全文获取类型
收费全文 | 60434篇 |
免费 | 10191篇 |
国内免费 | 8471篇 |
专业分类
化学 | 42788篇 |
晶体学 | 932篇 |
力学 | 3577篇 |
综合类 | 778篇 |
数学 | 6876篇 |
物理学 | 24145篇 |
出版年
2024年 | 204篇 |
2023年 | 1179篇 |
2022年 | 2352篇 |
2021年 | 2469篇 |
2020年 | 2528篇 |
2019年 | 2353篇 |
2018年 | 2052篇 |
2017年 | 2116篇 |
2016年 | 2830篇 |
2015年 | 3015篇 |
2014年 | 3545篇 |
2013年 | 4525篇 |
2012年 | 5416篇 |
2011年 | 5420篇 |
2010年 | 3952篇 |
2009年 | 3725篇 |
2008年 | 4089篇 |
2007年 | 3613篇 |
2006年 | 3330篇 |
2005年 | 2910篇 |
2004年 | 2202篇 |
2003年 | 1724篇 |
2002年 | 1589篇 |
2001年 | 1402篇 |
2000年 | 1305篇 |
1999年 | 1286篇 |
1998年 | 964篇 |
1997年 | 914篇 |
1996年 | 879篇 |
1995年 | 796篇 |
1994年 | 697篇 |
1993年 | 602篇 |
1992年 | 509篇 |
1991年 | 448篇 |
1990年 | 389篇 |
1989年 | 320篇 |
1988年 | 231篇 |
1987年 | 205篇 |
1986年 | 193篇 |
1985年 | 171篇 |
1984年 | 113篇 |
1983年 | 114篇 |
1982年 | 78篇 |
1981年 | 71篇 |
1980年 | 41篇 |
1979年 | 28篇 |
1977年 | 23篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
运用Bloch定理和传输矩阵方法,研究了与色散介质毗邻的由两种材料组成的半无限一维光子晶体局域表面态的电场和色散关系.和以空气为背景的一维光子晶体相比,毗邻色散介质的光子晶体表面模色散曲线在一定堆积次序下会在较低的带隙中发生断开,较高带隙中的表面模群速度在不同堆积次序下会有很大差异.当与色散介质毗邻的物质折射率较大时,较高带隙中的表面模群速度较小;与色散介质毗邻的物质折射率较小时,较高带隙中表面模的群速度较大. 相似文献
993.
Jian Jiao Min Chen Shengxin Sun Weijie Si Xiaobin Wang Weijie Ding Xincan Fu An Wang Chunlong Yang 《中国化学》2021,(2):323-329
To screen novel antifungal agents targeting the succinate dehydrogenase(SDH),a series of pyrazole-4-carbohydrazides were rationally designed,synthesized,and characterized under the guidance of the structures of succinate dehydrogenase inhibitors(SDHIs).Bioassay results in vitro indicated that most of the target compounds exhibited excellent activity against Rhizoctonia solani(R.solani),Fusarium graminearum(F.graminearum),Botrytis cinerea(B.cinerea)and Colletotrichum capsica(C.cinerea).Compounds 7d,7l,7t and 7x were identified as the most promoting candidates,and their anti-F.graminearum EC50 values were as low as 0.56,0.47,0.46 and 0.49μg/mL,respectively,presenting the similar antifungal activity as that of the commonly used fungicide carbendazim(0.43μg/mL).The 3D-QSAR models were built for a systematic structure-activity relationship profile to explore more potent pyrazole-4-carbohydrazides as novel fungicides.Molecular docking of 7d,7l and 7r with SDH was performed to reveal the binding modes in active pocket and analyze the interactions between the molecules and the SDH protein. 相似文献
994.
995.
996.
根据研制的大口径、高场强的超导强磁装置的特点,选择基于LabVIEW的数据采集和测控系统。低温传感器共六支,分别安装于磁体氦槽和冷屏不同位置,其中碳电阻温度计Cernox三支,铂电阻温度计Pt100两支、Pt1000一只,用于监测磁体温度;超导氦液面计一个,用于监测氦液面高度;根据磁体参数匹配研制了一套可调励磁速率的磁体专用直流电源及其失超保护系统,保证磁体安全运行。所有数据通过NI公司内插DAQ6251数据采集卡的PX I采集,用LabVIEW编写数据采集程序和人机界面。 相似文献
997.
Ionic wind induced by direct-current corona discharge has attracted considerable interest because of its low energy consumption, low noise emission, flexible designs, and lack of moving parts. The purpose of this study is to investigate the configuration parameters to improve the velocity of the ionic wind. Accordingly, this study develops a three-dimensional(3 D) model of circular tube with multi-needle-to-mesh electrode configurations, in this model, the influences of various parameters were explored,such as the mesh gap, the distribution of needle electrodes, the number of needle electrodes,and the radius of the circular channel. The numerical research results showed that the mesh gap, the distribution of needle electrodes, and the radius of the circular tube significantly affected the velocity of the ionic wind. When mesh gap is 12 mm,which indicates that there is an optimal mesh gap which can enhance the velocity of the ionic wind. What is more, changing the distribution of needle electrodes and increasing the number of needle electrodes can effectively improve the velocity of the ionic wind, the optimum distribution α of needle electrodes is 0.7–0.9, which greatly increase the velocity of the ionic wind. However, for multi-needle-to-mesh structure, the improvement of the radius of the circular channel is conducive to enhance the velocity and improve the velocity distribution. 相似文献
998.
讨论了用泊松分布和正态分布近似表示二项分布的精确程度问题,对于泊松分布,指出了它对二项分布B(n,p)的概率值的近似精确与否基本上只依赖于参数p而不依赖于n,并说明了经验条件“np≤5”的不确切. 相似文献
999.
1000.
Han Luo Wei Qin Hong Zhang Fu-Cai Ren Wen-Tao Fang Qing-Hua Kong Liu Yang Jian-Mei Zhang Cheng-Wu Fang Jiang-Miao Hu Shou-Jin Liu 《Molecules (Basel, Switzerland)》2022,27(5)
The present study aimed to identify the composition of the aerial parts of Rubia cordifolia L. A chemical investigation on the EtOAc extracts from the aerial parts of Rubia cordifolia resulted in the isolation of four new anthraquinones, namely Cordifoquinone A–D (1–4), along with 16 known anthraquinones. Their structures were elucidated on the basis of NMR and HR-ESIMS data. All isolates were assessed for their inhibitory effects on NO production in LPS-stimulated RAW 264.7 macrophage cells. Compounds 1, 3 and 10 exhibited significant inhibitory activities with IC50 values of 14.05, 23.48 and 29.23 μmol·L−1, respectively. Their antibacterial activities of four bacteria, Escherichia coli (ATCC 25922), Staphylococcus aureus subsp. aureus (ATCC 29213), Salmonella enterica subsp. enterica (ATCC 14028) and Pseudomonas aeruginosa (ATCC 27853), were also evaluated. Our results indicated that the antibacterial activity of these compounds is inactive. 相似文献