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   2748篇
  免费   230篇
  国内免费   51篇
耳鼻咽喉   27篇
儿科学   113篇
妇产科学   29篇
基础医学   334篇
口腔科学   287篇
临床医学   208篇
内科学   586篇
皮肤病学   67篇
神经病学   140篇
特种医学   210篇
外科学   227篇
综合类   104篇
预防医学   282篇
眼科学   30篇
药学   252篇
中国医学   24篇
肿瘤学   109篇
  2023年   24篇
  2022年   86篇
  2021年   96篇
  2020年   66篇
  2019年   76篇
  2018年   86篇
  2017年   98篇
  2016年   82篇
  2015年   93篇
  2014年   142篇
  2013年   143篇
  2012年   150篇
  2011年   188篇
  2010年   151篇
  2009年   133篇
  2008年   121篇
  2007年   156篇
  2006年   116篇
  2005年   85篇
  2004年   89篇
  2003年   52篇
  2002年   47篇
  2001年   50篇
  2000年   26篇
  1999年   32篇
  1998年   84篇
  1997年   67篇
  1996年   61篇
  1995年   54篇
  1994年   46篇
  1993年   43篇
  1992年   16篇
  1991年   12篇
  1990年   23篇
  1989年   28篇
  1988年   29篇
  1987年   20篇
  1986年   20篇
  1985年   20篇
  1984年   10篇
  1983年   14篇
  1982年   9篇
  1981年   6篇
  1980年   8篇
  1979年   6篇
  1978年   6篇
  1976年   12篇
  1975年   10篇
  1971年   5篇
  1969年   7篇
排序方式: 共有3029条查询结果,搜索用时 15 毫秒
961.
Cattle tick control has been limited by the resistance of these parasites to synthetic acaricides. Natural products are a possible alternative as they have different mechanisms of action. Acmella oleracea is a native plant with a large cultivated area in the Amazon region and could be easily used for large-scale preparation of a commercial product. This study evaluated the in vitro action of the hexane extract of the aerial parts of A. oleracea on larvae and engorged females of the cattle tick Rhipicephalus microplus. Spilanthol was the major constituent with a content of 14.8 % in the extract. The hexane extract of A. oleracea was highly effective against larvae of R. microplus with an LC50 of 0.8 mg mL?1. Against engorged females, hexane extract of A. oleracea reduced oviposition and hatchability of eggs with an LC50 of 79.7 mg mL?1. Larvae and engorged females were killed by the hexane extract with high efficiency (>95 %) at concentrations of 3.1 and 150.0 mg mL?1, respectively. These results demonstrate that the hexane extract of A. oleracea has significant activity against R. microplus and has potential to be developed into formulations for tick control.  相似文献   
962.
Infection by Trypanosoma cruzi, the aetiological agent of Chagas disease, causes an intense inflammatory reaction in several tissues, including the myocardium. We have previously shown that transplantation of bone marrow cells (BMC) ameliorates the myocarditis in a mouse model of chronic Chagas disease. We investigated the participation of BMC in lesion repair in the heart and skeletal muscle, caused by T. cruzi infection in mice. Infection with a myotropic T. cruzi strain induced an increase in the percentage of stem cells and monocytes in the peripheral blood, as well as in gene expression of chemokines SDF‐1, MCP1, 2, and 3 in the heart and skeletal muscle. To investigate the fate of BMC within the damaged tissue, chimeric mice were generated by syngeneic transplantation of green fluorescent protein (GFP+) BMC into lethally irradiated mice and infected with Trypanosoma cruzi. Migration of GFP+ BMC to the heart and skeletal muscle was observed during and after the acute phase of infection. GFP+ cardiomyocytes and endothelial cells were present in heart sections of chimeric chagasic mice. GFP+ myofibres were observed in the skeletal muscle of chimeric mice at different time points following infection. In conclusion, BMC migrate and contribute to the formation of new resident cells in the heart and skeletal muscle, which can be detected both during the acute and the chronic phase of infection. These findings reinforce the role of BMC in tissue regeneration.  相似文献   
963.
Periosteal osteoma is a rare benign pathologic lesion in the jaws and the mandible is the anatomic region most frequently involved. Elective treatment consists of surgical excision. The aim of this report was to report a rare case of bilateral periosteal osteoma involving the mandible--a painless, firm, and well-circumscribed lesion, with more bony prominence on the left than on the right side. The patient had no history of facial trauma or systemic changes that could intervene with the progression of the lesion. It was diagnosed as a periosteal osteoma, and surgical excision was performed. No recurrence after 4 years of follow-up was demonstrated. Surgical excision of the periosteal osteoma was demonstrated to be a useful technical strategy that simplifies and accelerates the surgical procedures and probably contributes to establish harmony of the jaws. Periodical clinical and radiographic follow-ups after surgery are advised.  相似文献   
964.
Background

In recent decades, studies in the field of public health have increasingly focused on social determinants that affect the health-illness process. The epidemiological perspective considers oral health to be a reflection of socioeconomic and environmental aspects, and it is particularly influenced by the social context. The aim of the present study was to assess the association between the severity of dental caries among adults aged 35 to 44 years and characteristics on the different levels at which the determinants of caries operate (individual, social structure and social context).

Methods

A home-based, cross-sectional field study was carried out involving a sample of 1,150 adults (35 to 44 years of age) residing in metropolitan Belo Horizonte, Brazil. The DMFT (decayed, missing, filled tooth) index (≥14) was used to determine the severity of dental caries. Bivariate and multivariate analyses were carried out using the Poisson regression model with the level of significance set at 5% (p < 0.05) and 95% confidence intervals.

