全文获取类型
收费全文 | 8631篇 |
免费 | 309篇 |
国内免费 | 87篇 |
专业分类
化学 | 5310篇 |
晶体学 | 83篇 |
力学 | 333篇 |
数学 | 1544篇 |
物理学 | 1757篇 |
出版年
2023年 | 56篇 |
2022年 | 162篇 |
2021年 | 200篇 |
2020年 | 200篇 |
2019年 | 215篇 |
2018年 | 206篇 |
2017年 | 187篇 |
2016年 | 298篇 |
2015年 | 233篇 |
2014年 | 349篇 |
2013年 | 587篇 |
2012年 | 556篇 |
2011年 | 613篇 |
2010年 | 359篇 |
2009年 | 399篇 |
2008年 | 480篇 |
2007年 | 409篇 |
2006年 | 348篇 |
2005年 | 307篇 |
2004年 | 303篇 |
2003年 | 254篇 |
2002年 | 258篇 |
2001年 | 182篇 |
2000年 | 171篇 |
1999年 | 102篇 |
1998年 | 87篇 |
1997年 | 90篇 |
1996年 | 116篇 |
1995年 | 93篇 |
1994年 | 78篇 |
1993年 | 86篇 |
1992年 | 65篇 |
1991年 | 64篇 |
1990年 | 57篇 |
1989年 | 56篇 |
1988年 | 45篇 |
1987年 | 62篇 |
1986年 | 65篇 |
1985年 | 69篇 |
1984年 | 57篇 |
1983年 | 54篇 |
1982年 | 52篇 |
1981年 | 50篇 |
1980年 | 35篇 |
1979年 | 49篇 |
1978年 | 43篇 |
1977年 | 38篇 |
1976年 | 44篇 |
1975年 | 37篇 |
1974年 | 28篇 |
排序方式: 共有9027条查询结果,搜索用时 15 毫秒
941.
942.
943.
944.
A two-dimensional layered niobium oxide and its exfoliated nanosheet were examined as potential solid acid supports for direct synthesis of hydrogen peroxide from hydrogen and oxygen under intrinsically safe and noncorrosive reaction conditions. The catalytic performance strongly depended on the acid strength of the support material. The Pd-supported protonated niobium oxide nanosheet catalyst (Pd/HNb3O8-NS) with remarkably enhanced acidity was superior to layered Pd/KNb3O8 or Pd/HNb3O8 to promote the reaction. Hydrogen peroxide decomposition testing revealed that, although HNb3O8 was comparable to its exfoliated counterpart, HNb3O8-NS, in suppressing hydrogen peroxide decomposition without hydrogen, HNb3O8 was virtually ineffective in preventing hydrogen peroxide hydrogenation in the presence of hydrogen. However, compared with HNb3O8, HNb3O8-NS was found to be still effective at suppressing hydrogen peroxide hydrogenation. The different efficiency observed between HNb3O8 and HNb3O8-NS in the prevention of hydrogen peroxide hydrogenation implies that use of a highly acidic support is advantageous to effectively suppress faster and therefore more unfavorable hydrogen peroxide hydrogenation compared with decomposition. This result clearly demonstrates that the highly acidic HNb3O8 nanosheet can serve as an efficient solid acid support for direct synthesis of hydrogen peroxide from hydrogen and oxygen. 相似文献
945.
Pham Bich Ngoc Thanh Binh Pham Hai Dang Nguyen Thu Trang Tran Hoang Ha Chu Van Minh Chau 《Natural product research》2016,30(12):1360-1365
One new β-carboline alkaloid 7-methoxy-(9H-β-carbolin-1-il)-(E)-1-propenoic acid (1) together with 9-methoxycanthin-6-one (2) and 9-hydroxycanthin-6-one (3) were isolated from the hairy-root cultures of Eurycoma longifolia. The effects of these compounds on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW264.7 cells were investigated. Compound 1 strongly inhibited the production of NO while 2 and 3 having weak or inactive effect. Consistently, compound 1 decreased the expression of cyclooxygenase-2 and inducible nitric oxide synthase. 相似文献
946.
Duc Nghia Nguyen Trinh Tung Ngo Dae Hee Lee Min Ju Cho Dong Hoon Choi 《Journal of polymer science. Part A, Polymer chemistry》2016,54(10):1339-1347
Diketopyrrolopyrrole (DPP)‐based terpolymers—P(DPP‐TPyT) and P(DPP‐T3MTT)—bearing bithiophene donating groups and weak accepting units such as pyridine (Py) or methyl thiophene‐3‐carboxylate (3MT), in the polymer backbone, were successfully synthesized. Although the two polymers had similar physical and electrochemical properties, grazing incidence X‐ray diffraction patterns of P(DPP‐TPyT) and P(DPP‐T3MTT) showed mixed and edge‐on orientations, respectively, in thermally annealed films. Accordingly, the P(DPP‐T3MTT) showed twice the hole mobility of P(DPP‐TPyT) in a thin‐film transistor, and a blended film of P(DPP‐T3MTT) and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) showed better power conversion efficiency in a polymer solar cell. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1339‐1347 相似文献
947.
948.
Antony V. Wilson Timothy Nguyen Felix Brosi Xuefeng Wang Lester Andrews Sebastian Riedel Adam J. Bridgeman Nigel A. Young 《ChemInform》2016,47(14):no-no
Binary palladium fluorides from PdF to PdF6 are investigated by matrix‐isolation methods using thermal evaporation and laser ablation to generate Pd atoms for reaction with F2‐doped Ar and Ne matrices as well as neat F2 matrices. 相似文献
949.
Molecular dynamics was used to study the hydration of superoxide (O). The Helmholtz free energy of hydration of O was estimated by the thermodynamic integration method. The diffusion of O and the water structure around O were also studied. Two water models were used in the calculations and the results were compared to experiments. 相似文献
950.