全文获取类型
收费全文 | 334篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
化学 | 146篇 |
晶体学 | 5篇 |
力学 | 10篇 |
数学 | 36篇 |
物理学 | 127篇 |
综合类 | 16篇 |
出版年
2023年 | 3篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2016年 | 3篇 |
2014年 | 3篇 |
2013年 | 14篇 |
2012年 | 11篇 |
2011年 | 18篇 |
2010年 | 7篇 |
2008年 | 18篇 |
2007年 | 13篇 |
2006年 | 16篇 |
2005年 | 13篇 |
2004年 | 9篇 |
2003年 | 8篇 |
2002年 | 15篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1969年 | 5篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1943年 | 2篇 |
1932年 | 2篇 |
1925年 | 2篇 |
1915年 | 2篇 |
排序方式: 共有340条查询结果,搜索用时 31 毫秒
21.
We use a result of Kauffman to explore the connection between Richard Thompson’s Group F and the four-color theorem. 相似文献
22.
Jimmy Yuk Kristina L. McIntyre Christian Fischer Joshua Hicks Kimberly L. Colson Ed Lui Dan Brown John T. Arnason 《Analytical and bioanalytical chemistry》2013,405(13):4499-4509
The use of 1H-NMR-based metabolomics to distinguish and identify unique markers of five Ontario ginseng (Panax quinquefolius L.) landraces and two ginseng species (P. quinquefolius and P. ginseng) was evaluated. Three landraces (2, 3, and 5) were distinguished from one another in the principal component analysis (PCA) scores plot. Further analysis was conducted and specific discriminating metabolites from the PCA loadings were determined. Landraces 3 and 5 were distinguishable on the basis of a decreased NMR intensity in the methyl ginsenoside region, indicating decreased overall ginsenoside levels. In addition, landrace 5 was separated by an increased amount of sucrose relative to the rest of the landraces. Landrace 2 was separated from the rest of the landraces by the increased level of ginsenoside Rb1. The Ontario P. quinquefolius was also compared with Asian P. ginseng by PCA, and clear separation between the two groups was detected in the PCA scores plot. The PCA loadings plot and a t-test NMR difference plot were able to identify an increased level of maltose and a decreased level of sucrose in the Asian ginseng compared with the Ontario ginseng. An overall decrease of ginsenoside content, especially ginsenoside Rb1, was also detected in the Asian ginseng’s metabolic profile. This study demonstrates the potential of NMR-based metabolomics as a powerful high-throughput technique in distinguishing various closely related ginseng landraces and its ability to identify metabolic differences from Ontario and Asian ginseng. The results from this study will allow better understanding for quality assessment, species authentication, and the potential for developing a fully automated method for quality control. Figure
Principal component analysis scores and loadings plot for differentiating between closely-related ginseng landraces in Ontario, Canada 相似文献
23.
We demonstrate a means of creating a digital image by using a two-axis tilt micromirror to scan a scene. For each different orientation we extract a single gray scale value from the mirror and combine them to form a single composite image. This allows one to choose the distribution of the samples, and so in principle a variable resolution image could be created. We demonstrate this ability to control resolution and projection by constructing a voltage table that compensates for the nonlinear response of the mirrors to the applied voltage. 相似文献
24.
Dr. Jamie Hicks Dr. Petra Vasko Andreas Heilmann Prof. Jose M. Goicoechea Prof. Simon Aldridge 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(46):20556-20560
The reactivity of the electron-rich anionic AlI aluminyl compound K2[(NON)Al]2 (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) towards mono- and disubstituted arenes is reported. C−H activation chemistry with n-butylbenzene gives exclusively the product of activation at the arene meta position. Mechanistically, this transformation proceeds in a single step via a concerted Meisenheimer-type transition state. Selectivity is therefore based on similar electronic factors to classical SNAr chemistry, which implies the destabilisation of transition states featuring electron-donating groups in either ortho or para positions. In the cases of toluene and the three isomers of xylene, benzylic C−H activation is also possible, with the product(s) formed reflecting the feasibility (or otherwise) of competing arene C−H activation at a site which is neither ortho nor para to a methyl substituent. 相似文献
25.
Welch Nathan J. Carey J. William Frash Luke P. Hyman Jeffrey D. Hicks Wes Meng Meng Li Wenfeng Menefee Anne H. 《Transport in Porous Media》2022,141(1):17-47
Transport in Porous Media - Fluid flow in fractures has the potential to drastically change the economic, environmental, and safety risks associated with a subsurface operation. This work focuses... 相似文献
26.
