首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6482篇
  免费   384篇
  国内免费   33篇
化学   5091篇
晶体学   62篇
力学   119篇
数学   461篇
物理学   1166篇
  2023年   29篇
  2022年   116篇
  2021年   138篇
  2020年   123篇
  2019年   129篇
  2018年   102篇
  2017年   98篇
  2016年   257篇
  2015年   187篇
  2014年   289篇
  2013年   467篇
  2012年   553篇
  2011年   570篇
  2010年   352篇
  2009年   295篇
  2008年   423篇
  2007年   401篇
  2006年   362篇
  2005年   346篇
  2004年   318篇
  2003年   256篇
  2002年   296篇
  2001年   108篇
  2000年   124篇
  1999年   69篇
  1998年   51篇
  1997年   36篇
  1996年   44篇
  1995年   38篇
  1994年   28篇
  1993年   27篇
  1992年   43篇
  1991年   27篇
  1990年   12篇
  1989年   18篇
  1988年   8篇
  1987年   12篇
  1986年   10篇
  1985年   25篇
  1984年   12篇
  1982年   7篇
  1981年   13篇
  1980年   10篇
  1979年   8篇
  1978年   6篇
  1977年   11篇
  1976年   5篇
  1975年   7篇
  1974年   11篇
  1973年   5篇
排序方式: 共有6899条查询结果,搜索用时 15 毫秒
1.
2.
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   
3.
A green and sustainable strategy synthesizes clinical medicine warfarin anticoagulant by using lipase‐supported metal–organic framework (MOF) bioreactors (see scheme). These findings may be beneficial for future studies in the industrial production of chemical, pharmaceutical, and agrochemical precursors.  相似文献   
4.
Four kinds of red phosphorescent organic light-emitting devices were fabricated and compared to investigate the effect of interfacial layers for hole transport and electron injection. 1 nm-thick LiF in the device A and C and 1 nm-thick Cs2CO3 in the device B and D were deposited as an electron injection layer between the anode and the electron transport layer, and 5 nm-thick layer of dipyrazion[2,3-f:2′,2′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile[HATCN] was inserted as a hole transport interfacial layer between the hole injection layer and the hole transport layer only in the device C and D. Under a luminance of 1000 cd/m2, the power efficiencies were 7.6 lm/W and 8.5 lm/W in the device A and B, and 8.6 lm/W and 13.4 lm/W in the device C and D. The quantum efficiency of the device D was 15.8% under 1000 cd/m2 which was somewhat lower than those of the device A and C, but a little higher than that of the device B. The luminance of the device D was much higher than those of the other devices at a given votage. The luminance of the device D at 7 V was 23,710 cd/m2, which was 13.0, 3.4, and 4.0 times higher than those of the device A, B, and C at the same voltage, respectively.  相似文献   
5.
Plant derived flavonoids have not been well explored in tissue engineering applications due to difficulties in efficient formulations with biomaterials for controlled presentation. Here, the authors report that surface coating of epigallocatechin gallate (EGCG) on polymeric substrates including poly (L‐lactic acid) (PLLA) nanofibers can be performed via oxidative polymerization of EGCG in the presence of cations, enabling regulation of biological functions of multiple cell types implicated in bone regeneration. EGCG coating on the PLLA nanofiber promotes osteogenic differentiation of adipose‐derived stem cells (ADSCs) and is potent to suppress adipogenesis of ADSCs while significantly reduces osteoclastic maturation of murine macrophages. Moreover, EGCG coating serves as a protective layer for ADSCs against oxidative stress caused by hydrogen peroxide. Finally, the in vivo implantation of EGCG‐coated nanofibers into a mouse calvarial defect model significantly promotes the bone regeneration (61.52 ± 28.10%) as compared to defect (17.48 ± 11.07%). Collectively, the results suggest that EGCG coating is a simple bioinspired surface modification of polymeric biomaterials and importantly can thus serve as a promising interface for tuning activities of multiple cell types associated with bone fracture healing.  相似文献   
6.
Baik  Hyungryul  Kim  Changsub  Kwak  Sanghoon  Shin  Hyunshik 《Geometriae Dedicata》2021,214(1):399-426
Geometriae Dedicata - We show that an Anosov map has a geodesic axis on the curve graph of the torus. The direct corollary of our result is the stable translation length of an Anosov map on the...  相似文献   
7.
8.
The barotropic compressible Navier–Stokes equations in an unbounded domain are studied. We prove the unique existence of the solution (u, p) of the system (1.1) in the Sobolev spaceHk + 3 × Hk + 2provided that the derivatives of the data of the problem are sufficiently small, wherek ≥ 0 is any integer. The proof follows from an analysis of the linearized problem, the solvability of the continuity equation, and the Schauder fixed point theory. Similar smoothness results are obtained for a linearized form of (1.1).  相似文献   
9.
10.
In this paper, we shall find the uniquerational price associated with the exchange option. Also, we find the decomposition of Snell envelope and value function of the American exchange option.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号