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   13020篇
  免费   215篇
  国内免费   18篇
耳鼻咽喉   186篇
儿科学   744篇
妇产科学   274篇
基础医学   957篇
口腔科学   802篇
临床医学   974篇
内科学   2852篇
皮肤病学   328篇
神经病学   869篇
特种医学   242篇
外科学   1961篇
综合类   552篇
预防医学   1446篇
眼科学   157篇
药学   480篇
  17篇
中国医学   170篇
肿瘤学   242篇
  2024年   8篇
  2023年   42篇
  2022年   134篇
  2021年   287篇
  2020年   169篇
  2019年   1797篇
  2018年   1424篇
  2017年   799篇
  2016年   123篇
  2015年   140篇
  2014年   300篇
  2013年   270篇
  2012年   247篇
  2011年   294篇
  2010年   263篇
  2009年   200篇
  2008年   173篇
  2007年   166篇
  2006年   108篇
  2005年   91篇
  2004年   63篇
  2003年   63篇
  2002年   40篇
  2001年   45篇
  2000年   57篇
  1999年   33篇
  1998年   25篇
  1997年   22篇
  1996年   17篇
  1995年   19篇
  1994年   21篇
  1993年   16篇
  1991年   8篇
  1990年   6篇
  1988年   6篇
  1987年   5篇
  1985年   483篇
  1984年   725篇
  1983年   477篇
  1982年   555篇
  1981年   550篇
  1980年   496篇
  1979年   483篇
  1978年   444篇
  1977年   314篇
  1976年   395篇
  1975年   318篇
  1974年   281篇
  1973年   232篇
  1972年   7篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
儿童感觉统合失调及其影响因素的调查分析   总被引:17,自引:1,他引:16  
目的 研究儿童感觉统合失调与学习障碍及环境因素的关系。方法 采用感觉统合评定量表和学习障碍(PRS)筛查量表,分别对755名学龄儿童进行检测、分析。结果 感觉统合严重失调率为13.25%;感觉统合正常与失调儿童的学习障碍有统计学差异(P<0.005);其中在LD儿童中感觉统合失调率占63.51%;感觉统合失调与母孕期的情绪、是否足月顺产、出生后的喂养方式、居住环境、孩子1岁内有无高热、家长对孩子的态度及期待等因素有关(P<0.05)。结论 儿童感觉统合失调与环境因素、学习障碍有一定的关系。  相似文献   
32.
Disodium cromoglycate (DSCG) prevents allergic asthma by inhibiting the release of chemical mediators of immediate-type allergic reactions. The mechanism of this action is unclear and prompted us to examine the effect of DSCG on cyclic adenosine 3',5'-monophosphate (cAMP), the implicated regulator of IgE-mediated reactions. We used the peripheral blood lymphocyte as a model to mirror the biochemical events occurring in the allergic shock organs. Isolated peripheral blood lymphocytes from perennial allergic asthmatic children receiving only DSCG had significantly (p less than 0.005) lower phosphodiesterase (PDE) activity (mean 1.05 +/- 0.17 SE per 10(6) cells) than normal individuals (2.93 +/- 0.14) and allergic children receiving methylxanthines (4.08 +/- 0.28) or no medications (3.58 +/- 0.2). DSCG (10 mug/ml) significantly lowered PDE activity in normal lymphocytes (p less than 0.005) in a beef heart extract (p less than 0.001), and 100 mug/ml lowered PDE activity in fetal rabbit lung homogenates (p less than 0.001). DSCG (10 mug/ml) significantly elevated (p less than 0.01) cAMP concentration in normal human lymphocytes (118 +/- 38 vs 30 +/- 10 picomoles cAMP/10(6) lymphocytes). Thus, DSCG appears to inhibit chemical mediator release by increasing intracellular cAMP through the inhibition of cAMP PDE.  相似文献   
33.
