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   4846篇
  免费   457篇
  国内免费   63篇
耳鼻咽喉   41篇
儿科学   157篇
妇产科学   117篇
基础医学   532篇
口腔科学   69篇
临床医学   592篇
内科学   1114篇
皮肤病学   53篇
神经病学   381篇
特种医学   214篇
外科学   948篇
综合类   101篇
一般理论   5篇
预防医学   568篇
眼科学   89篇
药学   215篇
中国医学   3篇
肿瘤学   167篇
  2021年   50篇
  2020年   42篇
  2019年   78篇
  2018年   89篇
  2017年   33篇
  2016年   50篇
  2015年   61篇
  2014年   103篇
  2013年   142篇
  2012年   146篇
  2011年   191篇
  2010年   121篇
  2009年   118篇
  2008年   197篇
  2007年   234篇
  2006年   200篇
  2005年   224篇
  2004年   214篇
  2003年   191篇
  2002年   200篇
  2001年   190篇
  2000年   189篇
  1999年   151篇
  1998年   88篇
  1997年   72篇
  1996年   60篇
  1995年   66篇
  1994年   61篇
  1993年   65篇
  1992年   142篇
  1991年   137篇
  1990年   93篇
  1989年   113篇
  1988年   118篇
  1987年   110篇
  1986年   102篇
  1985年   85篇
  1984年   78篇
  1983年   46篇
  1982年   50篇
  1981年   44篇
  1980年   40篇
  1979年   46篇
  1978年   48篇
  1977年   49篇
  1976年   45篇
  1975年   45篇
  1974年   45篇
  1973年   38篇
  1972年   45篇
排序方式: 共有5366条查询结果,搜索用时 31 毫秒
101.
OBJECTIVE: Earlier studies have suggested that symptoms of depressive disorder in adolescents may differ from those found in adults. Even so, diagnostic criteria developed in adults have come to be widely applied to younger subjects. This study examines the frequency of ICD-10 symptoms in depressive disorder and their association with severity in a large community sample of adolescents aged 15 to 18 years. METHOD: A six-wave prospective study of adolescent health and emotional wellbeing in 2032 Australian secondary school students provided an opportunity to conduct a two-phase study of adolescent onset depression. A self-administered computerised form of the revised Clinical Interview Schedule (CIS-R) was used as a first phase diagnostic measure. Second phase assessment using the Composite International Diagnostic Interview (CIDI) allowed the delineation of a group fulfilling criteria on both instruments. The ICD-10 symptoms and severity profiles for depression were generated with standard algorithms. RESULTS: 1947 (95.8%) out of 2032 subjects in the designated sample completed phase 1 assessment at least once. Participation rates at phase 2 interviews were 93%. Over the 30-month study period 69 subjects (10 male, 59 female) fulfilled criteria for ICD-10 depressive episodes on both the CIS-R and CIDI. Thirty-one per cent (n = 21) had experienced a severe episode, 46% (n = 32) moderate and 23% (n = 16) mild episodes. Loss of interest and pleasure, decreased energy and fatigue, sleep disturbance, suicidal ideation and diminished concentration most clearly distinguished adolescents with depressive disorder from controls. Self-reproach and guilt, psychomotor agitation and/or retardation and appetite disturbance with weight change showed the clearest increase in frequency with increasing severity of episode. The somatic syndrome was reported by close to one in three of those with a severe depressive episode, but was uncommon in those with mild and moderate episodes. CONCLUSIONS: The ICD-10 diagnostic criteria are applicable to depressive disorder in older adolescents. With the exception of depressed mood, found in one in five non-cases, all other symptoms were common in cases and uncommon in non-cases. Practitioner awareness of symptoms indicating the presence and severity of disorder should enhance early identification and choice of treatment in adolescent depression.  相似文献   
102.
In a large sample of Gulf War veterans (N = 2301) we examined the relations between PTSD symptoms assessed immediately upon returning from the Gulf War and self-reported health problems assessed 18–24 months later. PTSD symptomatology was predictive of self-reported health problems over time for both men and women veterans, even after the effects of combat exposure were removed from the analysis. Female veterans reported significantly more health problems than male veterans, however, there was no interactive effect of gender and PTSD on health problems. These findings provide further support for the theory that psychological response to stressors impacts health outcome.  相似文献   
103.
