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   1518篇
  免费   84篇
  国内免费   7篇
耳鼻咽喉   20篇
儿科学   53篇
妇产科学   14篇
基础医学   185篇
口腔科学   106篇
临床医学   98篇
内科学   268篇
皮肤病学   28篇
神经病学   100篇
特种医学   158篇
外科学   115篇
综合类   71篇
预防医学   210篇
眼科学   20篇
药学   90篇
中国医学   4篇
肿瘤学   69篇
  2023年   5篇
  2022年   12篇
  2021年   18篇
  2020年   17篇
  2019年   12篇
  2018年   32篇
  2017年   24篇
  2016年   28篇
  2015年   38篇
  2014年   52篇
  2013年   77篇
  2012年   93篇
  2011年   94篇
  2010年   82篇
  2009年   65篇
  2008年   78篇
  2007年   67篇
  2006年   85篇
  2005年   73篇
  2004年   57篇
  2003年   49篇
  2002年   52篇
  2001年   44篇
  2000年   39篇
  1999年   30篇
  1998年   33篇
  1997年   24篇
  1996年   23篇
  1995年   17篇
  1994年   25篇
  1993年   25篇
  1992年   11篇
  1991年   12篇
  1990年   8篇
  1989年   22篇
  1988年   17篇
  1987年   14篇
  1986年   11篇
  1985年   19篇
  1984年   10篇
  1983年   11篇
  1982年   5篇
  1981年   9篇
  1980年   5篇
  1979年   6篇
  1978年   6篇
  1977年   8篇
  1976年   9篇
  1975年   8篇
  1970年   5篇
排序方式: 共有1609条查询结果,搜索用时 156 毫秒
61.
Smythe  JS; Spring  FA; Gardner  B; Parsons  SF; Judson  PA; Anstee  DJ 《Blood》1995,85(10):2929-2936
This report describes the production and characterization of 13 rodent monoclonal antibodies to the human erythrocyte anion transport protein AE1 (syn. band 3). Eleven antibodies (4 murine and 7 rat) recognize epitopes dependent on the integrity of the third extracellular loop of the protein. Two antibodies (1 murine and 1 rat) recognize epitopes on the N-terminal cytoplasmic domain. Quantitative binding studies using radioiodinated IgG and Fab fragments of antibodies to extracellular epitopes on AE1 ranged from 77,000 to 313,000 (IgG) and from 241,000 to 772,000 (Fab) molecules bound at saturation. The results indicate that the epitopes recognized by different antibodies vary in their accessibility and suggest that there is heterogeneity in the organization of individual AE1 molecules in the red blood cell membrane. Quantitative binding studies on South East Asian ovalocytes using several antibodies to AE1 and an anti-Wrb show a marked reduction in the number of antibody molecules bound at saturation. These results are consistent with the existence of highly cooperative interactions between transmembrane domains of AE1 in normal erythrocytes and the disruption of these interactions in the variant AE1 found in South East Asian ovalocytes.  相似文献   
62.
63.
64.
 目的 探讨超声引导下心包穿刺置管引流急慢性心包积液的疗效。方法 回顾分析2009-01至2019-08医院161例行超声引导下心包穿刺置管引流术患者的临床资料,并对其病因、症状、缓解情况进行分析。结果 161例心包积液患者前三位的病因分别为肿瘤、心力衰竭、创伤或手术,经超声引导下心包穿刺置管术治疗后症状缓解率均在70%以上。结论 超声引导下心包穿刺置管引流术治疗心包积液疗效确切,可作为临床治疗心包积液特别是急性心包压塞的首选治疗方式。  相似文献   
65.
The increasing prevalence of antibiotic-resistant bacteria is a global threat to public health. Agricultural use of antibiotics is believed to contribute to the spread of antibiotic resistance, but the mechanisms by which many agricultural practices influence resistance remain obscure. Although manure from dairy farms is a common soil amendment in crop production, its impact on the soil microbiome and resistome is not known. To gain insight into this impact, we cultured bacteria from soil before and at 10 time points after application of manure from cows that had not received antibiotic treatment. Soil treated with manure contained a higher abundance of β-lactam–resistant bacteria than soil treated with inorganic fertilizer. Functional metagenomics identified β-lactam–resistance genes in treated and untreated soil, and indicated that the higher frequency of resistant bacteria in manure-amended soil was attributable to enrichment of resident soil bacteria that harbor β-lactamases. Quantitative PCR indicated that manure treatment enriched the blaCEP-04 gene, which is highly similar (96%) to a gene found previously in a Pseudomonas sp. Analysis of 16S rRNA genes indicated that the abundance of Pseudomonas spp. increased in manure-amended soil. Populations of other soil bacteria that commonly harbor β-lactamases, including Janthinobacterium sp. and Psychrobacter pulmonis, also increased in response to manure treatment. These results indicate that manure amendment induced a bloom of certain antibiotic-resistant bacteria in soil that was independent of antibiotic exposure of the cows from which the manure was derived. Our data illustrate the unintended consequences that can result from agricultural practices, and demonstrate the need for empirical analysis of the agroecosystem.Agriculture affects human health through both the consumption and production of food for the human diet. Manure from pig and cattle farms is commonly used as a substitute for inorganic nitrogen and phosphorus fertilizers for agricultural crops worldwide, especially in organic farming practices (16). With the increasing consumer demand for organically produced food, the use of animal manure, which conforms to organic conventions, will likely increase in the future. According to the National Organic Program, raw manure may be used up to 90–120 d before harvest, depending on the crop, and composted manure may be applied at any time. There are no restrictions on the source of manure (1).Animal manure is an important reservoir of antibiotic-resistant bacteria, antibiotic-resistance genes (collectively known as the “resistome”), and pathogens (2, 712). Although antibiotic use increases antibiotic-resistance genes and resistant bacteria in manure (1316), antibiotic-resistant bacteria are also abundant in manure from animals with no history of antibiotic treatment, indicating the natural presence of bacteria intrinsically resistant to antibiotics in animal gastrointestinal tracts (2, 17, 18).There is increasing concern about the use of manure as an agricultural amendment because of its possible contribution to the pool of resistance genes to resident soil bacteria and pathogens (2, 19). Antibiotic-resistance genes from the soil resistome can enter the food chain via contaminated crops or groundwater (5, 20), and have potential consequences for human health if transferred to human pathogens. Studies assessing the impact of fertilization with pig manure on the soil resistome have shown that excessive application of manure from farms with intensive sulfonamide use can lead to an increase of antibiotic-resistance genes in soil (2, 3); however, most studies have found that such increases are transient when the manure is applied at recommended rates (2, 21, 22). Cow manure from dairy farms, which use β-lactam antibiotics predominantly to prevent and treat diseases (23), is commonly used in crop production, but its impact on the soil resistome has yet to be investigated.Along with its impact on the soil resistome, the application of manure can affect the composition and functional properties of soil microbial communities, as has been demonstrated by community fingerprinting (21, 24). Recent advances in DNA-based analysis, such as metagenomics and quantitative PCR (qPCR), offer greater precision in such studies, enabling identification of affected community members (25) and their resistance genes (4).In the present study, we assessed the impact of cow manure on the composition and resistance profiles of bacterial communities in soil. Our results show that manure from cows that had not been treated with antibiotics increased the populations of resident soil bacteria harboring genes for resistance to β-lactam antibiotics, whereas inorganic fertilizers did not. These results demonstrate the complexity, and at times nonintuitive consequences, of agricultural practices.  相似文献   
66.
Incidence of invasive meningococcal disease is low in Germany at 0.5 cases/100,000 inhabitants. Serogroup B (MenB) is most common, causing 70% of cases, with highest incidence in infants (5.9/100,000). In 2013, a MenB vaccine was licensed in Europe. To assess pediatricians’ attitudes towards MenB vaccination and its potential use in Germany we conducted a nationwide cross-sectional survey among 5677 pediatricians. Of 3107 participants (response: 55%), 79.1% would recommend a MenB vaccination to parents, with 66.7% favoring a schedule at 6, 8 and 12 months over 2, 3, 4 and 12 months (13.4%). Administration separately from other vaccines was preferred (63.2%); 38.5% feared that a recommendation would lead to refusal of other recommended vaccinations. In conclusion, pediatricians showed distinct preferences regarding possible integration of MenB vaccination into the existent immunization schedule. As physicians play a crucial role in the implementation, findings will be useful in decision-making regarding potential introduction.  相似文献   
67.
68.
Color constancy is our ability to perceive constant colors across varying illuminations. Here, we trained deep neural networks to be color constant and evaluated their performance with varying cues. Inputs to the networks consisted of two-dimensional images of simulated cone excitations derived from three-dimensional (3D) rendered scenes of 2,115 different 3D shapes, with spectral reflectances of 1,600 different Munsell chips, illuminated under 278 different natural illuminations. The models were trained to classify the reflectance of the objects. Testing was done with four new illuminations with equally spaced CIEL*a*b* chromaticities, two along the daylight locus and two orthogonal to it. High levels of color constancy were achieved with different deep neural networks, and constancy was higher along the daylight locus. When gradually removing cues from the scene, constancy decreased. Both ResNets and classical ConvNets of varying degrees of complexity performed well. However, DeepCC, our simplest sequential convolutional network, represented colors along the three color dimensions of human color vision, while ResNets showed a more complex representation.  相似文献   
69.
70.