Eleven subjects demonstrating clinical, skin, and inhalation sensitivity to grass or ragweed pollen underwent serial inhalation challenges, with and without orally administered theophylline, terbutaline, and prednisone. Comparisons of antigen sensitivity and mediator release were made during these challenges. All three drugs significantly reduced antigen sensitivity (PD20 inhalation units increasing from 670 to ≧ 3,280). Peak plasma histamine levels after antigen challenge decreased from 11.4 ng/ml to ≦ 3.4 ng/ml during all drug administrations. Similarly, the percent increase in serum neutrophil chemotactic activity (NCA) also decreased, from 96% to ≦ 36% during drug administrations. However, even at antigen doses resulting in bronchospasm during drug administration the systemic appearance of NCA and histamine were reduced. We conclude that prednisone, theophylline, and terbutaline significantly reduce antigen-induced bronchospasm and mediator release. The occurrence of bronchospasm despite the inhibition of histamine and NCA suggests either that the local concentration of these mediators are critical or that other mediators produce the bronchospasm observed.  相似文献   
34.
Hepatocytes are highly polarized epithelia. Loss of hepatocyte polarity is associated with various liver diseases, including cholestasis. However, the molecular underpinnings of hepatocyte polarization remain poorly understood. Loss of β-catenin at adherens junctions is compensated by γ-catenin and dual loss of both catenins in double knockouts (DKOs) in mice liver leads to progressive intrahepatic cholestasis. However, the clinical relevance of this observation, and further phenotypic characterization of the phenotype, is important. Herein, simultaneous loss of β-catenin and γ-catenin was identified in a subset of liver samples from patients of progressive familial intrahepatic cholestasis and primary sclerosing cholangitis. Hepatocytes in DKO mice exhibited defects in apical-basolateral localization of polarity proteins, impaired bile canaliculi formation, and loss of microvilli. Loss of polarity in DKO livers manifested as epithelial-mesenchymal transition, increased hepatocyte proliferation, and suppression of hepatocyte differentiation, which was associated with up-regulation of transforming growth factor-β signaling and repression of hepatocyte nuclear factor 4α expression and activity. In conclusion, concomitant loss of the two catenins in the liver may play a pathogenic role in subsets of cholangiopathies. The findings also support a previously unknown role of β-catenin and γ-catenin in the maintenance of hepatocyte polarity. Improved understanding of the regulation of hepatocyte polarization processes by β-catenin and γ-catenin may potentially benefit development of new therapies for cholestasis.

A hallmark of epithelial cells is polarization, which is achieved by the orchestration of external cues, such as cellular contact, extracellular matrix, signal transduction, growth factors, and spatial organization.1 Hepatocytes in the liver show a unique polarity by forming several apical and basolateral poles within a cell.2 The apical poles of adjacent hepatocytes form a continuous network of bile canaliculi into which bile is secreted, whereas the basolateral membrane domain forms the sinusoidal pole, which secretes various components, such as proteins or drugs, into the blood circulation.3 Loss of hepatic polarity has been associated with several cholestatic and developmental disorders, including progressive familial intrahepatic cholestasis (PFIC) and primary sclerosing cholangitis (PSC).4,5 