全文获取类型
收费全文 | 18518篇 |
免费 | 1384篇 |
国内免费 | 461篇 |
专业分类
耳鼻咽喉 | 107篇 |
儿科学 | 583篇 |
妇产科学 | 173篇 |
基础医学 | 1282篇 |
口腔科学 | 307篇 |
临床医学 | 1456篇 |
内科学 | 1802篇 |
皮肤病学 | 276篇 |
神经病学 | 1368篇 |
特种医学 | 593篇 |
外国民族医学 | 5篇 |
外科学 | 1056篇 |
综合类 | 2291篇 |
现状与发展 | 3篇 |
一般理论 | 2篇 |
预防医学 | 2133篇 |
眼科学 | 314篇 |
药学 | 3936篇 |
19篇 | |
中国医学 | 1323篇 |
肿瘤学 | 1334篇 |
出版年
2024年 | 38篇 |
2023年 | 241篇 |
2022年 | 378篇 |
2021年 | 526篇 |
2020年 | 593篇 |
2019年 | 533篇 |
2018年 | 524篇 |
2017年 | 623篇 |
2016年 | 669篇 |
2015年 | 603篇 |
2014年 | 1177篇 |
2013年 | 1568篇 |
2012年 | 982篇 |
2011年 | 1019篇 |
2010年 | 770篇 |
2009年 | 805篇 |
2008年 | 828篇 |
2007年 | 842篇 |
2006年 | 721篇 |
2005年 | 670篇 |
2004年 | 579篇 |
2003年 | 557篇 |
2002年 | 438篇 |
2001年 | 360篇 |
2000年 | 302篇 |
1999年 | 254篇 |
1998年 | 265篇 |
1997年 | 262篇 |
1996年 | 220篇 |
1995年 | 196篇 |
1994年 | 193篇 |
1993年 | 178篇 |
1992年 | 205篇 |
1991年 | 190篇 |
1990年 | 175篇 |
1989年 | 163篇 |
1988年 | 171篇 |
1987年 | 167篇 |
1986年 | 152篇 |
1985年 | 170篇 |
1984年 | 181篇 |
1983年 | 102篇 |
1982年 | 147篇 |
1981年 | 96篇 |
1980年 | 102篇 |
1979年 | 94篇 |
1978年 | 65篇 |
1977年 | 69篇 |
1976年 | 59篇 |
1975年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
132.
Braakman R. Sipkema P. Westerhof N. 《Pflügers Archiv : European journal of physiology》1986,407(4):432-439
It has been reported that sodiumnitroprusside (SNP) decreases mean systemic pressure and simultaneously increases pressure pulse amplification towards the iliac periphery (Kenner and van Zwieten 1982). This unexpected finding was suggested to be due to a decrease in iliac peripheral resistance but an increase in iliac differential resistance. In order to investigate this apparent contradiction, the iliac periphery was hemodynamically isolated from the rest of the circulation and perfused with the dog's own blood by means of a pump. Perfusion pressure (P) and flow (F), femoral venous pressure (Pv), systemic pressure (Ps) and cardiac output (CO) were measured. Steady state pressure-flow relations of the isolated bed were obtained during control and during various i.v. infusion rates of SNP and adenosine (ADS) and were found to be straight (meanr=0.99). Their slope (P/F) was defined as differential resistance (Rd). Peripheral resistance (Rp) of the iliac bed was defined as Rp=(P-Pv)/F, calculated at the flow value where perfusion pressure equalled the prevailing systemic pressure. Total peripheral resistance (TPR) was defined as TPR=Ps/CO. The changes of Rd, Rp, Ps, CO and TPR with respect to control show that during low SNP infusion rates Rd and Rp were both increased while TPR was decreased. During all infusion rates of SNP CO did not change while Ps decreased. During low infusion rates of adenosine CO increased while Ps, Rd and Rp did not change and TPR decreased. During high infusion rates of ADS CO decreased again, Rd, Rp and Ps decreased, and TPR remained constant but at a decreased level.It is concluded that: (1) the suggestion of Kenner and van Zwieten is not supported, since SNP (as well as ADS) affects iliac peripheral and iliac differential resistance in a similar way; (2) SNP (as well as ADS) affects iliac peripheral resistance and total peripheral resistance in a differentiated way, and even in an opposite way during low infusion rates of SNP; (3) it is this opposite effect that explains the paradoxical observations of Kenner and van Zwieten; (4) for comparable reductions of TPR, CO is better maintained during infusion of SNP, while Ps is better maintained during infusion of ADS. 相似文献
133.
