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   100522篇
  免费   7598篇
  国内免费   371篇
耳鼻咽喉   1126篇
儿科学   2550篇
妇产科学   1648篇
基础医学   14229篇
口腔科学   2192篇
临床医学   10175篇
内科学   20958篇
皮肤病学   1796篇
神经病学   10691篇
特种医学   4329篇
外国民族医学   6篇
外科学   14547篇
综合类   1245篇
一般理论   73篇
预防医学   7710篇
眼科学   1704篇
药学   6883篇
中国医学   111篇
肿瘤学   6518篇
  2023年   522篇
  2022年   414篇
  2021年   1561篇
  2020年   1290篇
  2019年   1933篇
  2018年   2397篇
  2017年   1787篇
  2016年   2108篇
  2015年   2457篇
  2014年   3249篇
  2013年   4288篇
  2012年   6652篇
  2011年   6704篇
  2010年   3957篇
  2009年   3593篇
  2008年   5914篇
  2007年   6418篇
  2006年   5959篇
  2005年   5897篇
  2004年   5508篇
  2003年   4909篇
  2002年   4866篇
  2001年   1867篇
  2000年   1761篇
  1999年   1603篇
  1998年   1074篇
  1997年   881篇
  1996年   699篇
  1995年   832篇
  1994年   702篇
  1993年   652篇
  1992年   1146篇
  1991年   1074篇
  1990年   1011篇
  1989年   985篇
  1988年   874篇
  1987年   814篇
  1986年   840篇
  1985年   844篇
  1984年   672篇
  1983年   588篇
  1982年   571篇
  1981年   458篇
  1980年   401篇
  1979年   515篇
  1978年   402篇
  1977年   372篇
  1975年   330篇
  1974年   355篇
  1973年   342篇
排序方式: 共有10000条查询结果,搜索用时 39 毫秒
1.
Tympanic membranes (TM) that have healed spontaneously after perforation present abnormalities in their structural and mechanical properties; i.e., they are thickened and abnormally dense. These changes result in a deterioration of middle ear (ME) sound transmission, which is clinically presented as a conductive hearing loss (CHL). To fully understand the ME sound transmission under TM pathological conditions, we created a gerbil model with a controlled 50% pars tensa perforation, which was left to heal spontaneously for up to 4 weeks (TM perforations had fully sealed after 2 weeks). After the recovery period, the ME sound transmission, both in the forward and reverse directions, was directly measured with two-tone stimulation. Measurements were performed at the input, the ossicular chain, and output of the ME system, i.e., at the TM, umbo, and scala vestibuli (SV) next to the stapes. We found that variations in ME transmission in forward and reverse directions were not symmetric. In the forward direction, the ME pressure gain decreased in a frequency-dependent manner, with smaller loss (within 10 dB) at low frequencies and more dramatic loss at high frequency regions. The loss pattern was mainly from the less efficient acoustical to mechanical coupling between the TM and umbo, with little changes along the ossicular chain. In the reverse direction, the variations in these ears are relatively smaller. Our results provide detailed functional observations that explain CHL seen in clinical patients with abnormal TM, e.g., caused by otitis media, that have healed spontaneously after perforation or post-tympanoplasty, especially at high frequencies. In addition, our data demonstrate that changes in distortion product otoacoustic emissions (DPOAEs) result from altered ME transmission in both the forward and reverse direction by a reduction of the effective stimulus levels and less efficient transfer of DPs from the ME into the ear canal. This confirms that DPOAEs can be used to assess both the health of the cochlea and the middle ear.  相似文献   
2.
Cardiovascular Drugs and Therapy - To evaluate the effectiveness of vitamin D3 supplementation, in secondary prevention, on cardiac remodeling and function, as well as lipid profile, in a mouse...  相似文献   
3.
Graefe's Archive for Clinical and Experimental Ophthalmology - The purpose was to ascertain if any relation exists between the elevated intraocular pressure (IOP) in patients with...  相似文献   
4.
5.
The Patient - Patient-Centered Outcomes Research - Long coronavirus disease (COVID) is an emerging condition that could considerably burden healthcare systems. Prior qualitative studies...  相似文献   
6.
Bundesgesundheitsblatt - Gesundheitsforschung - Gesundheitsschutz -  相似文献   
7.
8.

Perfluoroalkyl substances (PFAS) are highly persistent organic pollutants that have been detected in a wide array of environmental matrices and, in turn, diverse biota including humans and wildlife wherein they have been associated with a multitude of toxic, and otherwise adverse effects, including ecosystem impacts. In the present study, we developed a toxicity assay for embryonic stages of mahi-mahi (Coryphaena hippurus), as an environmentally relevant pelagic fish species, and applied this assay to the evaluation of the toxicity of “legacy” and “next-generation” PFAS including, respectively, perfluorooctanoic acid (PFOA) and several perfluoroethercarboxylic acids (PFECA). Acute embryotoxicity, in the form of lethality, was measured for all five PFAS toward mahi-mahi embryos with median lethal concentrations (LC50) in the micromolar range. Consistent with studies in other similar model systems, and specifically the zebrafish, embryotoxicity in mahi-mahi generally (1) correlated with fluoroalkyl/fluoroether chain length and hydrophobicity, i.e., log P, of PFAS, and thus, aligned with a role of uptake in the relative toxicity; and (2) increased with continuous exposure, suggesting a possible role of development stage specifically including a contribution of hatching (and loss of protective chorion) and/or differentiation of target systems (e.g., liver). Compared to prior studies in the zebrafish embryo model, mahi-mahi was significantly more sensitive to PFAS which may be related to differences in either exposure conditions (e.g., salinity) and uptake, or possibly differential susceptibility of relevant targets, for the two species. Moreover, when considered in the context of the previously reported concentration of PFAS within upper sea surface layers, and co-localization of buoyant eggs (i.e., embryos) and other early development stages (i.e., larvae, juveniles) of pelagic fish species to the sea surface, the observed toxicity potentially aligns with environmentally relevant concentrations in these marine systems. Thus, impacts on ecosystems including, in particular, population recruitment are a possibility. The present study is the first to demonstrate embryotoxicity of PFAS in a pelagic marine fish species, and suggests that mahi-mahi represents a potentially informative, and moreover, environmentally relevant, ecotoxicological model for PFAS in marine systems.

  相似文献   
9.
10.
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