Although the molecular mechanisms governing hepatocyte polarity have been extensively studied in the in vitro systems, there is still a significant gap in our understanding of how polarity is established within the context of tissue during development or maintained during homeostasis.6,7 Similarly, the molecular pathways contributing to hepatic polarity are not entirely understood, and a better comprehension of hepatic polarity regulation is thus warranted.Previous studies have confirmed the role of hepatocellular junctions, such as tight and gap junctions, in the maintenance of hepatocyte polarity.8,9 Studies done in vitro and in vivo have shown that loss of junctional proteins, such as zonula occludens protein (ZO)-1, junctional adhesion molecule-A, and claudins, lead to impairment of polarity and distorted bile canaliculi formation.10, 11, 12, 13 In addition, proteins involved in tight junction assembly, such as liver kinase B1, are also involved in polarity maintenance.14 Among adherens junction proteins, various in vitro cell culture models have confirmed the role of E-cadherin in the regulation of hepatocyte polarity, possibly through its interaction with β-catenin.15,16 However, there is a lack of an in vivo model to study the role of adherens junction proteins in hepatocyte polarity and their misexpression contributing to various liver diseases.β-Catenin plays diverse functions in the liver during development, regeneration, zonation, and tumorigenesis.17, 18, 19 The relative contribution of β-catenin as part of the adherens junction is challenging to study because like in other tissues, γ-catenin compensates for the β-catenin loss in the liver.20,21 To address this redundancy, we previously reported a hepatocyte-specific β-catenin and γ-catenin double-knockout (DKO) mouse model was reported.22 Simultaneous deletion of β-catenin and γ-catenin in mice livers led to cholestasis, partially through the breach of cell-cell junctions. However, more comprehensive understanding of the molecular underpinnings of the phenotype is needed.In the current study, prior preclinical findings of dual β-catenin and γ-catenin loss were extended to a subset of PFIC and PSC patients. In vivo studies using the murine model with hepatocyte-specific dual loss of β-catenin and γ-catenin showed complete loss of hepatocyte polarity compared to the wild-type controls (CONs). Loss of polarity in DKO liver was accompanied by epithelial-mesenchymal transition (EMT), activation of transforming growth factor (TGF)-β signaling, and reduced expression of hepatocyte nuclear factor 4α (HNF4α). Our findings suggest that β-catenin and γ-catenin and in turn adherens junction integrity, are critical for the maintenance of hepatocyte polarity, and any perturbations in this process can contribute to the pathogenesis of cholestatic liver disease.  相似文献   
35.
目的 探讨香港与澳门两地中小学学校辅导的发展,就辅导工作的内容、开展情况、辅导人员在建设上的差别以及发展速度相异的原因等方面作分析。方法 本研究以香港及澳门中小学的学校辅导员/社工为调查对象,利用自编问卷方式进行调查.结果 (1)两地的辅导员都一致认为,通过学校辅导服务可以帮助中学生建立良好的社交行为及人际关系,(2)两地的中小学都在帮助学生更好地接纳他人及尊重他人这个项目上都做得较好;(3)两地的中小学校辅导的目标不再是以处理学生的偏差行为为主,转而注重学生的个人潜能发展;(4)就课堂辅导活动开展的情况来看,香港在班级辅导、全年级辅导及全校性辅导方面都做得比较好,而澳门的全校性辅导通有待加强。至于课堂以外的辅导活动,两地均以个别晤谈,团体辅导、心理卫生讲座以及工作坊等方式开展辅导活动为多。(5)在持介制度上,香港中小学都做得比较完善;(6)咨询服务方面,香港小学做得较多,而澳门则是中学做得较多;(7)新生适应服务方面,香港较澳门做得较多;(8)香港的学校比澳门学校更多地与其它机构共同合辩小区教育;(9)香港及澳门的中学辅导员主要是学校自聘/校内编制,两地的中学社工主要是由政府资助民间志愿机构派驻。香港的小学导员以学校自聘/校内编制和政府派驻为主,香港的小学社工以政府直接派驻为多;澳门的小学辅导员为政府派驻,小学社工则由政府资助民间志愿机构派驻为多。(10)对于两地学校辅导人员学历的比较,香港中学及小学专职辅导贝、专职社工的学历均较澳门为高.结论 两地在学校辅导目标上比较一致;两地均建立了发展辅导为主,预防辅导及治疗辅导并重的辅导模式;家庭问题及人际关系问题为两地中小学生的困扰问题;两地的学校辅导活动呈现一个多元化的局面,但香港较澳门丰富;澳门需要建立完善的转介机构。  相似文献   
36.
