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   1335926篇
  免费   99904篇
  国内免费   4274篇
耳鼻咽喉   16810篇
儿科学   43601篇
妇产科学   36450篇
基础医学   197878篇
口腔科学   35955篇
临床医学   129578篇
内科学   258116篇
皮肤病学   26374篇
神经病学   111898篇
特种医学   48172篇
外国民族医学   366篇
外科学   184073篇
综合类   28777篇
现状与发展   1篇
一般理论   460篇
预防医学   114387篇
眼科学   28982篇
药学   98865篇
  6篇
中国医学   3166篇
肿瘤学   76189篇
  2021年   10922篇
  2019年   11636篇
  2018年   16328篇
  2017年   12294篇
  2016年   13258篇
  2015年   15197篇
  2014年   20805篇
  2013年   32059篇
  2012年   44248篇
  2011年   46899篇
  2010年   27082篇
  2009年   24927篇
  2008年   42718篇
  2007年   45067篇
  2006年   45176篇
  2005年   43600篇
  2004年   41569篇
  2003年   39511篇
  2002年   38317篇
  2001年   60849篇
  2000年   62536篇
  1999年   52291篇
  1998年   14587篇
  1997年   13281篇
  1996年   13115篇
  1995年   12456篇
  1994年   11629篇
  1993年   10921篇
  1992年   41576篇
  1991年   40764篇
  1990年   39455篇
  1989年   37346篇
  1988年   34586篇
  1987年   33701篇
  1986年   32161篇
  1985年   30658篇
  1984年   23042篇
  1983年   19599篇
  1982年   11756篇
  1979年   20814篇
  1978年   14821篇
  1977年   12069篇
  1976年   11883篇
  1975年   12112篇
  1974年   14806篇
  1973年   14477篇
  1972年   13363篇
  1971年   12422篇
  1970年   11489篇
  1969年   10417篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Treatment decisions in patients with metastatic bone disease rely on accurate survival estimation. We developed the original PATHFx models using expensive, proprietary software and now seek to provide a more cost-effective solution. Using open-source machine learning software to create PATHFx version 2.0, we asked whether PATHFx 2.0 could be created using open-source methods and externally validated in two unique patient populations. The training set of a well-characterized, database records of 189 patients and the bnlearn package within R Version 3.5.1 (R Foundation for Statistical Computing), was used to establish a series of Bayesian belief network models designed to predict survival at 1, 3, 6, 12, 18, and 24 months. Each was externally validated in both a Scandinavian (n = 815 patients) and a Japanese (n = 261 patients) data set. Brier scores and receiver operating characteristic curves to assessed discriminatory ability. Decision curve analysis (DCA) evaluated whether models should be used clinically. DCA showed that the model should be used clinically at all time points in the Scandinavian data set. For the 1-month time point, DCA of the Japanese data set suggested to expect better outcomes assuming all patients will survive greater than 1 month. Brier scores for each curve demonstrate that the models are accurate at each time point. Statement of Clinical Significance: we successfully transitioned to PATHFx 2.0 using open-source software and externally validated it in two unique patient populations, which can be used as a cost-effective option to guide surgical decisions in patients with metastatic bone disease.  相似文献   
83.
In May 2017, the Health and Environmental Sciences Institute's Genetic Toxicology Technical Committee hosted a workshop to discuss whether mode of action (MOA) investigation is enhanced through the application of the adverse outcome pathway (AOP) framework. As AOPs are a relatively new approach in genetic toxicology, this report describes how AOPs could be harnessed to advance MOA analysis of genotoxicity pathways using five example case studies. Each of these genetic toxicology AOPs proposed for further development includes the relevant molecular initiating events, key events, and adverse outcomes (AOs), identification and/or further development of the appropriate assays to link an agent to these events, and discussion regarding the biological plausibility of the proposed AOP. A key difference between these proposed genetic toxicology AOPs versus traditional AOPs is that the AO is a genetic toxicology endpoint of potential significance in risk characterization, in contrast to an adverse state of an organism or a population. The first two detailed case studies describe provisional AOPs for aurora kinase inhibition and tubulin binding, leading to the common AO of aneuploidy. The remaining three case studies highlight provisional AOPs that lead to chromosome breakage or mutation via indirect DNA interaction (inhibition of topoisomerase II, production of cellular reactive oxygen species, and inhibition of DNA synthesis). These case studies serve as starting points for genotoxicity AOPs that could ultimately be published and utilized by the broader toxicology community and illustrate the practical considerations and evidence required to formalize such AOPs so that they may be applied to genetic toxicity evaluation schemes. Environ. Mol. Mutagen. 61:114–134, 2020. © 2019 Wiley Periodicals, Inc.  相似文献   
84.
