全文获取类型
收费全文 | 13424篇 |
免费 | 2228篇 |
国内免费 | 2235篇 |
专业分类
化学 | 10899篇 |
晶体学 | 201篇 |
力学 | 695篇 |
综合类 | 168篇 |
数学 | 1483篇 |
物理学 | 4441篇 |
出版年
2024年 | 11篇 |
2023年 | 151篇 |
2022年 | 221篇 |
2021年 | 338篇 |
2020年 | 441篇 |
2019年 | 495篇 |
2018年 | 407篇 |
2017年 | 345篇 |
2016年 | 676篇 |
2015年 | 685篇 |
2014年 | 824篇 |
2013年 | 1019篇 |
2012年 | 1144篇 |
2011年 | 1221篇 |
2010年 | 935篇 |
2009年 | 961篇 |
2008年 | 1127篇 |
2007年 | 944篇 |
2006年 | 847篇 |
2005年 | 718篇 |
2004年 | 622篇 |
2003年 | 514篇 |
2002年 | 673篇 |
2001年 | 512篇 |
2000年 | 411篇 |
1999年 | 268篇 |
1998年 | 192篇 |
1997年 | 137篇 |
1996年 | 148篇 |
1995年 | 122篇 |
1994年 | 114篇 |
1993年 | 99篇 |
1992年 | 66篇 |
1991年 | 65篇 |
1990年 | 41篇 |
1989年 | 32篇 |
1988年 | 27篇 |
1987年 | 30篇 |
1986年 | 19篇 |
1985年 | 25篇 |
1984年 | 15篇 |
1983年 | 16篇 |
1981年 | 11篇 |
1980年 | 27篇 |
1979年 | 12篇 |
1978年 | 25篇 |
1977年 | 48篇 |
1976年 | 17篇 |
1975年 | 19篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
2.
Liu Jun-Wei Shen Shu-Qian Li Ming Li Lei 《International Journal of Theoretical Physics》2021,60(5):1712-1719
International Journal of Theoretical Physics - Quantum coherence, coming from quantum superposition, occupies a significant position in the field of physics. We put forward a lower bound of the... 相似文献
3.
For an integer , a graph is -hamiltonian if for any vertex subset with , is hamiltonian, and is -hamiltonian connected if for any vertex subset with , is hamiltonian connected. Thomassen in 1984 conjectured that every 4-connected line graph is hamiltonian (see Thomassen, 1986), and Ku?zel and Xiong in 2004 conjectured that every 4-connected line graph is hamiltonian connected (see Ryjá?ek and Vrána, 2011). In Broersma and Veldman (1987), Broersma and Veldman raised the characterization problem of -hamiltonian line graphs. In Lai and Shao (2013), it is conjectured that for , a line graph is -hamiltonian if and only if is -connected. In this paper we prove the following.(i) For an integer , the line graph of a claw-free graph is -hamiltonian if and only if is -connected.(ii) The line graph of a claw-free graph is 1-hamiltonian connected if and only if is 4-connected. 相似文献
4.
以六水氯化镁和六次甲基四胺为原料,采用水热法合成四方体MgO,考察其对有机染料甲基橙和亚甲基蓝的吸附行为.通过TGA-DTA、SEM、XRD、N2-sorption和FT-IR等手段表征样品.结果表明,原料浓度、温度和表面活性剂对四方体MgO结构的形成影响较小,而反应时间的延长有助于有序结构的组装.温度170℃、时间24h、MgCl2·6H2O与C6H12N4浓度比为1∶2和表面活性剂PVP是制备四方体MgO的最佳条件.在溶液浓度10mg · L-1的单一吸附实验过程中,四方体MgO对甲基橙和亚甲基蓝的去除率分别为91.3;和22.3;,吸附过程均为单层吸附且符合Langmuir等温吸附模型和伪二级吸附动力学方程.在溶液浓度40 mg·L-1、甲基橙和亚甲基蓝浓度比3∶1的混合溶液吸附过程中,四方体MgO对甲基橙和亚甲基蓝的去除率分别为80.1;和97.9;. 相似文献
5.
Giorgia Scetta Jianzhu Ju Nathan Selles Patrick Heuillet Matteo Ciccotti Costantino Creton 《Journal of polymer science. Part A, Polymer chemistry》2021,59(8):685-696
We investigate the cyclic mechanical behavior in uniaxial tension of three different commercial thermoplastic polyurethane elastomers (TPU) often considered as a sustainable replacement for common filled elastomers. All TPU have similar hard segment contents and linear moduli but sensibly different large strain properties as shown by X-ray analysis. Despite these differences, we found a stiffening effect after conditioning in step cyclic loading which greatly differs from the common softening (also referred as Mullins effect) observed in chemically crosslinked filled rubbers. We propose that this self-reinforcement is related to the fragmentation of hard domains, naturally present in TPU, in smaller but more numerous sub-units that may act as new physical crosslinking points. The proposed stiffening mechanism is not dissimilar to the strain-induced crystallization observed in stretched natural rubber, but it presents a persistent nature. In particular, it may cause a local reinforcement where an inhomogeneous strain field is present, as is the case of a crack propagating in cyclic fatigue, providing a potential explanation for the well-known toughness and wear resistance of TPU. 相似文献
6.
Wang Dong Ming Fei Song Xue-Ke Ye Liu Chen Jing-Ling 《The European Physical Journal C - Particles and Fields》2020,80(8):1-16
The European Physical Journal C - We study the isentropic evolution of the matter produced in relativistic heavy-ion collisions for various values of the entropy-per-baryon ratio of interest for... 相似文献
7.
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
8.
Science China Chemistry - 相似文献
9.
10.