全文获取类型
收费全文 | 927篇 |
免费 | 63篇 |
国内免费 | 13篇 |
专业分类
耳鼻咽喉 | 2篇 |
儿科学 | 21篇 |
妇产科学 | 16篇 |
基础医学 | 81篇 |
口腔科学 | 22篇 |
临床医学 | 132篇 |
内科学 | 288篇 |
皮肤病学 | 29篇 |
神经病学 | 27篇 |
特种医学 | 141篇 |
外科学 | 97篇 |
综合类 | 12篇 |
预防医学 | 29篇 |
眼科学 | 5篇 |
药学 | 46篇 |
肿瘤学 | 55篇 |
出版年
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 14篇 |
2017年 | 10篇 |
2016年 | 7篇 |
2015年 | 18篇 |
2014年 | 9篇 |
2013年 | 29篇 |
2012年 | 24篇 |
2011年 | 35篇 |
2010年 | 20篇 |
2009年 | 41篇 |
2008年 | 30篇 |
2007年 | 43篇 |
2006年 | 31篇 |
2005年 | 25篇 |
2004年 | 16篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 25篇 |
2000年 | 14篇 |
1999年 | 20篇 |
1998年 | 53篇 |
1997年 | 48篇 |
1996年 | 23篇 |
1995年 | 28篇 |
1994年 | 16篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 16篇 |
1989年 | 21篇 |
1988年 | 22篇 |
1987年 | 26篇 |
1986年 | 20篇 |
1985年 | 23篇 |
1984年 | 19篇 |
1983年 | 24篇 |
1982年 | 12篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1979年 | 18篇 |
1978年 | 9篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 7篇 |
1972年 | 6篇 |
1971年 | 6篇 |
1947年 | 4篇 |
排序方式: 共有1003条查询结果,搜索用时 46 毫秒
91.
Ohne Zusammenfassung 相似文献
92.
93.
Klaus Halter 《Archives of dermatological research》1941,181(6):593-719
Ohne ZusammenfassungMit 19 zum Teil farbigen Textabbildungen und 37 Tabellen 相似文献
94.
In this study we have attempted to evaluate the role of dietary carbohydrate (CHO) in the decreased glucose tolerance of aging. Eighteen healthy young (mean age, 27 +/- 1 standard error of the mean) (SEM) and 18 old (71 +/- 1 SEM) subjects matched for relative weight and socioeconomic group were studied. Oral glucose tolerance tests were performed while eating ad lib diet and after being given high (85%), medium (45%), and low (20% to 30%) CHO formula diets for at least three days. A three- to seven-day food record was used to determine the major nutrients including CHO and fiber intake in the ad lib diet at home. Our older subjects consumed significantly less total calories and slightly less carbohydrate but there was no difference in dietary fiber, protein, and fat intake. When studies were performed on matched CHO diets, decreased glucose tolerance was present in the older group. However, the mechanism(s) involved may vary with dietary CHO and with age. During the low CHO formula diet and the medium CHO ad lib diet, impaired insulin secretion was prominent in the elderly but was not present in the young. During the high CHO formula diet, insulin response was adequate in both old and young, but decreased glucose tolerance persisted in the older group, suggesting that insulin resistance may be the major contributing factor. We conclude that decreased glucose tolerance in the elderly is modified by CHO intake, but is present even when dietary CHO variability is acutely controlled.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
95.
Electrical impedance tomography (EIT) is a non-invasive technique that aims to reconstruct images of internal electrical properties of a domain, based on electrical measurements on the periphery. Improvements in instrumentation and numerical modeling have led to three-dimensional (3D) imaging. The availability of 3D modeling and imaging raises the question of identifying the best possible excitation patterns that will yield to data, which can be used to produce the best image reconstruction of internal properties. In this work, we describe our 3D finite element model of EIT. Through singular value decomposition as well as examples of reconstructed images, we show that for a homogenous female breast model with four layers of electrodes, a driving pattern where each excitation plane is a sinusoidal pattern out-of-phase with its neighboring plane produces better qualitative images. However, in terms of quantitative imaging an excitation pattern where all electrode layers are in phase produces better results. 相似文献
96.
Kee F; McDonald P; Kirwan JR; Patterson CC; Love AH 《QJM : monthly journal of the Association of Physicians》1997,90(11):669-676
To determine the factors that influenced doctors' prioritization and
decisions on safe waiting time for coronary artery bypass surgery, 50
'paper patients', based on a random sample of cases who actually had
surgery, were assessed by 33 clinicians. We used linear regression models
to reflect the impact of clinical and non-clinical 'cues' on safe waiting
time and priority decisions. The benefits of surgery tended to be
over-estimated. For example, the average perceived gain in life expectancy
for patients with left main-stem disease was 6.74 years. However, models
incorporating only the perceptions of benefit as independent variables
(i.e. the anticipated symptom reduction, MI risk reduction and life
expectancy extension), had only modest explanatory power (mean R2 was 0.55
for safe waiting time, and 0.56 for priority decisions). Models which
incorporated perceptions of benefit and the cases' clinical and
non-clinical characteristics had generally much higher explanatory power
(mean R2, 0.83 and 0.86, respectively). Lifestyle and demographic variables
had much less impact on the doctors' judgements than the major clinical
cues of angina severity and left main-stem stenosis. Demographic and
lifestyle cues had different impacts on safe waiting time and priority for
about 25% of doctors.
