全文获取类型
收费全文 | 169013篇 |
免费 | 7698篇 |
国内免费 | 488篇 |
专业分类
耳鼻咽喉 | 2484篇 |
儿科学 | 5060篇 |
妇产科学 | 3832篇 |
基础医学 | 22922篇 |
口腔科学 | 5189篇 |
临床医学 | 10879篇 |
内科学 | 41697篇 |
皮肤病学 | 4860篇 |
神经病学 | 13891篇 |
特种医学 | 4545篇 |
外国民族医学 | 7篇 |
外科学 | 20735篇 |
综合类 | 929篇 |
一般理论 | 46篇 |
预防医学 | 16624篇 |
眼科学 | 3530篇 |
药学 | 11681篇 |
中国医学 | 746篇 |
肿瘤学 | 7542篇 |
出版年
2023年 | 1009篇 |
2022年 | 1263篇 |
2021年 | 3850篇 |
2020年 | 1931篇 |
2019年 | 3800篇 |
2018年 | 7246篇 |
2017年 | 4299篇 |
2016年 | 3514篇 |
2015年 | 3777篇 |
2014年 | 4714篇 |
2013年 | 6893篇 |
2012年 | 11456篇 |
2011年 | 12131篇 |
2010年 | 6349篇 |
2009年 | 4883篇 |
2008年 | 9859篇 |
2007年 | 10409篇 |
2006年 | 9723篇 |
2005年 | 9709篇 |
2004年 | 8777篇 |
2003年 | 8279篇 |
2002年 | 7833篇 |
2001年 | 4887篇 |
2000年 | 5570篇 |
1999年 | 4243篇 |
1998年 | 950篇 |
1997年 | 633篇 |
1996年 | 610篇 |
1995年 | 510篇 |
1994年 | 416篇 |
1993年 | 386篇 |
1992年 | 1759篇 |
1991年 | 1449篇 |
1990年 | 1364篇 |
1989年 | 1124篇 |
1988年 | 961篇 |
1987年 | 962篇 |
1986年 | 918篇 |
1985年 | 800篇 |
1984年 | 589篇 |
1983年 | 457篇 |
1979年 | 488篇 |
1975年 | 392篇 |
1974年 | 441篇 |
1973年 | 484篇 |
1972年 | 420篇 |
1971年 | 434篇 |
1970年 | 390篇 |
1969年 | 378篇 |
1968年 | 375篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
de Oliveira NM Vaca Sánchez R Rodriguez Fiesta S Lopez Salgado T Rodríguez R Bethencourt JC Blanes Zamora R 《Human reproduction (Oxford, England)》2004,19(2):262-265
BACKGROUND: There are few reports of pregnancy using immotile sperm, and none using a purely mechanical assessment of viability. METHODS: In this pilot study, we retrospectively analysed 66 cycles in 61 patients with determinant male factor, recording rates of fertilization, implantation, normal pregnancy and take-home babies achieved with ICSI. Sperm selection was based on morphologically normal appearance under the inverted microscope. Viability of immotile spermatozoa was assessed by the mechanical touch technique to observe tail flexibility and tail shape recovery. RESULTS: Of 17 ICSI cycles using frozen-thawed testicular sperm, six microinjected with immotile and 11 with motile sperm, we achieved fertilization rates of 65.7 and 74.3%, respectively, and five pregnancies (two and three, respectively). Of 49 ICSI cycles using fresh testicular sperm, 10 microinjected with immotile and 39 with motile sperm, we achieved fertilization rates of 73.4 and 64.4%, respectively, and 12 pregnancies (three and nine, respectively). CONCLUSIONS: Immotile (fresh and frozen-thawed) testicular sperm of normal morphological appearance can be used to achieve clinical pregnancy with ICSI. Our results strongly suggest that immotile sperm viability can be assessed by the mechanical touch technique. 相似文献
992.
