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   28415篇
  免费   1328篇
  国内免费   199篇
耳鼻咽喉   236篇
儿科学   568篇
妇产科学   254篇
基础医学   3851篇
口腔科学   547篇
临床医学   1879篇
内科学   7152篇
皮肤病学   469篇
神经病学   2390篇
特种医学   1090篇
外科学   5051篇
综合类   103篇
预防医学   767篇
眼科学   615篇
药学   2085篇
中国医学   82篇
肿瘤学   2803篇
  2023年   165篇
  2022年   311篇
  2021年   562篇
  2020年   296篇
  2019年   447篇
  2018年   603篇
  2017年   468篇
  2016年   563篇
  2015年   610篇
  2014年   766篇
  2013年   918篇
  2012年   1535篇
  2011年   1718篇
  2010年   905篇
  2009年   762篇
  2008年   1516篇
  2007年   1676篇
  2006年   1597篇
  2005年   1752篇
  2004年   1665篇
  2003年   1647篇
  2002年   1623篇
  2001年   512篇
  2000年   525篇
  1999年   579篇
  1998年   402篇
  1997年   299篇
  1996年   294篇
  1995年   278篇
  1994年   240篇
  1993年   229篇
  1992年   441篇
  1991年   420篇
  1990年   357篇
  1989年   407篇
  1988年   353篇
  1987年   317篇
  1986年   304篇
  1985年   280篇
  1984年   197篇
  1983年   161篇
  1982年   94篇
  1981年   82篇
  1980年   77篇
  1979年   148篇
  1978年   114篇
  1977年   68篇
  1975年   80篇
  1974年   67篇
  1973年   63篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.

Purpose  

To examine the preliminary survival outcomes and treatment-related toxicity for elderly patients with cervical cancer treated with radiotherapy (RT).  相似文献   
992.
993.
Cationic lipid-incorporated liposomes modified with pH-sensitive polymers were prepared by introducing 3, 5-didodecyloxybenzamidine as a cationic lipid to egg yolk phosphatidylcholine liposomes modified with 3-methylglutarylated hyperbranched poly(glycidol) (MGlu-HPG) as a pH-sensitive polymer. These liposomes were stable at neutral pH, but were destabilized below pH 6.0 because MGlu-HPG changed its characteristics from hydrophilic to hydrophobic in response to the pH decrease. Cationic lipid inclusion improved their pH sensitivity at weakly acidic pH and association of liposomes with murine dendritic cell (DC) lines. Cationic lipid-incorporated liposomes delivered entrapped ovalbumin (OVA) molecules not only to cytosol but also to endosome/lysosome. Treatment with cationic lipid-incorporated liposomes induced up-regulation of antigen presentation-involved molecules on DCs, the promotion of cytokine production, and antigen presentation via both major histocompatibility complex (MHC) class I and II molecules. Especially, antigen presentation via MHC class II was promoted by cationic lipid inclusion, which might correspond to efficient endosome/lysosome delivery of OVA. Subcutaneous administration of OVA-loaded cationic lipid-incorporated liposomes induced antigen-specific antibody production in serum and Th1-dominant immune responses in the spleen. Furthermore, administration of the cationic lipid-incorporated liposomes to mice bearing E.G7-OVA tumor more significantly reduced the tumor volume than liposomes without cationic lipids. Therefore, cationic lipid inclusion into pH-sensitive polymer-modified liposomes, which can achieve both efficient antigen intracellular delivery and activation of antigen presenting cell, is an effective approach to develop antigen carriers for efficient cancer immunotherapy.  相似文献   
994.
