全文获取类型
收费全文 | 658篇 |
免费 | 19篇 |
国内免费 | 5篇 |
专业分类
化学 | 546篇 |
晶体学 | 9篇 |
力学 | 5篇 |
综合类 | 1篇 |
数学 | 12篇 |
物理学 | 109篇 |
出版年
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 15篇 |
2013年 | 22篇 |
2012年 | 30篇 |
2011年 | 28篇 |
2010年 | 20篇 |
2009年 | 20篇 |
2008年 | 31篇 |
2007年 | 38篇 |
2006年 | 47篇 |
2005年 | 50篇 |
2004年 | 44篇 |
2003年 | 37篇 |
2002年 | 34篇 |
2001年 | 3篇 |
2000年 | 15篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 13篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1986年 | 13篇 |
1985年 | 16篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有682条查询结果,搜索用时 46 毫秒
151.
Qifeng Wang Sadaki Samitsu Yoshihisa Fujii Chiaki Yoshikawa Toyohide Miyazaki Hidekuni Banno Izumi Ichinose 《Journal of Polymer Science.Polymer Physics》2015,53(9):615-620
Polymer nanoparticles are readily obtainable by rapidly mixing a dilute polymer solution and a poor solvent. The nanoparticles of poly(vinylphenol), poly(vinylidene fluoride), and emeraldine base polyaniline prepared by nanoprecipitation become sticky when their diameters decrease down to a few tens of nanometers, and such polymer nanoparticles spontaneously assemble into rigid fractal networks of the nanoparticles. By filtering these fibrous nanoparticle networks on a microfiltration membrane, ultrafiltration membranes with a thin free‐standing filter cake layer made of nanoparticles are obtainable. The nanoparticle membranes are robust at least up to the applied pressure of 2 MPa and can separate 99% of 10 nm Au nanoparticles from the aqueous dispersion at the flux of more than 1835 L m?2 h?1 even at very low pressure difference of 0.08 MPa. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 615–620 相似文献
152.
153.
Yoshihisa Morita 《Journal of Dynamics and Differential Equations》1990,2(1):69-115
A study is made of systems of weakly coupled, semilinear, parabolic equations, namely reaction-diffusion systems, subject to the homogeneous Neumann boundary conditions in parametrized nonconvex domains inR
2. It is assumed that the domain approaches a union of two disjoint domains as the parameter varies. Under some conditions the long-time behavior of bounded solutions is discussed and the existence of a finite-dimensional invariant manifold is shown, together with its attractivity. This manifold is represented by a graph of some function defined in a possibly large bounded region of the phase space, and the original system is reduced to an ODE system on it. Since an explicit form of the reduced ODE system is given, its dynamics can be studied in detail, which in turn reveals the global dynamics of the original reaction-diffusion system. One can thereby prove, among other things, the existence of asymptotically stable equilibrium solutions of the original system having large spatial inhomogeneity. The existence and stability of a spatially inhomogeneous periodic solution of large amplitude are also discussed. 相似文献
154.
Osaka I Kondou M Selvapalam N Samal S Kim K Rekharsky MV Inoue Y Arakawa R 《Journal of mass spectrometry : JMS》2006,41(2):202-207
When an intramolecular cavity exists in a molecule, it can trap another chemical species to form a host-guest complex. We examine the formation of such an inclusion complex with cucurbit[n]uril (CBn, n = 6, 7) as the host to trap alkali metal or ammonium ions as the guest, by electrospray ionization mass spectrometry (ESI-MS). The results show that the inclusion complexes are formed between the three-dimensional cylinder of CBn hosts and the guest cations. Selectivity of the complex formation is dependent both on (1) ion-dipole interactions between the cylindrical portal of the CBn hosts and the guest cations and (2) the hydrophobic interactions at the inner cavity of CBn. 相似文献
155.
Harada Y Takeuchi T Kino H Fukushima A Takakura K Hieda K Nakao A Shin S Fukuyama H 《The journal of physical chemistry. A》2006,110(49):13227-13231
The electronic structures of a series of DNA nucleobases and their dinucleotides were investigated by N 1s X-ray absorption, X-ray photoemission, and resonant X-ray emission spectroscopy. Resonant X-ray emission spectra of the guanine base and its dinucleotide indicate that it has a weak structure at the lowest binding energy; at this energy, it isolates from the main valence band and forms the HOMO state. This indicates that the HOMO state is localized in the guanine base, as claimed by valence and core photoemissions and expected from theoretical predictions. In addition, the XAS and XES profiles of the guanine dinucleotide indicate that disruption of the aromatic character of the six-membered ring results in the localization of the pi state at the imine (-N=) site of the guanine base; this may favor charge transfer among stacked guanine bases and further influence the conductivity of DNA. 相似文献
156.