Results

The majority of the participants (68.5%) had high caries severity. The rate of high-severity caries in the group between 40 and 44 years of age was 1.15-fold (CI: 1.04-1.26) greater than that among those aged 35 to 39 years. A greater prevalence of high caries severity was found among those who frequently visited the dentist (PR = 1.18; CI: 1.07-1.30), those with a lower income (PR = 1.11; CI: 1.01-1.23), those who reported that their neighborhood did not come together in the previous year to petition political leaders for benefits (PR = 1.16; CI: 1.05-1.28) and those who are unable to make decisions (without empowerment) (PR = 1.12; CI: 1.01-1.24).

Conclusions

The present study revealed high dental caries severity in adults, which was associated with individual characteristics, health-related behavior and social structure and contextual variables. These findings underscore the importance of considering social determinants involved in the health-illness process when carrying out epidemiological studies on dental caries.

  相似文献   
965.
OBJECTIVE. Physiological root resorption is a programmed event that takes place in primary teeth leading to elimination of all root structures. The mechanism behind pulp elimination indicates apoptosis, but its pathway has not been well characterised yet. To better understand this event, we evaluated the gene expression of bax, bcl-2, caspase-3 and caspase-8 through real-time polymerase chain reaction (PCR) and immunohistochemistry expression of Caspase-8 and Bax in pulps. METHODS. Samples were split into two groups: pulps from primary teeth with physiological root resorption (n = 40) and control (n =40), pulps from permanent teeth. Samples of each group were split into PCR (n = 20) and immunohistochemistry (n = 20). RESULTS. Pulps from primary teeth showed a higher caspase-3 mRNA level than pulps from permanent teeth. The expression of bax gene was more intense than caspase-8 but both did not show difference between groups. The bcl-2 mRNA level was incipient and similar between groups. Histopath slides did not show any evidence of inflammatory infiltration, which implies that extrinsic via is not likely to be involved. Immunohistochemistry reaction to Bax and Caspase-8 supported PCR results. CONCLUSIONS. Pulp apoptosis is likely to occur via caspase-3 activation through the mitochondrial pathway.  相似文献   
966.
Background: Different enhanced peroxide formulations have been developed to overcome mineral loss during tooth whitening. This study investigated the impact on tooth whitening from combining a CPP‐ACP paste with home peroxide agents at several proportions. Methods: Ninety bovine incisors were randomly allocated into nine groups (n = 10) and exposed to 7.5% hydrogen peroxide (HP), 16% carbamide peroxide (CP), a CPP‐ACP paste (Tooth Mousse/MI Paste, GC Corporation, Tokyo, Japan) and blends of HP/CP:MI at three proportions (1:1, 2:1 and 1:2). Tooth whitening was performed for 14 days and its effectiveness was measured by a spectrophotometer utilizing the CIE L*a*b* system (ΔE, ΔL*, Δa* and Δb*). Colour readings were measured at baseline (T0), 7 days of bleaching (T7), 14 days of bleaching (T14) and 7 days after the end of bleaching (T21). Data were analysed by two‐way ANOVA for paired averages followed by the Tukey’s test and Pearson’s correlation at 5%. Results: Although CP produced the greatest colour change (ΔE), all whitening protocols were considered to be effective regardless of the CPP‐ACP presence. In general, greater changes in ΔE, ΔL*, Δa*  and Δb* were detected at T14, with T21 exhibiting similar results to those at T7. A greater number of strong correlations with ΔE values was found for a* (11/15). Conclusions: Within the limitations of this study, the results indicate that the CPP‐ACP paste did not affect tooth whitening efficacy.  相似文献   
967.
968.
Trichosporon spp. are yeasts capable of causing invasive disease, which mainly affect immunocompromised patients. A clinical strain of T. asahii was isolated from the blood cultures of patients admitted to the General Hospital of Fortaleza. Susceptibility tests were conducted by disk diffusion and broth microdilution. The isolated strain of T. asahii was resistant to fluconazole. The patient used amphotericin B and caspofungin in order to facilitate the microbiological cure. It was the first isolation and identification of T. asahii in blood culture in Ceará, Brazil.  相似文献   
969.

Purpose

Polymorphisms in the ABCB1 gene may influence P-glycoprotein (Pgp) expression and/or activity. Because the population in Brazil is markedly heterogeneous, we analyzed the relationship between ABCB1 polymorphisms and Pgp expression/activity in Brazilian acute myeloid leukemia (AML) patients.

Methods

Acute myeloid leukemia samples from 109 patients were studied. ABCB1 gene variants rs1128503 (C1236T) and rs1045643 (C3435T) were analyzed by PCR-RFLP assay. Pgp expression and Pgp activity were analyzed by flow cytometry.

Results

There was a similar distribution of Pgp expression and activity on polymorphisms C1236T, C1236C, and T1236T for exon 12, and C3435T, C3435C, and T3435T for exon 26. An exception was observed in the lowest ratio of mean fluorescence intensity (MFI) median for Pgp expression in the TT genotype for both studied exons, and its correspondence to a low MFI median for Pgp activity. Pgp expression did not show impact on the response to remission induction therapy, but the MFI median of Pgp expression in the remission failure group was higher than that of the complete remission (CR) group of patients (p?=?0.04). Overall survival (OS) was significantly influenced by CR (p?=?0.0001). Better 5-year OS and 5-year event-free survival rates (p?=?0.04 and p?=?0.007, respectively) were achieved in patients presenting the genetic variant CC in exon 12 followed by those presenting the variant CT in exon 26 (p?=?0.001).

Conclusions

Polymorphisms in the ABCB1 gene and the levels of Pgp expression could be useful to identify prognostic in AML patients.  相似文献   
970.
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