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   7928篇
  免费   422篇
  国内免费   50篇
耳鼻咽喉   81篇
儿科学   180篇
妇产科学   196篇
基础医学   1222篇
口腔科学   160篇
临床医学   806篇
内科学   1613篇
皮肤病学   85篇
神经病学   561篇
特种医学   802篇
外国民族医学   2篇
外科学   889篇
综合类   42篇
一般理论   1篇
预防医学   443篇
眼科学   81篇
药学   546篇
中国医学   8篇
肿瘤学   682篇
  2022年   53篇
  2021年   129篇
  2020年   64篇
  2019年   104篇
  2018年   123篇
  2017年   93篇
  2016年   115篇
  2015年   130篇
  2014年   191篇
  2013年   228篇
  2012年   384篇
  2011年   321篇
  2010年   187篇
  2009年   201篇
  2008年   326篇
  2007年   355篇
  2006年   372篇
  2005年   345篇
  2004年   331篇
  2003年   320篇
  2002年   322篇
  2001年   354篇
  2000年   338篇
  1999年   247篇
  1998年   113篇
  1997年   108篇
  1996年   84篇
  1995年   62篇
  1994年   47篇
  1993年   59篇
  1992年   135篇
  1991年   153篇
  1990年   134篇
  1989年   162篇
  1988年   135篇
  1987年   126篇
  1986年   100篇
  1985年   111篇
  1984年   78篇
  1983年   66篇
  1982年   51篇
  1979年   91篇
  1978年   50篇
  1977年   49篇
  1976年   50篇
  1975年   49篇
  1974年   67篇
  1973年   62篇
  1972年   56篇
  1970年   54篇
排序方式: 共有8400条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
OBJECTIVES: We have previously shown that the levels of circulatory fetal DNA are elevated in preeclampsia and that these increases correspond to disease severity. Several reports have indicated that increased levels of antiphospholipid (anti-PL) and anti-DNA antibodies may be associated with preeclampsia, in particular with the severe forms of the disorder. Since the release of cell-free DNA by the placenta is attributed to some form of cell death or damage and as anti-PL and anti-double-stranded DNA (dsDNA) antibodies have been proposed to lead to placental damage, we have studied the relationship between these parameters in preeclampsia. METHODS: Circulating fetal DNA levels in samples taken from pregnant women with mild (n = 12) or severe (n = 12) preeclampsia and from normal pregnant controls (n = 35) were quantified using a Taqman real-time Polymerase Chain Reaction (PCR) assay. The Anti-PL antibodies (IgG and IgM) were assayed by anticardiolipin ELISA and by commercial anti-beta2-Glycoprotein I (GPI) ELISA kits. Anti-dsDNA antibodies (IgG and IgM) were analyzed by a commercially available anti-dsDNA ELISA kit. RESULTS: No correlation could be drawn with the quantity of circulatory fetal DNA in the samples analyzed and corresponding anti-PL or anti-dsDNA antibody levels. Furthermore, no significant difference existed between the levels of these antibodies in the two study groups and the control cohort. CONCLUSION: Our data suggest that the mechanism leading to the increased release of cell-free circulatory DNA from the placenta does not involve trophoblast damage mediated by these agents. Our analysis also questions the reported involvement of anti-PL and anti-DNA antibodies in preeclampsia.  相似文献   
25.
Background and Objective: Although the empirical characteristics of ArF excimer laser corneal ablation have been well documented, the exact ablation mechanisms are not well understood. The present paper reports a quantitative analysis of corneal ablation plumes using in situ time resolved laser light scattering and Raman spectroscopy. Study Design/Materials and Methods: Bovine corneas were used as the ArF excimer laser ablation targets. Light scattering data were recorded from the ablation plume as a function of height above the tissue surface and as function of delay time with respect to the ablative ArF laser pulse. Results: Raman spectra of the ablation plume allow identification of the particles as water. Mean plume particle diameters are found to decrease with height, while the particle volume fractions are relatively constant. The total volume of plume particles correlates well with the total volume of water in the ablated corneal tissue. Conclusion: The finding of a non-evolving plume composed of water spherules, combined with the excellent agreement between total volume of water in the plume and the content of water in the ablated corneal tissue, support the concept of photodecomposition or “cold ablation” for corneal tissue during ArF excimer laser ablation. © 1995 Wiley-Liss, Inc.  相似文献   
26.
27.
1. Plasma renin activity (PRA) and platelet cytosolic free calcium concentration ([Ca2+]i) were simultaneously determined in 18 untreated essential hypertensive subjects and 17 normotensive controls. A significant positive correlation was found between [Ca2+]i and PRA (slope = 42 nmol/l/ng/ml/h) in these 35 subjects. 2. Two determinations more than one week apart in nine subjects confirmed the parallel fluctuations of [Ca2+]i and PRA. A strict sodium restriction produced a progressive PRA elevation associated with a parallel rise in [Ca2+]i in one subject. 3. These results are consistent with the hypothesis that angiotensin II causes a concentration-dependent calcium mobilization.  相似文献   
28.
 We present a rare case of a 27-year-old man sustaining a bilateral fracture dislocation of the sacroiliac joints without disruption of the anterior pelvis, following a fall from a height. Reconstructed images in the coronal plane and three-dimensional CT images were invaluable in the diagnosis and assessment of this injury.  相似文献   
29.
30.
Cognitive theory holds that dysfunctionalattitudes are important risk factors for depression.Critics have questioned this view, noting that, althoughdysfunctional attitudes are elevated in depression, they are not evident in vulnerable individualswho are asymptomatic. To deal with this criticism,Miranda and Persons (1988) have advanced the mood-statedependent hypothesis, which suggests that cognitive vulnerability factors are indeed present invulnerable individuals, but remain dormant untilactivated by negative mood. To test this hypothesis, 33women with and 67 women without histories of depression reported dysfunctional attitudes before andafter a film negative mood induction. As predicted,vulnerable subjects who reported increased negative moodreported increased dysfunctional attitudes.Unexpectedly, nonvulnerable subjects who reported increasednegative mood reported decreased dysfunctionalattitudes. These findings support the mood-statedependent hypothesis, and suggest that a deficit in theability to regulate negative emotions may be animportant feature of vulnerability todepression.  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