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   5522篇
  免费   548篇
  国内免费   87篇
耳鼻咽喉   42篇
儿科学   125篇
妇产科学   258篇
基础医学   721篇
口腔科学   65篇
临床医学   574篇
内科学   1098篇
皮肤病学   93篇
神经病学   435篇
特种医学   347篇
外科学   731篇
综合类   122篇
预防医学   337篇
眼科学   118篇
药学   403篇
中国医学   29篇
肿瘤学   659篇
  2023年   33篇
  2022年   53篇
  2021年   129篇
  2020年   98篇
  2019年   178篇
  2018年   188篇
  2017年   124篇
  2016年   143篇
  2015年   185篇
  2014年   220篇
  2013年   331篇
  2012年   390篇
  2011年   382篇
  2010年   264篇
  2009年   207篇
  2008年   292篇
  2007年   308篇
  2006年   266篇
  2005年   286篇
  2004年   257篇
  2003年   224篇
  2002年   213篇
  2001年   175篇
  2000年   148篇
  1999年   149篇
  1998年   50篇
  1997年   42篇
  1996年   35篇
  1995年   33篇
  1994年   21篇
  1993年   28篇
  1992年   83篇
  1991年   81篇
  1990年   55篇
  1989年   52篇
  1988年   54篇
  1987年   51篇
  1986年   44篇
  1985年   48篇
  1984年   41篇
  1983年   23篇
  1982年   21篇
  1981年   13篇
  1980年   14篇
  1979年   12篇
  1978年   16篇
  1977年   12篇
  1975年   12篇
  1974年   11篇
  1969年   9篇
排序方式: 共有6157条查询结果,搜索用时 15 毫秒
991.
Gene expression of visna virus is highly restricted in monocytes, but is induced when monocytes differentiate into macrophages. A previous study on differential regulation of visna virus gene expression revealed that a specific AP-1 site in the long terminal repeat of the viral DNA is required for phorbol-ester-induced gene expression in macrophages (Gabuzda, Hess, Small, and Clements, Mol. Cell. Biol., 9, 2728-2733). In the present investigation, we examined the association of two DNA binding proteins, the proto-oncogene proteins FOS and JUN, with this AP-1 site in the visna virus LTR. We demonstrated that the concentrations of these two proteins and their mRNAs increased in U937 cells after phorbol ester induction. Furthermore, the binding of cellular proteins from the U937 nuclear extracts to this AP-1 site was significantly decreased in the presence of antibodies to JUN and FOS. In vitro-translated JUN protein also binds to this AP-1 sequence, and this binding is enhanced by the FOS protein. These results indicate that JUN and FOS are directly involved in the differential regulation of visna virus gene expression.  相似文献   
992.
993.
Fluorescence imaging of tissues has gained significant attention in recent years due to the emergence of appropriate reporter technologies that enable noninvasive sensing of molecular function in vivo. Two major approaches have been used so far for fluorescence molecular imaging, i.e., epi-illumination (reflectance) imaging and fluorescence molecular tomography. Transillumination is an alternative approach that has been employed for imaging tissues in the past and could be similarly beneficial for fluorescence molecular imaging. We investigate data normalization schemes in reflectance and transillumination mode and experimentally demonstrate that normalized transillumination offers significant advantages over planar reflectance imaging and over nonnormalized methods. Our observations, based on phantoms and on postmortem and in vivo mouse measurements display image quality improvement, superior depth sensitivity, and improved imaging accuracy over the nonnormalized methods examined. Normalized planar imaging retains implementation simplicity and could be used to improve on standard fluorescence reflectance imaging and as a simplified alternative to the more integrated and accurate tomographic methods.  相似文献   
994.

Background

Total knee arthroplasty in the presence of a huge bone and soft-tissue defect is always a challenge. A rotating-hinged (RH) megaprosthesis is indicated for extensive soft-tissue loss with a huge bone defect such as a primary or metastatic neoplasm of the bone, repeat periprosthetic joint infection, or extensive trauma of the knee. However, the reported survivorship of RH megaprostheses is unsatisfactory. The aim of this study was to evaluate the survivorship of megaprostheses and the factors that contribute to implant survival.

Methods

A total of 103 RH knee megaprostheses were implanted in 85 patients between January 2001 and June 2013. Each prosthesis was a modular custom-made (CM) cemented or cementless fixed total knee system (United USTAR system). Clinical results and prosthesis survivorship were evaluated between the 2 groups.

