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   42496篇
  免费   3633篇
  国内免费   204篇
耳鼻咽喉   452篇
儿科学   1578篇
妇产科学   1025篇
基础医学   5150篇
口腔科学   774篇
临床医学   4821篇
内科学   8681篇
皮肤病学   700篇
神经病学   3579篇
特种医学   1194篇
外国民族医学   2篇
外科学   5538篇
综合类   940篇
一般理论   32篇
预防医学   3875篇
眼科学   1479篇
药学   2922篇
  1篇
中国医学   140篇
肿瘤学   3450篇
  2023年   334篇
  2022年   344篇
  2021年   1093篇
  2020年   748篇
  2019年   1111篇
  2018年   1222篇
  2017年   929篇
  2016年   989篇
  2015年   1121篇
  2014年   1502篇
  2013年   1923篇
  2012年   2934篇
  2011年   2985篇
  2010年   1705篇
  2009年   1463篇
  2008年   2532篇
  2007年   2539篇
  2006年   2339篇
  2005年   2178篇
  2004年   2155篇
  2003年   1920篇
  2002年   1752篇
  2001年   1219篇
  2000年   1069篇
  1999年   935篇
  1998年   410篇
  1997年   312篇
  1996年   284篇
  1995年   274篇
  1994年   247篇
  1993年   204篇
  1992年   549篇
  1991年   521篇
  1990年   462篇
  1989年   436篇
  1988年   386篇
  1987年   362篇
  1986年   351篇
  1985年   344篇
  1984年   248篇
  1983年   224篇
  1982年   166篇
  1981年   124篇
  1980年   139篇
  1979年   173篇
  1978年   105篇
  1977年   116篇
  1976年   91篇
  1974年   95篇
  1973年   80篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
Akt, a Serine/Threonine protein kinase, mediates growth factor-associated cell survival. Constitutive activation of Akt (phosphorylated Akt, P-Akt) has been observed in several human cancers, including lung cancer and may be associated with poor prognosis and chemotherapy and radiotherapy resistance. The clinical relevance of P-Akt in non-small cell lung cancer (NSCLC) is not well described. In the present study, we examined 82 surgically resected snap-frozen and paraffin-embedded stage I to IIIA NSCLC samples for P-Akt and Akt by Western blotting and for P-Akt by immunohistochemistry. P-Akt protein levels above the median, measured using reproducible semiquantitative band densitometry, correlated with a favorable outcome (P = 0.007). Multivariate analysis identified P-Akt as a significant independent favorable prognostic factor (P = 0.004). Although associated with a favorable prognosis, high P-Akt levels correlated with high tumor grade (P = 0.02). Adenocarcinomas were associated with low P-Akt levels (P = 0.039). Akt was not associated with either outcome or clinicopathologic variables.Cytoplasmic (CP-Akt) and nuclear (NP-Akt) P-Akt tumor cell staining was detected in 96% and 42% of cases, respectively. Both CP-Akt and NP-Akt correlated with well-differentiated tumors (P = 0.008 and 0.017, respectively). NP-Akt also correlated with nodal metastases (P = 0.022) and squamous histology (P = 0.037).These results suggest P-Akt expression is a favorable prognostic factor in NSCLC. Immunolocalization of P-Akt, however, may be relevant as NP-Akt was associated with nodal metastases, a known poor prognostic feature in this disease. P-Akt may be a potential novel therapeutic target for the management of NSCLC.  相似文献   
62.
63.
The clinical presentation and the biochemical and molecular genetic findings are described in a 13 year old Chinese boy with MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes). The diagnosis was initially suspected because of the characteristic clinical features and the strong family history of convulsions. Using polymerase chain reaction—restriction enzyme analysis, the heteroplasmic nt3243 A→G mutation in mtDNA of peripheral blood leucocytes and a muscle sample was demonstrated. The oligosymptomatic relatives were then screened by this method and the degree of heteroplasmy was analysed. This appears to be the first report of a MELAS family in Hong Kong with this described mutation. Molecular genetic techniques are advantageous in the diagnosis of MELAS.  相似文献   
64.
