全文获取类型
收费全文 | 8302篇 |
免费 | 254篇 |
国内免费 | 14篇 |
专业分类
化学 | 4774篇 |
晶体学 | 126篇 |
力学 | 174篇 |
综合类 | 1篇 |
数学 | 1376篇 |
物理学 | 2119篇 |
出版年
2023年 | 53篇 |
2022年 | 46篇 |
2021年 | 95篇 |
2020年 | 139篇 |
2019年 | 191篇 |
2018年 | 165篇 |
2017年 | 166篇 |
2016年 | 300篇 |
2015年 | 253篇 |
2014年 | 324篇 |
2013年 | 684篇 |
2012年 | 454篇 |
2011年 | 500篇 |
2010年 | 391篇 |
2009年 | 368篇 |
2008年 | 416篇 |
2007年 | 390篇 |
2006年 | 327篇 |
2005年 | 279篇 |
2004年 | 232篇 |
2003年 | 254篇 |
2002年 | 194篇 |
2001年 | 155篇 |
2000年 | 130篇 |
1999年 | 94篇 |
1998年 | 96篇 |
1997年 | 73篇 |
1996年 | 73篇 |
1995年 | 106篇 |
1994年 | 51篇 |
1992年 | 67篇 |
1991年 | 47篇 |
1990年 | 59篇 |
1989年 | 55篇 |
1988年 | 63篇 |
1987年 | 49篇 |
1986年 | 58篇 |
1985年 | 101篇 |
1984年 | 111篇 |
1983年 | 68篇 |
1982年 | 67篇 |
1981年 | 69篇 |
1980年 | 86篇 |
1979年 | 55篇 |
1978年 | 78篇 |
1977年 | 86篇 |
1976年 | 68篇 |
1975年 | 61篇 |
1974年 | 49篇 |
1973年 | 44篇 |
排序方式: 共有8570条查询结果,搜索用时 46 毫秒
1.
Dominik Vítek Prof. Aleš Růžička Lise Vermeersch Dr. Libor Dostál Dr. Jan Turek Prof. Roman Jambor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202202639
Reactivity studies of the GeII→B complex L(Cl)Ge⋅BH3 ( 1 ; L=2-Et2NCH2-4,6-tBu2-C6H2) were performed to determine the effect on the GeII→B donation. N-coordinated compounds L(OtBu)Ge⋅BH3 ( 2 ) and [LGe⋅BH3]2 ( 3 ) were prepared. The possible tuning of the GeII→B interaction was proved experimentally, yielding compounds 1-PPh2-8-(LGe)-C10H6 ( 4 ) and L(Cl)Ge⋅GaCl3 ( 5 ) without a GeII→B interaction. In 5 , an unprecedented GeII→Ga coordination was revealed. The experimental results were complemented by a theoretical study focusing on the bonding in 1 − 5 . The different strength of the GeII→E (E=B, Ga) donation was evaluated by using energy decomposition analysis. The basicity of different L(X)Ge groups through proton affinity is also assessed. 相似文献
2.
Gürbüzbalaban Mert Ruszczyński Andrzej Zhu Landi 《Journal of Optimization Theory and Applications》2022,194(3):1014-1041
Journal of Optimization Theory and Applications - We consider a distributionally robust formulation of stochastic optimization problems arising in statistical learning, where robustness is with... 相似文献
3.
4.
5.
Russian Chemical Bulletin - The discovery and studies of chemistry of dichlorocarbene and other electron deficient carbenes are discussed. 相似文献
6.
Prof. Piotr Bałczewski Dr. Emilia Kowalska Dr. Ewa Różycka-Sokołowska Dr. Joanna Skalik Dr. Krzysztof Owsianik Dr. Marek Koprowski Dr. Bernard Marciniak Dr. Dariusz Guziejewski Prof. Witold Ciesielski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(62):14148-14161
The highly substituted mono-aryl/alkylthio-(hetero)acenes prepared in this study have been found to be thermally more stable (Tdecomp.=331–354 °C) than the known di-aryl/alkylthio-substituted acenes by an average of 25 °C. They are also much more photostable at 254 and 365 nm (in both argon and air) than the parent anthracene and other reported anthracenes. The most photostable aryl/alkylthio-anthracenes at 254 nm were found to be 60–70 (in air) and 130 (in argon) times more stable in solution than the unsubstituted anthracene, and much more stable than known EDG/EWG-substituted anthracenes (EDG=electron-donating group, EWG=electron-withdrawing group) with an extended aromatic core. Furthermore, the acenes showed significantly higher photostability at 365 nm in both air and argon. The anthracenes were obtained by the novel thio-Friedel–Crafts/Bradsher cyclization reaction of hitherto unknown [o-(1,3-dithian-2-yl)aryl](aryl)methyl thioethers. The developed approach provides a general access to mono-aryl/alkylthio-substituted (hetero)acene frameworks containing at least three fused (hetero)aromatic rings. The characteristic feature of this approach, which leads to highly substituted acenes, is that the substituents, unlike in other methods, may be introduced at an early stage of the synthesis. DFT and TD-DFT calculations confirmed the stabilizing role of the aryl/alkylthio substituent in the mono-aryl/alkylthio-substituted anthracenes, which are the most stable anthracenes prepared to date. Their high photostability is mainly due to the quenching of singlet oxygen by the acene and the quenching of the acene S1 state by molecular oxygen. 相似文献
7.
Dehghanpour-Sahron Ja’far Mahdavi-Amiri Nezam 《4OR: A Quarterly Journal of Operations Research》2021,19(4):473-499
4OR - Partitioning a given data-set into subsets based on similarity among the data is called clustering. Clustering is a major task in data mining and machine learning having many applications... 相似文献
8.
Space-time directional Lyapunov exponents are introduced. They describe the maximal velocity of propagation to the right or to the left of fronts of perturbations in a frame moving with a given velocity. The continuity of these exponents as function of the velocity and an inequality relating them to the directional entropy is proved. 相似文献
9.
The quantum states are presented in these processions of fabricating poly-Si films. Amorphous silicon films prepared by PECVD has been crystallized by conventional furnace annealing (FA) and rapid thermal annealing (RTA), respectively. It is found that the thin films grain size present quantum states with the increasing of the gas flow ratios of SiH4, H2 mixture, substrate temperatures, frequency power, annealing temperature and time. 相似文献
10.