全文获取类型
收费全文 | 15897篇 |
免费 | 1301篇 |
国内免费 | 511篇 |
专业分类
耳鼻咽喉 | 172篇 |
儿科学 | 281篇 |
妇产科学 | 376篇 |
基础医学 | 2085篇 |
口腔科学 | 322篇 |
临床医学 | 1863篇 |
内科学 | 2892篇 |
皮肤病学 | 308篇 |
神经病学 | 1079篇 |
特种医学 | 643篇 |
外国民族医学 | 3篇 |
外科学 | 1932篇 |
综合类 | 1150篇 |
一般理论 | 2篇 |
预防医学 | 1028篇 |
眼科学 | 443篇 |
药学 | 1408篇 |
4篇 | |
中国医学 | 335篇 |
肿瘤学 | 1383篇 |
出版年
2024年 | 30篇 |
2023年 | 170篇 |
2022年 | 415篇 |
2021年 | 593篇 |
2020年 | 321篇 |
2019年 | 428篇 |
2018年 | 425篇 |
2017年 | 376篇 |
2016年 | 388篇 |
2015年 | 541篇 |
2014年 | 631篇 |
2013年 | 691篇 |
2012年 | 1131篇 |
2011年 | 1197篇 |
2010年 | 712篇 |
2009年 | 599篇 |
2008年 | 871篇 |
2007年 | 861篇 |
2006年 | 817篇 |
2005年 | 768篇 |
2004年 | 693篇 |
2003年 | 595篇 |
2002年 | 520篇 |
2001年 | 466篇 |
2000年 | 402篇 |
1999年 | 399篇 |
1998年 | 154篇 |
1997年 | 152篇 |
1996年 | 177篇 |
1995年 | 146篇 |
1994年 | 108篇 |
1993年 | 87篇 |
1992年 | 201篇 |
1991年 | 183篇 |
1990年 | 156篇 |
1989年 | 135篇 |
1988年 | 129篇 |
1987年 | 107篇 |
1986年 | 105篇 |
1985年 | 103篇 |
1984年 | 77篇 |
1983年 | 71篇 |
1982年 | 56篇 |
1981年 | 55篇 |
1980年 | 47篇 |
1979年 | 60篇 |
1978年 | 50篇 |
1977年 | 33篇 |
1975年 | 27篇 |
1974年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
No direct role for Epstein-Barr virus in American hepatocellular carcinoma 总被引:6,自引:0,他引:6
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)
Epstein-Barr virus (EBV) was recently linked to hepatocellular carcinogenesis in Japanese patients. It is not clear whether EBV infection is also associated with hepatocellular carcinoma (HCC) occurring in American patients. We studied 41 cases of HCC from the Los Angeles area for evidence of EBV infection by in situ hybridization, immunohistochemistry, and polymerase chain reaction methods. Of 41 cases, 16 were seropositive for hepatitis B virus surface antigen (39%), 9 of 29 tested were seropositive for hepatitis C virus antibody (31%); in total, 22 cases were seropositive for hepatitis B virus and/or hepatitis C virus (53%). Of 41 cases, 1 was positive for EBV-encoded small nonpolyadenylated RNA (EBER)-1 (2%) by in situ hybridization. By immunohistochemistry, two cases were positive for EBV nuclear antigen (EBNA)-1 (5%), one was positive for the transactivating immediate early BZLF1 (ZEBRA) (2%), and none was positive for latent membrane protein-1. None of the 41 cases was positive for latent membrane protein-1 and EBV nuclear antigen (EBNA)-4 DNAs by polymerase chain reaction assay. All four positive cases showed rare EBER-1-, ZEBRA-, or EBNA-1- positive cells (<0.1%); in none of these cases was there expression of any other EBV viral genes. In the one case each that was positive for EBER-1 and ZEBRA, both of which occurred in patients of non-Asian ethnicity, the staining was limited to infiltrating small lymphocytes, and tumor cells were negative. In the two cases that were positive for EBNA-1, both of which occurred in patients of Asian ethnicity, the staining was limited to tumor cells, and infiltrating small lymphocytes were negative. Our study indicates that rare cases of American HCC may contain EBV-infected cells, but it is unlikely that EBV plays a major role in the carcinogenesis of HCC. 相似文献
82.
