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   96141篇
  免费   8755篇
  国内免费   4710篇
耳鼻咽喉   716篇
儿科学   2067篇
妇产科学   1636篇
基础医学   11249篇
口腔科学   2158篇
临床医学   9645篇
内科学   15708篇
皮肤病学   1412篇
神经病学   7598篇
特种医学   1809篇
外国民族医学   31篇
外科学   7797篇
综合类   16596篇
现状与发展   13篇
预防医学   7595篇
眼科学   2838篇
药学   9272篇
  29篇
中国医学   3457篇
肿瘤学   7980篇
  2024年   161篇
  2023年   1114篇
  2022年   2118篇
  2021年   3392篇
  2020年   3069篇
  2019年   2788篇
  2018年   2779篇
  2017年   3159篇
  2016年   3473篇
  2015年   3393篇
  2014年   6057篇
  2013年   6748篇
  2012年   6298篇
  2011年   6953篇
  2010年   5797篇
  2009年   5444篇
  2008年   5675篇
  2007年   5683篇
  2006年   5118篇
  2005年   4538篇
  2004年   3840篇
  2003年   3317篇
  2002年   2744篇
  2001年   2370篇
  2000年   1990篇
  1999年   1709篇
  1998年   1462篇
  1997年   1251篇
  1996年   1127篇
  1995年   1025篇
  1994年   836篇
  1993年   652篇
  1992年   576篇
  1991年   442篇
  1990年   411篇
  1989年   310篇
  1988年   245篇
  1987年   193篇
  1986年   160篇
  1985年   253篇
  1984年   205篇
  1983年   126篇
  1982年   177篇
  1981年   100篇
  1980年   113篇
  1979年   65篇
  1978年   43篇
  1977年   33篇
  1976年   27篇
  1975年   23篇
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
991.
血管内皮生长因子在子宫内膜异位症发病中的作用   总被引:4,自引:1,他引:4  
目的探讨血管内皮生长因子(vascularendothelialgrowthfactor,VEGF)在子宫内膜异位症(endometriosis,EM)发病中的作用。方法应用免疫组织化学方法并结合图像分析技术。结果正常子宫内膜和EM在位内膜腺上皮细胞的VEGF随月经周期呈现规律性变化,分泌期腺上皮VEGF蛋白表达量显著高于增殖期(P<0.05)。在增殖期,EM在位子宫内膜腺上皮VEGF的表达与正常子宫内膜相比无明显差别,但在分泌期,EM在位子宫内膜腺上皮细胞中VEGF的表达强度明显高于正常子宫内膜(P<0.01)。EM在位内膜腺上皮的VEGF含量显著高于同组卵巢子宫内膜异位囊肿的异位腺上皮(P<0.01)。结论表明VEGF的表达异常与EM的发病有关。  相似文献   
992.
The effects of cystic fibrosis (CF) serum and culture medium from CF fibroblasts on ion distribution in rat submandibular gland cells were investigated by X-ray microanalysis. These effects were compared to the effects of normal serum and culture medium from normal fibroblasts, of cholinergic and adrenergic agonists, and of the uncoupler 2,4-dinitrophenol.

Incubation of gland tissue with CF serum or normal serum caused a significant decrease in potassium and calcium concentrations and an increase in sodium in mucous acinar and serous granular duct cells. CF serum gave a significantly larger decrease of the potassium level than normal serum.

Culture medium from CF fibroblasts altered the cellular ion content in a way similar to CF serum. Exposure to medium from cultured normal fibroblasts did not affect the elemental composition of the gland cells significantly, compared to incubation with fresh medium or buffer. Hence, fibroblast culture medium is more suitable than serum to test specific effects of CF-associated factors.

The changes in elemental composition of gland eelIs caused by CF serum or CF fibroblast culture medium mimic some of the effects of the agonist car-bachol. They could, however, also in part result from nonspecific changes in membrane permeability.  相似文献   
993.
Mutations in the fibroblast growth factor receptor genes (FGFR) have been known to be associated with many craniosynostosis syndromes with overlapping phenotypes. We studied a 15‐year‐old Thai boy with an unspecified craniosynostosis syndrome characterized by multiple suture craniosynostoses, a persistent anterior fontanel, corneal scleralization, choanal stenosis, atresia of the auditory meatus, broad thumbs and great toes, severe scoliosis, acanthosis nigricans, hydrocephalus, and mental retardation. Radiography revealed bony ankyloses of vertebral bodies of T9–12, humero‐radio‐ulnar joints, intercarpal joints, distal interphalangeal joints of fifth fingers, fibulo‐tibial joints, intertarsal joints, and distal interphalangeal joints of the first toes. The patient was a heterozygous for a 870G → T change resulting in a W290C amino acid substitution in the extracellular domain of the fibroblast growth factor receptor 2 gene (FGFR2). This mutation has previously been reported in a patient with severe Pfeiffer syndrome type 2 that is distinct from the craniosynostosis in our patient. These findings emphasize locus, allelic, and phenotypic heterogeneity of craniofacial‐skeletal‐dermatological syndrome due to FGFR2 mutations. © 2002 Wiley‐Liss, Inc.  相似文献   
994.
