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   8624篇
  免费   552篇
  国内免费   60篇
耳鼻咽喉   119篇
儿科学   303篇
妇产科学   177篇
基础医学   1019篇
口腔科学   265篇
临床医学   879篇
内科学   1806篇
皮肤病学   114篇
神经病学   829篇
特种医学   556篇
外国民族医学   1篇
外科学   1082篇
综合类   131篇
一般理论   2篇
预防医学   790篇
眼科学   131篇
药学   564篇
中国医学   6篇
肿瘤学   462篇
  2021年   87篇
  2020年   62篇
  2019年   110篇
  2018年   139篇
  2017年   100篇
  2016年   118篇
  2015年   151篇
  2014年   163篇
  2013年   292篇
  2012年   400篇
  2011年   417篇
  2010年   270篇
  2009年   257篇
  2008年   371篇
  2007年   402篇
  2006年   378篇
  2005年   375篇
  2004年   306篇
  2003年   286篇
  2002年   289篇
  2001年   298篇
  2000年   288篇
  1999年   204篇
  1998年   115篇
  1997年   112篇
  1996年   115篇
  1995年   75篇
  1994年   93篇
  1993年   79篇
  1992年   157篇
  1991年   167篇
  1990年   174篇
  1989年   183篇
  1988年   150篇
  1987年   165篇
  1986年   149篇
  1985年   184篇
  1984年   123篇
  1983年   111篇
  1982年   70篇
  1981年   77篇
  1980年   75篇
  1979年   109篇
  1978年   77篇
  1977年   61篇
  1976年   56篇
  1975年   63篇
  1974年   60篇
  1973年   56篇
  1972年   54篇
排序方式: 共有9236条查询结果,搜索用时 15 毫秒
51.
Monoclonal antibodies to the major Plasmodium falciparum merozoite surface coat and rhoptry antigens were produced. A combination of the affinity-purified polypeptides with Freund complete adjuvant which was given three times completely protected an Aotus lemurinus azure (karotype VI) monkey against homologous challenge; however, immunization with the same polypeptides with a muramyl dipeptide derivative [MDP-Lys(L18)] did not protect a second Aotus monkey, even though comparable high antibody titers were induced.  相似文献   
52.
Cystic fibrosis: Synthesis of ciliary inhibitor by amniotic cells   总被引:1,自引:0,他引:1  
The presence of a ciliary inhibitor in media of cultured amniotic cells obtained from a fetus heterozygous for cystic fibrosis has been observed by the oyster gill cilia assay. The chromatographic fraction containing the inhibitor corresponded to eluted fractions chromatographed from cystic fibrosis fibroblast media and serum. An analogous chromatographic fraction from media of cultured amniotic cells from two proportedly normal fetuses did not inhibit cilia. The chromatographic fraction from media of cultured amniotic cells of a fetus at high risk for cystic fibrosis did not inhibit ciliary activity. Serum was collected from this baby seven weeks after birth and also did not inhibit ciliary action, indicating a homozygous normal genotype. These observations may lead to the development of an antenatal test for cystic fibrosis.  相似文献   
53.
54.
Summary Adult black blowflies Phormia regina were trapped from April through October in Urbana, Illinois for the years 1963 and 1964. Samples of flies from each catch were examined for the presence of the microsporidian parasite Octosporea muscaedomesticae. In 1963, the monthly parasite incidence rate steadily increased with the progression of the seasons while the fly population declined over the same period. In 1964, the monthly parasite incidence rate followed no decernable pattern; this was probably attributable to the fact that the host remained comparatively scarce for the entire period following heavy spring rains. The observed monthly parasite incidence rates ranged from zero to 13% over the two-year period. The annual parasite incidence rate was 4% in 1963 and 4.5% in 1964. No significant differences were found in the parasite incidence rates of females versus males. The observed parasite incidence rates, while indicative of general trends, probably are lower than the actual rates in nature. Reasons for this are discussed. Finally it is suggested that O. muscaedomesticae may at times act as a suppressor of P. regina populations in the field.
