全文获取类型
收费全文 | 1530篇 |
免费 | 278篇 |
国内免费 | 163篇 |
专业分类
化学 | 1068篇 |
晶体学 | 10篇 |
力学 | 144篇 |
综合类 | 35篇 |
数学 | 182篇 |
物理学 | 532篇 |
出版年
2024年 | 5篇 |
2023年 | 43篇 |
2022年 | 55篇 |
2021年 | 49篇 |
2020年 | 70篇 |
2019年 | 65篇 |
2018年 | 39篇 |
2017年 | 43篇 |
2016年 | 68篇 |
2015年 | 78篇 |
2014年 | 90篇 |
2013年 | 102篇 |
2012年 | 144篇 |
2011年 | 139篇 |
2010年 | 101篇 |
2009年 | 95篇 |
2008年 | 102篇 |
2007年 | 83篇 |
2006年 | 93篇 |
2005年 | 54篇 |
2004年 | 61篇 |
2003年 | 44篇 |
2002年 | 31篇 |
2001年 | 21篇 |
2000年 | 30篇 |
1999年 | 18篇 |
1998年 | 26篇 |
1997年 | 22篇 |
1996年 | 25篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1993年 | 21篇 |
1992年 | 23篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有1971条查询结果,搜索用时 15 毫秒
121.
122.
Accelerated Simulation Study of Space Charge Effects in Quadrupole Ion Traps Using GPU Techniques 总被引:1,自引:0,他引:1
Xingchuang Xiong Wei Xu Xiang Fang Yulin Deng Zheng Ouyang 《Journal of the American Society for Mass Spectrometry》2012,23(10):1799-1807
Space charge effects play important roles in the performance of various types of mass analyzers. Simulation of space charge effects is often limited by the computation capability. In this study, we evaluate the method of using graphics processing unit (GPU) to accelerate ion trajectory simulation. Simulation using GPU has been compared with multi-core central processing unit (CPU), and an acceleration of about 390 times have been obtained using a single computer for simulation of up to 105 ions in quadrupole ion traps. Characteristics of trapped ions can be investigated at detailed levels within a reasonable simulation time. Space charge effects on the trapping capacities of linear and 3D ion traps, ion cloud shapes, ion motion frequency shift, mass spectrum peak coalescence effects between two ion clouds of close m/z are studied with the ion trajectory simulation using GPU. 相似文献
123.
高效液相色谱法同时测定生物质乳酸发酵液中有机酸及糖类化合物 总被引:3,自引:0,他引:3
建立了高效液相色谱(HPLC)同时测定生物质乳酸发酵液中有机酸及糖类的分析方法。使用Bio-Rad Aminex HPX-87H色谱柱,以5 mmol/L的H2SO4为流动相,在柱温55 ℃,流速0.6 mL/min条件下,采用示差折光检测器进行检测。结果表明,该方法可在17 min内实现发酵液中各种有机酸和糖类化合物等的完全分离与定量,6种有机酸和3种糖类化合物在0.15~5.19 g/L范围内的线性关系良好,回归方程的线性相关系数在0.9998以上。将该法用于米根霉发酵液的检测,两个水平的加标回收率为96.91%~103.11%,相对标准偏差(n=6)为0.81%~4.61%。该法适用于微生物发酵液中多种有机酸和糖类的快速、高效分离和定量测定。 相似文献
124.
Structural elucidation of new urinary tamoxifen metabolites by liquid chromatography quadrupole time‐of‐flight mass spectrometry
下载免费PDF全文
![点击此处可从《Journal of mass spectrometry : JMS》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jianghai Lu Chunji He Genye He Xiaobing Wang Youxuan Xu Yun Wu Ying Dong Gangfeng Ouyang 《Journal of mass spectrometry : JMS》2014,49(7):570-578
In this study, tamoxifen metabolic profiles were investigated carefully. Tamoxifen was administered to two healthy male volunteers and one female patient suffering from breast cancer. Urinary extracts were analyzed by liquid chromatography quadruple time‐of‐flight mass spectrometry using full scan and targeted MS/MS techniques with accurate mass measurement. Chromatographic peaks for potential metabolites were selected by using the theoretical [M + H]+ as precursor ion in full‐scan experiment and m/z 72, 58 or 44 as characteristic product ions for N,N‐dimethyl, N‐desmethyl and N,N‐didesmethyl metabolites in targeted MS/MS experiment, respectively. Tamoxifen and 37 metabolites were detected in extraction study samples. Chemical structures of seven unreported metabolites were elucidated particularly on the basis of fragmentation patterns observed for these metabolites. Several metabolic pathways containing mono‐ and di‐hydroxylation, methoxylation, N‐desmethylation, N,N‐didesmethylation, oxidation and combinations were suggested. All the metabolites were detected in the urine samples up to 1 week. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
125.