Background

There is no published data on the prognostic value of global myocardial perfusion values at stress dynamic CT myocardial perfusion imaging (CTMPI).

Methods

Data of 144 patients from 6 centers who had undergone coronary CT angiography (coronary CTA) and CTMPI were assessed. Coronary CTA studies were acquired at rest; CTMPI was performed under vasodilator stress. Coronary CTA data were evaluated for coronary artery stenosis (≥50% luminal narrowing) on a per-vessel basis. Volumes-of-interest were placed over the entire left ventricular myocardium to obtain global myocardial blood flow (MBF), myocardial blood volume (MBV), and volume transfer constant (Ktrans). Follow-up was obtained at 6/12/18 months. Major adverse cardiac events (MACE, defined as cardiac death, non-fatal myocardial infarction, unstable angina requiring hospitalization, and revascularization) served as the endpoint.

Results

MACE occurred in 40 patients (nonfatal myocardial infarction, n = 1, unstable angina, n = 13, PCI, n = 23, and CABG, n = 3). Patients with global MBF of <121 mL/100 mL/min were at increased risk for MACE (HR 2.07, 95% confidence interval [CI]: 1.12–3.84, p = 0.02). This association remained significant after adjusting for age, gender, and clinical risk factors (HR 2.17, 95%CI: 1.16–4.06, p = 0.02), after further adjusting for presence of ≥50% stenosis at coronary CTA (HR 2.18, 95%CI: 1.16–4.10, p = 0.02) and when excluding early (<6 months) revascularizations (HR 2.34, 95%CI: 1.01–5.43, p = 0.0486). Global MBV and Ktrans were not independent predictors of MACE.

Conclusion

Global quantification of left ventricular MBF at stress dynamic CTMPI may have incremental predictive value for future MACE over clinical risk factors and assessment of stenosis at coronary CTA.  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