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   3012篇
  免费   196篇
  国内免费   24篇
耳鼻咽喉   17篇
儿科学   56篇
妇产科学   67篇
基础医学   438篇
口腔科学   19篇
临床医学   374篇
内科学   582篇
皮肤病学   69篇
神经病学   350篇
特种医学   74篇
外科学   283篇
综合类   40篇
一般理论   2篇
预防医学   244篇
眼科学   28篇
药学   238篇
中国医学   5篇
肿瘤学   346篇
  2023年   27篇
  2022年   55篇
  2021年   70篇
  2020年   43篇
  2019年   54篇
  2018年   95篇
  2017年   67篇
  2016年   73篇
  2015年   91篇
  2014年   108篇
  2013年   143篇
  2012年   212篇
  2011年   222篇
  2010年   115篇
  2009年   110篇
  2008年   179篇
  2007年   187篇
  2006年   173篇
  2005年   182篇
  2004年   162篇
  2003年   137篇
  2002年   109篇
  2001年   57篇
  2000年   51篇
  1999年   53篇
  1998年   27篇
  1997年   19篇
  1996年   19篇
  1995年   19篇
  1994年   8篇
  1993年   12篇
  1992年   25篇
  1991年   32篇
  1990年   24篇
  1989年   27篇
  1988年   27篇
  1987年   20篇
  1986年   21篇
  1985年   25篇
  1984年   14篇
  1983年   16篇
  1982年   10篇
  1981年   12篇
  1979年   9篇
  1978年   10篇
  1976年   8篇
  1971年   11篇
  1970年   6篇
  1968年   6篇
  1945年   9篇
排序方式: 共有3232条查询结果,搜索用时 15 毫秒
1.
Birthweight data for 29 586 infants born in health-care facilities in Addis Ababa in 1973 and 1982 indicate that 40-60% of all deliveries took place within the formal health-care system. The mean birthweight increased by 107 g from 3075 ± 585 g in 1973 to 3181 ± 550 g in 1982. This increase was uniform over the entire birthweight range but was statistically significant only for infants of low birthweight, the frequency of such births decreasing from 13% to 8% over the period. Stratification of the data by sex indicated a similar increase in birthweight. The stillbirth rate decreased from 51.1 per 1000 births in 1973 to 34.1 per 1000 in 1982, but was statistically significant only for birthweights in the range 3000-4000 g. The shift in birthweight distribution reported here may reflect either changes in the demographic characteristics of the population or unidentified changes in medical treatment.  相似文献   
2.
BACKGROUND: The HOXA1 gene plays a major role in brainstem and cranial morphogenesis. The G allele of the HOXA1 A218G polymorphism has been previously found associated with autism. METHODS: We performed case-control and family-based association analyses, contrasting 127 autistic patients with 174 ethnically matched controls, and assessing for allelic transmission disequilibrium in 189 complete trios. RESULTS: A, and not G, alleles were associated with autism using both case-control (chi(2) = 8.96 and 5.71, 1 df, p <.005 and <.025 for genotypes and alleles, respectively), and family-based (transmission/disequilibrium test chi(2) = 8.80, 1 df, p <.005) association analyses. The head circumference of 31 patients carrying one or two copies of the G allele displayed significantly larger median values (95.0th vs. 82.5th percentile, p <.05) and dramatically reduced interindividual variability (p <.0001), compared with 166 patients carrying the A/A genotype. CONCLUSIONS: The HOXA1 A218G polymorphism explains approximately 5% of the variance in the head circumference of autistic patients and represents to our knowledge the first known gene variant providing sizable contributions to cranial morphology. The disease specificity of this finding is currently being investigated. Nonreplications in genetic linkage/association studies could partly stem from the dyshomogeneous distribution of an endophenotype morphologically defined by cranial circumference.  相似文献   
3.
The present study provides an analysis of the effects of particular patterns of teacher respose to students' entries in dialogue journals. It extended on previous research related to teacher-student instructional discourse by concentrating on written, teacher-student interactions. Second grade children who were participating in a daily dialogue journal activity were randomly subjected to two types of response patterns by their teacher. The results show that a teacher's elaborative responses to student journal entries directly lead to increase written output by students coupled with a distinct process #ophigher order#cp orientation of student entries.  相似文献   
4.
The junctional zone (Jz) of the mouse placenta consists of two main trophoblast populations, spongiotrophoblasts and glycogen cells (GCs), but the development and function of both cell types are unknown. We conducted a quantitative analysis of GC size, number, and invasion of cells into the decidua across gestation. Furthermore, we identified markers of GC function to investigate their possible roles in the placenta. While the spongiotrophoblast cell volume doubles, and cell number increases steadily from E12.5 to E16.5, there is a remarkable 80-fold increase in GC numbers. This finding is followed by a notable decrease by E18.5. Surprisingly, the accumulation of GCs in the decidua did not fully account for the decrease in GC number in the Jz, suggesting loss of GCs from the placenta. Glucagons were detected on GCs, suggesting a steady glucose release throughout gestation. Connexin31 staining was shown to be specific for GCs. GC migration and invasion may be facilitated by temporally regulated expression of matrix metalloproteinase 9 and the imprinted gene product, Decorin. Expression of the clearance receptor for type II insulin-like growth factor (IGF-II), IGF2R, in a short developmental window before E16.5 may be associated with regulating the growth effects of IGF-II from glycogen cells and/or labyrinthine trophoblast on the expansion of the Jz. Thus stereology and immunohistochemistry have provided useful insights into Jz development and function of the glycogen cells.  相似文献   
5.
