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   1475篇
  免费   165篇
  国内免费   25篇
耳鼻咽喉   5篇
儿科学   19篇
妇产科学   40篇
基础医学   99篇
口腔科学   3篇
临床医学   274篇
内科学   520篇
皮肤病学   55篇
神经病学   82篇
特种医学   54篇
外科学   125篇
综合类   191篇
预防医学   68篇
眼科学   9篇
药学   53篇
  2篇
中国医学   22篇
肿瘤学   44篇
  2024年   4篇
  2023年   48篇
  2022年   43篇
  2021年   107篇
  2020年   99篇
  2019年   74篇
  2018年   81篇
  2017年   94篇
  2016年   80篇
  2015年   63篇
  2014年   99篇
  2013年   109篇
  2012年   61篇
  2011年   82篇
  2010年   73篇
  2009年   65篇
  2008年   66篇
  2007年   72篇
  2006年   46篇
  2005年   51篇
  2004年   23篇
  2003年   28篇
  2002年   15篇
  2001年   12篇
  2000年   16篇
  1999年   12篇
  1998年   7篇
  1997年   16篇
  1996年   10篇
  1995年   8篇
  1994年   8篇
  1993年   5篇
  1992年   8篇
  1991年   10篇
  1990年   6篇
  1989年   8篇
  1988年   8篇
  1987年   7篇
  1986年   8篇
  1985年   8篇
  1984年   4篇
  1983年   6篇
  1982年   3篇
  1981年   5篇
  1980年   2篇
  1979年   1篇
  1978年   2篇
  1975年   1篇
  1973年   1篇
排序方式: 共有1665条查询结果,搜索用时 109 毫秒
61.
Emergency noninvasive external cardiac pacing   总被引:2,自引:0,他引:2  
Thirty-seven critical emergency department patients underwent attempts at external cardiac pacing over an 11-month period. Indications for pacing were asystole in 16, complete heart block (CHB) in 4, sinus bradycardia in 2, nodal bradycardia in 1, atrial fibrillation with bradycardia in 2, electromechanical dissociation in 1, idioventricular rhythm (IVR) in 10, and torsades de pointes in 1. Eight patients were successfully paced with improvement in their condition. Two were in asystole, two in CHB, three in sinus rhythm or atrial fibrillation with bradycardia, and one in idioventricular rhythm. Mean systolic blood pressure rise with pacing was 95 +/- 50 mm Hg. Six of these patients were ultimately discharged from the hospital. One asystolic patient survived to discharge. Other survivors presented with either CHB or bradycardia. Of the 29 patients who did not respond to pacing, 5 survived to hospital discharge. Surviving nonresponder presenting rhythms were CHB in one patient, sinus or nodal bradycardia in two, IVR in one, and torsades de pointes in one. External cardiac pacemaking appears to be effective in hemodynamically significant bradycardia. It does not appear to be effective in most instances of asystole or IVR resulting from prolonged cardiac arrest. When applied to patients with a responsive myocardium, it may result in significant hemodynamic improvement and may be lifesaving.  相似文献   
62.
目的:观察无创正压通气治疗非缺血型视网膜中央静脉阻塞(CRVO)合并重度阻塞性睡眠呼吸暂停低通气综合征患者的临床疗效。方法:回顾性分析我院2017-12/2018-12非缺血型CRVO合并重度阻塞性睡眠呼吸暂停低通气综合征患者66例66眼资料,其中30例患者30眼接受雷珠单抗和视网膜激光光凝联合无创正压通气(观察组),36例36眼患者仅接受雷珠单抗和视网膜激光光凝治疗(对照组)。对比分析两组患者治疗前,治疗1、3、6mo的病变部位视网膜厚度及最佳矫正视力(BCVA)的差异。结果:两组患者不同时间点视网膜厚度、BCVA比较均有差异(P<0.05)。治疗3、6mo,观察组患者视网膜厚度、BCVA均显著低于对照组患者(P<0.01)。对照组患者治疗3、6mo视网膜厚度的无差异(P>0.05),其余各时间点及观察组的各时间点两两比较有差异(P<0.05);观察组患者治疗1、3、6mo BCVA均显著优于治疗前(P<0.05),对照组患者治疗3、6mo BCVA均显著优于患者治疗1mo(P<0.05),其余两两比较,差异均无统计学意义(P>0.05)。结论:无创正压通气治疗有利于提高非缺血型CRVO合并重度阻塞性睡眠呼吸暂停低通气综合征患者的治疗效果。  相似文献   
63.
64.