Evening administration of melatonin and bright light: Interactions on the EEG during sleep and wakefulness 总被引:1,自引:0,他引:1
CHRISTIAN CAJOCHEN KURT KRÄUCHI KONSTANTIN V. DANILENKO & ANNA WIRZ-JUSTICE 《Journal of sleep research》1998,7(3):145-157
Both the pineal hormone melatonin and light exposure are considered to play a major role in the circadian regulation of sleep. In a placebo- controlled balanced cross-over design, we investigated the acute effects of exogenous melatonin (5 mg p.o. at 20.40 hours) with or without a 3-h bright light exposure (5000 lux from 21.00 hours–24.00 hours) on subjective sleepiness, internal sleep structure and EEG power density during sleep and wakefulness in healthy young men. The acute effects of melatonin, bright light and their interaction were measured on the first day (treatment day), possible circadian phase shifts were assessed on the post-treatment day. On the treatment day, the evening rise in subjective sleepiness was accelerated after melatonin and protracted during bright light exposure. These effects were also reflected in specific changes of EEG power density in the theta/alpha range during wakefulness. Melatonin shortened and bright light increased sleep latency. REMS latency was reduced after melatonin administration but bright light had no effect. Slow-wave sleep and slow-wave activity during the first non-rapid eye movement (NREMS) episode were suppressed after melatonin administration and rebounded in the second NREMS episode, independent of whether light was co-administered or not. Self rated sleep quality was better after melatonin administration whereas the awakening process was rated as more difficult after bright light. On the post-treatment day after evening bright light, the rise in sleepiness and the onset of sleep were delayed, independent of whether melatonin was co-administered or not. Thus, although acute bright light and melatonin administration affected subjective sleepiness, internal sleep structure and EEG power density during sleep and wakefulness in a additive manner, the phase shifting effect of a single evening bright light exposure could not be blocked by exogenous melatonin 相似文献
134.
Summary Calcitonin gene-related peptide (CGRP) is localized in capsaicin-sensitive nerve fibres in the kidney and urogenital tract whereas calcitonin reaches the kidney through the general circulation. Systemic infusion of CGRP and perfusion of isolated rat kidney reduces vascular resistance, and increases renal blood flow and glomerular filtration. CGRP stimulates renin secretion in vivo and in vitro and inhibits contraction of isolated rat mesangial cells by angiotensin II. Calcitonin does not affect vascular resistance, renal blood flow and glomerular filtration, and is less potent in stimulating renin secretion, and does not alter contraction of isolated rat mesangial cells by angiotensin II. CGRP also exerts renal tubular effects brought about probably through interaction with calcitonin receptors. To this end, increased excretion of sodium and chloride, and stimulation of urinary flow are less pronounced with CGRP than with calcitonin. Calcitonin, moreover, stimulates the fractional urinary excretion of calcium and phosphate. 相似文献
135.
K. -M. Braumann W. Kleemann U. Martens N. Maassen U. Maass W. Schmidt D. Böning 《Journal of molecular medicine (Berlin, Germany)》1988,66(9):397-403
Summary Parameters characterizing the hemoglobin oxygen affinity were determined in blood of 12 male patients suffering from arterial occlusive disease (AOD) of the legs and compared with data obtained earlier from healthy human subjects (controls). Due to a COHb content of 4.8%±2.2% in the cigarette-smoking AOD patients, the standard oxygen dissociation curve (ODC) was left-shifted, the half-saturation pressure (P50) amounted to 24.8±1.7 mmHg (3.30±0.23 kPa), although the 2,3-diphosphoglycerate concentration was increased to 15.3±1.7 µmol/g Hb. Correcting the effects of elevated COHb shifts the P50 to 26.3 mmHg (3.5 kPa) and increases the steepness of the ODC (Hill's n) from 2.79±0.27 to about 2.99, which is significantly different from controls. The Bohr coefficients after acidification of blood with lactic acid (BCLac) show high values at low oxygen saturations of hemoglobin (–0.50±0.04 in AOD patients, –0.32±0.04 in controls;P<0.05 at 10% SO2). The cause of the alterations in hemoglobin oxygen affinity may be a reduced mean erythrocyte age, but also the influence of unknown factors generated, e.g., from anaerobic muscle metabolism in AOD.Abbreviations AOD
Arterial occlusive disease of the legs
- BC
Bohr coefficient
- BCCO2
Bohr coefficient after acidification of blood with CO2
- BCLac
Bohr coefficient after acidification of blood with lactic acid
- DPG
2,3-Diphosphoglycerate
- ODC
Oxygen dissociation curve
- P50
Oxygen pressure when hemoglobin is half-saturated 相似文献
136.
Crowding can substantially affect the transition of a protein between its native (N) and unfolded (U) states via volume exclusion
effects. Also, it influences considerably the aggregation (A) of unfolded proteins. To examine the details, we developed an
approach for computing the kinetic rates of the process N ↔ U → A in which the concentration of the protein is explicitly
taken into account. We then compute the relative change with temperature of the protein denaturation for various fractional
volume occupancies and partition of proteins in solution. The analysis indicates that, in protein solutions in which the average
distance between proteins is comparable with the radius of gyration of an unfolded protein, steric effects increase the stability
of the proteins which are in compact, native states. In heterogeneous protein solutions containing various types of proteins
with different thermal stabilities, the unfolding of the most thermolabile proteins will increase the stability of the other
proteins. The results shed light on the way proteins change the thermal stability of a cell as they unfold and aggregate.
This study may be valuable in questions related to the dynamics of thermal injuries. 相似文献
137.
