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   25137篇
  免费   1309篇
  国内免费   172篇
耳鼻咽喉   193篇
儿科学   523篇
妇产科学   436篇
基础医学   2719篇
口腔科学   617篇
临床医学   2009篇
内科学   6599篇
皮肤病学   484篇
神经病学   2932篇
特种医学   775篇
外科学   3859篇
综合类   43篇
一般理论   5篇
预防医学   1006篇
眼科学   446篇
药学   1436篇
中国医学   30篇
肿瘤学   2506篇
  2023年   162篇
  2022年   163篇
  2021年   656篇
  2020年   443篇
  2019年   616篇
  2018年   691篇
  2017年   550篇
  2016年   620篇
  2015年   691篇
  2014年   1011篇
  2013年   1270篇
  2012年   1997篇
  2011年   1991篇
  2010年   1157篇
  2009年   1068篇
  2008年   1746篇
  2007年   1804篇
  2006年   1666篇
  2005年   1644篇
  2004年   1627篇
  2003年   1350篇
  2002年   1315篇
  2001年   182篇
  2000年   107篇
  1999年   128篇
  1998年   201篇
  1997年   165篇
  1996年   146篇
  1995年   166篇
  1994年   125篇
  1993年   125篇
  1992年   110篇
  1991年   87篇
  1990年   86篇
  1989年   64篇
  1988年   66篇
  1987年   62篇
  1986年   56篇
  1985年   57篇
  1984年   79篇
  1983年   44篇
  1982年   45篇
  1981年   43篇
  1980年   33篇
  1979年   20篇
  1978年   16篇
  1977年   30篇
  1976年   17篇
  1974年   15篇
  1973年   14篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Colorectal cancer (CRC) screening programs help diagnose cancer precursors and early cancers and help reduce CRC mortality. However, currently recommended tests, the fecal immunochemical test (FIT) and colonoscopy, have low uptake. There is therefore a pressing need for screening strategies that are minimally invasive and consequently more acceptable to patients, most likely blood based, to increase early CRC identification. MicroRNAs (miRNAs) released from cancer cells are detectable in plasma in a remarkably stable form, making them ideal cancer biomarkers. Using plasma samples from FIT-positive (FIT+) subjects in an Italian CRC screening program, we aimed to identify plasma circulating miRNAs that detect early CRC. miRNAs were initially investigated by quantitative real-time PCR in plasma from 60 FIT+ subjects undergoing colonoscopy at Fondazione IRCCS Istituto Nazionale dei Tumori, then tested on an internal validation cohort (IVC, 201 cases) and finally in a large multicenter prospective series (external validation cohort [EVC], 1121 cases). For each endoscopic lesion (low-grade adenoma [LgA], high-grade adenoma [HgA], cancer lesion [CL]), specific signatures were identified in the IVC and confirmed on the EVC. A two-miRNA-based signature for CL and six-miRNA signatures for LgA and HgA were selected. In a multivariate analysis including sex and age at blood collection, the areas under the receiver operating characteristic curve (95% confidence interval) of the signatures were 0.644 (0.607–0.682), 0.670 (0.626–0.714) and 0.682 (0.580–0.785) for LgA, HgA and CL, respectively. A miRNA-based test could be introduced into the FIT+ workflow of CRC screening programs so as to schedule colonoscopies only for subjects likely to benefit most.  相似文献   
2.
Background::Soft tissue sarcoma (STS) is a heterogeneous group of rare neoplasms whose aetiology is largely unknown. Dioxin and dioxin-like compounds, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and polychlorinated biphenyls (PCBs), are potential risk factors for STS.Objectives:To investigate the relation of 17 PCBs congeners, assessed in human plasma, with STS risk.Methods:We conducted a case-control study in Italy, including 52 STS cases and 99 hospital-based controls. Selected PCB were extracted by high-performance liquid chromatography (HPLC) and measured with gas chromatography-mass spectrometry (GC-MS). Odds ratios (OR), and the corresponding 95% confidence intervals (CI), were estimated through multivariate logistic regression models.Results:The most frequently detected PCB congeners were 138, 170, 180 and 149 (detected in 40-77% of controls). The OR for the sum of all 17 PCB congeners was 1.20 (95% CI 0.50-2.92). In categorical analysis no consistent association was found for individual congeners and for groups based on Wolff’s classification or the degree of chlorination. For continuous estimates, borderline positive associations emerged for Wolff’s groups 2A (OR 1.23, 95% CI 0.97-1.55), 2B (OR 1.34, 95% CI 1.00-1.77, and 3 (OR 1.19, 95% CI 0.96-1.49), for moderately (OR 1.20, 95% CI 0.96-1.51) and highly (OR 1.18, 95% CI 0.99-1.41) chlorinated PCBs, and for congeners 170 (OR 1.26, 95% CI 0.98-1.63), 180 (OR 1.26, 95% CI 0.97-1.64) and 138 (OR 1.45, 95% CI 1.02-2.04).Discussion:Most associations between PCBs and STS risk were not significant, but, given the limited sample size, we cannot exclude moderate associations.Key words: Soft tissue sarcoma, polychlorinated biphenyls, epidemiology, environmental risk factors, chemical contaminants, case-control study  相似文献   
3.
4.

