全文获取类型
收费全文 | 18412篇 |
免费 | 2684篇 |
国内免费 | 2145篇 |
专业分类
化学 | 14037篇 |
晶体学 | 294篇 |
力学 | 961篇 |
综合类 | 187篇 |
数学 | 1803篇 |
物理学 | 5959篇 |
出版年
2024年 | 8篇 |
2023年 | 266篇 |
2022年 | 327篇 |
2021年 | 514篇 |
2020年 | 648篇 |
2019年 | 640篇 |
2018年 | 500篇 |
2017年 | 523篇 |
2016年 | 842篇 |
2015年 | 798篇 |
2014年 | 977篇 |
2013年 | 1366篇 |
2012年 | 1664篇 |
2011年 | 1749篇 |
2010年 | 1222篇 |
2009年 | 1051篇 |
2008年 | 1233篇 |
2007年 | 1063篇 |
2006年 | 1052篇 |
2005年 | 1016篇 |
2004年 | 792篇 |
2003年 | 706篇 |
2002年 | 683篇 |
2001年 | 480篇 |
2000年 | 409篇 |
1999年 | 360篇 |
1998年 | 279篇 |
1997年 | 261篇 |
1996年 | 247篇 |
1995年 | 234篇 |
1994年 | 187篇 |
1993年 | 173篇 |
1992年 | 161篇 |
1991年 | 141篇 |
1990年 | 124篇 |
1989年 | 101篇 |
1988年 | 90篇 |
1987年 | 59篇 |
1986年 | 64篇 |
1985年 | 67篇 |
1984年 | 35篇 |
1983年 | 30篇 |
1982年 | 22篇 |
1981年 | 21篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1971年 | 3篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Bijun Gao Jin Zhou Hongliang Wang Guping Zhang Jinghui He Qingfeng Xu Najun Li Dongyun Chen Hua Li Jianmei Lu 《中国化学》2019,37(2):148-154
Tetracycline (TC) and other antibiotics accumulated in groundwater and soil pollute ecological environment and threaten human health. Gold nanoparticles doped on photocatalysts are able to enhance the photodegradation efficiency during removing these antibiotics, but preparation of Au nanoparticles of well‐dispersion on photocatalysts remains challenging. In this work, zeolite imidazolate (ZIF‐8) was employed as the precursor to prepare Au@ZnO photocatalyst via impregnation and in‐situ reduction method to efficiently degrade the tetracycline in the aqueous solution. Au nanoparticles are of 10 nm in size and uniformly dispersed on the surfaces of ZnO microstructures. The as‐prepared Au@ZnO is able to remove 85.5% of TC of 0.010 mg/mL within 2 h, presenting higher photocatalytic activity than pure ZnO catalyst. Most importantly, the catalyst shows its superior stability after five cycles without structure and activity changing. The mechanism of the photocatalytic degradation was discussed in detail. 相似文献
92.
Meccanica - A flow mixing nozzle can produce satisfactory atomization for heavy oil. However, the study of the internal flow pattern of this nozzle, along with the spray morphology and its... 相似文献
93.
94.
Self‐assembly of a resorcin[4]arene‐based ligand (TMR4A) with metal salts and H3PMo12O40·xH2O offers two isostructural complexes, namely, [Ni2Cl(TMR4A)2(CH3CN)2]·[PMo12O40]·4CH3CN ( 1 ) and [Co2Cl(TMR4A)2(CH3CN)2]·[PMo12O40]·4CH3CN ( 2 ). In both 1 and 2 , one Cl? anion bridges two metal cations, and each metal cation is further chelated by four 2‐mercaptopyridine N‐oxide groups of one TMR4A, producing a [M2Cl(TMR4A)2]3+ dimer (M = Ni or Co). The negative [PMo12O40]3? as a counter‐anion balances the positive charge. Markedly, 1 and 2 exhibit high stability in aqueous solutions with different pH values and in organic solvents. Remarkably, the efficient heterogeneous catalytic capability for oxidative desulfurization was studied by suing 1 and 2 as recycled catalysts. Moreover, the electrochemical behaviors of the two compounds were discussed as well. 相似文献
95.
