全文获取类型
收费全文 | 421165篇 |
免费 | 8652篇 |
国内免费 | 3125篇 |
专业分类
化学 | 216825篇 |
晶体学 | 5113篇 |
力学 | 20629篇 |
综合类 | 74篇 |
数学 | 71869篇 |
物理学 | 118432篇 |
出版年
2021年 | 2621篇 |
2020年 | 3042篇 |
2019年 | 3071篇 |
2018年 | 12829篇 |
2017年 | 12478篇 |
2016年 | 11291篇 |
2015年 | 5510篇 |
2014年 | 6475篇 |
2013年 | 17123篇 |
2012年 | 17016篇 |
2011年 | 25742篇 |
2010年 | 15250篇 |
2009年 | 15445篇 |
2008年 | 20572篇 |
2007年 | 22573篇 |
2006年 | 14300篇 |
2005年 | 13895篇 |
2004年 | 12777篇 |
2003年 | 11651篇 |
2002年 | 10506篇 |
2001年 | 10892篇 |
2000年 | 8501篇 |
1999年 | 6821篇 |
1998年 | 5478篇 |
1997年 | 5271篇 |
1996年 | 5441篇 |
1995年 | 4889篇 |
1994年 | 4572篇 |
1993年 | 4400篇 |
1992年 | 4777篇 |
1991年 | 4645篇 |
1990年 | 4325篇 |
1989年 | 4114篇 |
1988年 | 4384篇 |
1987年 | 4029篇 |
1986年 | 3916篇 |
1985年 | 5613篇 |
1984年 | 5671篇 |
1983年 | 4545篇 |
1982年 | 4855篇 |
1981年 | 4905篇 |
1980年 | 4667篇 |
1979年 | 4757篇 |
1978年 | 4748篇 |
1977年 | 4707篇 |
1976年 | 4670篇 |
1975年 | 4543篇 |
1974年 | 4389篇 |
1973年 | 4578篇 |
1972年 | 2581篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
91.
In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated biomaterial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic "pillar"structure and a nacreous "brick and mortar" structure. The prismatic layer looks like a "pillar forest" with variationsection pillars sized on the order of several tens of microns.The nacreous material looks like a "brick wall" with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively.The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material.In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones. 相似文献
92.
Algebras and Representation Theory - We introduce and study the category of twisted modules over a triangular differential graded bocs. We show that in this category idempotents split, that it... 相似文献
93.
Ben Jadi S. El Guerraf A. Bazzaoui E.A. Wang R. Martins J.I. Bazzaoui M. 《Journal of Solid State Electrochemistry》2019,23(8):2423-2433
Journal of Solid State Electrochemistry - Due to their distinctive chemical, electronic, and environmental properties, polypyrrole is used as a blocking barrier for methanol leakage in direct... 相似文献
94.
Liying Zhang Chuanrui Zhao Yujiao Bai Qian Wang Pan Ma Xiaojie Ma Peihua Zhu 《Electroanalysis》2022,34(2):302-309
The design and exploration of efficient, stable and environmentally compatible organic emitters for an electrochemiluminescence (ECL) sensor is a promising topic. Herein, a novel environmentally-friendly luminophore, ZnBCBTP@MWCNTs, were fabricated via self-assembly of porphyrin molecules (ZnBCBTP) onto multi-walled carbon nanotubes (MWCNTs). The resulting luminophore ZnBCBTP@MWCNTs displayed not only the highly ECL property and but also the good accelerated electron mobility. Then, a label-free ECL biosensor based ZnBCBTP@MWCNTs was constructed for the ultrasensitive detection of uric acid. Excitingly, this proposed ECL biosensor performed a good linear relationship in the range of 0–300 μM with a low detection limit of 1.4 μM, thus offering another reliable and feasible sensing platform for clinical bioanalysis with good selectivity, stability, and repeatability. 相似文献
95.
Peng-Yan Gui Xiao-Hui Yan Wen-Juan Yuan Yuan-Liang Ma Xiao Ding Shuai Liu 《Natural product research》2019,33(19):2830-2836
A new A, D-seco limonoid, named 12-acetyloxyperforatin (1), along with three known ones, were isolated from the leaves of Harrisonia perforata. Their structures were elucidated on the basis of spectroscopic analysis, including extensive NMR techniques and computational modelling. These compounds showed no inhibitory activity against the 11β-HSD1 enzyme. 相似文献
96.
Kounta Moussa Dawson Nathan J. 《Methodology and Computing in Applied Probability》2021,23(3):1155-1172
Methodology and Computing in Applied Probability - The problem of optimally controlling one-dimensional diffusion processes until they enter a given stopping set is extended to include Markov... 相似文献
97.
98.
99.
Ding Q. Yao M. Wu Sh. Zeng M. Xue N. Wu D. Xu J. 《Journal of Applied Spectroscopy》2022,89(4):712-718
Journal of Applied Spectroscopy - Based on partial least squares (PLS) analysis, the effects of different smoothing points and different preprocessing methods on the accuracy and precision of the... 相似文献
100.
Transport in Porous Media - The theme of coupling problems for adsorption, absorption and thermochemical transport in porous media is very important for engineering applications. Based on the... 相似文献