全文获取类型
收费全文 | 18336篇 |
免费 | 1539篇 |
国内免费 | 1210篇 |
专业分类
化学 | 10150篇 |
晶体学 | 310篇 |
力学 | 1297篇 |
综合类 | 82篇 |
数学 | 1959篇 |
物理学 | 7287篇 |
出版年
2024年 | 33篇 |
2023年 | 213篇 |
2022年 | 392篇 |
2021年 | 413篇 |
2020年 | 401篇 |
2019年 | 427篇 |
2018年 | 378篇 |
2017年 | 338篇 |
2016年 | 565篇 |
2015年 | 477篇 |
2014年 | 755篇 |
2013年 | 1019篇 |
2012年 | 1313篇 |
2011年 | 1460篇 |
2010年 | 1079篇 |
2009年 | 1058篇 |
2008年 | 1169篇 |
2007年 | 1016篇 |
2006年 | 958篇 |
2005年 | 836篇 |
2004年 | 687篇 |
2003年 | 603篇 |
2002年 | 573篇 |
2001年 | 722篇 |
2000年 | 592篇 |
1999年 | 442篇 |
1998年 | 371篇 |
1997年 | 321篇 |
1996年 | 326篇 |
1995年 | 251篇 |
1994年 | 261篇 |
1993年 | 182篇 |
1992年 | 208篇 |
1991年 | 195篇 |
1990年 | 162篇 |
1989年 | 146篇 |
1988年 | 96篇 |
1987年 | 61篇 |
1986年 | 69篇 |
1985年 | 68篇 |
1984年 | 51篇 |
1983年 | 39篇 |
1982年 | 44篇 |
1981年 | 38篇 |
1980年 | 33篇 |
1978年 | 33篇 |
1977年 | 26篇 |
1976年 | 25篇 |
1975年 | 24篇 |
1974年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 103 毫秒
991.
We study the evolutionary Prisoner's dilemma game on scale-free networks, focusing on the influence of different initial distributions for cooperators and defectors on the evolution of cooperation. To address this issue, we consider three types of initial distributions for defectors: uniform distribution at random, occupying the most connected nodes, and occupying the lowest-degree nodes, respectively. It is shown that initial configurations for defectors can crucially influence the cooperation level and the evolution speed of cooperation. Interestingly, the situation where defectors initially occupy the lowest-degree vertices can exhibit the most robust cooperation, compared with two other distributions. That is, the cooperation level is least affected by the initial percentage of defectors. Moreover, in this situation, the whole system evolves fastest to the prevalent cooperation. Besides, we obtain the critical values of initial frequency of defectors above which the extinction of cooperators occurs for the respective initial distributions. Our results might be helpful in explaining the maintenance of high cooperation in scale-free networks. 相似文献
992.
Two special classes of conserved densities involving arbitrary smooth functions are explicitly formulated for the generalized Riemann equation at arbitrary N. The particular case when N = 2 covers most of the known conserved densities of the equation, and the result is also extended to the famous Gurevich-Zybin, Monge-Ampere and two-component Hunter-Saxton equations by considering certain reductions. 相似文献
993.
Lyu Jiahui Han Huibin Wu Qiong Ma Hongchao Ma Chun Dong Xiaoli Fu Yinghuan 《Journal of Solid State Electrochemistry》2019,23(3):847-859
Journal of Solid State Electrochemistry - Rational hydrophobic anode has been considered as a promising approach for water pollution remediation. However, the construction method of the hydrophobic... 相似文献
994.
Haolin Lin Shenhe Fu Zhigui Deng Haiqiong Zhou Hao Yin Zhen Li Zhenqiang Chen 《Annalen der Physik》2019,531(11)
Superoscillation is an intriguing wave phenomenon which enables subwavelength features propagating into far field and hence has potential applications in super‐resolution microscopy as well as particle trapping and manipulation. While previous demonstrations mostly concentrate on designing complicated nanostructures for generating uncontrollable superoscillatory functions, here a new technique which allows for creating polynomially shaped superoscillatory functions that contain phase singularity arrays is demonstrated both theoretically and experimentally. Such a technique is implemented in optical experiments for the first time and controllable superoscillatory lobes with feature much below the diffraction limit is achieved. More importantly, a general theoretical framework, which, to our knowledge, has not been reported before, is developed to show how the created superoscillations propagate to a distance of many Rayleigh ranges and eventually disappear when the distance is sufficiently larger. The validity of the model is confirmed by the experiments. The results may trigger further studies in light field shaping and manipulations in subwavelength scale. 相似文献
995.
