全文获取类型
收费全文 | 319篇 |
免费 | 46篇 |
国内免费 | 45篇 |
专业分类
化学 | 184篇 |
晶体学 | 2篇 |
力学 | 21篇 |
综合类 | 4篇 |
数学 | 18篇 |
物理学 | 37篇 |
无线电 | 144篇 |
出版年
2024年 | 3篇 |
2023年 | 15篇 |
2022年 | 17篇 |
2021年 | 30篇 |
2020年 | 28篇 |
2019年 | 20篇 |
2018年 | 19篇 |
2017年 | 21篇 |
2016年 | 26篇 |
2015年 | 20篇 |
2014年 | 30篇 |
2013年 | 28篇 |
2012年 | 23篇 |
2011年 | 21篇 |
2010年 | 19篇 |
2009年 | 14篇 |
2008年 | 13篇 |
2007年 | 13篇 |
2006年 | 5篇 |
2005年 | 1篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有410条查询结果,搜索用时 15 毫秒
31.
32.
Separation and concentration of sulfonylurea herbicides in milk by ionic‐liquid‐based foam flotation solid‐phase extraction
下载免费PDF全文
![点击此处可从《Journal of separation science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Liyuan Zhang Bocheng Cao Di Yao Runzhong Yu Changqing Yu Hanqi Zhang Aimin Yu 《Journal of separation science》2015,38(10):1733-1740
The ultrasound‐assisted ionic liquid foam flotation solid‐phase extraction of sulfonylurea herbicides in milk was developed and validated. The proteins and lipids were isolated from the sample matrix by adding salt and adjusting the pH value. The target analytes eluted from the solid‐phase extraction cartridge were determined by high‐performance liquid chromatography. Some experimental parameters, including the pH value of sample solution, amount of NaCl, ionic liquid type, extraction time, flow rate of carrier gas, flotation time, and solid‐phase extraction cartridge type were investigated and optimized. Under the optimized experimental conditions, the limits of detection for metsulfuron, pyrazosulfuron, chlorimuron‐ethyl, and nicosulfuron were 1.3, 0.6, 0.7, and 1.1 μg/L, respectively. When the present method was applied to the analysis of milk samples the recoveries of the analytes ranged from 84.3 to 105.2% and relative standard deviations were >5.7%. 相似文献
33.
34.
对比了目前几种安卓电视智能升级方案,提出了一种在现有电视技术条件下,通过一个自定义接口完成安卓电视机芯智能升级的方案。该方法具有电视整机机芯升级简单、便捷、成本低、原有整机利用率高的优点。并以50个管脚的自定义接口为例,具体阐述了安卓电视机芯升级的软件、硬件解决方案。 相似文献
35.
Analysis and modeling of spatial data are of considerable interest in many applications. However, the prediction of geographical features from a set of chemical measurements on a set of geographically distinct samples has never been explored. We report a new, tree‐structured hierarchical model for the estimation of geographical location of spatially distributed samples from their chemical measurements. The tree‐structured hierarchical modeling used in this study involves a set of geographic regions stored in a hierarchical tree structure, with each nonterminal node representing a classifier and each terminal node representing a regression model. Once the tree‐structured model is constructed, given a sample with only chemical measurements available, the predicted regional location of the sample is gradually restricted as it is passed through a series of classification steps. The geographic location of the sample can be predicted using a regression model within the terminal subregion. We show that the tree‐structured modeling approach provides reasonable estimates of geographical region and geographic location for surface water samples taken across the entire USA. Further, the location uncertainty, an estimate of a probability that a test sample could be located within a pre‐estimated, joint prediction interval that is much smaller than the terminal subregion, can also be assessed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
36.
Zhang L Chai L Liu J Wang H Yu W Sang P 《Langmuir : the ACS journal of surfaces and colloids》2011,27(22):13729-13738
A method of pH manipulation has been used to improve chemically oxidative polymerization of m-phenylenediamine (mPD) through concurrent addition of NaOH when adding oxidant (NH(4))(2)S(2)O(8). pH detection and open-circuit potential technique were adopted to monitor the polymerization process of mPD and to explain the oxidation state-pH and yield-pH relationships. Results from Fourier transformed infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies indicate that a low oxidation state is under control by regulating NaOH concentration. At 2.5 M NaOH, the oxidation state of poly(m-phenylenediamine) (PmPD) is 64.7 mol % (measured by molar content of quinoid imine from XPS), while the yield is 84%. The synthesized PmPD possesses better Ag(+) adsorption performance when lowering its oxidation state. Moreover, the Ag(+) adsorbance of PmPD can reach 1693 mg g(-1). Meanwhile, Ag(+) adsorption mechanism was studied by pH tracking, X-ray diffraction (XRD) patterns, and X-ray photoelectron spectroscopy. The adsorption process includes redox reaction, chelation, and physical adsorption. 相似文献
37.
