全文获取类型
收费全文 | 355篇 |
免费 | 7篇 |
国内免费 | 6篇 |
专业分类
儿科学 | 14篇 |
妇产科学 | 2篇 |
基础医学 | 142篇 |
口腔科学 | 8篇 |
临床医学 | 30篇 |
内科学 | 83篇 |
皮肤病学 | 3篇 |
神经病学 | 18篇 |
特种医学 | 36篇 |
外科学 | 6篇 |
综合类 | 1篇 |
预防医学 | 3篇 |
药学 | 11篇 |
肿瘤学 | 11篇 |
出版年
2021年 | 1篇 |
2019年 | 2篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 3篇 |
2013年 | 2篇 |
2011年 | 1篇 |
2010年 | 2篇 |
2009年 | 6篇 |
2008年 | 9篇 |
2007年 | 24篇 |
2006年 | 33篇 |
2005年 | 22篇 |
2004年 | 30篇 |
2003年 | 21篇 |
2002年 | 17篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1972年 | 2篇 |
排序方式: 共有368条查询结果,搜索用时 562 毫秒
101.
Observation by transmission electron microscopy, coupled with morphometric analysis and estimation procedure, revealed unique
ultrastructural features in 25.94% of noradrenaline (NA)-containing granules and 16.85% of adrenaline (A)-containing granules
in the rat adrenal medulla. These consisted of evaginations of the granule limiting membrane to form budding structures having
different morphology and extension. In 14.8% of NA granules and 12.0% of A granules, outpouches were relatively short, looked
like small blebs emerging from the granule surface and generally contained electron-dense material. A proportion of 11.2%
of NA granules and 4.9% of A granules revealed the most striking ultrastructural features. These secretory organelles presented
thin, elongated, tail-like or stem-like appendages, which were variably filled by chromaffin substance and terminated with
spherical expansions of different electron density. A cohort of vesicles of variable size (30–150 nm in diameter) and content
was found either close to them or in the intergranular cytosol. Examination of adrenal medullary cells fixed by zinc iodide–osmium
tetroxide (ZIO) revealed fine electron dense precipitates in chromaffin granules, budding structures as well as cytoplasmic
vesicles. These data indicate that a common constituent is revealed by the ZIO histochemical reaction in chromaffin cells.
As catecholic compounds are the main tissue targets of ZIO complexes, catecholamines are good candidates to be responsible
for the observed ZIO reactivity. This study adds further to the hypothesis that release of secretory material from chromaffin
granules may be accomplished by a vesiclular transport mechanism typical of piecemeal degranulation. 相似文献
102.
103.
AB Houston MJ Brodie MR Moore GG Thompson JB Stephenson 《Archives of disease in childhood》1977,52(8):646-650
A 9-year-old boy with mental deterioration and epilepsy suffered an acute attack of hereditary coproporphyria associated with worsening of seizure control. Leucocyte coproporphyrinogen oxidase activity was undetectable in the patient during this attack, and was reduced in his mother, a latent case. The complex relationship between porphyria, epilepsy, and anticonvulsant drugs is discussed. 相似文献
104.
105.
Alteration in methyl-methanesulfonate-induced poly(ADP-ribosyl)ation by 2-butoxyethanol in Syrian hamster embryo cells 总被引:1,自引:0,他引:1
The effects of 2-butoxyethanol (2-BE) on poly(ADP-ribosyl)ation were
studied in Syrian hamster embryo (SHE) cells by measuring the cellular
concentrations of the polymer poly(ADP-ribose) (pADPr) and of NAD+, the
substrate of poly(ADP-ribose) polymerase (PARP). As biotransformation
pathways of ethylene glycol ethers involve NAD+-dehydrogenases, it was
hypothesized that 2-BE could reduce poly(ADP-ribosyl)ation by consuming
NAD+. As a result DNA repair could be altered, which would explain that
2-BE had been shown to potentiate the effects of clastogenic substances
such as methyl-methanesulfonate (MMS). In this study, the effects of 2- BE
on MMS-induced pADPr metabolism were analyzed. The results indicated that:
(i) 2-BE (5 mM) by itself did not influence significantly pADPr or NAD+
levels. (ii) 2-BE inhibited pADPr synthesis in MMS (0.2 mM)- pretreated
cells, without any change in NAD+ concentrations. (iii) MMS treatment,
which rapidly increased pADPr levels, also affected the
poly(ADP-ribosyl)ation system as a secondary effect by damaging cell
structures. Membrane permeabilization, which occurred at concentrations
>1 mM MMS, led to a dramatic leakage of cellular NAD+ resulting in a
strong reduction in pADPr levels. (iv) A bleomycin pulse (100 microM)
applied after MMS and/or 2-BE treatment confirmed that 2-BE reduced
poly(ADP-ribosyl)ation capacities of MMS-treated cells, though the glycol
ether had no effect alone. This study confirmed that the inhibition of
pADPr synthesis could be responsible for the synergistic effects of 2-BE
with genotoxic substances. The mechanism of this inhibition cannot be
explained by a lack of NAD+ at the concentrations of 2-BE tested.
