全文获取类型
收费全文 | 5955篇 |
免费 | 630篇 |
国内免费 | 444篇 |
专业分类
化学 | 1596篇 |
晶体学 | 56篇 |
力学 | 211篇 |
综合类 | 142篇 |
数学 | 2498篇 |
物理学 | 2526篇 |
出版年
2024年 | 15篇 |
2023年 | 49篇 |
2022年 | 100篇 |
2021年 | 117篇 |
2020年 | 125篇 |
2019年 | 145篇 |
2018年 | 150篇 |
2017年 | 179篇 |
2016年 | 214篇 |
2015年 | 164篇 |
2014年 | 344篇 |
2013年 | 448篇 |
2012年 | 324篇 |
2011年 | 368篇 |
2010年 | 307篇 |
2009年 | 373篇 |
2008年 | 427篇 |
2007年 | 421篇 |
2006年 | 347篇 |
2005年 | 299篇 |
2004年 | 276篇 |
2003年 | 280篇 |
2002年 | 221篇 |
2001年 | 179篇 |
2000年 | 175篇 |
1999年 | 149篇 |
1998年 | 132篇 |
1997年 | 131篇 |
1996年 | 123篇 |
1995年 | 79篇 |
1994年 | 55篇 |
1993年 | 47篇 |
1992年 | 39篇 |
1991年 | 31篇 |
1990年 | 30篇 |
1989年 | 15篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 20篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 22篇 |
1981年 | 9篇 |
1980年 | 3篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有7029条查询结果,搜索用时 15 毫秒
81.
82.
Xianwen Xie 《Journal of Dynamics and Differential Equations》1991,3(4):515-540
We study slowly oscillating periodic solutions of delay equations with small parameters. When the nonlinearity has finite and nonzero limits at infinities, the appearance of these solutions and their periods can be found though asymptotic analysis. Under further natural assumptions on the nonlinearity, we prove that slowly oscillating periodic solutions are unique and asymptotically stable when parameters are sufficiently small. 相似文献
83.
在实施井下钻孔水压致裂地应力测量的同时,评价岩层阻水性能,确定导升带高度,做到一孔多用。测试区实际观测表明,泥岩、粉砂岩、中砂岩、灰岩阻水性能由大到小,导升高度则由小变大,平均导升高度约32m; 地应力测量表明,该测试区原始地应力状态为SH>Sv>Sh,最大水平主应力方向NE至NEE。突水临界指数评价表明,-550m水平采煤工作面掘进时突水的可能性较大,应当采取防范措施。 相似文献
84.
A Sedimentological Approach to Upscaling 总被引:1,自引:0,他引:1
Optimised upscaling in reservoir simulations requires the construction of realistic petrophysical properties that are representative of the heterogeneity in the sedimentary deposits. Reservoir heterogeneities are controlled by the arrangement of various hierarchies of sedimentary facies and their internal bounding surfaces. The conventional sedimentological approach to reservoir upscaling involves subdivision and ranking of various hierarchies of architectural units and associated bounding surfaces of the reservoir sequence according to their geological significance. This global upscaling approach produces realistic scaled up models that retain both the structural and non-structural heterogeneities of the original sedimentological models. Analyses of sedimentary sequences from various depositional environments indicate that the fractional Levy model can adequately describe the heterogeneity and scaling characteristics of individual genetic sediment sequences in the clastic sedimentary system without further subdividing and ranking of the heterogeneous sequences. The heterogeneous nature of each sedimentary system can be quantified by the Levy index parameter, whereas the maximum upscaling magnitude (or upscaling index) for a particular sequence can be determined from the Levy width parameter plot. Depositional modelling mimics the sedimentary processes in a range of scales and honours hierarchies of sedimentary facies and their bounding surfaces. It can be used effectively for upgridding and upscaling in accordance with the stratigraphic framework and sedimentological models. Both the fractional Levy model and the depositional modelling provide quantitative alternatives to the conventional global sedimentological upscaling approach. 相似文献
85.
In the United States, the NATO Reference Mobility Model (NRMM) has been used for evaluating military ground vehicle mobility and the Vehicle Cone Index (VCI) has been selected as a mobility metric. VCI represents the minimum soil strength required for a vehicle to consistently make a specific number of passes, usually one or fifty passes. In the United Kingdom, the Mean Maximum Pressure (MMP) has been adopted as a metric for assessing military vehicle cross-country mobility. MMP is the mean value of the maxima occurring under all the wheel stations of a vehicle. Both VCI and MMP are empirically based. This paper presents a review of the basis upon which VCI and MMP were developed, as well as their applications to evaluating vehicle mobility in practice. With the progress in terramechanics and in modelling and simulation techniques in recent years, there is a growing desire to develop physics-based mobility metrics for next generation vehicle mobility models. Based on the review, criteria for selecting physics-based mobility metrics are proposed. Following these criteria, metrics for characterizing military vehicle traction limits and traversability on a given operating area are recommended. 相似文献
87.
We consider a pricing and advertising dynamic-optimization problem where the goodwill dynamics evolve à la Nerlove–Arrow. The firm maximizes its profit over a finite-planning horizon corresponding to the product’s lifespan, and it turns out that the Hamiltonian is non-concave. We show the existence and uniqueness of an optimal solution under some mild conditions. 相似文献
88.
Optical and static dielectric studies on a terminally fluorinated liquid crystalline compound have been carried out. Measurements of temperature variation of refractive indices of the compound are done by using thin prism method. A four-parameter model is validated by fitting the experimentally measured values of refractive indices, birefringence and average refractive indices of the compound with the theoretical ones. Refractive index and density data are utilized for determination of orientational order parameter. The temperature variation of dielectric permittivities of the compound are measured by a LCR meter. 相似文献
89.
Mei-Feng Dai Ting-Ting Ju Yong-Bo Hou Fang Huang Dong-Lei Tang Wei-Yi Su 《理论物理通讯》2020,72(5):55602-112
The weighted self-similar network is introduced in an iterative way. In order to understand the topological properties of the self-similar network, we have done a lot of research in this field.Firstly, according to the symmetry feature of the self-similar network, we deduce the recursive relationship of its eigenvalues at two successive generations of the transition-weighted matrix.Then, we obtain eigenvalues of the Laplacian matrix from these two successive generations.Finally, we calculate an accurate expression for the eigentime identity and Kirchhoff index from the spectrum of the Laplacian matrix. 相似文献
90.
Surasak Seesukphronrarak Shinichi Kawasaki Shigeki Kuwata Toshikazu Takata 《Journal of polymer science. Part A, Polymer chemistry》2019,57(24):2602-2605
Two novel 9,9‐difunctionalized fluorene‐type monomers, 9,9‐bis(4‐hydroxyphenyl‐ and 4‐aminophenyl)‐2,3:6,7‐dibenzofluorenes, are synthesized by the reaction of dibenzenzofluorenone with phenol and aniline. These monomers are used for the preparation of polyester and polyimide as the typical polymers to evaluate the property change such as thermal stability caused by the benzene rings fused to the fluorene skeleton with keeping good solubility, in comparison with the polymers derived from simple fluorenone. In fact, these two new polymers have the fairly enhanced thermal stability and refractive index value along with satisfactory solubility in organic solvents, enough to emphasize the fusion effect. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2602–2605 相似文献