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   261309篇
  免费   17282篇
  国内免费   1261篇
耳鼻咽喉   3056篇
儿科学   6332篇
妇产科学   4776篇
基础医学   33768篇
口腔科学   5121篇
临床医学   26433篇
内科学   54656篇
皮肤病学   4250篇
神经病学   25674篇
特种医学   11678篇
外国民族医学   13篇
外科学   40340篇
综合类   2666篇
现状与发展   4篇
一般理论   184篇
预防医学   17528篇
眼科学   5999篇
药学   18081篇
  1篇
中国医学   741篇
肿瘤学   18551篇
  2023年   1376篇
  2022年   2425篇
  2021年   6387篇
  2020年   3620篇
  2019年   5847篇
  2018年   6976篇
  2017年   5175篇
  2016年   5924篇
  2015年   7209篇
  2014年   9886篇
  2013年   13080篇
  2012年   19903篇
  2011年   20441篇
  2010年   11538篇
  2009年   10462篇
  2008年   17468篇
  2007年   18068篇
  2006年   17414篇
  2005年   17182篇
  2004年   16009篇
  2003年   14584篇
  2002年   13833篇
  2001年   2330篇
  2000年   1814篇
  1999年   2308篇
  1998年   2922篇
  1997年   2329篇
  1996年   2003篇
  1995年   1825篇
  1994年   1596篇
  1993年   1549篇
  1992年   1089篇
  1991年   1051篇
  1990年   891篇
  1989年   837篇
  1988年   763篇
  1987年   687篇
  1986年   713篇
  1985年   740篇
  1984年   950篇
  1983年   824篇
  1982年   1059篇
  1981年   987篇
  1980年   857篇
  1979年   517篇
  1978年   551篇
  1977年   472篇
  1976年   439篇
  1975年   366篇
  1974年   339篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
From the early 1980s to the present, neoliberal doctrine has called for government policies of privatization, funding cutbacks, and deregulation of public health and other domestic social programs in the belief that the market rather than the public sector can best organize and distribute crucial societal services. Proponents of a neoliberal and deregulatory mixed approach of command and control and self-regulation argue this approach provides the most adequate means to conduct regulation in the legalistic and adversarial U.S. regulatory process. In April 1994, the Occupational Safety and Health Administration issued a proposed rule to eliminate tobacco smoking in most workplace rooms, arguing secondhand tobacco smoke annually killed up to 13,700 nonsmokers. The tobacco industry purposely delayed public hearing procedures (later halted altogether by Congress and the president) primarily to advance unhindered private property rights and profits rather than submitting to a public command-and-control regulatory framework to reduce deaths due to secondhand tobacco smoke.  相似文献   
132.
133.
134.
The digestive properties of Australian elapid snake venoms have not been studied to any great extent. To address this, the in vitro digestive properties of Oxyuranus scutellatus (Australian Coastal Taipan) venom were investigated in a simulation of the in vivo conditions using the parameters reported for the stomach of snakes and representative prey for this species. The amount of soluble protein released was measured over time using a bicinchoninic acid (BCA) assay. Dismembered mouse hindlegs were injected intramuscularly with 0.1 ml O. scutellatus venom (concentration 10 mg/ml) and maintained in a micro-anaerobic, acidic environment (pH approximately 1.2-1.7) at 25 degrees C. The bathing liquid was sampled every 24 h for 7 days, and assayed for soluble protein. Statistical analysis revealed that O. scutellatus venom increased the rate at which proteins were released when compared to a negative control suggesting the potential importance of envenomation in the digestion of whole prey.  相似文献   
135.