相似文献
106.
While inhaled polycyclic aromatic hydrocarbons have long been suspected to
induce lung cancer in humans, their dosimetry has not been fully
elucidated. A key question is whether the critical exposure occurs during
absorption in the lungs, or if toxicants in the systemic circulation
contribute significantly to lung cancer risk. In particular, data are
needed to determine how the physical properties of inhalants affect local
dosimetry in the respiratory tract. Pyrene, a tobacco smoke component, was
selected for study because it has physical properties between those of
highly lipophilic benzo[a]pyrene and water- soluble nitrosamines. Aliquots
of 5 ng of pyrene dissolved in a phospholipid/ saline suspension were
instilled as a single-spray bolus in the posterior trachea of the dog just
anterior to the carina. For 3 h after instillation, blood was repeatedly
sampled from the azygous vein, which drains the mucosa around the point of
instillation, and from both sides of the systemic circulation. At 3 h
post-instillation, tissue samples were taken. Autoradiography was used to
determine the depth distribution of pyrene in the tracheal mucosa. The
concentration of pyrene-equivalent radioactivity in the azygous vein peaked
9 min after the instillation. At approximately 30 min after instillation, a
rapid early clearance phase shifted into a distinctly slower second
clearance phase. Rates of rapid clearance were, however, sufficiently slow
to indicate diffusion-limited absorption of pyrene in the trachea. This
finding was corroborated by high concentrations of pyrene in the epithelium
as determined by autoradiography. High epithelial concentration of pyrene
combined with a slow penetration into the circulating blood allowed
substantial first-pass metabolic conversion of pyrene in the tracheal
mucosa. A total of 13% of the instilled pyrene was retained in the tracheal
mucosa 3.2 h after instillation; of this, 29% was parent compound, 52% was
organic-extractable metabolites, 14% was water-soluble metabolites and 6%
(approximately 1% of the instilled amount) was covalently bound to tracheal
tissues. Results support the inference that lipophilic protoxicants,
because of slow, diffusion-limited absorption, are more likely than
water-soluble protoxicants to be bioactivated in the lining epithelium and,
in turn, induce first-pass toxicity at the site of entry. In addition,
limitations were identified in the use of systemically distributed
biomarkers of PAHs, such as urinary hydroxypyrene levels, as indicators of
the biologically effective dose in airway target cells.
相似文献
107.
The effects of nafenopin, a hypolipidemic drug, on the zona glomerulosa of the rat adrenal cortex were investigated. Chronic nafenopin treatment significantly lowered serum cholesterol level, but did not alter blood aldosterone concentration, though the biosynthesis of adrenal cortico-steroid hormones seems to be largely dependent upon a continuous uptake of cholesterol from plasma lipoproteins. Stereology showed that the treatment provoked a notable lipid droplet depletion, coupled with a significant proliferation of smooth endoplasmic reticulum (SER) profiles. Since SER is known to be involved in the endogenous synthesis of cholesterol, the hypothesis is advanced that SER hypertrophy is a compensatory response enabling zona glomerulosa cells to maintain an adequate level of aldosterone output even in the absence of a normal supply of exogenous cholesterol. 相似文献
108.