The first addition-elimination of nitroalkanes to 3-phenacylideneoxindoles was developed, affording the corresponding 3-alkenylphenacylidene-oxindoles with high yields.The addition-elimination mechanism of 3-phenacylideneoxindoles with nitroalkanes and removable NO2 group in concert guarantees the high regioselectivity. 相似文献
996.
Abdul Q. Ramle Asli Karakas Abdul K. M. Arof Mustafa Karakaya Mehmet Taser Aysun Gozutok Chee Chin Fei Nurhidayatullaili M. Julkapli Wan J. Basirun 《Journal of heterocyclic chemistry》2020,57(10):3566-3573
Two new macrocyclic dibenzotetraaza[14]annulene (DBTAA) compounds with indolenine ( 5 ) and pyridoindolenine ( 6 ) moieties were synthesized and characterized by spectroscopy. Both DBTAAs exhibit strong UV-Vis absorption properties in the Soret band region. The theoretical second-order nonlinear optical property, electric dipole moment (μ), dispersion-free dipole polarizability (α) and first hyper-polarizability values were calculated by density functional theory and time dependent density functional theory. The ab-initio quantum mechanical calculation by time-dependent Hartree-Fock method was utilized to investigate the dynamic dipole polarizabilities, dynamic second-order, static, and dynamic third-order (γ) hyper-polarizabilities of the DBTAAs. The configuration interaction technique of all doubly occupied molecular orbitals possesses theoretically defined single-photon absorption (OPA) specifications for the examined structures. The computed maximum OPA wavelengths on both macrocyclic compounds coincide with the preceding measurement outcomes. 相似文献
997.
The pressure-driven device is designed and the flow rates of the microfluidic systems can be supplied by the pressure-driven flows, which can significantly reduce the flow-rate fluctuations coming from the pump source. For pressure-driven flows, the flow rates of the fluids can be predicted by measuring the pressure drop along a polytetrafluoroethylene (PTFE) tubing. Especially, by varying the geometrical parameters of the PTFE tubing, the predicted flow rates of the fluids are compared with the experimental measurements, and the testing precision of the pressure-driven flows can be obtained. Meanwhile, the dynamic characteristics of the open-loop and closed-loop control pressure-driven device are comparatively studied. Particularly, a proportional and integral (PI) controller is integrated with the closed-loop control pressure-driven device, and the effects of the parameters of the PI controller on the dynamic characteristics of the pressure-driven devices are mainly discussed. Most importantly, by improving the dynamic characteristics of the pressure-driven devices, precise measurement and control of the pressure-driven flows can be achieved for microfluidic systems. 相似文献
998.
999.
Fanghua Zhang Jiwei Yin Chao Zhang Mengnan Han Xuming Wang Shuangqing Fu Jie Du Honglei Zhang Wei Li 《Macromolecular bioscience》2020,20(7)
Affibody‐conjugated RALA (affi‐RA) are designed for delivering oligomeric 5‐fluorodeoxyuridine (FUdR, metabolite of 5‐FU) strand to raise the selectivity of 5‐fluorouracil (5‐FU), decrease its toxicity and improve its suboptimal therapeutic efficacy. The nanodrugs, FUdR@affi‐RA, are spontaneously assembled by electrostatic interaction between positively charged affi‐RA and negatively charged FUdR15‐strands (15 consecutive FUdR). FUdR@affi‐RA exhibits excellent stability under simulated physiological conditions. Compared with free FUdR, FUdR@affi‐RA shows excellent targeting and higher cytotoxicity in human epidermal growth factor receptor 2 (HER2) overexpressing gastric cancer N87 cells. Moreover, the anticancer mechanism studies reveal that FUdR@affi‐RA enhances the expression and activity of apoptosis‐associated proteins in the Bcl‐2/Bax‐caspase 8,9‐caspase 3 apoptotic pathway induced by FUdR. This study indicates that the fusion vector, affi‐RA, presents a promising delivery system platform for nucleoside analogue drugs and provides a new strategy for the development of therapeutics of cancer treatment. 相似文献
1000.
Journal of Visualization - This study investigates self-sustained oscillation of the flow in a double-cavity channel with cavity length–width ratio L/H?=?3 using a time-resolved... 相似文献