全文获取类型
收费全文 | 28844篇 |
免费 | 4710篇 |
国内免费 | 3115篇 |
专业分类
化学 | 21381篇 |
晶体学 | 355篇 |
力学 | 1562篇 |
综合类 | 157篇 |
数学 | 3109篇 |
物理学 | 10105篇 |
出版年
2024年 | 57篇 |
2023年 | 558篇 |
2022年 | 865篇 |
2021年 | 1008篇 |
2020年 | 1254篇 |
2019年 | 1163篇 |
2018年 | 1035篇 |
2017年 | 866篇 |
2016年 | 1397篇 |
2015年 | 1391篇 |
2014年 | 1537篇 |
2013年 | 2220篇 |
2012年 | 2539篇 |
2011年 | 2553篇 |
2010年 | 1726篇 |
2009年 | 1723篇 |
2008年 | 1966篇 |
2007年 | 1737篇 |
2006年 | 1562篇 |
2005年 | 1424篇 |
2004年 | 1085篇 |
2003年 | 923篇 |
2002年 | 945篇 |
2001年 | 698篇 |
2000年 | 561篇 |
1999年 | 582篇 |
1998年 | 433篇 |
1997年 | 372篇 |
1996年 | 389篇 |
1995年 | 323篇 |
1994年 | 276篇 |
1993年 | 228篇 |
1992年 | 206篇 |
1991年 | 186篇 |
1990年 | 157篇 |
1989年 | 123篇 |
1988年 | 101篇 |
1987年 | 79篇 |
1986年 | 74篇 |
1985年 | 73篇 |
1984年 | 57篇 |
1983年 | 33篇 |
1982年 | 29篇 |
1981年 | 33篇 |
1980年 | 19篇 |
1979年 | 10篇 |
1976年 | 10篇 |
1975年 | 13篇 |
1973年 | 7篇 |
1971年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Guang Huang Hui-Ran Zhao Qing-Qing Meng Wen Zhou Qi-Jing Zhang Jin-Yun Dong Jia-Hua Cui Shao-Shun Li 《中国化学快报》2017,28(7):1553-1558
6-Substituted 5,8-O-dimethyl-1,4-naphthoquinones (6-DMNQ), the promising anticancer scaffolds, were selectively generated by oxidative demethylation of 2-substituted 1,4,5,8-tetramethoxynaphthalenes with CAN in EtOAc/H2O in comparatively high yields. An interesting finding was that apart from the reported electron-withdrawing effects of substituents on position 2 of naphthalene ring, regioselective synthesis of 6-DMNQ was largely dependent on the steric effects in CAN-mediated oxidation. The selective cytotoxicities of 6-DMNQ from the in vitro cell-based assays were exhibited between the cancer cells and normal cells. Moreover, most of sulfur-containing 6-DMNQ derivatives displayed better anticancer activities than the corresponding oxygen-containing ones, which could provide an available strategy for the design of 6-DMNQ derivatives as potential anticancer agents. 相似文献
992.
C. Garcia V. Coello Z. Han I. P. Radko S. I. Bozhevolnyi 《Applied physics. B, Lasers and optics》2012,107(2):401-407
Dielectric-loaded plasmonic waveguide-racetrack resonators (WRTRs) were designed and fabricated for operating at near-infrared wavelengths (750–850 nm) and characterized using leakage radiation microscopy. The transmission spectra of the WRTRs are found experimentally and compared to the calculated analytical expression. The wavelength-dependent parameters of the analytical expression, i.e. the propagation length and effective-index dispersion, were also estimated experimentally by leakage radiation imaging of direct and Fourier space, respectively. The fabricated structures exhibited high extinction ratio (~20 dB) and good agreement between calculated and measured transmission values. 相似文献
993.
Wenting Zhang Peide Han Aidong Lan Yuping Li Xue Zhang 《Physica E: Low-dimensional Systems and Nanostructures》2012,44(4):813-815
In this paper, a novel PCs defect mode is designed by inserting a Ag/LiNbO3/Ag sandwich structure into periodically stacked TiO2/MgF2 dielectric superlattice. The band gap calculation is conducted using transfer matrix method. An emergence of defect mode around 525 nm is demonstrated. By applying an external voltage on this defect mode, remarkable wavelength tuning can be achieved. At normal incidence, a tuning bandwidth up to 70 nm is obtained by moderate change of external voltage from −250 to 250 V. This feature can be employed to fabricate practical tunable filters in visible region. 相似文献
994.
995.
996.
997.
998.
Benny Luijsterburg Peter Jobse Daniel Hermida Merino Ton Peijs Han Goossens 《Journal of Polymer Science.Polymer Physics》2014,52(16):1071-1082
Isotactic polypropylene (i‐PP) can crystallize in different crystal modifications. In this article, the effect of sepiolite (one‐dimensional) and carbon black (three‐dimensional) fillers on the solid‐state drawability of i‐PP is discussed. The cross‐hatched structure of thermodynamically most stable α‐crystal phase in i‐PP does not allow for perfect chain alignment during solid‐state drawing. The β‐phase i‐PP, obtained by addition of specific nucleating agents, crystallizes in a non‐cross‐hatched spherulitic structure and allows more easy drawing. Depending on the filler type, β–α transformation takes place at different draw ratios, as was observed by in situ wide‐angle X‐ray diffraction measurements. It was observed that β‐nucleated i‐PP has a lower yield stress and can be drawn further than i‐PP crystallized in the α‐crystal phase. If added in the right amount, both carbon black and sepiolite have a reinforcing effect on PP tapes. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1071–1082 相似文献
999.
Guizhong Xie Jianming ZhangYunqiao Dong Cheng HuangGuangyao Li 《International Journal of Solids and Structures》2014
This paper presents an improved exponential transformation for nearly singular boundary element integrals in elasticity problems. The new transformation is less sensitive to the position of the projection point compared with the original transformation. In our work, the conventional distance function is modified into a new form in the polar coordinate system. Based on the refined distance function, an improved exponential transformation is proposed in the polar coordinate system. Moreover, to perform integrations on irregular elements, an adaptive integration scheme considering both the element shape and the projection point associated with the improved transformation is proposed. Furthermore, when the projection point is located outside the integration element, another nearest point is introduced to subdivide the integration elements into triangular or quadrilateral patches of fine shapes. Numerical examples are presented to verify the proposed method. Results demonstrate the accuracy and efficiency of our method. 相似文献
1000.