全文获取类型
收费全文 | 416篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 290篇 |
晶体学 | 1篇 |
力学 | 9篇 |
数学 | 79篇 |
物理学 | 48篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 17篇 |
2020年 | 14篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 15篇 |
2013年 | 13篇 |
2012年 | 17篇 |
2011年 | 30篇 |
2010年 | 18篇 |
2009年 | 13篇 |
2008年 | 28篇 |
2007年 | 42篇 |
2006年 | 26篇 |
2005年 | 20篇 |
2004年 | 21篇 |
2003年 | 19篇 |
2002年 | 18篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1989年 | 3篇 |
1987年 | 4篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
1906年 | 1篇 |
1904年 | 1篇 |
排序方式: 共有427条查询结果,搜索用时 15 毫秒
81.
Lupo MG Scotognella F Zavelani-Rossi M Lanzani G Manna L Tassone F 《Physical chemistry chemical physics : PCCP》2012,14(20):7420-7426
CdSe/CdS dot/rods nanocrystals show interesting physical properties related to the band-alignment at the hetero-interface, which controls the band-edge electron delocalization over the rods. Here the differential transmission spectra of CdSe/CdS nanorod samples with different core sizes have been measured using excitation resonant to the core transition. The photo bleaching ratio between dot and rod transitions increases with the dot size, indicating a trend towards electron localization. This trend has been further quantified by performing effective mass calculations in which the conduction band misalignment was varied in order to reproduce the observed bleaching feature ratio. The best agreement was found for negligible conduction band misalignment for small dots of around 2.3 nm in diameter, and about -0.1 eV misalignment was estimated for the larger dots, above 3.5 nm in diameter. This shows that the band misalignment might be dependent on the geometry of the system, and we argue that this might be related to different strain developed at the hetero-interface. 相似文献
82.
Fiorentino G Caracuta V Casiello G Longobardi F Sacco A 《Rapid communications in mass spectrometry : RCM》2012,26(3):327-335
The discovery of a storeroom full of barley and other cereals (L.9512) in the proto-historic site of Ebla has provided a unique opportunity to study the centralized storage system of the early city-state from a different perspective. Epigraphic evidence available within the site reveals a complex system of taxation which included gathering grain tributes from satellite sites and redistributing semi-finished products such as flour. In this paper, we intend to explore the possibilities of a combined approach to studying the storage system, based on estimated barley grain volumes and δ(13)C-δ(15)N analyses. This approach is used to distinguish between grain from different harvesting sites and to identify any grain cultivated using special agricultural practices (e.g. manuring or irrigation). The basic assumption for this kind of analysis is that the growth-site conditions, natural or anthropogenic, of harvested cereals are reflected in their grain size and δ(13)C-δ(15)N values. Since the remains found in the storeroom were charred, the first task was to evaluate the effect of carbonization on the δ(13)C-δ(15)N and the size of the grains. Thus, the effect of charring was tested on modern samples of Syrian barley landraces. Once it had been ascertained that fresh grains reduced to charred remains retain their original biometric and isotopic traits, the ancient material was examined. Thirteen groups were identified, each characterized by a specific average volume and specific carbon and nitrogen values. The analysis revealed that what had first appeared to be a homogeneous concentration of grain was in fact an assemblage of barley harvested from different sites. 相似文献
83.
Burke LA Gonella G Heirtzler F Dai HL Jones S Zubieta J Roche AJ 《Chemical communications (Cambridge, England)》2012,48(7):1000-1002
The dimeric self-assembly program of a new, multidentate ligand with cuprous ions overcomes crystal packing forces, which leads to C(i) symmetry in the solid state, to form a no less than partially C(2)-symmetric structure in solution. The resulting tetranitro-substituted dicopper(i) metallocyclophane displays an exceptionally strong second harmonic frequency response (β = (3000 ± 600) × 10(-30) esu for a fundamental at 800 nm). 相似文献
84.
C. Grotta-Ragazzo Coraci Pereira Malta K. Pakdaman 《Journal of Dynamics and Differential Equations》2010,22(2):203-252
We consider the scalar delayed differential equation e[(x)\dot](t)=-x(t) +f(x(t-1)){\epsilon\dot x(t)=-x(t)\,+f(x(t-1))}, where ${\epsilon\,{>}\,0}${\epsilon\,{>}\,0} and f verifies either df/dx > 0 or df/dx < 0 and some other conditions. We present theorems indicating that a generic initial condition with sign changes generates
a solution with a transient time of order exp(c/e){{\rm exp}(c{/}\epsilon)}, for some c > 0. We call it a metastable solution. During this transient a finite time span of the solution looks like that of a periodic
function. It is remarkable that if df/dx > 0 then f must be odd or present some other very special symmetry in order to support metastable solutions, while this condition is
absent in the case df/dx < 0. Explicit e{\epsilon}-asymptotics for the motion of zeroes of a solution and for the transient time regime are presented. 相似文献
85.