6.
As more patients survive cancer, and as more sophisticated multidrug antineoplastic protocols are developed, the chances of an anesthesiologist's coming into contact with patients who have been treated with such protocols are increasing. The anesthesiologist who must administer anesthesia to a patient who has had chemotherapy must be cognizant of the particular antineoplastic agents that have the potential for producing occult pulmonary dysfunction. Anesthetic management of these cases must be carefully planned and titrated to prevent further lung injury.  相似文献   
7.
PDB is genetically heterogeneous. Mutations of the sequestosome1 gene have been reported in sporadic and familial forms of Paget's in patients of French Canadian and British descent. Mutational analyses in different ethnic groups are needed to accurately investigate hereditary diseases. We describe two novel mutations of sequestosome1 in 62 Italian sporadic patients, confirming the role of the encoded protein in this disorder. INTRODUCTION: Paget's disease of bone (PDB) is a relatively common disease of bone metabolism reported to affect up to 3% of whites over 55 years of age. The disorder is genetically heterogeneous, and at present, there is scientific evidence that at least eight different human chromosomal loci are correlated with its pathogenesis. Mutations of the sequestosome1 (SQSTM1) gene were identified as responsible for most of the sporadic and familial forms of Paget in patients of French Canadian and British descent. Such mutations were located at exon 7 and 8 levels, encoding for the ubiquitin protein-binding domain (UBA) and representing a mutational hot spot area. MATERIALS AND METHODS: To verify the involvement of this gene in Italian subjects affected by PDB, we performed mutational analysis in 62 sporadic PDB cases. RESULTS: We described three different mutations at exon 8 level: P392L, already described in the French Canadian population and families predominantly of British descendent, and two novel mutations consisting of the amino acid substitutions M404V and G425R. No significant differences in the clinical history of PDB have been observed in patients with SQSTM1 mutations in respect to those without. CONCLUSIONS: Even though our findings suggest a minor involvement of the SQSTM1 gene in the pathogenesis of sporadic Italian Paget's cases, the identification of different significant mutations within the SQSTM1 gene in unrelated, but clinically similar individuals, offers extremely convincing evidence for a causal relationship between this gene and PDB. Longitudinal studies are needed to assess the penetrance of genotype/phenotype correlations. Our findings confirm the evidence of a clustered mutation area at this level in this disorder.  相似文献   
8.
Activities of the petroleum-inducible mixed function oxygenase CYP1A (EROD) were measured in livers of inshore demersal fish species at various sites around the coast of Shetland to determine the sub-lethal impact of oil spilled after the wreck of the tanker M.V. Braer in January 1993. Visible coastal pollution by the oil was only apparent for some two weeks after the incident and tissue PAH levels in muscle of gadoid fish such as rockling from these areas were not elevated 3 months afterwards, while hepatic EROD activities were elevated some 7-to 9-fold. A 6.5-fold elevation was still observed 5 months afterwards; however, the levels had returned to those of fish from non-polluted environments 7 months after the incident and remained at baseline levels after the following winter's storm action. These data demonstrate the usefulness of enzymatic analysis as a sensitive method for assessing the temporal and spatial impact of an oil spill.  相似文献   
9.
10.
Fatal occupational injuries in the United States, 1980 through 1985   总被引:12,自引:0,他引:12  
C A Bell  N A Stout  T R Bender  C S Conroy  W E Crouse  J R Myers 《JAMA》1990,263(22):3047-3050
The National Traumatic Occupational Fatality surveillance project was designed to gather demographic, employment, and injury information from death certificates for all deaths due to injuries at work in the United States. Approximately 7000 workers have died each year during the 6-year period from 1980 through 1985: 94% were men, and 6% were women. Unintentional injuries caused the deaths of 83% of the men and 50% of the women. Eleven percent of the men and 39% of the women died from homicide. While the greatest number of deaths occurred in the group aged 20 through 34 years, fatality rates were highest among those aged 70 years and older. Expressed as deaths per 100,000 workers, annual fatality rates for black workers (7.7) were slightly higher than for white workers (6.5). The four industrial groups with the highest fatality rates were mining (31.9); transportation, communication, and public utilities (25.4); construction (24.0); and agriculture, forestry, and fishing (20.7). From 1980 through 1985 the annual traumatic occupational fatality rate fell 23%.  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