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   12220篇
  免费   696篇
  国内免费   88篇
耳鼻咽喉   79篇
儿科学   273篇
妇产科学   230篇
基础医学   1296篇
口腔科学   190篇
临床医学   1189篇
内科学   2761篇
皮肤病学   183篇
神经病学   612篇
特种医学   390篇
外国民族医学   1篇
外科学   2403篇
综合类   348篇
现状与发展   1篇
一般理论   9篇
预防医学   741篇
眼科学   272篇
药学   1147篇
中国医学   185篇
肿瘤学   694篇
  2024年   19篇
  2023年   212篇
  2022年   610篇
  2021年   826篇
  2020年   455篇
  2019年   601篇
  2018年   608篇
  2017年   374篇
  2016年   415篇
  2015年   456篇
  2014年   564篇
  2013年   665篇
  2012年   1066篇
  2011年   1016篇
  2010年   510篇
  2009年   451篇
  2008年   673篇
  2007年   672篇
  2006年   572篇
  2005年   542篇
  2004年   403篇
  2003年   405篇
  2002年   228篇
  2001年   96篇
  2000年   68篇
  1999年   55篇
  1998年   42篇
  1997年   17篇
  1996年   30篇
  1995年   14篇
  1994年   20篇
  1993年   19篇
  1992年   35篇
  1991年   25篇
  1990年   16篇
  1989年   24篇
  1988年   15篇
  1987年   18篇
  1986年   8篇
  1985年   12篇
  1984年   17篇
  1983年   13篇
  1982年   20篇
  1981年   16篇
  1980年   10篇
  1978年   10篇
  1977年   7篇
  1976年   9篇
  1973年   8篇
  1969年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Compressive strength (CS) and splitting tensile strength (STS) are paramount parameters in the design of reinforced concrete structures and are required by pertinent standard provisions. Robust prediction models for these properties can save time and cost by reducing the number of laboratory trial batches and experiments needed to generate suitable design data. Silica fume (SF) is often used in concrete owing to its substantial enhancements of the engineering properties of concrete and its environmental benefits. In the present study, the M5P model tree algorithm was used to develop models for the prediction of the CS and STS of concrete incorporating SF. Accordingly, large databases comprising 796 data points for CS and 156 data records for STS were compiled from peer-reviewed published literature. The predictions of the M5P models were compared with linear regression analysis and gene expression programming. Different statistical metrics, including the coefficient of determination, correlation coefficient, root mean squared error, mean absolute error, relative squared error, and discrepancy ratio, were deployed to appraise the performance of the developed models. Moreover, parametric analysis was carried out to investigate the influence of different input parameters, such as the SF content, water-to-binder ratio, and age of the specimen, on the CS and STS. The trained models offer a rapid and accurate tool that can assist the designer in the effective proportioning of silica fume concrete.  相似文献   
102.
To enhance the moisture damage performance of hot mix asphalt (HMA), treating the aggregate surface with a suitable additive was a more convenient approach. In this research, two types of aggregate modifiers were used to study the effect of moisture damage on HMA. Three different aggregate sources were selected based on their abundance of use in HMA. To study the impact of these aggregate modifiers on moisture susceptibility of HMA, the indirect tensile strength test and indirect tensile modulus test were used as the performance tests. Moisture conditioning of specimens was carried out to simulate the effect of moisture on HMA. The prepared samples’ tensile strength ratio (TSR) and stiffness modulus (Sm) results indicated a decrease in the strength of the HMA after moisture conditioning. After treating the aggregate surface with additives, an improvement was seen in dry and wet strength and stiffness. Moreover, an increasing trend was observed for both additives. The correlation between TSR and strength loss reveals a strong correlation (R2 = 0.7219). Also, the two additives indicate increased wettability of asphalt binder over aggregate, thus improving the adhesion between aggregate and asphalt binder.  相似文献   
103.
