全文获取类型
收费全文 | 44174篇 |
免费 | 8530篇 |
国内免费 | 12855篇 |
专业分类
化学 | 32984篇 |
晶体学 | 1376篇 |
力学 | 2974篇 |
综合类 | 1563篇 |
数学 | 6511篇 |
物理学 | 20151篇 |
出版年
2024年 | 93篇 |
2023年 | 536篇 |
2022年 | 1330篇 |
2021年 | 1480篇 |
2020年 | 1546篇 |
2019年 | 1506篇 |
2018年 | 1411篇 |
2017年 | 1802篇 |
2016年 | 1654篇 |
2015年 | 2156篇 |
2014年 | 2631篇 |
2013年 | 3467篇 |
2012年 | 3508篇 |
2011年 | 3974篇 |
2010年 | 3508篇 |
2009年 | 3683篇 |
2008年 | 3959篇 |
2007年 | 3609篇 |
2006年 | 3580篇 |
2005年 | 3103篇 |
2004年 | 2436篇 |
2003年 | 1785篇 |
2002年 | 1761篇 |
2001年 | 1835篇 |
2000年 | 1956篇 |
1999年 | 1199篇 |
1998年 | 686篇 |
1997年 | 585篇 |
1996年 | 531篇 |
1995年 | 442篇 |
1994年 | 505篇 |
1993年 | 463篇 |
1992年 | 398篇 |
1991年 | 307篇 |
1990年 | 315篇 |
1989年 | 322篇 |
1988年 | 235篇 |
1987年 | 187篇 |
1986年 | 178篇 |
1985年 | 117篇 |
1984年 | 135篇 |
1983年 | 115篇 |
1982年 | 87篇 |
1981年 | 86篇 |
1980年 | 78篇 |
1979年 | 53篇 |
1978年 | 34篇 |
1976年 | 19篇 |
1974年 | 19篇 |
1965年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
Song Zhang Luke A. Galuska Xiaodan Gu 《Journal of polymer science. Part A, Polymer chemistry》2022,60(7):1108-1129
Thin films with a nanometer-scale thickness are of great interest to both scientific and industrial communities due to their numerous applications and unique behaviors different from the bulk. However, the understanding of thin-film mechanics is still greatly hampered due to their intrinsic fragility and the lack of commercially available experimental instruments. In this review, we first discuss the progression of thin-film mechanical testing methods based on the supporting substrate: film-on-solid substrate method, film-on-water tensile tests, and water-assisted free-standing tensile tests. By comparing past studies on a model polymer, polystyrene, the effect of different substrates and confinement effect on the thin-film mechanics is evaluated. These techniques have generated fruitful scientific knowledge in the field of organic semiconductors for the understanding of structure–mechanical property relationships. We end this review by providing our perspective for their bright prospects in much broader applications and materials of interest. 相似文献
3.
5.
科学评价大学生科研创新能力对我国科研水平的提高具有重要意义.采用机器学习模型来预测大学生科研能力可以起到良好的效果,提出一种GAXGBoost模型来实现对大学生的科研能力预测.此模型是以Xgboost算法为基础,然后充分利用遗传算法的全局搜索能力自动搜索Xgboost最优超参数,避免了人为经验调参不准确的缺陷,最后采用精英选择策略以此确保每一轮都是最佳的进化结果.通过分析表明,所采用的GAXGBoost模型在大学生科研能力预测的结果中具有很高的精度,将此模型与Logistic Regression、Random Forest、SVM等模型进行对比,GAXGBoost模型的预测精度最高. 相似文献
6.
7.
Wacker oxidation is an industry-adopted process to transform olefins into value-added epoxides and carbonyls. However, traditional Wacker oxidation involves the use of homogeneous palladium and copper catalysts for the olefin addition and reductive elimination. Here, we demonstrated an ultrahigh loading Cu single atom catalyst(14% Cu, mass fraction) for the palladium-free Wacker oxidation of 4-vinylanisole into the corresponding ketone with N-methylhydroxylamine hydrochloride as an additive under mild conditions. Mechanistic studies by 18O and deuterium isotope labelling revealed a hydrogen shift mechanism in this palladium-free process using N-methylhydroxylamine hydrochloride as the oxygen source. The reaction scope can be further extended to Kucherov oxidation. Our study paves the way to replace noble metal catalysts in the traditional homogeneous processes with single atom catalysts. 相似文献
8.
Meihua Shen Dr. Xinpeng Zhao Dr. Lu Han Nanxi Jin Prof. Song Liu Prof. Tao Jia Prof. Zhijun Chen Prof. Xiuhua Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(20):e202104137
Solar-driven interfacial vaporization by localizing solar-thermal energy conversion to the air−water interface has attracted tremendous attention. In the process of converting solar energy into heat energy, photothermal materials play an essential role. Herein, a flexible solar-thermal material di-cyan substituted 5,12-dibutylquinacridone (DCN−4CQA)@Paper was developed by coating photothermal quinacridone derivatives on the cellulose paper. The DCN−4CQA@Paper combines desired chemical and physical properties, broadband light-absorbing, and shape-conforming abilities that render efficient photothermic vaporization. Notably, synergetic coupling of solar-steam and solar-electricity technologies by integrating DCN−4CQA@Paper and the thermoelectric devices is realized without trade-offs, highlighting the practical consideration toward more impactful solar heat exploitation. Such solar distillation and low-grade heat-to-electricity generation functions can provide potential opportunities for fresh water and electricity supply in off-grid or remote areas. 相似文献
9.
10.