydroxyphenyl)-1-methoxy-1-oxopropan-2-yl)-1-(3,4-dihydroxyphenyl)-6,7-dihydroxy-1,2-dihydronaphthalene-2,3-dicarboxylate, 4-Oxy-(E)-caffeoyl-2,3-dihydroxybutanoic acid methyl ester and 4-Oxy-(Z)-caffeoyl-2,3-dihydroxybutanoic acid methyl ester, in addition to the widely distributed compounds rosmarinic acid methyl ester and (E)-caffeic acid, were purified and characterized from leaves of Echium amoenum. The structures were determined by a combination of several 2D NMR spectroscopic techniques, circular dichroism spectroscopy and high-resolution mass spectrometry. The fact that bis(3-(3,4-dihydroxyphenyl)-1-methoxy-1-oxopropan-2-yl)-1-(3,4-dihydroxyphenyl)-6,7-dihydroxy-1,2-dihydronaphthalene-2,3-dicarboxylate belongs to a rare group of natural products which have previously been patented for their significant anti-inflammatory activity may rationalize the traditional treatment of inflammations with E. amoenum. 相似文献