全文获取类型
收费全文 | 6367篇 |
免费 | 1311篇 |
国内免费 | 1127篇 |
专业分类
化学 | 5076篇 |
晶体学 | 173篇 |
力学 | 405篇 |
综合类 | 71篇 |
数学 | 727篇 |
物理学 | 2353篇 |
出版年
2024年 | 9篇 |
2023年 | 210篇 |
2022年 | 274篇 |
2021年 | 304篇 |
2020年 | 392篇 |
2019年 | 374篇 |
2018年 | 304篇 |
2017年 | 264篇 |
2016年 | 340篇 |
2015年 | 386篇 |
2014年 | 399篇 |
2013年 | 494篇 |
2012年 | 617篇 |
2011年 | 576篇 |
2010年 | 375篇 |
2009年 | 381篇 |
2008年 | 437篇 |
2007年 | 403篇 |
2006年 | 333篇 |
2005年 | 293篇 |
2004年 | 194篇 |
2003年 | 187篇 |
2002年 | 187篇 |
2001年 | 164篇 |
2000年 | 148篇 |
1999年 | 124篇 |
1998年 | 84篇 |
1997年 | 75篇 |
1996年 | 87篇 |
1995年 | 65篇 |
1994年 | 54篇 |
1993年 | 50篇 |
1992年 | 38篇 |
1991年 | 26篇 |
1990年 | 34篇 |
1989年 | 21篇 |
1988年 | 14篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1973年 | 3篇 |
1968年 | 1篇 |
1957年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有8805条查询结果,搜索用时 390 毫秒
101.
建立了一种同时检测塑料食品接触材料中13种紫外吸收剂的超高效合相色谱法。以甲醇为溶剂对塑料食品接触材料样品进行超声提取,经C18固相萃取柱净化,过0.22 μm有机滤膜,采用超高效合相色谱仪分析。选择ACQUTY UPC2 HSS C18 SB色谱柱(150 mm×3.0 mm,1.8 μm),以超临界二氧化碳为流动相,异丙醇为改性剂进行梯度洗脱,在最优色谱条件下,13种紫外吸收剂能够在4 min内实现有效分离。结果表明,在各自线性范围内,13种紫外吸收剂的线性关系良好,标准曲线相关系数不低于0.9985,检出限(S/N=3)为0.05~0.15 mg/kg,加标回收率为86.8%~115.7%,相对标准偏差为0.73%~5.61%。该方法快速简便,准确可靠,同时大大减少了有机溶剂的消耗,可用于塑料食品接触材料中13种紫外吸收剂的快速检测。 相似文献
102.
103.
考察了前文制得的水滑石及其焙烧产物在对甲酚氧化反应中的催化性能,发现经水滑石焙烧得到的具有尖晶石结构复合氧化物比没有焙烧的具有水滑石结构的以及由经物机械混合的样品具有更高的活性。 相似文献
104.
105.
合成了开环夹心羰基化合物[2,4-(CH_3)_2C_5H_5]_2GCO,得到了该分子的单晶结构,[2,4-(CH_3)_2C_5H_5]_2TiCO晶体属于正交晶系,P2_12_12_1空间群,晶胞参数a=1.0078(5)nm,b=1.1909(8)nm,c=1.1946(5)nm,b=1.4337(13)nm~3,Z=4,R=0.054。单晶结构表明该分子为平行覆盖型开环夹心化合物,用EHMO方法计算了[2,4-(CH_3)_2C_5H_6]_2TICO的电子结构。 相似文献
106.
A Novel Dimeric Coumarin from Clausena lenis 总被引:1,自引:0,他引:1
HongPingHE ShunTingCHEN YueMaoSHEN ChangXiangCHEN YiBinZHAO XiaoJiangHAO 《中国化学快报》2003,14(11):1150-1153
A novel dimeric coumarin (1), a dimeric of seselin named diseselin A, was isolated from the aerial part of Clausena lenis. The structure was elucidated based on the MS, 1D and 2D NMR data. 相似文献
107.
Kai‐lu Yu Chang‐jun Liu Yue‐ping Zhang Fei He Xin‐li Zhu Baldur Eliasson 《Plasma Chemistry and Plasma Processing》2004,24(3):393-403
PdO/Al2O3 catalysts prepared by glow discharge plasma treatment followed by thermal calcination show a much higher dispersion and a better catalytic activity for methane combustion at relatively low temperatures. The dispersion of palladium active species by such plasma prepared catalysts is 29.7%, 5.4 times higher than that of conventional catalysts. XPS analysis indicates that a surface enrichment of Pd active species (PdO) has been achieved after plasma treatment. The surface atomic composition of PdO of plasma prepared catalysts reaches 10.5%. XRD characterization also confirms a wellcrystallized PdO phase present on the plasma prepared catalyst. The lightoff temperature of the plasma prepared catalyst is 370°C, 50°C lower than that obtained from the conventional catalyst. 相似文献
108.
Dispersion of copper(Ⅱ) phthalocyanine (CuPc), copper(Ⅱ) phthalocyaninesulfonate (CuPcS) and cobalt(Ⅱ)phthalocyaninetetrasulfonate (CoPcTS) on the surface of titanium dioxide was investigated by XRD, XPS, FT-IR and UV-Vis techniques. Results show that interaction between CuPc and TiO2 was very weak and CuPc was difficult to disperse on the surface of the support. While partly sulfurized CuPcS could be dispersed on the surface of support through sulfo-groups and its dispersion capacity was determined to be 0.085 g CuPcS/g TiO2. Completely sulfurlzed CoPcTS could also be dispersed on the surface of TiO2 as a monolayer and its dispersion capacity was 0.12 g CoPcTS/g TiO2. Interactions of the sulfo-groups as well as the electrons of CoPcTS with the surface of TiO2 could be evidenced by FT-IR characterization. Therefore, it was suggested that CoPcTS molecules be adsorbed on the surface of TiO2 in a flat-lying mode while CuPcS in a slanting one. UV-Vis spectra show that the dispersed CuPcS and CoPcTS molecules exist in both forms of monomers and dimers. 相似文献
109.
Chen L Jiang F Lin Z Zhou Y Yue C Hong M 《Journal of the American Chemical Society》2005,127(24):8588-8589
A blue luminescent tetradecavanadate compound, [Et4N]5[V14O36Cl], has been synthesized. It possesses an unprecedented half-open basket framework. Through the {ABAB}-type stacking, the {V14O36} clusters form infinite one-dimensional channels with considerable accessible volume in the crystalline state. 相似文献
110.
The major drawback of liquid chromatography/mass spectrometry (LC/MS) for the analysis of mixtures is the non-quantitative nature of these studies. The ionization efficiency of the various components in the mixture (e.g., a compound and its metabolites) can vary greatly and, therefore, relative intensities of signals cannot be related to relative abundance. A chip-based nanoelectrospray ionization source was used to compare the ionization efficiencies of compounds with different physical-chemical characteristics. The data indicate that the ionization efficiencies vary much less with the chip-based device than by LC/MS. This was ascribed to the generation of a much higher electric field around the nozzles, which supplies a large excess of protons to the small droplets and reduces/eliminates the differences in the ionization efficiency for the analytes. 相似文献