Background: The interaction of aging-related, genetic, and environmental factors is thought to contribute to the etiology of late-onset, sporadic Alzheimer’s disease (AD). We previously reported that serum levels of p,p′-dichlorodiphenyldichloroethylene (DDE), a long-lasting metabolite of the organochlorine pesticide dichlorodiphenyltrichloroethane (DDT), were significantly elevated in patients with AD and associated with the risk of AD diagnosis. However, the mechanism by which DDT may contribute to AD pathogenesis is unknown.Objectives: This study sought to assess effects of DDT exposure on the amyloid pathway in multiple in vitro and in vivo models.Methods: Cultured cells (SH-SY5Y and primary neurons), transgenic flies overexpressing amyloid beta (Aβ), and C57BL/6J and 3xTG-AD mice were treated with DDT to assess impacts on the amyloid pathway. Real time quantitative polymerase chain reaction, multiplex assay, western immunoblotting and immunohistochemical methods were used to assess the effects of DDT on amyloid precursor protein (APP) and other contributors to amyloid processing and deposition.Results: Exposure to DDT revealed significantly higher APP mRNA and protein levels in immortalized and primary neurons, as well as in wild-type and AD-models. This was accompanied by higher levels of secreted Aβ in SH-SY5Y cells, an effect abolished by the sodium channel antagonist tetrodotoxin. Transgenic flies and 3xTG-AD mice had more Aβ pathology following DDT exposure. Furthermore, loss of the synaptic markers synaptophysin and PSD95 were observed in the cortex of the brains of 3xTG-AD mice.Discussion: Sporadic Alzheimer’s disease risk involves contributions from genetic and environmental factors. Here, we used multiple model systems, including primary neurons, transgenic flies, and mice to demonstrate the effects of DDT on APP and its pathological product Aβ. These data, combined with our previous epidemiological findings, provide a mechanistic framework by which DDT exposure may contribute to increased risk of AD by impacting the amyloid pathway. https://doi.org/10.1289/EHP10576  相似文献   
104.
Purpose:This study aims to facilitate researchers’ and clinicians’ understanding of research frontiers and trends in nocturia. It explores the scientific research outcomes and key bibliometric indices and plots global research on nocturia.Methods:A bibliometric retrospective study was designed, and an online search was conducted in the Web of Science Core Collection database using the potential search keywords related to nocturia in the title field with some specific filtration. HistCite™ and VOSviewer software for windows were used to analyze the data obtained for authors, journals, countries, institutions, keywords, and visualization mapping.Results:The initial search retrieved 1479 hits. A total of 1445 publications were included in the final analysis. Of these, 43.53% were published as articles. The most studied area in nocturia is urology nephrology. The most productive year was 2019 (n = 121, citations = 335), and the most prolific author, both in terms of publications (n = 97) and citations (1658) was Weiss JP. The most cited journal in nocturia research was the Journal of Urology (n = 293, citations = 3050). The most widely used keyword in nocturia publications was nocturia (n = 1249). Visualization mapping shows that the USA was the most influential and highly cited country in nocturia research.Conclusion:This study showed that there has been an increasing research trend in nocturia over the past few years. The current findings provide important empirical evidence for researchers, clinicians, and physicians to understand research frontiers and trends, achievements, collaborative networks, and hotspot research topics in the research field of nocturia.  相似文献   
105.
Fludarabine is an active agent in low-grade non-Hodgkin’s lymphoma and chronic lymphocytic leukemia. Paclitaxel is also active in patients with refractory lymphoma, and preclinical data suggest an additive effect with fludarabine in vitro. We performed a phase I trial of fludarabine (25 mg/m2 d 1–3) plus a 3-h infusion of paclitaxel (125, 150, or 175 mg/m2) on d 3 every 28 d in 13 patients with non-Hodgkin’s lymphoma. The paclitaxel dose was escalated in cohorts of 3–4 patients using standard phase I design schema. Dose-limiting toxicity was defined as febrile neutropenia, platelet nadir less than 50,000/μL, or grade 3–4 nonhematologic toxicity. Thirteen patients were accrued to the study, 8 of these 13 patients (62%) had received prior chemotherapy. At the 125-, 150-, and 175-mg/m2 dose levels of paclitaxel, dose-limiting toxicity occurred in 1/4, 0/4, and 0/4 patients, respectively. The single patient with dose-limiting toxicity had febrile neutropenia. Partial response occurred in two of eight patients with low-grade lymphoma and none of five patients with other types of lymphoma. A paclitaxel dose of 175 mg/m2 given as a 3-h infusion on d 3 in conjunction with fludarabine (25 mg/m2 d 1–3 every 4 wk) is a well-tolerated regimen for non-Hodgkin’s lymphoma. Further study will be required in order to determine whether the fludarabine-paclitaxel is more active than fludarabine alone in patients with low-grade lymphoma and chronic lymphocytic leukemia.  相似文献   
106.
