全文获取类型

收费全文 |
14528篇 |

免费 |
1207篇 |

国内免费 |
1658篇 |

专业分类

化学 |
3292篇 |

晶体学 |
52篇 |

力学 |
1196篇 |

综合类 |
281篇 |

数学 |
10690篇 |

物理学 |
1882篇 |

出版年

2024年 |
26篇 |

2023年 |
135篇 |

2022年 |
218篇 |

2021年 |
295篇 |

2020年 |
328篇 |

2019年 |
362篇 |

2018年 |
349篇 |

2017年 |
422篇 |

2016年 |
472篇 |

2015年 |
333篇 |

2014年 |
646篇 |

2013年 |
1071篇 |

2012年 |
642篇 |

2011年 |
772篇 |

2010年 |
699篇 |

2009年 |
898篇 |

2008年 |
970篇 |

2007年 |
1019篇 |

2006年 |
901篇 |

2005年 |
771篇 |

2004年 |
728篇 |

2003年 |
681篇 |

2002年 |
645篇 |

2001年 |
541篇 |

2000年 |
542篇 |

1999年 |
414篇 |

1998年 |
416篇 |

1997年 |
374篇 |

1996年 |
299篇 |

1995年 |
235篇 |

1994年 |
190篇 |

1993年 |
156篇 |

1992年 |
126篇 |

1991年 |
115篇 |

1990年 |
87篇 |

1989年 |
48篇 |

1988年 |
54篇 |

1987年 |
58篇 |

1986年 |
41篇 |

1985年 |
49篇 |

1984年 |
48篇 |

1983年 |
39篇 |

1982年 |
29篇 |

1981年 |
34篇 |

1980年 |
32篇 |

1979年 |
28篇 |

1978年 |
23篇 |

1977年 |
7篇 |

1976年 |
12篇 |

1959年 |
3篇 |

**排序方式：**共有10000条查询结果，搜索用时 31 毫秒

1.

We consider the plane-strain buckling of a cylindrical shellof arbitrary thickness which is made of a Varga material andis subjected to an external hydrostatic pressure on its outersurface. The WKB method is used to solve the eigenvalue problemthat results from the linear bifurcation analysis. We show thatthe circular cross-section buckles into a non-circular shapeat a value of µ

_{1}which depends on*A*_{1}/*A*_{2}and a mode number,where*A*_{1}and*A*_{2}are the undeformed inner and outer radii, andµ_{1}is the ratio of the deformed inner radius to*A*_{1}. Inthe large mode number limit, we find that the dependence ofµ_{1}on*A*_{1}/*A*_{2}has a boundary layer structure: it is constantover almost the entire region of 0 <*A*_{1}/*A*_{2}< 1 and decreasessharply from this constant value to unity as*A*_{1}/*A*_{2}tends tounity. Our asymptotic results for*A*_{1}– 1 = O(1) and*A*_{1}– 1 = O(1/*n*) are shown to agree with the numerical resultsobtained by using the compound matrix method. 相似文献2.

We study initial boundary value problems for linear scalar evolutionpartial differential equations, with spatial derivatives of

*arbitrary order*, posed on the domain {*t*> 0, 0 <*x*<*L*}. We show that the solution can be expressed as an integralin the complex*k*-plane. This integral is defined in terms ofan*x*-transform of the initial condition and a*t*-transform ofthe boundary conditions. The derivation of this integral representationrelies on the analysis of the*global relation*, which is an algebraicrelation defined in the complex*k*-plane coupling all boundaryvalues of the solution. For particular cases, such as the case of periodic boundaryconditions, or the case of boundary value problems for*even*-orderPDEs, it is possible to obtain directly from the global relationan alternative representation for the solution, in the formof an infinite series. We stress, however, that there existinitial boundary value problems for which the only representationis an integral which*cannot*be written as an infinite series.An example of such a problem is provided by the linearized versionof the KdV equation. Similarly, in general the solution of odd-orderlinear initial boundary value problems on a finite interval*cannot*be expressed in terms of an infinite series. 相似文献3.

In an earlier paper on a malignant cell invasion model (Marchant

*et al*.,*SIAM J. Appl. Math*,**60**, 2000) we introduced a novelform of discontinuous travelling wave solution. These solutionscould be studied easily by combining behaviour within a phaseplane with the Rankine–Hugoniot shock conditions, whichdescribe properties (such as the ratio of the jump discontinuitiesto the speed of propagation) that solutions may possess. Theseresults were new for several reasons. The shock conditions relateto hyperbolic equations (which the model is) but were appliedin a travelling wave ordinary differential equation phase planeusing techniques that usually apply to parabolic reaction–diffusionsystems. In addition the solutions possess singular behaviournear several points in the phase plane but in spite of thisthere exists a robust and stable family of physically interestingsolutions. In this paper we discuss two previously studied models, oneof detonation theory and one of angiogenesis. We show that eachof these models also possesses a family of discontinuous travellingwave solutions which was not previously discovered. Of particularinterest is the solution which has a blunt interface at thefront of the invading profile. In all three models it is thissolution that is seen to stably evolve from physically relevantinitial data, and for physically relevant parameter values. This work confirms the robustness of these novel travellingwave solutions and their applicability to a wider range of mathematicalmodelling situations. 相似文献4.