七种中药小分子物质对淋巴细胞杀伤活性的影响   总被引:6,自引:0,他引:6  
用透析的方法从枸杞、槐籽、五谷虫(家蝇幼虫)、三七、小牛胸腺、白芍、茯苓,七种中药中获得小分子物质(分子量小于12000),系统地研究这些中药提取物对小鼠脾细胞杀伤活性的影响。结果发现枸杞、槐籽、五谷虫的透析外液不同程度地增强小鼠脾细胞杀伤活性。枸杞外液能抑制小鼠体内S180的生长;手术后乳腺癌病人使用枸杞小分子注射液,其外周血淋巴细胞的杀伤活性明显高于对照组。研究表明枸杞小分子成分经加热处理后,其有效性消失。  相似文献   
995.
Abstract: The effect of TGFβ1 and IL-12 on calcium-independent cytotoxic pathways was investigated. We have previously demonstrated that the regulatory effect of TGFβ1 and IL-12 on human alloreative CTL activity was associated with regulation of perform and granzyme B gene expression. To determine the effect of both cytokines on the alternative cytotoxic pathway involving FasL and mTNF, we first investigated the expression of both molecules on human primary alloactivated T cells. Our results show that human allostimulated T lymphocytes express FasL. Cell lysis experiments demonstrate that the FasL cytotoxic pathway is involved in the killing of specific target cells mediated by human alloreactive CTL. In addition, allogeneic stimulation induced significant mTNF expression on both CD4+ and CD8+ responder T cells. Using TNF-sensitive target cells, we also demonstrate that the mTNF-mediated cytotoxic pathway is involved in the cytotoxic activity of human primary allostimulated T lymphocytes. Neither TGFβ1 nor IL-12 had an effect on FasL or mTNF expression. Furthermore, addition of TGFβ1 or IL-12 at the initiation of the MLR had no significant effect on Fas- and mTNF-mediated cytotoxicity.
Taken together, our results provide a novel insight into the differences between regulation by cytokines of perforin-dependent and -independent cytotoxic mechanisms. Unlike their role in the perforin/granzyme B pathway, TGFβ1 and IL-12 do not appear to mediate any regulatory effect on FasL and mTNF cytotoxic pathways used by human alloreactive primary CTL.  相似文献   
996.
997.
The intent of the present study was to use chemical or electrical stimulation of cerebellar afferents to determine how different stimulation paradigms affect the pattern of activation of different populations of neurons in the cerebellar cortex. Specifically, we analyzed immediate changes in neuronal activity, identified neurons affected by different stimulation paradigms, and determined the time course over which neuronal activity is altered. In the present study, we used either systemic (harmaline) or electrical stimulation of the inferior cerebellar peduncle (10 and 40 Hz) to alter the firing rate of climbing and mossy fiber afferents to the rat cerebellum and an antibody made against the proto-oncogene, c-fos, as a marker to identify activated neurons and glia. In control animals, only a few scattered granule cells express nuclear Fos-like immunoreactivity. Although no other cells show Fos-like immunoreactivity in their nuclei, Purkinje cells express Fos-like immunoreactivity within their somatic and dendritic cytoplasm in control animals. Within 15 min of chemical or electrical stimulation, numerous granule and glial cells express Fos-like immunoreactivity in their nuclei. Cells in the molecular layer express Fos-like immunoreactivity following harmaline stimulation in a time and lobule specific manner; they do not appear to be activated in the electrical stimulation paradigm. Following harmaline injections, there is an initial loss of Fos-like immunoreactivity in the cytoplasm of Purkinje cells; 90 min later, nuclear staining is observed in a few scattered Purkinje cells. Following electrical stimulation, the cytoplasmic staining in Purkinje cells is enhanced; it is never present in the nucleus. Data derived from this study reveal cell-specific temporal and spatial patterns of c-Fos activation that is unique to each paradigm. Further, it reveals the presence of an activity dependent protein in the cytoplasm of Purkinje cell somata and dendrites.  相似文献   
998.
