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   1562篇
  免费   100篇
  国内免费   7篇
耳鼻咽喉   10篇
儿科学   54篇
妇产科学   19篇
基础医学   162篇
口腔科学   61篇
临床医学   174篇
内科学   248篇
皮肤病学   87篇
神经病学   119篇
特种医学   139篇
外科学   175篇
综合类   48篇
预防医学   124篇
眼科学   84篇
药学   123篇
中国医学   3篇
肿瘤学   39篇
  2021年   29篇
  2020年   17篇
  2019年   10篇
  2018年   26篇
  2017年   13篇
  2016年   28篇
  2015年   18篇
  2014年   28篇
  2013年   47篇
  2012年   59篇
  2011年   47篇
  2010年   42篇
  2009年   52篇
  2008年   46篇
  2007年   66篇
  2006年   57篇
  2005年   50篇
  2004年   47篇
  2003年   57篇
  2002年   58篇
  2001年   35篇
  2000年   33篇
  1999年   47篇
  1998年   43篇
  1997年   30篇
  1996年   25篇
  1995年   22篇
  1994年   28篇
  1993年   26篇
  1992年   21篇
  1991年   26篇
  1990年   28篇
  1989年   27篇
  1988年   29篇
  1987年   45篇
  1986年   42篇
  1985年   38篇
  1984年   43篇
  1983年   26篇
  1982年   29篇
  1981年   28篇
  1980年   21篇
  1979年   12篇
  1978年   14篇
  1976年   16篇
  1974年   11篇
  1971年   9篇
  1968年   12篇
  1967年   17篇
  1966年   11篇
排序方式: 共有1669条查询结果,搜索用时 15 毫秒
41.
胃肠胰胰岛淀粉样多肽的定位和表达   总被引:2,自引:3,他引:2  
胰岛淀粉样多肽(islet armyloid polypeptide,IAPP)是1986年瑞典学者Westermarket al[1,2 ]从胰岛素瘤患者的瘤组织,糖尿病猫及Ⅱ型糖尿病患者胰岛淀粉样沉积物中分离出来的一种多肽,几乎在同时,英国生物化学家Cooper et al[3,4]也从Ⅱ型糖尿病患者的胰岛淀粉样沉积物中分离出该肽.IAPP又称为amylin.对IAPP的分子结构、基因表达和生理作用等已有许多报道[5].近年来,在IAPP定位、表达及胃肠胰IAPP免疫反应(immunoreactive,IR)细胞定位、发生、发育方面的研究报道,为探讨IAPP的生理作用及疾病状态下的改变,提供了形态学依据,现综述如下.  相似文献   
42.
Mouse polyclonal antisera were raised to the Mr 130,000 and Mr 115,000 cell surface glycoproteins, desmocollins, of desmosomes from bovine nasal epithelium. Immunoblotting confirmed that the antisera were specific for the desmocollins. An immunofluorescence study showed that the antisera distinguished between the basal and suprabasal layers of bovine and human epidermis. The antibodies reacted with cultured keratinocytes only after calcium-induced stratification. In epidermis, therefore, there appears to be a difference between the desmocollins of basal and suprabasal cells that may be important in relation to epidermal differentiation. Previous work has shown that polyclonal antisera raised in other animals (guinea pigs and rabbits) against desmocollins, as well as against other desmosomal components, react with all desmosome-containing epithelia. In contrast, an immunofluorescence survey of bovine, rat, and human tissues showed that the present mouse antisera stained only suprabasal skin cells and the arachnoid layer of the meninges, demonstrating that these have common determinants that distinguished their desmocollins from those of all other tissues. The antibodies also stained 11 of 12 meningiomas and, therefore, may be useful as a marker not only for the diagnosis of these tumors but also for investigation of their histogenesis.  相似文献   
43.
This short-term, longitudinal interview study used an ecological framework to explore protective factors within the child, the caregiver, the caregiver-child relationship, and the community that might moderate relations between community violence exposure and subsequent internalizing and externalizing adjustment problems and the different patterns of protection they might confer. Participants included 101 pairs of African American female caregivers and one of their children (56% male, M = 11.15 yrs, SD = 1.28) living in high-violence areas of a mid-sized southeastern city. Child emotion regulation skill, felt acceptance from caregiver, observed quality of caregiver-child interaction, and caregiver regulation of emotion each were protective, but the pattern of protection differed across level of the child's ecology and form of adjustment. Implications for prevention are discussed.  相似文献   
44.
The medial preoptic area (MPOA) is an integral site for male sexual behavior. Dopamine is released in the MPOA before and during copulation and facilitates male rat sexual behavior. Repeated sexual experience and noncopulatory exposures to an estrous female facilitate subsequent copulation. However, the neurobiological mechanisms that mediate such enhancement remain unclear. Here, we examined the role of dopamine D? receptors in the MPOA in experience-induced enhancement of male sexual behavior in rats. In experiment 1, microinjections of the D? antagonist SCH-23390 into the MPOA before each of seven daily 30-min noncopulatory exposures to a receptive female impaired copulation on a drug-free test on Day 8, compared to vehicle-treated female-exposed animals. Copulatory performance in drug-treated animals was similar to that of vehicle-treated males that had not been preexposed to females. This effect was site specific. There were no group differences in locomotor activity in an open field on the copulation test day. In experiment 2, a separate cohort of animals was used to examine phosphorylation of dopamine- and cAMP-regulated phosphoprotein (DARPP-32) in the MPOA of animals with acute and/or chronic sexual experience. DARPP-32 is a downstream marker of D? receptor signaling and substrate of cAMP-dependent protein kinase (PKA). Western immunoblot analysis revealed that p-DARPP-32 expression was greatest in the MPOA of males that received both acute and chronic sexual experience, compared to all other mated conditions and na?ve controls. These data suggest that D? receptors in the MPOA contribute to experience-induced enhancement of male sexual behavior, perhaps through a PKA regulated mechanism.  相似文献   
45.
At the University of California Davis Medical Center, a screening fetal ultrasound examination (level I or II) incorporates a comprehensive segmental evaluation of the fetal heart. This study evaluated the reliability of the fetal ultrasound exam in the detection of abnormal heart anatomy. Our retrospective study reviewed results of 614 antenatal patients that had a screening fetal ultrasound exam. All patients subsequently underwent a detailed targeted fetal cardiac ultrasound exam performed by a pediatric cardiac sonographer and reviewed by a board-certified pediatric cardiologist. Of these 614 patients, 60 fetuses had structural heart disease by the targeted fetal exam. The screening fetal ultrasound exam correctly identified 55 of the 60, with 5 false negatives (8.3% false-negative rate) and 1 false positive (1.7% false-positive rate). Our study suggests that if a screening fetal ultrasound exam incorporates a segmental evaluation of the fetal heart it can reliably detect abnormal heart anatomy. At our institution a targeted fetal cardiac exam is now used to confirm and provide detailed assessment of the heart anatomy when a screening fetal exam is positive for heart disease.  相似文献   
46.
Purpose: the purpose of this study is to identify risk factors for familial, likely genetically-determined, preterm birth.

