全文获取类型
收费全文 | 6841篇 |
免费 | 824篇 |
国内免费 | 1518篇 |
专业分类
化学 | 5228篇 |
晶体学 | 169篇 |
力学 | 1356篇 |
综合类 | 77篇 |
数学 | 523篇 |
物理学 | 1830篇 |
出版年
2024年 | 26篇 |
2023年 | 95篇 |
2022年 | 228篇 |
2021年 | 212篇 |
2020年 | 311篇 |
2019年 | 243篇 |
2018年 | 221篇 |
2017年 | 301篇 |
2016年 | 347篇 |
2015年 | 267篇 |
2014年 | 378篇 |
2013年 | 654篇 |
2012年 | 382篇 |
2011年 | 458篇 |
2010年 | 325篇 |
2009年 | 382篇 |
2008年 | 443篇 |
2007年 | 440篇 |
2006年 | 478篇 |
2005年 | 437篇 |
2004年 | 378篇 |
2003年 | 353篇 |
2002年 | 258篇 |
2001年 | 242篇 |
2000年 | 219篇 |
1999年 | 190篇 |
1998年 | 159篇 |
1997年 | 145篇 |
1996年 | 120篇 |
1995年 | 109篇 |
1994年 | 80篇 |
1993年 | 69篇 |
1992年 | 54篇 |
1991年 | 35篇 |
1990年 | 28篇 |
1989年 | 19篇 |
1988年 | 18篇 |
1987年 | 23篇 |
1986年 | 15篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有9183条查询结果,搜索用时 15 毫秒
961.
962.
963.
964.
Karakoti AS Das S Thevuthasan S Seal S 《Angewandte Chemie (International ed. in English)》2011,50(9):1980-1994
Application of inorganic nanoparticles in diagnosis and therapy has become a critical component in the targeted treatment of diseases. The surface modification of inorganic oxides is important for providing diversity in size, shape, solubility, long-term stability, and attachment of selective functional groups. This Minireview describes the role of polyethylene glycol (PEG) in the surface modification of oxides and focuses on their biomedical applications. Such a PEGylation of surfaces provides "stealth" characteristics to nanomaterials otherwise identified as foreign materials by human body. The role of PEG as structure-directing agent in synthesis of oxides is also presented. 相似文献
965.
Tatiana Y. Karogodina Igor G. Dranov Dr. Svetlana V. Sergeeva Dr. Dmitry V. Stass Prof. Dr. Ulrich E. Steiner 《Chemphyschem》2011,12(9):1714-1728
Oxidation of dihydrorhodamine 123 (DHR) to rhodamine 123 (RH) by oxoperoxonitrite (ONOO?), formed through recombination of NO and O2.? radicals resulting from thermal decomposition of 3‐morpholinosydnonimine (SIN‐1) in buffered aerated aqueous solution at pH 7.6, represents a kinetic model system of the reactivity of NO and O2.? in biochemical systems. A magnetic‐field effect (MFE) on the yield of RH detected in this system is explored in the full range of fields between 0 and 18 T. It is found to increase in a nearly linear fashion up to a value of 5.5±1.6 % at 18 T and 23 °C (3.1±0.7 % at 40 °C). A theoretical framework to analyze the MFE in terms of the magnetic‐field‐enhanced recombination rate constant krec of NO and O2.? due to magnetic mixing of T0 and S spin states of the radical pair by the Δg mechanism is developed, including estimation of magnetic properties (g tensor and spin relaxation times) of NO and O2.? in aqueous solution, and calculation of the MFE on krec using the theoretical formalism of Gorelik at al. The factor with which the MFE on krec is translated to the MFE on the yield of ONOO? and RH is derived for various kinetic scenarios representing possible sink channels for NO and O2.?. With reasonable assumptions for the values of some unknown kinetic parameters, the theoretical predictions account well for the observed MFE. 相似文献
966.
967.
A numerical study is reported on the fully developed unsteady laminar fluid flow in microchannel parallel-plates partially filled with a uniform porous medium and partially filled with a clear fluid. The flow is induced by the movement of one of the plates and the pressure gradient. The Brinkman-extended Darcy model is utilized to model the flow in the porous region, while the Stokes equation is used in the clear fluid region. A theoretical analysis is also presented for the fully developed steady flow to find closedform expressions for the interfacial velocity and the velocity and skin frictions at the bounding plates. Numerical computations shows excellent agreement between the closedform solutions for fully developed steady flow and the numerical solution to unsteady flow at large values of time. 相似文献
968.
众所周知Lamb波在复合材料中的传播呈各向异性的特点,经典有限元法模拟这类问题效率不高,所以,本文采用谱有限元法进行研究。先建立了一种新的谱有限板单元,该单元以Gauss-Lobatto-Legendre点作为节点,使质量矩阵是对角矩阵;另外,该单元采用了扩展的位移场,能够较好地模拟板结构的三维特性。然后,对复合材料板结构中Lamb波在对称模式与反对称模式下的传播速度进行了求解,将计算结果与Mindlin板谱单元的结果以及三维弹性理论的结果进行了比较,并讨论了Lamb波在反对称层合板中的传播特点。最后,模拟了Lamb波在含和不含损伤复合材料层合板中的传播,数值结果表明所建立的谱有限板单元可以较好地模拟出Lamb波在复合材料板结构中的传播特性。 相似文献
969.
970.
Imperfect bonding between the constitutive components can greatly affect the properties of the composite structures.An asymptotic analysis of different types of imperfect interfaces arising in the problem of 2D fibrereinforced composite materials are proposed.The performed study is based on the asymptotic reduction of the governing biharmonic problem into two harmonic problems.All solutions are obtained in a closed analytical form.The obtained results can be used for the calculation of pull-out and pushout tests,as well as for the investigation of the fracture of composite materials. 相似文献