全文获取类型
收费全文 | 152053篇 |
免费 | 25068篇 |
国内免费 | 16512篇 |
专业分类
化学 | 104670篇 |
晶体学 | 1927篇 |
力学 | 9873篇 |
综合类 | 974篇 |
数学 | 18378篇 |
物理学 | 57811篇 |
出版年
2024年 | 338篇 |
2023年 | 2889篇 |
2022年 | 4524篇 |
2021年 | 5370篇 |
2020年 | 6026篇 |
2019年 | 5902篇 |
2018年 | 5041篇 |
2017年 | 4850篇 |
2016年 | 7176篇 |
2015年 | 6988篇 |
2014年 | 8560篇 |
2013年 | 11145篇 |
2012年 | 13551篇 |
2011年 | 14061篇 |
2010年 | 9676篇 |
2009年 | 9186篇 |
2008年 | 9770篇 |
2007年 | 8847篇 |
2006年 | 8105篇 |
2005年 | 6950篇 |
2004年 | 5284篇 |
2003年 | 4175篇 |
2002年 | 3900篇 |
2001年 | 3205篇 |
2000年 | 2780篇 |
1999年 | 3134篇 |
1998年 | 2693篇 |
1997年 | 2465篇 |
1996年 | 2624篇 |
1995年 | 2200篇 |
1994年 | 2050篇 |
1993年 | 1664篇 |
1992年 | 1482篇 |
1991年 | 1365篇 |
1990年 | 1081篇 |
1989年 | 781篇 |
1988年 | 648篇 |
1987年 | 531篇 |
1986年 | 526篇 |
1985年 | 451篇 |
1984年 | 324篇 |
1983年 | 243篇 |
1982年 | 195篇 |
1981年 | 144篇 |
1980年 | 103篇 |
1979年 | 60篇 |
1976年 | 56篇 |
1975年 | 54篇 |
1974年 | 52篇 |
1973年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
11.
12.
Zhengcheng Wang Shangyan Zhou Wei Liao Qian Zhou Meida Chen Jin Long Prof. Qingmei Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(66):e202201987
The designs of efficient and inexpensive Pt-based catalysts for methanol oxidation reaction (MOR) are essential to boost the commercialization of direct methanol fuel cells. Here, the highly catalytic performance PtFe alloys supported on multiwalled carbon nanotubes (MWCNTs) decorating nitrogen-doped carbon (NC) have been successfully prepared via co-engineering of the surface composition and electronic structure. The Pt1Fe3@NC/MWCNTs catalyst with moderate Fe3+ feeding content (0.86 mA/mgPt) exhibits 2.26-fold enhancement in MOR mass activity compared to pristine Pt/C catalyst (0.38 mA/mgPt). Furthermore, the CO oxidation initial potential of Pt1Fe3@NC/MWCNTs catalyst is lower relative to Pt/C catalyst (0.71 V and 0.80 V). Benefited from the optimal surface compositions, the anti-corrosion ability of MWCNT, strong electron interaction between PtFe alloys and MWCNTs and the N-doped carbon (NC) layer, the Pt1Fe3@NC/MWCNTs catalyst presents an improved MOR performance and anti-CO poisoning ability. This study would open up new perspective for designing efficient electrocatalysts for the DMFCs field. 相似文献
13.
Hua Saixiang Zhu Huichao Wang Xiao Wu Mingyuan Wu Qingyun Liu Jiuyi Yang Jianjun Zhang Jianan 《Cellulose (London, England)》2022,29(13):7465-7475
Cellulose - Ultraviolet (UV) protective cotton fabric is a convenient and reliable way to protect human body from sunlight. Herein, a polymerizable UV-absorber,... 相似文献
14.
Let p ∈ [1, ∞), q ∈ [1, ∞), α∈ R, and s be a non-negative integer. Inspired by the space JNp introduced by John and Nirenberg(1961) and the space B introduced by Bourgain et al.(2015), we introduce a special John-Nirenberg-Campanato space JNcon(p,q,s) over Rn or a given cube of R;with finite side length via congruent subcubes, which are of some amalgam features. The limit space of such spaces as p →∞ is just the Campanato space which coincides with the space BMO(the space of functions with bounded mean oscillations)when α = 0. Moreover, a vanishing subspace of this new space is introduced, and its equivalent characterization is established as well, which is a counterpart of the known characterization for the classical space VMO(the space of functions with vanishing mean oscillations) over Rn or a given cube of Rn with finite side length.Furthermore, some VMO-H1-BMO-type results for this new space are also obtained, which are based on the aforementioned vanishing subspaces and the Hardy-type space defined via congruent cubes in this article. The geometrical properties of both the Euclidean space via its dyadic system and congruent cubes play a key role in the proofs of all these results. 相似文献
15.
Hao Lu Xiaodong Wang Hang Wang Andong Zhang Xinming Zheng Na Yu Zheng Tang Xinjun Xu Yahui Liu Ya-Nan Chen Zhishan Bo 《中国科学:化学(英文版)》2022,65(3):594-601
Three nonfused ring electron acceptors (NFREAs) TTC6,TT-C8T and TT-TC8 were purposefully designed and synthesized.The molecular geometry can be adjusted by the steric hindrance of lateral substituents.According to the DFT calculations,from TTC6 to TT-C8T and TT-TC8,planarity of the molecular backbone is gradually improved,accompanying with the enhancing of intramolecular charge transfer effect.As for TT-TC8,the two phenyl substituents are almost perpendicular to the molecular backbone,which endues the acceptor with good solubility and suppresses it to form over-aggregation.Multidirectional regular molecular orientation and closer molecular stacking are formed in TT-TC8 film.As a result,TT-TC8 based devices afford the highest PCE of 13.13%,which is much higher than that of TTC6 (4.41%) and TT-C8T (10.42%) and among the highest PCE values based on NFREAs. 相似文献
16.
Wang Rong Li Xu Zhou Youshi Cao Shuxuan Xu Honghao Han Wenjuan Zhang Yuxia Liu Junhai 《Journal of Russian Laser Research》2022,43(4):476-481
Journal of Russian Laser Research - We demonstrate a passively-mode-locked Pr3+: LuLiF4 laser operated at the 604 nm orange wave-length, using monolayer graphene as a saturable absorber. The... 相似文献
17.
Applied Mathematics and Mechanics - Spiral springs have a wide range of applications in various fields. As a result of the complexity of friction, few theoretical analyses of spring belts under... 相似文献
18.
Nonlinear Dynamics - In order to solve the constrained-input problem and reduce the computing resources, a novel event-triggered optimal control method is proposed for a class of discrete-time... 相似文献
19.
科学评价大学生科研创新能力对我国科研水平的提高具有重要意义.采用机器学习模型来预测大学生科研能力可以起到良好的效果,提出一种GAXGBoost模型来实现对大学生的科研能力预测.此模型是以Xgboost算法为基础,然后充分利用遗传算法的全局搜索能力自动搜索Xgboost最优超参数,避免了人为经验调参不准确的缺陷,最后采用精英选择策略以此确保每一轮都是最佳的进化结果.通过分析表明,所采用的GAXGBoost模型在大学生科研能力预测的结果中具有很高的精度,将此模型与Logistic Regression、Random Forest、SVM等模型进行对比,GAXGBoost模型的预测精度最高. 相似文献
20.
Nonlinear Dynamics - The classical Kuramoto model serves as a useful tool for studying synchronization transitions in coupled oscillators that is limited to the sinusoidal and pairwise... 相似文献