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   26970篇
  免费   2649篇
  国内免费   1928篇
耳鼻咽喉   171篇
儿科学   372篇
妇产科学   376篇
基础医学   3267篇
口腔科学   484篇
临床医学   3658篇
内科学   4371篇
皮肤病学   249篇
神经病学   1568篇
特种医学   990篇
外国民族医学   21篇
外科学   2701篇
综合类   4126篇
现状与发展   5篇
一般理论   1篇
预防医学   2000篇
眼科学   650篇
药学   2783篇
  23篇
中国医学   1413篇
肿瘤学   2318篇
  2024年   110篇
  2023年   505篇
  2022年   1164篇
  2021年   1522篇
  2020年   1118篇
  2019年   978篇
  2018年   1013篇
  2017年   944篇
  2016年   832篇
  2015年   1268篇
  2014年   1492篇
  2013年   1365篇
  2012年   1983篇
  2011年   2177篇
  2010年   1264篇
  2009年   989篇
  2008年   1374篇
  2007年   1305篇
  2006年   1293篇
  2005年   1289篇
  2004年   902篇
  2003年   722篇
  2002年   700篇
  2001年   563篇
  2000年   610篇
  1999年   699篇
  1998年   433篇
  1997年   422篇
  1996年   329篇
  1995年   283篇
  1994年   218篇
  1993年   166篇
  1992年   234篇
  1991年   185篇
  1990年   160篇
  1989年   164篇
  1988年   139篇
  1987年   127篇
  1986年   117篇
  1985年   107篇
  1984年   49篇
  1983年   37篇
  1982年   26篇
  1981年   24篇
  1980年   17篇
  1979年   18篇
  1978年   13篇
  1974年   9篇
  1971年   10篇
  1970年   9篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
ObjectiveTo present array comparative genomic hybridization (aCGH) characterization of partial monosomy 13q (13q21.32→qter) and partial trisomy 8p (8p12→pter) presenting with anencephaly and increased nuchal translucency (NT).Case ReportA 34-year-old primigravid woman was referred to the hospital at 12 weeks of gestation for termination of the pregnancy because of major structural abnormalities of the fetus. Prenatal ultrasound revealed a malformed fetus with anencephaly and an increased NT thickness of 5 mm at 12 weeks of gestation. Cytogenetic analysis of the fetus revealed a derivative chromosome 13. The mother was subsequently found to carry a balanced reciprocal translocation between 8p12 and 13q21. Bacterial artificial chromosome-based aCGH using fetal DNA demonstrated partial trisomy 8p and partial monosomy 13q [arr cgh 8p23.3p12 (RP11-1150M5→RP11-1145H12)×3, 13q21.32q34 (RP11-326B4→RP11-450H16)×1]. Oligonucleotide-based aCGH showed a 36.7-Mb duplication of distal 8p and a 48.4-Mb deletion of distal 13q. The fetal karyotype was 46,XY,der(13) t(8;13)(p12;q21.32)mat. The maternal karyotype was 46,XX,t(8;13)(p12;q21.32).ConclusionThe 13q deletion syndrome can be associated with neural tube defects and increased NT in the first trimester. Prenatal sonographic detection of neural tube defects should alert chromosomal abnormalities and prompt cytogenetic investigation, which may lead to the identification of an unexpected parental translocation involving chromosomal segments associated with neural tube development.  相似文献   
992.
ObjectiveThis retrospective study aimed to investigate the use of an oxytocin antagonist in improving the pregnancy outcome of in vitro fertilization–embryo transfer (IVF–ET) in patients with repeated implantation failure (RIF).Materials and MethodsA total of 150 infertile couples with RIF undergoing IVF–ET were divided into three groups. Patients who did not receive atosiban were used as controls (Group 1; n = 80). Forty patients received a single bolus dose (6.75 mg, 0.9 mL/vial) of atosiban before ET (Group 2), and 30 patients received a bolus dose of 6.75 mg atosiban followed by infusion at 18 mg/hr for 3 hours immediately after ET (Group 3).ResultsA significantly higher implantation rate (30.21%) was noted in Group 2 compared with Groups 1 and 3 (11.8% and 15.9%, respectively; p = 0.0006). The clinical pregnancy rate of Group 2 (37.5%) was significantly higher than that of Groups 1 (12.5%) and 3 (20%) (p = 0.0057). The live birth rate was significantly higher in Group 2 (35%) than in Groups 1 and 3 (10% and 16.67%, respectively; p = 0.0031).ConclusionThese results suggest that IVF–ET using lower dosage of atosiban may improve pregnancy outcomes of patients with RIF.  相似文献   