Results

The overall survivorship of this CM knee megaprosthesis was 91% at 2 years, 83% at 5 years, and 68% at 10 years. The cumulative component survivorship was 87% in the cemented group and 96% in the cementless group at 2 years compared with 75% in the cemented group and 94% in the cementless group at 5 years. The failure mechanism included loosening in 5 and breakage in 6 patients in the cemented stem group. The survivorship of the cementless fixed component was significantly superior to that of the cemented fixed component.

Conclusion

Our data suggest that modular RHCM knee megaprosthesis provides an acceptable clinical result. A diaphyseal long stem with cementless fixation was more reliable and durable than its cemented counterpart.  相似文献   
995.
996.
Raspberries (Rubus idaeus L.) have been extensively studies worldwide because of their beneficial effects on health. Recently reports indicate that crude extracts of Rubus idaeus (RIE) have antioxidant and anticancer ability. The aim of this study was to evaluate the mechanism of its antimetastatic ability in oral cancer cells. In this study, SCC‐9 and SAS oral cancer cells were subjected to a treatment with RIE and then analyzed the effect of RIE on migration and invasion. The addition of RIE inhibited the migration and invasion ability of oral cancer cells. Real time PCR, western blot and zymography analysis demonstrated that mRNA, protein expression and enzyme activity of matrix metalloproteinases‐2 (MMP‐2) were down‐regulated by RIE. Moreover, the phosphorylation of Focal adhesion kinase (FAK), src, and extracellular signal‐regulated kinase (ERK) were inhibited after RIE treatment. In conclusion, these results demonstrated that RIE exerted an inhibitory effect of migration and invasion in oral cancer cells and alter metastasis by suppression of MMP‐2 expression through FAK/Scr/ERK signaling pathway. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1037–1046, 2017.  相似文献   
997.
Burning incense to worship deities is a popular religious ritual in large parts of Asia, and is a popular custom affecting more than 1.5 billion adherents. Due to incomplete combustion, burning incense has been well recognized to generate airborne hazards to human health. However, the correlation between burning incense and lung cancer in epidemiological studies remains controversy. Therefore, we speculated that some unknown materials in incense smoke are involved in the initiation or progression of lung cancer. Based on this hypothesis, we identified a major compound auramine O (AuO) from the water‐soluble fraction of incense burned condensate using mass spectrometry. AuO is commonly used in incense manufacture as a colorant. Due to thermostable, AuO released from burned incenses becomes an unexpected air pollutant. AuO is classified as a Group 2B chemical by the International Agency of Research on Cancer (IARC), however, the damage of AuO to the respiratory system remains elusive. Our study revealed that AuO has no apparent effect on malignant transformation; but, it dramatically promotes lung cancer malignancy. AuO accumulates in the nucleus and induces the autophagy activity in lung tumor cells. AuO significantly enhances migration and invasive abilities and the in vitro and in vivo stemness features of lung tumor cells through activating the expression of aldehyde dehydrogenase family 1 member A1 (ALDH1A1), and ALDH1A1 knockdown attenuates AuO‐induced autophagy activity and blocks AuO‐induced lung tumor malignancy. In conclusion, we found that AuO, an ingredient of incense smoke, significantly increases the metastatic abilities and stemness characters of lung tumor cells through the activation of ALDH1A1, which is known to be associated with poor outcome and progression of lung cancer. For public health, reducing or avoiding the use of AuO in incense is recommended.  相似文献   
998.
Taiwanin E is a natural compound which is structurally analogous to estrogen II and is abundantly found in Taiwania cryptomerioides. It has been previously reported for its anticancer effects; however, the pharmaceutical effect of Taiwanin E on Human LoVo colon cancer cells is not clear. In this study, we investigated the effects of Taiwanin E on metastasis and the associated mechanism of action on Human LoVo colon cancer cells with respect to the modulations in their cell migration and signaling pathways associated with migration. The results showed that Taiwanin E inhibited cell migration ability correlated with reduced expression and activity of MMP‐2 and MMP‐9. In addition, Taiwanin E induced activation of p38 through phosphorylation. Inhibition of p38α/β significantly abolished the effect of Taiwanin E on cell migration and MMP‐2/‐9 activity. Our results conclude that Taiwanin E inhibited cell migration chiefly via p38α MAPK pathway and in a lesser extend via p38β MAPK. The results elucidate the potential of the phytoestrogen natural compound Taiwanin E as a cancer therapeutic agent in inhibiting the cell migration. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 2021–2031, 2017.  相似文献   
999.
1000.
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