全文获取类型
收费全文 | 10496篇 |
免费 | 448篇 |
国内免费 | 222篇 |
专业分类
耳鼻咽喉 | 15篇 |
儿科学 | 189篇 |
妇产科学 | 175篇 |
基础医学 | 1483篇 |
口腔科学 | 99篇 |
临床医学 | 811篇 |
内科学 | 2161篇 |
皮肤病学 | 42篇 |
神经病学 | 1130篇 |
特种医学 | 458篇 |
外科学 | 575篇 |
综合类 | 845篇 |
现状与发展 | 1篇 |
预防医学 | 667篇 |
眼科学 | 46篇 |
药学 | 1885篇 |
中国医学 | 269篇 |
肿瘤学 | 315篇 |
出版年
2023年 | 121篇 |
2022年 | 241篇 |
2021年 | 300篇 |
2020年 | 244篇 |
2019年 | 212篇 |
2018年 | 251篇 |
2017年 | 217篇 |
2016年 | 260篇 |
2015年 | 257篇 |
2014年 | 531篇 |
2013年 | 631篇 |
2012年 | 442篇 |
2011年 | 523篇 |
2010年 | 401篇 |
2009年 | 463篇 |
2008年 | 433篇 |
2007年 | 453篇 |
2006年 | 356篇 |
2005年 | 363篇 |
2004年 | 296篇 |
2003年 | 247篇 |
2002年 | 214篇 |
2001年 | 185篇 |
2000年 | 172篇 |
1999年 | 163篇 |
1998年 | 143篇 |
1997年 | 149篇 |
1996年 | 160篇 |
1995年 | 165篇 |
1994年 | 169篇 |
1993年 | 174篇 |
1992年 | 141篇 |
1991年 | 155篇 |
1990年 | 146篇 |
1989年 | 126篇 |
1988年 | 115篇 |
1987年 | 130篇 |
1986年 | 134篇 |
1985年 | 174篇 |
1984年 | 147篇 |
1983年 | 85篇 |
1982年 | 136篇 |
1981年 | 112篇 |
1980年 | 109篇 |
1979年 | 84篇 |
1978年 | 82篇 |
1977年 | 54篇 |
1976年 | 74篇 |
1975年 | 41篇 |
1973年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Cardiovascular changes associated with decreased aerobic capacity and aging in long-distance runners 总被引:1,自引:0,他引:1
T. Fuchi K. Iwaoka M. Higuchi S. Kobayashi 《European journal of applied physiology》1989,58(8):884-889
Summary Fifty-five male runners aged between 30 to 80 years were examined to determine the relative roles of various cardiovascular
parameters which may account for the decrease in maximal oxygen uptake (
) with aging. All subjects had similar body fat composition and trained for a similar mileage each week. The parameters tested
were
, maximal heart rate (HR
max), cardiac output (Q), and arteriovenous difference in oxygen concentration (C
a —C
ˉv) O2 during graded, maximal treadmill running. Average body fat and training mileage were roughly 12% and 50 km·week−1, respectively. The average 10-km runtime slowed significantly by 6.0%·decade−1 {[10-km run-time (min)=0.323 x age (years)+24.4] (n=49,r=0.692,p<0.001)}. A strong correlation was found between age and
{[
(ml·kg−1·min−1)=- 0.439xage+76.5] (n=55,r=-0.768, p<0.001)}. Thus,
decreased by 6.9%·decade−1 along with reductions ofHR
max (3.2%·decade−1, p<0.001) andQ (5.8%·decade−1, p<0.001), while no significant change with age was observed in estimated (C
a —C
ˉv) O2. It was concluded that the decline of
with aging in runners was mainly explained by the central factors (represented by the decline ofHR andQ in this study), rather than by the peripheral factor (represented by (C
a —C
ˉv) O2).
This study was supported, in part, by a Research Grant on Aging and Health, Ministry of Health and Welfare, Japan, and by
a Research Grant for young researchers, Meiji Life Foundation of Health and Welfare, Japan. 相似文献
82.
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
83.
