全文获取类型
收费全文 | 154786篇 |
免费 | 12339篇 |
国内免费 | 3753篇 |
专业分类
耳鼻咽喉 | 1107篇 |
儿科学 | 2111篇 |
妇产科学 | 1845篇 |
基础医学 | 13855篇 |
口腔科学 | 2494篇 |
临床医学 | 22148篇 |
内科学 | 16079篇 |
皮肤病学 | 1088篇 |
神经病学 | 19238篇 |
特种医学 | 25102篇 |
外国民族医学 | 21篇 |
外科学 | 11584篇 |
综合类 | 19066篇 |
现状与发展 | 7篇 |
预防医学 | 11648篇 |
眼科学 | 2075篇 |
药学 | 12010篇 |
153篇 | |
中国医学 | 3204篇 |
肿瘤学 | 6043篇 |
出版年
2024年 | 512篇 |
2023年 | 2479篇 |
2022年 | 4704篇 |
2021年 | 6309篇 |
2020年 | 5868篇 |
2019年 | 5055篇 |
2018年 | 4960篇 |
2017年 | 5334篇 |
2016年 | 5765篇 |
2015年 | 5682篇 |
2014年 | 10286篇 |
2013年 | 10233篇 |
2012年 | 9236篇 |
2011年 | 10215篇 |
2010年 | 8287篇 |
2009年 | 8212篇 |
2008年 | 8271篇 |
2007年 | 7794篇 |
2006年 | 7006篇 |
2005年 | 6045篇 |
2004年 | 5096篇 |
2003年 | 4258篇 |
2002年 | 3386篇 |
2001年 | 3078篇 |
2000年 | 2606篇 |
1999年 | 2187篇 |
1998年 | 2152篇 |
1997年 | 2013篇 |
1996年 | 1682篇 |
1995年 | 1579篇 |
1994年 | 1383篇 |
1993年 | 1189篇 |
1992年 | 1023篇 |
1991年 | 914篇 |
1990年 | 729篇 |
1989年 | 639篇 |
1988年 | 593篇 |
1987年 | 552篇 |
1986年 | 499篇 |
1985年 | 587篇 |
1984年 | 494篇 |
1983年 | 301篇 |
1982年 | 326篇 |
1981年 | 292篇 |
1980年 | 277篇 |
1979年 | 175篇 |
1978年 | 163篇 |
1977年 | 137篇 |
1976年 | 98篇 |
1974年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The adjuvant monophosphoryl lipid A increases the function of antigen-presenting cells 总被引:3,自引:0,他引:3
De Becker G Moulin V Pajak B Bruck C Francotte M Thiriart C Urbain J Moser M 《International immunology》2000,12(6):807-815
The induction of immune responses in vivo is typically performed with antigens administered in external adjuvants, like alum, complete Freund's adjuvant, LPS and, more recently, monophosphoryl lipid A (MPL). However, the role of the adjuvant is still poorly defined. The aim of this study was to test whether the MPL affects the function of antigen-presenting cells (APC) in vitro and in vivo. Antigen-pulsed APC [including macrophages, B cells and dendritic cells (DC)] were incubated or not with MPL, and their ability to sensitize naive T cells was tested in vitro and in vivo. The data show that MPL enhances the ability of macrophages and B cells to sensitize naive T cells, and confers to them the capacity to induce the development of T(h)1 and T(h)2. Administration of MPL i.v. in mice results in the redistribution of fully mature DC in the T cell area of the spleen. These observations suggest that MPL may induce an antigen-specific primary immune response by provoking the migration and maturation of DC that are the physiological adjuvant of the immune system. 相似文献
992.
