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   1132篇
  免费   72篇
  国内免费   9篇
耳鼻咽喉   11篇
儿科学   87篇
妇产科学   11篇
基础医学   95篇
口腔科学   31篇
临床医学   107篇
内科学   276篇
皮肤病学   21篇
神经病学   23篇
特种医学   243篇
外科学   69篇
综合类   59篇
预防医学   61篇
眼科学   20篇
药学   44篇
中国医学   9篇
肿瘤学   46篇
  2021年   4篇
  2020年   6篇
  2019年   10篇
  2018年   13篇
  2017年   10篇
  2016年   7篇
  2015年   20篇
  2014年   40篇
  2013年   63篇
  2012年   31篇
  2011年   32篇
  2010年   38篇
  2009年   61篇
  2008年   31篇
  2007年   48篇
  2006年   29篇
  2005年   28篇
  2004年   20篇
  2003年   15篇
  2002年   20篇
  2001年   23篇
  2000年   21篇
  1999年   26篇
  1998年   78篇
  1997年   53篇
  1996年   63篇
  1995年   44篇
  1994年   49篇
  1993年   44篇
  1992年   10篇
  1991年   5篇
  1990年   11篇
  1989年   39篇
  1988年   27篇
  1987年   25篇
  1986年   19篇
  1985年   12篇
  1984年   17篇
  1983年   15篇
  1982年   14篇
  1981年   20篇
  1980年   13篇
  1979年   8篇
  1978年   9篇
  1977年   16篇
  1976年   8篇
  1975年   11篇
  1973年   2篇
  1972年   1篇
  1955年   1篇
排序方式: 共有1213条查询结果,搜索用时 0 毫秒
61.
The aim of this study was to compare 70 couples who had conceived by in- vitro fertilization (IVF) with 63 matched controls for the prevalence of anxiety and quality of attachment to the baby during pregnancy. Results for mothers showed no group differences using a global measure of anxiety, the Spielberger State-Trait Anxiety Inventory. However, pregnancy-specific measures revealed significantly higher levels of anxiety in IVF mothers about the survival and normality of their unborn babies, about damage to their babies during childbirth and about separating from their babies after birth. When IVF mothers were differentiated according to the number of treatment cycles, more differences in anxiety level were revealed, with most increases occurring in mothers who had experienced two or more treatment cycles. IVF fathers did not differ from controls on the global anxiety measure. No data on pregnancy-specific anxiety were available for fathers. Neither IVF mothers nor IVF fathers differed from controls on measures of attachment to the baby during pregnancy. Results are discussed in the context of the need for researchers to employ differentiated and issue-specific measures to identify concerns that may be unique to IVF couples. Clinical implications regarding the need for psychological support during pregnancy are also discussed.   相似文献   
62.
A study of the degree of progesterone support required for the maintenance of various stages of pregnancy was undertaken in mice. Mated females were ovariectomized at various stages of pregnancy and progesterone and oestradiol support provided by s.c. Silastic implants with known release characteristics. In the earliest stages of pregnancy (days 1-5), very low concentrations of progesterone (<25% of normal physiological values) were sufficient to maintain pre-implantation stages and allow implantation. In the immediate post-implantation period (days 5-9), the development of implantation sites and decidualization required considerably higher progesterone support. In mid-pregnancy (days 11-14), progesterone alone could not maintain pregnancy unless present in very high amounts; however, the presence of oestradiol during this period lowered the progesterone requirements to well within the physiological range. This effect of oestradiol started on day 11 but required the level of oestradiol support to be kept within strictly defined limits, with high concentrations inducing abortion. Progesterone alone was able to maintain pregnancy from day 15. These results indicate that the minimal progesterone support required for pregnancy in mice varies considerably at different stages of pregnancy and is at least partly modulated by oestradiol.   相似文献   
63.
Synchronization of neuronal activity has been proposed as a binding mechanism for integration of image properties into one coherent percept. In the present study, we investigated the contextual modulation of synchronization to random dot patterns. Coherent motion of random dots evoked well synchronized responses in area 17 of anaesthetized cats when the stimulus was presented in the compound receptive field of recorded sites. Gradually changing the directional coherence of random dots in the surround while maintaining fully coherent motion of the stimulus in the receptive field significantly suppressed synchronization of neuronal activity for some stimulus conditions. However, usually one or two peaks of increased synchronization were found in the surround coherence tuning curves with low (8–12%) and/or moderate (25–50%) coherence in the surround. At the population level, synchronization was significantly depressed with incoherent motion in the receptive field and when both the surround and the receptive field were jointly stimulated with 0% coherence. The intriguing finding was the discovery of two distinct groups of cells with opposite synchronization changes dependent on the presence or absence of significant synchronization in their spontaneous activity. The latter group of neurons showed peaks of increased synchronization with lower surround coherence, thus probably being more sensitive to the direction of the surround motion. Overall, our findings support the notion that binding of stimulus properties can be achieved by synchronized activity of cortical cells. However, our findings go further than the original hypothesis of feature binding by synchrony to show that synchronization of cortical activity may be directly related to the decision making processes, which in turn are related to the threshold of perception of coherent motion.  相似文献   
64.
