全文获取类型
收费全文 | 17362篇 |
免费 | 1366篇 |
国内免费 | 42篇 |
专业分类
耳鼻咽喉 | 166篇 |
儿科学 | 576篇 |
妇产科学 | 473篇 |
基础医学 | 2386篇 |
口腔科学 | 186篇 |
临床医学 | 1995篇 |
内科学 | 3433篇 |
皮肤病学 | 259篇 |
神经病学 | 2009篇 |
特种医学 | 332篇 |
外科学 | 1784篇 |
综合类 | 100篇 |
一般理论 | 18篇 |
预防医学 | 2482篇 |
眼科学 | 232篇 |
药学 | 1034篇 |
中国医学 | 9篇 |
肿瘤学 | 1296篇 |
出版年
2024年 | 40篇 |
2023年 | 336篇 |
2022年 | 569篇 |
2021年 | 1164篇 |
2020年 | 696篇 |
2019年 | 966篇 |
2018年 | 1030篇 |
2017年 | 683篇 |
2016年 | 700篇 |
2015年 | 758篇 |
2014年 | 970篇 |
2013年 | 1193篇 |
2012年 | 1736篇 |
2011年 | 1696篇 |
2010年 | 784篇 |
2009年 | 650篇 |
2008年 | 1047篇 |
2007年 | 898篇 |
2006年 | 776篇 |
2005年 | 601篇 |
2004年 | 480篇 |
2003年 | 403篇 |
2002年 | 326篇 |
2001年 | 33篇 |
2000年 | 26篇 |
1999年 | 30篇 |
1998年 | 44篇 |
1997年 | 27篇 |
1996年 | 9篇 |
1995年 | 15篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1964年 | 3篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Smad4 overexpression causes germ cell ablation and leydig cell hyperplasia in transgenic mice
下载免费PDF全文
![点击此处可从《The American journal of pathology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Narula A Kilen S Ma E Kroeger J Goldberg E Woodruff TK 《The American journal of pathology》2002,161(5):1723-1734
Members of the transforming growth factor-beta (TGF-beta) superfamily play a variety of important roles in testicular development and function. The tumor suppressor gene, Smad4, is a common mediator of TGF-beta, activin, and bone morphogenetic protein-mediated signaling pathways. To investigate the role of the Smad4 gene during testicular development and function, transgenic mice were generated using a Flag-tagged Smad4 gene driven by 180-bp fragment of the Mullerian inhibiting substance upstream promoter sequence. Three Smad4 transgenic founders (A, B, and G) were detected by Southern blot analysis; line B showed the highest expression of the Smad4 transgene and was further studied. The fertility in F1 generation (B) and F2 generation (BB) of the Smad4 transgenic mice was not impaired. However, in the F3 generation (B2x) all animals were impacted by the overexpression of the Smad4 transgene and two kinds of phenotypes were observed. In one group animals were completely infertile, while in the other group animals were fertile and sired the normal number of pups/litter. These groups are designated as infertile and fertile in the text. Histological evaluation of the testes from the infertile group showed variable degrees of Leydig cell hyperplasia, apoptosis of germ cells, spermatogenic arrest, seminiferous tubule degeneration, and infertility. In the fertile group, there was no apparent change in the histology of the testis except for a slight increase in the number of Leydig cells. Serum follicle-stimulating hormone levels in the adult animals of both groups of Smad4 transgenic male mice were not significantly different from normal littermates; however, testosterone levels in both groups were significantly (P < 0.05) increased. These results suggest that overexpression of Smad4 leads to testicular abnormalities and infertility supporting the hypothesis that the TGF-beta signaling pathways are carefully orchestrated during testicular development. In the absence of normal levels of Smad4 testicular function is compromised. 相似文献
42.
The Competencies Conference: Future Directions in Education and Credentialing in Professional Psychology was held in Arizona in November 2002. One of the workshops, Individual and Cultural Differences (ICD), focused on racism, homophobia, and ageism. The consensus was that self-awareness and knowledge about the three "isms" are critical components in the education and training of psychologists. This article, authored by four of the workshop attendees, is a review of the current research and theoretical literature. Implications that address both content and context in graduate programs and training sites are presented. This is one of a series of articles published in this issue of the Journal of Clinical Psychology. Several other articles that resulted from the Competencies Conference will appear in Professional Psychology: Research and Practice and The Counseling Psychologist. 相似文献
43.
