全文获取类型
收费全文 | 121078篇 |
免费 | 8355篇 |
国内免费 | 5367篇 |
专业分类
化学 | 55669篇 |
晶体学 | 1274篇 |
力学 | 9356篇 |
综合类 | 269篇 |
数学 | 36427篇 |
物理学 | 31805篇 |
出版年
2024年 | 116篇 |
2023年 | 943篇 |
2022年 | 1090篇 |
2021年 | 1611篇 |
2020年 | 1938篇 |
2019年 | 1902篇 |
2018年 | 11621篇 |
2017年 | 11360篇 |
2016年 | 8035篇 |
2015年 | 2915篇 |
2014年 | 2989篇 |
2013年 | 3644篇 |
2012年 | 7845篇 |
2011年 | 14509篇 |
2010年 | 8311篇 |
2009年 | 8526篇 |
2008年 | 9400篇 |
2007年 | 11188篇 |
2006年 | 2736篇 |
2005年 | 3290篇 |
2004年 | 3015篇 |
2003年 | 3204篇 |
2002年 | 2260篇 |
2001年 | 1250篇 |
2000年 | 1077篇 |
1999年 | 1075篇 |
1998年 | 976篇 |
1997年 | 892篇 |
1996年 | 970篇 |
1995年 | 764篇 |
1994年 | 605篇 |
1993年 | 527篇 |
1992年 | 494篇 |
1991年 | 450篇 |
1990年 | 369篇 |
1989年 | 324篇 |
1988年 | 228篇 |
1987年 | 205篇 |
1986年 | 235篇 |
1985年 | 179篇 |
1984年 | 133篇 |
1983年 | 121篇 |
1982年 | 99篇 |
1981年 | 91篇 |
1980年 | 82篇 |
1979年 | 64篇 |
1978年 | 58篇 |
1977年 | 43篇 |
1973年 | 51篇 |
1914年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
21.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant. 相似文献
22.
23.
Sarah Peluse 《Israel Journal of Mathematics》2018,227(1):379-396
We prove that the group of diffeomorphisms of the interval [0, 1] contains surface groups whose action on (0, 1) has no global fix point and such that only countably many points of the interval (0, 1) have non-trivial stabiliser. 相似文献
24.
25.
26.
27.
Richiro Ushimaru Zhang Chen Houyuan Zhao Po-hsun Fan Prof. Dr. Hung-wen Liu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(9):3586-3590
Albomycin δ2 is a sulfur-containing sideromycin natural product that shows potent antibacterial activity against clinically important pathogens. The l -serine-thioheptose dipeptide partial structure, known as SB-217452, has been found to be the active seryl-tRNA synthetase inhibitor component of albomycin δ2. Herein, it is demonstrated that AbmF catalyzes condensation between the 6′-amino-4′-thionucleoside with the d -ribo configuration and seryl-adenylate supplied by the serine adenylation activity of AbmK. Formation of the dipeptide is followed by C3′-epimerization to produce SB-217452 with the d -xylo configuration, which is catalyzed by the radical S-adenosyl-l -methionine enzyme AbmJ. Gene deletion suggests that AbmC is involved in peptide assembly linking SB-217452 with the siderophore moiety. This study establishes how the albomycin biosynthetic machinery generates its antimicrobial component SB-217452. 相似文献
28.
Panpan Li Quanbin Liang Eugene Yau-Hin Hong Chin-Yiu Chan Yat-Hin Cheng Ming-Yi Leung Mei-Yee Chan Kam-Hung Low Hongbin Wu Vivian Wing-Wah Yam 《Chemical science》2020,11(42):11601
A class of acceptor–donor–acceptor chromophoric small-molecule non-fullerene acceptors, 1–4, with difluoroboron(iii) β-diketonate (BF2bdk) as the electron-accepting moiety has been developed. Through the variation of the central donor unit and the modification on the peripheral substituents of the terminal BF2bdk acceptor unit, their photophysical and electrochemical properties have been systematically studied. Taking advantage of their low-lying lowest unoccupied molecular orbital energy levels (from −3.65 to −3.72 eV) and relatively high electron mobility (7.49 × 10−4 cm2 V−1 s−1), these BF2bdk-based compounds have been employed as non-fullerene acceptors in organic solar cells with maximum power conversion efficiencies of up to 4.31%. Moreover, bistable resistive memory characteristics with charge-trapping mechanisms have been demonstrated in these BF2bdk-based compounds. This work not only demonstrates for the first time the use of a boron(iii) β-diketonate unit in constructing non-fullerene acceptors, but also provides more insights into designing organic materials with multi-functional properties.Boron(iii) β-diketonates have been demonstrated to serve as multi-functional materials in NFA-based OPVs and organic resistive memories. 相似文献
29.
30.
The biodegradability of phtalic acid esters in marine and freshwater environments was characterized by their binding free energy with corresponding degrading enzymes. According to comprehensive biodegradation effects weights, the binding free energy values were converted into dimensionless efficacy coefficient using ratio normalization method. Then, considering comprehensive dual biodegradation effects value and the structural parameters of PAEs in both marine and freshwater environments, a 3D-QSAR pharmacophore model was constructed, five PAE derivatives (DBP−COOH, DBP−CHO, DBP−OH, DINP−NH2, and DINP−NO2) were screened out based on their environmental friendliness, functionality and stability. The prediction of biodegradation effects on five PAE derivatives by biodegradation models in marine and freshwater environment increased by 15.90 %, 15.84 %, 27.21 %, 12.33 %, and 8.32 %, and 21.57 %, 15.21 %, 20.99 %, 15.10 %, and 9.74 %, respectively. By simulating the photodegradation path of the PAE derivative molecular, it was found that DBP−OH can generate .OH and provides free radicals for the photodegradation of microplastics in the environment. 相似文献