85.
BACKGROUND AND PURPOSE:Cervical spine axial MRI T2-hyperintense fluid signal of the anterior median fissure and round hyperintense foci resembling either the central canal or base of the anterior median fissure are associated with a craniocaudad sagittal line, also simulating the central canal. On the basis of empiric observation, we hypothesized that hyperintense foci, the anterior median fissure, and the sagittal line are seen more frequently in patients with Chiari malformation type I, and the sagittal line may be the base of the anterior median fissure in some patients.MATERIALS AND METHODS:Saggital line incidence and the incidence/frequency of hyperintense foci and anterior median fissure in 25 patients with Chiari I malformation and 25 contemporaneous age-matched controls were recorded in this prospective exploratory study as either combined (hyperintense foci+anterior median fissure in the same patient), connected (anterior median fissure extending to and appearing to be connected with hyperintense foci), or alone as hyperintense foci or an anterior median fissure. Hyperintense foci and anterior median fissure/patient, hyperintense foci/anterior median fissure ratios, and anterior median fissure extending to and appearing to be connected with hyperintense foci were compared in all, in hyperintense foci+anterior median fissure in the same patient, and in anterior median fissure extending to and appearing to be connected with hyperintense foci in patients with Chiari I malformation and controls.RESULTS:Increased sagittal line incidence (56%), hyperintense foci (8.5/patient), and anterior median fissure (4.0/patient) frequency were identified in patients with Chiari I malformation versus controls (28%, 3.9/patient, and 2.7/patient, respectively). Increased anterior median fissure/patient, decreasing hyperintense foci/anterior median fissure ratio, and increasing anterior median fissure extending to and appearing to be connected with hyperintense foci/patient were identified in Chiari subgroups. A 21%–58% increase in observed anterior median fissure extending to and appearing connected to hyperintense foci in the entire cohort and multiple sagittal line subgroups compared with predicted occurred.CONCLUSIONS:In addition to the anticipated increased incidence/frequency of sagittal line and hyperintense foci in patients with Chiari I malformation, an increased incidence and frequency of anterior median fissure and anterior median fissure extending to and appearing to be connected with hyperintense foci/patient were identified. We believe an anterior median fissure may contribute to a saggital line appearance in some patients with Chiari I malformation. While thin saggital line channels are usually ascribed to the central canal, we believe some may be due to the base of the anterior median fissure, created by pulsatile CSF hydrodynamics.

Axial MR imaging of the cervical spine frequently demonstrates hyperintense, linear, anatomically, sagittally-oriented T2 fluid signal of the anterior median fissure (AMF) and hyperintense foci (HIF) resembling the central canal or the base of the AMF.1-3 These axial T2 findings may be associated with a channel-like T2-hyperintense craniocaudad line on images parallel to the sagittal plane (a sagittal line [SL]), simulating the central canal (Fig 1).4,5 A previous analysis of HIF, AMF, and a thin SL in a population without Chiari I malformation provided not only a baseline for their identification but also a confirmation of a relationship between not only the AMF and HIF but also their relationship to the SL.1 It found the following:
  1. HIF were greater in number than AMFs, but AMFs increase in the presence of increasing HIF, suggesting an anatomic relationship.
  2. SLs were associated with greater numbers of both HIF and AMF/patient (pt.) versus no SL, 6.7 versus 2.7/pt. and 3.3 versus 2.0/pt., respectively. SL presence correlated more closely to HIF than to AMF presence within the entire 358-patient group.
