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   8464篇
  免费   656篇
  国内免费   164篇
耳鼻咽喉   46篇
儿科学   173篇
妇产科学   70篇
基础医学   939篇
口腔科学   222篇
临床医学   1181篇
内科学   1554篇
皮肤病学   81篇
神经病学   616篇
特种医学   231篇
外科学   653篇
综合类   718篇
一般理论   10篇
预防医学   1547篇
眼科学   96篇
药学   607篇
  3篇
中国医学   290篇
肿瘤学   247篇
  2024年   28篇
  2023年   238篇
  2022年   357篇
  2021年   482篇
  2020年   336篇
  2019年   378篇
  2018年   336篇
  2017年   320篇
  2016年   306篇
  2015年   328篇
  2014年   482篇
  2013年   766篇
  2012年   446篇
  2011年   468篇
  2010年   405篇
  2009年   350篇
  2008年   397篇
  2007年   354篇
  2006年   284篇
  2005年   251篇
  2004年   252篇
  2003年   217篇
  2002年   163篇
  2001年   165篇
  2000年   125篇
  1999年   104篇
  1998年   98篇
  1997年   96篇
  1996年   91篇
  1995年   76篇
  1994年   69篇
  1993年   40篇
  1992年   59篇
  1991年   44篇
  1990年   43篇
  1989年   42篇
  1988年   44篇
  1987年   32篇
  1986年   32篇
  1985年   28篇
  1984年   29篇
  1983年   22篇
  1982年   14篇
  1981年   16篇
  1980年   15篇
  1979年   11篇
  1978年   10篇
  1976年   11篇
  1975年   5篇
  1974年   5篇
排序方式: 共有9284条查询结果,搜索用时 15 毫秒
31.
目的:观察犬双侧上颌骨前牵引的不同时期眶下神经组织学结构的改变,探讨其对眶下神经的影响。方法:选12周龄杂种犬13只为实验对象,实验组12只,用特制牵引器进行上颌骨前牵引;对照组1只,未配戴牵引器。牵引过程包括15d牵引期和20d固定期,牵引力为800g。于术后不同时间点分组处死动物,取双侧眶下神经,制成常规切片,光镜下观察不同时期的神经组织形态。结果:随着牵引的进行,上颌骨明显前移,眶下神经出现明显病理变化,牵引结束时神经损伤最严重;固定期神经出现修复性变化。结论:双侧上颌骨前牵引对眶下神经可产生一定的损伤,但这种损伤是暂时的、可逆的,随着时间的延长,神经的形态结构可恢复正常。  相似文献   
32.
Increased fruit and vegetable (FV) intake is associated with decreased risk of nutrition-related chronic diseases. Sociodemographic disparities in FV intake indicate the need for strategies that promote equitable access to FVs. The United States Department of Agriculture’s Gus Schumacher Nutrition Incentive Program (GusNIP) supports state and local programs that offer nutrition incentives (NIs) that subsidize purchase of FVs for people participating in the Supplemental Nutrition Assistance Program (SNAP). While a growing body of research indicates NIs are effective, the pathways through which GusNIP achieves its results have not been adequately described. We used an equity-focused, participatory process to develop a retrospective Theory of Change (TOC) to address this gap. We reviewed key program documents; conducted a targeted NI literature review; and engaged GusNIP partners, practitioners, and participants through interviews, workshops, and focus groups in TOC development. The resulting TOC describes how GusNIP achieves its long-term outcomes of increased participant FV purchases and intake and food security and community economic benefits. GusNIP provides NIs and promotes their use, helps local food retailers develop the capacity to sell FVs and accept NIs in accessible and welcoming venues, and supports local farmers to supply FVs to food retailers. The TOC is a framework for understanding how GusNIP works and a tool for improving and expanding the program.  相似文献   
33.
体质从化理论肇始于《内经》等经典著作,对临床治疗急性热病具有较强的指导作用。手足口病的临床转归与感染者体质因素有密切的关系,感染者体质决定患者是否发病,以及是否能发展为危重症。手足口病的病邪兼具有热、湿的某些特点,其传变符合"实则阳明、虚则太阴"的规律。基于体质从化理论,应根据其病机转变趋势,采用早期截断病势的治疗原则。应深入临床研究,从中医体质从化理论以及现代医学疾病易感性方面深入研究,寻找客观的物质基础,更加科学有效地指导手足口病的诊治。  相似文献   
34.