l‐Afadin was originally purified from rat brain as an actin filament (F‐actin)‐binding protein that was homologous to the AF‐6 gene product. Concomitantly, s‐afadin that did not show an F‐actin‐binding capability was copurified with l‐afadin. Structurally, s‐afadin lacks the C‐terminal F‐actin‐binding domain but has two short sequences that were not present in l‐afadin. The properties and roles of l‐afadin have intensively been investigated, but those of s‐afadin have poorly been understood. We show here an additional difference in their biochemical properties other than binding to F‐actin between l‐afadin and s‐afadin. Both l‐afadin and s‐afadin bound to nectins, immunoglobulin‐like cell adhesion molecules, whereas s‐afadin more preferentially bound to nectins than l‐afadin. The PDZ domain of l‐afadin and s‐afadin was essential for their binding to nectin‐3. The dilute domain of l‐afadin negatively regulated its binding to nectin‐3, but the deletion of the C‐terminal F‐actin‐binding domain of l‐afadin did not increase the binding of l‐afadin to nectin‐3. These results indicate that the s‐afadin‐specific C‐terminal inserts may be involved in its preference of binding to nectin‐3 and raise the possibility that there are proteins other than nectins that more preferentially bind s‐afadin than l‐afadin.  相似文献   
995.
Many families of centromeric repetitive DNA sequences isolated from Struthioniformes, Galliformes, Falconiformes, and Passeriformes are localized primarily to microchromosomes. However, it is unclear whether chromosome size-correlated homogenization is a common characteristic of centromeric repetitive sequences in Aves. New World and Old World quails have the typical avian karyotype comprising chromosomes of two distinct sizes, and C-positive heterochromatin is distributed in centromeric regions of most autosomes and the whole W chromosome. We isolated six types of centromeric repetitive sequences from three New World quail species (Colinus virginianus, CVI; Callipepla californica, CCA; and Callipepla squamata, CSQ; Odontophoridae) and one Old World quail species (Alectoris chukar, ACH; Phasianidae), and characterized the sequences by nucleotide sequencing, chromosome in situ hybridization, and filter hybridization. The 385-bp CVI-MspI, 591-bp CCA-BamHI, 582-bp CSQ-BamHI, and 366-bp ACH-Sau3AI fragments exhibited tandem arrays of the monomer unit, and the 224-bp CVI-HaeIII and 135-bp CCA-HaeIII fragments were composed of minisatellite-like and microsatellite-like repeats, respectively. ACH-Sau3AI was a homolog of the chicken nuclear membrane repeat sequence, whose homologs are common in Phasianidae. CVI-MspI, CCA-BamHI, and CSQ-BamHI showed high homology and were specific to the Odontophoridae. CVI-MspI was localized to microchromosomes, whereas CVI-HaeIII, CCA-BamHI, and CSQ-BamHI were mapped to almost all chromosomes. CCA-HaeIII was localized to five pairs of macrochromosomes and most microchromosomes. ACH-Sau3AI was distributed in three pairs of macrochromosomes and all microchromosomes. Centromeric repetitive sequences may be homogenized in chromosome size-correlated and -uncorrelated manners in New World quails, although there may be a mechanism that causes homogenization of centromeric repetitive sequences primarily between microchromosomes, which is commonly observed in phasianid birds.  相似文献   
996.

