全文获取类型
收费全文 | 214691篇 |
免费 | 25324篇 |
国内免费 | 17951篇 |
专业分类
化学 | 99957篇 |
晶体学 | 1752篇 |
力学 | 9626篇 |
综合类 | 923篇 |
数学 | 17762篇 |
物理学 | 56831篇 |
综合类 | 71115篇 |
出版年
2024年 | 866篇 |
2023年 | 3703篇 |
2022年 | 5984篇 |
2021年 | 6815篇 |
2020年 | 6532篇 |
2019年 | 5899篇 |
2018年 | 5398篇 |
2017年 | 5278篇 |
2016年 | 7682篇 |
2015年 | 8206篇 |
2014年 | 10600篇 |
2013年 | 13066篇 |
2012年 | 15390篇 |
2011年 | 15851篇 |
2010年 | 11381篇 |
2009年 | 11402篇 |
2008年 | 12387篇 |
2007年 | 11521篇 |
2006年 | 10305篇 |
2005年 | 9019篇 |
2004年 | 6976篇 |
2003年 | 5496篇 |
2002年 | 5326篇 |
2001年 | 4773篇 |
2000年 | 4547篇 |
1999年 | 6306篇 |
1998年 | 5696篇 |
1997年 | 5581篇 |
1996年 | 5536篇 |
1995年 | 4702篇 |
1994年 | 4486篇 |
1993年 | 3714篇 |
1992年 | 3271篇 |
1991年 | 2901篇 |
1990年 | 2503篇 |
1989年 | 2089篇 |
1988年 | 1740篇 |
1987年 | 1263篇 |
1986年 | 904篇 |
1985年 | 618篇 |
1984年 | 421篇 |
1983年 | 303篇 |
1982年 | 245篇 |
1981年 | 179篇 |
1980年 | 144篇 |
1979年 | 103篇 |
1978年 | 87篇 |
1976年 | 78篇 |
1975年 | 78篇 |
1974年 | 88篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Raman spectroscopic analysis of supersaturated aqueous solution of MgO.B2O3-32%MgCl2-H2O during acidification and dilution 总被引:1,自引:0,他引:1
Zhihong L Bo G Shuni L Mancheng H Shuping X 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(13):3125-3128
Raman spectra of supersaturated aqueous solution of MgO.B2O3-32%MgCl2-H2O during acidification/alkalization and dilution have been studied. The assignments of the recorded Raman shift are given. The main existing forms of polyborate anions and their interaction in borate aqueous solution have been proposed through spectroscopic analysis. The experimental results indicate that the higher concentration of cation are beneficial not only to the dissolution of boric acid but also to the polymerization of polyborate anions. The existing forms and interaction among them also depend on the concentration of boron and the pH value in solution. 相似文献
992.
Simple and sensitive electrochemical method for the determination of metronidazole, based on a nanostructured film coated glassy carbon electrode (GCE), is described. Multi-walled carbon nanotubes (MWNT) was dispersed into water in the presence of a hydrophobic surfactant to give very stable and homogeneous MWNT suspension, and a MWNT-film coated GCE was achieved via evaporating solvent. Metronidazole yields a well-defined reduction peak whose potential is −0.71 V at the MWNT-film coated GCE in pH 9.0 Britton-Robinson buffer. Compared with bare GCE, the MWNT-film modified GCE significantly enhances the reduction peak current of metronidazole. All the experimental parameters were optimized for the determination of metronidazole. The detection limit is 6×10−9 mol/l at 2 min accumulation. This method has been successfully used to determine metronidazole in the drugs. Furthermore, results obtained by the proposed method have been compared with spectrophotometric method. 相似文献
993.
994.
995.
Based on gaseous compound introduction as 1-phenyl-3-methyl-4-benzoylpyrazolone[5](PMBP) chelate of aluminum by electrothermal vaporization in ICP-AES, a method for determination of trace aluminum was developed. Trace aluminum was vaporized at temperature of 1000 degrees C, and the vaporization behavior of aluminum chelate was detailedly investigated. Under the optimum conditions, the detection limit of aluminum was 0.6 ng ml(-1), and the relative standard deviation for 0.1 mug ml(-1) aluminum was 4.7% (n=8). The proposed method was applied to the determination of trace aluminum in rice flour reference materials, and the results well agreed with the reference values. 相似文献
996.
997.
镉—溴化物—罗丹明B高灵敏显色反应的研究:离心光度法测定镉 总被引:10,自引:0,他引:10
本研究了一个高灵敏的测定镉的方法,离心光度法,该体系络合物λmax=560nm,表观摩尔吸系数ε560=5.06×10^8L.mol^-1.cm^-1,Cd^2+浓度0.10×10^-2-1.0×10^-2μg/10mL呈线性关系,本法已用于血清和水中痕量镉的测定,探讨了高灵敏的显色反应机理。 相似文献
998.
999.
冷态德士古气化炉流场与停留时间分布的研究 总被引:5,自引:1,他引:5
测定了德士古气化炉的冷态速度分布和停留时间分布。结果表明:德士古气化炉内在轴向2.5~3.0倍直径范围内存在回流,最大回流量为射流量的3.5倍左右;在平均停留时间之前,已有50%左右的物料逸出炉外。本文指出,德士古气化炉中存在的问题,如结渣、耐火砖寿命短、有效气体成分偏低均与炉内流场有关。 相似文献
1000.