全文获取类型
收费全文 | 4359篇 |
免费 | 123篇 |
国内免费 | 75篇 |
专业分类
耳鼻咽喉 | 27篇 |
儿科学 | 196篇 |
妇产科学 | 84篇 |
基础医学 | 819篇 |
口腔科学 | 69篇 |
临床医学 | 716篇 |
内科学 | 508篇 |
皮肤病学 | 16篇 |
神经病学 | 186篇 |
特种医学 | 177篇 |
外科学 | 543篇 |
综合类 | 495篇 |
预防医学 | 199篇 |
眼科学 | 24篇 |
药学 | 346篇 |
1篇 | |
中国医学 | 104篇 |
肿瘤学 | 47篇 |
出版年
2023年 | 24篇 |
2022年 | 61篇 |
2021年 | 95篇 |
2020年 | 65篇 |
2019年 | 72篇 |
2018年 | 71篇 |
2017年 | 57篇 |
2016年 | 73篇 |
2015年 | 102篇 |
2014年 | 217篇 |
2013年 | 220篇 |
2012年 | 182篇 |
2011年 | 220篇 |
2010年 | 196篇 |
2009年 | 209篇 |
2008年 | 186篇 |
2007年 | 212篇 |
2006年 | 194篇 |
2005年 | 158篇 |
2004年 | 166篇 |
2003年 | 142篇 |
2002年 | 129篇 |
2001年 | 126篇 |
2000年 | 117篇 |
1999年 | 107篇 |
1998年 | 99篇 |
1997年 | 89篇 |
1996年 | 109篇 |
1995年 | 82篇 |
1994年 | 99篇 |
1993年 | 53篇 |
1992年 | 65篇 |
1991年 | 58篇 |
1990年 | 40篇 |
1989年 | 47篇 |
1988年 | 51篇 |
1987年 | 25篇 |
1986年 | 44篇 |
1985年 | 48篇 |
1984年 | 33篇 |
1983年 | 13篇 |
1982年 | 25篇 |
1981年 | 18篇 |
1980年 | 26篇 |
1979年 | 20篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 22篇 |
1973年 | 20篇 |
1969年 | 10篇 |
排序方式: 共有4557条查询结果,搜索用时 15 毫秒
61.
Y. Shimada K. Nakashima Y. Fujiwara T. Komatsu M. Kawanishi J. Takezawa S. Takatani 《Medical & biological engineering & computing》1991,29(5):557-561
The design of a noninvasive reflectance pulse oximeter that uses the same principle of transmittance pulse oximeter and analyses the oxygen saturation of arterial blood was described. Four sets of red and infra-red LEDs were used as light sources. The respective reflectance photoelectric outputs were used to make an internal calibration curve of the instrument relative to the arterial oxygen saturation values measured with a Co-Oximeter (OSM-3) in five healthy nonsmoking subjects during steady-state hypoxaemia. The accuracy of the present instrument was studied in six patients with respiratory failure. From 22 samples, a good correlation coefficient (0.98) with a standard deviation of 1.42 was obtained in the range between 73 and 100 per cent between the arterial oxygen saturation measured with the present instrument and that with the Co-Oximeter. The result strongly suggests the usefulness of this oximeter in monitoring patients with hypoxaemia. 相似文献
62.
M. Vegfors L. -G. Lindberg P. Å. Öberg C. Lennmarken 《Medical & biological engineering & computing》1993,31(2):135-141
In situations in which it may be impossible and/or unethical to evaluate pulse oximetry in humans, an in vitro model with
circulating blood may be a necessity. The main objective was to develop such an in vitro model and, in this model, validate
the pulse oximetry technique at various haematocrit levels. The pulsating character of arterial blood flow in a tubing system
was simulated by using a specially constructed pressure-regulated roller pump. The tubing system was designed to minimise
damage to red blood cells. The pulse oximeter readings (SpO2) were compared with oxygen saturation analyses by a haemoximeter (SaO2). The pulse oximetry readings were recorded at various haematocrit levels and during haemolysis in the SaO2 range 60–100 per cent. At a haematocrit level of 41–44 per cent, there was no correlation between SaO2 and SpO2 readings. After diluting the blood with normal saline to a haematocrit of 10–11 per cent, a good correlation between SaO2 and SpO2 was found. Following haemolysis, the agreement between SaO2 and SpO2 was further improved. Using the developed in vitro model, the results indicate that the accuracy of a pulse oximeter may
be dependent on the haematocrit level. 相似文献
63.
