全文获取类型
收费全文 | 80228篇 |
免费 | 507篇 |
国内免费 | 380篇 |
专业分类
化学 | 26061篇 |
晶体学 | 809篇 |
力学 | 6760篇 |
数学 | 32040篇 |
物理学 | 15445篇 |
出版年
2022年 | 53篇 |
2021年 | 78篇 |
2020年 | 63篇 |
2019年 | 71篇 |
2018年 | 10463篇 |
2017年 | 10284篇 |
2016年 | 6148篇 |
2015年 | 929篇 |
2014年 | 410篇 |
2013年 | 480篇 |
2012年 | 3994篇 |
2011年 | 10712篇 |
2010年 | 5758篇 |
2009年 | 6146篇 |
2008年 | 6759篇 |
2007年 | 8878篇 |
2006年 | 346篇 |
2005年 | 1425篇 |
2004年 | 1628篇 |
2003年 | 2046篇 |
2002年 | 1088篇 |
2001年 | 291篇 |
2000年 | 319篇 |
1999年 | 186篇 |
1998年 | 209篇 |
1997年 | 157篇 |
1996年 | 214篇 |
1995年 | 123篇 |
1994年 | 87篇 |
1993年 | 101篇 |
1992年 | 54篇 |
1991年 | 67篇 |
1990年 | 58篇 |
1989年 | 64篇 |
1988年 | 61篇 |
1987年 | 57篇 |
1986年 | 57篇 |
1985年 | 50篇 |
1984年 | 43篇 |
1983年 | 41篇 |
1982年 | 41篇 |
1981年 | 41篇 |
1980年 | 49篇 |
1979年 | 45篇 |
1978年 | 37篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Mohammad A. Khalilzadeh Soo Young Kim Ho Won Jang Rafael Luque Rajender S. Varma Richard A. Venditti Mohammadreza Shokouhimehr 《Materials Today Chemistry》2022
The requirement of green and sustainable materials to prepare heterogeneous catalysts has intensified for practical reasons over the past few decades. Carbohydrates are possibly the most plentiful and renewable organic materials in nature with inimitable physiochemical properties, plausible low-cost and large-scale production, and sustainability features could be exploited in the generation of nanostructured heterogeneous catalysts. This review article outlines the organic transformations catalyzed by diverse carbohydrate-based nanostructured catalysts in greener and environmentally friendly processes. Selected examples are highlighted for a variety of organic reactions exploiting the proposed catalysts’ reactivity and reusability, and interactions with the intrinsic nature of the applied carbohydrate supports; advantages and speculated challenges of the introduced catalysts are deliberated as well. 相似文献
2.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers. 相似文献
3.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant. 相似文献
4.
5.
Sarah Peluse 《Israel Journal of Mathematics》2018,227(1):379-396
We prove that the group of diffeomorphisms of the interval [0, 1] contains surface groups whose action on (0, 1) has no global fix point and such that only countably many points of the interval (0, 1) have non-trivial stabiliser. 相似文献
6.
7.
8.
9.
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
10.
S. V. Panin I. V. Vlasov V. P. Sergeev B. B. Ovechkin P. O. Marushchak Sunder Ramasubbu P. S. Lyubutin V. V. Titkov 《Physical Mesomechanics》2015,18(3):261-272
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method. 相似文献