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   2687篇
  免费   233篇
  国内免费   22篇
耳鼻咽喉   10篇
儿科学   40篇
妇产科学   81篇
基础医学   413篇
口腔科学   44篇
临床医学   269篇
内科学   574篇
皮肤病学   21篇
神经病学   430篇
特种医学   77篇
外科学   356篇
综合类   21篇
预防医学   102篇
眼科学   66篇
药学   160篇
中国医学   2篇
肿瘤学   276篇
  2023年   16篇
  2022年   18篇
  2021年   55篇
  2020年   34篇
  2019年   50篇
  2018年   67篇
  2017年   52篇
  2016年   60篇
  2015年   62篇
  2014年   98篇
  2013年   130篇
  2012年   214篇
  2011年   192篇
  2010年   94篇
  2009年   94篇
  2008年   163篇
  2007年   140篇
  2006年   168篇
  2005年   166篇
  2004年   166篇
  2003年   150篇
  2002年   112篇
  2001年   52篇
  2000年   40篇
  1999年   52篇
  1998年   35篇
  1997年   32篇
  1996年   16篇
  1995年   16篇
  1994年   17篇
  1993年   12篇
  1992年   35篇
  1991年   20篇
  1990年   28篇
  1989年   33篇
  1988年   24篇
  1987年   40篇
  1986年   29篇
  1985年   26篇
  1984年   17篇
  1983年   14篇
  1982年   16篇
  1981年   5篇
  1979年   11篇
  1978年   5篇
  1976年   11篇
  1975年   9篇
  1974年   6篇
  1973年   5篇
  1971年   6篇
排序方式: 共有2942条查询结果,搜索用时 0 毫秒
111.
112.
113.
Placental protein 13 (PP13) is a galectin expressed by the syncytiotrophoblast. Women who subsequently develop preterm pre-eclampsia have low first trimester maternal serum PP13 concentrations. This study revealed that third trimester maternal serum PP13 concentration increased with gestational age in normal pregnancies (p < 0.0001), and it was significantly higher in women presenting with preterm pre-eclampsia (p = 0.02) and hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome (p = 0.01) than in preterm controls. Conversely, placental PP13 mRNA (p = 0.03) and protein, as well as cytoplasmic PP13 staining of the syncytiotrophoblast (p < 0.05) was decreased in these pathological pregnancies compared to controls. No differences in placental expression and serum concentrations of PP13 were found at term between patients with pre-eclampsia and control women. In contrast, the immunoreactivity of the syncytiotrophoblast microvillous membrane was stronger in both term and preterm pre-eclampsia and HELLP syndrome than in controls. Moreover, large syncytial cytoplasm protrusions, membrane blebs and shed microparticles strongly stained for PP13 in pre-eclampsia and HELLP syndrome. In conclusion, parallel to its decreased placental expression, an augmented membrane shedding of PP13 contributes to the increased third trimester maternal serum PP13 concentrations in women with preterm pre-eclampsia and HELLP syndrome.  相似文献   
114.
Identifying the pathways that are significantly impacted in a given condition is a crucial step in understanding the underlying biological phenomena. All approaches currently available for this purpose calculate a P-value that aims to quantify the significance of the involvement of each pathway in the given phenotype. These P-values were previously thought to be independent. Here we show that this is not the case, and that many pathways can considerably affect each other''s P-values through a “crosstalk” phenomenon. Although it is intuitive that various pathways could influence each other, the presence and extent of this phenomenon have not been rigorously studied and, most importantly, there is no currently available technique able to quantify the amount of such crosstalk. Here, we show that all three major categories of pathway analysis methods (enrichment analysis, functional class scoring, and topology-based methods) are severely influenced by crosstalk phenomena. Using real pathways and data, we show that in some cases pathways with significant P-values are not biologically meaningful, and that some biologically meaningful pathways with nonsignificant P-values become statistically significant when the crosstalk effects of other pathways are removed. We describe a technique able to detect, quantify, and correct crosstalk effects, as well as identify independent functional modules. We assessed this novel approach on data from four experiments involving three phenotypes and two species. This method is expected to allow a better understanding of individual experiment results, as well as a more refined definition of the existing signaling pathways for specific phenotypes.The correct identification of the signaling and metabolic pathways involved in a given phenotype is a crucial step in the interpretation of high-throughput genomic experiments. Most approaches currently available for this purpose treat the pathways as independent. In fact, pathways can affect each other''s P-values through a phenomenon we refer to as crosstalk. This crosstalk may be due to the regulatory interactions among different pathways or to the gene overlap among pathways. In this work, we will use the term crosstalk to refer to the effect that pathways exercise on each other due to the presence of overlapping genes. Although it is intuitive that various pathways could influence each other, especially when they share genes, the presence and extent of this phenomenon have not been rigorously studied and, most importantly, there is no currently available technique able to quantify the amount of such crosstalk. There are three major categories of methods that aim to identify significant pathways: enrichment analysis (e.g., Fisher''s exact test–hypergeometric) (Tavazoie et al. 1999; Draghici et al. 2003); functional scoring (e.g., GSEA) (Mootha et al. 2003; Subramanian et al. 2005); and topology-based methods (e.g., impact analysis) (Draghici et al. 2007; Tarca et al. 2009). Another classification of gene set analysis methods is based on the definition of the null hypothesis and divides the methods into competitive and self-contained (Goeman and Bühlmann 2007; Nam and Kim 2008). In this work, we focus on competitive methods, and in particular on the Fisher''s exact test, although the problems identified likely apply also for self-contained methods.Here we show that the results of all these methods are affected by crosstalk effects and that this phenomenon is related to the structure of the pathways. We propose the first approach that can (1) detect crosstalk when it exists, (2) quantify its magnitude, (3) correct for it, resulting in a more meaningful ranking among pathways in a specific biological condition, and (4) identify novel functional modules that can play an independent role and have different functions than the pathway they are currently located on. This method is expected to allow a better understanding of individual experiment results, as well as a more refined definition of the existing signaling pathways for specific phenotypes.  相似文献   
115.