BACKGROUND: 1Alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2) Vitamin D(3)] induces growth inhibition in squamous cell carcinoma (SCC) cell lines of the head and neck by arresting the cells in the G0/G1 phase of the cell cycle, probably due to an enhanced expression of p21, which could be demonstrated in other cell lines (JPPA, SCC9) before. In SCC25, a SCC cell line isolated from tongue, growth inhibition but no overexpression of p21 was detected. The retinoblastoma gene, as a direct target of G1 cyclin-CDK complexes, showed an obvious shift from the hyperphosphorylated to the hypophosphorylated form under 1,25(OH)(2)Vitamin D(3), which indicates that the growth inhibition takes place in the G0/G1 phase. To explore the possible pathway of growth inhibition in SCC25 we investigated other cell cycle inhibitors (p18, p19, p27). METHODS: Synchronized cells were treated with 1,25(OH)(2)Vitamin D(3) over 96 h. The cell cycle status and expression of cell cycle-regulating proteins was determined by fluorescence-activated cell sorting (FACS) and Western blotting. An overexpression of p18 in 1,25(OH)(2)Vitamin D(3) vs. ethanol-treated cells was determined until 30 h in SCC25. No influence was detectable on the expression of p27 and p19. CONCLUSION: One mechanism by which 1,25(OH)(2)Vitamin D(3) controls cell growth might be the upregulation of p21. As p21 was unsusceptible to 1,25(OH)(2)Vitamin D(3) in SCC25, other inhibiting proteins were necessary to be tested. The proven upregulation of p18 seems to be the responsible step for growth inhibition of 1,25(OH)(2)Vitamin D(3) in SCC25.  相似文献   
136.
137.
BACKGROUND & AIMS: Breath methane measurements reflect the in situ activity of the methanogenic colonic flora. Thirty-five years ago we found that 34% of healthy adult subjects were methane producers (breath methane level >1 ppm above atmospheric methane levels). The current study presents a new survey of breath methane levels designed to determine if the activity of the methanogenic flora has changed over the past 35 years. In addition, we review insights into the methanogenic flora that have resulted from breath methane measurements. METHODS: The end-alveolar breath methane concentrations of 212 healthy adults living in the Minneapolis area were determined via gas chromatography. The influence of sex, age, and bowel movement frequency on methane production was assessed. RESULTS: The findings that 36.4% of participants were methane producers, with a mean methane concentration in these producers of 16.6 ppm, are strikingly similar to the values of 33.6% and 15.2 ppm observed 35 years ago. Neither sex nor age showed a statistically significant relationship to methane production. There was a negative correlation between frequency of bowel movements and breath methane concentration in methane producers. CONCLUSIONS: The activity of the methanogenic flora of healthy adults remained remarkably stable over the past 35 years despite widespread antibiotic use and dietary changes. A literature review revealed that many associations have been shown between methane production and clinical states, but it remains to be determined if methanogens actively influence human physiology or are simply a marker of colonic function.  相似文献   
138.
139.
Objective: To document the breastfeeding practices of Aboriginal mothers delivering in Perth. Design and methods: A cohort of mothers was followed from the time of delivery for six months to obtain details of infant feeding practices. Subjects: A total of 455 mothers delivered during the study period and were asked to participate. A total of 425 mothers completed the initial questionnaire. Setting: The study was undertaken in six public hospitals in Perth, Western Australia. Data analyses: The data were analysed using spss . Breastfeeding duration was calculated using Kaplan–Meier survival analysis. Main outcome measures: Breastfeeding initiation and duration. Results: The mean age of the Aboriginal mothers was 21.8 years (range 14–39 years, SD 5.32) and the average gestational age was 38.3 weeks. Almost 50% of the mothers in the study delivered by Caesarean section. At discharge from hospital 89.4% (CI 86.6–92.1) of mothers were breastfeeding, declining to 58.8% (CI 53.5–64.1) at six months. When compared with non‐Aboriginal mothers, the Aboriginal breastfeeding rates were higher than the non‐Aboriginal average breastfeeding rates, but lower than the highest socioeconomic group. Conclusions: The breastfeeding rates of Aboriginal mothers are higher than for other Australians. This is despite the low maternal age and level of education and the high rates of low‐birth‐weight infants and Caesarean section among this population. The World Health Organization recommendation for infant feeding is exclusive breastfeeding until six months, but less than one‐third of Aboriginal mothers achieved this recommendation.  相似文献   
140.
The incidence of wound botulism is increasing and the epidemiology of the disease is changing. The majority of new cases are associated with injection drug use, in particular, the use of Mexican black tar heroin. This case report and discussion of wound botulism illustrate the following important points: Dysphagia, dysphonia, diplopia, and descending paralysis, in association with injection drug use, should alert the treating physician to the possibility of wound botulism. In such patients, the onset of respiratory failure may be sudden and without clinically obvious signs of respiratory weakness. For the reported patient, maximum inspiratory force measurements were the only reliable indicator of respiratory muscle weakness. This is a measurement not routinely performed in the ED, but may prove essential for patients with suspected wound botulism. To minimize the effect of the botulinum toxin and to decrease length of hospital stay, antitoxin administration and surgical wound debridement should be performed early.  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