全文获取类型
收费全文 | 5000篇 |
免费 | 359篇 |
国内免费 | 253篇 |
专业分类
化学 | 3538篇 |
晶体学 | 54篇 |
力学 | 148篇 |
综合类 | 39篇 |
数学 | 648篇 |
物理学 | 1185篇 |
出版年
2023年 | 31篇 |
2022年 | 97篇 |
2021年 | 138篇 |
2020年 | 131篇 |
2019年 | 146篇 |
2018年 | 111篇 |
2017年 | 106篇 |
2016年 | 181篇 |
2015年 | 182篇 |
2014年 | 201篇 |
2013年 | 331篇 |
2012年 | 317篇 |
2011年 | 335篇 |
2010年 | 218篇 |
2009年 | 238篇 |
2008年 | 305篇 |
2007年 | 244篇 |
2006年 | 220篇 |
2005年 | 216篇 |
2004年 | 215篇 |
2003年 | 178篇 |
2002年 | 228篇 |
2001年 | 182篇 |
2000年 | 130篇 |
1999年 | 110篇 |
1998年 | 59篇 |
1997年 | 56篇 |
1996年 | 51篇 |
1995年 | 55篇 |
1994年 | 54篇 |
1993年 | 44篇 |
1992年 | 54篇 |
1991年 | 34篇 |
1990年 | 34篇 |
1989年 | 17篇 |
1988年 | 35篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 37篇 |
1984年 | 23篇 |
1983年 | 19篇 |
1982年 | 36篇 |
1981年 | 21篇 |
1980年 | 22篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1975年 | 10篇 |
1974年 | 17篇 |
排序方式: 共有5612条查询结果,搜索用时 15 毫秒
1.
2.
Mariam Hakami Dr. Geetanjali Deokar Jasmin Smajic Dr. Nitin M. Batra Prof. Pedro M. F. J. Costa 《化学:亚洲杂志》2021,16(11):1466-1474
In the last decade, catalytic chemical vapor deposition (CVD) has been intensively explored for the growth of single-layer graphene (SLG). Despite the scattering of guidelines and procedures, variables such as the surface texture/chemistry of catalyst metal foils, carbon feedstock, and growth process parameters have been well-scrutinized. Still, questions remain on how best to standardize the growth procedure. The possible correlation of procedures between different CVD setups is an example. Here, two thermal CVD reactors were explored to grow graphene on Cu foil. The design of these setups was entirely distinct, one being a “showerhead” cold-wall type, whereas the other represented the popular “tubular” hot-wall type. Upon standardizing the Cu foil surface, it was possible to develop a procedure for cm2-scale SLG growth that differed only by the carrier gas flow rate used in the two reactors. 相似文献
3.
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
4.
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
5.
6.
7.
8.
E. C. Ferreira J. A. P. da Costa J. A. K. Freire G. A. Farias V. N. Freire 《Applied Surface Science》2002,190(1-4):191-194
Confined excitons in non-abrupt GaAs/AlxGa1−xAs single quantum wells are studied. The graded interfaces are described taking into account fluctuations in their thickness a and positioning with respect to the abrupt interface picture. Numerical results for confined (0,0),(1,1) and (0,2) excitons in GaAs/Al0.3Ga0.7As quantum wells show that while the interfacial fluctuations produce small changes (<0.5 meV) in the exciton binding energies, the confined exciton energies can be red- or blue-shifted as much as 25 meV for wells with mean width of 50 Å and 2 ML wide interfaces. 相似文献
9.
Flávio A. Pavan Yoshitaka Gushikem Celso C. Moro Tania M. Costa Edilson V. Benvenutti 《Colloid and polymer science》2003,281(2):173-177
Anilinepropylsilica xerogel was obtained by using an appropriate organosilane and tetraethyl orthosilicate as precursor reagents. The gelation was carried out using HF and NaF as catalysts. The presence of Na+ (when NaF was used) resulted in a decrease in the final organic content of the materials. This effect was interpreted as an inhibition of the organosilane polycondensation possibly due to the Na+ interaction with the SiO- groups of the hydrolyzed organosilane. The presence of Na+ also results in morphological changes in the xerogels. 相似文献
10.
Jie Da Thieo E. Hogen‐Esch 《Journal of polymer science. Part A, Polymer chemistry》2004,42(2):360-373
The synthesis is reported of copolymers of N,N‐dimethylacrylamide (DMA) and methacrylates containing 2,2′‐dihydroperfluorodecanoyl (RF) groups separated from the methacrylate by long polyethylene glycol (PEG) tether groups (between 1000 and 14,000 Da). At concentrations of between 1 and 8 wt % the copolymers with macromonomer contents of 1 mol % or less give gels in organic solvents such as dioxane, THF, or methanol, as well as in water. Given the low molecular weights, this indicates very efficient association of very low numbers of RF groups. Association and gel formation is enormously enhanced in the presence of longer PEG tethers. This is consistent with smaller poly(N,N,‐dimethylacrylamide) (PDMA) intermolecular excluded volume effects that are mediated by the longer PEG tethers and possibly by the incompatibility of PEG and PDMA that may lead to the formation of PEG microdomains. This increases the local concentrations of the RF groups in the PEO domains that are not diluted by the PDMA chains, as would be the case in the absence of PEG tethers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 360–373, 2004 相似文献