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   7970篇
  免费   676篇
  国内免费   17篇
耳鼻咽喉   59篇
儿科学   365篇
妇产科学   226篇
基础医学   918篇
口腔科学   151篇
临床医学   941篇
内科学   1370篇
皮肤病学   55篇
神经病学   706篇
特种医学   453篇
外科学   1270篇
综合类   170篇
一般理论   2篇
预防医学   740篇
眼科学   180篇
药学   545篇
中国医学   4篇
肿瘤学   508篇
  2021年   99篇
  2020年   67篇
  2019年   97篇
  2018年   124篇
  2017年   93篇
  2016年   97篇
  2015年   113篇
  2014年   145篇
  2013年   255篇
  2012年   302篇
  2011年   339篇
  2010年   185篇
  2009年   158篇
  2008年   306篇
  2007年   336篇
  2006年   338篇
  2005年   295篇
  2004年   293篇
  2003年   265篇
  2002年   264篇
  2001年   284篇
  2000年   287篇
  1999年   266篇
  1998年   167篇
  1997年   138篇
  1996年   135篇
  1995年   126篇
  1994年   118篇
  1993年   91篇
  1992年   201篇
  1991年   187篇
  1990年   189篇
  1989年   163篇
  1988年   187篇
  1987年   138篇
  1986年   171篇
  1985年   159篇
  1984年   143篇
  1983年   122篇
  1982年   81篇
  1981年   69篇
  1980年   56篇
  1979年   109篇
  1978年   75篇
  1977年   72篇
  1976年   60篇
  1975年   74篇
  1974年   74篇
  1973年   77篇
  1972年   62篇
排序方式: 共有8663条查询结果,搜索用时 15 毫秒
121.

Background

Adequate vitamin D concentrations during pregnancy are necessary to neonatal calcium homeostasis, bone maturation and mineralization. The aim of study is to evaluate serum vitamin D concentrations in mothers and their newborns and effect of vitamin D deficiency on pregnancy outcomes.

Methods

552 pregnant women were recruited from Tehran University educating hospitals in the winter of 2002. Maternal and cord blood samples were taken at delivery. The serum was assayed for 25-hydroxyvitamin D3, calcium, phosphorus and parathyroid hormone.

Results

The prevalence of vitamin D deficiency in maternal and cord blood samples were 66.8% and 93.3%, respectively (<35 nmol/l). There was significant correlation between maternal and cord blood serum concentrations of vitamin D. In mothers with vitamin D deficiency, cord blood vitamin D concentrations was lower than those from normal mothers (P = .001). Also, a significant direct correlation was seen between maternal vitamin D intake and weight gain during pregnancy.

Conclusion

Consideration to adequate calcium and vitamin D intake during pregnancy is essential. Furthermore, we think it is necessary to reconsider the recommendation for vitamin D supplementation for women during pregnancy.  相似文献   
122.
BackgroundMeningiomas are the most common primary intracranial tumor in adults. Clinical care is currently guided by the World Health Organization (WHO) grade assigned to meningiomas, a 3-tiered grading system based on histopathology features, as well as extent of surgical resection. Clinical behavior, however, often fails to conform to the WHO grade. Additional prognostic information is needed to optimize patient management.MethodsWe evaluated whether chromosomal copy-number data improved prediction of time-to-recurrence for patients with meningioma who were treated with surgery, relative to the WHO schema. The models were developed using Cox proportional hazards, random survival forest, and gradient boosting in a discovery cohort of 527 meningioma patients and validated in 2 independent cohorts of 172 meningioma patients characterized by orthogonal genomic platforms.ResultsWe developed a 3-tiered grading scheme (Integrated Grades 1-3), which incorporated mitotic count and loss of chromosome 1p, 3p, 4, 6, 10, 14q, 18, 19, or CDKN2A. 32% of meningiomas reclassified to either a lower-risk or higher-risk Integrated Grade compared to their assigned WHO grade. The Integrated Grade more accurately identified meningioma patients at risk for recurrence, relative to the WHO grade, as determined by time-dependent area under the curve, average precision, and the Brier score.ConclusionWe propose a molecularly integrated grading scheme for meningiomas that significantly improves upon the current WHO grading system in prediction of progression-free survival. This framework can be broadly adopted by clinicians with relative ease using widely available genomic technologies and presents an advance in the care of meningioma patients.  相似文献   
123.