We estimated body fat in 20 normal adults (10 males and 10 females) from 18O- and 2H-dilution spaces and from the equations of Durnin & Womersley and Pollock, Schmidt & Jackson based on skinfold thickness measurements. Differences between methods for body fat estimation were found to be sex-dependent: subsequent analyses indicated significant differences between methods within each sex. Regardless of sex, the highest fat estimates were obtained with the 18O-dilution method, followed by those obtained with the 2H-dilution method or the Durnin & Womersley equation. The lowest fat estimates were obtained using the Pollock, Schmidt & Jackson equation. The 18O-dilution method and the Durnin & Wormersley anthropometric method are both suitable and appropriate for body fat estimation in adults studied under field conditions.  相似文献   
65.
66.
67.
本实验研究血液与非血液灌流条件下缺血预处理(IP)对心肌的保护作用。应用离体大鼠Langendorf灌流模型,分血液灌流IP组、非血液(KrebsHenseleit液,KH液)灌流IP组及相应的对照组。测量心肌电生理特性等指标。结果与KH液灌流心脏相似,用血液灌流的大鼠心脏经IP后,在随后的停灌和复灌期间,心室颤动阈升高,心律失常发生率明显降低。实验结论为在用血液灌流离体大鼠心脏模型上,IP对心肌的保护作用与用生理溶液灌流的模型基本相同。  相似文献   
68.
The doubly labelled water method was used to estimate energy expenditure in 20 formula-fed infants (10 aged 1 month and 10 aged 4 months). We then compared the energy expenditure values with energy balance values calculated from energy intake and energy cost of growth. Our purpose was to compare various published equations for calculating CO2 expiration rates (and thus energy expenditure values) from the isotopic data. Those equations in which we used measured values for 18O and 2H isotope dilution spaces and estimated or measured values for insensible water losses yielded energy expenditure values (69.7 +/- 8.4 kcal/kg/d) that agreed most closely with energy balance data (70.3 +/- 11.9 kcal/kg/d). Equations in which we used a constant ratio of 1.03 between the 2H and 18O isotope dilution spaces resulted in energy expenditure values (66.3 +/- 10.2 kcal/kg/d) lower than those predicted by the energy balance data. Data analysis by nonlinear curve fitting compared to logarithmic transformation did not alter the estimates of energy expenditure obtained in these infants.  相似文献   
69.
For a number of years, optometrists have had informal working and referral relationships with many hospitals. Many hospitals were requesting diagnostic and treatment services from community optometrists while many optometrists were also requesting official recognition. With changes in the medical staff standard of the Joint Commission on Accreditation of Hospitals (JCAH)a that allowed independently licensed practitioners to be on staff, a number of optometrists have been requesting clinical privileges and to be on the Medical Staff. Practicing in a hospital can augment one's practice and can allow the optometrist greater opportunities to interact with other professionals and utilize the hospital's diagnostic facilities.  相似文献   
70.
In order to ascertain the tamponade effect of air and silicone oil we examined the contact angles subtended by ex vivo human retina, Teflon and Perspex to find a suitable experimental material which would mimic the surface properties of the retina at a three-phase interface. Using the captive bubble technique to measure the contact angle, it was found that air subtended a larger contact angle (38.8°) with the retina than did silicone oil (18.2°). On coating the Perspex surface with protein (PCP), it was observed that the surface properties were modified such that PCP subtended contact angles with air (43.0°) and silicone oil (16.4°) similar to those subtended by ex vivo human retina. Using PCP as an experimental material that mimics ex vivo human retina, spherical chambers were employed in order to examine qualitatively and to quantify the arc of contact obtained with air and silicone oil. It was found that air gave a greater arc of contact for the same percentage fill than silicone oil.  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