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   18103篇
  免费   1769篇
  国内免费   534篇
耳鼻咽喉   130篇
儿科学   1539篇
妇产科学   531篇
基础医学   1846篇
口腔科学   494篇
临床医学   2385篇
内科学   2684篇
皮肤病学   186篇
神经病学   953篇
特种医学   704篇
外国民族医学   4篇
外科学   1563篇
综合类   2063篇
现状与发展   2篇
一般理论   1篇
预防医学   1704篇
眼科学   547篇
药学   1864篇
  9篇
中国医学   570篇
肿瘤学   627篇
  2024年   35篇
  2023年   278篇
  2022年   533篇
  2021年   665篇
  2020年   637篇
  2019年   737篇
  2018年   723篇
  2017年   710篇
  2016年   726篇
  2015年   689篇
  2014年   1134篇
  2013年   1473篇
  2012年   1005篇
  2011年   1062篇
  2010年   854篇
  2009年   743篇
  2008年   784篇
  2007年   812篇
  2006年   714篇
  2005年   641篇
  2004年   537篇
  2003年   530篇
  2002年   419篇
  2001年   418篇
  2000年   336篇
  1999年   277篇
  1998年   273篇
  1997年   261篇
  1996年   249篇
  1995年   184篇
  1994年   192篇
  1993年   168篇
  1992年   158篇
  1991年   140篇
  1990年   122篇
  1989年   118篇
  1988年   107篇
  1987年   95篇
  1986年   65篇
  1985年   156篇
  1984年   118篇
  1983年   83篇
  1982年   108篇
  1981年   84篇
  1980年   70篇
  1979年   44篇
  1978年   23篇
  1977年   26篇
  1976年   26篇
  1973年   18篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Objective: Plasma soluble thrombomodulin level reflects endothelial damage. The plasma thrombomodulin level at birth is increased in asphyxiated full-term infants. There is no report of plasma thrombomodulin level in premature infants. To determine the thrombomodulin level in premature infants and whether it might reflect endothelial damage, we examined the plasma thrombomodulin level in very low birthweight (VLBW) infants at birth. Methods: Forty-five VLBW infants, of whom 14 had perinatal asphyxia complications, were recruited. As a control, 50 full-term infants wimout complications were also studied. Plasma thrombomodulin concentration, pH, base deficit, serum creatinine and D-dimer concentration, platelet count and fibrinogen concentration were measured within 1 hour after birth. Results: There were significant differences in plasma pH, creatinine concentration, platelet count, antithrombin in activity and D-dimer concentration between VLBW infants and full-term infants. Plasma thrombomodulin concentration (39. 0 (16. 6–93. 7) vs 27. 0 (16. 6–39. 1) μg/L, p < 0. 0001) and plasma taombomodulin-to-serum creatinine ratio (0. 82 (0. 19–2. 65) vs 0. 47 (0. 24–0. 70) μg/μmol, p < 0. 0001) were significantly higher in VLBW infants than those in full-term infants. By univariate analyses for all neonates, there were significant relations between plasma thrombomodulin concentration and gestational age, birthweight, plasma pH, creatinine concentration, platelet count and antithrombin in activity. A stepwise multiple linear regression model using the above variables as dependent factors showed only birthweight contributed significantly to plasma thrombomodulin concentration (plasma thrombomodulin concentration (μg/1) = 45. 677–0. 006 (birthweight; g), r2= 0. 323, p < 0. 0001, n= 94). Plasma thrombomodulin concentration and plasma thrombomodulin-to -serum creatinine ratio in VLBW infants with asphyxia were higher than in those without asphyxia, but not significantly different (43. 2 ± 17. 7 vs 38. 3 ± 8. 5 μg/1 and 0. 92 ± 0. 60 vs 0. 83 ± 0. 37 μg/μmol). Conclusion: Plasma thrombomodulin level in VLBW infants shows a high value at birth, and we consider the main factor responsible for this elevation may be endothelial damage or low clearance rate of thrombomodulin, which may be related to early gestational age.  相似文献   
42.