Seiler Petra; Fischer Bernd; Lindenau Antje; Beier Henning M. 《Human reproduction (Oxford, England)》1994,9(10):1920-1926
The commercial polychlorinated biphenyl (PCB) formulation Aroclor1260 (4 mg/kg body weight), technical grade dichlorodiphenyltrichloroethane(DDT; 3 mg) and Lindane (-hexachlorocyclohexane; 0.8 mg) wereadministered orally, either separately or in combination, tosexually mature female rabbits three times per week for 1215weeks. Oviductal and uterine luminal fluid, cleavage stage embryos(day 1 post coitum), blastocysts (day 6), fetuses, exocoelicfluid and placentae (day 11) were analysed, firstly for chlorinatedhydrocarbon residues, and secondly for embryonic and fetal development.The doses applied were well tolerated by the treated animals.PCB and DDT accumulated in uterine secretions (day 6) but notin oviductal luminal fluid (day 1). Both chlorinated hydrocarbonswere found in preimplantation blastocysts. Residues in day 11fetuses were 16- (DDT) or 18-fold (PCB) higher than in day 6blastocysts. Significant amounts were also detected in placentaltissue and in exocoelic fluid. A specific accumulation of thehighly chlorinated biphenyl congener no. 180 was noted in fetuses,placentae and exocoelic fluid. The clear accumulation of thechlorinated hydrocarbon compounds in luminal fluid and embryonictissue is contrasted by rather weak effects on fertility. Nostatistically significant differences between treated animalsand controls were observed for fertilization rate and pre- andpost-implantation (up to day 11 post coitum) losses. However,in females exposed to PCB, a 20% higher loss of blastocystswas noticed, as compared with controls (P > 0.05). This effectwas shown on day 6 of embryonic development and may be due tothe embryotoxic activities of PCB. 相似文献
138.
Judith E. N. Albino Sandra D. Lawrence Lisa A. Tedesco 《Journal of behavioral medicine》1994,17(1):81-98
Adolescents with commonly occurring forms of malocclusion often are presumed to be at risk for negative self-esteem and social maladjustment. A randomized control group design was used to assess the psychosocial effects of orthodontic treatment for esthetic impairment. Ninety-three participants, 11 to 14 years old, with mild to moderate malocclusions, were randomly assigned to receive orthodontic treatment immediately or after serving as delayed controls. A battery of psychological and social measures was administered before treatment, during treatment, and three times after completion of treatment, the last occurring one year after termination. Repeated measures analyses of variance assessed group differences at the five time points. Parent-, peer-, and self-evaluations of dental-facial attractiveness significantly improved after treatment, but treatment did not affect parent- and self-reported social competency or social goals, nor subjects' self-esteem. In summary, dental-specific evaluations appear to be influenced by treatment, while more general psychosocial responses are not.This research was supported by Grant NIH-NIDR-R01-DE06154 from the National Institute of Dental Research. 相似文献
139.
Johnson H Haggard P 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2003,150(4):490-496
Attending to a cued location in space leads to faster reaction times when a stimulus is presented there. The reasons for this
attentional effect, and its specific locus in the information-processing chain between stimulus and response, remain unclear.
One suggestion is that attention speeds the conscious detection of stimuli. Surprisingly, this possibility appears not to
have been tested directly. To resolve this question, we asked subjects to make simple responses to lateralised targets that
followed either a valid, invalid or neutral cue, and to judge the perceived time of the target onset, or of their response,
by delayed report of the position of a clock hand. Our results showed that only a small and non-significant part of the attentional
effect is due to delayed conscious awareness of the stimulus. The greater part of the attentional effect is localised either
subsequent to conscious detection of stimuli or occurs in a separate, parallel processing stream from that which generates
the motor response.
Electronic Publication 相似文献
140.
De novo 13q partial duplication identified by cytogenetic, biochemical and molecular approaches 总被引:1,自引:0,他引:1
S. Schwartz M. Harris R. Ehrenpreis A. Zaslav L. J. Raffel M. F. Schwartz E. Lieber M. M. Cohen 《Clinical genetics》1991,40(6):417-422
A 3.5-month-old female infant manifesting dysmorphic facies, developmental delay and failure to thrive was referred for cytogenetic evaluation. Peripheral lymphocytes revealed three chromosomally distinct cell lines: 46,XX/46,XX,10p+/47,XX,10p+,+mar. Dermal fibroblasts revealed only the 46,XX,10p+cell line. High resolution G-, R-, and Q-banding suggested that the extra chromosomal material (10p+) represented a duplication of the segment 13q14----13qter. Parental karyotypes were normal. As absolute identification of de novo chromosomal abnormalities, based solely on cytogenetic studies, is sometimes difficult, both biochemical and molecular approaches were undertaken to elucidate this abnormality in more detail. Dosage effects were examined using esterase D (localized to 13q14.1) and the DNA probes p1E8 and p9A7 (localized to 13q22 and 13q31/32, respectively). These studies suggested the presence of only 2 copies of esterase D, but 3 copies of both DNA probes, allowing identification of the breakpoint at 13q14.2. 相似文献