Qian BF El-Salhy M Melgar S Hammarström ML Danielsson A 《Clinical and experimental immunology》2000,120(3):424-433
Neuroendocrine peptides have a variety of physiological functions in the gastrointestinal tract. This study was carried out to investigate the impact of IL-2 deficiency on the neuroendocrine system in normal colon, and the neuroendocrine changes during colonic inflammation. Mice with homozygous disrupted IL-2 gene (IL-2-/-) spontaneously developed a bowel disease with similarities to human ulcerative colitis. Different types of colonic endocrine cells and myenteric nerves were analysed in the IL-2-/- mice using immunomorphometry. The neuropeptide contents in the colonic tissues were determined by radioimmunoassay. Age-matched healthy IL-2+/- and IL-2+/+ mice served as controls and the colonic IL-2 levels were compared between these two groups of mice by ELISA. Our data showed that less than half the amount of IL-2 was synthesized in the colon of IL-2+/- mice compared with the IL-2+/+ wild-type mice. Two major differences in the neuroendocrine colon were found between the mice with an intact and disrupted IL-2 gene. One was age-related. The frequencies of various endocrine cells and myenteric nerves increased with age in the IL-2+/+ mice. However, no such increases were seen in the mice with a disrupted IL-2 gene. Instead, the volume densities of enteroglucagon, serotonin cells and substance P (SP), vasoactive intestinal polypeptide (VIP) and total myenteric nerves were lower in the older IL-2+/- and IL-2-/- mice compared with the wild type. The other was disease-related. Polypeptide YY (PYY) cells and tissue levels of PYY, SP and VIP were significantly decreased in the IL-2-/- mice during the course of bowel inflammation compared with the healthy IL-2+/- and IL-2+/+ controls. These findings indicate that colonic neuroendocrine alterations did occur in the mice with a disrupted IL-2 gene and diminished local IL-2 level, suggesting a role of IL-2 in the regulation of the neuroendocrine system and a prevalent interaction between the immune and neuroendocrine systems in normal colon. On the other hand, there were some changes that seemed to correlate with the bowel inflammatory process. They might be associated with the impaired function in inflamed gut and contribute to the development and/or prolongation of disease. 相似文献
993.
N. Lindefors S. Brené M. Herrera-Marschitz H. Persson 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1990,80(3):489-500
Summary In situ hybridization was used to study the expression of prepro-neuropeptide Y (NPY), preprosomatostatin (SOM), preprotachykinin (PPT) and preprocholecystokinin (CCK) mRNA in caudate-putamen and frontoparietal cortex of rat brain with unilateral lesion of midbrain dopamine neurons. Neurons expressing NPY and SOM mRNA showed a similar distribution and the expression of both NPY and SOM appears to be regulated by dopamine in a similar fashion. Following a dopamine deafferentation, the numerical density of both NPY and SOM mRNA producing neurons almost doubled in the lesioned caudate-putamen with no change in the average grain density over positive neurons. Hence, in the intact caudate-putamen dopamine appears to suppress expression of these two neuropeptide genes leading to an activation of both NPY and SOM mRNA expression in many non- or low-expressing neurons when the level of dopamine is decreased. In the fronto-parietal cortex, on the other hand, dopamine appears to stimulate NPY and SOM gene expression. Thus, in the absence of dopamine about half of the NPY positive neurons disappeared. However, for SOM the number of positive neurons did not change, but rather most positive neurons appeared to have down-regulated their SOM mRNA expression. No evidence was found for a change in CCK mRNA expression by the dopamine deafferentation, while PPT mRNA expression decreased in the deafferented caudate-putamen. Consequently, dopamine exerts dissimilar effects on the expression of different neuropeptide genes, that in turn do not respond in the same way in different brain regions. 相似文献
994.
原位PCR技术检测石蜡包埋脑组织中人巨细胞病毒DNA 总被引:6,自引:0,他引:6
应用原位聚合酶链反应(ISPCR)技术检测了25例尸检畸形胎儿石蜡包埋脑组织中人巨细胞病毒(HCMV)DNA,并与普通PCR及原位杂交(ISH)进行了比较。ISPCR、PCR及ISH检测阳性率分别为44%,36%及20%。与ISH相比较,ISPCR不仅检出阳性率高,而且信号强度增强。研究结果提示,IS-PCR是诊断HCMV感染的快速、敏感、特异的实用方法。 相似文献
995.
N. Freudenberg P. Rahner C. Darda U. N. Riede M. Schubert K. Frenzer-Welle A. Kiss G. Veres T. Nees R. Lamers C. Kortsik 《Virchows Archiv : an international journal of pathology》1996,428(3):187-194
We investigated the reaction of the cellular immune system of liver and blood in the C57BL/6 mouse to a metastasizing Lewis lung carcinoma. The cellular immune system of the liver consists of mature and immature macrophages, B-cells, T-cells including their subpopulations, and natural killer cells, and their percentage frequencies differ significantly from those in the corresponding mononuclear blood cell (MBC) compartment. This suggests that the hepatic immune cells represent a system with autonomous function showing a typical homing of its members. Imminent metastasis to the liver is signalled by impressive alterations in the percentage frequencies of nonparenchymal liver cells (NPLC). There are a dramatic loss of mature macrophages, an increase in immature macrophages, a reduction of T-helper cells leading to a low CD4/CD8 ratio, and an increase in natural killer cells. In the blood, the corresponding precursor cells show comparable changes with a delay of at least 2 days. Early metastasis is accompanied by a significant increase in mononuclear NPLC producing tumour necrosis factor . The alterations in percentage frequencies of the NPLC during tumour metastasis differ markedly from the changes in these cells in the liver during endotoxinaemia. 相似文献
996.
