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   112121篇
  免费   11297篇
  国内免费   6191篇
耳鼻咽喉   836篇
儿科学   1141篇
妇产科学   1622篇
基础医学   31322篇
口腔科学   3368篇
临床医学   7243篇
内科学   15434篇
皮肤病学   2436篇
神经病学   8334篇
特种医学   2070篇
外国民族医学   24篇
外科学   9195篇
综合类   16515篇
现状与发展   21篇
一般理论   2篇
预防医学   3155篇
眼科学   2920篇
药学   11296篇
  17篇
中国医学   3527篇
肿瘤学   9131篇
  2024年   147篇
  2023年   1235篇
  2022年   2224篇
  2021年   3503篇
  2020年   3379篇
  2019年   3094篇
  2018年   3201篇
  2017年   3724篇
  2016年   4243篇
  2015年   4684篇
  2014年   7171篇
  2013年   8840篇
  2012年   6854篇
  2011年   8016篇
  2010年   6503篇
  2009年   6136篇
  2008年   6415篇
  2007年   6321篇
  2006年   5793篇
  2005年   4967篇
  2004年   4243篇
  2003年   3475篇
  2002年   2655篇
  2001年   2241篇
  2000年   1903篇
  1999年   1648篇
  1998年   1585篇
  1997年   1456篇
  1996年   1294篇
  1995年   1353篇
  1994年   1181篇
  1993年   1051篇
  1992年   856篇
  1991年   810篇
  1990年   697篇
  1989年   681篇
  1988年   580篇
  1987年   541篇
  1986年   468篇
  1985年   718篇
  1984年   664篇
  1983年   475篇
  1982年   577篇
  1981年   446篇
  1980年   381篇
  1979年   334篇
  1978年   226篇
  1977年   178篇
  1976年   165篇
  1975年   72篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Acute murine infection with T.cruzi results in polyclonal lymphocyteresponses manifested by blast transformation of a large fractionof B, CD4+, and CD8+ cells. We describe here the finding ofsignificant increases in the splenic representation of minorpopulations, Ly-1+ B cells and CD4-CD8- T cells. These lymphocytepopulations might play an important role in the host response,as shown by T.cruzi infection of hosts that had been lethallyirradiated and reconstituted with autologous bone marrow. Underthese conditions, the splenic polyclonal PFC responses are nearlyabrogated, and not restored by the transfer of syngeneic peritonealcells which, however, reconstitute T15 idiotype production inthe same hosts. Control levels of PFC responses, however, arereconstituted by transfer of syngeneic splenic T cells. Sincebone marrow-reconstituted animals contain normal numbers ofCD4+ and CD8+ T cells which are actually activated by infection,these results suggest the participation of other T cell populationsin the host response to infection, as also suggested by themarked increases in T cell receptor and messages detectedin the spleen of infected animals. The implications of thesefindings in immunopathology of Chagas' disease are discussed.  相似文献   
992.
We have previously shown that natural killer (NK) cell activity against K562 tumor cells is severely depressed in thermal injury patients. In this study we have investigated whether the low NK cell activity present in peripheral blood lymphocytes (PBL) from thermal injury patients could be enhanced byin vitro culture with interleukin 2 (IL2) and whether PBL obtained from these patients could generate lymphokine-activated killer (LAK) cell activity against NK insensitive tumor targets. NK cell activity in PBL obtained from 12 different patients was greatly enhanced against K562 tumor cells afterin vitro culture with IL2 for 3 days. In contrast, PBL obtained from these patients and incubated with IL2 had little to no cytotoxic activity when measured against a number of NK-insensitive tumor targets. The failure of PBL obtained from thermal injury patients to generate LAK cell activity was observed regardless of the culture time or the amount of IL2 added to the cultures. PBL from thermal injury patients demonstrated reduced proliferative responses to IL2 and, more importantly, contained suppressor cells which could inhibit the generation of LAK cell activity of normal PBL obtained from control individuals. These results clearly show that in some thermal injury patients NK cell activity can be enhanced by IL2 but these patients are defective in their ability to generate LAK cell activity.  相似文献   
993.
