全文获取类型
收费全文 | 19733篇 |
免费 | 4175篇 |
国内免费 | 7466篇 |
专业分类
化学 | 14978篇 |
晶体学 | 1011篇 |
力学 | 1390篇 |
综合类 | 912篇 |
数学 | 3357篇 |
物理学 | 9726篇 |
出版年
2024年 | 38篇 |
2023年 | 149篇 |
2022年 | 636篇 |
2021年 | 644篇 |
2020年 | 624篇 |
2019年 | 619篇 |
2018年 | 568篇 |
2017年 | 839篇 |
2016年 | 651篇 |
2015年 | 975篇 |
2014年 | 1115篇 |
2013年 | 1586篇 |
2012年 | 1510篇 |
2011年 | 1645篇 |
2010年 | 1609篇 |
2009年 | 1792篇 |
2008年 | 2099篇 |
2007年 | 1819篇 |
2006年 | 1769篇 |
2005年 | 1526篇 |
2004年 | 1288篇 |
2003年 | 985篇 |
2002年 | 957篇 |
2001年 | 1022篇 |
2000年 | 1052篇 |
1999年 | 657篇 |
1998年 | 328篇 |
1997年 | 268篇 |
1996年 | 291篇 |
1995年 | 272篇 |
1994年 | 250篇 |
1993年 | 235篇 |
1992年 | 202篇 |
1991年 | 152篇 |
1990年 | 162篇 |
1989年 | 156篇 |
1988年 | 138篇 |
1987年 | 112篇 |
1986年 | 86篇 |
1985年 | 69篇 |
1984年 | 83篇 |
1983年 | 82篇 |
1982年 | 69篇 |
1981年 | 57篇 |
1980年 | 44篇 |
1979年 | 35篇 |
1978年 | 16篇 |
1977年 | 14篇 |
1976年 | 15篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
当煤层上方为坚硬顶板时,在工作面回采期间容易出现大面积悬顶,导致巷旁充填体出现大变形破坏,极大威胁采煤安全.为解决这一问题,以某矿1205工作面沿空留巷为工程背景,分析了爆炸围岩裂隙范围和坚硬顶板破断特征,建立了切顶卸压围岩结构力学模型,研究表明,相邻炮孔爆炸后,炮孔间裂隙互相贯穿,降低了顶板强度,同时当切顶角为15°时,巷道稳定性较好.工程实践结果表明:采用爆破切顶技术后,顶板下沉量减小了62.3%,较好地保证了围岩稳定性. 相似文献
2.
3.
4.
Da Hyeon Choi Jiwon Park Ju Kwang Choi Kyeong Eun Lee Won Hee Lee Jinho Yang Ju Yeon Lee Yoon Jeong Park Chan Oh Ho-Ryun Won Bon Seok Koo Jae Won Chang Yoon Shin Park 《Experimental & molecular medicine》2020,52(9):1564
Oral microbes have the capacity to spread throughout the gastrointestinal system and are strongly associated with multiple diseases. Given that tonsils are located between the oral cavity and the laryngopharynx at the gateway of the alimentary and respiratory tracts, tonsillar tissue may also be affected by microbiota from both the oral cavity (saliva) and the alimentary tract. Here, we analyzed the distribution and association of the microbial communities in the saliva and tonsils of Korean children subjected to tonsillectomy because of tonsil hyperplasia (n = 29). The microbiome profiles of saliva and tonsils were established via 16S rRNA gene sequencing. Based on the alpha diversity indices, the microbial communities of the two groups showed high similarities. According to Spearman’s ranking correlation analysis, the distribution of Treponema, the causative bacterium of periodontitis, in saliva and tonsils was found to have a significant positive correlation. Two representative microbes, Prevotella in saliva and Alloprevotella in tonsils, were negatively correlated, while Treponema 2 showed a strong positive correlation between saliva and tonsils. Taken together, strong similarities in the microbial communities of the tonsils and saliva are evident in terms of diversity and composition. The saliva microbiome is expected to significantly affect the tonsil microbiome. Furthermore, we suggest that our study creates an opportunity for tonsillar microbiome research to facilitate the development of novel microbiome-based therapeutic strategies.Subject terms: Comparative genomics, Metagenomics 相似文献
5.
6.
Zhang Jia-Rui Zhang Jia-Qi Zheng Zhao-Lin Lin Da Shen Yu-Jia 《Nonlinear dynamics》2022,108(2):1005-1026
Nonlinear Dynamics - Parametrically excited oscillators are used in several domains, in particular to improve the dynamical behaviour of systems like in the case of the parametric amplification or... 相似文献
7.
8.
9.
XU Jun YAN Ai-Zhen XU Qin-Hua Department of Chemistry Nanjing University Nanjing Jiangsu China 《中国化学》1995,(2)
The strength of basic sites has been measured by pyrrole-IR on alkali metal cation exchanged β and X zeolites, as well as NaOH loaded Naβ. The influence of cation type and the structure of zeolites on their basicity has been studied. The acidic and basic properties of the samples were investigated by NH3-TPD and isopropanol reaction. It was shown that the strength of basic sites on samples could be characterized by the shift of vNH band in the pyrrole-IR spectra. The framework oxygen charges were calculated from the Sanderson electronegativity. The changes in basic properties with various alkali metal cation are consistent with the changes of local oxygen charges of the zeolite framework. 相似文献
10.