Introduction

Femoral neck fractures are the most frequent fractures in the elderly and hemiarthroplasty is the treatment of choice. The objective of this multicenter study is to identify predictive factors of acetabular erosion after bipolar hemiarthroplasty (surgery between 1997 and 2007) in a mobile independent population during a follow-up of ten years.

Materials and methods

Data were prospectively collected and retrospectively analyzed. Inclusion criteria were: age >60 and <85 years, BMI?<?35, normal Abbreviated MiniMental Test score, ability to walk 0.8?km and live independently, non-pathological fracture, hip with no or minimal osteoarthritic changes, and availability of clinical and radiological follow-up. For each Patient were recorded: demographic data, comorbidities, time from fracture to surgery, characteristics of the implant, duration of surgery. Patients included underwent clinical and radiological follow-up.

Results

Overall, 209 Patients met inclusion criteria. A press-fit implant was performed in 172 subjects; in contrast a cemented prosthesis was implanted in 37 patients. Nineteen patients underwent implant revision to total hip arthroplasty for acetabular erosion and pain. Classification of X-ray using Baker criteria showed a grade 0 in 54.5%, a grade 1 in 19.6%, a grade 2 in 18.1% and a grade 3 in 7.6%. Multivariate analysis revealed that the size of the femoral head (FH) was the only predictive factor of a higher risk of acetabular erosion. The Kaplan-Meier survival curve verified the risk of implant revision in Group 1 (FH sized >48?mm) and Group 2 (FH sized <48?mm). The probability of implant revision for acetabular erosion at ten years from surgery were 5.5% in Group 1 and 15.6% in Group 2.

Conclusion

In bipolar hemiarthroplasty smaller head size lead to a polar wear implying a higher risk of acetabular erosion and migration; in our population this risk was consistent with the use of implant head <48?mm diameter. Considering the absolute risk of a smaller FH size, the surgeon must evaluate the accuracy of measurement of the caliber, since the size can be significantly underestimated.  相似文献   
5.
Rocks from the lunar interior are depleted in moderately volatile elements (MVEs) compared to terrestrial rocks. Most MVEs are also enriched in their heavier isotopes compared to those in terrestrial rocks. Such elemental depletion and heavy isotope enrichments have been attributed to liquid–vapor exchange and vapor loss from the protolunar disk, incomplete accretion of MVEs during condensation of the Moon, and degassing of MVEs during lunar magma ocean crystallization. New Monte Carlo simulation results suggest that the lunar MVE depletion is consistent with evaporative loss at 1,670 ± 129 K and an oxygen fugacity +2.3 ± 2.1 log units above the fayalite-magnetite-quartz buffer. Here, we propose that these chemical and isotopic features could have resulted from the formation of the putative Procellarum basin early in the Moon’s history, during which nearside magma ocean melts would have been exposed at the surface, allowing equilibration with any primitive atmosphere together with MVE loss and isotopic fractionation.