126.
127.
128.
Electrochemical Behavior and Voltammetric Determination of Curcumin at Electrochemically Reduced Graphene Oxide Modified Glassy Carbon Electrode
下载免费PDF全文
![点击此处可从《Electroanalysis》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This work presents a sensitive voltammetric method for determination of curcumin by using a electrochemically reduced graphene oxide (ERGO) modified glass carbon electrode (GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The electrochemical behaviors of curcumin at ERGO/GCE were investigated by cyclic voltammetry, suggesting that the ERGO/GCE exhibits excellent electrocatalytic activity towards curcumin, compared with bare GCE and GO/GCE electrodes. The electrochemical reaction mechanisms of curcumin, demethoxycurcumin and bisdemethoxycurcumin at the ERGO/GCE were also investigated and discussed systematically. Under physiological condition, the modified electrode showed linear voltammetric response from 0.2 μM to 60.0 μM for curcumin, with the detection limit of 0.1 μm. This work demonstrates that the graphene‐modified electrode is a promising strategy for electrochemical determination of biological important phenolic compounds. 相似文献
129.
Antibiotics, once being released into the environment, become recalcitrant organic pollutants, which pose a potential risk to ecological balance and human health. In this study, a Z-scheme heterojunction of bismuth oxyiodide (BiOI)/exfoliated g-C3N4 (BiOI/ECN hereafter) was synthesized by the combination of thermal exfoliation of g-C3N4 and chemical precipitation of BiOI for efficient photocatalytic degradation of tetracycline in aqueous solutions under visible light irradiation. The optimized BiOI/ECN delivered an outstanding degradation rate at circa 0.0705 min?1, which was 10 times higher than that of the bulk g-C3N4. The photocatalytic degradation efficiency of tetracycline remained almost unchanged in a pH range of 3–11, and the BiOI/ECN displayed an excellent photostability upon recycled usage. The photocatalytic mechanism of tetracycline was ascribed to the main reactive oxidation species of photogenerated holes and superoxide radicals. In addition, the possible degradation pathways of tetracycline were investigated by HPLC-MS to identify intermediates. The toxicity of photocatalytic-generated intermediates of tetracycline was found significantly alleviated according to the calculation of quantitative structure–activity relationship prediction. This work not only provides an attractive photocatalyst for the removal of tetracycline but also opens a new avenue for rational design of Z-scheme heterojunction composites for tetracycline degradation. 相似文献
130.
Yuan Wang Xuemei Liu Quyun Chen Tian C. Zhang Like Ouyang Shaojun Yuan 《Materials Today Chemistry》2022
Addressing arsenite pollution in groundwater has drawn great attention. It is attractive to pre-oxidize highly mobile As(III) to relatively low-toxic As(V) with a subsequent adsorption separation process. Herein, BiOI anchoring on γ-Fe2O3 is performed to synthesize BiOI/γ-Fe2O3 core–shell nanoparticles for efficient removal of As(III) via a simultaneous photocatalytic oxidization–adsorption process. The physical and chemical structures of BiOI/γ-Fe2O3 are investigated by transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction measurements. The photoluminescence and electron spin resonance (ESR) characterization were employed to ascertain the possible reaction mechanism of visible-light-driven photocatalytic oxidation of As(III). Such BiOI/γ-Fe2O3 delivers a superior As(III) removal capability under visible light irradiation with an arsenic removal efficiency of 99.8% within 180 min, higher than those of BiOCl/γ-Fe2O3 (81.7%) and BiOBr/γ-Fe2O3 (98.9%). The optimal BiOI/γ-Fe2O3 (molar ratio of 2:1) is obtained by rationally adjusting the molar ratio of BiOI to γ-Fe2O3. The as-synthesized BiOI/γ-Fe2O3 performs well in a wide pH range of 2–8. Only coexisting PO43? anions have a significant effect on the As(III) removal. The free radical trapping experiment and ESR results demonstrate that the ?O2? and h+ are the main active substances for the photocatalytic oxidation of As(III) on BiOI/γ-Fe2O3. This work not only gives a novel magnetic core–shell nanoparticle photocatalyst for efficient photocatalytic oxidation and adsorption of As(III) but also offers a new strategy to rationally design BiOX for its related practical applications. 相似文献