全文获取类型
收费全文 | 462266篇 |
免费 | 8426篇 |
国内免费 | 4035篇 |
专业分类
化学 | 252118篇 |
晶体学 | 6964篇 |
力学 | 20844篇 |
综合类 | 232篇 |
数学 | 53862篇 |
物理学 | 140707篇 |
出版年
2021年 | 4039篇 |
2020年 | 4688篇 |
2019年 | 5016篇 |
2018年 | 6460篇 |
2017年 | 6331篇 |
2016年 | 9063篇 |
2015年 | 5761篇 |
2014年 | 8745篇 |
2013年 | 20135篇 |
2012年 | 15879篇 |
2011年 | 18922篇 |
2010年 | 13389篇 |
2009年 | 13057篇 |
2008年 | 17353篇 |
2007年 | 17365篇 |
2006年 | 16174篇 |
2005年 | 14558篇 |
2004年 | 12938篇 |
2003年 | 11707篇 |
2002年 | 11512篇 |
2001年 | 12282篇 |
2000年 | 9771篇 |
1999年 | 7700篇 |
1998年 | 6741篇 |
1997年 | 6755篇 |
1996年 | 6334篇 |
1995年 | 5624篇 |
1994年 | 5730篇 |
1993年 | 5454篇 |
1992年 | 5955篇 |
1991年 | 5945篇 |
1990年 | 5827篇 |
1989年 | 5610篇 |
1988年 | 5604篇 |
1987年 | 5477篇 |
1986年 | 5208篇 |
1985年 | 6864篇 |
1984年 | 7187篇 |
1983年 | 5905篇 |
1982年 | 6301篇 |
1981年 | 6092篇 |
1980年 | 5854篇 |
1979年 | 6026篇 |
1978年 | 6390篇 |
1977年 | 6315篇 |
1976年 | 6377篇 |
1975年 | 5954篇 |
1974年 | 5994篇 |
1973年 | 6282篇 |
1972年 | 4392篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Chemistry of Heterocyclic Compounds - 2-Imino-2,5-dihydrofurans are a highly valuable class of heterocyclic compounds that show versatile biological activity and are used in diverse fields of... 相似文献
22.
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
23.
Numerical Algorithms - In this work, we propose a fractional extension of the one-dimensional nonlinear vibration problem on an elastic string. The fractional problem is governed by a hyperbolic... 相似文献
24.
Siberian Mathematical Journal - Let $ \{(A_{i},B_{i})\}_{i=1}^{m} $ be a set pair system. Füredi, Gyárfás, and Király called it $ 1 $ -cross intersecting if $... 相似文献
25.
Edward G. Sheetz Zhao Zhang Alyssa Marogil Minwei Che Dr. Maren Pink Dr. Veronica Carta Prof. Dr. Krishnan Raghavachari Prof. Dr. Amar H. Flood 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201584
The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R−BF3−). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R−BF3−, by cyanostar macrocycles that are size-complementary to the inorganic BF4− progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K+ salts of R−BF3− anions. 相似文献
26.
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
27.
28.
Zeng Qing-Wei Wen Zhuo-Yu Fu Jun-Feng Zhou Nan-Run 《International Journal of Theoretical Physics》2021,60(9):3306-3333
International Journal of Theoretical Physics - A new quantum watermark algorithm is presented by combining maximum pixel difference partitioning with the least significant bit substitution... 相似文献
29.
Optics and Spectroscopy - Optical investigations of crystals of solid solutions NdxGd1 – xCr3(BO3)4, 0.01 ≤ x ≤ 1, have been performed. Absorption spectra in the... 相似文献
30.
Designs, Codes and Cryptography - Large sets of combinatorial designs has always been a fascinating topic in design theory. These designs form a partition of the whole space into combinatorial... 相似文献