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   34912篇
  免费   1414篇
  国内免费   332篇
耳鼻咽喉   568篇
儿科学   359篇
妇产科学   465篇
基础医学   5626篇
口腔科学   901篇
临床医学   2823篇
内科学   6446篇
皮肤病学   1333篇
神经病学   2485篇
特种医学   2265篇
外国民族医学   1篇
外科学   4191篇
综合类   296篇
一般理论   5篇
预防医学   1688篇
眼科学   591篇
药学   3385篇
  10篇
中国医学   484篇
肿瘤学   2736篇
  2024年   130篇
  2023年   291篇
  2022年   784篇
  2021年   1266篇
  2020年   621篇
  2019年   850篇
  2018年   982篇
  2017年   811篇
  2016年   1165篇
  2015年   1554篇
  2014年   1851篇
  2013年   2125篇
  2012年   3133篇
  2011年   3091篇
  2010年   1762篇
  2009年   1559篇
  2008年   2148篇
  2007年   1958篇
  2006年   1715篇
  2005年   1578篇
  2004年   1224篇
  2003年   1057篇
  2002年   902篇
  2001年   789篇
  2000年   735篇
  1999年   512篇
  1998年   202篇
  1997年   131篇
  1996年   114篇
  1995年   81篇
  1994年   90篇
  1993年   78篇
  1992年   147篇
  1991年   153篇
  1990年   171篇
  1989年   134篇
  1988年   119篇
  1987年   111篇
  1986年   93篇
  1985年   65篇
  1984年   43篇
  1983年   38篇
  1982年   28篇
  1981年   38篇
  1979年   23篇
  1978年   22篇
  1977年   23篇
  1975年   18篇
  1974年   17篇
  1970年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Porcine epidemic diarrhea virus (PEDV) is a highly contagious enteric pathogen of swine. Acute PEDV outbreaks have continually emerged in most swine-producing Asian countries and, recently, in the United States, causing significant economic losses in the pig industry. The spike (S) protein of PEDV is a type 1 transmembrane envelope glycoprotein and consists of the S1 and S2 domains, which are responsible for virus binding and fusion, respectively. Since the S1 domain is involved in a specific high-affinity interaction with the cellular receptor and induction of neutralizing antibody in the natural host, it is a primary target for the development of effective vaccines against PEDV. In this study, a codon-optimized PEDV S1 gene containing amino acid residues 25–738 was synthesized based on a multiple alignment of the S amino acid sequences of PEDV field isolates and used to establish a stable porcine cell line constitutively expressing the PEDV S1 protein. The purified recombinant S1 protein was found to mediate highly potent antibody responses in immunized rabbits. The antibodies strongly recognized the recombinant S1 protein from cell lysates and supernatants of S1-expressing cells, whereas they bound weakly to the authentic S protein of PEDV vaccine strain SM98-1. Furthermore, a serum neutralization test revealed that the rabbit antisera completely inhibit infection of the PEDV vaccine strain at a serum dilution of 1:16. We then tested the ability of vaccination with the recombinant S1 protein to protect piglets against PEDV. Late-term pregnant sows were inoculated intramuscularly with the purified S1 protein, and the outcome was investigated in passively immunized suckling piglets after a virulent PEDV challenge. The results showed that vaccination with S1 protein efficiently protected neonatal piglets against PEDV. Our data suggest that the recombinant S1 protein shows potential as an effective and safe subunit vaccine for PED prevention.  相似文献   
992.
993.
994.
995.
The accuracy of metabolite concentrations measured using in vivo proton (1H) MRS is enhanced following correction for spin–spin (T2) relaxation effects. In addition, metabolite proton T2 relaxation times provide unique information regarding cellular environment and molecular mobility. Echo‐time (TE) averaging 1H MRS involves the collection and averaging of multiple TE steps, which greatly simplifies resulting spectra due to the attenuation of spin‐coupled and macromolecule resonances. Given the simplified spectral appearance and inherent metabolite T2 relaxation information, the aim of the present proof‐of‐concept study was to develop a novel data processing scheme to estimate metabolite T2 relaxation times from TE‐averaged 1H MRS data. Spectral simulations are used to validate the proposed TE‐averaging methods for estimating methyl proton T2 relaxation times for N‐acetyl aspartate, total creatine, and choline‐containing compounds. The utility of the technique and its reproducibility are demonstrated using data obtained in vivo from the posterior‐occipital cortex of 10 healthy control subjects. Compared with standard methods, distinct advantages of this approach include built‐in macromolecule resonance attenuation, in vivo T2 estimates closer to reported values when maximum TE ≈ T2, and the potential for T2 calculation of metabolite resonances otherwise inseparable in standard 1H MRS spectra recorded in vivo. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
996.
The accurate diagnosis of glioma subtypes is critical for appropriate treatment, but conventional histopathologic diagnosis often exhibits significant intra‐observer variability and sampling error. The aim of this study was to investigate whether histogram analysis using an automatically segmented region of interest (ROI), excluding cystic or necrotic portions, could improve the differentiation between low‐grade and high‐grade gliomas. Thirty‐two patients (nine low‐grade and 23 high‐grade gliomas) were included in this retrospective investigation. The outer boundaries of the entire tumors were manually drawn in each section of the contrast‐enhanced T1‐weighted MR images. We excluded cystic or necrotic portions from the entire tumor volume. The histogram analyses were performed within the ROI on normalized apparent diffusion coefficient (ADC) maps. To evaluate the contribution of the proposed method to glioma grading, we compared the area under the receiver operating characteristic (ROC) curves. We found that an ROI excluding cystic or necrotic portions was more useful for glioma grading than was an entire tumor ROI. In the case of the fifth percentile values of the normalized ADC histogram, the area under the ROC curve for the tumor ROIs excluding cystic or necrotic portions was significantly higher than that for the entire tumor ROIs (p < 0.005). The automatic segmentation of a cystic or necrotic area probably improves the ability to differentiate between high‐ and low‐grade gliomas on an ADC map. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
997.
The purpose of this study was to examine the implication of high‐risk human papillomavirus (HPV) load in cervical intraepithelial neoplasia (CIN) and cancer, and to detect biomarkers in cervical disease. We conducted high‐risk HPV DNA load and cervical cytology tests in 343 women, cervical tissue biopsy in 143 women, and immunohistochemistry for p16INK4A, cyclin D1, p53, cyclooxygenase‐2, Ki‐67, GLUT1, hPygopus2, and beta‐catenin. As a result, HPV load [relative light units (RLU) value] was correlated with the histological severity of cervical disease (p < 0.05). In the ‘atypical squamous cells of undetermined significance’ cytology group, 2.385 of HPV load seemed to be the cut‐off value at which ‘benign’ or CIN I can be differentiated from ‘CIN II or more severe’ (AUC = 0.712), but not statistically significant. The relative risk (odds ratio) of p16INK4A and GLUT1 overexpression increased gradually according to the histological severity of cervical disease. The p16INK4A showed statistically significant odds ratios in CIN II, CIN III, and cancer; GLUT1, in CIN II and CIN III; hPygopus2, in CIN III; and beta‐catenin, in CIN III and cancer. Conclusively, HPV load, p16INK4A, and GLUT1 can be instrumental in predicting the severity of HPV‐related cervical disease. The beta‐catenin/hPygopus2 signaling may be involved in proceeding to CIN III.  相似文献   
998.
Ectoenzyme nucleotide pyrophosphate phosphodiesterase 1 (ENPP1) gene has been studied in relation to type 2 diabetes mellitus (T2DM) and insulin resistance (IR). We hypothesized that the difference in genotype may be one of the factors that affect the outcome of intervention. We genotyped 448 men with fasting glucose≥5.6 mM/L, including 371 in subjects with K allele (KK) (69 control group [CG]; and 302 intervention group [IG]) and 77 in subjects with Q allele (KQ+QQ) (13 CG and 64 IG). The web-based intervention based on a lifestyle modification was delivered by e-mail once a month for 10 months. In the KK, IG demonstrated significantly decreased levels of fasting serum insulin (FSI) as compared to CG and homeostasis model of assessment of insulin resistance (HOMA-IR). In the KQ+QQ IG group, hemoglobin A1c (HbA1c), FSI and HOMA-IR were significantly decreased, and showed further reduction in the HOMA-IR than KQ+QQ CG. After analysis of covariance, K121Q did significantly influence the change of HbA1c in CG after appropriate adjustment. In a multivariate model, BMI change predicted HOMA-IR change (adjusted β=0.801; P=0.022) in KK IG subjects with T2DM. ENPP1 K121Q did not influence the change in IR. However, individuals with T2DM carrying the K121 variant are very responsive to the effect of BMI reduction on HOMA-IR.