目的调查分析本院2004-2006年血培养主要病原菌的变迁,为临床的诊治提供依据。方法分析3年来血培养的致病菌种类及临床分布。结果从4 579份血液标本中共分离出471致病菌,阳性率为10.29%。分离率居前五位的病原菌分别是大肠埃希菌130株,真菌62株,肺炎克雷伯氏菌55株,凝固酶阴性葡萄球菌51株及金黄色葡萄球菌47株。临床送检血培养以肾脏内科最多,达899份。结论了解血培养主要病原菌的变迁趋势和临床分布情况,有助于临床确立诊疗方案。  相似文献   
35.
PURPOSEA large number of studies have suggested the practicability and predictability of immediate implant function, but few studies have reported marginal bone level changes during sequential loading periods. The purpose of this study was to evaluate the marginal bone remodeling of immediately loaded self-tapping implants both at each time point and during each loading period between two time points.MATERIALS AND METHODSThe patients included in this retrospective study were treated with immediately loaded NobelSpeedy Replace implants between August 2008 and July 2009. Differences in the marginal bone level (MBL) at each time point and the marginal bone level change (ΔMBL) between two time points were analyzed with Bonferroni correction (P < .05).RESULTSOverall, 24 patients (mean age, 47.3 ± 12.8 years) with 42 immediately loaded implants and a median follow-up of 6.5 years (IQR, 67.8 months) were included. The cumulative survival rate after 10 - 12 years was 95.2%. Continuous but slow marginal bone loss was observed during long-term follow-up. MBL at both 7.5 years and 11 years was significantly lower than that at loading, 6 months, 2 years and 4 years (P < .05). No bone loss difference was found in any period before 4 years of follow up (P > .05). The loading period of 4 years to 7.5 years showed the largest ΔMBL compared to those of other time periods (P < .05).CONCLUSIONSlight bone loss occurred continuously, and more radical changes of marginal bone can be observed during the period of 4-7.5 years. Thus, long-term effective follow-up of immediately loaded implants is needed.  相似文献   
36.
梅花为我国传统药材,具有疏肝和中,化痰散结的作用,常用于治疗梅核气,肝胃气痛,食欲不振,头晕,瘰疬.梅原产中国,其栽培应用历史悠久,品种复杂繁多,现代研究将梅分为果梅与花梅两类,品种达数百个之多.但关于古代文献中统究竟以何种颜色梅花人药为佳,以及药用梅花类群与植物系统学的关联性等尚未有相关的研究报道.为正本清源,笔者对...  相似文献   
37.
目的:探讨清炎颗粒治疗肾盂肾炎的作用机制。方法:采用孙建实方法改进造模,除空白组正常喂养外,治疗组给予清炎颗粒,模型组给予生理盐水,对照组给予至灵胶囊灌胃,分别喂养至3,7,15,30,60 d处死。取胸腺称重,计算胸腺指数,并取肾做病理分析。结果:清炎颗粒能提高不同时段小鼠的胸腺指数,并减轻相应时段的病理改变。结论:清炎颗粒通过提高小鼠的免疫功能来达到治疗肾盂肾炎的目的。  相似文献   
38.
The evolutionary history of African hunter-gatherers holds key insights into modern human diversity. Here, we combine ethnographic and genetic data on Central African hunter-gatherers (CAHG) to show that their current distribution and density are explained by ecology rather than by a displacement to marginal habitats due to recent farming expansions, as commonly assumed. We also estimate the range of hunter-gatherer presence across Central Africa over the past 120,000 years using paleoclimatic reconstructions, which were statistically validated by our newly compiled dataset of dated archaeological sites. Finally, we show that genomic estimates of divergence times between CAHG groups match our ecological estimates of periods favoring population splits, and that recoveries of connectivity would have facilitated subsequent gene flow. Our results reveal that CAHG stem from a deep history of partially connected populations. This form of sociality allowed the coexistence of relatively large effective population sizes and local differentiation, with important implications for the evolution of genetic and cultural diversity in Homo sapiens.