Nickel-titanium (NiTi) shape memory alloys possess super-elasticity in addition to the well-known shape memory effect and are potentially suitable for orthopedic implants. However, a critical concern is the release of harmful Ni ions from the implants into the living tissues. We propose to enhance the corrosion resistance and other surface and biological properties of NiTi using carbon plasma immersion ion implantation and deposition (PIII&D). Our corrosion and simulated body fluid tests indicate that either an ion-mixed amorphous carbon coating fabricated by PIII&D or direct carbon PIII can drastically improve the corrosion resistance and block the out-diffusion of Ni from the materials. Our tribological tests show that the treated surfaces are mechanically more superior and cytotoxicity tests reveal that both sets of plasma-treated samples favor adhesion and proliferation of osteoblasts. 相似文献
83.
Cellular adhesion molecules play a central role in leucocyte migration through peripheral blood and tissues. A crucial stage in these events in selectin-mediated adhesion involving E-selectin expressed on activated endothelium interacting with a range of carbohydrate ligands expressed by specific subpopulations of leucocytes. As such mechanisms may be relevant to bone marrow-derived dendritic epidermal Langerhans' cell (LC) migration, expression of these carbohydrate ligands was assessed immunocytochemically in whole skin biopsies and in epidermal cell suspensions obtained from adult humans. Double-labelling experiments revealed that sialyl Lewis x, recognized by the monoclonal antibody CSLEX1, was expressed on epidermal LC (n = 9). Furthermore, expression was enhanced at 24 hr following epicutaneous application of antigen and in the inflammatory disorder psoriasis (n = 10). E-selectin was concomitantly strongly expressed on dermal endothelium in psoriasis and allergic contact dermatitis. Intradermal injection of the T-cell-derived cytokine interferon-gamma (IFN-gamma) led to increased LC expression of sialyl Lewis x. In epidermal cell suspensions, in contrast to keratinocytes, CD1a+ cells expressed sialyl Lewis x, intensity of which was enhanced after 4 days in culture. CSLEX1 staining could be abolished and CD15 (non-sialated Lewis x) expression induced by saponification and treatment with neuraminidase. Expression of other selectin ligands was also examined. While the cutaneous lymphocyte antigen defined by the monoclonal antibody HECA-452 reacted with a small minority of LC, sialyl Lewis a and sulphatide were not expressed under any experimental conditions. These studies indicate that E-selectin-sialyl Lewis x interactions are potentially important in LC migration, both into and out of skin. 相似文献
84.
人际交往训练降低医学生心理应激反应的实验研究 总被引:3,自引:0,他引:3
目的 探讨人际交往训练降低医学生心理应激反应的有效模式 ,以培养交往手段 ,促进身心健康 ,提高学习效率。方法 从云南中医学院中医专业 2 0 0 0级 8个班 ,41 2名学生中随机抽取 2个班 ,共 1 0 6人为被试对象 ,结合专业学习 ,在生理学课堂教学中贯穿人际交往训练 ,训练前后分别测查 90项症状自评量表 ( SCL-90 )和防御方式问卷 ( DSQ) ,并用 Q分类法检验被试课前和课后自我评价。最后 ,对被试和其余 6个班的学生进行生理测验 ,并对测验成绩进行比较。结果 被试在交友信心、乐观豁达、口头表达、积极接纳、说服技巧方面均比训练前有显著和极显著提高 ;且考前心理应激反应明显降低 ,防御方式趋向成熟 ,测验及格率高于其余 6个班。结论 结合专业进行人际交往训练可在近期内改善医学生的心理健康水平 ,有利于提高学习效率 ,深受大学生欢迎 相似文献
85.
Xiaoyan Sun Gregory M Cole Teresa Chu Weiming Xia Douglas Galasko Haruyasu Yamaguchi Kentaro Tanemura Sally A Frautschy Akihiko Takashima 《Neurobiology of aging》2002,23(2):195-203
Intracellular Abeta was examined in both a neuronal cell line (B103) expressing human APP with Swedish mutation and a non-neuronal cell line (Chinese hamster ovary, CHO) expressing wild human APP. Exposure of the APP695sw-transfected B103 cells to okadaic acid for 3 h, Abeta immunostaining was enhanced, as demonstrated by two independent anti-Abeta antibodies. The confocal microscopic study revealed that the immunoreactivity of Abeta was mainly colocalized with a Golgi marker and partially with an ER marker. Quantitative analyses, using Abeta sandwich ELISA, showed significantly increased intracellular Abeta. False positive detection of Abeta by antibody cross-reaction with APP was ruled out by extracting the fraction with formic acid and making it alkaline before subjecting it to ELISA. This procedure resulted in a fraction that contained little APP. Using CHO cells, OA treatment was also shown to be effective in increasing Abeta, as demonstrated by Western blot. The increased full-length APP and decreased APPC99 were also observed. This is the first study to demonstrate that OA treatment significantly increases intracellular Abeta. 相似文献
86.