PURPOSE: Monocyte CD14 and its soluble form (sCD14) mediate the proinflammatory response to endotoxemia. The aim of this study was to measure the changes to these factors after major aortic surgery and the possible inhibitory role of transforming growth factor-beta(1) (TGF-beta(1)) during these procedures. METHODS: Twenty-four patients with supraceliac aortic crossclamping during thoracoabdominal aortic aneurysm (TAAA) repair and 12 patients with infrarenal aortic crossclamping as part of infrarenal aneurysm repair (AAA) were studied. Blood was collected at incision, aortic clamping, and reperfusion and at 1, 8, and 24 hours after reperfusion. Samples were assayed for endotoxin, peripheral blood monocyte CD14 expression, sCD14, tumor necrosis factor-alpha, and TGF-beta(1). RESULTS: Although there was significant endotoxemia on reperfusion in both groups of patients, peak plasma endotoxin levels were significantly higher in patients with TAAA (P =.001). Monocyte CD14 and plasma sCD14 were significantly decreased in patients with TAAA at reperfusion and 1 hour after reperfusion (P <.01, both points). In patients with AAA, a significant upregulation of CD14 was observed at 24 hours after reperfusion (P <.01), but no significant changes in sCD14 were observed. TNF-alpha showed no significant changes during the study period in both groups. In patients with TAAA, TGF-beta(1) showed significant elevation at all time points (P <.01); whereas in patients with AAA, TGF-beta(1) showed no significant changes. CONCLUSION: Splanchnic ischemia reperfusion in patients who undergo supraceliac aortic clamping is associated with peripheral blood monocyte CD14 suppression and significant elevation of TGF-beta(1). TGF-beta(1) may play an important role in modulating the immune response to endotoxemia during major aortic aneurysm surgery.  相似文献   
104.
OBJECTIVES: To determine the spectrum of N and G genotypes of respiratory syncytial virus (RSV) causing respiratory tract infection and whether particular genotypes are associated with severity of infection. PATIENTS AND METHODS: Nasopharyngeal aspirates (NPAs) were obtained from 114 infants with acute respiratory tract infection due to RSV over two seasons. Viral mRNA was extracted from NPAs or cultured virus, reverse transcribed, and the cDNA amplified by the polymerase chain reaction using primers directed to parts of the N and G gene respectively. Amplicons were separately digested with four different restriction endonucleases for each gene. The fragments were separated by agarose gel, electrophoresis, and the electrophoretic patterns used to assign the various genotypes. Disease severity was assessed as very mild (upper respiratory tract signs only), mild (coryza and signs of lower respiratory tract infection), moderate (requiring nasogastric or intravenous fluids), and severe (requiring oxygen or ventilation). RESULTS: Five of the six known N genotypes were detected, but NP4 and NP2 were found most frequently. There was no association between N genotype and disease severity. Six G (SHL) genotypes were detected. Significantly (p = 0.04) more of the infants infected with the SHL2 genotype had severe or moderate disease. CONCLUSIONS: During the seasonal peaks of RSV respiratory tract infection at least 10 different RSV genotypes cocirculated. While there is no association between N genotypes and disease severity, infection with the SHL2 G genotype appears to result in moderate to severe disease.  相似文献   
105.
Haegele  AD; Wolfe  P; Thompson  HJ 《Carcinogenesis》1998,19(7):1319-1321
Ionizing radiation is a carcinogen that induces oxidative DNA damage. 8- Hydroxy-2'-deoxyguanosine (8-OHdG) is a relatively abundant, mutagenic lesion that is widely regarded as a reliable index of oxidative DNA damage. The purpose of this study was to examine the effects of X- radiation on levels of 8-OHdG in the context of an experimental model for breast cancer in which chronic radiation exposure has been shown to be carcinogenic in Sprague-Dawley rats. A secondary objective of this study was to determine if the use of phenol during DNA isolation affected the concentration of 8-OHdG subsequently measured. Our results indicate that a profoundly carcinogenic dose of radiation induced a small but significant increase in 8-OHdG concentration in mammary gland DNA, and that the use of a phenol-based versus a salt-based method of DNA isolation had no significant impact on the levels of 8-OHdG detected in either control or irradiated tissue.   相似文献   
106.
107.
