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   21043篇
  免费   1911篇
  国内免费   46篇
耳鼻咽喉   232篇
儿科学   707篇
妇产科学   584篇
基础医学   2974篇
口腔科学   303篇
临床医学   2429篇
内科学   4122篇
皮肤病学   276篇
神经病学   2312篇
特种医学   412篇
外科学   2205篇
综合类   202篇
一般理论   21篇
预防医学   2928篇
眼科学   279篇
药学   1295篇
中国医学   11篇
肿瘤学   1708篇
  2023年   321篇
  2022年   495篇
  2021年   1207篇
  2020年   728篇
  2019年   1017篇
  2018年   1104篇
  2017年   730篇
  2016年   767篇
  2015年   814篇
  2014年   1042篇
  2013年   1311篇
  2012年   1909篇
  2011年   1860篇
  2010年   889篇
  2009年   745篇
  2008年   1191篇
  2007年   1060篇
  2006年   940篇
  2005年   790篇
  2004年   607篇
  2003年   551篇
  2002年   476篇
  2001年   160篇
  2000年   179篇
  1999年   166篇
  1998年   95篇
  1997年   70篇
  1996年   52篇
  1995年   65篇
  1994年   59篇
  1993年   41篇
  1992年   135篇
  1991年   110篇
  1990年   111篇
  1989年   97篇
  1988年   94篇
  1987年   74篇
  1986年   72篇
  1985年   79篇
  1984年   62篇
  1983年   51篇
  1982年   48篇
  1980年   37篇
  1979年   63篇
  1978年   43篇
  1976年   30篇
  1974年   34篇
  1973年   35篇
  1972年   35篇
  1970年   35篇
排序方式: 共有10000条查询结果,搜索用时 922 毫秒
101.
102.
The research evaluated an intervention strategy designed to prevent skin cancer in young adolescents. The intervention used parents as change agents to effectively communicate the risks of skin cancer and encourage their children to avoid high-risk sun-related behaviors while increasing positive sun-safe behaviors. Three hundred and forty parents in two regions of the United States were educated about the dangers of risky sun behaviors and how to convey information about skin cancer prevention to their children. Parents were then encouraged to talk with their children about these issues over a 1-month period prior to the onset of summer. Following this time period, children whose parents received and implemented the intervention materials were compared with a control sample of 129 children. These two groups were matched on age, gender, and school on number of sunburns and sunburn severity, attitudes and beliefs, and sunbathing behavior. Children in the treatment condition differed significantly from controls in the predicted directions on all outcome variables. The findings are discussed in terms of reducing skin cancer risk behaviors of children via parent-based intervention approaches.  相似文献   
103.
Mental health services are underutilized in our society by both adults and children. This finding presents a potential problem for researchers conducting community‐based research. Previous studies have demonstrated that community‐based researchers frequently do not screen participants for the presence of psychopathology nor do they ascertain whether therapeutic services are currently utilized. The present study explored the prevalence of psychopathology and treatment involvement in a sample of families recruited from the community. Results indicated that a fifth of the participants in this community‐based sample met diagnostic criteria for a psychiatric disorder or were in treatment for psychological difficulties at the time of recruitment for this study. Furthermore, mothers, fathers, and adolescents who met the criteria according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM‐IV; American Psychiatric Association, 1994 ) for a psychological disorder had higher symptomatology than those who did not meet criteria. Methodological suggestions are provided. © 2008 Wiley Periodicals, Inc.  相似文献   
104.
Observations of impaired glucose regulation in schizophrenia are long-standing, although their pathological and etiological significance is uncertain. One approach to the issue that minimizes environmental variables (e.g., medication and diet) is to determine whether genes related to glucose regulation show genetic linkage to schizophrenia. We examined the potential role of glucose metabolism in schizophrenia through a genome scan of affection status in schizophrenia and an empirical method for deriving P-values. Data were utilized from the NIMH Genetics Initiative for Schizophrenia dataset, which comprises a total sample consisting of 71 pedigrees containing 218 nuclear families and 987 individuals. A genome scan with 459 markers spaced at an average of 10 cM intervals was conducted using the linkage analysis program Genehunter separately for European- and African-American groups. Enzymes that regulate glycolysis were identified and the genes regulating these enzymes were located through the Online Mendelian Inheritance in Man (OMIM) website. The focus in this study was on genes located near previously reported schizophrenia susceptibility regions. The genome-wide significance of these genes to schizophrenia was assessed using permutation testing. When results were adjusted for multiple testing within and across ethnic groups, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 2 (PFKFB2; chromosome 1q32.2) achieved genome-wide significance (P = 0.04). In addition, hexokinase 3 (HK3; chromosome 5q35.3) was also suggestive of linkage (P = 0.09). For the European-American sample, PFKFB2 (1q32.2), hexokinase 3 (HK3; 5q35.3), and pyruvate kinase 3 (PK3; chromosome 15q23) achieved significance at the 0.05 level. None of the genes showed significance in the African-American sample. Our results provide further support for the view that genes that regulate glucose metabolism may also influence susceptibility to schizophrenia. More generally, they support the view that relationships between glucose dysregulation and schizophrenia are inherent to the disorder, and are not merely epiphenomena related to medication or other treatment factors.  相似文献   
105.