International Consortium for Blood Pressure Genome-Wide Association Studies Ehret GB Munroe PB Rice KM Bochud M Johnson AD Chasman DI Smith AV Tobin MD Verwoert GC Hwang SJ Pihur V Vollenweider P O'Reilly PF Amin N Bragg-Gresham JL Teumer A Glazer NL Launer L Zhao JH Aulchenko Y Heath S Sõber S Parsa A Luan J Arora P Dehghan A Zhang F Lucas G Hicks AA Jackson AU Peden JF Tanaka T Wild SH Rudan I Igl W Milaneschi Y Parker AN Fava C Chambers JC Fox ER Kumari M Go MJ van der Harst P Kao WH 《Nature》2011,478(7367):103-109
Blood pressure is a heritable trait influenced by several biological pathways and responsive to environmental stimuli. Over one billion people worldwide have hypertension (≥140?mm?Hg systolic blood pressure or ≥90?mm?Hg diastolic blood pressure). Even small increments in blood pressure are associated with an increased risk of cardiovascular events. This genome-wide association study of systolic and diastolic blood pressure, which used a multi-stage design in 200,000 individuals of European descent, identified sixteen novel loci: six of these loci contain genes previously known or suspected to regulate blood pressure (GUCY1A3-GUCY1B3, NPR3-C5orf23, ADM, FURIN-FES, GOSR2, GNAS-EDN3); the other ten provide new clues to blood pressure physiology. A genetic risk score based on 29 genome-wide significant variants was associated with hypertension, left ventricular wall thickness, stroke and coronary artery disease, but not kidney disease or kidney function. We also observed associations with blood pressure in East Asian, South Asian and African ancestry individuals. Our findings provide new insights into the genetics and biology of blood pressure, and suggest potential novel therapeutic pathways for cardiovascular disease prevention. 相似文献
27.
Tumour evolution inferred by single-cell sequencing 总被引:1,自引:0,他引:1
Navin N Kendall J Troge J Andrews P Rodgers L McIndoo J Cook K Stepansky A Levy D Esposito D Muthuswamy L Krasnitz A McCombie WR Hicks J Wigler M 《Nature》2011,472(7341):90-94
Genomic analysis provides insights into the role of copy number variation in disease, but most methods are not designed to resolve mixed populations of cells. In tumours, where genetic heterogeneity is common, very important information may be lost that would be useful for reconstructing evolutionary history. Here we show that with flow-sorted nuclei, whole genome amplification and next generation sequencing we can accurately quantify genomic copy number within an individual nucleus. We apply single-nucleus sequencing to investigate tumour population structure and evolution in two human breast cancer cases. Analysis of 100 single cells from a polygenomic tumour revealed three distinct clonal subpopulations that probably represent sequential clonal expansions. Additional analysis of 100 single cells from a monogenomic primary tumour and its liver metastasis indicated that a single clonal expansion formed the primary tumour and seeded the metastasis. In both primary tumours, we also identified an unexpectedly abundant subpopulation of genetically diverse 'pseudodiploid' cells that do not travel to the metastatic site. In contrast to gradual models of tumour progression, our data indicate that tumours grow by punctuated clonal expansions with few persistent intermediates. 相似文献
28.
Lorch JM Meteyer CU Behr MJ Boyles JG Cryan PM Hicks AC Ballmann AE Coleman JT Redell DN Reeder DM Blehert DS 《Nature》2011,480(7377):376-378
White-nose syndrome (WNS) has caused recent catastrophic declines among multiple species of bats in eastern North America. The disease's name derives from a visually apparent white growth of the newly discovered fungus Geomyces destructans on the skin (including the muzzle) of hibernating bats. Colonization of skin by this fungus is associated with characteristic cutaneous lesions that are the only consistent pathological finding related to WNS. However, the role of G. destructans in WNS remains controversial because evidence to implicate the fungus as the primary cause of this disease is lacking. The debate is fuelled, in part, by the assumption that fungal infections in mammals are most commonly associated with immune system dysfunction. Additionally, the recent discovery that G. destructans commonly colonizes the skin of bats of Europe, where no unusual bat mortality events have been reported, has generated further speculation that the fungus is an opportunistic pathogen and that other unidentified factors are the primary cause of WNS. Here we demonstrate that exposure of healthy little brown bats (Myotis lucifugus) to pure cultures of G. destructans causes WNS. Live G. destructans was subsequently cultured from diseased bats, successfully fulfilling established criteria for the determination of G. destructans as a primary pathogen. We also confirmed that WNS can be transmitted from infected bats to healthy bats through direct contact. Our results provide the first direct evidence that G. destructans is the causal agent of WNS and that the recent emergence of WNS in North America may represent translocation of the fungus to a region with a naive population of animals. Demonstration of causality is an instrumental step in elucidating the pathogenesis and epidemiology of WNS and in guiding management actions to preserve bat populations against the novel threat posed by this devastating infectious disease. 相似文献
29.
Barclay TM Hicks RG Lemaire MT Thompson LK Xu Z 《Chemical communications (Cambridge, England)》2002,(16):1688-1689
The synthesis of a verdazyl radical with a carboxylate substituent renders the radical highly soluble in water, thereby permitting the aqueous synthesis of Ni(II) and Co(II) verdazyl complexes which have been structurally and magnetically characterized. 相似文献
30.
Measurements of the 50Ti(γ, n) and 50Ti(γ, n0) cross sections have been made in the energy range of the giant dipole resonance (GDR). Assuming the GDR is split into two isospin components, approximated as Lorentzians, a calculation based on statistical decay of the GDR states is consistent with the experimental results. 相似文献