G G Nussdorfer G Mazzocchi C Robba A S Belloni A M Gambino 《The Anatomical record》1977,188(1):125-131
The radioactivity decay of the mitochondrial compartment from the zona fasciculata of the adrenal cortex of 3H-thymidine-injected rats was followed by high resolution autoradiography. The number of days in which the radioactivity of the mitochondrial compartment was reduced to a half was calculated from the semilogarithmic plots of radioactivity versus time. Since DNA is a very stable molecule, it was assumed that this parameter can be an estimate of the half-life of adrenocortical mitochondria. The half-life of mitochondria from the zona fasciculata of the normal rat averaged 11.17 days, and ACTH was found to increase significantly this figure to about 15 days. It is hypothesized that the ACTH-elicited stimulation of the growth of rat adrenal zona fasciculata mitochondria involves not only hypertrophy and proliferation of the organelles (Nussdorfer et al., '74b), but also the slowing down of the degeneration rate of mitochondria. 相似文献
109.
Folin M Baiguera S Conconi MT Di Liddo R De Carlo E Parnigotto PP Nussdorfer GG 《International journal of molecular medicine》2004,14(4):609-613
Apolipoprotein E (ApoE) is the major lipid-carrier protein in the brain, and several studies provided evidence that ApoE epsilon4 allele can be considered a genetic risk factor for vascular diseases. Findings indicate that Alzheimer disease (AD) and vascular dementia (VaD) may have common risk factors and/or pathogenesis, but their interrelationships still need to be clearly defined. Since ApoE4 imparts risk for both hyperlipidemia and AD, it seemed worthwhile to investigate the possible role of ApoE in the pathogenesis of AD and VaD. To this task, we examined in healthy volunteers, and AD and VaD patients: i) the frequency of ApoE isoforms; and ii) the influence of ApoE genotype on serum lipid levels. Our findings suggest that epsilon4 allele is an important risk factor for the development not only of the Alzheimer type, but also of the vascular type of dementia. In contrast, epsilon2 allele could have a protective role in AD dementia. These results confirm the hypothesis that serum ApoE concentration is dependent on ApoE genotype, but do not support the view that it has to be considered a relevant biochemical marker for AD and VaD. 相似文献
110.
Biological fate of tissue-engineered porcine valvular conduits xenotransplanted in the sheep thoracic aorta 总被引:2,自引:0,他引:2
Conconi MT Rocco F Spinazzi R Tommasini M Valfrè C Busetto R Polesel E Albertin G Dei Tos A Iacopetti I Cecchetto A Zussa C Grigioni M Parnigotto PP Nussdorfer GG 《International journal of molecular medicine》2004,14(6):1043-1048
The ideal prosthesis to replace the diseased human aortic valve is not yet available. We have previously shown that porcine acellular aortic-valve conduits, obtained by detergent-enzymatic method, display hemodynamic performances similar to those of their native counterparts. Hence, it seemed worthwhile to ascertain whether these tissue-engineered prostheses can be successfully xenotransplanted. Porcine acellular conduits, which immunocytochemistry demonstrated to lack MHC class I and II antigens, were implanted in the thoracic aorta of 9 sheep. Two animals died just after surgery, and the other 7 sheep were sacrificed 1 or 5 months after transplantation. A rather favorable outcome of the implant was observed in 4 sheep. In these animals, aortic valves remained pliable and coaptive, and the luminal surface of the conduits was endothelized just after one month from surgery. An intense inflammatory response was present at 1 month, and, although attennuated, it persisted for 5 months, located mainly between the tunica intima and media and at the border of the implant. Vimentin-positive and smooth muscle actin-positive myofibroblasts proliferated within tunica media and adventitia, and an obvious thickening of the tunica intima was also observed. Small vessels were seen in the adventitia, and elastic fibers were well-preserved in both the aorta wall and valve leaflets. In the cases of unfavorable outcome (3 of 7 survived sheep), implants were detached from the aorta recipient and surrounded by a connective mass that almost completely obstructed their lumen. These masses were composed of a fibromyxoid background where proliferating cells, resembling those occurring in human reactive myofibroblastic lesions (proliferative fascitis), were embedded. Collectively, these rather disappointing findings indicate that acellular valve conduits, obtained by the detergent-enzymatic method, are presently not suitable for clinical applications because of the persistent inflammatory response, which conceivably triggers overgrowth mechanisms that lead to implant failure. 相似文献