The survival of low birthweight infants £2000g born in the central Queensland area during the years 1979 to 1991 was examined. Five hundred and sixty such infants were either delivered at one of the two Rockhampton obstetric units (Rockhampton Base Hospital and the Mater Misericordiae Hospital) or retrieved from outlying central Queensland areas. Both hospitals had intensive care nurseries capable of ventilation and infants were transferred to tertiary centres only for cardiac or surgical treatment. The study involved all liveborn infants', including those with lethal malformations and all deaths up to the time of discharge. Survival rates were as follows: £500 g 0%, 501 £750 g 30%, 751 £1000 g 51%, 1001 ± 1500 g 79%, 1501 £2000g 93%. The survival of Aboriginal infants and outborn infants were found to be essentially the same as the overall group.  相似文献   
43.
Background. Transferrin binds extracellular iron and protectstissues from iron-induced oxidative stress. The binding of ironand transferrin is pH dependent and conventional peritonealdialysis (PD) solutions have unphysiologically low pH values.Herein, we investigated whether conventional PD solution releasesiron from transferrin and if the released iron causes oxidativestress. Methods. Effects of PD solutions on iron binding to transferrinwere examined with purified human transferrin and transferrinin dialysates drained from PD patients. Oxidative stress inducedby iron released from transferrin was evaluated in terms ofthe formation of thiobarbituric acid reactive substance (TBARS)and protein carbonylation in the human red blood cell (RBC)membrane. The iron deposition in peritoneal tissue from PD patientswas evaluated by Perls' staining with diaminobenzidine intensification. Results. Low pH PD solution released iron from transferrin.This iron release occurred within 1 min. Iron release was notobserved in neutralized PD solution. Iron released from transferrinin low pH PD solution increased TBARS formation and proteincarbonylation in the human RBC membrane. Iron deposition, whichis prominent in the fibrotic area facing the peritoneal cavity,was observed in the peritoneum of PD patients. Conclusions. Iron released from transferrin in low pH PD solutioncan produce oxidative stress in the peritoneum of a PD patient.Neutralizing PD solution can avoid this problem. Iron depositionin the peritoneum may participate in the pathogenesis of peritonealfibrosis in PD patients.  相似文献   
44.
父母亲社会经济状况与低出生体质量儿的相关性探讨   总被引:1,自引:0,他引:1  
①目的 探讨父母亲社会经济状况与低出生体质量儿发生的关系。②方法 采用病例对照研究方法,对190名低出生体质量儿和750名正常出生体质量儿的父母亲进行了相关因素调查,用Logistic回归分析进行了危险因素分析。③结果 母亲年龄大于35岁、母亲的职业为教师或农民、父亲吸烟、母亲孕期吸烟及年家庭收人低是发生低出生体质量儿的危险因素(OR=1.280~7.290),母亲身高与低出生体质量儿的发生率呈负相关关系(OR=0.898)。④结论 父母亲的社会经济状况与低出生体质量儿的发生有关。  相似文献   
45.
Osteoporosis is a common disease in older adults. The basic evidence for the diagnosisof osteoporosis is the decrease of bone mineral density (BMD) [1]. Studies showed that the risk of fractures would rise as the bone mineral density decreased, and the me…  相似文献   
46.
ABSTRACT: Background: The percentage of United States’ births delivered by cesarean section has increased rapidly in recent years, even for women considered to be at low risk for a cesarean section. The purpose of this paper is to examine infant and neonatal mortality risks associated with primary cesarean section compared with vaginal delivery for singleton full‐term (37–41 weeks’ gestation) women with no indicated medical risks or complications. Methods: National linked birth and infant death data for the 1998–2001 birth cohorts (5,762,037 live births and 11,897 infant deaths) were analyzed to assess the risk of infant and neonatal mortality for women with no indicated risk by method of delivery and cause of death. Multivariable logistic regression was used to model neonatal survival probabilities as a function of delivery method, and sociodemographic and medical risk factors. Results: Neonatal mortality rates were higher among infants delivered by cesarean section (1.77 per 1,000 live births) than for those delivered vaginally (0.62). The magnitude of this difference was reduced only moderately on statistical adjustment for demographic and medical factors, and when deaths due to congenital malformations and events with Apgar scores less than 4 were excluded. The cesarean/vaginal mortality differential was widespread, and not confined to a few causes of death. Conclusions: Understanding the causes of these differentials is important, given the rapid growth in the number of primary cesareans without a reported medical indication. (BIRTH 33:3 September 2006)  相似文献   
47.