Graphical Abstract

相似文献   
999.
Right-sided infective endocarditis (RIE) occurs predominantly in intravenous drug users in western countries, and it has a relatively good prognosis. Clinical features and prognosis of RIE occurring in non-drug users are not well known. We investigated the clinical findings of RIE in non-drug users. We retrospectively reviewed 345 cases diagnosed with IE. Cases with RIE or left-sided infective endocarditis (LIE) defined by the vegetation site were included and cases having no vegetation or both-side vegetation were excluded. Clinical findings and in-hospital outcome of RIE were compared to those of LIE. Among the 245 cases, 39 (16%) cases had RIE and 206 (84%) cases had LIE. RIE patients were younger (40±19 yr vs 50±18 yr, P=0.004), and had a higher incidence of congenital heart disease (CHD) (36% vs 13%, P<0.001) and central venous catheter (CVC) (21% vs 4%, P=0.001) compared to LIE patients. A large vegetation was more common in RIE (33% vs 9%, P<0.001). Staphylococcus aureus was the most common cause of RIE, while Streptococcus viridans were the most common cause of LIE. In-hospital mortality and cardiac surgery were not different between the two groups. CHD and use of CVC were common in non-drug users with RIE. The short-term clinical outcome of RIE is not different from that of LIE.

Graphical Abstract

相似文献   
1000.
Knowledge of clinical demographics and outcomes of mechanically ventilated patients is important but there are few prospectively collected data in Korea. The objective of the present study was to describe the current status of mechanically ventilated patients in Korea as of 2010. We analyzed the data of Korean patients (275 patients in 12 Korean intensive care units [ICU]) participating in a multinational prospective cohort study on mechanical ventilation. The most common indication for mechanical ventilation was pneumonia (23%). Pressure-limited ventilation modes were preferred over volume-cycled ventilation modes. Non-invasive positive pressure ventilation was used in only seven (2%) patients as the initial ventilatory support. Median duration of mechanical ventilation was 7 days and ICU mortality was 36%. The multiple logistic regression model revealed that the Simplified Acute Physiology Score II (SAPS II) score at ICU admission (odds ratio [OR], 1.034; 95% confidence interval [CI], 1.001-1.036; P=0.033), peak pressure (OR, 1.054; 95% CI, 1.016-1.095; P=0.006), and the number of failed organs (OR, 2.132; 95% CI, 1.634-2.781; P<0.001) were independently associated with ICU mortality. This study provides a snapshot of current practice of mechanical ventilation in Korea.

Graphical Abstract

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