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排序方式: 共有309条查询结果,搜索用时 93 毫秒
61.
Min Tu Helge Reinsch Sabina Rodríguez‐Hermida Rhea Verbeke Timothe Stassin Werner Egger Marcel Dickmann Bjorn Dieu Johan Hofkens Ivo F. J. Vankelecom Norbert Stock Rob Ameloot 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2445-2449
Metal–organic frameworks (MOFs) enable the design of host–guest systems with specific properties. In this work, we show how the confinement of anthracene in a well‐chosen MOF host leads to reversible yellow‐to‐purple photoswitching of the fluorescence emission. This behavior has not been observed before for anthracene, either in pure form or adsorbed in other porous hosts. The photoresponse of the host–guest system is caused by the photodimerization of anthracene, which is greatly facilitated by the pore geometry, connectivity, and volume as well as the structural flexibility of the MOF host. The photoswitching behavior was used to fabricate photopatternable and erasable surfaces that, in combination with data encryption and decryption, hold promise in product authentication and secure communication applications. 相似文献
62.
Aim
To study the effect of long-term glucose feeding on aortic lipid composition by using the time of flight-secondary ion mass spectrometry (TOF-SIMS).Method
Rats were divided into two groups, drinking water with or without 10% glucose from birth to 6 months of age. The aortic wall was dissected out, high-pressure frozen, freeze-fractured, freeze-dried and analyzed by TOF-SIMS using a Bismuth cluster ion source. Surface spectra were taken from standardized regions of the vessel wall.Results
Different peaks, such as cholesterol, fatty acids (FAs) and diacylglycerols (DAGs), were identified by the principal component analysis as carries of variance between two groups. These peaks were then compared by conventional t-test. Our data showed that the intensity of cholesterol, but not FAs and DAGs, was significantly decreased in the glucose-drinking rat. Moreover, the long-term glucose intake changed ratios between different FAs in the aorta.Conclusion
The long-term glucose intake led to decreased cholesterol intensity in the aortic wall and this effect was revealed through a global analytical approach with objective selection of significant variables. 相似文献63.
Square‐Planar Ruthenium(II) Complexes: Control of Spin State by Pincer Ligand Functionalization 下载免费PDF全文
Dr. Bjorn Askevold Dr. Marat M. Khusniyarov Dr. Wolfgang Kroener Dr. Klaus Gieb Prof. Paul Müller Dr. Eberhardt Herdtweck Dr. Frank W. Heinemann Dr. Martin Diefenbach Prof. Max C. Holthausen Veacheslav Vieru Prof. Liviu F. Chibotaru Prof. Sven Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):579-589
Functionalization of the PNP pincer ligand backbone allows for a comparison of the dialkyl amido, vinyl alkyl amido, and divinyl amido ruthenium(II) pincer complex series [RuCl{N(CH2CH2PtBu2)2}], [RuCl{N(CHCHPtBu2)(CH2CH2PtBu2)}], and [RuCl{N(CHCHPtBu2)2}], in which the ruthenium(II) ions are in the extremely rare square‐planar coordination geometry. Whereas the dialkylamido complex adopts an electronic singlet (S=0) ground state and energetically low‐lying triplet (S=1) state, the vinyl alkyl amido and the divinyl amido complexes exhibit unusual triplet (S=1) ground states as confirmed by experimental and computational examination. However, essentially non‐magnetic ground states arise for the two intermediate‐spin complexes owing to unusually large zero‐field splitting (D>+200 cm?1). The change in ground state electronic configuration is attributed to tailored pincer ligand‐to‐metal π‐donation within the PNP ligand series. 相似文献
64.
Design of diffractive axicons for partially coherent light 总被引:2,自引:0,他引:2
We propose a novel method of designing diffractive axicons for use in spatially partially coherent illumination. The design procedure is based on the results obtained by the stationary-phase method. The technique leads to a coherence-dependent differential equation with appropriate boundary conditions for the axicon phase function. We demonstrate the method with annular-aperture axicons generating extended focal line segments of uniform on-axis intensity. 相似文献
65.
Variability of UV irradiance in Europe 总被引:1,自引:1,他引:0
Seckmeyer G Pissulla D Glandorf M Henriques D Johnsen B Webb A Siani AM Bais A Kjeldstad B Brogniez C Lenoble J Gardiner B Kirsch P Koskela T Kaurola J Uhlmann B Slaper H den Outer P Janouch M Werle P Gröbner J Mayer B de la Casiniere A Simic S Carvalho F 《Photochemistry and photobiology》2008,84(1):172-179
66.