993.
目的:评价托特罗定治疗前列腺电切术后膀胱不适症状的疗效与安全。方法:将124例行前列腺电切术后的前列腺增生症患者随机分为试验组(n=62)和对照组(n=62),分别给予托特罗定和安慰剂2mg/次,2次/d,至拔除尿管前24小时,记录术后6天内患者的膀胱不适症状,将膀胱不适症状分为轻、中、重。结果:试验组膀胱不适症状发生率明显低于对照组(P<0.05),且膀胱不适症状的严重程度也低于对照组(P<0.05),但40.32%试验组患者有口干等不良反应。结论:托特罗定是治疗前列腺电切术的膀胱不适症状安全、有效药物。  相似文献   
994.
Chi PC  Balter P  Luo D  Mohan R  Pan T 《Medical physics》2006,33(9):3116-3123
The accuracy of delivering gated-radiation therapy to lung tumors using an external respiratory surrogate relies on not only interfractional and intrafractional reproducibility, but also a strong correlation between external motion and internal tumor motion. The purpose of this work was to use the cine images acquired by four-dimensional computed tomography acquisition protocol to study the relation between external surface motion and internal tumor motion. The respiratory phase information of tumor motion and chest wall motion was measured on the cine images using a proposed region-of-interest (ROI) method and compared to measurement of an external respiratory monitoring device. On eight lung patient data sets, the phase shifts were measured between (1) the signal of a real-time positioning-management (RPM) respiratory monitoring device placed in the abdominal region and four surface locations on the chest wall, (2) the RPM signal in the abdominal region and tumor motions, and (3) chest wall surface motions and tumor motions. Respiratory waveforms measured at different surface locations during the same respiratory cycle often varied and had significant phase shifts. Seven of the 8 patients showed the abdominal motion leading chest wall motion. The best correlation (smallest phase shift) was found between the abdominal motion and the superior-inferior (S-I) tumor motion. A wide range of phase shifts was observed between external surface motion and tumor anterior-posterior (A-P)/lateral motion. The result supported the placement of the RPM block in the abdominal region and suggested that during a gated therapy utilizing the RPM system, it is necessary to place the RPM block at the same location as it is during treatment simulation in order to reduce potential errors introduced by the position of the RPM block. Correlations between external motions and lateral/A-P tumor motions were inconclusive due to a combination of patient selection and the limitation of the ROI method.  相似文献   
995.
RNA‐binding nuclear antigens are a major class of self‐antigen to which immune tolerance is lost in rheumatic diseases. Serological tolerance to one such antigen, La/Sjögren's syndrome (SS)‐B (La), is controlled by CD4+ T cells. This study investigated peripheral tolerance to human La (hLa) by tracking the fate of hLa‐specific CD4+ T cells expressing the transgenic (Tg) 3B5.8 T cell receptor (TCR) after adoptive transfer into lymphocyte‐replete recipient mice expressing hLa as a neo‐self‐antigen. After initial antigen‐specific cell division, hLa‐specific donor CD4+ T cells expressed forkhead box protein 3 (FoxP3). Donor cells retrieved from hLa Tg recipients displayed impaired proliferation and secreted interleukin (IL)?10 in vitro in response to antigenic stimulation. Transfer of highly purified FoxP3‐negative donor cells demonstrated that accumulation of hLa‐specific regulatory T cells (Treg) was due primarily to expansion of small numbers of donor Treg. Depletion of recipient