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   3149164篇
  免费   252060篇
  国内免费   5641篇
耳鼻咽喉   45758篇
儿科学   101387篇
妇产科学   85128篇
基础医学   445624篇
口腔科学   89845篇
临床医学   286451篇
内科学   614067篇
皮肤病学   65686篇
神经病学   260455篇
特种医学   125626篇
外国民族医学   1301篇
外科学   476437篇
综合类   74107篇
现状与发展   2篇
一般理论   1236篇
预防医学   252424篇
眼科学   73752篇
药学   235867篇
  6篇
中国医学   5945篇
肿瘤学   165761篇
  2018年   32472篇
  2017年   24870篇
  2016年   27434篇
  2015年   30975篇
  2014年   44300篇
  2013年   67571篇
  2012年   91757篇
  2011年   97105篇
  2010年   57380篇
  2009年   54833篇
  2008年   92263篇
  2007年   98375篇
  2006年   99018篇
  2005年   96347篇
  2004年   93234篇
  2003年   90232篇
  2002年   88675篇
  2001年   145970篇
  2000年   151166篇
  1999年   128142篇
  1998年   37091篇
  1997年   33623篇
  1996年   33484篇
  1995年   32300篇
  1994年   30273篇
  1993年   28277篇
  1992年   103083篇
  1991年   100175篇
  1990年   96792篇
  1989年   93200篇
  1988年   86306篇
  1987年   85042篇
  1986年   80259篇
  1985年   76776篇
  1984年   58218篇
  1983年   49549篇
  1982年   29815篇
  1981年   26751篇
  1979年   54231篇
  1978年   37979篇
  1977年   32137篇
  1976年   30202篇
  1975年   32100篇
  1974年   39134篇
  1973年   37295篇
  1972年   34770篇
  1971年   31996篇
  1970年   30296篇
  1969年   28031篇
  1968年   25525篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Pediatric trachyonychia is an acquired nail disease that can cause distress to families. It is a poorly understood disease, and long‐term follow‐up data are lacking. We present an institutional review of 11 children with isolated pediatric trachyonychia followed over time. Children with the diagnosis of pediatric trachyonychia were identified and invited to participate. Pictures were taken on follow‐up and a questionnaire was answered. Exclusion criteria include having another diagnosis at the initial visit that causes nail dystrophy. Eleven patients with the diagnosis of pediatric trachyonychia were available for follow‐up. The mean age of appearance was 2.7 years (range 2–7 yrs) and the average follow‐up was 66 months (range 10–126 mos). Nine patients were treated with potent topical corticosteroids, one used only petrolatum, and one took vitamin supplements. One patient was found to have an additional skin and hair diagnosis of alopecia areata on follow‐up. On follow‐up, 82% noted improvement of the nails, whereas 18% noted no change. A majority of cases of pediatric trachyonychia are isolated and improve with time, regardless of treatment.  相似文献   
72.
73.
74.
Bipolar disorder (BD) is a common psychiatric mood disorder affecting more than 1-2% of the general population of different European countries. Unfortunately, there is no objective laboratory-based test to aid BD diagnosis or monitor its progression, and little is known about the molecular basis of BD. Here, we performed a comparative proteomic study to identify differentially expressed plasma proteins in various BD mood states (depressed BD, manic BD, and euthymic BD) relative to healthy controls. A total of 10 euthymic BD, 20 depressed BD, 15 manic BD, and 20 demographically matched healthy control subjects were recruited. Seven high-abundance proteins were immunodepleted in plasma samples from the 4 experimental groups, which were then subjected to proteome-wide expression profiling by two-dimensional electrophoresis and matrix-assisted laser desorption/ionization-time-of-flight/time-of-flight tandem mass spectrometry. Proteomic results were validated by immunoblotting and bioinformatically analyzed using MetaCore. From a total of 32 proteins identified with 1.5-fold changes in expression compared with healthy controls, 16 proteins were perturbed in BD independent of mood state, while 16 proteins were specifically associated with particular BD mood states. Two mood-independent differential proteins, apolipoprotein (Apo) A1 and Apo L1, suggest that BD pathophysiology may be associated with early perturbations in lipid metabolism. Moreover, down-regulation of one mood-dependent protein, carbonic anhydrase 1 (CA-1), suggests it may be involved in the pathophysiology of depressive episodes in BD. Thus, BD pathophysiology may be associated with early perturbations in lipid metabolism that are independent of mood state, while CA-1 may be involved in the pathophysiology of depressive episodes.  相似文献   
75.