Multistrain diseases, which are infected through individual contacts, pose severe public health threat nowadays. In this paper, we build competitive and mutative two‐strain edge‐based compartmental models using probability generation function (PGF) and pair approximation (PA). Both of them are ordinary differential equations. Their basic reproduction numbers and final size formulas are explicitly derived. We show that the formula gives a unique positive final epidemic size when the reproduction number is larger than unity. We further consider competitive and mutative multistrain diseases spreading models and compute their basic reproduction numbers. We perform numerical simulations that show some dynamical properties of the competitive and mutative two‐strain models. 相似文献
96.
Rajalingam Agneeswari Yeongkwon Kang Jihoon Lee Ji Hyeon Kwon Vellaiappillai Tamilavan Seong Soo Park Sung Heum Park Youngeup Jin 《Journal of polymer science. Part A, Polymer chemistry》2019,57(4):545-552
We synthesized two new alternating polymers, namely P(Tt‐FQx) and P(Tt‐DFQx) , incorporating electron rich tri‐thiophene and electron deficient 6‐fluoroquinoxaline or 6,7‐difluoroquinoxaline derivatives. Both polymers P(Tt‐FQx) and P(Tt‐DFQx) exhibited high thermal stabilities and the estimated 5% weight loss temperatures are 425 and 460 °C, respectively. Polymers P(Tt‐FQx) and P(Tt‐DFQx) displayed intense absorption band between 450 and 700 nm with an optical band gap (Eg) of 1.78 and 1.80 eV, respectively. The determined highest occupied/lowest unoccupied molecular orbital's (HOMO/LUMO) of P(Tt‐DFQx) (?5.48 eV/?3.68 eV) are slightly deeper than those of P(Tt‐FQx) ( ?5.32 eV/?3.54 eV). The polymer solar cells fabricated with a device structure of ITO/PEDOT:PSS/ P(Tt‐FQx) or P(Tt‐DFQx) :PC70BM (1:1.5 wt %) + 3 vol % DIO/Al offered a maximum power conversion efficiency (PCE) of 3.65% with an open‐circuit voltage (Voc) of 0.59 V, a short‐circuit current (Jsc) of 10.65 mA/cm2 and fill factor (FF) of 59% for P(Tt‐FQx) ‐based device and a PCE of 4.36% with an Voc of 0.69 V, a Jsc of 9.92 mA/cm2, and FF of 63% for P(Tt‐DFQx) ‐based device. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 545–552 相似文献
97.
International Journal of Theoretical Physics - We propose the scheme for cyclic controlled symmetry quantum teleportation by using one three-dimensional hyper-entangled state as the quantum... 相似文献
98.
In this paper, we continue to discuss the normality concerning omitted holomorphic function and get the following result. Let F be a family of meromorphic functions on a domain D, k ≥ 4 be a positive integer, and let a(z) and b(z) be two holomorphic functions on D, where a(z) 0 and f(z) ≠ ∞ whenever a(z)=0. If for any f ∈ F, f'(z) -a(z)fk(z) ≠ b(z), then F is normal on D. 相似文献
99.
Acta Mathematicae Applicatae Sinica, English Series - As an extension of partially linear models and additive models, partially linear additive model is useful in statistical modelling. This paper... 相似文献
100.
Yonghui Liu Huaying Gao Xiaoli Sheng Yuming Zhou Beibei Wang Xiao Sha Maolu Jin Jie Zhao Wenqi Liu 《应用有机金属化学》2019,33(11)
In this work, a series of novel acidic polymerized ionic liquids were used as heterogeneous catalyst for alkylation of o‐Xylene with styrene. And the effect of the amount of initiator and the type of acid used for ion exchange on catalyst structure and the catalytic performance of catalysts for alkylation were studied thoroughly. The experiment results show: when the percentage of the amount of initiator in the total material is 3%, the polymerized ionic liquid catalyst MPM‐SO3H‐[C3V][SO3CF3] has the most uniform with a specific surface area of 97.30 m2/g and a pore volume of 0.35 cm3/g. Benefiting from the unique structure features, MPM‐SO3H‐[C3V][SO3CF3] manifested an excellent catalytic performance for alkylation of o‐Xylene with styrene, along with the conversion of styrene was 96.8% and the yield of 1‐Phenyl‐1‐ortho‐xylene ethane was 94.7%. Therefore, this work provides a novel reference to the synthesis of polymerized ionic liquids and clearly explains the advantage of novel acidic polymerized ionic liquids on alkylation. 相似文献