Cell-free translation of tobacco vein mottling virus RNA 总被引:1,自引:0,他引:1
Tobacco vein mottling virus (TVMV), a member of the potyvirus group, was translated in a rabbit reticulocyte cell-free system. The RNA was approximately 5% as active as rabbit globin mRNA in directing protein synthesis. Translation was stimulated approximately 15% by the cap analog pppm7G, a phenomenon which has also been observed with uncapped viral RNAs. Treatment with NaIO4 and NaB(3H]4 under conditions which label the caps of globin and ovalbumin mRNA failed to produce labeled cap structures in TVMV RNA. Approximately 20 polypeptides, ranging from 20,000 to 100,000 daltons, were produced in the reticulocyte system programmed with TVMV RNA. The predominant species (P75) had a molecular weight of 75,000. The same major polypeptides were produced in the wheat germ system, but there was relatively greater synthesis of the smaller polypeptides. Incubation of the reticulocyte system in the presence of cycloheximide following an initial period of synthesis failed to cause breakdown of larger polypeptides into smaller polypeptides. Preincubation of TVMV RNA with the reticulocyte system before addition of labeled amino acids caused greater synthesis of the smaller polypeptides, suggesting that they are derived from fragments of the RNA produced during the incubation. Translation of TVMV RNA which had been bound to oligo(dT)-cellulose yielded nearly the same spectrum of polypeptides, but synthesis of polypeptides smaller than 52,000 daltons was reduced. At low ionic strength, only polypeptides of 52,000 daltons and smaller were synthesized. At high ionic strength, P75 was essentially the only product synthesized. Antibody to whole virus precipitated many of the polypeptides, including P75, suggesting that they contain the coat protein sequence. No polypeptide with the electrophoretic mobility of authentic coat protein, however, was precipitated. Comparison of partial proteolytic digests of P75 and authentic coat protein provided further evidence for sequence homology. 相似文献
87.
Chan PK To KF Lo AW Cheung JL Chu I Au FW Tong JH Tam JS Sung JJ Ng HK 《Journal of medical virology》2004,74(1):1-7
Severe acute respiratory syndrome coronavirus (SARS-CoV) can produce gastrointestinal symptoms. The intestinal tract is the only extrapulmonary site where viable viruses have been detected. This study examined seven established human intestinal cell lines, DLD-1, HCT-116, HT-29, LoVo, LS-180, SW-480 and SW-620, for their permissiveness to SARS-CoV infection. The results showed that only LoVo cells were permissive to SARS-CoV infection as evident by positive findings from indirect immunofluorescence staining for intracellular viral antigens, in situ hybridization for intracellular viral RNA, and electron microscopy for intracellular viral particles. In contrast to Vero cells, SARS-CoV did not produce cytopathic effects on LoVo cells. However, LoVo cells were found to be highly permissive for productive infection with a high viral titre (>3 x 10(7) viral copies/ml) produced in culture supernatant following a few days of incubation. SARS-CoV established a stable persistent chronic infection that could be maintained after multiple passages. Being a cell line of human origin, LoVo cells could be a useful in vitro model for studying the biology and persistent infection of SARS-CoV. Our results on the expression of angiotensin-converting enzyme 2 (ACE2), a recently identified cellular receptor for SARS-CoV, in these cell lines indicated that it might not be the sole determinant for cells to be susceptible to SARS-CoV infection. 相似文献
88.
Nasopharyngeal carcinoma (NPC) is predominantly of the undifferentiated histological subtype. Histological differentiation is of limited prognostic significance in NPC. Recent studies have suggested that downregulation of the cadherin-catenin cell adhesion complex may play a crucial role in the initial stage of cancer invasion and metastasis and is associated with poor prognosis in human cancers. Expression of E-cadherin has not been reported previously in NPC, and its prognostic value in NPC is unknown. The purpose of this study was to examine the expression pattern of E-cadherin and its associated partner, beta-catenin, in NPC and their possible applications as prognostic markers to predict the clinical outcome of NPC. Expression of the E-cadherin and beta-catenin was examined by immunohistochemical methods in 74 cases of primary NPC and 17 of their corresponding lymph node metastases. Normal nasopharyngeal epithelium showed strong and homogeneous immunocytochemical staining of E-cadherin and beta-catenin at the cell membranes and intercellular junctions. In contrast, primary NPC showed variable and heterogeneous staining patterns of E-cadherin and beta-catenin. Loss of membranous E-cadherin expression was significantly associated with advanced stages of diseases (P<.001). Eighty percent to ninety percent of NPC in stages IV and V (Ho's staging), respectively, showed a reduced (<35%) membranous staining of E-cadherin compared with normal nasopharyngeal epithelium. Expression of beta-catenin also was downregulated in advanced NPC. Ninety percent to one hundred percent of NPC in stages IV and V (Ho's staging) expressed a reduction (<35%) of imnmunocytochemical staining of beta-catenin. The expression pattern of beta-catenin staining was strongly associated with the expression of E-cadherin (P<.001). Unlike E-cadherin, nuclear staining of beta-catenin expression was observed in some of the primary NPC and lymph node metastasis. Reduced expression of E-cadherin and beta-catenin expression was associated with a shorter survival of NPC patients (P<.001). In advanced NPC patients (stages IV and V), a significant difference in survival was observed in tumors with higher or lower levels of E-cadherin expression (P=.0224, log-rank test). These observations suggests that expression of E-cadherin and beta-catenin may have prognostic values in NPC patients. 相似文献
89.