Various inhibitors of cyclooxygenase are known to mediate cancer chemopreventive effects. We currently describe two in vitro assay systems for measuring cyclooxygenase activity. These assays can be used in combination and thereby provide a rapid, reliable, and economical approach that is applicable for large-scale evaluation of test samples. This approach employs peroxidase co-substrate oxidation and oxygen consumption assays. The former system, adapted to a 96-well plate format, detects inhibitors that function as a radical scavengers or interact with the enzyme directly. The latter system specifically monitors cyclooxygenase inhibitors that interact with the enzyme itself. Thus, the peroxidase co-substrate oxidation assay serves as a pre-screening method, whereas the oxygen consumption assay is used subsequently to investigate the mode of action mediated by samples which test positive. 相似文献
64.
Puente-Maestu L Sánz ML Sánz P Nuñez A González F Whipp BJ 《European journal of applied physiology》2001,85(5):434-441
To be clinically useful as indices reflective of altered physiological function consequent to interventions in patients with
chronic obstructive pulmonary disease (COPD), the time constant (τ) and steady-state amplitude of the kinetic responses for
oxygen uptake (
) carbon dioxide output (
) ventilation (
) and heart rate (HR) have to be appropriately differentiable and reproducible. We therefore assessed the reproducibility
of τ and steady state amplitude values in 41 patients with severe COPD [mean (SD)] [forced expiratory volume in 1 s=41 (7)%
predicted], aged 64 (5) years. Of the total, 6 of the patients (15%) did not produce breath-by-breath data of sufficient quality
to warrant kinetic analysis. The remaining 35 patients completed two moderate-intensity 10 min square-wave exercise tests
separated by 2 h, both before and after an endurance training programme. Tests were conducted on an electromagnetically-braked
cycle ergometer at an exercise intensity corresponding to 80% of the estimated lactate threshold (θLa) or 50% of peak oxygen uptake if θLa was insufficiently differentiable. Breath-by-breath measurements of
,
,
and HR were averaged into 10 s bins and the on-transient response kinetics were estimated using a mono-exponential model.
Analysing the pre-training and the post-training test 1 and test 2 comparisons together, the test 1 –test 2 differences were
not significantly different from 0 for either τ or A. The standard deviation of the test 1 –test 2 differences allowed us
to define the magnitude of change that would reach statistical significance. For τ, this averaged some 8, 10, 11 and 8 s,
for
,
,
and HR, respectively, for a one-tailed paired-comparisons test (i.e. appropriate for assessing hypothesised improvements resulting
from an intervention); for a two-tailed comparison, the differences were approximately 2 s greater. The corresponding one-tailed
values for A were 100 ml·min–1, 95 ml·min–1, 2.5 1·min–1 and 4 beats·min–1, respectively; the two-tailed values were 10%–15% greater. We therefore conclude that both τ and A for moderate-intensity
exercise can be reproducibly estimated in patients with COPD when the data set provides a sufficiently large amplitude of
response and sufficiently low sample variability to allow appropriate parameter estimation.
Electronic Publication 相似文献
65.
Oxygen uptake during whole-body vibration exercise: comparison with squatting as a slow voluntary movement 总被引:2,自引:0,他引:2
In this study we investigated metabolic power during whole-body vibration exercise (VbX) compared to mild resistance exercise.
Specific oxygen consumption (
) and subjectively perceived exertion (rating of perceived exertion, RPE; Borg scale) were assessed in 12 young healthy subjects
(8 female and 4 male). The outcome parameters were assessed during the last minute of a 3-min exercise bout, which consisted
of either (1) simple standing, (2) squatting in cycles of 6 s to 90° knee flexion, and (3) squatting as before with an additional
load of 40% of the subject's body weight (35% in females). Exercise types 1–3 were performed with (VbX+) and without (VbX–)
platform vibration at a frequency of 26 Hz and an amplitude of 6 mm. Compared to the VbX– condition, the specific
was increased with vibration by 4.5 ml·min–1·kg–1. Likewise, squatting and the additional load were factors that further increased
. Corresponding changes were observed in RPE. There was a correlation between VbX– and VbX+ values for exercise types 1–3
(r=0.90). The correlation coefficient between squat/no-squat values (r=0.70 without and r=0.71 with the additional load) was significantly lower than that for VbX–/VbX+. Variation in specific
was significantly higher in the squatting paradigm than with vibration. It is concluded that the increased metabolic power
observed in association with VbX is due to muscular activity. It is likely that this muscular activity is easier to control
between individuals than is simple squatting.
Electronic Publication 相似文献
66.