相似文献
97.
Thrombosis in inflammatory bowel disease: clinical setting, procoagulant profile and factor V Leiden 总被引:7,自引:0,他引:7
Jackson LM; O'Gorman PJ; O'Connell J; Cronin CC; Cotter KP; Shanahan F 《QJM : monthly journal of the Association of Physicians》1997,90(3):183-188
Patients with inflammatory bowel disease have an increased frequency of
thromboembolism, and microvascular thrombosis has been proposed as a
contributory pathogenic factor. The mechanism of enhanced procoagulant
activity is not understood. We examined the clinical setting of
thromboembolic events in 52 patients with Crohn's disease or ulcerative
colitis, and assessed the procoagulant laboratory profile, including Factor
V Leiden, in a subset of 20 patients to identify procoagulant risk factors.
Patients who developed thrombosis tended to be young; 60% of thrombotic
events occurred in patients under 50 years. Multiple thromboembolic
episodes occurred in 13% and unusual sites of thrombosis (e.g.
intracardiac, cerebral, inominate veins) in 11%. No risk factor was
identifiable in 52% of cases and two-thirds of thromboses occurred in an
out-patient setting. The mortality rate was 8%. Evidence for inflammatory
disease activity was found in only 45% of patients with ulcerative colitis
at the time of the thromboembolic event, in contrast to 89% of those with
Crohn's disease. Assays for specific coagulation defects were negative in
all cases tested (protein S, C were normal in 17/17; anti-thrombin III,
anti-phospholipid antibodies and activated protein C resistance were
negative in 20/20, and only 1/20 patients was found to be heterozygous for
Factor V leiden. Thrombosis in inflammatory bowel disease is important
because it occurs in a young population, often in unusual sites, and has a
high mortality. The development of thrombosis is related to active
inflammatory disease in most patients with Crohn's disease but apparently
not in those with ulcerative colitis. Since approximately half of the
patients had no other identifiable risk factor, there remains a substantial
group of patients with IBD who develop thrombosis for unknown reasons.
相似文献
98.
BACKGROUND: Transfusion-associated graft-versus-host disease can be prevented by gamma radiation of blood components. The increased use of blood components donated for patients by their family members has resulted in an increased demand for the storage and handling of irradiated units, and the ability to freeze the cells would allow storage beyond their current expiration date. STUDY DESIGN AND METHODS: To assess the effect of freezing and deglycerolization on irradiated red cells, studies of autologous radiolabeled red cell recovery were performed using normal volunteers. Each unit of CPDA-1 red cells was immediately divided into two equal volumes. Further handling of each half was identical except that one was irradiated (3500 cGy). The units were grouped under three protocols: I, irradiated on Day 0 and frozen on Day 5 (n = 4); II, irradiated on Day 7, rejuvenated, and frozen on Day 14 (n = 5); and III, irradiated on Day 14, rejuvenated, and frozen on Day 18 (n = 3). All cells were frozen for 3 to 10 months at -80 degrees C. RESULTS: Irradiated and control units showed no significant differences in supernatant potassium or hemoglobin. Autologous 24-hour posttransfusion recoveries (mean +/− SD) for the three groups were: I, 89.7 +/− 5.6 percent (control, 90.6 +/− 3.2%); II, 85.3 +/− 5.7 percent (control, 83.7 +/− 3.0%); and III, 79.5 +/− 1.4 percent (control, 82.6 +/− 5.2%). CONCLUSION: Irradiated red cells can be frozen after being stored under various conditions and can still meet established guidelines requiring 75-percent recovery 24 hours after transfusion. 相似文献
99.