Returned samples of basaltic rocks from the Moon provided evidence decades ago that the Moon is depleted in volatile elements compared to the Earth (1), with lunar basalt abundances of moderately volatile elements (MVEs) being ∼1/5 that of terrestrial basalt abundances for alkali elements and ∼1/40 for other MVE, such as Zn, Ag, In, and Cd (2). The theme of lunar volatiles thus seemed settled. Yet, the unambiguous detection in 2008 of lunar indigenous hydrogen and other volatile elements, such as F, Cl, and S in pyroclastic glasses (3), heralded a new era of research into lunar volatiles, overturning the decades-old paradigm of a bone-dry Moon (e.g., refs. 4 and 5). Here, we define volatile elements as those with 50% condensation temperatures below these of the major rock-forming elements Fe, Mg, and Si (6). This paradigm shift was accompanied by new measurements of volatile stable isotope compositions (e.g., H, C, N, Cl, K, Cr, Cu, Zn, Ga, Rb, and Sn) in a wealth of bulk lunar samples (718) and in the mineral phases and melt inclusions they host (1928). These studies have shown that the stable isotope compositions of most MVEs (e.g., K, Zn, Ga, and Rb) are enriched in their heavier isotopes with respect to the bulk silicate Earth (BSE) (9, 11, 1315, 17). Such heavy isotope enrichment is associated with elemental depletion, which has been variously attributed to liquid–vapor exchange and vapor loss from the protolunar disk (17, 18), incomplete accretion of MVEs during condensation of the Moon (13, 29, 30), and degassing of these elements during lunar magma ocean crystallization (9, 11, 14, 15, 25, 31). Almost all these hypotheses have typically assumed that the MVE depletions and associated MVE isotope fractionations are relevant to the whole Moon. However, our lunar sample collections are biased, as all Apollo and Luna returned samples come from the lunar nearside from within or around the anomalous Procellarum KREEP Terrane (PKT) region (e.g., ref. 32), where KREEP stands for enriched in K, REEs, and P. Barnes et al. (26) proposed that the heavy Cl isotope signature measured in KREEP-rich Apollo samples resulted from metal-chloride degassing from late-stage lunar magma ocean melts in response to a large crust-breaching impact event, spatially associated with the PKT region, which facilitated exposure of these late-stage melts to the lunar surface. Here, we further investigate whether a localized impact event could have been responsible for the general MVE depletion and heavy MVE isotope enrichment measured in lunar samples.  相似文献   
6.
7.
Clinical Rheumatology - We report a case of a 56-year-old woman with an alleged diagnosis of an acute coronary syndrome that was later correctly identified in our Cardiology Unit as antisynthetase...  相似文献   
8.
Prior studies have conflicting findings regarding the association between gastroesophageal reflux disease (GERD) and esophageal squamous cell carcinoma (ESCC). We examined this relationship in a prospective cohort in a region of high ESCC incidence. Baseline exposure data were collected from 50 045 individuals using in-person interviews at the time of cohort entry. Participants were followed until they developed cancer, died, or were lost to follow up. Participants with GERD symptoms were categorized into any GERD (heartburn or regurgitation), mixed symptoms, or heartburn alone. Multivariable Cox regression was used to assess the relationship between GERD symptom group and histologically confirmed ESCC. The model was adjusted for known risk factors for GERD and ESCC. 49 559 individuals were included in this study, of which 9005 had GERD symptoms. Over 13.0 years of median follow up, 290 individuals were diagnosed with ESCC. We found no association between any GERD and risk of ESCC (aHR 0.90, 95% CI: 0.66-1.24, P = .54). Similar findings were observed for the GERD symptom subtypes. Significant interactions between any GERD and sex (P = .013) as well as tobacco smoking (P = .028) were observed. In post-hoc analyses, GERD was associated with a decreased risk of ESCC in men (aHR 0.51, 95% CI: 0.27-0.98 P = .04) and in smokers (aHR 0.26, 95% CI: 0.08-0.83 P = .02). While there was little evidence for an overall association between GERD symptoms and ESCC risk, significant interactions with sex and smoking were observed. Men and smokers with GERD symptoms had a lower risk of ESCC development.  相似文献   
9.
Clinical Oral Investigations - By means of a systematic review and network meta-analysis, this study aims to answer the following questions: (a) does the placement of a biomaterial over an...  相似文献   
10.
In this article, we report a case of isolated podal osteochondroma from the prehistoric Hypogeum of Calaforno (Giarratana, Ragusa, Sicily). Although the phalanx exhibiting the benign tumoral mass comes from a context featuring several commingled remains, the very good state of preservation of this bone allowed us to perform a comprehensive study of the neoplasm by applying a multidisciplinary approach encompassing archeology, morphology, stereomicroscopy, and radiology. The results from this very ancient specimen have been assessed in the light of the available paleopathological literature and clinical implications currently encountered in modern patients.  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