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   2359篇
  免费   134篇
  国内免费   9篇
耳鼻咽喉   1篇
儿科学   79篇
妇产科学   71篇
基础医学   278篇
口腔科学   80篇
临床医学   201篇
内科学   538篇
皮肤病学   209篇
神经病学   105篇
特种医学   261篇
外国民族医学   9篇
外科学   218篇
综合类   60篇
一般理论   6篇
预防医学   148篇
眼科学   22篇
药学   106篇
中国医学   8篇
肿瘤学   102篇
  2021年   26篇
  2019年   23篇
  2018年   40篇
  2016年   29篇
  2015年   22篇
  2014年   39篇
  2013年   60篇
  2012年   85篇
  2011年   98篇
  2010年   42篇
  2009年   64篇
  2008年   89篇
  2007年   85篇
  2006年   93篇
  2005年   76篇
  2004年   78篇
  2003年   79篇
  2002年   68篇
  2001年   42篇
  2000年   67篇
  1999年   49篇
  1998年   31篇
  1997年   24篇
  1996年   29篇
  1995年   22篇
  1993年   36篇
  1992年   61篇
  1991年   51篇
  1990年   60篇
  1989年   75篇
  1988年   65篇
  1987年   54篇
  1986年   55篇
  1985年   77篇
  1984年   49篇
  1983年   41篇
  1981年   26篇
  1980年   22篇
  1979年   49篇
  1978年   32篇
  1977年   24篇
  1976年   28篇
  1974年   22篇
  1973年   29篇
  1972年   25篇
  1971年   29篇
  1970年   24篇
  1969年   21篇
  1967年   22篇
  1966年   21篇
排序方式: 共有2502条查询结果,搜索用时 15 毫秒
71.

Background  

Despite the well-recognised Indigenous-non-Indigenous health disparity, some reports suggest improvements in Indigenous mortality. Our aim was to quantify Indigenous mortality in Outer Regional (OR), Remote (R), and Very Remote (VR) areas in New South Wales, Queensland, South Australia, Western Australia, and the Northern Territory and changes in mortality from 1998 to 2005.  相似文献   
72.
Polymorphism of the thiopurine S-methyltransferase gene in African- Americans   总被引:12,自引:0,他引:12  
The molecular basis for the genetic polymorphism of thiopurine S - methyltransferase (TPMT) has been estab-lished for Caucasians, but it remains to be elucidated in African populations. In the current study, we determined TPMT genotypes in a population of 248 African-Americans and compared it with allele frequencies in 282 Caucasian Americans. TPMT genotype was determined in all individuals with TPMT activity indicative of a heterozygous genotype (</=10.1 U/ml pRBC, n = 23African- Americans, n = 21 Caucasians) and a control group with TPMT activity indicative of a homozygous wild-type genotype (>10.2 U/ml pRBC, n = 23 African-Americans, n = 21 Caucasians). No mutant alleles were found in the high activity control groups. The overall mutant allele frequencies were similar in African-Americans and Caucasians (4.6 and 3.7% of alleles, respectively). However, while TPMT*3C was the most prevalent mutant allele in African-Americans (52.2% of mutant alleles), it represented only 4.8% of mutant alleles in Caucasians ( P < 0.001). In contrast, TPMT*3A and TPMT*2 were less common in African-Americans (17.4 and 8.7% of mutant alleles), whereas TPMT*3A was the most prevalent mutant allele in Caucasians (85.7% of mutant alleles). A novel allele ( TPMT*8 ), containing a single nucleotide transition (G644A), leading to an amino acid change at codon 215 (Arg-->His), was found in one African-American with intermediate activity. These data indicate that the same TPMT mutant alleles are found in American black and white populations, but that the predominant mutant alleles differ in these two ethnic groups.   相似文献   
73.
Solid tumors exhibit heterogeneous microenvironments, often characterized by limiting concentrations of oxygen (O2), glucose, and other nutrients. How oncogenic mutations alter stress response pathways, metabolism, and cell survival in the face of these challenges is incompletely understood. Here we report that constitutive mammalian target of rapamycin complex 1 (mTORC1) activity renders hypoxic cells dependent on exogenous desaturated lipids, as levels of de novo synthesized unsaturated fatty acids are reduced under low O2. Specifically, we demonstrate that hypoxic Tsc2−/− (tuberous sclerosis complex 2−/−) cells deprived of serum lipids exhibit a magnified unfolded protein response (UPR) but fail to appropriately expand their endoplasmic reticulum (ER), leading to inositol-requiring protein-1 (IRE1)-dependent cell death that can be reversed by the addition of unsaturated lipids. UPR activation and apoptosis were also detected in Tsc2-deficient kidney tumors. Importantly, we observed this phenotype in multiple human cancer cell lines and suggest that cells committed to unregulated growth within ischemic tumor microenvironments are unable to balance lipid and protein synthesis due to a critical limitation in desaturated lipids.  相似文献   
74.
