全文获取类型
收费全文 | 4361篇 |
免费 | 240篇 |
国内免费 | 16篇 |
专业分类
耳鼻咽喉 | 18篇 |
儿科学 | 118篇 |
妇产科学 | 33篇 |
基础医学 | 550篇 |
口腔科学 | 143篇 |
临床医学 | 346篇 |
内科学 | 1290篇 |
皮肤病学 | 67篇 |
神经病学 | 280篇 |
特种医学 | 222篇 |
外科学 | 550篇 |
综合类 | 103篇 |
预防医学 | 189篇 |
眼科学 | 25篇 |
药学 | 328篇 |
中国医学 | 8篇 |
肿瘤学 | 347篇 |
出版年
2023年 | 24篇 |
2022年 | 31篇 |
2021年 | 84篇 |
2020年 | 47篇 |
2019年 | 69篇 |
2018年 | 84篇 |
2017年 | 69篇 |
2016年 | 61篇 |
2015年 | 78篇 |
2014年 | 95篇 |
2013年 | 117篇 |
2012年 | 199篇 |
2011年 | 210篇 |
2010年 | 154篇 |
2009年 | 143篇 |
2008年 | 203篇 |
2007年 | 208篇 |
2006年 | 181篇 |
2005年 | 188篇 |
2004年 | 194篇 |
2003年 | 196篇 |
2002年 | 165篇 |
2001年 | 145篇 |
2000年 | 137篇 |
1999年 | 148篇 |
1998年 | 100篇 |
1997年 | 68篇 |
1996年 | 73篇 |
1995年 | 56篇 |
1994年 | 57篇 |
1993年 | 48篇 |
1992年 | 95篇 |
1991年 | 85篇 |
1990年 | 84篇 |
1989年 | 82篇 |
1988年 | 70篇 |
1987年 | 49篇 |
1986年 | 80篇 |
1985年 | 60篇 |
1984年 | 47篇 |
1983年 | 42篇 |
1982年 | 28篇 |
1981年 | 19篇 |
1980年 | 25篇 |
1979年 | 43篇 |
1978年 | 39篇 |
1977年 | 19篇 |
1976年 | 17篇 |
1975年 | 15篇 |
1973年 | 18篇 |
排序方式: 共有4617条查询结果,搜索用时 31 毫秒
11.
12.
G K Asimakis J B Zwischenberger K Inners-McBride L A Sordahl V R Conti 《Circulation》1992,85(6):2212-2220
BACKGROUND. Adenine nucleotides (AdNs) are lost from the mitochondrial fraction of the heart cell during ischemia. It is unknown whether this pool of AdNs can be replenished after reperfusion. The purpose of this study was to evaluate the postischemic recovery of the mitochondrial AdN pool. METHODS AND RESULTS. The left anterior descending coronary artery (LAD) of the canine heart was occluded for 30 minutes followed by either no reflow, 30-minute reflow, 1-day reflow, or 7-day reflow. Systolic shortening in the LAD-supplied region was absent during occlusion but recovered to approximately 30% of preocclusion values during early reperfusion. Mitochondrial and tissue AdNs (ATP, ADP, and AMP) were determined in the LAD-supplied and left circumflex-supplied (control) regions of the heart. The AdN content (expressed as percent of control values) of mitochondria from the LAD region was 55 +/- 10% (p less than 0.002), 64 +/- 7% (p less than 0.001), 81 +/- 6% (p less than 0.03), and 94 +/- 8% for the no-reflow, 30-minute-reflow, 1-day-reflow, and 7-day-reflow groups, respectively. The AdN content (expressed as percent of control values) of tissue samples from the LAD region was 52 +/- 9% (p less than 0.002), 48 +/- 12% (p less than 0.02), 68 +/- 5% (p less than 0.002), and 70 +/- 9% for the no-reflow, 30-minute-reflow, 1-day-reflow, and 7-day-reflow groups, respectively. There was a good correlation between mitochondrial and tissue AdN (r = 0.95). Using initial exchange rates, adenine nucleotide translocase activities of mitochondria from the LAD and control regions were not significantly different. State 3 respiration of LAD mitochondria was depressed (approximately 25%, p less than 0.05) only in the no-reflow group. Acceptor control ratios of the LAD mitochondria were not significantly different from control values in any group. CONCLUSIONS. After 30 minutes of regional ischemia, postischemic restoration of the mitochondrial AdN pool occurs between 1 and 7 days; this restoration is preceded by recovery of respiratory and adenine nucleotide translocase functions. Although the abnormally low levels of AdN persist in the mitochondrial compartment during the early reperfusion period, postischemic contractile dysfunction cannot be explained by depressed mitochondrial respiratory activity. 相似文献
13.
