全文获取类型
收费全文 | 68334篇 |
免费 | 13754篇 |
国内免费 | 22349篇 |
专业分类
化学 | 49860篇 |
晶体学 | 2757篇 |
力学 | 5196篇 |
综合类 | 2341篇 |
数学 | 11064篇 |
物理学 | 33219篇 |
出版年
2024年 | 177篇 |
2023年 | 807篇 |
2022年 | 2489篇 |
2021年 | 2466篇 |
2020年 | 2525篇 |
2019年 | 2460篇 |
2018年 | 2310篇 |
2017年 | 3187篇 |
2016年 | 2577篇 |
2015年 | 3586篇 |
2014年 | 4341篇 |
2013年 | 5549篇 |
2012年 | 5852篇 |
2011年 | 6285篇 |
2010年 | 5848篇 |
2009年 | 6163篇 |
2008年 | 6729篇 |
2007年 | 6025篇 |
2006年 | 5937篇 |
2005年 | 4917篇 |
2004年 | 3763篇 |
2003年 | 2743篇 |
2002年 | 2656篇 |
2001年 | 2696篇 |
2000年 | 2730篇 |
1999年 | 1700篇 |
1998年 | 920篇 |
1997年 | 761篇 |
1996年 | 694篇 |
1995年 | 656篇 |
1994年 | 640篇 |
1993年 | 610篇 |
1992年 | 593篇 |
1991年 | 394篇 |
1990年 | 357篇 |
1989年 | 358篇 |
1988年 | 325篇 |
1987年 | 263篇 |
1986年 | 242篇 |
1985年 | 180篇 |
1984年 | 164篇 |
1983年 | 150篇 |
1982年 | 109篇 |
1981年 | 87篇 |
1980年 | 78篇 |
1979年 | 93篇 |
1978年 | 26篇 |
1977年 | 23篇 |
1965年 | 39篇 |
1959年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
11.
12.
An approach of dynamic mesh adaptation for simulating 3‐dimensional unsteady moving‐immersed‐boundary flows
下载免费PDF全文
![点击此处可从《国际流体数值方法杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
13.
Jie Lu Ju-Kang Wu Yao Jiang Dr. Peng Tan Lin Zhang Yu Lei Prof. Xiao-Qin Liu Prof. Lin-Bing Sun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(16):6490-6496
Hierarchically porous metal–organic frameworks (HP-MOFs) are promising in various applications. Most reported HP-MOFs are prepared based on the generation of mesopores in microporous frameworks, and the formed mesopores are connected by microporous channels, limiting the accessibility of mesopores for bulky molecules. A hierarchical structure is formed by constructing microporous MOFs in uninterrupted mesoporous tunnels. Using the confined space in as-prepared mesoporous silica, highly dispersed metal precursors for MOFs are coated on the internal surface of mesoporous tunnels. Ligand vapor-induced crystallization is employed to enable quantitative formation of MOFs in situ, in which sublimated ligands diffuse into mesoporous tunnels and react with metal precursors. The obtained hierarchically porous composites exhibit record-high adsorption capacity for the bulky molecule trypsin. The thermal and storage stability of trypsin is improved upon immobilization on the composites. 相似文献
14.
15.
16.
采用水热法制备花状Bi2 WO6,并利用超声分散法制备了Cu2 O/TiO2-Bi2 WO6复合光催化剂,通过FESEM、XRD、XPS、FI-IR、UV-vis DRS和PL对光催化剂进行了分析和表征.表征结果证明:花状Bi2 WO6表面负载着碎片状的TiO2和立方体Cu2 O形成Cu2 O/TiO2-Bi2 WO6复合光催化剂;以短链脂肪酸(SCFAs)为牺牲剂,考察复合光催化剂的光催化产生氢气和烷烃的性能.实验结果表明:Cu2 O/TiO2-Bi2 WO6复合光催化剂以乙酸为牺牲剂,主要产氢气和甲烷,降解率高达91.82;;以丙酸为牺牲剂,产物主要是乙烷和丁烷,降解率高达90.70;;以丁酸为牺牲剂,除了氢气,甲烷,乙烷,丙烷,丁烷外,气体产物还含有一定量的戊烷,其降解率高达91.50;.结合反应液中间产物的成分进行检测,由此推断出光催化反应的可能机理. 相似文献
17.
Lithium-sulfur batteries (LSBs) with high energy density and low cost have been recognized as one of the most promising next-generation energy storage systems. Although it has taken decades of development, the practical application of LSBs has been hindered by several inherent obstacles, particularly the severe shuttle effect and sluggish reaction kinetics in the sulfur cathode. Various strategies have been proposed to address these problems via rational design of electrode materials and configurations. Freestanding sulfur cathode could be a promising strategy to improve the sulfur mass loading at the cathode level and energy density of LSBs. This minireview will briefly summary the recent advances in freestanding cathodes for LSBs. The advantages and disadvantages of various freestanding cathodes are discussed and the prospects for the development of flexible cathodes are envisioned. 相似文献
18.
Hierarchical motion planning at the acceleration level based on task priority matrix for space robot
Nonlinear Dynamics - A capacitive micromachined ultrasonic transducer (CMUT) due to many benefits is being considered as an imaging and therapeutic technology recently. The critical challenge is to... 相似文献
19.
Chen Fenge Li Bing Peng Xingchun 《Methodology and Computing in Applied Probability》2022,24(2):635-659
Methodology and Computing in Applied Probability - This paper is devoted to the study of an optimal investment and risk control problem for an insurer. The risky asset process and the insurance... 相似文献
20.
以1,4-二溴-2,5-二甲基苯和4-吡啶硼酸为原料,经两步合成了一种新颖的含吡啶基团的二羧酸配体。通过核磁共振氢谱及傅里叶变换红外光谱对配体结构进行表征,通过热重分析对配体的热稳定性进行了测试;通过溶剂热法对配体的单晶进行培养,并考察反应温度、时间、pH和溶剂等条件对单晶培养的影响。结果表明:在反应温度为80 ℃,反应时间为12 h、溶剂为蒸馏水、溶液pH=5的条件下可获得高质量单晶。该配体为单斜晶系,属于C2/c空间群,结构中含有4个氧原子和2个氮原子,可为金属离子的配位提供足够的位点,有望应用于配合物的设计或催化、吸附和医药载体等行业。 相似文献