From January 2003 to June 2006, 6 patients with leakage of the cervical esophagogastrostomy after esophagectomy and gastric pull-up underwent endoscopic stenting using the self-expandable covered tracheal type device. Anastomotic healing was satisfactory. Stent extraction was performed after an average interval of 91 days. Initial stent migration occurred in 2 patients and post-extraction stenosis developed in 3 patients. Insertion of a self-expandable covered metal tracheal stent represents a safe approach resulting in immediate closure and subsequent healing of cervical anastomotic leakage.  相似文献   
116.
Introduction: Medical therapy of glaucoma aims to maintain the patient’s visual function and quality of life. This generally commences with monotherapy, but it is often difficult to reach the predetermined target pressure with this approach. Fixed combinations (FCs) are therefore selected as the next step of the medical therapy algorithm. By employing a prostaglandin/timolol fixed combination (PTFC) the desired target 24-hour intraocular pressure can be reached in many glaucoma patients with the convenience of once-a-day administration and the associated high rate of adherence.

Areas covered: The current role and value of FCs in the medical therapy of glaucoma is critically appraised. Special attention is paid to the PTFCs and the emerging role of preservative-free PTFCs. This review summarizes existing information on the efficacy and tolerability of the new preservative-free tafluprost/timolol FC (Taptiqom®).

Expert opinion: The preservative-free tafluprost/timolol FC represents a promising stepwise treatment option for those patients whose intraocular pressure is insufficiently controlled with available monotherapy options. This novel FC has the potential to substantially improve glaucoma management and through evolution of the current glaucoma treatment paradigm, to become a core therapeutic option in the future. Nonetheless, future research is needed to better delineate the therapeutic role of current and future preservative-free FCs in glaucoma therapy.  相似文献   
117.
Sinus lifting is performed with a variety of materials and techniques without a precise knowledge of the quantity of augmentation. This study based on three-dimensional finite element analysis was designed to show which surgical procedure and which amount of peri-implant packing yields the best bony support for dental implants. Eight 3D-FE models were used. Four modeled standard situations simulated quantitatively different packing situations produced by differences in surgical approach: i. no packing; ii. thin 1 mm bony sheath; iii. oblique subcomplete packing; iv. complete bony peri-implant packing up to the implant end. A fifth model compared a standard implant with a length of 13.5 mm and a diameter of 3.75 mm with a 7-mm-long and 5-mm-thick implant. In three additional models the stress response of the bone-implant system was evaluated in the absence of a cortical layer, thus simulating an extreme degree of maxillary atrophy. In all models the modeled implants were loaded at their points of emergence with an assumed force of 100 N. The vector of the loading force was inclined 30 degrees posteriorly relative to the implant axis and 30 degrees away from the sagittal plane. The bone-implant interface was assumed to be perfect simulating full osseointegration. The final evaluation of the FE models showed complete peri-implant packing to reduce displacements of the implant tip by 32% vs. no sheathing/packing. Van Mises' equivalent stresses were used to assess the stresses in both human bone and titanium alloy implants. The highest stress levels in bone were predicted for the case without sufficient implant sheathing. In the models with adequate bony implant support, intrabony stresses were generally reduced by up to - 40%. The structural stiffness of the bone-implant system increased with the extent of sinus floor elevation. The results indicate that more extensive peri-implant packing reduces implant displacement, intrabony stresses and stresses at the bone-implant interface.  相似文献   
118.
Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors are efficacious lipid-lowering agents, but more precise estimates of their effects on major adverse cardiovascular events (MACE), mortality, and safety are needed. We systematically reviewed and meta-analyzed randomized controlled trials with durations ≥ 6 months comparing MACE, mortality, and safety with PCSK9 inhibitors vs control. We searched CENTRAL, Embase, MedLine and the grey literature to November 7, 2018. From 2048 articles, we included 23 trials (n = 60,723). PCSK9 inhibitors reduced MACE (relative risk, 0.83; 95% confidence interval, 0.78-0.88), but did not clearly reduce mortality (relative risk, 0.93; 95% confidence interval, 0.85-1.02) or increase adverse events. In conclusion, PCSK9 inhibitors reduce nonfatal MACE, are well tolerated, but effects on mortality remain unclear.  相似文献   
119.
An unprecedented mortality crisis befell the former socialist countries between 1989 and 1995, representing one of the greatest demographic shocks of the period after the Second World War. While it is likely that country‐level variation in the post‐socialist mortality crisis in Eastern Europe can be explained by a constellation of political and socio‐economic factors, no comprehensive review of the existing scholarly attempts at explaining these factors exists. We review 39 cross‐national multi‐variable peer reviewed studies of social determinants of mortality in post‐socialist Europe in order to assess the social factors behind the post‐socialist mortality crisis, determine the gaps in the existing literature and to make suggestions for future research. We propose a novel methodology to determine the relative importance of variables based on the ratio of significant to insignificant findings for each variable. The literature identifies inequality, welfare payments, religious composition, democracy, economic performance and unemployment as the leading factors that have a significant influence on mortality outcomes. Existing cross‐country studies fail to establish a definitive connection between mortality and diets, drinking patterns, liberalisation, trust, health expenditure and war. We also point out that the level of analysis is not a neutral methodological choice but might influence the results themselves.  相似文献   
120.
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