全文获取类型
收费全文 | 422篇 |
免费 | 12篇 |
国内免费 | 3篇 |
专业分类
化学 | 266篇 |
晶体学 | 10篇 |
力学 | 9篇 |
数学 | 65篇 |
物理学 | 87篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 10篇 |
2016年 | 5篇 |
2015年 | 15篇 |
2014年 | 14篇 |
2013年 | 18篇 |
2012年 | 37篇 |
2011年 | 33篇 |
2010年 | 26篇 |
2009年 | 22篇 |
2008年 | 33篇 |
2007年 | 27篇 |
2006年 | 23篇 |
2005年 | 24篇 |
2004年 | 17篇 |
2003年 | 16篇 |
2002年 | 10篇 |
2001年 | 12篇 |
2000年 | 14篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 16篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1972年 | 1篇 |
1930年 | 2篇 |
排序方式: 共有437条查询结果,搜索用时 15 毫秒
101.
Mary F. Wang Alena N. Joignant Alexandria L. Sohn Kenneth P. Garrard David C. Muddiman 《Journal of mass spectrometry : JMS》2023,58(3):e4911
The field of mass spectrometry imaging (MSI) is constantly evolving to analyze a diverse array of biological systems. A common goal is the need to resolve cellular and subcellular heterogeneity with high spatial resolution. As the field continues to progress towards high spatial resolution, other parameters must be considered when developing a practical method. Here, we discuss the impacts of high spatial resolution on the time of acquisition and the associated implications they have on an MSI analysis (e.g., area of the region of interest). This work presents a brief tutorial serving to evaluate high spatial resolution MSI relative to time of acquisition and data file size. 相似文献
102.
Bruce C. Berndt Sen-Shan Huang Jaebum Sohn Seung Hwan Son 《Transactions of the American Mathematical Society》2000,352(5):2157-2177
In his first two letters to G. H. Hardy and in his notebooks, Ramanujan recorded many theorems about the Rogers-Ramanujan continued fraction. In his lost notebook, he offered several further assertions. The purpose of this paper is to provide proofs for many of the claims about the Rogers-Ramanujan and generalized Rogers-Ramanujan continued fractions found in the lost notebook. These theorems involve, among other things, modular equations, transformations, zeros, and class invariants. 相似文献
103.
In this paper we first give the value of a periodic continued fraction which was recorded incorrectly by Ramanujan on page 341 of his lost notebook. Next, we describe several pairs of equivalent continued fractions in which one is the odd part of the other. One of the results is for the Rogers-Ramanujan continued fraction which was recently proved by Berndt and Yee. Finally, using the Bauer-Muir transformation we prove the equivalence of two continued fractions. One was recorded on page 44 in Ramanujan’s lost notebook, and the other is found in the unorganized pages at the end of Ramanujan’s second notebook.This work was supported by Yonsei University Research Fund of 2003. 相似文献
104.
105.
In order to investigate the secondary cluster ion emission process of organo-metallic compounds under keV ion bombardment, self-assembled monolayers (SAMs) of alkanethiols on gold are ideal model systems. In this experimental study, we focussed on the influence of the primary ion species on the emission processes of gold-alkanethiolate cluster ions from a hexadecanethiol SAM on gold. For this purpose, we carried out time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements using the following primary ion species and acceleration voltages: Ar+, Xe+, SF5+ (10 kV), Bi+, Bi3+(25 kV), Bi32+, Bi52+, Bi72+ (25 kV).It is well known that molecular ions M− and gold-alkanethiolate cluster ions AuxMy− with M = S-(CH2)15-CH3, x − 3 ≤ y ≤ x + 1, x, y > 0, show intense peaks in negative mass spectra. We derived yields YSI exemplarily for the molecular ions M− and the gold-hexadecanethiolate cluster ions Auy+1My− up to y = 8 and found an exponentially decreasing behaviour for increasing y-values for the cluster ions.In contrast to the well-known increase in secondary ion yield for molecular secondary ions when moving from lighter to heavier (e.g. Ar+ to Xe+) or from monoatomic to polyatomic (e.g. Xe+ to SF5+) primary ions, we find a distinctly different behaviour for the secondary cluster ions. For polyatomic primary ions, there is a decrease in secondary ion yield for the gold-hexadecanethiolate clusters whereas the relative decrease of the secondary ion yield ξY with increasing y remains almost constant for all investigated primary ions. 相似文献
106.
Taegong Ryu H. Y. Sohn Young-Ugk Kim Miguel Olivas-Martinez 《Journal of nanoparticle research》2010,12(8):2851-2857
Nanosized tungsten carbide and cobalt composite powder was synthesized by a two-step reaction via a thermal plasma process. Ammonium paratungstate (APT) and cobalt oxide were used as the precursors. The injected precursors were vaporized in the plasma flame and the subsequent reduction of the vaporized precursors produced uniformly mixed nanosized tungsten and cobalt composite powder. The subsequent carburization of this powder by CH4–H2 mixture resulted in the formation of nanosized WC–Co composite powder with a particle size <110 nm. This new method represents an alternative route that avoids the post-treatment required for the WC1?x produced when methane was used for direct carburization in the powder production step. 相似文献
107.
