全文获取类型
收费全文 | 26070篇 |
免费 | 4626篇 |
国内免费 | 4200篇 |
专业分类
化学 | 13808篇 |
晶体学 | 350篇 |
力学 | 880篇 |
综合类 | 355篇 |
数学 | 2098篇 |
物理学 | 6820篇 |
无线电 | 10585篇 |
出版年
2024年 | 84篇 |
2023年 | 511篇 |
2022年 | 822篇 |
2021年 | 920篇 |
2020年 | 972篇 |
2019年 | 942篇 |
2018年 | 871篇 |
2017年 | 912篇 |
2016年 | 1112篇 |
2015年 | 1377篇 |
2014年 | 1504篇 |
2013年 | 1930篇 |
2012年 | 2218篇 |
2011年 | 2249篇 |
2010年 | 1839篇 |
2009年 | 1922篇 |
2008年 | 1985篇 |
2007年 | 1873篇 |
2006年 | 1741篇 |
2005年 | 1597篇 |
2004年 | 1240篇 |
2003年 | 990篇 |
2002年 | 1081篇 |
2001年 | 871篇 |
2000年 | 793篇 |
1999年 | 512篇 |
1998年 | 318篇 |
1997年 | 278篇 |
1996年 | 249篇 |
1995年 | 231篇 |
1994年 | 192篇 |
1993年 | 153篇 |
1992年 | 114篇 |
1991年 | 82篇 |
1990年 | 69篇 |
1989年 | 71篇 |
1988年 | 39篇 |
1987年 | 46篇 |
1986年 | 33篇 |
1985年 | 27篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1973年 | 4篇 |
1957年 | 5篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
861.
Tong Su Yafei Wang Yi Liu William G. Branton Eugene Asahchop Christopher Power Bei Jiang Linglong Kong Niansheng Tang 《Entropy (Basel, Switzerland)》2020,22(11)
Distance weighted discrimination (DWD) is an appealing classification method that is capable of overcoming data piling problems in high-dimensional settings. Especially when various sparsity structures are assumed in these settings, variable selection in multicategory classification poses great challenges. In this paper, we propose a multicategory generalized DWD (MgDWD) method that maintains intrinsic variable group structures during selection using a sparse group lasso penalty. Theoretically, we derive minimizer uniqueness for the penalized MgDWD loss function and consistency properties for the proposed classifier. We further develop an efficient algorithm based on the proximal operator to solve the optimization problem. The performance of MgDWD is evaluated using finite sample simulations and miRNA data from an HIV study. 相似文献
862.
863.
864.
865.
Yi Xu Siyu Guo Xinjian Mao Jian Feng 《Journal of Dispersion Science and Technology》2018,39(3):443-451
The self-assembly behaviors of a series of zwitterionic heterogemini surfactants CmH2m+1-PO4–(CH2)2-N+(CH3)2-CnH2n+1, abbreviated as Cm-P-N-Cn (m, n?=?9, 9; 9, 12; 9, 15; 9, 18; 12, 12; 12, 15; 12, 18; 15, 15; 15, 18; 18, 18), have been investigated in aqueous solution by the dissipative particle dynamics (DPD) method. Morphologies such as sphere (S), rod (R), planar grid (PG), lamella (L), honeycomb (H), one-, two-, and three-dimensional tunnels (1DT, 2DT, and 3DT) have been observed showing more diversities than those of the corresponding symmetric gemini surfactants Cm-N-N-Cm (m?=?9, 12, 15, 18). With the increase of surfactant concentration in the aqueous solution, a distinct transition path ‘‘S—R—PG—3DT—L—2DT—1DT’’ is proved to be common for all the Cm-P-N-Cn systems. Besides, the hydrophobic chain length has a significant influence on the self-assembly behaviors in the case of m?≠?n. Radial distribution function is an effective method to quantitatively evaluate the interaction and relationship between each functional group in the surfactant molecule and water. Results can provide a new insight into the self-assembly behaviors of zwitterionic heterogemini surfactants and the corresponding applications. 相似文献
866.
867.
868.
In this work, the microstructural changes occurring during cooling of friction-stir welded aluminum alloy AA1100 were evaluated. To this end, friction-stir welding (FSW) was performed in a wide range of cooling rates of 20–62 K/s and the evolved microstructures were studied by using electron backscatter diffraction. Below 0.6 Tm (Tm being the melting point), the stir zone material was found to experience no significant changes during cooling. At higher FSW temperatures, however, notable changes occurred in the welded material, including grain growth, sharpening of texture, reduction of the fraction of high-angle boundaries and material softening. 相似文献
869.
Mengjiao Li Feng-Shou Yang Hung-Chang Hsu Wan-Hsin Chen Chia Nung Kuo Jiann-Yeu Chen Shao-Heng Yang Ting-Hsun Yang Che-Yi Lin Yi Chou Mu-Pai Lee Yuan-Ming Chang Yung-Cheng Yang Ko-Chun Lee Yi-Chia Chou Chen-Hsin Lien Chun-Liang Lin Ya-Ping Chiu Chin Shan Lue Shu-Ping Lin Yen-Fu Lin 《Advanced functional materials》2021,31(5):2007587
Defect engineering represents a significant approach for atomically thick 2D semiconductor material development to explore the unique material properties and functions. Doping-induced conversion of conductive polarity is particularly beneficial for optimizing the integration of layered electronics. Here, controllable doping behavior in palladium diselenide (PdSe2) transistor is demonstrated by manipulating its adatom-vacancy groups. The underlying mechanisms, which originate from reversible adsorption/desorption of oxygen clusters near selenide vacancy defects, are investigated systematically via their dynamic charge transfer characteristics and scanning tunneling microscope analysis. The modulated doping effect allows the PdSe2 transistor to emulate the essential characteristics of photo nociceptor on a device level, including firing signal threshold and sensitization. Interestingly, electrostatic gating, acting as a neuromodulator, can regulate the adaptive modes in nociceptor to improve its adaptability and perceptibility to handle different danger levels. An integrated artificial nociceptor array is also designed to execute unique image processing functions, which suggests a new perspective for extension of the promise of defect engineered 2D electronics in simplified sensory systems toward use in advanced humanoid robots and artificial visual sensors. 相似文献
870.
Zhewen Lu Junqiu Jiang Yi Yang Joshua Lacey Michael J. Brear 《Proceedings of the Combustion Institute》2021,38(1):243-250
This work investigates the oxidation of hydrogen near its second explosion limit in a turbulent flow reactor at pressures of 1 to 8 bar, temperatures of 950 K and an equivalence ratio of 0.035. The concentrations of H2, O2 and H2O are measured along the reactor and simulated using several kinetic models from the literature. These experiments demonstrate evident negative pressure dependence from roughly 1 to 4 bar, with further increases in pressure resuming its positive impact on reaction rates. The simulated and measured species concentrations along the reactor generally agree within a factor of 2.Further investigation is then conducted to measure the rate coefficient of reaction H + O2 (+ M) = HO2 (+M) (R2), which is one of the most sensitive reactions in hydrogen's oxidation chemistry at these conditions. This investigation is conducted by using nitric oxide (NO) as a dopant and measuring the resulting, quasi-steady-state concentrations of NO2. The rate coefficients are obtained at 950 – 1010 K. Combined with literature results, an Arrhenius expression is proposed, = 4.50 × 1020 (T/K)?1.73 [cm6 mole?2 s?1], for the reaction rate at the low-pressure limit over 500 K – 2000 K with N2 as the bath gas. Simulations using the models from the literature with the proposed Arrhenius expression for this reaction then demonstrate improved agreement with the experiments. 相似文献