全文获取类型
收费全文 | 25791篇 |
免费 | 4175篇 |
国内免费 | 4520篇 |
专业分类
化学 | 19127篇 |
晶体学 | 552篇 |
力学 | 1588篇 |
综合类 | 423篇 |
数学 | 3353篇 |
物理学 | 9443篇 |
出版年
2024年 | 36篇 |
2023年 | 357篇 |
2022年 | 626篇 |
2021年 | 784篇 |
2020年 | 884篇 |
2019年 | 939篇 |
2018年 | 823篇 |
2017年 | 919篇 |
2016年 | 1165篇 |
2015年 | 1242篇 |
2014年 | 1495篇 |
2013年 | 1977篇 |
2012年 | 2278篇 |
2011年 | 2366篇 |
2010年 | 1818篇 |
2009年 | 1795篇 |
2008年 | 1971篇 |
2007年 | 1745篇 |
2006年 | 1639篇 |
2005年 | 1351篇 |
2004年 | 1203篇 |
2003年 | 999篇 |
2002年 | 1138篇 |
2001年 | 1008篇 |
2000年 | 751篇 |
1999年 | 611篇 |
1998年 | 381篇 |
1997年 | 277篇 |
1996年 | 289篇 |
1995年 | 236篇 |
1994年 | 228篇 |
1993年 | 198篇 |
1992年 | 140篇 |
1991年 | 133篇 |
1990年 | 100篇 |
1989年 | 114篇 |
1988年 | 65篇 |
1987年 | 61篇 |
1986年 | 58篇 |
1985年 | 55篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 20篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1959年 | 13篇 |
1958年 | 11篇 |
1957年 | 16篇 |
1956年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
通过用毛细管测量纯水表面张力系数实验,得到管内径d与接触角θ的相对误差之间的关系曲线,由此说明实验测得的表面张力系数α和理论公式相比呈现一定的偏差,并简单地讨论了实验的理想状态与实际情况的差别. 相似文献
62.
63.
64.
65.
Junchai Zhao Shichun Jiang Xiangling Ji Lijia An Bingzheng Jiang 《Journal of Polymer Science.Polymer Physics》2004,42(18):3496-3504
The surface morphologies of poly(styrene‐b‐4vinylpyridine) (PS‐b‐P4VP) diblock copolymer and homopolystyrene (hPS) binary blend thin films were investigated by atomic force microscopy as a function of total volume fraction of PS (?PS) in the mixture. It was found that when hPS was added into symmetric PS‐b‐P4VP diblock copolymers, the surface morphology of this diblock copolymer was changed to a certain degree. With ?PS increasing at first, hPS was solubilized into the corresponding domains of block copolymer and formed cylinders. Moreover, the more solubilized the hPS, the more cylinders exist. However, when the limit was reached, excessive hPS tended to separate from the domains independently instead of solubilizing into the corresponding domains any longer, that is, a macrophase separation occurred. A model describing transitions of these morphologies with an increase in ?PS is proposed. The effect of composition on the phase morphology of blend films when graphite is used as a substrate is also investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3496–3504, 2004 相似文献
66.
Hydrogels containing benzo-18-crown-6 were used to modify microcantilevers for measurements of the concentration of Pb2+ in aqueous solutions. These microcantilevers undergo bending deflection upon exposure to solutions containing various Pb2+ concentrations as the result of a swelling of the hydrogels. It was found that a concentration of 10(-6) M Pb2+ can be detected using this technology. Other cations, such as Na+, have no effect on the deflection of this cantilever. The cation K+, which also complexes with benzo-18-crown-6, could interfere with Pb2+ detection, but only at high concentrations (> 10(-4) M). 相似文献
67.
Won Keun Son Ji Ho Youk Taek Seung Lee Won Ho Park 《Journal of Polymer Science.Polymer Physics》2004,42(1):5-11
Electrospinning of cellulose acetate (CA) in a new solvent system and the deacetylation of the resulting ultrafine CA fibers were investigated. Ultrafine CA fibers (∼2.3 μm) were successfully prepared via electrospinning of CA in a mixed solvent of acetone/water at water contents of 10–15 wt %, and more ultrafine CA fibers (0.46 μm) were produced under basic pH conditions. Ultrafine cellulose fibers were regenerated from the homogeneous deacetylation of ultrafine CA fibers in KOH/ethanol. It was very rapid and completed within 20 min. The crystal structure, thermal properties, and morphology of ultrafine CA fibers were changed according to the degree of deacetylation, finally to those of pure cellulose, but the nonwoven fibrous mat structure was maintained. The activation energy for the deacetylation of ultrafine CA fibers was 10.3 kcal/mol. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 5–11, 2004 相似文献
68.
69.
70.
半自由声场环境下的声源重建和声场预测研究对声全息技术走向实际应用具有非常重要的意义.在提出基于分布源边界点法的半自由声场全息重建和预测方法的基础上,对此展开了实验研究.并将重建和预测的结果与常规方法重建和预测的结果进行了比较和讨论,说明了重建预测过程中反射声压的影响和考虑反射声压的必要性,证明了所提出方法在解决半自由声场环境下存在地面反射时的声源重建和声场预测时的有效性和准确性.还提出了采用奇异值截断滤波和Tikhonov正则化方法来削弱测量误差的影响,从而进一步优化了重建结果,提高了全息成像的可信度.
关键词:
声全息
半自由场
边界点
声辐射
反射声 相似文献