V. Vihko J. SoimajÄrvi E. Karvinen P. Rahkila M. Havu 《European journal of applied physiology》1978,39(3):209-218
Summary On the basis of maximal oxygen uptake (
O2 max) 18 normal, healthy men were divided into two groups of equal size: moderately trained subjects (MTR) each having
O2 max below 65.0 ml·min–1·kg–1 body weight (54.0±8.3) and well trained subjects (WTR), whose
O2 max exceeded 65.0 ml·min–1·kg–1 body weight (69.2±4.1). The WTR group had slightly (non significant, n.s.) higher percentage of slow twitch, oxidative (SO) fibers in M. vastus lateralis and higher (n.s.) activities of cytochrome c oxidase (CytOx), succinate dehydrogenase (SDH), 3-hydroxyacyl-CoA-dehydrogenase (HADH), and citrate synthase (CS), while lactate dehydrogenase (LDH) activity was lower (n.s.). In the MTR group only, the SO-%, and the activities of CytOx, SDH and HADH correlated positively with
O2 max, and LDH negatively with
O2 max. These correlations were not significant in the WTR group possibly because of the adaptations produced by training in this group. Multiple regression analysis was used to elucidate the best combination of variables to explain the variance in
O2 max. The best model consisted of the sum of relative activities of oxidative muscle enzymes (CytOx, SDH, HADH, CS), muscle LDH activity, body fat content (% F) and lean body mass. This model explained 69% of the variance in
O2 max; and of the individual variables % F was of utmost importance. 相似文献
84.
González M Flores C Pearson JD Casanello P Sobrevia L 《Pflügers Archiv : European journal of physiology》2004,448(4):383-394
Insulin induces vasodilatation in human subjects and increases l-arginine transport and NO synthesis in human umbilical vein endothelial cells (HUVEC). Cell signalling events associated with insulin effects on activity and mRNA expression of the human cationic amino acid transporters 1 (hCAT-1) and 2B (hCAT-2B) are unknown. l-Arginine transport and eNOS activity were determined in HUVEC exposed to insulin. mRNA levels for hCAT-1, hCAT-2B and eNOS were quantitated by real time RT-PCR and endothelial NO synthase (eNOS) protein was identified by Western blot analysis. Intracellular Ca2+, l-arginine and l-citrulline levels, l-[3H]citrulline formation from l-[3H]arginine, cGMP formation, nitrite level, ATP release and membrane potential were determined. Insulin increased l-arginine transport and the mRNA levels for hCAT-1 and hCAT-2B and eNOS expression and activity. Insulin also induced membrane hyperpolarization and increased intracellular Ca2+, l-[3H]citrulline, cGMP and nitrite formation. Insulin-mediated stimulation of the l-arginine/NO pathway is thus associated with increased hCAT-1 and hCAT-2B mRNA, and eNOS expression, via mechanisms involving membrane hyperpolarization, mitogen-activated protein kinases p42 and p44, phosphatidylinositol 3-kinase, NO and protein kinase C. We have characterized a cell signalling pathway by which hyperinsulinaemia could lead to vasodilatation in human subjects, and which could have implications in patients in whom plasma insulin levels are altered, such as in diabetes mellitus. 相似文献
85.
Magni P Sparacino G Bellazzi R Toffolo GM Cobelli C 《Annals of biomedical engineering》2004,32(7):1027-1037
The identification of the insulin minimal model (MM) for the estimation of insulin secretion rate (ISR) and physiological indexes (e.g. beta-cell sensitivity) requires the knowledge of C-peptide (CP) kinetics. The four parameters of the two-compartment model of CP kinetics in a given individual can be derived either from an additional bolus experiment or, more frequently, from a population model. However, in both situations, the CP kinetics is uncertain and, in MM identification, it should be treated as such. This paper shows how to handle CP kinetics uncertainty by using a Bayesian methodology. In seven subjects, MM indexes and ISR were estimated together with their confidence intervals, using either the bolus data or the population model to assess CP kinetics. The two main results that arise from the application of the new methodology are: (i) the use of the population model in place of the bolus data to determine CP kinetics does not affect, on average, the point estimates of ISR profile and MM parameters but only the confidence intervals which becomes wider (less than 50%); (ii) in both the bolus and population situation neglecting the uncertainty of CP kinetics, as done in MM literature so far, introduces no bias, on average, on point estimates of MM indexes but only an underestimation of confidence intervals. 相似文献
86.
Experiment 1: Weanling male rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats); sham-operated animals served as controls. Rats were killed four hours and three and seven days postoperatively (post-op). Plasma was obtained and epididymal fat pads, diaphragm and liver aliquots were harvested and the in vitro incorporation of U-14C-glucose into CO2, glycogen, lipid and saponifiable fatty acids (FAs) were measured. Body weight, carcass lipid and food intake were significantly lower in DMNL rats than in controls. The only significant lesion-induced metabolic changes were hypoglycemia and greater tracer incorporation into epididymal fat pad lipid and diaphragm glycogen. Both DMNL rats and controls showed similar time courses of tracer incorporation into epididymal CO2 and FAs, diaphragm lipid and liver CO2, glycogen, lipid and FAs. Lesioned rats also showed more pronounced decreases of tracer incorporation from day 0 to day 3 in epididymal glycogen and lipid and diaphragm CO2 and glycogen. These data make it appear unlikely that very early deficits in glucose metabolism are the cause of the growth retardation seen in long-term studies with DMNL rats. The data also demonstrate considerable locus specificity, since weanling rats with ventromedial hypothalamic lesions (VMNL rats) in similar short-term studies have shown dramatic alterations in the above parameters. Experiment 2: Weanling DMNL rats and sham-operated rats were injected via tail vein with tritiated water one hour post-op. One hour after the injection they were decapitated. There were no significant differences between DMNL rats and controls in mumoles tritiated water incorporated into total liver, grams liver tissue, mg liver glycogen and ml or mg plasma glucose.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
87.