Materials and methods: We performed a case–control study, enrolling 211 patients (103 cases and 108 controls). Cases delivered between 20 and 35 weeks gestation, with a prior preterm birth or first-degree relative born prematurely. Controls delivered between 37–42 weeks. Groups were compared using a comprehensive questionnaire validated by medical record. Multivariate logistic regression assessed risk factor associations.

Results: Of cases, 30% reported bleeding during pregnancy compared with 5% of controls, adjusted odds ratio (adjOR) 9.0, 95%CI 3.31–24.47. Of cases that delivered at 20–28 weeks, 44.8% reported bleeding during pregnancy compared with 24.6% at 29–35 weeks, p?=?.04. Other associations were prior first-trimester miscarriage adjOR 2.55 (CI 1.21–5.35) or second-trimester miscarriage, adjOR 6.3 (CI 1.76–22.56).

Conclusions: Bleeding during pregnancy and prior miscarriage were significantly associated with familial preterm birth. The magnitude of effect for bleeding in pregnancy was higher with earlier preterm births. These associations warrant further investigation.  相似文献   
47.
48.
We developed a simplified microarray test for detecting and identifying mutations in rpoB, katG, inhA, embB, and rpsL and compared the analytical performance of the test to that of phenotypic drug susceptibility testing (DST). The analytical sensitivity was estimated to be at least 110 genome copies per amplification reaction. The microarray test correctly detected 95.2% of mutations for which there was a sequence-specific probe on the microarray and 100% of 96 wild-type sequences. In a blinded analysis of 153 clinical isolates, microarray sensitivity for first-line drugs relative to phenotypic DST (true resistance) was 100% for rifampin (RIF) (14/14), 90.0% for isoniazid (INH) (36/40), 70% for ethambutol (EMB) (7/10), and 89.1% (57/64) combined. Microarray specificity (true susceptibility) for first-line agents was 95.0% for RIF (132/139), 98.2% for INH (111/113), and 98.6% for EMB (141/143). Overall microarray specificity for RIF, INH, and EMB combined was 97.2% (384/395). The overall positive and negative predictive values for RIF, INH, and EMB combined were 84.9% and 98.3%, respectively. For the second-line drug streptomycin (STR), overall concordance between the agar proportion method and microarray analysis was 89.5% (137/153). Sensitivity was 34.8% (8/23) because of limited microarray coverage for STR-conferring mutations, and specificity was 99.2% (129/130). All false-susceptible discrepant results were a consequence of DNA mutations that are not represented by a specific microarray probe. There were zero invalid results from 220 total tests. The simplified microarray system is suitable for detecting resistance-conferring mutations in clinical M. tuberculosis isolates and can now be used for prospective trials or integrated into an all-in-one, closed-amplicon consumable.  相似文献   
49.

Background  

Arsenic in groundwater and its accumulation in plants and animals have assumed a menacing proportion in a large part of West Bengal, India and adjoining areas of Bangladesh. Because of the tremendous magnitude of the problem, there seems to be no way to tackle the problem overnight. Efforts to provide arsenic free water to the millions of people living in these dreaded zones are being made, but are awfully inadequate. In our quest for finding out an easy, safe and affordable means to combat this problem, a homeopathic drug, Arsenicum Album-30, appears to yield promising results in mice. The relative efficacies of two micro doses of this drug, namely, Arsenicum Album-30 and Arsenicum Album-200, in combating arsenic toxicity have been determined in the present study on the basis of some accepted biochemical protocols.  相似文献   
50.
目的数值模拟抗血管生成因子Angiostatin和Endostatin对肿瘤血管生成的影响。方法建立肿瘤内外血管生成的二维离散数学模型。模型耦合两种抗血管生成因子Angiostatin和Endostatin的抑制效应,数值模拟在促血管生成因子诱导下肿瘤微血管网生成,讨论血管生成抑制因子的影响。结果抗血管生成因子Angiostatin对肿瘤内外血管网络生成的速度和成熟度有抑制作用。抗血管生成因子Angiostatin和Endostatin耦合作用时,在肿瘤血管生成的早期有明显的抑制效应;在肿瘤血管生成的中后期,它们可以降低肿瘤血管化程度。结论本文模型能够较好的模拟抗血管生成因子Angiostatin和Endostatin对内皮细胞迁移和增殖的抑制作用。  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