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   2659篇
  免费   128篇
  国内免费   13篇
化学   2177篇
晶体学   28篇
力学   56篇
数学   95篇
物理学   444篇
  2023年   19篇
  2022年   50篇
  2021年   61篇
  2020年   51篇
  2019年   51篇
  2018年   32篇
  2017年   45篇
  2016年   78篇
  2015年   79篇
  2014年   101篇
  2013年   183篇
  2012年   226篇
  2011年   240篇
  2010年   133篇
  2009年   108篇
  2008年   188篇
  2007年   177篇
  2006年   177篇
  2005年   183篇
  2004年   131篇
  2003年   128篇
  2002年   124篇
  2001年   46篇
  2000年   33篇
  1999年   25篇
  1998年   24篇
  1997年   16篇
  1996年   14篇
  1995年   5篇
  1994年   8篇
  1993年   11篇
  1992年   6篇
  1991年   5篇
  1990年   4篇
  1989年   5篇
  1988年   3篇
  1987年   4篇
  1986年   2篇
  1984年   4篇
  1983年   2篇
  1982年   2篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1977年   2篇
  1974年   3篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
  1967年   1篇
排序方式: 共有2800条查询结果,搜索用时 15 毫秒
861.
862.
The aim of this study was to determine the anti-osteoarthritic effects of LI73014F2, which consists of Terminalia chebula fruit, Curcuma longa rhizome, and Boswellia serrata gum resin in a 2:1:2 ratio, in the monosodium iodoacetate (MIA)-induced osteoarthritis (OA) rat model. LI73014F2 was orally administered once per day for three weeks. Weight-bearing distribution and arthritis index (AI) were measured once per week to confirm the OA symptoms. Synovial membrane, proteoglycan layer, and cartilage damage were investigated by histological examination, while synovial fluid interleukin-1β level was analyzed using a commercial kit. Levels of pro-inflammatory mediators/cytokines and matrix metalloproteinases (MMPs) in the cartilage tissues were investigated to confirm the anti-osteoarthritic effects of LI73014F2. LI73014F2 significantly inhibited the MIA-induced increase in OA symptoms, synovial fluid cytokine, cartilage damage, and expression levels of pro-inflammatory mediators/cytokines and MMPs in the articular cartilage. These results suggest that LI73014F2 exerts anti-osteoarthritic effects by regulating inflammatory cytokines and MMPs in MIA-induced OA rats.  相似文献   
863.
864.
865.
We successfully synthesize the three‐ and six‐branched star poly(ε‐caprolactone)s with extremely small branched segments (USB‐SPCLs) using a facile pseudo‐one‐pot process in a pilot scale and investigate the effect of ultra‐small branches on their crystallization behaviors. The number of branched segments and the individual branched segment lengths for USB‐SPCLs are precisely controlled via manipulating monomer‐to‐core ratio, adjusting monomer‐to‐polymer conversion, end‐capping the terminal hydroxyl groups, and vacuum purification, which results in USB‐SPCLs having the branched segments below five degree of polymerization with a high yield exceeding 93%. The molecular weights obtained from 1H NMR spectroscopy are consistent with that obtained from MALDI‐TOF‐MS and the molecular weight distributions are narrow with Mw/Mn ≤ 1.2, indicating that USB‐SPCLs have mono‐dispersed branches. USB‐SPCLs have low melting temperatures and broad double‐melting peaks attributed to their extremely small branches, and the crystallization behaviors for USB‐SPCLs depend on the end group concentration. On the other hand, the glass transitions for USB‐SPCLs depend on the total molecular weights, regardless of the number and length of branched segments. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1134–1142  相似文献   
866.
867.
Bone is a vascularized tissue that is comprised of collagen fibers and calcium phosphate crystals such as hydroxyapatite (HAp) and whitlockite (WH). HAp and WH are known to elicit bone regeneration by stimulating osteoblast activities and osteogenic commitment of stem cells. In addition, vascular endothelial growth factor (VEGF) is shown to promote osteogenesis and angiogenesis which is considered as an essential process in bone repair by providing nutrients. In this study, VEGF‐secreting human adipose‐derived stem cells (VEGF‐ADSCs) are developed by transducing ADSCs with VEGF‐encoded lentivirus. Additionally, WH‐reinforced gelatin/heparin cryogels (WH‐C) are fabricated by loading WH into gelatin/heparin cryogels. VEGF‐ADSC secrete tenfold more VEGF than ADSC and show increased VEGF secretion with cell growth. Also, incorporation of WH into cryogels provides a mineralized environment with ions secreted from WH. When the VEGF‐ADSCs are seeded on WH‐C, sustained release of VEGF is observed due to the specific affinity of VEGF to heparin. Finally, the synergistic effect of VEGF‐ADSC and WH on osteogenesis is successfully confirmed by alkaline phosphatase and real‐time polymerase chain reaction analysis. In vivo bone formation is demonstrated via implantation of VEGF‐ADSC seeded WH‐C into mouse calvarial bone defect model, resulted in enhanced bone development with the highest bone volume/total volume.  相似文献   
868.

Optical emission spectroscopy and mass spectrometry was used to characterize gaseous plasma in an industrial reactor of volume 5 m3 during deposition of protective coatings. Plasma was created in mixtures of hexamethyldisiloxane (HMDSO) and oxygen at the powers between 1 and 8 kW. The plasma density was somehow below 1014 m?3. The flows of both gases were varied up to 200 sccm while the effective pumping speed was adjusted by changing the roots pump rotation speed between 250 and 4000 rpm. At such conditions the HMDSO was only partially dissociated to fragments. The behaviour of optical emission lines and mass ion currents was well correlated indicating that even one single technique was sufficient to monitor the behaviour of plasma at various discharge conditions. The optical emission spectroscopy as a simple and economic method is therefore suitable for controlling key processing parameters in such a plasma reactor.

  相似文献   
869.
The differential responses of six cancer cell lines after treatment of non-thermal plasma from dielectric barrier discharge (DBD) were studied. Two plasma exposure methods including cell suspension exposure and media only exposure were used, and the effects were examined in six cancer cell lines including KB, MCF-7, HeLa, H460, SNU-80 and T98G from different human organs. The result indicates that both methods affected six cell lines similarly in proliferation, mitochondria activity, and apoptosis related gene expression, which implies that the cell culture media have significant role in plasma–cell interaction. H460 showed a significant reduction in cell number after plasma exposure, whereas MCF-7 showed less reduction. Mitochondria activity of all the cancer cell lines reduced following exposure and incubation times except MCF-7. The mRNA expression of Bax, the apoptosis related gene, was highly enhanced in KB, HeLa, MCF-7 and SNU-80, while none was detected in T98G. All six cancer cell lines showed unexpectedly low mRNA expression of tumor suppressor gene p53. These differential responses of six cell lines suggest that non-thermal plasma should activate different pathways in each cancer cell line. Further researches on tissue-specific responses to plasma treatment should be conducted, comparing their responses with normal tissue–cell responses.  相似文献   
870.
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