Background  

Epidemiological studies have identified important causal and prognostic factors for back pain, but these frequently only identify a proportion of the variance, and new factors add little to these models. Recently, interest has increased in studying diseases over the life course, stimulated by the 1997 book by Kuh and Ben-Shlomo, a move accompanied by important conceptual and methodological developments. This has resulted in improvements in the understanding of other conditions like cardiovascular and respiratory disease. This paper aims to examine how conceptual frameworks from life course epidemiology could enhance back pain research.  相似文献   
124.
To characterize the heterogeneity of severe (type III) von Willebrand disease (vWD), plasma and platelet von Willebrand factor antigen (vWF:Ag) and ristocetin cofactor activity (Ricof) were measured in 28 obligatory heterozygotes (ie, parents or children of probands from 15 different kindreds with severe vWD). On the average, heterozygotes had low levels of vWF in both platelets and plasma. There was, however, considerable heterogeneity, with four distinct patterns. Eleven heterozygotes had concordant reduction of vWF:Ag and Ricof in both plasma and platelets; five had low levels of vWF:Ag and Ricof in plasma contrasting with normal levels in platelets; eight had a peculiar pattern, the reverse of the above (ie, low levels in platelets and normal levels in plasma); and in one, both vWF measurements were normal in plasma and platelets. These patterns were genetically determined: they were consistent in four couples of consanguineous heterozygotes and in two couples carrying the same gene deletion. Only the remaining three heterozygotes had no clearly identifiable pattern. Other findings of this study were that although most of the heterozygotes had normal bleeding times, the 7 of 28 who had prolonged bleeding times had concordantly low levels of vWF measurements in both plasma and platelets. In conclusion, this large series of obligatory heterozygotes provides evidence for phenotypic and genotypic heterogeneity of severe vWD.  相似文献   
125.
An association between a polymorphism of the angiotensin-converting enzyme (ACE) gene and myocardial infarction (MI) in men has been previously reported. The present study examines the association between ACE genotype, atherosclerosis, MI, hypertension and other cardiovascular risk factors in Caucasian men (n=576) and women (n=124) who have undergone coronary angiography. Gene frequencies are also reported for African-American men (n=56). Genotype determination was based on the presence (allele I) or absence (allele D) of a 287 nucleotide Alu sequence in intron 16 of the ACE gene. Genotype frequencies for DD, ID and II were: 30.9, 47.7, 21.4% for Caucasian men; 28.2, 48.4, 23.4% for Caucasian women; and 30.4, 46.4, 23.2% for African-American men. There were no statistically significant associations between ACE genotype and number of plaques (> or =10% obstruction), lipid variables, or body mass index (BMI) for Caucasian men. Caucasian women with the DD genotype had on average fewer plaques, but this was accounted for by their younger ages. In Caucasian males, the DD genotype independently contributed to the presence of hypertension (odds ratio=1.8, 95% CI 1.1-2.9) after adjusting for age and BMI. In Caucasian males with total cholesterol levels less than 200 mg/dl (n=237), the DD (odds ratio=2.5, 95% CI 1.2-5.4) and ID genotypes (odds ratio=2.2, 95% CI 1.1-4.4) were associated with a history of MI.  相似文献   
126.