Gore DC  Ferrando A  Barnett J  Wolf SE  Desai M  Herndon DN  Goodwin C  Wolfe RR 《The Journal of trauma》2000,49(4):673-7; discussion 677-8
BACKGROUND: In critically ill patients, elevation in the plasma lactate concentration has traditionally been interpreted as indicating a deficiency in oxygen availability and is often an impetus to increase oxygen delivery clinically. However, another possible basis for increased lactate concentrations may be simply a mass effect from increased pyruvate availability (i.e., accelerated glycolysis). METHODS: In six hypermetabolic burned patients, the rates of glucose production and oxidation were quantified using a tracer infusion of 6,6 d2 glucose combined with indirect calorimetry. Measurements were obtained after a 9-hour fast and after a 3-hour infusion of unlabeled glucose at 30 micromol/kg/min. No patient was overtly septic, hypoxic, or hypovolemic. RESULTS: The infusion of glucose significantly increased the arterial glucose concentration and rate of glucose oxidation, with a corresponding increase in the arterial plasma concentration of lactate and pyruvate. Resting energy expenditure and oxygen consumption were not affected by the infusion of glucose. CONCLUSIONS: These findings show that elevations in plasma lactate in severely injured patients may, in part, be related to increases in glucose flux and not entirely a reflection of any deficit in oxygen availability. Such findings highlight a potential pitfall for interpreting plasma lactate concentrations as an index of tissue oxygen availability in hypermetabolic patients.  相似文献   
108.
The effect of post-mortem delay on the stability of the protein subunits that combine to form NMDA and AMPA type glutamate receptors has been assessed in samples of human brain tissue. While most of the subunits (i.e. GluR1, GluR2/3, GluR4, NR1) appear to be stable for up to 18 h post-mortem, the NR2A and NR2B subunits appear to be proteolyzed rapidly following death. These results are consistent with the concept that the proteolytic products of NR2A and NR2B, although at smaller molecular sizes than the full-length protein, are all identifiable on Western blots. Thus, a method is proposed that allows for the estimation of the levels of these labile proteins even in samples obtained up to 18 h post-mortem. Using this method we have estimated the levels of all AMPA and NMDA receptor subunits in selected (i.e. hippocampus, frontal and entorhinal cortex) brain tissue samples obtained from control patients and patients who have died with Alzheimer's disease. Modest decreases in NMDA receptor subunits NR1, NR2A, and NR2B were found in the hippocampus and in frontal cortex while little or no change in any of these subunits were documented in entorhinal cortex. Subunits for AMPA receptors (GluR1, GluR2/3, and GluR4) appeared to show a generalized decrease in all these tissues. As a surrogate marker for overall decreases due to generalized neuronal cell death, levels of neuron-specific enolase were measured in all tissues and were found to be nearly identical in control and Alzheimer's brains.  相似文献   
109.
Laparoscopic needle catheter jejunostomy   总被引:1,自引:0,他引:1  
  相似文献   
110.
BACKGROUND: While internal mammary artery (IMA) use predicts improved survival after coronary bypass grafting (CABG), it remains unknown whether patients undergoing concomitant aortic valve replacement (AVR) realize a similar benefit. METHODS: All patients at a single teaching institution, undergoing combined AVR-CABG, which included a graft to the left anterior descending coronary artery (LAD) from 1984 to 1994 (n = 227) were examined retrospectively. RESULTS: Patients receiving an IMA graft (yesIMA, n = 135) and patients receiving only saphenous vein grafts (nonIMA, n = 92) were not different in their presenting symptoms, or in their incidence of preoperative risk factors. The patients with IMA were more likely to be male, have a later year of operation, be younger, and have a greater body surface. Morbidity was not different between groups. IMA use did not affect 30-day mortality. Long-term actuarial survival was greater in the group with IMA (63% +/- 7% vs 42% +/- 6% at 5 years, p < 0.01). A multivariate Cox proportional hazards model demonstrated that use of an IMA graft improved survival, while recent myocardial infarction, diabetes, earlier year of operation, and lower ejection fraction diminished long-term survival. The relative risk of IMA grafting was 0.570. CONCLUSIONS: Within the limits of a retrospective analysis, patients in a modern era of cardiac operation, who undergo combined AVR-CABG, do not suffer increased morbidity from IMA use, and may realize a survival benefit from use of the IMA as a conduit for bypass of the LAD coronary artery.  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