  3. When HIF and AMF were classified as combined (concurrent HIF and AMF, with ≥1 of each both present in the same patient [HIF+AMF]) or continuous (AMF appearing to extend to and join an HIF [AMF>HIF]), HIF and AMF/pt. each differed numerically and patients with an SL had more combined HIF+AMF and continuous AMF>HIF than patients without an SL.
  4. In patients with both SL and combined HIF+AMF (a circumstance allowing the possibility of a relationship of all 3 structures), HIF become proportionally fewer compared with AMFs. In patients with an SL actually exhibiting continuous AMF>HIF, the HIF/AMF ratio decreased further.
Open in a separate windowFIG 1.A patient with Chiari I with 19 HIF up to 3 mm in diameter, 1 AMF, no AMF>HIF, and an SL of various hyperintensity and diameter from C4 through T1, consistent with hydromyelia.While it is expected that manifestations of the central canal as an SL and HIF are more frequent in patients with Chiari syndrome type I,6 past experience leads us to hypothesize that AMFs are also seen more frequently in patients with Chiari I malformation and that the SL or channel may represent the base of a wide AMF, rather than the central canal, in some patients (Figs 1 and and2).2). Therefore, we performed an exploratory prospective analysis of HIF, AMF, and SL in patients with Chiari I malformation to examine their relationships.Open in a separate windowFIG 2.Postdecompressive craniectomy patient with Chiari I with 9 HIF, 4 AMFs, 1 AMF>HIF, and sharp and hyperintense SLs at C6–C7 and less hyperintense, sharp, and defined SLs at C2–C6.  相似文献   
86.
87.
88.
Abstract

This study is a single-center, retrospective analysis of postmenopausal women presenting with dyspareunia and vulvar pain, aiming to evaluate relative effectiveness of vestibular CO2 laser therapy as a treatment. Three monthly sessions of laser were performed to each patient and thereafter a three-months follow-up was stablished. A total number of 72 patients undergoing vestibular laser treatment were recruited from patient files in the period between 2016 and 2018. Among these, 39 women also received a concomitant treatment with ospemifene (60?mg/day) during the study period. There was a statistically significant reduction of all the symptoms in both groups up to the three month follow-up. Regarding dryness and dyspareunia, the relief tent to be more prominent in the ospemifene?+?laser group at all follow-ups and remained statistically significant at three-month follow-up. Specifically, vestibular dryness was significantly lower in the ospemifene?+?laser group compared with the laser treatment group (?87% vs???34%, respectively), and the vestibular health score started declining faster in the ospemifene?+?laser group. Although, additional research is needed to understand the mechanism of action, our data shows that a combination regimen of laser and ospemifene may improve clinical effectiveness for long-term treatment of symptoms associated with the under-recognized genitourinary syndrome of menopause.  相似文献   
89.
90.
Inbred mouse strains are the most widely used mammalian model organism in biomedical research owing to ease of genetic manipulation and short lifespan; however, each inbred strain possesses a unique repertoire of deleterious homozygous alleles that can make a specific strain more susceptible to a particular disease. In the current study, we report dystrophic cardiac calcinosis (DCC) in C.B‐17 SCID male mice at 10 weeks of age with no significant change in cardiac function. Acquisition of DCC was characterized by myocardial injury, fibrosis, calcification, and necrosis of the tissue. At 10 weeks of age, 38% of the C.B‐17 SCID mice from two different commercial colonies exhibited significant calcinosis on the ventricular epicardium, predominantly on the right ventricle. The frequency of calcinosis was more than 50% for mice obtained from Taconic's Cambridge City colony and 25% for mice obtained from Taconic's German Town colony. Interestingly, the DCC phenotype did not affect cardiac function at 10 weeks of age. No differences in echocardiography or electrocardiography were observed between the calcinotic and non‐calcinotic mice from either colony. Our findings suggest that C.B‐17 SCID mice exhibit DCC as early as 10 weeks of age with no significant impact on cardiac function. This strain of mice should be cautiously considered for the study of cardiac physiology.  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