75.
76.
The Medtronic Riata implantable cardioverter–defibrillator (ICD) lead is a 7-Fr ICD lead shown to have a propensity for cardiac perforation. This report details two pediatric cases of cardiac perforation in patients with a Riata ICD lead. Analysis regarding the effect of ICD implantation techniques on cardiac perforation specific to pediatric patients is discussed.  相似文献   
77.
78.
背景与目的: 环氧合酶2(cyelooxygenase-2,COX-2)是花生四烯酸转化为前列腺素(prostaglandins,PGs)代谢中重要的限速酶,幽门螺杆菌(Helicobacterpylori,Hp)感染诱导胃黏膜COX-2的过度表达是胃癌发生的重要环节,但Hp感染胃黏膜细胞COX-2表达的机制尚不清楚.本研究旨在揭示Hp对人胃癌MKN45细胞COX-2表达和p38MAPK信号通路的影响,探讨COX-2表达的可能机制.方法: 采用实时荧光定量PCR(real time-PCR)检测Hp标准株NCTC11637感染对人胃痛MKN45细胞COX-2 mRNA转录的影响,Western blot检测坳COX-2蛋白表达的影响和p38MAPK信号通路的激活及其下游因子ATF-2的表达.结果: Hp感染人胃癌MKN45细胞后,COX-2 mRNA的表达明显上调,Hp感染3、6、9、12 h后COX-2 mRNA的表达量分别为正常值的3倍、7.2倍、5.1倍和4.3倍,各时间组COX-2 mRNA表达均明显高于对照组(P<0.01);Up与MKN45细胞共培养24 h后,COX-2蛋白的表达亦显著增加(P<0.01).Hp感染MKN45 20 min后,p38MAPK信号通路被激活,60 min达峰值;p38MAPK下游因子ATF-2的表达也明显增加,2 h达高峰,随着作用时间的延长,表达逐渐下降,24 h仍有表达.结论: Hp感染能诱导人胃癌MKN45细胞COX-2的表达;激活p38MAPK信号通路,增加其下游因子ATF-2的表达,可能是其诱导COX-2表达的机制.  相似文献   
79.
Congestive heart failure is a chronic, debilitating illness, with increasing prevalence in the elderly. It is one of the most common causes for hospital admission, and associated treatment costs are estimated at $20.2 billion. Despite improved survival with medical therapy, beneficial effects on quality of life have not been consistently reported. In addition, optimum medical therapy, as recommended by evidence-based guidelines, are not always implemented. Counseling and education involving dietary modifications, activity recommendations, medication management, self-monitoring, prognosis, coping skills, social support, caregiver stress, and spiritual needs are critical components in the management of heart failure through initial diagnosis to end of life. Within the last decade, close follow-up for congestive heart failure has been associated with decreased hospitalizations, reduced hospital length of stay, improved functional status, better compliance, lower costs, and improved survival. Research trials have mainly been observational and small, and they have used different interventions. Little has been written regarding outpatient management of the patient with advanced congestive heart failure, and none of the current published guidelines addresses recommendations for the New York Heart Association class IV (other than for transplant candidacy). New models of close follow-up for chronic and advanced congestive heart failure should be investigated. These models could be implemented in urban and rural settings and be supported by private insurance or Medicare.  相似文献   
80.
Cryopreserved sperm have lowered fertility when compared with fresh sperm in artificial insemination by donor programs. The purpose of this study was to compare pregnancy rates following intrauterine insemination (IUI) and intracervical insemination (ICI) with cryopreserved sperm in a prospective trial using the patient as her own control. A total of 154 patients were randomized into alternating treatment cycles and underwent 238 cycles of IUI and 229 cycles of ICI. The pregnancy rate per treatment cycle was 9.7% following IUI and 3.9% following ICI. Treatment outcome was influenced by patient age, ovulatory status, and endometriosis. Pregnancy success correlated well with the post-thaw survival of sperm and the number of motile cells inseminated. In spite of having normal semen parameters, some donors were found to have markedly reduced sperm fecundity. We conclude that IUI with cryopreserved sperm can be an effective treatment for couples with infertility, genetic indications, or other reasons.  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