Dal-Ho Kim Jin-Kyu Chang Hyun-Joo Sohn Byong-Gu Cho Sung-Ryong Ko Kil-Bong Nho Dae-Sig Jang Sang-Myung Lee 《Accreditation and quality assurance》2010,15(2):81-87
A pure certified reference material (CRM) for the ginsenoside Rg 1 was prepared from roots of Panax ginseng by extraction and separation of ginsenosides. The mass fraction of the main component (ginsenoside Rg 1 ) in the reference material was determined and its uncertainty was assessed from various input quantities, such as organic impurities, residual moisture, residual solvent, ash, and insoluble matters. To measure these input quantities, HPLC/CAD, Karl Fischer (KF) coulometry, gravimetry, and GC/FID were used. Homogeneity and long-term stability of the reference material are discussed. The certified mass fraction of Rg 1 in the reference material is 0.974 ± 0.006 (k = 2) with a shelf life of 1 year. 相似文献
108.
Xun Jin Samuel Beck Young-Woo Sohn Jun-Kyum Kim Sung-Hak Kim Jinlong Yin Xumin Pian Sung-Chan Kim Yun-Jaie Choi Hyunggee Kim 《Experimental & molecular medicine》2010,42(8):574-582
Although human telomerase catalytic subunit (TERT) has several cellular functions including telomere homeostasis, genomic stability, cell proliferation, and tumorigenesis, the molecular mechanism underlying anti-apoptosis regulated by TERT remains to be elucidated. Here, we show that ectopic expression of TERT in spontaneously immortalized human fetal fibroblast (HFFS) cells, which are a telomerase- and p53-positive, leads to increases of cell proliferation and transformation, as well as a resistance to DNA damage response and inactivation of p53 function. We found that TERT and a mutant TERT (no telomerase activity) induce expression of basic fibroblast growth factor (bFGF), and ectopic expression of bFGF also allows cells to be resistant to DNA-damaging response and to suppress activation of p53 function under DNA-damaging induction. Furthermore, loss of TERT or bFGF markedly increases a p53 activity and DNA-damage sensitivity in HFFS, HeLa and U87MG cells. Therefore, our findings indicate that a novel TERT-bFGF axis accelerates the inactivation of p53 and consequent increase of resistance to DNA-damage response. 相似文献
109.
We have designed and synthesised new anion receptors 1 and 2, both of their C–H groups were at the α positions to carbonyl groups and further polarised by the attached polarising substituents. This enabled us to study hydrogen bonding donor ability of C–H bonds. The polarising substituents are electron withdrawing cyano group for host 1, while charged pyridinium group for host 2. As expected from charge effects, host 2 shows roughly an order of magnitude higher binding constants against various anion guests than those of receptor 1. Since the magnitude of polarisation change should be greatest for C–H group among various hydrogen bonding groups, this indicates the importance of C–H hydrogen bonding. In contrast, the relative order of binding constants was the same for both host 1 and 2. The order of association constants was found to be (CH3)2POO? > CH3COO? > C6H5COO? > Cl? > Br?. DFT calculation results were in good agreement with experimental binding constants and confirmed the importance of charged group substitution. In addition, receptor 1 showed the highest association constant for dimethyl phosphinate, which is implicated in many metabolic diseases. 相似文献
110.
Jong‐Seong Kim Hyunchul Kim Jihwan Yoon Kyuyoung Heo Moonhor Ree 《Journal of polymer science. Part A, Polymer chemistry》2005,43(18):4079-4088
Various heterogeneous zinc glutarate (ZnGA) catalysts were synthesized in solvent systems of various polarities from zinc acetate dihydrate and glutaric acid with and without the aid of an amphiphilic block copolymer, poly(ethylene glycol‐b‐propylene glycol‐b‐ethylene glycol) (PE6400), as a template. The presence of the PE6400 template and the polarity of the solvent significantly affected the morphology, particle size, surface area, and crystallinity of the resulting catalyst. However, all the catalysts had the same crystal lattice unit cell structure and similar surface compositions. The surface compositions of the catalysts were quite different from those of conventionally prepared ZnGA catalysts, that is, those prepared from zinc oxide and glutaric acid in toluene. All these characteristics of the catalysts influenced the ZnGA‐catalyzed copolymerization of carbon dioxide and propylene oxide. The catalytic activities of the catalysts in this copolymerization depended primarily on their surface area and secondarily on their crystallinity; a larger surface area and a higher crystallinity resulted in higher catalytic activity. Of the catalysts that we prepared, the ZnGA catalyst that was prepared in ethanol containing 5.5 wt % water with the PE6400 template, ZnGA‐PE3, exhibited the highest catalytic activity in the copolymerization. The catalytic activity of ZnGA‐PE3 was attributed to its wrinkled petal bundle morphology, which provided a large surface area and high crystallinity. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4079–4088, 2005 相似文献