Clade analysis and surface antigen polymorphism of hepatitis B virus American genotypes 总被引:4,自引:0,他引:4
Eight genotypes (A-H) of hepatitis B virus (HBV) have been described, HBV genotypes F and H being autochthonous to America. HBV genotype F has been classified in four clusters. The objective of this study was to gain insight into the molecular epidemiology of HBV American genotypes, as well as to analyze the genotype-related polymorphism in some functional domains of the surface proteins. The sequences of the S region of 106 isolates genotype F and H were analyzed, out of which 47 isolates genotype F circulated in different Venezuelan populations. Most of the Venezuelan isolates genotype F were grouped in cluster III (n = 39) and 7 in cluster II. One isolate obtained from a blood donor could not be classified in any clade and harbored amino acid substitutions characteristic of a vaccine escape mutant (G145R) and a stop codon in the surface antigen. Amino acid analysis of the PreS and S gene products showed unique genetic characteristics in genotype F and H sequences in some important domains involved in the early steps of infection. Out of 30 available sequences, two complete genome sequences of HBV genotype F from Venezuela were obtained. Phylogenetic analysis of these complete genomes confirmed the presence of four clusters inside genotype F, differing in more than 4% nucleotide divergence. Our extended analysis showed that genotype F clades Ia, III, and IV exhibit a restricted geographic distribution (Central America, the North and the South of South America, respectively) while clades Ib and II are found in all the Americas except in the Northern South America and North America respectively. 相似文献
993.
González MB Gutiérrez NC García JL Schoenmakers EF Solé F Calasanz MJ San Miguel JF Hernández JM 《Cancer Genetics and Cytogenetics》2004,150(2):136-143
Abnormalities in the long arm of chromosome 7 are a frequent chromosomal aberration in myeloid disorders. Most studies have focused on the analysis of del(7q), demonstrating the presence of several minimal deleted regions in 7q22 approximately q31. By contrast, few studies in myeloid disorders have been devoted to the analysis of translocations, either balanced or unbalanced, involving 7q. In this study, we used fluorescence in situ hybridization (FISH) to characterize the 7q31.3 approximately q34 region (markers D7S480-D7S2227) in patients with deletion or translocation of 7q. A total of 910 cases of myeloid disorders were studied by conventional cytogenetics. Fifty-eight (6%) patients had structural aberrations of 7q. FISH studies were carried out in the 27 patients with involvement of 7q31 approximately q34: 14 cases had an acute myelogenous leukemia and 13 cases had a myelodysplastic syndrome. FISH analysis revealed the existence of high complexity in the 7q31.3 approximately q34 region in patients with unbalanced translocations. No breakpoints in 7q31.3 approximately q34 were found in the cases with deletion or balanced translocation. Nevertheless, studies of unbalanced translocations showed several breakpoints in markers D7S480-D7S2227, which delineate a commonly altered region. The complexity of 7q rearrangements suggests that a synergy of different genetic factors, rather than the alteration of a single tumor suppressor gene, could be involved in the pathogenesis of del(7q) in myeloid disorders. 相似文献
994.
Gene profiling reveals increased expression of uteroglobin and other anti-inflammatory genes in glucocorticoid-treated nasal polyps 总被引:3,自引:0,他引:3
Benson M Carlsson L Adner M Jernås M Rudemo M Sjögren A Svensson PA Uddman R Cardell LO 《The Journal of allergy and clinical immunology》2004,113(6):58-1143
BACKGROUND: Treatment with local glucocorticoids (GCs) decreases symptoms and the size of nasal polyps. This might depend on the downregulation of proinflammatory genes, as well as the upregulation of anti-inflammatory genes. OBJECTIVE: We sought to identify GC-regulated anti-inflammatory genes in nasal polyps. METHODS: Affymetrix DNA microarrays were used to analyze the expression of 22,283 genes in 4 nasal polyps before and after local treatment with fluticasone (400 microg/d). Expression of uteroglobin and mammaglobin B was analyzed with real-time PCR in 6 nasal polyps and in nasal biopsy specimens from 6 healthy control subjects. RESULTS: Two hundred three genes had changed in expression in treated polyps, and 139 had known functions: 54 genes were downregulated, and 85 were upregulated. Genes associated with inflammation constituted the largest single functional group. These genes affected key steps in inflammation (eg, immunoglobulin production; antigen processing and presentation; and the chemoattraction and activation of granulocytes, T cells, and B cells). Several proinflammatory genes were downregulated. In contrast, some anti-inflammatory genes were upregulated. The gene that increased most in terms of expression was uteroglobin. This was confirmed with real-time PCR. By contrast, expression of uteroglobin was lower in untreated polyps than in healthy nasal mucosa. Immunohistochemical investigation showed staining of uteroglobin in the epithelium and in seromucous glands in control subjects and in nasal polyps. CONCLUSION: Upregulation of anti-inflammatory genes, such as uteroglobin, might contribute to the effects of local treatment with GCs in nasal polyps. 相似文献
995.