Gerald A. Gronert David A. White 《Pflügers Archiv : European journal of physiology》1988,411(2):226-228
Continuous intravenous infusion in pigs of norepinephrine, to blood concentrations of 140 ng.ml–1, provided a test of the hypothesis that this sympathetic hormone can initiate malignant hyperthermia (MH). This study was performed during nitrous oxidepentobarbital anesthesia, and in part utilized sodium nitroprusside to maintain normal blood pressure and peripheral perfusion. Metabolic stimulation, or evidence of MH, did not occur in normal of susceptible pigs, as indicated by the lack of increase in both whole body O2 consumption and arterial lactate concentration. Next, in contrast, susceptible pigs manifested MH when exposed to halothane and succinylcholine, while normal pigs did not. We conclude that norepinephrine does not mediate or initiate porcine whole body stress responses characteristic of MH. 相似文献
997.
Partitioning in aqueous 2-phase systems was used to separate free and bound ligand in an immunoassay for beta 2-microglobulin. In order to get efficient separation in the phase system, the antibodies were modified to favour their partition in a different phase from that of antigen. However such modification of antibodies significantly decreased their binding capacity. This was overcome by using antibodies bound to previously modified staphylococci, which had proper partitioning behaviour. Alternatively, antibodies conjugated with biotin could be used in combination with modified avidin. This paper presents a method for the evaluation of data from immunoassays whereby 2-phase systems have been used to separate free and bound antigen. 相似文献
998.
hTRT催化功能区基因克隆及其在肿瘤中的表达 总被引:19,自引:2,他引:19
目的 研究端粒酶蛋白hTRT基因在肿瘤中的表达及其意义。方法 用RT-PCR法检查Hela细胞与PG细胞的hTRT表达水平,将Hela细胞的hTRT催化功能克隆,并进行测序比较,应用原位杂交技术对肿瘤组织中的hTRT和hTR(端粒酶RNA组分)基因进行检测。结果 Hela细胞与PG细胞均有hTRT表达,Hela细胞hTRT催化功能区cDNA序列与文献报道一致,原位杂交结果显示hTRT与hTR的协同 相似文献
999.
Sharma Sheela Wyatt Gail P. Elmore Eugene L. Steele Vernon E. 《Methods in Cell Science》1997,19(1):9-12
An in vitro model for screening potential chemopreventive agents using inhibition of anchorage-independent growth of a human lung tumor cell line, A427, is described. A427 cells were selected for the model development, as they are known to be tumorigenic in animals, can grow in soft agarose, and their growth can be inhibited by a well-known chemopreventive agent, 13-cis-retinoic acid. Cells are plated on agarose, allowed to develop colonies for 28 days, the stained colonies are enumerated, and the inhibition of spontaneous colony formation measured. A cytotoxicity test is used concurrently with anchorage independent assay for measuring the relative survival of cells to ensure that any observed inhibition of anchorage independent growth is due to the biological activity of the chemopreventive agents, as it uses human cells as substrates rendering the efficacy data feasible for direct extrapolation to humans. 相似文献
1000.
The chronological changes in the gene expression for three species of cytosolic fatty acid-binding proteins (FABPs) in the rat brain were examined by Northern and in situ hybridization analyses. The expression for heart(H)-FABP became evident after birth, with a gradual increase and confined to the gray matter, suggesting that the expression of H-FABP mRNA is neuron-specific in postnatal brain. The expression for brain(B)-FABP was very intense in the ventricular germinal zone, without expression in the cerebellar external granule cell layer, suggesting the dominant expression in the cells of glial lineage. B-FABP mRNA was transiently expressed in perinatal gray as well as white matter and the expression in glial cells persists only in the olfactory nerve fiber layer at the adult stage. On the other hand, the expression for skin type(S)-FABP was evident in the both ventricular germinal zone and cerebellar external granule cell layer, suggesting the expression in cells of neuronal lineage. The expression for S-FABP was evident in the prenatal gray matter and S-FABP mRNA was expressed in glial cells at early postnatal stage, whereafter the expression decreased to, but remained at weak levels in the adult brain. Discrete functions of the three FABPs were suggested in neurons and glia differentially at various developmental stages. 相似文献