Takahashi M Morimoto H Miyake K Yamashita M Kawai H Sei Y Yamaguchi K 《Chemical communications (Cambridge, England)》2006,(29):3084-3086
Quantitative evaluation of F?rster-type fluorescence resonance energy transfer (FRET) was undertaken by statistical investigations on perylene-cored anthracene dendrimers. 相似文献
157.
Twelve conformations of a chiral donor-acceptor (charge-transfer) dyad and six conformations of its dimer complex were structurally optimized by using the Kohn-Sham density functional theory (BLYP/TZV2P) incorporating a recently developed empirical correction scheme that uses C6/R6 potentials for van der Waals interactions (DFT-D). Subsequent time-dependent DFT calculations with BH-LYP and B3-LYP functionals (with triple-zeta basis set) were performed to obtain theoretical circular dichroism (CD) spectra. The experimental CD spectra obtained independently were properly reproduced by averaging the calculated spectra of individual conformers according to a Boltzmann population derived from single-point SCS-MP2 energies. The optical rotations of the monomer were also calculated by using the same functionals with an aug-cc-pVDZ basis set. Dielectric continuum solvation models (COSMO) applied to correct the relative energies from the isolated molecule calculations resulted in conformer distributions that piled the same or even poorer level of agreement with the experimental CD spectrum. Our results clearly show the advantage of the DFT-D method for the geometry optimization of large systems with donor-acceptor interactions and the TD-DFT/BH-LYP calculations for reproducing the experimental CD spectra. As compared with the calculated optical rotations, the wealthy information embedded in the experimental/calculated CD spectra is requisite for the configurational and/or conformational analyses of relatively large and flexible chiral organic molecules in solution. 相似文献
158.
Sivaguru J Saito H Solomon MR Kaanumalle LS Poon T Jockusch S Adam W Ramamurthy V Inoue Y Turro NJ 《Photochemistry and photobiology》2006,82(1):123-131
On photooxygenation of the optically active Z/E enecarbamates 1 (X = i-Pr) and 2 (X = Me) equipped with the oxazolidinone chiral auxiliary in methylene-blue (MB)-incorporated, alkali-metal (M = Li, Na, K, Cs, Rb), exchanged Y-type zeolites (MY-MB), oxidative cleavage of the alkenyl functionality releases the enantiomerically enriched methyldesoxybenzoin (MDB) product. The extent (%ee) and/or the sense (R or S) of the stereoselectivity in the formation of the MDB product depends on the choice of the alkyl substiuent (i-Pr or Me) at the C-4 position of the oxazolidinone chiral auxiliary, the Z/E configuration of the alkene functionality in the enecarbamates, and the type of alkali metal in the zeolite. Most significantly-the highlight of this study-is the reversed sense (R or S) in the stereoselection when the photooxygenation is run in CDCl3 solution versus inside the MY-MB zeolite. As a mechanistic rationale for this novel stereochemical behavior, we propose the combined action of spatial confinement and metal-ion coordination (assessed by density-functional calculations) of the substrate within the zeolite supercage, both of which greatly reduce the freedom of the substrate and entropically manipulate the stereochemical outcome. 相似文献
159.
Rekharsky MV Yamamura H Kawai M Osaka I Arakawa R Sato A Ko YH Selvapalam N Kim K Inoue Y 《Organic letters》2006,8(5):815-818
[STRUCTURE: SEE TEXT] A unique ternary 1:1:1 cucurbit[6]uril (CB[6])-cyclodextrin (CD)-dihexylammonium (DHA) complex was designed and noncovalently synthesized in stepwise fashion: first, CB[6] interacts strongly with DHA to form a 1:1 complex; second, addition of CD into the solution of the 1:1 complex leads to the exclusive formation of the 1:1:1 ternary complex. The ternary complex was characterized by various experimental techniques including ITC, NMR, and ESI-MS. 相似文献
160.
[reaction: see text] Supramolecular chiral recognition based on two-point host-guest interactions coupled with the different host's conformational response using the enantiopure bischlorin hosts and different antipodal amine guests is reported. The bulkiness at the guest's stereogenic center controls the chiral recognition properties resulting in switching of the enantioselectivity. 相似文献