α-Alkylation of amino acid derivatives: Synthesis and chiral resolution of [C]β-aminoisobutyric acid
A synthesis of 11C-labeled β-aminoisobutyric acid ([11C]β-AIB) and its enantiomeric resolution by high performance liquid chromatography (HPLC) are reported. β-Alanine ethyl ester 2 was converted to benzaldimine-β-alanine ethyl ester 3 in 87% yield. Treatment of the imine derivative 3 with lithium diisopropylamide (1.1 eq) in tetrahydrofuran at −78 °C, followed by addition of cold iodomethane (1.1 eq) produced the α-methylated benzaldimine-β-alanine ethyl ester 4 in 73% chemical yield. Deprotection of the amino group by acidic hydrolysis followed by basic hydrolysis of the ester group produced the desired product 1 in 37% chemical yield. Labeling was accomplished using [11C]methyl iodide. The radiola-beled product was purified by HPLC using a semipreparative reversed-phase C-18 column and 2 mM phosphate buffer (pH 5.9) as the mobile phase. The synthesis time was 35–40 min including HPLC purification, with 20–60% radiochemical yield (decay corrected). Radiochemical purity was >99%, with average specific activity being 450 mCi/μmol. Enantiomers of β-AIB were well separated by analytical HPLC using a chiral column and aqueous perchloric acid as the mobile phase. (S)-β-AIB was eluted at 17.4 min and the (R)-enantiomer was eluted at 20.0 min when the jacketed column was maintained at low temperature by circulation of ice-cold water, and the pH of the mobile phase was 1.05. 相似文献
14.
G. Rosa G. Conti P. Orsi F. D'Alessandro I. La Rosa G. Di Giugno A. Gasparetto 《Acta anaesthesiologica Scandinavica》1992,36(2):128-131
The effects of sedative-hypnotic doses of propofol on respiratory drive and pattern have not yet been extensively described. Repeated small boluses of propofol (0.6-0.3 mg.kg-1) were administered to ten ASA I patients undergoing carpal tunnel release using regional anaesthesia. Airway pressure, capnography and pneumotachography were continuously recorded. With respect to basal values, no significant variations of respiratory rate, minute volume, tidal volume, inspiratory and expiratory time, total expiratory cycle, Ti/Ttot, TV/Ti, P0.1, EtCO2 and blood gas analysis were observed. Low doses of propofol, to maintain conscious sedation of light sleep, have not been shown to cause respiratory depression. 相似文献
15.
Data on the prevalence of antibody to hepatitis C virus among 278 subjects in an institution for the mentally handicapped were analysed by risk factors. A prevalence of 4% was found, higher than blood donors belonging to the same area (1.4%). No differences in prevalence with regard the length of residence, age, sex, degree of retardation or for presence of HBV markers were observed. 相似文献
16.
17.
18.
19.
Enrico Bertino Carolina Bisson Claudio Martano Alessandra Coscia Claudio Fabris Giovanna Monti Tiziana Testa Amedeo Conti 《Pediatric allergy and immunology》2006,17(7):484-488
AIM: A positive correlation between maternal and cord-blood IgE levels is well documented for total IgEs, but not for specific IgEs. The difficulty in detecting specific cord-blood IgEs is due to their low concentrations, which hinder their dosage by low-sensitivity methods. The study aimed to correlate maternal and foetal specific IgEs against individual cow's milk proteins, detected by highly sensitive and specific techniques. METHODS: Cow's milk specific IgE detection was performed by chemiluminescence on 52 specimens of maternal and cord blood after cow's milk protein separation by 1D and 2D gel electrophoresis. Cow's milk protein (CMP) antigens were identified by mass spectrometry techniques. RESULTS: Specific IgEs for CMPs were found in 25/52 (48.1%) of maternal sera and in 19/52 (37%) of cord-blood sera. In order of decreasing frequency, the proteins found were BSA, IgG heavy chain, caseins and, in a single case, b-lactoglobulin. Positive cord-blood sera in all cases corresponded to a positive maternal result, and maternal and foetal immunoreactivity patterns were closely correlated. Moreover, in no case was there a positive cord-blood response with a negative maternal response. CONCLUSION: The study demonstrates a close relationship between maternal and cord-blood specific IgE patterns. The phenomenon observed could provide a model to elucidate the general production method of foetal IgEs, which might only be produced in the presence of both the corresponding maternal IgE and the related allergen. 相似文献
20.
Franz H Messerli Giuseppe Mancia Charles Richard Conti Carl J Pepine 《European heart journal》2006,27(23):2902-3; author reply 2903