全文获取类型
收费全文 | 19553篇 |
免费 | 3390篇 |
国内免费 | 3195篇 |
专业分类
化学 | 10885篇 |
晶体学 | 268篇 |
力学 | 693篇 |
综合类 | 197篇 |
数学 | 1330篇 |
物理学 | 4984篇 |
无线电 | 7781篇 |
出版年
2024年 | 118篇 |
2023年 | 517篇 |
2022年 | 787篇 |
2021年 | 916篇 |
2020年 | 857篇 |
2019年 | 891篇 |
2018年 | 772篇 |
2017年 | 834篇 |
2016年 | 879篇 |
2015年 | 1050篇 |
2014年 | 1246篇 |
2013年 | 1502篇 |
2012年 | 1659篇 |
2011年 | 1655篇 |
2010年 | 1378篇 |
2009年 | 1302篇 |
2008年 | 1420篇 |
2007年 | 1165篇 |
2006年 | 1119篇 |
2005年 | 1025篇 |
2004年 | 842篇 |
2003年 | 709篇 |
2002年 | 716篇 |
2001年 | 662篇 |
2000年 | 474篇 |
1999年 | 339篇 |
1998年 | 212篇 |
1997年 | 133篇 |
1996年 | 152篇 |
1995年 | 116篇 |
1994年 | 130篇 |
1993年 | 114篇 |
1992年 | 81篇 |
1991年 | 85篇 |
1990年 | 63篇 |
1989年 | 39篇 |
1988年 | 35篇 |
1987年 | 32篇 |
1986年 | 25篇 |
1985年 | 20篇 |
1984年 | 13篇 |
1983年 | 19篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1965年 | 3篇 |
1959年 | 4篇 |
1936年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
1.
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
2.
Hongjin Wang Tengfei Long Hao Zhang Meng Li Qi Sun Xin Zhai Lixin Sun 《Biomedical chromatography : BMC》2022,36(4):e5301
3,4-Difluorobenzyl(1-ethyl-5-(4-((4-hydroxypiperidin-1-yl)-methyl)thiazol-2-yl)-1H-indol-3-yl)carbamate (NAI59), a small molecule with outstanding therapeutic effectiveness to anti-pulmonary fibrosis, was developed as an autotaxin inhibitor candidate compound. To evaluate the pharmacokinetics and plasma protein binding of NAI59, a UPLC–MS/MS method was developed to quantify NAI59 in plasma and phosphate-buffered saline. The calibration curve linearity ranged from 9.95 to 1990.00 ng/mL in plasma. The accuracy was −6.8 to 5.9%, and the intra- and inter-day precision was within 15%. The matrix effect and recovery, as well as dilution integrity, were within the criteria. The chromatographic and mass spectrometric conditions were also feasible to determine phosphate-buffered saline samples, and it has been proved that this method exhibits good precision and accuracy in the range of 9.95–497.50 ng/mL in phosphate-buffered saline. This study is the first to determine the pharmacokinetics, absolute bioavailability, and plasma protein binding of NAI59 in rats using this established method. Therefore, the pharmacokinetic profiles of NAI59 showed a dose-dependent relationship after oral administration, and the absolute bioavailability in rats was 6.3%. In addition, the results of protein binding showed that the combining capacity of NAI59 with plasma protein attained 90% and increased with the increase in drug concentration. 相似文献
3.
Bin Feng Xin Jiang Guisheng Zou Wengan Wang Tianming Sun Heng Yang Guanlei Zhao Mingye Dong Yu Xiao Hongwei Zhu Lei Liu 《Advanced functional materials》2021,31(29):2102359
The realization of liquid metal-based wearable systems will be a milestone toward high-performance, integrated electronic skin. However, despite the revolutionary progress achieved in many other components of electronic skin, liquid metal-based flexible sensors still suffer from poor sensitivity due to the insufficient resistance change of liquid metal to deformation. Herein, a nacre-inspired architecture composed of a biphasic pattern (liquid metal with Cr/Cu underlayer) as “bricks” and strain-sensitive Ag film as “mortar” is developed, which breaks the long-standing sensitivity bottleneck of liquid metal-based electronic skin. With 2 orders of magnitude of sensitivity amplification while maintaining wide (>85%) working range, for the first time, liquid metal-based strain sensors rival the state-of-art counterparts. This liquid metal composite features spatially regulated cracking behavior. On the one hand, hard Cr cells locally modulate the strain distribution, which avoids premature cut-through cracks and prolongs the defect propagation in the adjacent Ag film. On the other hand, the separated liquid metal cells prevent unfavorable continuous liquid-metal paths and create crack-free regions during strain. Demonstrated in diverse scenarios, the proposed design concept may spark more applications of ultrasensitive liquid metal-based electronic skins, and reveals a pathway for sensor development via crack engineering. 相似文献
5.
7.
Su X. F. Zhang Y. L. Maximov A. L. Zhang K. Xin Q. Feng C. Q. Bai X. F. Wu W. 《Russian Journal of Applied Chemistry》2020,93(1):127-136
Russian Journal of Applied Chemistry - Nanoscale ZSM-5 (AlZ5-D) and Ga-substituted ZSM-5 zeolites ((Al,Ga)Z5-D and GaZ5-D) were synthesized by a green dry-gel conversion strategy. For comparison,... 相似文献
9.
10.
应急避难场所广播体系由应急广播、场所广播室、接收端、网络接收、广播管理群、监测系统等6部分组成.针对电台在市区建立应急避难场所广播作出设计,在学校、社区、广场上安装广播系统,做到市区全方面覆盖. 相似文献