Zusammenfassung Erwachsene Fliegen der Art Phormia regina wurden vom April bis Oktober in Urbana, Illinois, in den Jahren 1963 und 1964 gefangen. Einige Fliegen aus jedem Fang wurden auf Microsporidien der Art Octosporea muscaedomesticae untersucht. Im Jahre 1963 erhöhte sich die monatliche Infektionsrate ständig mit dem Fortschreiten des Jahres, während sich die Fliegenpopulation in derselben Periode verminderte. Im Jahre 1964 war eine solche Beziehung nicht erkennbar; dieser Umstand wird darauf zurückgeführt, daß der Wirt während der ganzen folgenden Periode der schweren Frühlingsregenfälle relativ spärlich auftrat. Die beobachtete monatliche Parasitenhäufigkeit wechselte während der 2-Jahresperiode zwischen 0 und 13%. Die jährliche Parasitenhäufigkeit lag 1963 bei 4% und im Jahre 1964 bei 4,5%. Es war keine significante Differenz in der Parasitenhäufigkeit zwischen weiblichen und männlichen Tieren festzustellen. Die beobachtete Parasitenhäufigkeit war, wenn man den generellen Trend betrachtet, wahrscheinlich eher geringer als die aktuelle Rate in der freien Natur. Die Gründe für diese Umstände werden diskutiert. Schließlich wird angenommen, daß sich O. muscaedomesticae als ein begrenzender Faktor (supressor) für P. regina Population in der freien Natur anzusehen ist.


This study was supported in part by Research Grant AI-05068 from the National Institute of Allergy and Infectious Diseases of the National Institutes of Health, U.S. Public Health Service.  相似文献   
55.
Human Fallopian tubal epithelial cells in culture lose morphological features associated with the epithelium in situ and the extent to which they retain their in-vivo phenotype or function is unknown. In order to address this question, immunocytochemical markers were identified which distinguish secretory (HMFG2+, LhS28-) from ciliated (HMFG2-, LhS28+) epithelial cells in tissue sections of Fallopian tube. These markers were used to analyse the phenotype of tubal cells in vitro. Primary cultures of human tubal epithelial cells were seeded onto glass and grown to confluence before addition of oestradiol-17beta. In the absence of hormone, tubal epithelial cells expressed cytokeratins and nuclear receptors for oestrogen and progesterone and adopted a homogeneous (HMFG2+, LhS28-) secretory cell phenotype. Following the addition of oestradiol-17beta, a proportion of cells became positive for LhS28. The induction of a ciliated epithelial cell phenotype was confirmed by scanning electron microscopy, where on permeable collagen membranes, approximately one-third of tubal epithelial cells became ciliated in the presence of oestradiol-17beta. We suggest that in vitro, tubal epithelial cells adopt an immature secretory-like phenotype and that oestrogen can induce differentiation to a ciliated epithelial cell phenotype.   相似文献   
56.
57.
Effects of learned helplessness on brain GABA receptors   总被引:2,自引:0,他引:2  
GABA is involved in both clinical depression and in animal models of depression; however, the roles of GABA(A) and GABA(B) receptors in specific brain regions are not clear. Changes in densities of both GABA(A) and GABA(B) receptors have been reported with the learned helplessness animal model of depression and with chronic antidepressant drug treatment. However, some of these findings are discrepant. Thus, we used quantitative autoradiography to study the GABA(A) and GABA(B) receptors in learned helplessness and we used an experimental paradigm that allows non-specific effects of stress to be differentiated from learned helplessness. Densities of GABA binding were measured in prefrontal cortex, septum, hippocampus, hypothalamus and amygdala. In the septum, learned helpless rats had increased densities of GABA(A) receptors and rats that did not become helpless after inescapable stress had decreased GABA(B) receptor densities. No significant group differences of GABA(A) or GABA(B) receptor densities were observed in any other brain region studied. These results suggest a unique role for the septum in modulating GABA in the learned helplessness animal model of depression.  相似文献   
58.
59.
Heterogeneity of executive tasks has made it difficult to determine whether there are age-related declines in executive functioning. To address this issue, 112 individuals, 20-79 years old, took the California Trail Making Test (CTMT) and the California Stroop Test (CST), subtests of the Delis-Kaplan Executive Function Scale (D. C. Delis, E. Kaplan, & J. H. Kramer, in press) that include measurement of component skills embedded in the executive function tasks. Multiple regression analyses revealed that after controlling for component skills, age had a significant effect on the executive requirement of the CST, namely speed on the interference condition. Age did not affect switching performance on the letter-number condition of the CTMT. Additional analyses revealed that age was significantly associated with commission of certain types of errors. This study confirms the importance of partialing out components in the assessment of multidimensional cognitive tasks, particularly when making age comparisons. It also emphasizes specificity over generalizability when examining the impact of age on cognition.  相似文献   
60.
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