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
88.
We investigated the oxygen uptake (O2) response to exhaustive square wave exercise of approximately 2, 5 and 8 min duration in cycling and running. Nine males completed a ramp test and three square wave tests on a motorised treadmill and the same four tests on a cycle ergometer, throughout which gas exchange was assessed (Douglas bag method). The peak O2 from the ramp test was higher for running than for cycling [mean (SD): 58.4 (2.8) vs. 55.9 (3.7) ml.kg–1.min–1; P=0.04]. However O2max (defined as the highest O2 achieved in any of the four tests) did not differ between running and cycling [60.0 (2.9) vs. 58.5 (3.3) ml.kg–1.min–1; P=0.15]. The peak O2 was similar (P>0.1) for the 5 and 8 min square wave tests [98.5 (1.8) and 99.2 (2.3) %O2max for running; 97.0 (4.2) and 97.5 (2.0) %O2max for cycling] but lower (P<0.001) for the 2-min test [91.8 (2.5) and 89.9 (5.5) %O2max for running and cycling respectively]. O2 increased over the final two 30-s collection periods of the 2-min test for cycling [O2=0.18 (0.15) l.min–1; P<0.01] but not running [O2=0.00 (0.09) l.min–1; P=0.98]. We conclude that in the aerobically fit the peak O2 for square wave running or cycling at an intensity severe enough to result in exhaustion in approximately 2 min is below O2max. In running, O2 plateaus at this sub-maximal rate. 相似文献
89.
P. Delamarche M. Monnier A. Gratas-Delamarche H. E. Koubi M. H. Mayet R. Favier 《European journal of applied physiology》1992,65(1):66-72
Summary Ten prepubertal boys performed 60-min cycle exercise at about 60% of their maximal oxygen uptake as previously measured. To measure packed cell volume, plasma glucose, free fatty acids (FFA), glycerol and catecholamines, blood samples were drawn at rest using a heparinized cathether and at the 15th, 30th and 60th min of the exercise and after 30 min of recovery. At rest, the blood glucose concentrations were at the lowest values for normal. Exercise induced a small decrease of blood glucose which was combined with an abrupt increase of the noradrenaline concentration during the first 15 min. The FFA and glycerol concentrations increased throughout the exercise linearly with that of adrenaline. Compared to adults, the FFA uptake expressed per minute and per litre of oxygen uptake was greater in children. These results suggested that it is difficult for children to maintain a constant blood glucose concentration and that prolonged exercise provided a real stimulus to hypoglycaemia. An immediate and large increase in noradrenaline concentration during exercise and a greater utilization of FFA was probably used by children to prevent hypoglycaemia. 相似文献
90.
The possibility of involvement of a Na–Ca exchange mechanism in the contractile responses induced by a reduction of external Na concentration ([Na]0) has been studied in isolated guinea-pig aorta. Low-Na (11.9 mM) solution (Lisubstituted) produced a contraction in ouabain-treated muscles in the presence of phentolamine (10–6 M). The magnitude of the contraction was dependent on the duration of the pretreatment with ouabain (2×10–5 M). Ca-free solution, but not verapamil (10–6 M), abolished the contraction induced by low-Na solution. The muscles were loaded with various amounts of Na by incubating the tissue with ouabain and varying [Na]0 (11.9–148.7 mM) in the absence of Ca. The magnitude of the contractions induced in these muscles by low-Na solution containing Ca (2.5 mM) was dependent on the cellular Na content. Loss of cellular Na into low-Na solution followed a single exponential time course and the rate coefficient of Na-loss in the presence of external Ca was about twice as great as in the absence of Ca. Cellular45Ca uptake in low-Na solution was significantly greater in Na-loaded tissues (pretreated with ouabain for 3 h) than in normal tissues. The45Ca uptake in low-Na solution was not inhibited by verapamil. These results suggest that the contraction induced by low-Na solution is caused by a Ca influx which is dependent on internal Na (a Na–Ca exchange mechanism). 相似文献