Holly James Westervelt Jessica Somerville Ruffolo Geoffrey Tremont 《Archives of clinical neuropsychology》2005,20(6):761-769
The relationship between odor identification and cognition has not been previously well characterized. The neuroanatomy of the olfactory system and the frequent finding of olfactory dysfunction in neurodegenerative diseases suggest a likely relationship between odor identification and memory, language, and executive functioning, though previous studies have often failed to demonstrate the expected relationship. The current study examined this relationship in across a continuum of ability levels (N=100). Strongest correlations were found between odor identification and language, most aspects of memory, and a measure of general cognitive functioning. Significant but more modest correlations were seen between odor identification and attention, motor, visuospatial, and executive functions. A regression analysis revealed language as the only significant predictor of olfactory performance. These findings suggest that odor identification is most closely associated with other measures of temporo-limbic functioning. The implications of these findings, particularly in consideration of the assessment of older adults, are discussed. 相似文献
44.
45.
Telomere lengths of translocation-associated and nontranslocation-associated sarcomas differ dramatically
下载免费PDF全文
![点击此处可从《The American journal of pathology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Montgomery E Argani P Hicks JL DeMarzo AM Meeker AK 《The American journal of pathology》2004,164(5):1523-1529
Sarcomas can be divided into those with specific translocations displaying monotonous cytomorphology, and those with complex karyotypes and marked cellular pleomorphism. Telomeres contain terminal DNA sequence repeats that maintain chromosomal stability. Telomeres shorten with cell division and may become dysfunctional leading to chromosomal instability. Using a fluorescence in situ hybridization/immunofluorescence method to assess telomere lengths in archival tissues we analyzed these two types of sarcomas using paraffin-embedded primary tumor specimens. Tissues from nine sarcomas with characteristic translocations (two synovial sarcomas, two alveolar rhabdomyosarcomas, two desmoplastic round cell tumors, and one each of infantile fibrosarcoma, myxoid liposarcoma, cellular congenital mesoblastic nephroma) and nine without (four malignant fibrous histiocytomas, two leiomyosarcomas, one pleomorphic rhabdomyosarcoma, one dedifferentiated chondrosarcoma, and one malignant peripheral nerve sheath tumor) were analyzed. In all (nine of nine) cases with specific translocations, which generally have few karyotypic abnormalities, telomere lengths were similar to or reduced compared to surrounding nonneoplastic tissues. In contrast, telomeres in cases lacking specific translocations, which generally contain complex karyotypes, were often found to be dramatically lengthened and heterogeneous. In addition to markedly elongated telomeres, seven of nine (78%) complex cases exhibited large brightly stained regions corresponding to a specific type of promyelocytic leukemia nuclear body found in immortalized cells that maintain telomeres in a telomerase-independent manner [alternative lengthening of telomeres (ALT) pathway]. This phenotype is unlike that of epithelial neoplasms that typically display complex karyotypes with abnormally short telomeres maintained by the enzyme telomerase. The discovery of heterogeneous telomere lengths and evidence of the ALT pathway in the majority of sarcomas with complex karyotypes supports the existence of a telomere maintenance pathway incapable of full karyotypic stabilization in pleomorphic sarcomas. These findings provide additional molecular-genetic evidence supporting the dichotomous grouping of sarcomas into those with characteristic signature translocations without extensive additional karyotypic abnormalities, and those without such signature translocations that typically display very complex karyotypes, and point to telomere dysfunction as a plausible contributor to the chromosomal aberrations found in complex sarcomas. 相似文献
46.