Hepatic NADPH-cytochrome P450 oxidoreductase null (HRN?) mice exhibit normal hepatic and extrahepatic biotransformation enzyme activities when compared to wild-type (WT) mice, but express no functional hepatic cytochrome P450 activities. When incubated in vitro with [14C]-diclofenac, liver microsomes from WT mice exhibited extensive biotransformation to oxidative and glucuronide metabolites and covalent binding to proteins was also observed. In contrast, whereas glucuronide conjugates and a quinone-imine metabolite were formed when [14C]-diclofenac was incubated with HRN? mouse liver, only small quantities of P450-derived oxidative metabolites were produced in these samples and covalent binding to proteins was not observed. Livers from vehicle-treated HRN? mice exhibited enhanced lipid accumulation, bile duct proliferation, hepatocellular degeneration and necrosis and inflammatory cell infiltration, which were not present in livers from WT mice. Elevated liver-derived alanine aminotransferase, glutamate dehydrogenase and alkaline phosphatase activities were also observed in plasma from HRN? mice. When treated orally with diclofenac for 7 days, at 30 mg/kg/day, the severities of the abnormal liver histopathology and plasma liver enzyme findings in HRN? mice were reduced markedly. Oral diclofenac administration did not alter the liver histopathology or elevate plasma enzyme activities of WT mice. These findings indicate that HRN? mice are valuable for exploration of the role played by hepatic P450s in drug biotransformation, but poorly suited to investigations of drug-induced liver toxicity. Nevertheless, studies in HRN? mice could provide novel insights into the role played by inflammation in liver injury and may aid the evaluation of new strategies for its treatment.  相似文献   
76.
77.
78.
79.
Analyzing functional species’ characteristics (species traits) that represent physiological, life history and morphological characteristics of species help understanding the impacts of various stressors on aquatic communities at field conditions. This research aimed to study the combined effects of pesticides and other environmental factors (temperature, dissolved oxygen, dissolved organic carbon, floating macrophytes cover, phosphate, nitrite, and nitrate) on the trait modality distribution of aquatic macrofauna communities. To this purpose, a field inventory was performed in a flower bulb growing area of the Netherlands with significant variation in pesticides pressures. Macrofauna community composition, water chemistry parameters and pesticide concentrations in ditches next to flower bulb fields were determined. Trait modalities of nine traits (feeding mode, respiration mode, locomotion type, resistance form, reproduction mode, life stage, voltinism, saprobity, maximum body size) likely to indicate pesticides impacts were analyzed. According to a redundancy analysis, phosphate -and not pesticides- constituted the main factor structuring the trait modality distribution of aquatic macrofauna. The functional composition could be ascribed for 2–4 % to pesticides, and for 3–11 % to phosphate. The lack of trait responses to pesticides may indicate that species may have used alternative strategies to adapt to ambient pesticides stress. Biomass of animals exhibiting trait modalities related to feeding by predation and grazing, presence of diapause form or dormancy, reproduction by free clutches and ovoviviparity, life stage of larvae and pupa, was negatively correlated to the concentration of phosphate. Hence, despite the high pesticide pollution in the area, variation in nutrient-related stressors seems to be the dominant driver of the functional composition of aquatic macrofauna assembly in agricultural ditches.  相似文献   
80.
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