Eight laboratories in six countries cooperated to clarify several issues concerning the phenotypes of heterozygous carriers of hemophilia "A." Plasma levels of factor VIII (F.VIII:C, formerly VIII:C) and von Willebrand factor (VWF:Ag, formerly VIIIR:Ag) of carriers and normal women were determined by various "in-house" methods; a single lyophilized plasma standard was used for all assays. Analysis of the collated data from 336 carriers (296 obligatory carriers and 40 sporadic carriers) and 137 normal women showed that there was no difference in the F.VIII:C levels of "paternal" carriers (women who had obtained the abnormal gene from their fathers) and "maternal" carriers. Neither was there a difference in the VWF:Ag levels of normal women and either type of carrier. Age was found to have a significant effect on both F.VIII:C and VWF:Ag, values being higher at very young and very old ages, the minima occurring in the 25- to 30-year range. ABO blood type had a striking effect. Women of types A, B, and AB (designated non- O in the study), both normals and carriers, had significantly higher levels of both factors than did women of type O. Analysis by laboratories showed that differences in mean levels of both factors between laboratories were highly significant. It was concluded that age, ABO blood type, and laboratory variation should be taken into account in carrier detection.  相似文献   
127.
Erythema nodosum associated with all-trans-retinoic acid (ATRA) for acute promyelocytic leukemia (APL) is very rare. We describe four patients with classic APL who developed erythema nodosum during ATRA therapy. Fever and subsequent multiple painful erythematous nodules over extremities developed on D11, D16, D17, and D19, respectively, after ATRA therapy. The skin biopsy taken from each patient was consistent with erythema nodosum. All patients received short course of steroids. Fever subsided rapidly and the skin lesions regressed completely. All patients achieved complete remission without withdrawal of ATRA. ATRA seemed to be the most possible etiology of erythema nodosum in our patients. Short-term use of steroid is very effective in ATRA-induced erythema nodosum.  相似文献   
128.
129.
Fibrinogen and Fibrin Clot Structure in Diabetes   总被引:3,自引:0,他引:3  
Dunn EJ  Ariëns RA 《Herz》2004,29(5):470-479
Diabetes is associated with an increased risk of developing cardiovascular disease, which is not fully accounted for by the accumulation of classic cardiovascular risk factors in patients. Recent evidence has demonstrated fibrinogen to be a powerful independent risk marker for cardiovascular disease in the general population, and it is also likely to contribute toward the increased atherosclerotic risk in diabetes. The etiology of hyperfibrinogenemia in diabetes is likely to be multifactorial, and at present the mechanisms involved have not been clarified. However, insulin, insulin resistance and inflammation are likely to be involved, especially in type 2 diabetes. The influence of diabetes in determining an individual's atherothrombotic risk is likely to extend beyond that of elevated fibrinogen levels, and may also act via changes in the structure and function of the fibrin clot that forms. Further research is needed to determine the mechanisms underlying these changes, which may lead to development of future interventions to reduce the excessive vascular risk associated with this disease.  相似文献   
130.
Insulin receptors on leukemia and lymphoma cells   总被引:1,自引:0,他引:1  
Chen  PM; Kwan  SH; Hwang  TS; Chiang  BN; Chou  CK 《Blood》1983,62(2):251-255
Tumor cells obtained from leukemia and lymphoma patients were investigated for specific insulin receptors. Using radioactive 125I- labeled insulin, specific insulin binding sites were demonstrated on most acute lymphocytic leukemia (ALL) and acute myelocytic leukemia (AML) cells, including acute promyelocytic leukemia (APL), chronic myelocytic leukemia (CML), and acute monocytic leukemia (AMoL) cells. Insulin receptors were not found on chronic lymphocytic leukemia (CLL) and malignant lymphoma (ML) cells. Specific insulin binding sites were also found on monocytes and thymocytes after treatment with phytohemagglutinin (PHA-P), but not on inactivated tonsil cells, peripheral blood lymphocytes, or thymocytes. There was no inverse correlation between the content of insulin receptors and the basal level of circulating insulin. These data suggest that the insulin receptor may be a new marker of acute leukemia and chronic myelocytic leukemia.  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