目的探讨常温及低温体外循环心脏直视手术对细胞因子及补体的影响。方法选择先天性和风湿性心脏病患者40例,随机分为常温组及低温组各20例,分别于术晨、体外循环结束时及术后1、4、7、14 d抽取患者静脉血标本,测定血浆TNF、IL-2、C3、C4值。结果两组术前各项检查指标无显著差异。(1)两组术后1~4 d的IL-2水平较术前显著下降,至术后7 d恢复正常。体外循环结束至术后4 d,低温组IL-2显著低于常温组。(2)体外循环结束时以及术后1、4、7 d,常温组TNF水平显著低于低温组。两组体外循环结束时及术后1、4 d均高于术前,常温组至术后7 d、低温组术后14 d恢复正常。(3)体外循环结束时及术后1、7 d,常温组C3水平高于低温组,术后4 d两组无差别;常温组及低温组于体外循环结束时、术后1、4 d均低于术前,至术后7 d常温组恢复正常,低温组至术后14 d恢复至术前水平。(4)两组体外循环结束时及术后1、4 d C4水平均低于术前。体外循环结束时、术后1 d,常温组C4水平高于低温组。结论常温体外循环心脏直视手术对细胞因子及补体的影响显著轻于低温组,因而对术后机体的恢复优于低温方法。  相似文献   
48.
49.
目的:探讨用长链核酸扩增技术评价病毒灭活效果的可行性.方法:针对伪狂犬病毒(pseudorabies virus,PRV)糖蛋白gD基因前后的保守区设计预计产物长短不一的5对引物,用半巢式PCR技术扩增经低pH法(4.0±0.1)、巴氏消毒法[(60±1.0)℃]和s/D法(有机溶剂/洗涤荆)处理后的PRV核酸,同时以细胞感染法做平行对照.结果:低pH对PRV核酸有破坏作用,处理时间越长,核酸损伤程度越明显,处理60 min时,6.62 lgTCID50的PRV完全被灭活.5条不同长度PCR扩增产物中,只有3.9 kb的长片段检出与细胞培养结果一致.7.25 lgTCID50的PRV经(60±1.0)℃处理20 min后即被完全灭活,7.13 lgTCID50的PRV经s/D法处理1 h后被完全灭活,但各长度核酸片段扩增均为阳性,与细胞感染试验结果不符.结论:低pH对PRV核酸的损伤程度随处理时间的延长而增加;用长链PCR(3.9 kb)技术来评价经低pH法灭活病毒的效果是可行的,而该法不适合评价巴氏消毒法和S/D法灭活病毒的效果.  相似文献   
50.
Aim: Sodium/bicarbonate co‐transport (NBC) has been suggested to have a role in muscle pH regulation. We investigated the presence of NBC proteins in rat and human muscle samples and the fibre type distribution of the identified NBCs. Methods and results: Western blotting of muscle homogenates and sarcolemmal membranes (sarcolemmal giant vesicles) were used to screen for the presence of NBCs. Immunohistochemistry was used for the subcellular localization. The functional test revealed that approximately half of the pH recovery in sarcolemmal vesicles produced from rat muscle is mediated by bicarbonate‐dependent transport. This indicates that the NBCs are preserved in the vesicles. The western blotting experiments demonstrated the existence of at least two NBC proteins in skeletal muscle. One NBC protein (approximately 150 kDa) seems to be related to the kidney/pancreas/heart isoform NBC1, whereas the other protein (approximately 200 kDa) is related to the NBC4 isoform. The two NBC proteins represent the electrogenic isoforms named NBCe1 and NBCe2. Membrane fractionation and immunofluorescence techniques confirmed that the two NBCs are located in the sarcolemmal membrane as well as in some internal membranes, probably the T‐tubules. The two NBCs localized in muscle have distinct fibre type distributions. Conclusions: Skeletal muscle possesses two variants of the sodium/bicarbonate co‐transporter (NBC) isoforms, which have been called NBCe1 and NBCe2.  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