The relation between
and work rate (WR) was examined in seven male subjects who performed ramp (1 W·3 s–1) two-legged cycle ergometry to exhaustion while inspiring either hypoxic (12% O2), normoxic (21% O2), or hyperoxic (40% O2) air. The anaerobic threshold was estimated from respiratory gas exchange data and is thus referred to as the respiratory gas exchange threshold (RGET). Prior to the RGET, the
was greater under normoxic [mean (SD); 10. 19(1.04) ml O2·min–1·W–1] and hyperoxic [10.44 (0.72)] conditions compared with hypoxia [9.34 (0.89)]. Above the RGET, the
for hypoxia [8.91 (0.63)], normoxia [10.40 (0.77)], and hyperoxia [11.08 (0.48)] were all significantly different from each other. These data indicated that for two-legged, cycle, ramp ergometry in normoxia below the RGET, both the
and response time was constant. Above the RGET, the normoxic
response was the net result of a declining
and a longer response time to the unsteady state character of a ramp exercise protocol. 相似文献
67.
A. J. M. Langbroek A. Nijmeijer P. Rispens W. G. Zijlstra 《Pflügers Archiv : European journal of physiology》1990,417(2):157-160
Arterial pH and blood gases were measured at intervals in conscious dogs after their first human contact of the day. Blood was sampled through an indwelling catheter in the aorta without disturbing the animals. It appeared that in the first 90 min arterial PO2, oxygen saturation and haemoglobin concentration significantly declined. PCO2 and pH changed less consistently when the acid/base status of the dogs was normal, but when a non-respiratory acidosis was present there was a significant decrease in pH and a significant increase in PCO2. Arterial pH and blood gases were also measured before and after feeding the animals. It appeared that an appreciable metabolic alkalosis developed within 2 h after a meal. The alkaline tide was accompanied by a trend to higher values for PCO2. It is concluded that, after a period of seclusion, renewed human contact causes behavioural changes in a dog, which may result in appreciable transitory changes in arterial pH and blood gas values. Blood sampling from conscious dogs should therefore take place after a proper period of habituation; preferably, a few samples should be taken at intervals to check that a steady state has been reached. If possible, blood should be collected before feeding; in any case the relationship in time of blood sampling to feeding should be constant throughout. 相似文献
68.
The present study was designed to compare the differential cardiopulmonary and hemodynamic responses of Type A and B women to an exercise and a psychological stressor. In addition, the effects of menstrual cycle phase on the resting and response levels of a wide range of physiological variables were explored. Thirty-two women participated in a progressive exercise stress test and a threat of shock video game during both the luteal and follicular phases of the menstrual cycle. Half of these subjects expressed the coronary-prone behavior pattern referred to as Type A, as assessed by the Jenkins Activity Survey. The remaining women were relatively free of these behaviors (Type B). Heart rate, oxygen consumption, carbon dioxide production, minute ventilation, and end-tidal carbon dioxide were monitored and recorded on a breath-by-breath basis. Systolic and diastolic blood pressure measures were taken at 2-min intervals. Results indicated similar baseline, exercise, and behavioral stress responses among Type A and B women. The stress responses were also the same between the follicular and luteal phases for all measured physiological variables. However, resting levels of heart rate, metabolism, and ventilation were all elevated at rest during the luteal phase. A regression analysis based on the exercise heart rate and oxygen consumption data demonstrated that a majority of subjects exhibited heart rate responses in excess of that expected during the psychological stressor. These data are discussed with special reference to possible mechanisms of the pathophysiology of cardiovascular disease. 相似文献
69.
Oxygen plays an important role in the cultivation of primary cellsex vivo. In this study, we used hermetically sealed tissue culture well inserts equipped with oxygen electrodes to measure the oxygen
utilization of cultured human bone marrow mononuclear cells (BM MNCs). The oxygen uptake rate (OUR) of BM MNCs was determined
during a 14-day culture in which both adherent and nonadherent cells were present. Early in the culture, the cells exhibited
very low OURs. The specific OURs (uptake rate per cell) were at approximately 0.005 μmol/106 cells/hr shortly after the initiation of culture. The OUR then increased as the cultures developed. After about 8 to 10 days
of cultivation the specific OURs had increased to 0.038±0.006 and 0.025±0.005 μmol/106 cells/hr for adherent and nonadherent cells, respectively, after which no further increase was observed. Based on these oxygen
uptake rate data, a mathematical model of oxygen diffusion was formulated and use to investigate issues associated with hematopoietic
bioreactor design, including initial cell density, medium depth, reactor configuration, and oxygen partial pressure.In situ OUR measurements confirmed predicted oxygen limitations based on the mathematical model and the experimentally determined
OURs. High-density hematopoietic cultures present design challenges in terms of sufficient and uniform delivery of oxygen
to an active hematopoietic culture. These challenges can be met by using parallelplate bioreactors with thin liquid layers. 相似文献
70.