Production and Characterization of Polyclonal and Monoclonal Abs Against the RNA-Binding Protein QKI
Zhang J Huang B Yu F Wei M Yang G Fu H Jin L Bai L He X Lu Z 《Applied biochemistry and biotechnology》2011,164(3):283-293
RNA-binding protein QKI, a member of the Signal Transduction and Activation of RNA family, is found to be essential in the
blood vessel development and postnatal myelination in central nervous system (Woo et al., Oncogene 28:1176–1186, 2009; Lu et al., Nucleic Acids Res 31(15):4616–4624, 2003; Bohnsack et al., Genesis 44(2):93–104, 2006). However, its wide expression pattern suggests other fundamental roles in vivo (Kondo et al., Mamm Genome 10(7):662–669, 1999). To facilitate the understanding of QKI function in various systems, we prepared the polyclonal and monoclonal antibodies
against QKI. To obtain the antigen, recombinant His-tagged QKI was expressed in Escherichia coli and highly purified by Ni2+-chelated column combined with hydrophobic and ion exchange methods. Following three types of immunizations with different
adjuvants, including Freund’s, PAGE gel, and nitrocellulose membrane, only the antiserum produced with Freund’s adjuvant is
effective for Western blot detection. Several McAb clones are able to recognize both endogenous and over-expressed QKI with
high affinity in Western blot and immunofluorescence. The specificity of Ab was validated as weakening, and no specific signals
were observed in cells with QKI knocking down. Immunohistochemistry analysis further showed positive staining of QKI in kidney
where QKI mRNA was abundantly expressed, ensuring the wide applications of the QKI Abs in the ongoing mechanistic studies. 相似文献
38.
Ehsan Jazaeri Liyuan Zhang Xungai Wang Takuya Tsuzuki 《Cellulose (London, England)》2011,18(6):1481-1485
The possibility of fabricating carbon nanofibers from cellulose nanofibers was investigated. Cellulose nanofiber of ~50 nm
in diameter was produced using ball milling in an eco-friendly manner. The effect of the drying techniques of cellulose nanofibers
on the morphology of carbon residue was studied. After pyrolysis of freeze-dried cellulose nanofibers below 600 °C, amorphous
carbon fibers of ~20 nm in diameter were obtained. The pyrolysis of oven-dried precursors resulted in the loss of original
fibrous structures. The different results arising from the two drying techniques are attributed to the difference in the spatial
distance between cellulose nanofiber precursors. 相似文献
39.
Zhang L Xu J Sun L Ma J Yang K Liang Z Zhang L Zhang Y 《Analytical and bioanalytical chemistry》2011,399(10):3399-3405
In this study, zirconium oxide (ZrO2) aerogel was synthesized via a green sol–gel approach, with zirconium oxychloride, instead of the commonly used alkoxide
with high toxicity, as the precursor. With such material, phosphopeptides from the digests of 4 pmol of β-casein with the
coexistence of 100 times (mol ratio) BSA could be selectively captured, and identified by MALDI-TOF MS. Due to the large surface
area (416.0 m2 g−1) and the mesoporous structure (the average pore size of 10.2 nm) of ZrO2 aerogel, a 20-fold higher loading capacity for phosphopeptide, YKVPQLEIVPN[pS]AEER (MW 1952.12), was obtained compared to
that of commercial ZrO2 microspheres (341.5 vs. 17.87 mg g−1). The metal oxide aerogel was further applied in the enrichment of phosphopeptides from 100 ng nonfat milk, and 17 phosphopeptides
were positively identified, with a 1.5-fold improvement in phosphopeptide detection compared with previously reported results.
These results demonstrate that ZrO2 aerogel can be a powerful enrichment material for phosphoproteome study. 相似文献
40.
We report the vibrational and orientational dynamics of water molecules in isotopically diluted NaOH and NaOD solutions using polarization-resolved femtosecond vibrational spectroscopy and terahertz time-domain dielectric relaxation measurements. We observe a speed-up of the vibrational relaxation of the O-D stretching vibration of HDO molecules outside the first hydration shell of OH(-) from 1.7 ± 0.2 ps for neat water to 1.0 ± 0.2 ps for a solution of 5 M NaOH in HDO:H(2)O. For the O-H vibration of HDO molecules outside the first hydration shell of OD(-), we observe a similar speed-up from 750 ± 50 fs to 600 ± 50 fs for a solution of 6 M NaOD in HDO:D(2)O. The acceleration of the decay is assigned to fluctuations in the energy levels of the HDO molecules due to charge transfer events and charge fluctuations. The reorientation dynamics of water molecules outside the first hydration shell are observed to show the same time constant of 2.5 ± 0.2 ps as in bulk liquid water, indicating that there is no long range effect of the hydroxide ion on the hydrogen-bond structure of liquid water. The terahertz dielectric relaxation experiments show that the transfer of the hydroxide ion through liquid water involves the simultaneous motion of ~7 surrounding water molecules, considerably less than previously reported for the proton. 相似文献