Purpose

Gain-of-function mutations in complement factor B (CFB) were recently identified in patients with atypical hemolytic uremic syndrome (aHUS), but are extremely rare. Our purpose is to describe a large kindred with aHUS associated with a CFB mutation and to further understand CFB-mutated aHUS patients.

Methods and Results

We report a large kindred in which 3 members had aHUS. This kindred revealed that 9 of 12 members, including 2 affected patients, had persistent activation of the alternative pathway with low complement component 3 and that those 9 members showed a CFB mutation (c.1050G?>?C, p.Lys350Asn) in exon 8. This missense mutation was heterozygous in 8 of them and homozygous in only one. From structural studies, this mutation is shown to be located in close proximity to the Mg2-binding site within a von Willebrand factor type A domain of CFB, resulting in a gain-of-function effect of CFB and predisposition to aHUS. At present, 2 of the 3 members with aHUS have maintained normal renal function for a long-term period.

Conclusions

This kindred illustrates that a CFB mutation (c.1050G?>?C, p.Lys350Asn) can result in aHUS. In the future, phenotype-genotype correlations and outcome in CFB-mutated aHUS patients need to be further investigated by accumulation of a number of cases.  相似文献   
997.
To establish a diagnostic index for predicting enzootic bovine leukosis (EBL), proviral bovine leukemia virus (BLV) copies in whole blood, lymph nodes and spleen were examined by quantitative real-time PCR (qPCR). Cattle were divided into two groups, EBL and BLV-infected, based on meat inspection data. The number of BLV copies in all specimens of EBL cattle was significantly higher than those of BLV-infected cattle (p < 0.0001), and the number of BLV copies in the lymph nodes was particularly large. Over 70 % of the superficial cervical, medial iliac and jejunal lymph nodes from EBL cattle had more than 1,000 copies/10 ng DNA, whereas lymph nodes from BLV-infected cattle did not. These findings suggest that the cattle harboring more than 1,000 BLV copies may be diagnosed with EBL.  相似文献   
998.
Chagas disease is one of the main public health issues in Latin America. Increasingly during the past few decades, Trypanosoma cruzi infection has been detected in North America, Europe, and the Western Pacific, mainly as a result of population movement. The limited availability of rapid serological diagnostic tests hinders rapid diagnosis and early treatment in areas of endemicity and nonendemicity. In collaboration with 11 national reference laboratories (NRLs) from different geographical areas, we evaluated the performances of commercialized serological rapid diagnostic tests (RDT) for T. cruzi infection. Eleven commercialized T. cruzi infection RDTs were evaluated on a total of 474 samples extensively tested with at least three different techniques for Chagas disease, maintained at controlled low temperatures, and stored in the serum banks of the 11 NRLs. We measured the sensitivity, specificity, and concordance of each RDT and provided an additional questionnaire to evaluate its ease of use. The selected RDTs in this study were performed under controlled laboratory conditions. Out of the 11 RDTs, we found 8 of them to be useful, with the cassette format favored over the strip. We did not observe significant differences in RDT performances in the different regions. Overall, the performance results were lower than those disclosed by the manufacturers. The results of this evaluation validate the possibility of using RDTs to diagnose Chagas disease, thereby decreasing the time to treatment at a primary health care facility for patients who are willing to be treated. Further studies should be conducted in the laboratory and in the field to confirm these data, expressly to evaluate reproducibility in resource-limited settings, or using whole blood in clinical settings in areas of endemicity and nonendemicity.  相似文献   
999.
Objective: To evaluate the frequencies of fetal facial expressions among appropriate-for-gestational-age (AGA), small-for-gestational-age (SGA), and growth-restricted (FGR) fetuses.

Methods: Four-dimensional (4D) ultrasound was used to examine the facial expressions of 50 AGA, 25 SGA, and six FGR fetuses between 28 and 35 weeks of gestation. The frequencies of seven facial expressions during 15-minute recordings were assessed. Comparison of facial expressions among the three groups was performed.

Results: Mouthing was the commonest facial expression at 28–35 weeks, and the frequency of mouthing was significantly higher than those of the other six facial expressions in AGA fetuses. Mouthing was the most frequent facial expression, but there was no significant difference in the frequency among mouthing, smiling and blinking in SGA fetuses. Moreover, mouthing displayed a significantly higher frequency than the other facial expressions, except for yawning, smiling, and blinking in FGR fetuses. However, there was no significant difference in the frequency of each facial expression among the three groups.

Conclusions: Our results suggest that the frequencies of fetal facial expressions are not decreased in either SGA or FGR pregnancies. The absence of a decrease in the frequency of each fetal expression in FGR fetuses may be due to increased brain blood flow because of the brain-sparing effect. Moreover, accelerated maturation and development of the brain function, especially the central dopamine system, might be suspected in SGA and FGR fetuses.  相似文献   

1000.

Research question

What is the incidence, origin and clinical significance of blastomere movement after the first cell division in the human embryo?

Design

A total of 1096 embryos, cultured in the EmbryoScope+ ® time-lapse system and subjected to a single fresh cleaved embryo transfer, were retrospectively analysed. Type and duration of blastomere movement (dBMov) between the first (t2) and second cell division (t3) was monitored, and the ratio of dBMov during the 2-cell stage [dBMov/(t3–t2)] was calculated. Morphological evaluation of embryos was performed by referring to the size of the blastomere and fragmentation after first division in addition to Veeck's criteria on Day 2. The correlation between dBMov and ongoing pregnancy was evaluated and the association of dBMov with patient and embryonic characteristics was determined.

Results

Both movement type and the value of dBMov/(t3–t2) were significantly associated with asymmetrical first division, fragment formation and morphological grade on Day 2. Multivariate logistic regression analysis revealed that a higher value of dBMov/(t3–t2) significantly correlated with a decreased ongoing pregnancy rate, even after adjustment for co-founders (odds ratio 0.399, P?=?0.0419). The time intervals of pronuclear (PN) alignment and PN fading were significantly correlated with the dBMov/(t3–t2) value.

Conclusions

Embryos with extended blastomere movement after the first cell division, which is associated with the delay of PN fading and first cell division, have a lower competence to initiate an ongoing pregnancy after fresh embryo transfer on Day 2. Thus, blastomere movement could be a useful predictive parameter for selecting embryos at the early cleavage stage.  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