全文获取类型
收费全文 | 23591篇 |
免费 | 3526篇 |
国内免费 | 2605篇 |
专业分类
化学 | 16597篇 |
晶体学 | 289篇 |
力学 | 1508篇 |
综合类 | 208篇 |
数学 | 2446篇 |
物理学 | 8674篇 |
出版年
2024年 | 45篇 |
2023年 | 421篇 |
2022年 | 652篇 |
2021年 | 813篇 |
2020年 | 873篇 |
2019年 | 845篇 |
2018年 | 737篇 |
2017年 | 746篇 |
2016年 | 1046篇 |
2015年 | 1050篇 |
2014年 | 1192篇 |
2013年 | 1648篇 |
2012年 | 1954篇 |
2011年 | 2085篇 |
2010年 | 1381篇 |
2009年 | 1334篇 |
2008年 | 1515篇 |
2007年 | 1420篇 |
2006年 | 1286篇 |
2005年 | 1041篇 |
2004年 | 830篇 |
2003年 | 698篇 |
2002年 | 666篇 |
2001年 | 491篇 |
2000年 | 477篇 |
1999年 | 528篇 |
1998年 | 446篇 |
1997年 | 449篇 |
1996年 | 484篇 |
1995年 | 386篇 |
1994年 | 395篇 |
1993年 | 287篇 |
1992年 | 268篇 |
1991年 | 243篇 |
1990年 | 176篇 |
1989年 | 132篇 |
1988年 | 120篇 |
1987年 | 98篇 |
1986年 | 96篇 |
1985年 | 85篇 |
1984年 | 58篇 |
1983年 | 49篇 |
1982年 | 38篇 |
1981年 | 28篇 |
1980年 | 31篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
942.
Fang Lu 《Applicable analysis》2013,92(8):1567-1586
In the context of Euclidean spaces, we present an extension of the Newton-like method for solving vector optimization problems, with respect to the partial orders induced by a pointed, closed and convex cone with a nonempty interior. We study both exact and inexact versions of the Newton-like method. Under reasonable hypotheses, we prove stationarity of accumulation points of the sequences produced by Newton-like methods. Moreover, assuming strict cone-convexity of the objective map to the vector optimization problem, we establish convergence of the sequences to an efficient point whenever the initial point is in a compact level set. 相似文献
943.
944.
Abstract: Titanium tetrachloride was reduced by zinc powder in THF to produce low-valent titanium which reacted with 4,4-dicyano-1,3-diaryl-1-buanone to give the derivatives of 1-amino-2-cyanocyclopentene. 相似文献
945.
Pingli Lv Rongxiu Zhu Tongxiang Lu Steven E. Wheeler Dongju Zhang Ruoxi Wang Chengbu Liu 《Tetrahedron: Asymmetry》2013,24(24):1598-1604
Computational studies to determine the origin of enantioselectivity in the (1R,2R)-1,2-diphenylethane-1,2-diamine (DEPN)–Brønsted acid catalyzed epoxidation of 2-cyclohexen-1-one have been performed using density functional theory. Transition states for conjugate addition and ring closure steps of the epoxidations catalyzed by three different catalyst systems were characterized. Our calculations show that the Csp2H?O H-bond interaction between the benzene ring of the catalyst and H2O is mainly responsible for the chiral discrimination observed. The Brønsted acid counterion plays a very important role in ensuring high enantioselectivity by improving the rigidity of the transition state structures to allow the efficient formation of the Csp2H?O H-bond. Moreover, we explain why these two diamine catalysts (1S,2S)-DACH and (1R,2R)-DPEN display consistent enantioselectivities in the catalytic epoxidation of 2-cyclohexen-1-one when combining with three different cocatalysts; achiral TFA, and chiral (R)- and (S)-TRIP. 相似文献
946.
Jinting Zhou Wei Lu Fangyu Hu Mengyu Zhang Liming Jiang Zhiquan Shen 《Journal of polymer science. Part A, Polymer chemistry》2014,52(16):2248-2257
A novel AB type of clickable monomer, (S)‐2‐[(2‐azido‐1‐phenylethylimino)methyl]‐5‐propargyloxyphenol (AMPP) was designed and polymerized to yield a class of main‐chain chiral poly(imine‐triazole)s through the metal‐free click reaction. With the thermally induced polymerization, the desired polytriazoles can be easily prepared in high yields by a stepwise heating‐up process and have the number‐average molecular masses ranging from 5.1 × 103 to 58.1 × 103 (polydispersity indices = 1.38?1.68). The polymers were characterized by Fourier Transform Infrared spectroscopy (FTIR), 1H Nuclear Magnetic Resonance (NMR), and gel permeation chromatography, and their optical properties were studied by fluorescence and circular dichroism (CD) spectroscopies. As a chemosensor, these polymers exhibited a selective “turn‐on” fluorescence enhancement response toward Zn2+ ion over other cations such as Na+, K+, Mg2+, Ca2+, Ag+, Pb2+, Cd2+, Hg2+, Mn2+, and Ni2+ in dimethyl sulfoxide. However, the Zn2+‐induced fluorescence signal was subject to serious interference by Al3+, Cu2+, Cr3+, and Fe3+ ions. Interestingly, the chiral polymer showed distinctive changes in the CD spectra on complexation with Zn2+, which allowed for the discrimination of this ion in the presence of other species tested including those interfering ions observed in the fluorescent detection. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2248–2257 相似文献
947.
International Journal of Theoretical Physics - In classical information processing, the windowed Fourier transform (WFT), or short-time Fourier transform, which is a variant of the Fourier... 相似文献
948.
Chinese Journal of Polymer Science - We synthesize and compare four near-infrared absorbing fused-ring electron acceptors named as nTTIC (n=2, 3, 4, and 5), based on different number of... 相似文献
949.
Luís Antônio Dantas Silva Fernanda Vieira Teixeira Raphael Caixeta Serpa Najla Locatelli Esteves Rayane Ramos dos Santos Eliana Martins Lima Marcílio Sérgio Soares da Cunha-Filho Adriano Antunes de Souza Araújo Stephânia Fleury Taveira Ricardo Neves Marreto 《Journal of Thermal Analysis and Calorimetry》2016,123(3):2337-2344
950.