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   29779篇
  免费   2643篇
  国内免费   49篇
耳鼻咽喉   222篇
儿科学   1116篇
妇产科学   840篇
基础医学   3836篇
口腔科学   572篇
临床医学   3385篇
内科学   5558篇
皮肤病学   687篇
神经病学   2977篇
特种医学   683篇
外国民族医学   5篇
外科学   3697篇
综合类   419篇
一般理论   79篇
预防医学   4028篇
眼科学   453篇
药学   1984篇
  1篇
中国医学   48篇
肿瘤学   1881篇
  2023年   335篇
  2022年   536篇
  2021年   1099篇
  2020年   653篇
  2019年   904篇
  2018年   1058篇
  2017年   748篇
  2016年   780篇
  2015年   813篇
  2014年   1135篇
  2013年   1489篇
  2012年   2113篇
  2011年   2129篇
  2010年   1114篇
  2009年   923篇
  2008年   1622篇
  2007年   1728篇
  2006年   1471篇
  2005年   1326篇
  2004年   1257篇
  2003年   1179篇
  2002年   995篇
  2001年   439篇
  2000年   498篇
  1999年   424篇
  1998年   249篇
  1997年   208篇
  1996年   137篇
  1995年   148篇
  1994年   138篇
  1993年   163篇
  1992年   310篇
  1991年   302篇
  1990年   290篇
  1989年   341篇
  1988年   240篇
  1987年   262篇
  1986年   235篇
  1985年   276篇
  1984年   178篇
  1983年   137篇
  1982年   122篇
  1981年   134篇
  1980年   105篇
  1979年   168篇
  1978年   131篇
  1977年   123篇
  1974年   102篇
  1973年   114篇
  1972年   101篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
Although there are well-established clinical human milk banks in the United States, there are no milk banks specifically intended to foster research on human milk. The authors' goal was to establish a milk bank with a core data set to support exploratory and hypothesis-driven studies on human milk. Donations to the Cincinnati Children's Research Human Milk Bank are accepted within the context of ongoing, hypothesis-driven research or on an ad hoc basis. Donors must give informed consent, and scientists wishing to use the samples must have Institutional review board approval for their use. Development of more research human milk banks can potentially provide resources for multidisciplinary collaboration and advance the study of human milk and lactation.  相似文献   
42.
The cytoskeleton is susceptible to oxidative stress and this occurs prior to membrane blebbing and cell lysis. Vimentin intermediary filaments in rheumatoid synoviocytes are more susceptible than in normal synoviocytes and this may have pathological significance. They are however no more susceptible to heat shock than other cell types.  相似文献   
43.
44.
45.
46.
47.
Emphysematous pyelonephritis is a severe life-threatening infection which continues to carry significant morbidity and mortality. We present a case recently managed at our institution by laparoscopic nephrectomy. The patient survived, and in comparison to some of the more conventionally managed patients in the literature, made an extremely speedy recovery. We would advocate this option to be seriously considered when patients are suitable and appropriately trained surgeons are available.  相似文献   
48.
OBJECTIVE: To quantify the dietary calcium and vitamin D intake in adult renal-transplant recipients attending at a large teaching hospital in Ireland for follow-up. SETTING: Outpatient renal-transplant follow-up clinic. SUBJECTS: Fifty-nine adult renal transplant recipients (58% male) with a mean age of 46 years, a median transplant duration of 6 years, and a mean estimated glomerular filtration rate (eGFR) of 50 mL/min per 1.73 m2. Fifty-three percent were at National Kidney Foundation stage 3 chronic kidney disease, and 14% had stage 4 chronic kidney disease. INTERVENTION: This cross-sectional, observational study used a tailored food frequency questionnaire specific for calcium and vitamin D intake in Irish adults, which was completed during a face-to-face interview with each subject. MAIN OUTCOME MEASURE: The main outcome measure was the average daily dietary and supplemented calcium and vitamin D intake. RESULTS: The median interquartile range (IQR) dietary calcium intake was 820 mg/day (range, 576-1,177 mg/day), and was similar in men and women (recommended intake > or = 1,000 mg/day in adult men and nonmenopausal adult women, > or = 1,500 mg/day in menopausal women). Five participants received calcium supplementation. Overall, 59% of men and 64% of women had total calcium intakes below the recommended amounts. The median IQR estimated dietary vitamin D intake was 5.2 microg/day (range, 2.4-6.4 microg/day) in women, and 4.6 microg/day (range, 2.2-6.6 microg/day) in men (recommended intake, > or = 10 microg/day). Six subjects received vitamin D supplementation. Total vitamin D intakes were suboptimal in 91% of men and 87% of women. Dietary calcium and vitamin D intakes significantly correlated with each other, but neither was significantly related to eGFR category, and was similarly low in both presumed menopausal women and in the initial year posttransplantation. CONCLUSION: These findings suggest that dietary and total calcium and vitamin D intakes in adult renal-transplant patients are in many cases inadequate.  相似文献   
49.
BACKGROUND AND OBJECTIVE: Contradictory and confusing reports on serum dehydroepiandrosterone (DHEA) levels in schizophrenia led us to compare the serum concentration of its precursor, pregnenolone (PREG), between medicated schizophrenia patients and healthy subjects. The neurosteroid levels were monitored for two months and the relationship of these neurosteroids with schizophrenic symptomatology, emotional distress, and anxiety was examined. METHOD: We determined blood levels of PREG, and DHEA in 15 schizophrenia patients and 12 healthy controls at four time points: at the start of the study, after 2, 4 and 8 weeks. Analysis of covariance and canonical correlations across four time points were applied. RESULTS: Controlling for age, serum concentrations of PREG were lower, while the DHEA level and the molar ratio values of DHEA/PREG were higher in schizophrenia patients compared to healthy controls. Both levels of PREG and DHEA and their molar ratio did not change significantly during the study's period either among schizophrenia patients or healthy controls. The blood levels of PREG appear to be associated with trait-anxiety scores in the schizophrenia patients, while associations of clinical symptoms with two neurosteroids did not reach a significant level when the confounding effect of emotional distress, and anxiety scores was controlled. CONCLUSION: Low serum pregnenolone concentrations in schizophrenia appear to be associated with trait-anxiety scores independent of symptoms. Further research into the role of pregnenolone in schizophrenia is warranted.  相似文献   
50.
Multiphase radon generation and transport in porous materials   总被引:5,自引:0,他引:5  
Radon generation and transport in porous materials involve solid, liquid, and gas phases in the processes of emanation, diffusion, advection, absorption, and adsorption. Oversimplifications, such as representing moist soil systems by air-phase emanation and transport models, cause theoretical inconsistencies and biases in resulting calculations. Detailed Rn rate balance equations for solid, liquid, and gas phases were analyzed and combined using phase equilibrium constants to derive a single diffusive-advective rate balance equation in the traditional form. The emanation, diffusion, and permeability coefficients in the new equation have expanded definitions and interpretations to include Rn phase transfer. Radon adsorption was characterized by an exponential moisture dependence, and diffusion and permeability constants utilized previous moisture relationships. Correct boundary and interface conditions were defined, and the unified theoretical approach was applied to field data from a diffusion-dominated system and to laboratory data from an advection-dominated system. Measured 222Rn fluxes and concentrations validated the modeled values within the measurement variability in both applications.  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