plasmacytoid dendritic cells (pDC), but not B cells, severely hampered the accumulation of FoxP3+ donor Treg in hLa Tg recipients. Recipient pDC expressed tolerogenic markers and higher levels of co‐stimulatory and co‐inhibitory molecules than B cells. Adoptive transfer of hLa peptide‐loaded pDC into mice lacking expression of hLa recapitulated the accumulation of hLa‐specific Treg. Blockade of the type 1 interferon (IFN) receptor in hLa Tg recipients of hLa‐specific T cells impaired FoxP3+ donor T cell accumulation. Therefore, peripheral expansion of Treg specific for an RNA‐binding nuclear antigen is mediated by antigen‐presenting pDC in a type 1 IFN‐dependent manner. These results reveal a regulatory function of pDC in controlling autoreactivity to RNA‐binding nuclear antigens.  相似文献   
996.
We investigated the allele and haplotype frequencies of HLA‐A, HLA‐B and HLA‐DRB1 loci in Dalian Chinese Han population using blood samples of unrelated marrow donors who live in Dalian. The genetic relationship between Dalian and different regions worldwide was further explored based on HLA status of different populations. A total of 14 529 samples were genotyped at 2‐digit level only by sequence‐specific oligonucleotide and sequence‐based typing methods. Allele frequencies of HLA‐A, HLA‐B and HLA‐DRB1 were calculated by the direct counting method. Haplotype frequencies and linkage disequilibrium (LD) values were calculated by the maximum likelihood method. FST values were calculated by allele frequency data of each locus. Phylogeny tree of Nei's DA genetic distances was constructed by the UPGMA method. HLA‐A*02 was the most frequent allele at HLA‐A locus followed by A*11 and A*24. Alleles at HLA‐B locus ranked in decreasing order by frequency were B*40, B*15 and B*13. The three highest frequency alleles were DRB1*15, DRB1*09 and DRB1*12 at HLA‐DRB1 locus. A*30‐B*13‐DRB1*07 was the most frequent three‐locus haplotype. For the population relationships, Dalian had a relative close genetic relationship with Liaoning and Yantai‐Weihai and a relative distant genetic relationship with Australia. The information obtained in this study may provide useful information for anthropological studies, for disease‐association studies and helping bone marrow transplantation patients to search HLA‐matched donors.  相似文献   
997.
PurposeTo evaluate the prognosis of nasopharyngeal carcinoma (NPC) patients who developed bone-only metastasis after primary treatment and the stratification of these patients into different risk groups based on independent prognostic factors.ResultsThe median follow-up time was 15.5 months (range, 2–67 months) for the whole cohort. The median overall metastatic survival (OMS) time and the 2-year estimate OMS rate were 26.5 months and 52%, respectively. Multivariate analysis indicated that patients with short metastases-free interval, multiple bone metastases sites, high serum lactic dehydrogenase levels, and treated with radiotherapy or chemotherapy alone had significantly worse outcomes. Patients were stratified into three different risk groups based on the number of adverse factors present. The OMS curves of the three groups were all significantly different (p<0.001).ConclusionSeverl prognostic factors were found to be associated with worse outcomes. According to the number of adverse factors present, bone-only metastasis patients can be stratified into three risk groups with significantly different prognoses. Such grouping may help in improving the design of clinical trials and in guiding individualized treatment for NPC patients with bone-only metastasis.  相似文献   
998.