目的:探讨心房钠尿肽(ANP)对脂多糖(LPS)血症大鼠急性肺损伤的作用和机制。方法: 大鼠静脉给予LPS(2 mg·kg-1)后立即静脉给予ANP(2 μg·kg-1),记录动物平均动脉血压(MAP)、检测血浆一氧化氮(NO)和内皮素(ET)浓度、测定肺水含量并做肺组织病理学检查。结果: 给予LPS的大鼠,MAP持续下降,至4 h MAP(8.1±2.6)kPa;血浆NO和ET浓度均显著升高(P<0.01 vs control);4 h肺湿干比(5.15±0.43),显著高于对照组(P<0.05);大鼠肺组织病理学检查呈现肺间质水肿。LPS+ANP组大鼠MAP在给药初期的短暂下降后逐步回升,至4h MAP(13.4±2.9)kPa(P<0.05 vs LPS);4 h血浆NO水平和ET浓度均显著下降(P<0.05 vs LPS),但仍明显高于对照组(P<0.01 vs control);肺湿干比(4.57±0.35)与对照组没有显著差异;肺组织病理学改变较LPS组明显减轻。结论: ANP对LPS引起的急性肺损伤有治疗作用,能调节LPS引起的动脉血压的持续下降,上述作用可能与ANP拮抗ET的产生、降低NO的分泌有关。  相似文献   
999.
Aims: Little is known about the physiological regulation of the human intestinal di/tri‐peptide transporter, hPepT1. In the present study we evaluated the effects of epidermal growth factor (EGF) and insulin on hPepT1‐mediated dipeptide uptake in the intestinal cell line Caco‐2. Methods: Caco‐2 cells were grown on filters for 23–27 days. Apical dipeptide uptake was measured using [14C]glycylsarcosine([14C]Gly‐Sar). HPepT1 mRNA levels were investigated using RT‐PCR, cytosolic pH was determined using the pH‐sensitive fluorescent probe BCECF. Results: Basolateral application of EGF increased [14C]Gly‐Sar uptake with an ED50 value of 0.77 ± 0.25 ng mL?1 (n = 3?6) and a maximal stimulation of 33 ± 2% (n = 3?6). Insulin stimulated [14C]Gly‐Sar uptake with an ED50 value of 3.5 ± 2.0 ng mL?1 (n = 3?6) and a maximal stimulation of approximately 18% (n = 3?6). Gly‐Sar uptake followed simple Michaelis‐Menten kinetics. Km in control cells was 0.98 ± 0.11 mM (n = 8) and Vmax was 1.86 ± 0.07 nmol cm?2 min?1 (n = 8). In monolayers treated with 200 ng mL?1 of EGF, Km was 1.11 ± 0.05 mM (n = 5) and Vmax was 2.79 ± 0.05 nmol cm?2 min?1 (n = 5). In monolayers treated with 50 ng mL?1 insulin, Km was 1.03 ± 0.08 mM and Vmax was 2.19 ± 0.06 nmol cm?2 min?1 (n = 5). Kinetic data thus indicates an increase in the number of active transporters, following stimulation. The incrased Gly‐Sar uptake was not accompanied by changes in hPepT1 mRNA, nor by measurable changes in cytosolic pH. Conclusions: Short‐term stimulation with EGF and insulin caused an increase in hPepT1‐mediated uptake of Gly‐Sar in Caco‐2 cell monolayers, which could not be accounted for by changes in hPepT1 mRNA or proton‐motive driving force.  相似文献   
1000.
Varicocele--the most common cause of male factor infertility?   总被引:5,自引:0,他引:5  
Varicocele is often cited as the most common cause of male factor infertility. Arguments in support of this statement include reports of increased prevalence of varicocele in populations of infertile men compared with fertile or otherwise unselected men, association of varicocele with abnormal semen parameters, and improvements in semen parameters and/or pregnancy rates after varicocele repair. Logically, there would appear to be three possibilities regarding the relationship between varicocele and fertility: (i) varicocele has no association with or effect on male fertility; (ii) varicocele may be associated with, but is not the cause of, male subfertility; and (iii) varicocele is a direct cause of male subfertility. In the following, we review evidence from the literature for and against these three possibilities: at the current time, available evidence appears inadequate to confirm or deny any of these three possibilities. Since the ultimate goal of infertile couples is to conceive, it seem logical that future varicocele research should focus primarily on adequately powered, controlled clinical trials in well-characterized infertile couples, randomized to intervention or appropriate controlled observation, with pregnancy as the primary outcome.  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