Vázquez-García M Elías-Viñas D Reyes-Guerrero G Domínguez-González A Verdugo-Díaz L Guevara-Guzmán R 《Physiology & behavior》2004,82(4):685-690
The effect of exposure to low-frequency electromagnetic fields (ELF EMFs) on social recognition was studied. The test was based upon a comparison between two encounters of an adult rat and a conspecific juvenile, separated by an interexposure interval (IEI). The exposure to ELF EMF of 1 mT intensity during 2 h for 9 days increased the duration of short-term memory of adult male Wistar rats up to 300 min. These data indicate, for the first time, that ELF EMF improves social recognition memory in rats. 相似文献
996.
997.
Testing genotypic and phenotypic resistance in human immunodeficiency virus type 1 isolates of clade B and other clades from children failing antiretroviral therapy 总被引:5,自引:0,他引:5
下载免费PDF全文
![点击此处可从《Journal of clinical microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
998.
Angiocentric lymphomatoid granulomatosis is a rare lymphoproliferative disease, mainly associated with pulmonary manifestation. Its origin is unknown, but Epstein-Barr virus may be one of the etiological factors. A 51-year-old male had an abdominal laparotomy in 1994 and a large granulomatous mass was removed from behind the cecum. No specific therapy was administered. In February 1998 multiple pulmonary lesions were found by X-ray and thoracoscopic biopsy was made. The histopathological diagnosis was angiocentric lymphomatoid granulomatosis. The patient received 6 cycles of CHOP chemotherapy, with which a complete remission was achieved. A consistent severe hypogammaglobulinaemia was detected, so the diagnosis of common variable immunodeficiency (CVID) was established. The diagnosed CVID was the probable causative factor of the angiocentric lymphomatoid granulomatosis. After the CHOP treatment, the patient is on intravenous immunoglobulin substitution and is well up to today. 相似文献
999.
Dina Ruano António Macedo Maria Jo?o Soares José Valente Maria Helena Azevedo Carlos Pato Mara Helena Hutz Clarissa S Gama Maria Inês Lobato Paulo Belmonte-de-Abreu Peter Heutink Joana Almeida Palha 《American journal of medical genetics. Part B, Neuropsychiatric genetics》2007,(5):642-646
Several observations point to the involvement of disturbed lipid biology in schizophrenia. Reduced response to niacin flushing test, which involves vasodilatation induced by prostaglandin D2 (PGD2), is among the evidences, together with decreased CSF levels of lipocalin-type prostaglandin D2 synthase (PTGDS), the enzyme responsible for the synthesis of PGD2 in the brain. Since PTGDS is also a carrier for lipophilic molecules such as retinoids and thyroid hormones, altered PTGDS levels might influence both PGD2-mediated signaling, and vitamin A and thyroid hormone availability. To test whether genetic variants of PTGDS are involved in the etiology of schizophrenia, we searched for variants in the coding and regulatory regions of the gene. We identified four previously described polymorphisms. Using two case-control samples from Portugal and Brazil, none of the polymorphisms tested was associated with the disease. In addition, no transmission distortion was observed in an independent parents-offspring sample from the Azorean Islands. Our data do not support the involvement of the PTGDS gene in the etiology of schizophrenia. 相似文献