全文获取类型
收费全文 | 918篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 527篇 |
晶体学 | 19篇 |
力学 | 35篇 |
数学 | 72篇 |
物理学 | 279篇 |
出版年
2022年 | 13篇 |
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 19篇 |
2018年 | 14篇 |
2017年 | 10篇 |
2016年 | 16篇 |
2015年 | 9篇 |
2014年 | 34篇 |
2013年 | 70篇 |
2012年 | 44篇 |
2011年 | 57篇 |
2010年 | 33篇 |
2009年 | 23篇 |
2008年 | 36篇 |
2007年 | 26篇 |
2006年 | 34篇 |
2005年 | 32篇 |
2004年 | 24篇 |
2003年 | 19篇 |
2002年 | 26篇 |
2001年 | 16篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 10篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 14篇 |
1991年 | 16篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 18篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 13篇 |
1974年 | 7篇 |
1973年 | 12篇 |
排序方式: 共有932条查询结果,搜索用时 31 毫秒
61.
The use of rotational-echo double resonance NMR to measure distances from an observed tightly coupled cluster of 13C spins to a distant 15N, 31P, or 19F is practical if 13C chemical shifts and homonuclear 13C-13C isotropic J interactions are refocused by a combination of rotor-synchronized 13C pi and pi/2 pulses. This scheme is illustrated by experiments performed on diluted and recrystallized L-[13C(3),15N]alanine and L-[13C(6),alpha-15N]histidine. 相似文献
62.
[reaction: see text] A new method for synthesizing phenanthridine and its related compounds was developed using the condensation of o-phenylaniline and its homologues with cyclic ketones under hydrothermal conditions. 相似文献
63.
Dibromoacetyl benzene derivatives on condensation with thiourea give 2-amino-4-arylthiazoles instead of the expected 2-amino-4-aryl-5-bromothiazoles. Attempts have been made to find the reaction pathway. 相似文献
64.
1,5,6,10b-Tetrahydropyrrolo[2,1-alpha]isoquinolin-3(2H)-ones 17a,b, 17d,e, and 5,12b-dihydroisoindolo[1,2-alpha]isoquinolin-8(6H)-ones 22a-e were prepared by intramolecular cyclizations of 1-(2-arylethyl)-5-benzotriazolyl-pyrrolidin-2-ones 15a,b, 15d,e, and 3-benzotriazolyl-2-(2-arylethyl)-1-isoindolinones 20a-e, respectively, in the presence of titanium chloride. Products from chiral amines were obtained with stereoselectivities of > or = 94%. 相似文献
65.
Manish K. Jaiswal Shailee Mehta Rinti Banerjee D. Bahadur 《Colloid and polymer science》2012,290(7):607-617
A comparative study of thermoresponsive poly(N-isopropylacrylamide)(PNIPAAm)-chitosan (CS)-based magnetic nanohydrogels (MNHGs) encapsulating functionalized Fe3O4 nanoparticles (NPs) in terms of the parameters governing their suitability for real hyperthermia is reported. Iron oxide
NPs functionalized with (a) citric acid (CA-Fe3O4), (b) ethylenediamine (Amine-Fe3O4) and (c) dimercaptosuccininc (DMSA-Fe3O4) have been synthesized and their encapsulation into MNHGs was obtained through physical encapsulation method. The structural
characterizations of synthesized materials include X-ray diffraction, FT-IR, TGA, ICP-AES and X-ray photoelectron spectroscopy
(XPS). Encapsulation of the functionalized NPs into MNHGs were observed in TEM micrographs, while SEM and AFM micrographs
confirmed their spherical morphology (~250–300 nm). Lower critical solution temperature (LCST) variation was measured by UV–visible
spectrophotometer and differential scanning calorimetry (DSC). MNHGs exhibited sufficient magnetization and heating ability
for hyperthermia. Typically, hydrogels containing CA-Fe3O4 (50 mg/ml) raised the temperature of the medium to 43 °C, a suitable dose for in vivo application in tumor-bearing mice. 相似文献
66.
H. R. Khajuria S. K. Mehta Ashok K. Gupta 《Journal of Thermal Analysis and Calorimetry》1986,31(1):15-20
Clay from the Purmandal area of J&K State was separated into its different size fractions by the method of sedimentation and with Sharple's super centrifuge process. Dilatometric studies were performed on each clay fraction; the results obtained from the dilatation curves are discussed in detail. The results revealed that the finer fraction of clay is bentonitic in nature, whereas the other fractions are felsphatic and micaceous in nature. 相似文献
67.
