全文获取类型
收费全文 | 34076篇 |
免费 | 5878篇 |
国内免费 | 4113篇 |
专业分类
化学 | 24534篇 |
晶体学 | 370篇 |
力学 | 2189篇 |
综合类 | 287篇 |
数学 | 3681篇 |
物理学 | 13006篇 |
出版年
2024年 | 39篇 |
2023年 | 627篇 |
2022年 | 735篇 |
2021年 | 1058篇 |
2020年 | 1418篇 |
2019年 | 1373篇 |
2018年 | 1169篇 |
2017年 | 995篇 |
2016年 | 1624篇 |
2015年 | 1622篇 |
2014年 | 1922篇 |
2013年 | 2611篇 |
2012年 | 3034篇 |
2011年 | 3253篇 |
2010年 | 2148篇 |
2009年 | 2072篇 |
2008年 | 2230篇 |
2007年 | 2026篇 |
2006年 | 1932篇 |
2005年 | 1651篇 |
2004年 | 1424篇 |
2003年 | 1102篇 |
2002年 | 1043篇 |
2001年 | 854篇 |
2000年 | 696篇 |
1999年 | 688篇 |
1998年 | 582篇 |
1997年 | 516篇 |
1996年 | 510篇 |
1995年 | 474篇 |
1994年 | 428篇 |
1993年 | 330篇 |
1992年 | 342篇 |
1991年 | 299篇 |
1990年 | 240篇 |
1989年 | 202篇 |
1988年 | 130篇 |
1987年 | 119篇 |
1986年 | 108篇 |
1985年 | 109篇 |
1984年 | 62篇 |
1983年 | 60篇 |
1982年 | 51篇 |
1981年 | 38篇 |
1980年 | 24篇 |
1979年 | 10篇 |
1975年 | 12篇 |
1973年 | 8篇 |
1971年 | 7篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 26 毫秒
11.
Li Y. Shi W. H. Dong L. M. Xu S. X. Huang H. J. Yin J. R. 《Journal of Applied Spectroscopy》2022,89(3):534-541
Journal of Applied Spectroscopy - Sr3B2O6:Dy3+, Eu3+ single-matrix white-light-emitting materials are prepared using the high-temperature solid-state method. The microstructure, emission spectrum,... 相似文献
12.
A complete manifold is said to be nonparabolic if it does admit a positive Green’s function. To ?nd a sharp geometric criterion for the parabolicity/nonparbolicity is an attractive question inside the function theory on Riemannian manifolds. This paper devotes to proving a criterion for nonparabolicity of a complete manifold weakened by the Ricci curvature. For this purpose, we shall apply the new Laplacian comparison theorem established by the ?rst author to show the existence of a non-constant bounded subharmonic function. 相似文献
13.
化学工业生产中,用氢气为还原剂,通过选择性加氢可以制备多种重要化学品。5-羟甲基糠醛是重要的生物质基平台化合物,而5-甲基糠醛是用途广泛的化学品。由5-羟甲基糠醛加氢得到5-甲基糠醛是一条非常理想的路径,但是选择性活化C-OH非常困难。本文设计并制备了Pt@PVP/Nb2O5(PVP: 聚乙烯吡咯烷酮)催化剂,该催化体系巧妙地结合了位阻效应、氢溢流和催化剂界面的电子效应,系统研究了该催化剂对5-羟甲基糠醛选择性加氢制备5-甲基糠醛催化性能,在最优条件下,5-甲基糠醛的选择性可达92%。利用密度泛函理论计算研究了5-羟甲基糠醛选择性加氢制备5-甲基糠醛反应路径。 相似文献
14.
Asymmetric mode transformation in waveguide is of great significance for on-chip integrated devices with one-way effect, while it is challenging to achieve asymmetric nonlinear-mode-conversion (NMC) due to the limitations imposed by phase-matching. In this work, we theoretically proposed a new scheme for realizing asymmetric NMC by combining frequency-doubling process and periodic PT symmetric modulation in an optical waveguide. By engineering the one-way momentum from PT symmetric modulation, we have demonstrated the unidirectional conversion from pump to second harmonic with desired guided modes. Our findings offer new opportunities for manipulating nonlinear optical fields with PT symmetry, which could further boost more exploration on on-chip nonlinear devices assisted by non-Hermitian optics. 相似文献
15.