Background

Tolerance seriously impedes the application of morphine in clinical medicine. Thus, it is necessary to investigate the exact mechanisms and efficient treatment. Microglial activation and neuroinflammation in the spinal cord are thought to play pivotal roles on the genesis and maintaining of morphine tolerance. Activation of adenosine monophosphate-activated kinase (AMPK) has been associated with the inhibition of inflammatory nociception. Metformin, a biguanide class of antidiabetic drugs and activator of AMPK, has a potential anti-inflammatory effect. The present study evaluated the effects and potential mechanisms of metformin in inhibiting microglial activation and alleviating the antinociceptive tolerance of morphine.

Methods

The microglial cell line BV-2 cells and mouse brain-derived endothelial cell line bEnd3 cells were used. Cytokine expression was measured using quantitative polymerase chain reaction. Cell signaling was assayed by western blot and immunohistochemistry. The antinociception and morphine tolerance were assessed in CD-1 mice using tail-flick tests.

Results

We found that morphine-activated BV-2 cells, including the upregulation of p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation, pro-inflammatory cytokines, and Toll-like receptor-4 (TLR-4) mRNA expression, which was inhibited by metformin. Metformin suppressed morphine-induced BV-2 cells activation through increasing AMPK phosphorylation, which was reversed by the AMPK inhibitor compound C. Additionally, in BV-2 cells, morphine did not affect the cell viability and the mRNA expression of anti-inflammatory cytokines. In bEnd3 cells, morphine did not affect the mRNA expression of interleukin-1β (IL-1β), but increased IL-6 and tumor necrosis factor-α (TNF-α) mRNA expression; the effect was inhibited by metformin. Morphine also did not affect the mRNA expression of TLR-4 and chemokine ligand 2 (CCL2). Furthermore, systemic administration of metformin significantly blocked morphine-induced microglial activation in the spinal cord and then attenuated the development of chronic morphine tolerance in mice.

Conclusions

Metformin significantly attenuated morphine antinociceptive tolerance by suppressing morphine-induced microglial activation through increasing AMPK phosphorylation.
  相似文献   
999.
Oesophageal squamous cell carcinoma (ESCC) has a generally poor prognosis, due to the lack of effective treatment methods. Immunotherapeutic approaches based on tumour‐infiltrating lymphocytes (TILs) have demonstrated that durable responses are produced in some patients with solid tumours, which suggests the potential feasibility of clinical application of immunotherapy for ESCC. However, many of the basic characteristics of TILs in ESCC are poorly understood, including clonality, specificity and spatial heterogeneity of the response of TILs, which depends on the interaction between antigens and T cell receptors (TCRs). We used ultra‐deep sequencing of rearranged genes in TCR β‐chain (TCRβ) to profile the basic characteristics of T cells in tumour tissues (four to six regions from each tumour) as well as matched adjacent normal tissue and peripheral blood from seven patients diagnosed with primary ESCC. We found that T cell clones within ESCCs were quite different from those of the peripheral blood and even the adjacent normal tissues in general. Although there was a relatively higher degree of overlap of intratumoural TCRβ repertoires than those between the tumour and other tissues, intratumoural TCRβ repertoires were spatially heterogeneous. Due to the restricted sampling, high‐throughput TCRβ sequencing could characterize the diversity and composition of a limited (compartment‐dependent) fraction of the respective T cell clones in any individual ESCC, expanding our understanding of immune behaviour and immune response and shedding more light on ESCC immunotherapy. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.  相似文献   
1000.
A sequencing‐based typing of the HLA‐DPB1 gene was carried out in 51 unrelated healthy individuals from the Yunnan Pumi ethnic minority. A total of 18 DPB1 alleles, in which DPB1*0501 (52.0%) and DPB1*0402 (15.7%) greatly predominated, were found, of which alleles DPB1*20011, 2201, 3601, 3701, 3801, 4901, 5001 and 8001 were recorded for the first time in the Chinese population. This may be because the typing methods used in previous genotyping of Chinese populations were of lower sensitivity than that used in our study. A dendrogram constructed by the maximum likelihood method showed that the Pumi ethnic minority belongs to the Asian/Australasian cluster and has the closest relationship to Trobriander, implying an unusual relationship between Australasian and South China populations. However, the Yi ethnic minority, which also comes from the ancient Qiang, did not show a very close relationship with the Pumi. This is probably because the Pumi were historically assimilated by local south‐west China populations.  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