目的对无创呼吸机辅助治疗急性左心衰竭临床效果进行分析。方法选取我院收治的急性左心衰竭患者162例,随机分为两组患者,单纯组患者80例,常规进行临床药物的静脉滴注和各项生命体征的监测;联合组患者82例,在常规治疗和监测基础上进行无创呼吸机辅助治疗,对比两组患者的临床治疗效果。结果联合组患者呼吸困难完全缓解时间、血氧饱和度监测值、低血氧发生比例、临床疗效显著优越于单纯组患者(P〈0.05)。两组患者均未发生因急救措施和用药导致严重不良后果发生。结论对于急性左心衰竭患者在常规治疗基础上,应用无创呼吸机进行辅助治疗,可明显提高临床治疗效果、缩短呼吸困难缓解时间、明显改善患者的血氧饱和度、减低低血氧的发生比例,提高成功救治几率,对于急性左心衰竭患者的治疗和康复具有重要的临床意义。  相似文献   
65.
66.
Background:A wide range of optical techniques has recently been presented for the development of noninvasive methods for blood glucose sensing based on multivariate skin spectrum analysis, and most recent studies are reviewed in short by us. The vibrational spectral fingerprints of glucose, as especially found in the mid-infrared or Raman spectrum, have been suggested for achieving largest selectivity for the development of noninvasive blood glucose methods.Methods:Here, the different aspects on integral skin measurements are presented, which are much dependent on the absorption characteristics of water as the main skin constituent. In particular, different mid-infrared measurement techniques as realized recently are discussed. The limitations of the use of the attenuated total reflection technique in particular are elaborated, and confounding skin or saliva spectral features are illustrated and discussed in the light of recently published works, claiming that the attenuated total reflection technique can be utilized for noninvasive measurements.Results:It will be shown that the penetration depth of the infrared radiation with wavelengths around 10 µm is the essential parameter, which can be modulated by different measurement techniques as with photothermal or diffuse reflection. However, the law of physics is limiting the option of using the attenuated total reflection technique with waveguides from diamond or similar optical materials.Conclusions:There are confounding features from mucosa, stratum corneum, or saliva, which have been misinterpreted for glucose measurements. Results of an earlier study with multivariate evaluation based on glucose fingerprint features are again referred to as a negative experimental proof.  相似文献   
67.
68.
We present the case of a 29‐year‐old man who developed ventricular tachycardia (VT) secondary to a cardiac lipoma located adjacent to the interventricular groove, which could not be fully resected. Antiarrhythmic drugs and endocardial and epicardial ablation failed to prevent VT recurrence. Finally, noninvasive stereotactic body radiation therapy (SBRT) targeting the lipoma was performed, with a total dose of 24 Gy delivered in three fractions. The number of VT episodes was reduced from 189/24 h before SBRT to 0 after the procedure. At 4‐month follow‐up, there were no signs of therapy‐related complications. Our experience suggests that SBRT could emerge as a viable treatment option for patients with cardiac tumors who develop refractory ventricular arrhythmias.  相似文献   
69.
70.
Ecological flexibility, extended lifespans, and large brains have long intrigued evolutionary biologists, and comparative genomics offers an efficient and effective tool for generating new insights into the evolution of such traits. Studies of capuchin monkeys are particularly well situated to shed light on the selective pressures and genetic underpinnings of local adaptation to diverse habitats, longevity, and brain development. Distributed widely across Central and South America, they are inventive and extractive foragers, known for their sensorimotor intelligence. Capuchins have among the largest relative brain size of any monkey and a lifespan that exceeds 50 y, despite their small (3 to 5 kg) body size. We assemble and annotate a de novo reference genome for Cebus imitator. Through high-depth sequencing of DNA derived from blood, various tissues, and feces via fluorescence-activated cell sorting (fecalFACS) to isolate monkey epithelial cells, we compared genomes of capuchin populations from tropical dry forests and lowland rainforests and identified population divergence in genes involved in water balance, kidney function, and metabolism. Through a comparative genomics approach spanning a wide diversity of mammals, we identified genes under positive selection associated with longevity and brain development. Additionally, we provide a technological advancement in the use of noninvasive genomics for studies of free-ranging mammals. Our intra- and interspecific comparative study of capuchin genomics provides insights into processes underlying local adaptation to diverse and physiologically challenging environments, as well as the molecular basis of brain evolution and longevity.