86.
Grazia Raciti 《Annali dell'Universita di Ferrara》1989,35(1):99-112
Riassunto In questo lavoro diamo una caratterizzazione aritmetica della differenza prima ΔH(X,−) della funzione di Hilbert di un sottoschema chiuso 0-dimensionaleX diP
3.
Il risultato principale viene applicato per dimostrare che seX è contenuto in una completa intersezione di tipo(a, b, c), a≦b≦c allora ΔH(X, n) è decrescente pern≧a+c−2.
Lavoro svolto con finanziamento MPI. 相似文献
Summary In this paper we give an aritmetical characterization of the first difference ΔH(X,−) of the Hilbert function of a closed 0-dimensional subschemeX ofP 3. The main result is then applied to prove that ifX is contained in a complete intersection of type(a, b, c), a≦b≦c then ΔH(X, n) is decreasing forn≧a+c−2.
Lavoro svolto con finanziamento MPI. 相似文献
87.
L. Finelli N. Lotti A. Munari M. Gazzano V. Malta 《Journal of Polymer Science.Polymer Physics》2004,42(3):553-566
The melting behavior and crystallization kinetics of poly(thiodiethylene adipate) (PSDEA) were investigated with differential scanning calorimetry and hot‐stage optical microscopy. The observed multiple endotherms, commonly displayed by polyesters, were influenced by the crystallization temperature (Tc) and ascribed to melting and recrystallization processes. Linear and nonlinear treatments were applied to estimate the equilibrium melting temperature for PSDEA with the corrected values of the melting temperature. The nonlinear estimation yielded a higher value by about 9 °C. Isothermal crystallization kinetics were analyzed according to Avrami's treatment. Values of Avrami's exponent close to 3 were obtained, independently of Tc, in agreement with a crystallization process originating from predetermined nuclei and characterized by three‐dimensional spherulitic growth. As a matter of fact, space‐filling spherulites were observed by optical microscopy at all Tc's. The rate of crystallization became lower as Tc increased, as usual at a low undercooling, the crystallization process being controlled by nucleation. Moreover, the crystal structure of PSDEA was determined from powder X‐ray diffraction data by full profile fitting. A triclinic unit cell containing two polymer chains arranged parallel to the c axis was found. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 553–566, 2004 相似文献
88.
The IR and Raman spectra of 4-cyclopentene-1,3-dione have been studied. A complete assignment of the observed bands is proposed on the basis of the usual criteria (contours of the IR bands in the vapour phase and depolarization state of the Raman bands). For the planar species the assignment is confirmed by a normal-coordinate calculation. 相似文献
89.
Ercules E.S. Teotonio Hermi F. Brito Hans Viertler Wagner M. Faustino Oscar L. Malta Gilberto F. de S Maria Cludia F.C. Felinto Regina H.A. Santos Marco Cremona 《Polyhedron》2006,25(18):3488-3494
Europium complexes presenting general formulas [Eu(ACIND)3(H2O)2] and [Eu(ACIND)3(TPPO)2] have been synthesized and characterized. In these formulas ACIND is stands for the ligands 2-acetyl-1,3-indandionate (AIND), 2-isovaleryl-1,3-indandionate (ISOVIND) or 2-benzyl-1,3-indandionate (BIND). The [Eu(ISOVIND)3(H2O)(EtOH)] complex was also prepared and its structure determined by single crystal X-ray analysis, showing that this complex crystallize in a monoclinic space group P21/n with the water molecules bridging through the hydrogen bond. The Eu(III) ion is eight-coordinate in a bicapped trigonal prismatic geometry defined by the oxygen donor atoms with a site of symmetry close to C2ν. Isovaleryl groups in the ISOVIND molecules in the structure are disordered over two positions of the europium complex. Carbon atoms in ethanol molecule are disordered by the thermal vibration. Photoluminescence properties of these complexes in solid state were investigated both experimentally and theoretically, suggesting an efficient ligand-to-metal intramolecular energy transfer process. 相似文献
90.
Grazia Zassinovich Roberto Bettella Giovanni Mestroni Nevenka Bresciani-Pahor Silvano Geremia Lucio Randaccio 《Journal of organometallic chemistry》1989,370(1-3):187-202
Some diastereoisomeric pentacoordinate complexes of the type [Ir(COD)-(NNR)I] (COD = cis,cis-1,5-cyclooctadiene; NNR = 2-pyridinal-1-phenylethylimine (PPEI) (I), 2-acetylpyridine-1-phenylethylimine (APPEI) (II)) have been synthesized. The complexes are active and selective catalysts for asymmetric hydrogen transfer from propan-2-ol to prochiral ketones. Optical yields of up to 84% have been obtained in the reduction of t-butyl phenyl ketone. The structure and absolute configuration of complexes I and II were determined by X-ray diffraction. 相似文献