ABSTRACT: Changes in lymphocyte subsets in whole blood of normal pregnant and postpartum women were examined by flow cytometry with an automated leukocyte differential system. From the first trimester and throughout pregnancy, the absolute counts of T(CD3) and B(CD20) and T-cell subsets (CD4, CD8) decreased with a decrease in the absolute lymphocyte count, although the proportions of these cells remained unchanged except for a decrease in the percentage of T helper-inducer (CD4) cells in the first trimester. On the contrary, the percentage of NK/K (Leu 7) cells, but not of NK/K (CD16) cells, increased in the first trimester and then both gradually decreased in the second and third trimesters. In the postpartum period, the percentages and absolute counts of T(CD3) and NK/K (Leu 7) cells, but not of other cells, increased transiently. These changes of lymphocyte subsets may indicate suppression of immunological activity during pregnancy and its “increase” in the postpartum period.  相似文献   
994.
A reverse modification of the recently described enzyme-linked immunospot assay (ELISPOT), based on localized enzyme-substrate reactions in gel, is described for the enumeration of antigen-secreting cells using petri dishes coated with specific antibodies. As a model the detection of mouse and human immunoglobulin-secreting cells has been evaluated. Simple and sensitive, this new method, termed RELISPOT, can be adapted for the quantitation of secreted antigen thus providing additional information on the metabolic state of the population of cells tested.  相似文献   
995.
Summary 10 cases of thyroid medullary carcinoma (TMC) have been studied ultrastructurally and histochemically. Well differentiated calcitonin-producing C cells were present in all tumours, being prevalent in 9 cases. 5-Hydroxytryptamine (5HT) storing cells were found in two cases, somatostatin immunoreactive cells in at least 5 cases and ACTH-immunoreactive cells in 4 cases. Ultrastructurally, at least 3 types of apparently non-C cells were observed. Type 1 cells with large, poorly osmiophilic granules resembling those of gastroenteropancreatic D cells, were present in 6 cases; they appeared to correlate well with somatostatin immunoreactive cells. Type 2 cells with large osmiophilic granules were found in 5 cases; they resembled ACTH-MSH cells of the human pituitary and may correspond to the ACTH-immunoreactive cells of light microscopy. Type 3 cells with small granules and an unknown function were found in 6 cases, always in scarce number. It is concluded that TMC, although mainly made up of C cells, usually contains large proportions of other endocrine cell types.Supported in part by grant N. 75.00630.04 from the Italian National Research Council (C.N.R.). P.F. is a fellow of the Fondazione Anna Villa Rusconi, Varese  相似文献   
996.
Objective To study the distribution and quantity of CD44VCD24- cells in breast cancer tissue and the cell lines,and as well as its correlation with the expression of various breast cancer markers and molecular subtyping of breast carcinoma.Methods The expression of CD44 / CD24,estrogen receptor,progesterone receptor,HER2,human estrogen-induced protein PS2,bcl-2 and nm23 in 60 cases of invasive ductal carcinoma of breast were studied by either single or double immunohistochemical staining.The co-expression of CD44 and CD24 in 3 breast cancer cell lines (MCF-7,MDA-MB-468,and MDA-MB- 231) was also examined.Results The quantity and distribution of CD44 + /CD24- cells varied greatly and no specific patterns were identified.The percentage of CD44 + /CD24- in breast cancer was 65%.The amount of CD44+/CD24- cells did not correlate with the age of patients,lymph node metastasis,tumor  size,molecular subtypes and expression of various breast cancer markers in breast carcinoma.The proportion of CD44+/CD24- cells in MCF-7,MDA-MB-468,and MDA-MB-231 cell lines was < 1%,5% and > 80% ,respectively.Conclusions CD44+ /CD24- cells are demonstrated in certain breast cancer tissues and cell lines.However,there is no relationship obtained between the quantity or the distribution of these cells and the molecular subtyping or the clinicopathologic parameters in breast cancer.  相似文献   
997.
