全文获取类型
收费全文 | 20543篇 |
免费 | 1260篇 |
国内免费 | 1099篇 |
专业分类
化学 | 18835篇 |
晶体学 | 33篇 |
力学 | 625篇 |
综合类 | 69篇 |
数学 | 332篇 |
物理学 | 3008篇 |
出版年
2024年 | 41篇 |
2023年 | 265篇 |
2022年 | 488篇 |
2021年 | 454篇 |
2020年 | 648篇 |
2019年 | 621篇 |
2018年 | 584篇 |
2017年 | 752篇 |
2016年 | 926篇 |
2015年 | 869篇 |
2014年 | 842篇 |
2013年 | 1283篇 |
2012年 | 1359篇 |
2011年 | 1268篇 |
2010年 | 1031篇 |
2009年 | 1256篇 |
2008年 | 1107篇 |
2007年 | 1309篇 |
2006年 | 1070篇 |
2005年 | 989篇 |
2004年 | 900篇 |
2003年 | 766篇 |
2002年 | 597篇 |
2001年 | 394篇 |
2000年 | 366篇 |
1999年 | 350篇 |
1998年 | 311篇 |
1997年 | 261篇 |
1996年 | 274篇 |
1995年 | 254篇 |
1994年 | 218篇 |
1993年 | 178篇 |
1992年 | 162篇 |
1991年 | 192篇 |
1990年 | 108篇 |
1989年 | 86篇 |
1988年 | 63篇 |
1987年 | 46篇 |
1986年 | 38篇 |
1985年 | 35篇 |
1984年 | 28篇 |
1983年 | 19篇 |
1982年 | 24篇 |
1981年 | 18篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1976年 | 7篇 |
1973年 | 4篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
133.
Jürgen Grotemeyer Edward W. Schlag 《Angewandte Chemie (International ed. in English)》1988,27(4):447-459
Mass spectrometry is one of the most important analytical tools in chemistry, biology, medicine and related areas. During the past 30 years, methods have been developed, both for the qualitative as well as the quantitative analysis of a wide variety of substances. The introduction of lasers into chemistry has also profited mass spectrometry, since its nonlinear properties and its tunability open up fundamentally new frontiers. Multiphoton ionization mass spectrometry combines UV-spectroscopy and mass spectrometry, thus providing a two-dimensional method that enables substance-specific and even state-specific analyses. This progress report presents the fundamentals and possibilities of MUPI mass spectrometry and discusses investigations on amino acids, peptides, chlorophylls and sugars. For each substance, multiphoton ionization can be tuned in such a way that only the molecular ion is formed. An increase of laser intensity induces substance-specific fragmentations of the molecule, thus contributing to a quick and easy identification of the substance. 相似文献
134.
135.
Vora A. Riga A. Dollimore D Alexander K. 《Journal of Thermal Analysis and Calorimetry》2004,75(3):709-717
This study attempts to identify the degradative process which folic acid undergoes in the solid-state under thermal stress.
In order to facilitate the process, the various pieces of the chemical structure, namely, p-amino benzoic acid, pterin and glutamic acid as both its d- and l-isomers were investigated as separate entities. These structured solid-state pieces were then compared to the composite solid
state folic acid degradative curves in order to identify the peaks seen and provide direction for the interpolation of the
degradative mechanism. It was observed that none of the structural pieces could be superimposed as assumed earlier and hence
an attempt was made to identify the decomposition products using various analytical techniques such as infrared spectroscopy,
mass spectroscopy and X-ray diffraction which suggested that the glutamic acid fragment is lost first as evidenced by acid
loss and amide enhancement in the IR spectra. The vitamin was ultimately degrading to carbon fragments and that further identification
was not necessary.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
136.
河口水体中痕量稀土元素的共沉淀预富集-电感耦合等离子体质谱法测定研究 总被引:3,自引:0,他引:3
建立了氢氧化铟共沉淀预富集 -电感耦合等离子体质谱法测定河口水体中痕量稀土元素的方法。实验结果表明 ,在80mg·L -1的In3 +和pH9.5的实验条件下 ,在1.0L水样中添加5.0~200.0ng的混合稀土标准溶液 ,均能定量回收 ,回收率在82.2 %~106.9 %之间。方法的分析流程空白为0.04(Tb)~10.17(La)ng·L -1,检出限在0.17(Yb)~1.46(La)ng·L-1之间 ,精密度 (RSD ,n=3)小于11.7 % ,可满足河口淡水和海水样品中的痕量稀土元素定量分析的要求 相似文献
137.
LC-MS/MS method for the confirmatory determination of aromatic amines and its application in textile analysis 总被引:1,自引:0,他引:1
Sutthivaiyakit P Achatz S Lintelmann J Aungpradit T Chanwirat R Chumanee S Kettrup A 《Analytical and bioanalytical chemistry》2005,381(1):268-276
A confirmation method for the determination of 18 aromatic amines originating from azo dyes after reductive cleavage was developed. The method is based on the use of high-performance liquid chromatography/tandem mass spectrometry with atmospheric-pressure chemical ionization. For the identification of the analytes one precursor ion and two daughter ions (multi-reaction monitoring, MRM) were selected and the LC-MS/MS parameters optimized to obtain high sensitivity and selectivity. The linear ranges varied from 0.1–1 to 30–50 g mL–1 with correlation coefficients of 0.99 or better. The applicability of the method to determine o-tolidine (3,3-dimethylbenzidine) and 3,3-dimethoxybenzidine in textiles following reductive cleavage of acid red 114, trypan blue, and Chicago sky blue 6B was demonstrated. 相似文献
138.
139.
140.