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   8711篇
  免费   645篇
  国内免费   36篇
耳鼻咽喉   65篇
儿科学   313篇
妇产科学   146篇
基础医学   1373篇
口腔科学   189篇
临床医学   1098篇
内科学   1822篇
皮肤病学   164篇
神经病学   635篇
特种医学   422篇
外科学   786篇
综合类   128篇
一般理论   4篇
预防医学   823篇
眼科学   288篇
药学   576篇
中国医学   3篇
肿瘤学   557篇
  2021年   96篇
  2019年   95篇
  2018年   119篇
  2017年   81篇
  2016年   115篇
  2015年   140篇
  2014年   174篇
  2013年   283篇
  2012年   287篇
  2011年   339篇
  2010年   217篇
  2009年   170篇
  2008年   272篇
  2007年   345篇
  2006年   360篇
  2005年   305篇
  2004年   290篇
  2003年   242篇
  2002年   273篇
  2001年   252篇
  2000年   253篇
  1999年   198篇
  1998年   151篇
  1997年   152篇
  1996年   156篇
  1995年   131篇
  1994年   125篇
  1993年   125篇
  1992年   196篇
  1991年   217篇
  1990年   189篇
  1989年   245篇
  1988年   188篇
  1987年   200篇
  1986年   210篇
  1985年   172篇
  1984年   163篇
  1983年   104篇
  1982年   80篇
  1981年   94篇
  1980年   114篇
  1979年   117篇
  1978年   86篇
  1977年   88篇
  1976年   76篇
  1975年   84篇
  1974年   61篇
  1972年   70篇
  1971年   74篇
  1960年   68篇
排序方式: 共有9392条查询结果,搜索用时 375 毫秒
121.
122.
Examined associations between effortful control temperament and externalizing problems in 220 3-year-old boys and girls, controlling for co-occurring cognitive and social risk factors. We also considered possible additive and/or interactive contributions of child dispositional anger and psychosocial adversity, and whether relations between effortful control and early externalizing problems were moderated by child gender. Individual differences in children's effortful control abilities, assessed using behavioral and parent rating measures, were negatively associated with child externalizing problems reported by mothers, fathers, and preschool teachers. These associations were not overshadowed by other cognitive or social risk factors, or by other relevant child temperament traits such as proneness to irritability. Further analyses revealed that associations between externalizing problem behavior and effortful control were specific to components of child problem behavior indexing impulsive-inattentive symptoms. Thus, children's effortful control skills were important correlates of children's early disruptive behavior, a finding that may provide insight into the developmental origins of chronic behavioral maladjustment.  相似文献   
123.

Background  

Chronic lymphocytic leukemia (CLL) is characterized by accumulation of mature appearing lymphocytes and is rarely complicated by thrombosis. One possible explanation for the paucity of thrombotic events in these patients may be the presence of the ecto-nucleotidase CD39/NTDPase-1 on the surface of the malignant cells in CLL. CD39 is the major promoter of platelet inhibition in vivo via its metabolism of ADP to AMP. We hypothesize that if CD39 is observed on CLL cells, then patients with CLL may be relatively protected against platelet aggregation and recruitment and that CD39 may have other effects on CLL, including modulation of the disease, via its metabolism of ATP.  相似文献   
124.
The DNA of the human serum amyloid A (SAA) gene GSAA1 contains several repetitive regions within its introns. We have studied length variations at one such region in the 2nd intron by selective amplification using the polymerase chain reaction (PCR) and defined oligonucleotide primers. The lengths of the repetitive regions frequently differ between individual chromosomes and can be transmitted as Mendelian markers, making them useful for genetic linkage analysis.  相似文献   
125.
Heart rate reactivity to mental stress is substantially blunted early after heart transplantation, suggesting that the loss of neural modulation limits the cardiovascular response to mental stress. We tested whether reactivity to mental stress recovers during the first year after heart transplantation. Hemodynamic and respiratory responses to mental arithmetic challenge were studied in 20 heart transplant recipients 3, 6, and 12 months after surgery. A normal comparison group was studied at equivalent intervals. Heart rate reactivity to mental arithmetic was significantly reduced in the cardiac transplant group compared to the normal subjects. This effect persisted up to 1 year after transplantation. Heart period variability in the heart transplant recipients was minimal in all three-test sessions. The findings suggest that no functional reinnervation or other compensatory adaptation occurs up to 1 year after heart transplantation.  相似文献   
126.