107.
108.
109.
AIM OF THE STUDY: The present study was aimed at documentation of botanical anthelmintics used in the traditional veterinary practices in Sahiwal district of Punjab, Pakistan. MATERIALS AND METHODS: In rapid rural appraisal, 331 traditional veterinary healers (TVH) were identified as key respondents in the study area followed by participatory rural appraisal for data collection using a well-structured questionnaire. Information was collected through interviews, focused group discussions and field visits over a period of 2 years. RESULTS: A total of 49 traditional recipes, with 41 plant species representing 39 genera and 27 families, were recorded for the treatment of helminthosis in animals. Most frequently used plants (>/=5 times) were Brassica campestris L. and Mallotus philippinensis (Lam.) Muell.-Arg. and most frequently used families (>/=5 times) were Brassicaceae, Euphorbiaceae and Solanaceae. Most frequently used part of the plant was leaves (n=10) followed in order by seeds (n=9), whole fruit (n=5), aerial parts and whole plant (n=4), fruit (n=3), bulb (n=2) and bark, rhizome, stem, stem plus root and twigs (n=1). Five recipes out of 49 (10.2%) contained more than one plant species and rest 44 (89.8%) contained single plant species. CONCLUSIONS: Twenty out of 41 plants (48.78%) are reported for the first time for their traditional use as anthelmintics in Pakistan. Further studies on pharmacokinetics using scientific procedures may prove these plants as promising candidates for their future use as anthelmintics.  相似文献   
110.
Objective To evaluate the rate and characteristics of postoperative intrauterine adhesions (IUA) that might be formed following hysteroscopic reproductive surgery from both a gross and a histologic perspective as determined by early and late follow-up diagnostic hysteroscopy. Methods Retrospective analysis of 61 women wishing a pregnancy and suffering from a significant intrauterine pathology affecting their reproductive outcome were reviewed. All patients were treated hysteroscopically. Subsequently, they were randomly assigned to perform a follow-up diagnostic hysteroscopy at a variable intervals from their initial surgery. Multiple hysteroscopic-guided biopsies from IUA, when present, were obtained in several cases. Twenty patients were in the early group and had follow-up hysteroscopy performed 2–4 weeks after the initial operation. The late diagnostic group consisted of 41 patients with follow-up hysteroscopy at about 12 months (8–16 months). The two groups were similar to composition. Postoperatively, none of the early diagnostic group underwent hysterosalpingography (HSG) whereas all of the late group performed HSG 4 months following the initial surgery, which showed at least one-third of the cavity free of adhesions. When adhesions were present, no effort was made to lyse them. Results At follow-up hysteroscopy, 25% of both groups had no significant adhesions. Grade I adhesions (thin, filmy) occurred in 60% of the early hysteroscopy patients and in only 12% of the late group (P < 0.05). Grade II adhesions were present in 10% of the early group and in up to 41% in the late group (P < 0.05), whereas Grade III adhesions were present in only 5% of the early hysteroscopy group, but in 22% of the late one (P < 0.05). Correlation between hysteroscopic and histologic findings were good in most of cases in both groups. Follow-up to determine the subsequent reproductive outcome revealed similar conception rates in both groups. Conclusion The IUA that might be formed immediately following hysteroscopic reproductive surgery are histologically different from those appearing a longer time after the original operation. Routine early follow-up hysteroscopy can influence the prognosis resulting from the original surgery.  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