Alveolar inflation during generation of a quasi-static pressure/volume curve in the acutely injured lung 总被引:2,自引:0,他引:2
Schiller HJ Steinberg J Halter J McCann U DaSilva M Gatto LA Carney D Nieman G 《Critical care medicine》2003,31(4):1126-1133
OBJECTIVE: Lower and upper inflection points on the quasi-static curve representing a composite of pressure/volume from the whole lung are hypothesized to represent initial alveolar recruitment and overdistension, respectively, and are currently utilized to adjust mechanical ventilation in patients with acute respiratory distress syndrome. However, alveoli have never been directly observed during the generation of a pressure/volume curve to confirm this hypothesis. In this study, we visualized the inflation of individual alveoli during the generation of a pressure/volume curve by direct visualization using in vivo microscopy in a surfactant deactivation model of lung injury in pigs. DESIGN: Prospective, observational, controlled study. SETTING: University research laboratory. SUBJECTS: Eight adult pigs. INTERVENTIONS: Pigs were anesthetized and administered mechanical ventilation, underwent a left thoracotomy, and were separated into two groups: control pigs (n = 3) were subjected to surgical intervention, and Tween lavage pigs (n = 5) were subjected to surgical intervention plus surfactant deactivation by Tween lavage (1.5 mL/kg 5% solution of Tween in saline). The microscope was then attached to the lung, and the size of each was alveolus quantified by measuring the alveolar area by computer image analysis. Each alveolus in the microscopic field was assigned to one of three types, based on alveolar mechanics: type I, no visible change in alveolar size during ventilation; type II, alveoli visibly change size during ventilation but do not totally collapse at end expiration; and type III, alveoli visibly change size during tidal ventilation and completely collapse at end expiration. After alveolar classification, the animals were disconnected from the ventilator and attached to a super syringe filled with 100% oxygen. The lung was inflated from 0 to 220 mL in 20-mL increments with a 10-sec pause between increments for airway pressure and alveolar confirmation to stabilize. These data were utilized to generate both quasi-static pressure/volume curves and individual alveolar pressure/area curves. MEASUREMENTS AND MAIN RESULTS: The normal lung quasi-static pressure/volume curve has a single lower inflection point, whereas the curve after Tween has an inflection point at 8 mm Hg and a second at 24 mm Hg. Normal alveoli in the control group are all type I and do not change size appreciably during generation of the quasi-static pressure/volume curve. Surfactant deactivation causes a heterogenous injury, with all three alveolar types present in the same microscopic field. The inflation pattern of each alveolar type after surfactant deactivation by Tween was notably different. Type I alveoli in either the control or Tween group demonstrated minimal change in alveolar area with lung inflation. Type I alveolar area was significantly (p <.05) larger in the control as compared with the Tween group. In the Tween group, type II alveoli increased significantly in area, with lung inflation from 0 mL (9666 +/- 1340 microm2) to 40 mL (12,935 +/- 1725 microm2) but did not increase further (220 mL, 14,058 +/- 1740 microm2) with lung inflation. Type III alveoli initially recruited with a relatively small area (20 mL lung volume, 798 +/- 797 microm2) and progressively increased in area throughout lung inflation (120 mL, 7302 +/- 1405 microm2; 220 mL, 11,460 +/- 1078 microm2) CONCLUSION: The normal lung does not increase in volume by simple isotropic (balloon-like) expansion of alveoli, as evidenced by the horizontal (no change in alveolar area with increases in airway pressure) pressure/area curve. After surfactant deactivation, the alveolar inflation pattern becomes very complex, with each alveolar type (I, II, and III) displaying a distinct pattern. None of the alveolar pressure/area curves directly parallel the quasi-static lung pressure/volume curve. Of the 16, only one type III atelectatic alveolus recruited at the first inflection point and only five recruited concomitant with the second inflation point, suggesting that neither inflection point was due to inflection point was due to massive alveolar recruitment. Thus, the components responsible for the shape of the pressure/volume curve include all of the individual alveolar pressure/area curves, plus changes in alveolar duct and airway size, and the elastic forces in the pulmonary parenchyma and the chest wall. 相似文献
100.
Kee F; McDonald P; Kirwan JR; Patterson CC; Love G 《QJM : monthly journal of the Association of Physicians》1997,90(2):117-123
In a clinical judgement analysis, we used linear regression models to
reflect the impact of clinical and non-clinical cues on priority decisions,
by comparing the stated prioritization policies of 30 clinicians with their
actual policies as revealed by an appraisal of 50 'paper patients'.
Correspondence was modest for some cues, e.g. 25 doctors said they
accounted for age, but age only had a significant bearing in the derived
decision models of two doctors. Correspondence between the derived and
expressed weights was greatest for clinical angina grade and the presence
of left main stem stenosis. Correlation between the rank order of
importance between the two models was poor for most of the cues, and
statistically significant only for smoking. However, stated policies made
it appear that lifestyle factors such as smoking habit would influence
prioritization decisions for most clinicians but policies derived from
actual prioritization decisions seldom related to lifestyle or demographic
variables. There were significant differences in the degree of correlation
between the two models according to the experience of the clinician.
However, correspondence was not significantly better for doctors with
cardiological training than those without. The overall contribution of
demographic and lifestyle factors to decision making appears to be small,
suggesting that they should be omitted from prioritization guidelines.
相似文献