Spleen cells from F1 hybrid mice injected into newborn parental mice induce a state of cytolytic unresponsiveness to the corresponding alloantigens. However, these mice develop a transient autoimmune syndrome characterized by the production of multiple autoantibodies and glomerulonephritis. Previous reports indicated that the depletion of F1 donor T cells, shortly prior the injection into parental mice, does not interfere with any of these events. Here, we have explored whether the continuous absence of T cells in F1 mice influences the ability of their spleen cells to induce neonatal tolerance to alloantigens and the associated autoimmune manifestations. Our results revealed that spleen cells from athymic (BALB/c × C57BL/6) F1 hybrid (CB6F1) nulnu mice or from euthymic CB6F1 mice depleted from birth of CD4+ T cells, but not of CD8+ T cells, are unable to induce neonatal tolerance to alloantigens and autoimmune manifestations. By contrast, the partial reconstitution of T cells in CB6F1 nulnu mice, after the neonatal graft of a syngeneic thymus, restored the capacity of spleen cells from these mice to induce tolerance and autoimmunity when injected into newborn BALB/c mice. These results demonstrate that the functional defect of spleen cells from athymic CB6F1 nulnu mice to induce neonatal tolerance to alloantigens is directly related to the long-term absence of mature CD4+ T cells. Interestingly, a new increase in the titers of anti-DNA Ab was observed when spleen cells from athymic CB6F1 nulnu mice were injected into adult BALB/c mice that had been tolerized at birth with normal CB6F1 spleen cells. This finding indicates that B cells from CB6F1 nulnu mice recover their capacity to interact with alloreactive Th2 cells when they are placed into mice having functional CD4+ T cells. These data indicate that the continuous absence of CD4+ T cells causes a reversible functional defect in F1 spleen cells that determines their inability to induce neonatal tolerance and autoimmunity.  相似文献   
37.
目的探讨脊柱侧弯后路矫形内固定术的配合及护理方法。方法对10例青少年患者行脊柱侧弯后路矫形内固定术,配合医生手术并严密观察病情变化。结果所有患者手术过程顺利,无一例脑脊液漏,脊髓损伤及切口感染等术后并发症发生,术后随访两年脊柱侧弯畸形均得到了明显矫正。结论手术护士熟悉手术步骤,全面掌握各种仪器及器械操作是手术配合成功的关键。完善的术前准备及密切的术中观察是减少脊柱侧弯病人术中并发症的重要因素。  相似文献   
38.
The turnover rates of adrenaline in the medial preoptic area and mediobasal hypothalamus, areas which, respectively, include the cell bodies and terminals of luteinizing hormone-releasing hormone neurons, have been measured in female rats on pro-oestrus, the day of the preovulatory surge of luteinizing hormone, and on dioestrus, the preceding day. A rise in the rate of turnover was found in the medial preoptic area coinciding with the surge of luteinizing hormone in the late afternoon of pro-oestrus; the rate of turnover at this time was higher than at the same time on dioestrus. No changes in turnover rate were found in the mediobasal hypothalamus within either of these days.The results indicate that the adrenaline-containing projections to the preoptic area may be actively involved in the production of the spontaneous preovulatory surge of luteinizing hormone in rats.  相似文献   
39.
Aqueous extracts of tree pollen were partially purified and polymerized with methods previously established for preparation of ragweed and grass polymers. The polymerized tree preparations were antigenic as demonstrated by ability to elicit immediate-type skin reactivity in humans and to induce an immune response in rabbits. The polymerized tree antigen was 100- to 10,000-fold less skin reactive than monomer tree antigen in tree pollen-sensitive patients but both preparations had similar antigenicity in rabbits. These results demonstrate that polymerized tree antigens can be prepared and should have the therapeutic potential already demonstrated for polymerized ragweed preparations.  相似文献   
40.
The serum levels of IgE, IgG, IgA, and IgM of 27 American-born Filipino children 5 to 17 years of age were measured and found to be significantly higher than those of a control group of 24 Caucasian children of similar age distribution and attending the same general pediatric clinics. The geometric mean of serum IgE of the Filipinos was 227 U. per milliliter and of the Caucasians, 69 U. per milliliter (p < 0.01). The geometric means of other serum immunoglobulin levels of the Filipinos by comparison with the Caucasians were: IgG, 1,303 and 1,010 mg. per 100 ml. (p < 0.01); IgA, 195 and 120 mg. per 100 ml. (p < 0.001); and IgM, 141 and 92 mg. per 100 ml. (p < 0.02), respectively. The incidence of atopic disease was higher in the Filipino study group (48 per cent) than in the Caucasian control group (25 per cent); eczema was especially prevalent in the Filipino group. Elevated serum IgE levels were associated with atopic disease in both racial groups; however, there was no correlation between serum level of IgG, IgA, or IgM and atopy.  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