Missense mutation in a von Willebrand factor type A domain of the alpha 3(VI) collagen gene (COL6A3) in a family with Bethlem myopathy 总被引:2,自引:0,他引:2
Pan TC; Zhang RZ; Pericak-Vance MA; Tandan R; Fries T; Stajich JM; Viles K; Vance JM; Chu ML; Speer MC 《Human molecular genetics》1998,7(5):807-812
The Bethlem myopathy is a rare autosomal dominant proximal myopathy
characterized by early childhood onset and joint contractures. Evidence for
linkage and genetic heterogeneity has been established, with the majority
of families linked to 21q22.3 and one large family linked to 2q37,
implicating the three type VI collagen subunit genes, COL6A1 (chromosome
21), COL6A2 (chromosome 21) and COL6A3 (chromosome 2) as candidate genes.
Mutations of the invariant glycine residues in the triple-helical
domain-coding region of COL6A1 and COL6A2 have been reported previously in
the chromosome 21-linked families. We report here the identification of a
G-->A mutation in the N-terminal globular domain-coding region of COL6A3
in a large American pedigree (19 affected, 12 unaffected), leading to the
substitution of glycine by glutamic acid in the N2 motif, which is
homologous to the type A domains of the von Willebrand factor. This
mutation segregated to all affected family members, to no unaffected family
members, and was not identified in 338 unrelated Caucasian control
chromosomes. Thus mutations in either the triple-helical domain or the
globular domain of type VI collagen appear to cause Bethlem myopathy.
相似文献
90.
Usefulness of immunohistochemistry in delineating renal spindle cell tumours. A retrospective study of 31 cases 总被引:3,自引:0,他引:3
Wang J Weiss LM Hu B Chu P Zuppan C Felix D Rausei-Mills V Chase DR 《Histopathology》2004,44(5):462-471
AIMS: To assess the usefulness of immunohistochemistry in delineating tumour diagnoses on a series of morphologically diagnosed renal spindle cell tumours (RSCTs). METHODS AND RESULTS: Formalin-fixed paraffin-embedded tissues from 31 morphologically diagnosed tumours were reinterpreted in light of newly obtained immunohistochemical information. By morphology, six had originally been classified as sarcomatoid carcinoma, five as spindle cell tumour (NOS), four as sarcoma (NOS), three as leiomyoma, three as leiomyosarcoma, and one each as fibrous polyp, hamartoma, neurilemmoma, mesoblastic nephroma, medullary fibroma, angiomyolipoma, haemangiopericytoma, malignant rhabdoid tumour, malignant Triton tumour, and carcinosarcoma. The application of immunohistochemistry verified the original diagnosis in 18 cases (18/31, 58%), confirming the diagnosis of sarcomatoid renal carcinoma (4/6), leiomyoma (2/3), leiomyosarcoma (3/3), sarcoma (NOS) (2/4), carcinosarcoma (1/1), malignant rhabdoid tumour (1/1), malignant Triton tumour (1/1), fibrous polyp (1/1), mesoblastic nephroma (1/1), hamartoma (1/1), and angiomyolipoma (1/1). Different tumour designations were suggested in 13 cases (13/31, 42%), including carcinosarcoma, sarcoma (NOS), leiomyosarcoma, solitary fibrous tumour, monomorphic/biphasic angiomyolipoma, endometrial stromal tumour, and congenital mesoblastic nephroma. CONCLUSIONS: Our data indicate that although morphology is most important in formulating the initial differential diagnosis, the addition of immunohistochemistry is vital in arriving at the correct classification of RSCTs. 相似文献