Presence of the cfxA gene in Bacteroides distasonis 总被引:1,自引:0,他引:1
Avelar KE Otsuki K Vicente AC Vieira JM de Paula GR Domingues RM Ferreira MC 《Research in microbiology》2003,154(5):369-374
In this study we investigated the presence of the cfxA gene (encoding a class A beta-lactamase) in 73 strains of the Bacteroides fragilis group belonging to the species B. distasonis (34), B. vulgatus (14), B. thetaiotaomicron (8), B. merdae (6), B. caccae (9) and B. ovatus (2) isolated from human intestinal microflora of healthy children and adults. Employing specific primers to the cfxA gene, a 312-bp amplified fragment was obtained in 2 strains of B. vulgatus and 9 strains, the majority from children, of B. distasonis. The expression of this enzyme was analysed by determining the MICs to cefoxitin and cefotaxime and values varied from 2 to >256 microg/ml of both cefoxitin and cefotaxime. Sequence analysis of the amplicons corresponding to the cfxA gene from B. distasonis and B. vulgatus revealed identical sequences between these isolates and high similarity with other beta-lactamase genes of anaerobes such as cfxA of B. vulgatus (99%) and cfxA2 of Prevotella intermedia (99%), both sequences of which deposited in Genbank under accession numbers U38243 and AF118110, respectively. However, a fragment obtained from a B. distasonis strain (EC17-4) showed a unique RFLP profile and 87% nucleotide similarity with cfxA and cfxA2 genes. These results seem to suggest a dissemination of these resistance determinants among Bacteroides species. 相似文献
47.
Comparison of Real-Time, Quantitative PCR with Molecular Beacons to Nested PCR and Culture Methods for Detection of Mycobacterium avium subsp. paratuberculosis in Bovine Fecal Samples
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)
Ying Fang Wai-Hong Wu Jessica L. Pepper Jill L. Larsen Salvatore A. E. Marras Eric. A. Nelson William B. Epperson Jane Christopher-Hennings 《Journal of clinical microbiology》2002,40(1):287-291
An automated PCR with fluorescent probes (molecular beacons) detected Mycobacterium avium subsp. paratuberculosis in bovine feces. When the PCR was compared with culture in testing 41 fecal samples, kappa scores of 0.94 to 0.96, a sensitivity of 93 to 96%, and a specificity of 92% were obtained. Results were quantitated by using a standard curve derived from a plasmid containing IS900. A minimum quantity of 1.7 x 10(-4) pg of DNA, correlating to 1 to 8 CFU, was detected. 相似文献
48.
Mechanical properties of dilated human ascending aorta 总被引:3,自引:0,他引:3
Okamoto RJ Wagenseil JE DeLong WR Peterson SJ Kouchoukos NT Sundt TM 《Annals of biomedical engineering》2002,30(5):624-635
Dilation of the ascending aorta, associated with Marfan Syndrome, bicuspid aortic valve, or advanced age, may lead to aortic dissection and rupture. Mathematical models can be used to assess the relative importance of increased wall stresses and decreased strength in these mechanical failures. To obtain needed inputs for such models, mechanical properties of dilated human ascending aorta were measured in vitro. Specimens for opening angle, biaxial elastic, and uniaxial circumferential strength tests were cut from excised tissue obtained from 54 patients (age 18–81 years) undergoing elective aortic graft replacement surgery. Opening angle was significantly greater in patients older than 50 years (262°±76°, n=21) compared to younger patients (202°±70°, n=13 All biaxial elastic specimens n=40 exhibited nonlinear stress-strain behavior. Rapid increases in circumferential and axial stresses occurred at lower strains in the older patient group than in the younger. Mean strength was significantly lower in older patients (1.35±0.37 MPa, n=14) than younger (2.04 ± 0.46 MPa, n=11, age <50 years). These changes in mechanical properties suggest that age may influence the risk of aortic dissection or rupture of dilated ascending aorta. © 2002 Biomedical Engineering Society.
PAC2002: 8719Rr, 8719Hh 相似文献
49.
50.
Turrisi R Hillhouse J Heavin S Robinson J Adams M Berry J 《Journal of behavioral medicine》2004,27(4):393-412
The research evaluated an intervention strategy designed to prevent skin cancer in young adolescents. The intervention used parents as change agents to effectively communicate the risks of skin cancer and encourage their children to avoid high-risk sun-related behaviors while increasing positive sun-safe behaviors. Three hundred and forty parents in two regions of the United States were educated about the dangers of risky sun behaviors and how to convey information about skin cancer prevention to their children. Parents were then encouraged to talk with their children about these issues over a 1-month period prior to the onset of summer. Following this time period, children whose parents received and implemented the intervention materials were compared with a control sample of 129 children. These two groups were matched on age, gender, and school on number of sunburns and sunburn severity, attitudes and beliefs, and sunbathing behavior. Children in the treatment condition differed significantly from controls in the predicted directions on all outcome variables. The findings are discussed in terms of reducing skin cancer risk behaviors of children via parent-based intervention approaches. 相似文献