The evolutionary history of African hunter-gatherers may hold key insights into patterns and processes behind the evolution of modern human diversity. Recent genomic studies have revealed that these populations represent the oldest and most diverse human genetic lineages and have been genetically differentiated from one another since the origin of humans (13) (SI Appendix, Table S1). Therefore, a first question is whether their current ecological niches were also characteristic of early Homo sapiens populations. However, genetic data alone can neither determine the geographic distribution of hunter-gatherers in the past nor demonstrate a deep history of adaptation of hunter-gatherers to their current environments. In fact, various studies have proposed that farming expansions within the past 5,000 years (in particular by the ancestors of Bantu speakers) would have only recently displaced hunter-gatherers to marginalized regions less favorable to agriculture (such as rainforests and deserts) (47).For example, the central part of Africa, between latitudes 5°N and 5°S currently is inhabited by ∼20 scattered hunter-gatherer ethnic groups (8). These Central African hunter-gatherers (CAHG) form a genetic clade thought to have diverged from other African populations as far back as 120,000 to 200,000 years ago (2, 9). The lack of any major linguistic specificity between them is often implied to reflect extensive contacts with surrounding farmer populations (8, 10), and seen as evidence of recent displacement into marginal forest environments by expanding farming populations. However, anthropologists have remarked on the huge variability in lifestyle, habitat, techniques, and tools between CAHG (11), suggestive of long-term cultural diversification and adaptation to forest environments. Research on the drivers of demography and adaptation of CAHG populations remains extremely limited, which can be partially attributed to the lack of archaeological and osteological data resulting from a rapid disintegration of fossil remains in the rainforest’s acidic soils, in addition to social instability in the region (12). Therefore, we are still left with crucial questions regarding the time depth of occupation of Central Africa by hunter-gatherers, the breadth of the niche exploited by earlier populations in the region, and variations in levels of interconnectivity at different points in time.To address those questions, we first compiled ethnographic data on the distribution of 749 camps from 11 hunter-gatherer groups extending from West to East Central Africa. We used them as inputs for environmental niche models (ENMs) to determine the relative influence of several bioclimatic and ecological factors, as well as the presence of farming populations, on the distribution and abundance of CAHG (13, 14). Then, we used high-resolution paleoclimatic reconstructions and topographic maps to make continuous predictions about where CAHG could have lived over the past 120,000 years and the potential extension of their interaction networks. Next, we compiled all reliably dated archaeological assemblages ascribed to hunter-gatherer groups in the Congo Basin (n = 168) and confirmed the model’s ability to predict the location and date of the sites. We further contextualized genomic estimates of population divergences with changes in population densities and interpopulation connectivity predicted by our model. Last, we complemented these analyses with a detailed assessment of present and historical gene flow between nine CAHG populations (n = 265 individuals), which we used to assess recent interactions between previously diverged CAHG populations, after farming expansions. Our study therefore provides a causal link between past environmental changes and human population dynamics over evolutionary time, by predicting where and when populations across Central Africa could have exchanged genetic and/or cultural information throughout their evolutionary history.  相似文献   
39.
目的通过低密度脂蛋白(LDL)的刺激,观察LDL对体外培养的大鼠肾小球系膜细胞表型转化的诱导作用。方法采用不同浓度的LDL(0,25,50,100,150μg/ml)刺激体外培养的大鼠肾小球系膜细胞的水平,以台盼蓝染色检测LDL对系膜细胞的毒性作用,MTT比色法检测细胞增殖,透射电镜观察系膜细胞的形态学变化,免疫细胞化学染色及Western blot检测α-SMA、CTGF、Ⅳ型胶原及FN的表达。结果在LDL作用下,倒置显微镜下细胞变为长梭形,透射电镜下细胞表面微绒毛减少。免疫细胞化学染色及Western blot显示α-SMA、CTGF、Ⅳ型胶原及FN表达增强。结论在LDL刺激下,系膜细胞可以发生表型转化。  相似文献   
40.
留置导尿集尿袋更换时间与尿路感染的相关性研究   总被引:14,自引:0,他引:14  
目的:探讨留置导尿患者集尿袋更换时间与尿路感染的相关性及护理预防对策;方法:选择我院内科病区脑血管意外留置导尿患者61例,分实验组与对照组在不同间隔时间内予以更换集尿袋,追踪监测尿培养,对出现尿培养阳性结果进行统计学分析。结论:在严格按照护理质控与院内感染要求下,临床上集尿袋更换间隔时间以一周一次较为科学有效。  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