Nilsen LT Hannevik M Aalerud TN Johnsen B Friberg EG Veierød MB 《Photochemistry and photobiology》2008,84(5):1100-1108
Abstract Indoor tanning increases skin cancer risk, but the importance of different parts of the UV spectrum is unclear. We assessed irradiance of tanning devices in Norway for the period 1983-2005. Since 1983, all tanning models needed approval before being sold or used. UV Type 3 limits were valid from late 1992 (<0.15 W m(-2) for CIE-weighted, i.e. erythemally weighted, short and long wave irradiances). We analyzed data from 90% of the approved tanning models (n = 446 models) and two large inspection surveys in 1998/1999 and 2003 (n = 1341 tanning devices). Mean CIE-weighted short wave irradiance of approved models increased from 0.050 W m(-2) (95% confidence interval [CI] 0.045-0.055) in 1983-1992 to 0.101 W m(-2) (95% CI 0.098-0.105) in 1993-2005, and mean long wave from 0.091 W m(-2) (95% CI 0.088-0.095) to 0.112 W m(-2) (95% CI 0.109-0.115), respectively. Inspection surveys revealed short wave irradiances much higher than that approved. In 1998-1999, only 28% (293/1034) of the devices were equipped with correct sunlamps and only 1 out of 130 inspected establishments fulfilled all requirements. In 2003, corresponding numbers were 59% (180/307) of devices and 2 out of 52 establishments. Mean short and long wave irradiances of the inspected tanning devices in 2003 were 1.5 and 3.5 times, respectively, higher than the irradiance of natural summer sun in Oslo. In conclusion, the short wave irradiance has increased in indoor tanning devices in Norway over the last 20 years. Due to the high long wave irradiance throughout this period, the percentage of short wave irradiance was much lower than for natural sun. 相似文献
67.
The correlation of the recognition properties of a molecularly imprinted polymer (MIP) with the recognition events in pre-polymerisation mixtures is of central importance to our understanding of the molecular imprinting technique. Using the NSAID naproxen as a model template, we have applied parallel theoretical (molecular dynamics) and practical ((1)H-NMR, X-ray crystallography, HPLC, radioligand binding) methods to examine the nature of template-functional monomer complexation. An effective imprint is achieved, despite the presence of only one site on the template which provides for the formation of effective electrostatic interactions with the functional monomer used, 4-vinylpyridine. This is attributed to the creation of a well-defined receptor site for the acidic terminus of the molecule and complementary van der Waals interactions, as described in preliminary simulations of the pre-polymerisation system, and as confirmed for the resultant MIP by HPLC data. Qualitative agreement is also observed between simulation and proton NMR data examining monomer self-association in the presence and absence of the template. On the basis of the data obtained, the role of a cross-linker appears to be more significant for this system than previously anticipated. 相似文献
68.
Adriaens A Dowsett M Leyssens K Van Gasse B 《Analytical and bioanalytical chemistry》2007,387(3):861-868
Immersion of corroded copper artefacts in dilute sodium sesquicarbonate solution is a well-recognized stabilization technique—especially
in the conservation of objects recovered from marine environments and therefore saturated with chlorides. Here we describe
three linked experiments performed to investigate a variation on this treatment, involving the application of a low potential
to the artefact in order to drive the chloride extraction process. This includes a new spectroelectrochemical approach which
allows 2-D pseudorandom X-ray reflection diffraction patterns to be obtained without interrupting the reaction in solution.
Experiments were carried out on synthetically produced chloride layers on copper (nantokite and atacamite). We show that a
thick chloride layer is, in general, replaced by a thin cuprite layer through a mechanism which involves detachment of the
chloride crystallites from the surface prior to dissolution. 相似文献
69.
70.
Howell GP Fletcher SP Geurts K ter Horst B Feringa BL 《Journal of the American Chemical Society》2006,128(46):14977-14985
Herein, we report efficient acyclic stereocontrol in tandem 1,4-addition-aldol reactions triggered by catalytic asymmetric organometallic addition. Grignard reagents add to alpha,beta-unsaturated thioesters in a 1,4-fashion and the resulting magnesium enolates are trapped with aromatic or aliphatic aldehydes. The process provides a range of tandem products bearing three contiguous stereocenters with excellent control of relative and absolute stereochemistry. The various diastereomeric products have been fully characterized using single-crystal X-ray analysis and the origins of stereocontrol in this tandem protocol are discussed. The versatility and efficiency of this methodology are demonstrated in the first catalytic asymmetric synthesis of (-)-phaseolinic acid with 54% overall yield via a short and concise route. 相似文献