Brenda J. Latka 《Journal of Graph Theory》2003,42(3):165-192

A finite tournament

*T*is*tight*if the class of finite tournaments omitting*T*is well‐quasi‐ordered. We show here that a certain tournament*N*_{5}on five vertices is tight. This is one of the main steps in an exact classification of the tight tournaments, as explained in [10]; the third and final step is carried out in [11]. The proof involves an encoding of the indecomposable tournaments omitting*N*_{5}by a finite alphabet, followed by an application of Kruskal's Tree Theorem. This problem arises in model theory and in computational complexity in a more general form, which remains open: the problem is to give an effective criterion for a finite set {*T*_{1},…,*T*} of finite tournaments to be tight in the sense that the class of all finite tournaments omitting each of_{k}*T*_{1},…,*T*is well‐quasi‐ordered. © 2003 Wiley Periodicals, Inc. J Graph Theory 42: 165–192, 2003 相似文献_{k}5.

B. Kowalczyk 《Journal of Thermal Analysis and Calorimetry》2000,60(1):163-166

The comparison of thermal and calorimetric properties of metal derivatives of 6-aminopicolinic acid (APH) is presented. The
salts and complexes of APH with Cr(III), Cd(II), Cu(II), Ni(II), Pb(II), Co(II)and Ag(I) have been studied by TG-DTA and DSC
methods up to 1200°C in a nitrogen atmosphere. Decomposition processes are proposed. The decarboxylation, deamination and
carbonation of the organic fragments of molecules take place. The compounds decompose to metal or to metal oxides. The values
of the transition enthalpy were determinated.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献

6.

Coexistence Relations, Preparation and Properties of Ternary Compounds in the System Cu/Mo/O The phase diagram of the ternary system Cu/Mo/O is presented at 773 K. The compounds CuMoO

_{4}, Cu_{3}Mo_{2}O_{9}, Cu_{4}Mo_{5}O_{17}, Cu_{6}Mo_{5}O_{18}, Cu_{4–x}Mo_{3}O_{12}, and Cu_{x}MoO_{3}are found to be thermodynamical stable. The homogeneity range of Cu_{4–x}Mo_{3}O_{12}runs to x = 0.1–0.2. Single crystals of CuMoO_{4}and Cu_{3}Mo_{2}O_{9}were grown by chemical transport reactions with TeCl_{4}, Cl_{2}, HCl, and Br_{2}as transport agent. The results were compared with thermochemical calculations. The decomposition of CuMoO_{4}and Cu_{3}Mo_{2}O_{9}was investigated with thermal analysis and decompositon pressure measurements. 相似文献7.

On the basis of copper sulphate pentahydrate thermal dissociation, for analyzed reactions I to IV, 6 thermokinetic equations was discussed. Arrhenius law parameters were determined and the isokinetic effect (IE) and Kissinger law appearing was analyzed. It was found that only dependence resulting from isokinetic effect, in the form

*k*_{m}=*q*/*T*_{m}, relates to the suitable thermokinetic Eq. (2) and Kissinger law in modified form (14). The confirmation was made that the possibility of determining the averaged activation energy from thermokinetic equations using suitable correction coefficients exists.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献8.

Quasi-isothermal-isobaric analysis was applied as a main method for investigation of thermal decomposition of borates. The
structural mechanism of the dehydration and dehydroxylation of selected borates is considered. It has been found that they
consist of two independent stages: formation of gaseous water molecules localized into the structural framework and their
release. The internal pressure of gaseous water molecules is the factor influencing the course of these processes. The strengths
of the chemical bonds of the components and the freedom of their displacement also determine thermal stability of hydrated
borates.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献

9.

Naumov P. Jordanovska V. Boyanov B. Jovanovski G. 《Journal of Thermal Analysis and Calorimetry》2001,66(2):469-477

The complexes [M(HIm)

_{4}(H_{2}O)_{2}](sac)_{2}(*M*=Co, Ni) and [Cd(HIm)_{2}(sac)_{2}]_{2}with saccharin (sac) and imidazole (HIm) were synthesized and their thermal (TG, DTG and DTA) behaviour in the interval from room temperature up to 1000°C in a static air atmosphere was investigated. Irrespectively of whether the deprotonated saccharinato residues are present as ligands or ions or both as ligands and ions, the anhydrous complexes regularly decompose in two stages. The thermal data of 16 saccharinato complexes (including the title compounds) were correlated with the respective structural data. The general thermal stability order of the saccharinato complexes can be represented as: Pb(II)<Zn(II)<Co(II)Ni(II)<Cd(II) (the stability of the Cu saccharinates depends on the particular compound) and is dictated by several structural factors, e.g. metal ionic radii, participation of the water in the coordination sphere of the metal and other structural characteristics. This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献10.

《Arabian Journal of Chemistry》2022,15(12):104329

To reduce the amount of hazardous chemical bottle waste in the environment, we report the optimization research of silica extraction in chemical bottle waste into silica gel. Alkali fusion and sol–gel process were utilised to prepare silica gel effectively. The alkali fusion process was carried out by adding sodium hydroxide to produce sodium silicate. Afterwards, silica gel was prepared by the sol–gel method using hydrochloric acid. Box-Behnken Design (BBD) was applied to Optimisation factors the poptimiseactors affecting the silica recovery. The factors that optimised mass ratio, particle size, and temperature. The optimum recovery of silica gel was obtained by SiO

_{2}: NaOH mass ratio of 1:3, the particle size of 63–74 µm, and a temperature of 800 °C. The purity of silica gel optimum is 63.74% characterised using X-ray fluorescence. The structure of silica gel is the appearance of amorphous peaks at 2θ 20-30° characterised using an x-ray diffractogram. The silica gel surface was characterises using scanning electron microscopy-energy dispersive x-ray. It showed an irregular surface and characteristic showed that silica gel had a radius of 15.74 nm and a specific surface area of 297.08 m^{2}. 相似文献