全文获取类型
收费全文 | 25171篇 |
免费 | 4359篇 |
国内免费 | 3169篇 |
专业分类
化学 | 12740篇 |
晶体学 | 261篇 |
力学 | 1134篇 |
综合类 | 198篇 |
数学 | 1794篇 |
物理学 | 7095篇 |
无线电 | 9477篇 |
出版年
2024年 | 142篇 |
2023年 | 662篇 |
2022年 | 993篇 |
2021年 | 1067篇 |
2020年 | 1080篇 |
2019年 | 1053篇 |
2018年 | 936篇 |
2017年 | 968篇 |
2016年 | 1166篇 |
2015年 | 1373篇 |
2014年 | 1567篇 |
2013年 | 1942篇 |
2012年 | 2263篇 |
2011年 | 2183篇 |
2010年 | 1652篇 |
2009年 | 1822篇 |
2008年 | 1797篇 |
2007年 | 1617篇 |
2006年 | 1501篇 |
2005年 | 1277篇 |
2004年 | 911篇 |
2003年 | 682篇 |
2002年 | 613篇 |
2001年 | 552篇 |
2000年 | 461篇 |
1999年 | 406篇 |
1998年 | 284篇 |
1997年 | 271篇 |
1996年 | 235篇 |
1995年 | 212篇 |
1994年 | 164篇 |
1993年 | 169篇 |
1992年 | 136篇 |
1991年 | 100篇 |
1990年 | 87篇 |
1989年 | 55篇 |
1988年 | 60篇 |
1987年 | 42篇 |
1986年 | 41篇 |
1985年 | 35篇 |
1984年 | 19篇 |
1983年 | 27篇 |
1982年 | 10篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1975年 | 5篇 |
1965年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
An approach of dynamic mesh adaptation for simulating 3‐dimensional unsteady moving‐immersed‐boundary flows 下载免费PDF全文
In this paper, we present an approach of dynamic mesh adaptation for simulating complex 3‐dimensional incompressible moving‐boundary flows by immersed boundary methods. Tetrahedral meshes are adapted by a hierarchical refining/coarsening algorithm. Regular refinement is accomplished by dividing 1 tetrahedron into 8 subcells, and irregular refinement is only for eliminating the hanging points. Merging the 8 subcells obtained by regular refinement, the mesh is coarsened. With hierarchical refining/coarsening, mesh adaptivity can be achieved by adjusting the mesh only 1 time for each adaptation period. The level difference between 2 neighboring cells never exceeds 1, and the geometrical quality of mesh does not degrade as the level of adaptive mesh increases. A predictor‐corrector scheme is introduced to eliminate the phase lag between adapted mesh and unsteady solution. The error caused by each solution transferring from the old mesh to the new adapted one is small because most of the nodes on the 2 meshes are coincident. An immersed boundary method named local domain‐free discretization is employed to solve the flow equations. Several numerical experiments have been conducted for 3‐dimensional incompressible moving‐boundary flows. By using the present approach, the number of mesh nodes is reduced greatly while the accuracy of solution can be preserved. 相似文献
2.
Jiatian Chen Le Yang Ying Li Qinghua Hou Lanlan Li Peng Jin 《International journal of quantum chemistry》2019,119(16):e25961
Inorganic planar ring-shape molecules with 4n + 2 π electrons are always the focus of experimental synthesis and theoretical research due to their potential aromaticity and stability. In this work, the whole series of five-membered heterocycle monoanions X nY5-n− (X, Y = group 15 elements; n = 1-4) were thoroughly investigated by means of density functional theory calculations. They all have large formation energies and HOMO-LUMO gap energies, suggesting the potential thermodynamic and kinetic stability. Their aromaticities are comparable to that of typical aromatic hydrocarbons. Their thermal stabilities were firmly established by the ab initio molecular dynamics simulations. As most of them are predicted for the first time, their various spectra were simulated for experimental characterization. Furthermore, we demonstrate that these five-membered cyclic anions can be employed as η5-ligand to construct novel all-inorganic metallocenes, which may serve as the building blocks of low-dimensional nanomaterials. 相似文献
3.
本文采用脉冲激光沉积方法在LaAlO3(001)单晶衬底上制备了反钙钛矿GaCMn3薄膜,通过控制制备过程中脉冲激光的能量,研究了不同激光能量条件对GaCMn3薄膜结构与物理性能的影响.分别利用X射线衍射仪、原子力显微镜、超导量子干涉仪和物理性能测试系统,对所制备的薄膜的晶体结构、表面形貌和磁性、电输运性质进行了研究.结果表明,制备的样品均为具有多个晶面取向的反钙钛矿薄膜,且薄膜结构和物性明显随制备激光能量的变化而变化.当激光能量为450mJ时,制备的薄膜多晶面取向性最弱,结晶性和表面形貌最优良.实验所得的薄膜均表现出顺磁-铁磁-反铁磁相转变,然而转变过程比块材较平缓,同时薄膜的电阻率并未表现出块材中的突变特征,我们推测该现象很可能是由衬底的应力及衬底的晶格膨胀对薄膜反常晶格变化的抑制作用造成的. 相似文献
4.
5.
A decision support system for interactive decision making - Part II: analysis and output interpretation 总被引:2,自引:0,他引:2
Liping Fang K.W. Hipel D.M. Kilgour Xiaoyong Peng 《IEEE transactions on systems, man and cybernetics. Part C, Applications and reviews》2003,33(1):56-66
For pt.I see ibid., p.42-55 (2003). The development of a comprehensive decision support system, GMCR II, for the systematic study of real-world interactive decision problems is presented. The companion paper (Part I), discusses how GMCR II elicits, stores, and manages conflict models; here (Part II), the focus is on GMCR IIs analysis and output interpretation subsystems. Specifically, this paper describes the powerful and efficient analysis engine contained in GMCR II, its informative output presentation and interpretation facilities, and a number of follow-up analyses. Furthermore, an illustrative case study is used to demonstrate how GMCR II can be conveniently applied in practice. 相似文献
6.
7.
黑龙江邮政独立运营四年多来,按照“商业化经营、多元化发展”的总体思路,克服重重困难,拓展业务,改善服务,推进改革,加强管理,在认真履行邮政普遍服务义务的同时,顺利实现了扭亏为盈的历史性跨越,并逐步向可持续发展的轨道迈进。但随着社会和企业的不断发展,传统的邮政业务面临巨大挑战。在外部,现代信息技术飞速发展,以函件为代表的各传统业务受到严重冲击;快递、报刊等市场将陆续对外资开放,EMS、邮政报刊发行等业务的市场竞争将更加激烈;今年八月份,国家对邮政储蓄政策进行重大调整,这对储蓄收入占总收入比重超过六成的黑龙江邮政的影… 相似文献
8.
9.
10.
在氢化丁苯共聚物13C-NMR谱脂肪碳部分谱带归属的基础上,根据各谱带的主要来源,推导出六个二单元浓度的计算公式。计算出二单元、一单元的相对含量,各结构单元的数均序列长度、嵌段含量和其它结构参数。加氢前后的1H-和13C-NMR谱的组成计算结果基本一致。初步探讨了作为粘度指数改进剂的氢化丁苯共聚物微观结构与性能的关系,为合成提供了依据。 相似文献