目的 对兔肝脏及其附属管道进行应用解剖学研究。 方法 对20只日本大耳兔分别进行活体和离体形态学观察,制作门静脉和肝静脉管道铸型标本观察其分支与走行,测定各肝叶质量及其所占肝脏百分比。 结果 兔肝肝裂明显,依据肝叶形态、肝裂走行和门静脉主干分支形式将兔肝脏分为五叶,分别为尾状叶、左外叶、左中叶、右中叶、右外叶,各肝叶质量分别为(g):3.93±1.13、15.93±3.50、14.83±3.31、15.08±4.34、12.08±3.55。左中叶和右中叶根部肝组织融合,其余各肝叶相对独立,尾状叶包括相对独立的乳头突和尾状突两部分。各肝叶有相对独立的Glisson系统和肝静脉走行于肝蒂内。 结论 兔肝解剖学特点与多数哺乳类实验动物肝脏解剖相似,同时又具有其自身特点,适合于肝脏外科疾病动物模型的制作。  相似文献   
65.
Porphyria cutanea tarda (PCT) arises from decreased hepatic activity of uroporphyrinogen decarboxylase (UROD). Both genetic and environmental factors interplay in the precipitation of clinically overt PCT, but these factors may vary between different geographic areas. Decreased activity of UROD in erythrocytes was used to identify patients with UROD mutations among a group of 130 Spanish PCT patients. Nineteen patients (14.6%) were found to harbor a mutation in the UROD gene. Eight mutations were novel: M1I, 5del10, A22V, D79N, F84I, Q116X, T141I and Y182C. Five others were previously described: F46L, V134Q, R142Q, P150L and E218G. The new missense mutations and P150L were expressed in Escherichia coli. D79N and P150L resulted in proteins that were localized to inclusion bodies. The other mutations produced recombinant proteins that were purified and showed reduced activity (range: 2.3–73.2% of wild type). These single amino acid changes were predicted to produce complex structural alterations and/or reduced stability of the enzyme. Screening of relatives of the probands showed that 37.5% of mutation carriers demonstrated increased urinary porphyrins. This study emphasizes the role of UROD mutations as a strong risk factor for PCT even in areas where environmental factors (hepatitis C virus) have been shown to be highly associated with the disease.  相似文献   
66.
目的 对比分析下肢骨肉瘤的X线与MRI表现,探讨MRI对骨肉瘤的诊断价值。方法 收集经手术或病理穿刺活检证实的下肢骨肉瘤15例,男11例,女4例,均行MRI平扫及增强扫描(4例行CT扫描),并摄有X线平片,对其MRI征象与X线征象作逐一对比。结果 MRI及X线平片对下肢骨肉瘤的诊断准确率均为100%,MRI在显示病变范围、放射状骨针、Codman三角两层结构以及跳跃病灶等方面明显优于X线平片检查。结论 X线平片是诊断骨肉瘤最简便而实用的方法,但MRI可以更好的显示病变的范围,发现早期病变。  相似文献   
67.
神经节细胞瘤是一种神经内分泌肿瘤,其发生与自主神经系统的交感或副交感神经节有关。罕见发生于膀胱、前列腺和子宫。本文作者报道1例发生于儿童头皮的原发性皮肤神经节细胞瘤。对此肿瘤进行了组织学、免疫组化和超微结构研究。该病例可能代表神经嵴细胞向鳃弓发育过程中的一种异常迁移。此外,研究结果还强调在胚胎发育过程中神经嵴和鳃弓/裂之间有复杂的相互作用。  相似文献   
68.
69.
一例AML中一种新的TCRδ基因重排及其分析方法   总被引:5,自引:0,他引:5  
李扬秋 Wichm.  A 《癌症》1996,15(2):90-93
T细胞抗原受体(TCR)功能的表达有赖于该基因在正常T淋巴细胞发育过程中的重排。近年来,已发现一些肿瘤及白血病中出现该基因的异常重排。我们采用聚合链反应(PCR)、“磁珠”固相纯化方法和PCR产物直接测序等方法,从一例AML中发现了一种在白血病中未报道过的TCRδ基因重排,该重排是一种新报道的Dδ区DδX片段的重排,为DδXDδDδJδ不完全重排。在研究白血病TCR基因重排中,采用本文所报道的方法  相似文献   
70.
Essential fatty acids are claimed to have positive effects in atopic diseases. In a double blind, placebo controlled, parallel group study 58 out of 60 children, with atopic dermatitis and the need for regular treatment with topical skin steroids, completed a 16 weeks' treatment period with either Epogam evening primrose oil or placebo capsules. Twenty two of these subjects also had asthma. The parents used diaries to record symptom scores and concomitant medication. Peak expiratory flow was measured and disease activity was monitored by the clinician every four weeks. The plasma concentrations of essential fatty acids increased significantly in the group treated with Epogam capsules. The study demonstrated significant improvements of the eczema symptoms but no significant difference was found between the placebo and the Epogam groups. No therapeutic effect was shown on asthma symptoms or fidget.  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