Bohuai Xiao Jianqiao Dong Zhiye Wang Xu Wang Mingjun Sun Jing Guo Gongming Qian Yunchuan Li Shuai Chang 《Chemphyschem》2022,23(7):e202100833
One important prerequisite for the fabrication of molecular functional device strongly relies on the understanding the conducting behaviors of the metal-molecule-metal junction that can respond to an external stimulus. The model Lewis basic molecule 4,4′-(pyridine-3,5-diyl)dibenzonitrile (DBP), which can react with Lewis acid and protic acid, was synthesized. Then, the molecular conducting behavior of DBP, DBP-B(C6F5)3, and DBP-TfOH (DBP-B(C6F5)3, and DBP-TfOH were produced by Lewis acid and protonic acid treatment of DBP) was researched and compared. Given that their identical physical paths for DBP, DBP-B(C6F5)3, and DBP-TfOH to sustain charge transport, our results indicate that modifying the molecular electronic structure, even not directly changing the conductive physical backbone, can tune the charge transporting ability by nearly one order of magnitude. Furthermore, the addition of another Lewis base triethylamine (of stronger alkaline than DBP), to Lewis acid-base pair reverts the electrical properties back to that of a single DBP junction, that is constructive to propose a useful but simple strategy for the design and construction of reversible and controllable molecular device based on pyridine derived molecule. 相似文献
16.
In this paper, we study a category of restricted modules for the Ovsienko-Roger algebra, which is an extension of the Virasoro algebra of its tensor density module of degree one. We construct and characterize simple modules in this category and give natural free field realizations of certain restricted modules using the Weyl vertex algebra.
相似文献17.
Heterostructured MoS2/GPC anode: the synergistic lithium storage performance and lithiation kinetics
Zhang Xia Dong Chaoyang Sun Yangang Liu Binyang Sun Lili Lu Yongjuan Yu Jing Wei Yajun Xu Yuandong 《Journal of Solid State Electrochemistry》2022,26(2):491-501
Journal of Solid State Electrochemistry - Grapefruit peel carbon (GPC) is prepared from waste grapefruit peel and further used as substrate for in situ construction of MoS2 arrays, forming MoS2/GPC... 相似文献
18.
19.
Enyuan Wang Xiangguo Kong Shaobin Hu Zhonghui Li Quanlin Liu 《Transport in Porous Media》2018,121(3):703-724
With coal mining entering the geological environment of “high stress, rich gas, strong adsorption and low permeability,” the difficulty of joint coal and gas extraction clearly augments, the risk of solid–gas coupling dynamic disasters greatly increases, and the underlying mechanisms become more complex. In this paper, based on the characteristics of coal’s multi-scale structure and spatiotemporal variation, the multi-scale fractured coal gas–solid coupling model (MSFM) was built. In this model, the interaction between coal matrix and its fractures and the mechanical characteristics of gas-bearing coal were considered, as well as their coupling relationship. By MATLAB software, the stress–damage–seepage numerical computation programs were developed, which were applied into Comsol Multiphysics to simulate gas flow caused by coal mining. The simulation results showed the spatial variability of coal elastic modulus and cross-flow behaviors of coal seam gas, which were superior to the results of traditional gas–solid coupling model. And the numerical results obtained from MSFM were closer to the measured results in field, while the computation results of traditional model were slightly higher than the measured results. Furthermore, the MSFM in a large scale was verified by field engineering project. 相似文献
20.
Dr. Ran Du Dr. Jan-Ole Joswig Dr. René Hübner Lin Zhou Dr. Wei Wei Prof. Yue Hu Prof. Dr. Alexander Eychmüller 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(21):8370-8377
Noble-metal aerogels (NMAs) have drawn increasing attention because of their self-supported conductive networks, high surface areas, and numerous optically/catalytically active sites, enabling their impressive performance in diverse fields. However, the fabrication methods suffer from tedious procedures, long preparation times, unavoidable impurities, and uncontrolled multiscale structures, discouraging their developments. By utilizing the self-healing properties of noble-metal aggregates, the freezing-promoted salting-out behavior, and the ice-templating effect, a freeze–thaw method is crafted that is capable of preparing various hierarchically structured noble-metal gels within one day without extra additives. In light of their cleanliness, the multi-scale structures, and combined catalytic/optical properties, the electrocatalytic and photoelectrocatalytic performance of NMAs are demonstrated, which surpasses that of commercial noble-metal catalysts. 相似文献