Triggering Receptor Expressed on Myeloid cells (TREM)2 deficiency originates a genetic syndrome characterized by bone cysts and presenile dementia, named Nasu-Hakola disease (NHD). Early onset dementia and marked involvement of frontal regions are features characterizing both NHD and other kinds of neurodegenerative disorders, such as Frontotemporal Lobar Degeneration (FTLD), and, in some cases, Alzheimer's disease (AD). Three Single Nucleotide Polymorphisms (SNPs) in TREM2 coding region were screened by allelic discrimination in a population of probable AD patients as well as FTLD patients as compared with age-matched controls. In addition, mutation scanning of the coding region of TREM2 gene was carried out in 7 patients with early onset AD (EOAD), 16 FTLD, and 20 controls. None of the SNPs analyzed was present, either in patients or controls. Moreover, mutation scanning of the five exons of TREM2 failed to detect the presence of novel polymorphisms. These data demonstrate that TREM2 coding region is highly conserved, implying a crucial role of this receptor. Further studies, including a functional analysis, are certainly required to clarify the role of TREM2 in neurodegenerative processes.  相似文献   
998.
潘萌  蒋浩琴  周芸  郑捷 《现代免疫学》2006,26(2):98-101
为研究、比较不同佐剂对诱导小鼠产生获得性免疫应答的不同作用,以卵清白蛋白(OVA)为抗原,分别混合完全弗氏佐剂(CFA)或Al(OH)3佐剂,对C57BL/6小鼠进行常规免疫,采用流式细胞技术对细胞内细胞因子IFN-γ和IL-4进行检测;ELISA方法对特异性抗OVA抗体滴度及抗体亚型进行了检测。结果显示在免疫后CFA组产生以IFN-γ为主的细胞因子而Al(OH)3组产生以IL-4为主的细胞因子;两组中均产生特异性抗OVA IgG抗体,但CFA组以IgG2a亚型为主,而Al(OH)3组则以IgG1亚型为主,不产生IgG2a亚型抗体。实验表明,经CFA加抗原免疫后机体产生的免疫应答以Th1型细胞免疫为主,抗体类型为IgG2a;而Al(OH)3佐剂则诱导机体产生Th2型细胞免疫应答,抗体类型为IgG1。  相似文献   
999.
Cadherin-17 (CDH17), also called liver–intestine cadherin, is a structurally unique member of the cadherin superfamily. Our serial analysis of gene expression demonstrated that CDH17 was one of the most up-regulated genes in advanced gastric carcinomas. CDH17 expression is known to be regulated by Cdx2. In the present study, we examined the expression of CDH17 in primary gastric carcinoma tissues by immunohistochemistry, and analyzed the correlation of CDH17 expression with clinicopathological characteristics and patients prognosis. CDH17 expression was detected in 63/94 (67%) of gastric adenocarcinomas in addition to intestinal metaplasia. The expression of CDH17 tended to be associated with intestinal type carcinoma, and carcinomas with CDH17 expression was significantly more frequent in advanced stage cases (80%) than in early stage (53%). The prognosis of patients with positive CDH17 expression was significantly poorer than that of the negative cases (P=0.0314). However, multivariate analysis revealed that CDH17 was not an independent prognostic factor. Six of seven cases that showed positive expression of Cdx2 simultaneously expressed CDH17 protein. These results suggested that the expression of CDH17 was characteristic of the advanced gastric carcinoma that is associated with poor prognosis.  相似文献   
1000.
B cell-activating factor of the tumor necrosis factor family (BAFF/BLys) plays a critical role in B cell survival and immune responses through its three receptors: BAFF receptor (BAFF-R/BR3), transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) and B cell maturation antigen (BCMA). Using specific antibodies, we have investigated the expression of BAFF-R on human tonsillar B cells and their functional roles in naive and germinal center (GC) B cell differentiation. Our studies show that BAFF-R is the dominant receptor on naive B cells. However, three receptors are differentially modulated during in vitro GC-B cell differentiation. BAFF-R expression increased initially and then decreased with a corresponding induction of TACI and BCMA expression during differentiation to plasma cells (PCs). Consistently, blocking of BAFF-R alone with specific mAb inhibited GC-B cell proliferation and PC generation in the early period of their differentiation, whereas depletion of BAFF with TACI-Ig exhibited consistent inhibition throughout the differentiation. Finally, histological and molecular analyses of human tonsil tissue revealed that follicular dendritic cells produce BAFF. In conclusion, BAFF in the GC plays an important role through more than one receptor, and the three known receptors are differentially modulated as GC-B cells differentiate to PCs.  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