全文获取类型
收费全文 | 2350397篇 |
免费 | 171245篇 |
国内免费 | 3333篇 |
专业分类
耳鼻咽喉 | 32052篇 |
儿科学 | 75910篇 |
妇产科学 | 62688篇 |
基础医学 | 348186篇 |
口腔科学 | 63634篇 |
临床医学 | 211362篇 |
内科学 | 457354篇 |
皮肤病学 | 51727篇 |
神经病学 | 185285篇 |
特种医学 | 88024篇 |
外国民族医学 | 489篇 |
外科学 | 353899篇 |
综合类 | 47509篇 |
现状与发展 | 12篇 |
一般理论 | 848篇 |
预防医学 | 182734篇 |
眼科学 | 54327篇 |
药学 | 175115篇 |
11篇 | |
中国医学 | 4575篇 |
肿瘤学 | 129234篇 |
出版年
2021年 | 18989篇 |
2019年 | 19543篇 |
2018年 | 27070篇 |
2017年 | 20362篇 |
2016年 | 22752篇 |
2015年 | 25653篇 |
2014年 | 36103篇 |
2013年 | 53966篇 |
2012年 | 74697篇 |
2011年 | 79417篇 |
2010年 | 47065篇 |
2009年 | 44573篇 |
2008年 | 74618篇 |
2007年 | 79488篇 |
2006年 | 80312篇 |
2005年 | 77790篇 |
2004年 | 74376篇 |
2003年 | 71696篇 |
2002年 | 69368篇 |
2001年 | 108744篇 |
2000年 | 111459篇 |
1999年 | 93495篇 |
1998年 | 26994篇 |
1997年 | 23658篇 |
1996年 | 24055篇 |
1995年 | 22715篇 |
1994年 | 20896篇 |
1993年 | 19714篇 |
1992年 | 72006篇 |
1991年 | 70072篇 |
1990年 | 68391篇 |
1989年 | 65663篇 |
1988年 | 60305篇 |
1987年 | 59125篇 |
1986年 | 55217篇 |
1985年 | 53004篇 |
1984年 | 39311篇 |
1983年 | 33396篇 |
1982年 | 19859篇 |
1979年 | 35866篇 |
1978年 | 25652篇 |
1977年 | 21233篇 |
1976年 | 20333篇 |
1975年 | 21816篇 |
1974年 | 26148篇 |
1973年 | 24803篇 |
1972年 | 23200篇 |
1971年 | 22037篇 |
1970年 | 20247篇 |
1969年 | 19315篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
T.A. Tomsick L.L. Wang M. Zuccarello A.J. Ringer 《AJNR. American journal of neuroradiology》2021,42(4):801
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:
- HIF were greater in number than AMFs, but AMFs increase in the presence of increasing HIF, suggesting an anatomic relationship.
- 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.
- 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.
- 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.
123.
124.
Oga Emmanuel. A. Peters Erica. N. Mark Katrina Trocin Kathleen Coleman-Cowger Victoria. H. 《Maternal and child health journal》2019,23(2):250-257
Maternal and Child Health Journal - Background Prenatal substance use screening is recommended. The 4 P’s Plus screener includes questions on perceived problematic substance use in parents... 相似文献
125.
126.
Elizabeth A. Mosley PhD MPH Amy J. Schulz PhD MPH MSW Lisa H. Harris MD PhD Barbara A. Anderson PhD 《Women & health》2020,60(7):806-820
ABSTRACT Abortion is legal in South Africa, but negative abortion attitudes remain common and are poorly understood. We used nationally representative South African Social Attitudes Survey data to analyze abortion attitudes in the case of fetal anomaly and in the case of poverty from 2007 to 2016 (n = 20,711; ages = 16+). We measured correlations between abortion attitudes and these important predictors: religiosity, attitudes about premarital sex, attitudes about preferential hiring and promotion of women, and attitudes toward family gender roles. Abortion acceptability for poverty increased over time (b = 0.05, p < .001), but not for fetal anomaly (b = ?0.008, p = .284). Highly religious South Africans reported lower abortion acceptability in both cases (Odds Ratio (OR)anomaly = 0.85, p = .015; ORpoverty = 0.84, p = .02). Premarital sex acceptability strongly and positively predicted abortion acceptability (ORanomaly = 2.63, p < .001; ORpoverty = 2.46, p < .001). Attitudes about preferential hiring and promotion of women were not associated with abortion attitudes, but favorable attitudes about working mothers were positively associated with abortion acceptability for fetal anomaly ((ORanomaly = 1.09, p = .01; ORpoverty = 1.02, p = .641)). Results suggest negative abortion attitudes remain common in South Africa and are closely tied to religiosity, traditional ideologies about sexuality, and gender role expectations about motherhood. 相似文献
127.
128.
Javed A. Shaik Nima Estharabadi Ronda S. Farah Maria K. Hordinsky 《Experimental dermatology》2020,29(10):1004-1011
Platelet α-granules release growth factors (GFs) that promote healing and tissue regeneration. Platelet-rich plasma (PRP) is shown to be beneficial in treating alopecia, and however, clinical response can be inconsistent. Due to several fold enrichment of platelets secreting large quantities of GFs following PRP injections, heterogeneity in amounts of GFs secreted by platelets may contribute to inconsistent clinical responses. Herein, we evaluated factors that could potentially contribute to heterogeneous secretion of GFs by platelets. We measured platelet secretion of transforming growth factor beta1 (TGFβ1), platelet-derived growth factor (PDGF-BB), epidermal growth factor (EGF), vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF2) in aliquots of de-identified PRP samples from female patients undergoing therapy in the hair disease clinic. Although secretion of GFs by platelets was comparable in PRP samples of patients with non-cicatricial and cicatricial alopecia, a Shapiro-Wilk test for normal distribution indicated significant variability across all patient samples. The amount of GF secreted by platelets was comparable when PRP prepared from two FDA-cleared devices with distinct techniques were compared. We provide evidence of platelets secreting heterogeneous amounts of GFs within each sample as high and low secretion of random factors could be simultaneously detected. These results suggest inherent heterogeneity in secretion of GFs by platelets in patient samples that are not influenced by the device used to prepare PRP. Since some GFs could have antagonistic effects on hair growth, a balance between amounts of growth promoting and inhibiting factors may be crucial in determining clinical response to PRP therapy. 相似文献
129.
130.