Large brains, long lifespans, extended juvenescence, tool use, and problem solving are hallmark characteristics of great apes, and are of enduring interest in studies of human evolution (14). Similar suites of traits have arisen in other lineages, including some cetaceans, corvids and, independently, in another radiation of primates, the capuchin monkeys. Like great apes, they have diverse diets, consume and seek out high-energy resources, engage in complex extractive foraging techniques (5, 6) to consume difficult-to-access invertebrates and nuts (6), and have an extended lifespan, presently recorded up to 54 y in captivity (7, 8). While they do not show evidence of some traits linked with large brain size in humans (e.g., human-like social networks and cultural and technological transmission from older to younger groupmates), their propensity for tool use and their ecological flexibility may have contributed to their convergence with the great apes (9), offering opportunities for understanding the evolution of key traits via the comparative method (1012). Similar approaches have revealed positive selection on genes related to brain size and long lives in great apes and other mammals (13, 14), but our understanding of the genetic underpinnings of these traits remains far from complete.Capuchins also offer excellent opportunities to study local adaptation to challenging seasonal biomes. They occupy diverse habitats, including rainforests and, in the northern extent of their range, tropical dry forests. Particular challenges of the tropical dry forest are staying hydrated during the seasonally prominent droughts, high temperatures in the absence of foliage, and coping metabolically with periods of fruit dearth (Fig. 1). The long-term study of white-faced capuchins (Cebus imitator) occupying these seasonal forests has demonstrated that high infant mortality rates accompany periods of intense drought, illustrating the strength of this selective pressure (15). Furthermore, the seasonally low abundance of fruit is associated with muscular wasting and low circulating levels of urinary creatinine among these capuchins (16). Additionally, the sensory challenges of food search in dry versus humid biomes are also distinct. Odor detection and propagation is affected by temperature and humidity (17), and color vision is hypothesized to be adaptive in the search for ripe fruits and young reddish leaves against a background of thick, mature foliage (18), which is absent for long stretches in dry deciduous forests. The behavioral plasticity of capuchins is widely acknowledged as a source of their ability to adapt to these dramatically different habitats (1921). However, physiological processes, including water balance and metabolic adaptations to low caloric intake, and sensory adaptations to food search, are also anticipated to be targets of natural selection, as seen in other mammals (2224). Understanding population-level differences between primates inhabiting different biomes, contextualized by their demographic history, genomic diversity, and historical patterns of migration, will generate new insights.Open in a separate windowFig. 1.SSR during wet (Left) and dry (Center) seasons. (Right) Map of sampling locations in Costa Rica. The two northern sites, SSR and Cañas, have tropical dry-forest biomes, whereas the two southern sites, Quepos and Manuel Antonio, are tropical wet forests. Photos courtesy of A.D.M. Drawing of white-faced capuchin monkey by Alejandra Tejada-Martinez; map courtesy of Eric Gaba–Wikimedia Commons user: Sting.Unfortunately, high-quality biological specimens from wild capuchins are not readily available. As is the case with most of the world’s primates, many of which are rare or threatened (25), this has limited the scope of questions about their biology that can be answered. Although recent advances in noninvasive genomics have allowed for the sequencing of partial genomes by enriching the proportion of endogenous DNA in feces (2629), it has not yet been feasible to sequence whole genomes from noninvasive samples at high coverage; this has limited the extent to which noninvasive samples can be used to generate genomic resources for nonmodel organisms, such as capuchins.Toward identifying the genetic underpinnings of local adaptation to seasonally harsh environments, large brains, and long lifespans, we assembled and annotated a reference genome of C. imitator (SI Appendix, Table S1). Additionally, we sequenced the genomes of individuals inhabiting two distinct environments in Costa Rica: Lowland evergreen rainforest (southern population) and lowland tropical dry forest (northern population). We conducted high-coverage resequencing (10× to 47×) for 10 of these individuals, and sequenced an additional 13 at low-coverage (0.1× to 4.4×). Importantly, to facilitate the population-wide analyses without the need for potentially harmful invasive sampling of wild primates, we developed a method for minimally biased, whole-genome sequencing of fecal DNA using fluorescence-activated cell sorting (fecalFACS) that we used to generate both high- and low-coverage genomes (Fig. 2). With these genomes, we assess the genetic underpinnings of capuchin-specific biology and adaptation in a comparative framework. First, we scanned the high-coverage genomes (six from the northern dry forest and four from the southern rainforest) for regions exhibiting population specific divergence to assess the extent of local adaptation to dry forest and rainforest environments. We examine how genes related to water balance, metabolism, muscular wasting, and chemosensation have diverged between populations. Second, we conduct an analysis of positive selection on the white-faced capuchin genome through codon-based models of evolution and enrichment tests focusing on genes that may underlie brain development and lifespan. Third, we identify the population structure, genomic diversity, and demographic history of the species using a mixture of traditional and noninvasive fecalFACS genomes (n = 23).Open in a separate windowFig. 2.Mapping percentages of sequencing reads from RNAlater preserved fecal DNA libraries prepared with FACS for (A) all samples (box-plot elements: center line, median; box limits, upper and lower quartiles; whiskers, 1.5× interquartile range; points, outliers), and (B) individual libraries. (C) Increase in mapping rate for RNAlater preserved samples. (D) Relationship between mapped read duplication and number of cells with LOESS smoothing. The duplication rate decreases sharply once a threshold of about 1,000 cells is reached.  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