全文获取类型
收费全文 | 21799篇 |
免费 | 3274篇 |
国内免费 | 3208篇 |
专业分类
化学 | 17107篇 |
晶体学 | 301篇 |
力学 | 1128篇 |
综合类 | 279篇 |
数学 | 2710篇 |
物理学 | 6756篇 |
出版年
2024年 | 50篇 |
2023年 | 322篇 |
2022年 | 614篇 |
2021年 | 667篇 |
2020年 | 773篇 |
2019年 | 763篇 |
2018年 | 623篇 |
2017年 | 695篇 |
2016年 | 1039篇 |
2015年 | 1017篇 |
2014年 | 1308篇 |
2013年 | 1660篇 |
2012年 | 1912篇 |
2011年 | 1956篇 |
2010年 | 1521篇 |
2009年 | 1360篇 |
2008年 | 1511篇 |
2007年 | 1299篇 |
2006年 | 1252篇 |
2005年 | 1066篇 |
2004年 | 905篇 |
2003年 | 814篇 |
2002年 | 996篇 |
2001年 | 793篇 |
2000年 | 509篇 |
1999年 | 514篇 |
1998年 | 341篇 |
1997年 | 247篇 |
1996年 | 235篇 |
1995年 | 196篇 |
1994年 | 187篇 |
1993年 | 145篇 |
1992年 | 138篇 |
1991年 | 148篇 |
1990年 | 100篇 |
1989年 | 89篇 |
1988年 | 73篇 |
1987年 | 67篇 |
1986年 | 69篇 |
1985年 | 58篇 |
1984年 | 28篇 |
1983年 | 15篇 |
1982年 | 23篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 13篇 |
1977年 | 11篇 |
1959年 | 13篇 |
1958年 | 11篇 |
1957年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
In this work, the natural convection in a concentric annulus between a cold outer square cylinder and a heated inner circular cylinder is simulated using the differential quadrature (DQ) method. The vorticity‐stream function formulation is used as the governing equation, and the coordinate transformation technique is introduced in the DQ computation. It is shown in this paper that the outer square boundary can be approximated by a super elliptic function. As a result, the coordinate transformation from the physical domain to the computational domain is set up by an analytical expression, and all the geometrical parameters can be computed exactly. Numerical results for Rayleigh numbers range from 104 to 106 and aspect ratios between 1.67 and 5.0 are presented, which are in a good agreement with available data in the literature. It is found that both the aspect ratio and the Rayleigh number are critical to the patterns of flow and thermal fields. The present study suggests that a critical aspect ratio may exist at high Rayleigh number to distinguish the flow and thermal patterns. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
32.
非参数回归函数估计的渐近正态性 总被引:6,自引:0,他引:6
本文研究了独立或相依样本时非参数回归函数的Nadaraya-Watson估计,在简洁合理的条件下,证明了估计量的渐近正态性.获得的结论可在时间序列分析中得到应用. 相似文献
33.
离子交换富集-导数火焰原子吸收法测定自来水中Cu,Fe和Zn 总被引:7,自引:0,他引:7
本文研究了用 2 0 1× 7阳离子交换树脂对自来水中的微量元素进行交换富集 ,采用微量脉冲进样 导数火焰原子吸收法测定富集后溶液中的Cu ,Fe和Zn ,该方法灵敏度分别为 0 2 9,0 5 9和 0 0 6 μg·L- 1 ,精密度分别为 4 2 8% ,1 95 %和 2 2 8% ,检测限分别为 1 2 8,5 85和 0 6 8μg·L- 1 ,回收率分别为 91 13% ,10 1 34%和99 84 % ,本方法大大减少了需样量 ,简便快速 ,灵敏度高。 相似文献
34.
35.
Based on the Collins formula and irradiance moments definition, the propagation of the kurtosis parameter of super-Gaussian beams through a spherically aberrated lens is studied. Detailed numerical results are given. It is shown that, as compared with aberration-free super-Gaussian beams, the profile of spherically aberrated super-Gaussian beams can be leptokurtic, mesokurtic or platykurtic, depending on the aberration and propagation distance. The results for the spherically aberrated Gaussian beams can be dealt with as a special case treated in this paper. Finally, the advantage of our method is pointed out. 相似文献
36.
37.
Summary Some estimators of maximum likelihood type are constructed for estimating functionals of one-dimensional Gibbs states. We also show that those estimators are strongly consistent, asymptotically normal and asymptotically efficient. 相似文献
38.
39.
40.
Mao‐Chuan Yuan Ping‐I Shih Chen‐Han Chien Ching‐Fong Shu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(14):2925-2937
We have synthesized a blue‐light‐emitting polyfluorene (PF) derivative ( PF‐CBZ‐OXD ) that presents bulky hole‐transporting carbazole and electron‐transporting oxadiazole pendent groups functionalized at the C‐9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF‐CBZ‐OXD and its analogue PF‐TPA‐OXD with a red‐light‐emitting iridium phosphor for use as components of phosphorescent red‐light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF‐CBZ‐OXD , in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2925–2937, 2007 相似文献