Jeevan Jaisingh Jack Barron Shailendra Mehta Alok Chaturvedi 《European Journal of Operational Research》2008
The issues we address here are – How should a firm (e.g. Internet service provider (ISP)) that is capable of collecting personal information (browsing information, purchase history, etc.) about consumers, price its service, given that consumers vary in their valuation for privacy, and also vary in terms of the value of their personal information to a third party (firms that need consumer information)? Should the firm have a blanket policy of never collecting, or a policy of always collecting and revealing information? Surprisingly we find that in some cases the collector of information may be no worse off in the asymmetric information case than in the full information case. The paper provides a justification for the strategy of some firms such as ISP’s which never collect information and also for the strategy of other firms, like grocery stores that do. We also find that it is non-optimal for the firm to design contracts where the consumer can choose an intermediate level of privacy. 相似文献
68.
JPC – Journal of Planar Chromatography – Modern TLC - Adensitometric HPTLC method has been established for analysis in alcohol extracts of the seeds and leaves of Achyranthes aspera L.... 相似文献
69.
Bhupendra Chudasama Anjana K. ValaNidhi Andhariya R.V. UpadhyayR.V. Mehta 《Journal of magnetism and magnetic materials》2011,323(10):1233-1237
In recent years, rapid increase has been observed in the population of microbes that are resistant to conventionally used antibiotics. Antifungal drug therapy is no exception and now resistance to many of the antifungal agents in use has emerged. Therefore, there is an inevitable and urgent medical need for antibiotics with novel antimicrobial mechanisms. Aspergillus glaucus is the potential cause of fatal brain infections and hypersensitivity pneumonitis in immunocompromised patients and leads to death despite aggressive multidrug antifungal therapy. In the present article, we describe the antifungal activity of multifunctional core-shell Fe3O4-Ag nanocolloids against A. glaucus isolates. Controlled experiments are also carried out with Ag nanocolloids in order to understand the role of core (Fe3O4) in the antifungal action. The minimum inhibitory concentration (MIC) of nanocolloids is determined by the micro-dilution method. MIC of A. glaucus is 2000 μg/mL. The result is quite promising and requires further investigations in order to develop a treatment methodology against this death causing fungus in immunocompromised patients. 相似文献
70.
Jennifer L. Mass Robert Opila Barbara Buckley Marine Cotte Jonathan Church Apurva Mehta 《Applied Physics A: Materials Science & Processing》2013,111(1):59-68
Evidence for the alteration of the yellow paints in Henri Matisse’s Le Bonheur de vivre (1905–1906, The Barnes Foundation) has been observed since the 1990s. The changes in this iconic work of Matisse’s Fauvist period include lightening, darkening, and flaking of the yellow paints. Handheld X-ray fluorescence (XRF) and multispectral imaging surveys reveal that the degradation is confined to cadmium yellow (CdS) paints. The discoloration of cadmium yellow paints in Impressionist, Post-Impressionist and early modernist work from the 1880s through the 1920s has been ascribed to the photo-oxidative degradation of CdS. Preliminary investigations of the degraded yellow paints in this work involved Cd LIII-edge X-ray Absorption Near Edge Spectroscopy (XANES) at the Stanford Synchrotron Radiation Light Source (SSRL Menlo Park, California) and Scanning Electron Microscopy-energy dispersive X-ray analysis (SEM-EDS) at the Winterthur Museum Scientific Research and Analysis Laboratory. To determine if the visual changes in the paints did in fact indicate photo-oxidative degradation and if different chemistries could be observed for the lightened versus darkened regions, synchrotron radiation-micro Fourier Transform InfraRed (SR-μFTIR) spectroscopy, X-ray Fluorescence (SR-μXRF) mapping and micro X-ray Absorption Near Edge Spectroscopy (μXANES) mapping at the Cd LIII-edge of the altered paint cross-sections were carried out at the European synchrotron radiation facility (ESRF, Grenoble, France) beamline ID-21. The goal is to elucidate the discoloration mechanisms observed in the paint using elemental and speciation mapping. The μXANES mapping and SR-FTIR imaging showed a substantial enrichment of CdCO3 in the off-white surface crust of the faded/discolored CdS paint. This suggests that the CdCO3 is present as an insoluble photodegradation product rather than solely a paint filler or starting reagent. Additionally, oxalates and sulfates were found to be concentrated at the alteration surface. 相似文献