全文获取类型
收费全文 | 18587篇 |
免费 | 2797篇 |
国内免费 | 2195篇 |
专业分类
化学 | 12922篇 |
晶体学 | 128篇 |
力学 | 1567篇 |
综合类 | 160篇 |
数学 | 2842篇 |
物理学 | 5960篇 |
出版年
2024年 | 29篇 |
2023年 | 178篇 |
2022年 | 277篇 |
2021年 | 521篇 |
2020年 | 672篇 |
2019年 | 557篇 |
2018年 | 461篇 |
2017年 | 588篇 |
2016年 | 746篇 |
2015年 | 756篇 |
2014年 | 1027篇 |
2013年 | 1519篇 |
2012年 | 1137篇 |
2011年 | 1437篇 |
2010年 | 1188篇 |
2009年 | 1274篇 |
2008年 | 1335篇 |
2007年 | 1293篇 |
2006年 | 1238篇 |
2005年 | 1034篇 |
2004年 | 930篇 |
2003年 | 787篇 |
2002年 | 770篇 |
2001年 | 507篇 |
2000年 | 454篇 |
1999年 | 418篇 |
1998年 | 346篇 |
1997年 | 308篇 |
1996年 | 272篇 |
1995年 | 260篇 |
1994年 | 212篇 |
1993年 | 171篇 |
1992年 | 154篇 |
1991年 | 121篇 |
1990年 | 102篇 |
1989年 | 78篇 |
1988年 | 75篇 |
1987年 | 46篇 |
1986年 | 41篇 |
1985年 | 44篇 |
1984年 | 45篇 |
1983年 | 17篇 |
1982年 | 38篇 |
1981年 | 24篇 |
1980年 | 22篇 |
1979年 | 18篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 13篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 757 毫秒
31.
研究了不同比例的PVK与齐聚PPV衍生物DBVP掺杂体系的能量转移和发光特性.通过对PVK,DBVP及PVK:DBVP掺杂体系的UV-vis,PL和PLE光谱的研究,分析了PVK与DBVP之间的能量转移过程.利用PVK在体系中类似于溶剂的分散作用,制备了结构为ITO/PEDOT/PVK:DBVP/LiF/Al的电致发光器件,研究了掺杂体系的电致发光性能.结果表明,在掺杂体系的光致发光和电致发光中,PVK的发射被有效地抑制,PVK与DBVP之间发生了非常有效的能量转移,通过调节PVK与DBVP的比例,可以获得蓝色和绿色发光,同时可以改善器件的发光性能,当PVK与DBVP的重量比为1∶2时,器件的绿色发光效率达到1·06cd/A,此时发光亮度为52cd/m2. 相似文献
32.
33.
受激发射损耗荧光显微镜利用荧光饱和和激发态荧光受激损耗的非线性关系,通过限制损耗区域,可突破远场光学显微术的衍射极限分辨力并实现三维成像。基于对粒子速率方程组的修正,建立了描述荧光团各能级粒子数概率时间特性的模型,并定义了时间平均损耗效率判据。采用高斯函数模拟两束入射激光脉冲通过对模型的数值计算,模拟了激发脉冲的SIED激光脉冲的光强、脉冲宽度以及两束光的延迟时间等参量与损耗效率之间的关系,并获得了各参量的最佳值,优化了损耗效率,为提高系统分辨力提供了有效的途径。 相似文献
34.
35.
36.
37.
38.
V. I. Sakharov 《Fluid Dynamics》2007,42(6):1007-1016
The results of numerical simulation are presented for thermally and chemically nonequilibrium air plasma flows in a plasmatron discharge channel and underexpanded dissociated and partially ionized air jets flowing past a cylindrical model with a blunt leading edge and cooled copper surface under the experimental conditions realized in a VGU-4 100 kW induction plasmatron (Institute for Problems in Mechanics of the Russian Academy of Sciences) (see, for example, [1, 2]). The nonequilibrium excitation of the vibrational degrees of freedom of the molecules in the modal approximation and the difference between the electron and translational heavy-particle temperatures are taken into account in the calculations. The calculated data on the heat transfer and pressure at the stagnation point are compared with the results obtained within the framework of the thermally equilibrium model. Comparison with the experimental data obtained in the Institute for Problem in Mechanics of the Russian Academy of Sciences (Laboratory for interaction between plasma and radiation and materials) and kindly provided for comparison purposes gives satisfactory agreement. 相似文献
39.
Anuj Mittal Swaminathan Sivaram 《Journal of polymer science. Part A, Polymer chemistry》2005,43(21):4996-5008
A tridentate ligand, BPIEP: 2,6‐bis[1‐(2,6‐diisopropyl phenylimino) ethyl] pyridine, having central pyridine unit and two peripheral imine coordination sites was effectively employed in controlled/“living” radical polymerization of MMA at 90°C in toluene as solvent, CuIBr as catalyst, and ethyl‐2‐bromoisobutyrate (EBiB) as initiator resulting in well‐defined polymers with polydispersities Mw/Mn ≤ 1.23. The rate of polymerization follows first‐order kinetics, kapp = 3.4 × 10?5 s?1, indicating the presence of low radical concentration ([P*] ≤ 10?8) throughout the reaction. The polymerization rate attains a maximum at a ligand‐to‐metal ratio of 2:1 in toluene at 90°C. The solvent concentration (v/v, with respect to monomer) has a significant effect on the polymerization kinetics. The polymerization is faster in polar solvents like, diphenylether, and anisole, as compared to toluene. Increasing the monomer concentration in toluene resulted in a better control of polymerization. The molecular weights (Mn,SEC) increased linearly with conversion and were found to be higher than predicted molecular (Mn,Cal). However, the polydispersity remained narrow, i.e., ≤1.23. The initiator efficiency at lower monomer concentration approaches a value of 0.7 in 110 min as compared to 0.5 in 330 min at higher monomer concentration. The aging of the copper salt complexed with BPIEP had a beneficial effect and resulted in polymers with narrow polydispersitities and higher conversion. PMMA obtained at room temperature in toluene (33%, v/v) gave PDI of 1.22 (Mn = 8500) in 48 h whereas, at 50°C the PDI is 1.18 (Mn = 10,300), which is achieved in 23 h. The plot of lnkapp versus 1/T gave an apparent activation energy of polymerization as (ΔE≠app) 58.29 KJ/mol and enthalpy of equilibrium (ΔH0eq) to 28.8 KJ/mol. Reverse ATRP of MMA was successfully performed using AIBN in bulk as well as solution. The controlled nature of the polymerization reaction was established through kinetic studies and chain extension experiments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4996–5008, 2005 相似文献
40.