 Glial cell line-derived neurotrophic factor (GDNF) has recently been shown to signal by binding to GDNF receptor-alpha (GDNFR-α), after which the GDNF-GDNFR-α associates with and activates the tyrosine kinase receptor Ret. We have localized Ret messenger RNA (mRNA) in the developing and adult rodent and compared with to the expression of GDNF and GDNFR-α mRNA. Ret mRNA is strongly expressed in dopamine neurons and α-motorneurons as well as in thalamus, ruber and occlumotor nuclei, the habenular complex, septum, cerebellum, and brain stem nuclei. Ret mRNA was also found in several sensory systems, in ganglia, and in nonneuronal tissues such as teeth and vibrissae. Very strong Ret mRNA signals are present in kidney and the gastrointestinal tract, where Ret and GDNF mRNA expression patterns are precisely complementary. The presence of Ret protein was confirmed in adult dopamine neurons using immunohistochemistry. GDNFR-α mRNA was strongly expressed in the developing and adult dopamine neurons. It was also found in neurons in deep layers of cortex cerebri, in hippocampus, septum, the dentate gyrus, tectum, and the developing spinal cord. In the kidney and the gastrointestinal tract, GDNFR-α mRNA and Ret mRNA distribution overlapped. Dorsal root ganglia, cranial ganglia, and developing peripheral nerves were also positive. GDNFR-α was additionally found in sensory areas and in developing teeth. Sensory areas included inner ear, eye, olfactory epithelium, and the vomeronasal organ, as well as developing tongue papillae. The temporospatial pattern of expression of GDNFR-α mRNA did not always match that of Ret mRNA. For instance, GDNFR-α mRNA was also found in the developing ventral striatum, including the olfactory tubercle, and in hippocampus. These areas seemed devoid of Ret mRNA, suggesting that GDNFR-α might also have functions unrelated to Ret. Received: 2 January 1997 / Accepted: 26 February 1997  相似文献   
127.
IgG antibody to gE, the Fc gamma-binding herpes simplex 1 (HSV-1) viral glycoprotein, was studied in 49 rheumatoid arthritis (RA) patients and 43 normal controls. Antibody to gD, another important HSV-1 antigen, was assayed in parallel. No difference between RA patients and normal controls was found in levels of anti-gE antibody measured by reactivity of IgG F(ab')2 fragments reacting with gE coated to ELISA plates. No difference in anti-gD antibody was recorded between normals and patients with RA. Levels of IgG anti-IgE antibody did not correlate with quantitative elevations of serum rheumatoid factor (RF) in RA patients. When IgG anti-gE and anti-gD were assayed in 20 patients with juvenile rheumatoid arthritis and 22 children controls, no significant differences were noted. However, when individual RFs from patients with RA were tested for reactivity against a panel of affinity-isolated F(ab')2 antibodies to gE, some evidence for individual autospecificity was obtained. Four of 20 monoclonal IgM RFs produced from RA patients' B cells showed marked elevations of reactivity with some RA patients' F(ab')2 antibodies to gE. All four of the monoclonal RFs showing this specificity were derived from RA synovial tissue B cells. These findings may provide support for the concept that some RFs in patients with RA show individual specificity for internal image determinants of IgG antibodies to viral Fc gamma-binding proteins.  相似文献   
128.
129.
Giant cell myocarditis is a highly lethal disorder characterized by rapidly progressive congestive heart failure. The aim of this study was to describe the clinical course of patients with giant cell myocarditis who received a ventricular assist device. Patients with giant cell myocarditis were identified from the Multicenter Giant cell Myocarditis Registry. Bridging to cardiac transplantation in the giant cell myocarditis patients who received a ventricular assist device was compared with bridging in the general population of heart failure patients, as reported in the literature. Median posttransplantation survival for patients with giant cell myocarditis who received and did not receive ventricular assist devices was calculated by the Kaplan-Meier method and compared with use of the log-rank test. Nine patients with giant cell myocarditis who received ventricular assist devices were identified. Seven patients survived to transplantation, four were alive 30 days posttransplantation, and two survived to 1 year. The rate of successful bridging to transplantation in seven of nine patients (78%) is similar to that reported for other ventricular assist device recipients. Posttransplantation survival of 57% (4 of 7) at 30 days and 29% (2 of 7) at 1 year was significantly lower compared with 93% 1-year survival of the 30 patients with giant cell myocarditis who did not receive ventricular assist devices before transplantation (p<0.001). Ventricular assist devices can be an effective bridge to transplantation for patients with heart failure caused by giant cell myocarditis. Although their posttransplantation survival was poor in our series, a few patients had long-term survival.  相似文献   
130.
Adults and immatures of Ixodes pacificus Cooley & Kohls were collected by flagging vegetation and from lizards during a 3-mo period in the Hualapai Mountain Park, Mohave County, AZ, in 1991. Collections were made at altitudes > or = 2,134 m. Two of 48 gut-salivary gland extracts of adult ticks were positive by IFA using a monoclonal antibody (H5332) specific to Borrelia burgdorferi. These are the first records of I. pacificus and of spirochetes tentatively identified as B. burgdorferi in Arizona.  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