全文获取类型
收费全文 | 649篇 |
免费 | 27篇 |
国内免费 | 60篇 |
专业分类
化学 | 88篇 |
力学 | 486篇 |
综合类 | 10篇 |
数学 | 67篇 |
物理学 | 85篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 4篇 |
2021年 | 18篇 |
2020年 | 20篇 |
2019年 | 21篇 |
2018年 | 14篇 |
2017年 | 21篇 |
2016年 | 24篇 |
2015年 | 29篇 |
2014年 | 15篇 |
2013年 | 29篇 |
2012年 | 39篇 |
2011年 | 24篇 |
2010年 | 30篇 |
2009年 | 39篇 |
2008年 | 38篇 |
2007年 | 29篇 |
2006年 | 42篇 |
2005年 | 39篇 |
2004年 | 35篇 |
2003年 | 22篇 |
2002年 | 19篇 |
2001年 | 20篇 |
2000年 | 17篇 |
1999年 | 19篇 |
1998年 | 15篇 |
1997年 | 16篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有736条查询结果,搜索用时 31 毫秒
641.
考虑地震力方向的倾倒式危岩可靠度分析 总被引:2,自引:2,他引:0
侧向卸荷作用导致高陡边坡发育大量危岩体,危岩体在降雨、地震作用下易发生失稳破坏,判断其失稳的概率对危岩防治具有重要意义.该文以倾倒式危岩体为例,建立了考虑地震力作用方向下最危险方向的物理力学模型,利用函数极值理论建立了最危险地震力作用方向的表达式,结合可靠度理论建立了倾倒式危岩体可靠度指标、失稳概率表达式及判断标准.通过对重庆南川金佛山危岩体案例的分析表明:工况1的最危险地震力作用方向与水平方向的偏转角θ在5°范围内,工况2的最危险地震力作用方向与水平方向的偏转角θ在10°左右;危岩体最危险作用方向不是一个固定角,其值与危岩体形态、裂隙水作用力大小、岩腔深度等有关.当主控结构面裂隙长度较小时,最危险地震力作用方向与水平夹角很小,随主控结构面裂隙长度增大,最危险地震力作用方向与水平夹角显著增大;危岩体失稳概率随主控结构面裂隙长度增加而增大,工况2较工况1增大幅度更明显.该研究成果对危岩的防灾减灾具有重要意义. 相似文献
642.
Let p ∈(0, 1], q ∈(0, ∞] and A be a general expansive matrix on R~n. Let H_A~(p,q )(R~n) be the anisotropic Hardy-Lorentz spaces associated with A defined via the nontangential grand maximal function. In this article, the authors characterize H_A~(p,q )(R~n) in terms of the Lusin-area function, the Littlewood-Paley g-function or the Littlewood-Paley g~*_λ-function via first establishing an anisotropic Fefferman-Stein vector-valued inequality in the Lorentz space L_(p,q)(R~n). All these characterizations are new even for the classical isotropic Hardy-Lorentz spaces on R~n. Moreover, the range of λ in the g~*_λ-function characterization of H_A~(p,q )(R~n) coincides with the best known one in the classical Hardy space H~p(R~n) or in the anisotropic Hardy space H_A~p (R~n). 相似文献
643.
Based on the three-dimensional linearized theory of stability, the stability problem is solved for the multilayer lining of a vertical circular mine opening in rock mass under inelastic conditions. The effect of the geometric and physicomechanical parameters of the lining and rock on the critical contact pressures is evaluated 相似文献
644.
A lot of granitoid rocks occur in Panxi area, SW China, which were formed during Jinningnian-Chengjiangnian, Hercynian-Indosinian and Yenshanian. According to their trace elements geochemical and petrochemical characteristics, they can be divided into calc-alkaline and alkaline granites. The petrogenesis and magma sources of these granitoid rocks are different. The Jinningnian-Chengjiangnian granitoid rocks include Mopanshan granite body, Moshaying granite body and Lugu granite body. The Mopanshan body might be formed by partial melting of the lower crust and due to refusion of basic volcanic rocks. The magma source of the Moshaying and the Lugu bodies might be formed by partial melting of the upper crust. The Hongge-Ailanghe granites belonging to the Hercynian-Indosinian may be products of complex melting from the crust-mantle materials caused by the increase of temperature during rifting stage in the area. The Cida and Taihe alkaline granites belonging to the Hercynian-Indosinian might be derived from 相似文献
645.
Katsutoshi Tamura Masanori Nakamura Sachio Murakami 《Journal of solution chemistry》1997,26(12):1199-1207
Excess molar volumes
of water + acetonitrile, and water + dimethylsulfoxide mixtures were measured at 30°C. Excess thermal expansivity coefficients E were calculated from values of
at 30° and 25°C previously reported.(1,2) The E of polar mixtures are relatively large, several times 10-5 K-1 and as much 10-4 K-1, while those of nonpolar mixtures are at most several times 10-6 K-1. These values are several percent of the total expansivity coefficient of the mixture and significantly affect thermodynamic calculation of the estimation of isothermal compressibilities and isochoric heat capacities from isentropic compressibilities and isobaric heat capacities. 相似文献
646.
Summary A combined cation-exchange separation-spectrophotometric procedure has been worked out for the accurate determination of traces
of copper in silicate rocks. Silicates are opened up with sulfuric and hydrofluoric acids. The residue is taken up into a
0.5 M hydrochloric acid −0.05 M oxalic acid −1% hydrogen peroxide solution and loaded on a strongly acidic cation-exchange
resin column. Polyvalent ions including ferric ions do not adsorb on the column, while copper (II) retains together with divalent
metal ions as well as aluminum (III). Copper (II) can selectively be eluted by a small volume of 0.05 M thiosulfate solution.
This fraction is sufficiently pure to allow a direct spectrophotometric determination of copper with Na-DDTC without the addition
of tartrate and EDTA as masking agents. Quantitative results are quoted for the determination of copper in international standard
rocks of the Geological Survey of Japan (GSJ) and the U.S. Geological Survey (USGS). 相似文献
647.
在间歇反应器中 ,反应温度为 30~ 6 0℃ ,硝酸初始浓度 30~ 5 4 % ,磷矿初始粒径 0 .375~ 1.0 75毫米 ,搅拌强度 4 0 0转 分的条件下研究了硝酸分解磷矿的反应过程机理及宏观动力学。结果表明 ,磷矿分解速率及转化率随着搅拌强度、反应温度、硝酸浓度和颗粒细度的增加而增加 ;氢离子通过液膜的扩散传质是该过程的速率控制步骤。应用固体粒径减小的缩芯模型 ,将上述各影响因素的实验数据回归得到如下的宏观动力学模型 :1- (1-xB) 2 3=8.36 6exp - 6 .198× 10 3RT c1 .31 1AO R- 0 .1 0 91S lnτ活化能Ea=6 .198kJ mol,属液膜扩散传质控制 相似文献
648.
649.
650.
Diffeomorphisms with persistency 总被引:2,自引:0,他引:2
Kazuhiro Sakai 《Proceedings of the American Mathematical Society》1996,124(7):2249-2254
The interior of the set of all diffeomorphisms satisfying Lewowicz's persistency is characterized as the set of all diffeomorphisms satisfying Axiom A and the strong transversality condition.