A developing therapy for complete or partial loss of function in various tissues and organs involves transplanting an appropriate cell population, capable of compensating for the existing deficiencies. Clinical application of this type of strategy is currently limited by the death or dedifferentiation of the transplanted cells after delivery to the recipient. A delay in thorough vascularization of the implant area creates an environment low in oxygen and other nutrients, and likely contributes to the initial death of transplanted cells. We have addressed this problem by sustained delivery of vascular endothelial growth factor (VEGF), an initiator of angiogenesis, from a porous polymer matrix utilized simultaneously for cell delivery. As expected from previous studies, VEGF delivered from these constructs elicited an enhanced angiogenic response over a 2-week period when implanted subcutaneously in SCID mice. Hepatocytes implanted using VEGF-containing matrices demonstrated significantly greater survival after 1 week in vivo as compared with cells implanted on matrices without growth factor. The results of this study therefore indicate that enhancing vascularization in the location of transplanted cells promotes their survival. In addition, this delivery system may be used in future studies to directly promote cell survival and function by also providing growth factors specific to the transplanted cells.  相似文献   
106.
We have proposed a new model of rat intestinal sugar absorption in which high glucose concentrations promote rapid insertion of GLUT2 into the apical membrane, so that absorptive capacity is precisely regulated to match dietary intake. Construction and building work during expansion and refurbishment of our department permitted opportunistic experiments on the effects of building-induced stress on the GLUT2 component of absorption. In fed rats perfused with 75 m m glucose in vivo , stress rapidly inhibited glucose absorption 36.4 ± 3.0% compared with control rats. Selective inhibition of the GLUT2 component with phloretin demonstrated that stress inhibited the GLUT2 component by 42.8 ± 3.8%, which correlated with a corresponding diminution in apical GLUT2 levels: the SGLT1 component and its level were unaltered by stress. Effects of stress were reversed by the administration in drinking water of metyrapone, which inhibits 11-β-hydroxylase. Injection of dexamethasone into control rats 60 min before perfusion resulted in absorption and transporter properties indistinguishable from stressed rats. Our data are consistent with the view that stress activates the hypothalamus–pituitary–adrenal (HPA) axis, causing release of glucocorticoid. The ensuing inhibition of GLUT2 trafficking and absorption seems necessary to prevent enhanced intestinal delivery of glucose to the circulation from antagonizing the essential stress response of glucorticoid in mobilizing peripheral energy stores for emergency purposes.  相似文献   
107.
108.
Capillary basement membrane (CBM) thickening is an ultrastructural hallmark in diabetic patients and in animal models of diabetes. However, the wide variety of tissues sampled and diverse methods employed have made the interpretation of thickness data difficult. We showed previously that acellular glomerular BMs in OVE26 transgenic diabetic mice were thickened beyond normal age-related thickening, and in the current study we hypothesized that other microvascular BMs likewise would show increased widths relative to age-matched controls. Accordingly, a series of tissues, including skeletal and cardiac muscle, ocular retina and choriod, peripheral nerve, lung, pancreas, and renal glomerulus was collected from 300-350-day-old normal and transgenic mice. Transmission electron micrographs of cross sections through capillary walls were prepared, and CBM thickness (CBMT) was determined by the "orthogonal intercept" method. Morphometric analyses showed highly variable transgene-related BMT increases in the sampled tissues, with glomerular BM showing by far the greatest increase (+87%). Significant thickness increases were also seen in the retina, pulmonary alveolus, and thoracoabdominal diaphragm. BMT increases were not universal; however, most were modestly widened, and those that were thickest in controls generally showed the greatest increase. Although the pathogenesis of diabetes-related increases in CBM is poorly understood, data in the current study showed that in OVE26 transgenic mice increased BMT was a frequent concomitant of hyperglycemia. Accordingly, it seems likely that hyperglycemia-induced microvascular damage may be a contributing factor in diabetic BM disease, and that microvessel cellular and extracellular heterogeneity may limit the extent of CBM thickening in diverse tissues.  相似文献   
109.
A whole body plethysmograph (body box) equipped with a flow meter (see Figure 1) was used for objective quantification of the effects of single doses of clemastine fumarate 2.68 mg, chlorpheniramine 4 mg and placebo in a double-blind study of 48 patients with seasonal allergic rhinitis. This technique offers an objective means of assessing drug effects on nasal congestion and obstruction. Before the development of whole body plethysmography, only subjective assessments of antihistamines' effects on nasal blockage or congestion were available. These subjective reports usually noted that nasal blockage or congestion was refractory to antihistamines or minimally relieved by them. However, in this study, nasal and oral airway resistances, each measured by whole body plethysmography, were lowered by clemastine fumarate and chlorpheniramine. These results were corroborated by the patients' and physician's assessments of changes in symptom severity and the physician's evaluation of intranasal photographs taken for each patient. Oral airway resistance of patients treated with clemastine fumarate was improved to a significantly greater extent than in patients receiving placebo. At two hours post-drug, patients receiving clemastine fumarate usually showed a greater response in most assessments than those receiving chlorpheniramine, and the trend of most comparisons was clearly in favor of clemastine fumarate. Patients in all three treatment groups experienced drowsiness but both incidence and severity were lower with clemastine fumarate.  相似文献   
110.
The complete nucleotide sequence of RNAα from the Type strain of barley stripe mosaic virus has been determined. The RNA is 3768 nucleotides long and contains a single open reading frame which codes for a polypeptide of 1139 amino acids (mw 129,634). The open reading frame is flanked by a 5′-terminal sequence of 91 nucleotides and a 3′-nontranslated region composed of a short poly(A) tract followed by a 238-nucleotide tRNA-like structure. The amino acid sequence of the polypeptide (αa) encoded by the open reading frame has homology with the TMV 126K protein and with related polypeptides from other viruses. The carboxy-terminal portion of the as polypeptide also has limited homology with the 58K (βb) protein encoded by BSMV RNAβ and includes a consensus sequence found in mononucleotide-binding polypeptides.  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