全文获取类型
收费全文 | 1496081篇 |
免费 | 111508篇 |
国内免费 | 12409篇 |
专业分类
耳鼻咽喉 | 21079篇 |
儿科学 | 42411篇 |
妇产科学 | 40585篇 |
基础医学 | 210785篇 |
口腔科学 | 42638篇 |
临床医学 | 132118篇 |
内科学 | 284956篇 |
皮肤病学 | 32209篇 |
神经病学 | 114519篇 |
特种医学 | 59170篇 |
外国民族医学 | 513篇 |
外科学 | 224358篇 |
综合类 | 57527篇 |
现状与发展 | 39篇 |
一般理论 | 463篇 |
预防医学 | 102997篇 |
眼科学 | 35505篇 |
药学 | 118222篇 |
140篇 | |
中国医学 | 11733篇 |
肿瘤学 | 88031篇 |
出版年
2021年 | 15528篇 |
2019年 | 13386篇 |
2018年 | 17391篇 |
2017年 | 14825篇 |
2016年 | 15571篇 |
2015年 | 19078篇 |
2014年 | 25560篇 |
2013年 | 33888篇 |
2012年 | 45216篇 |
2011年 | 47730篇 |
2010年 | 29599篇 |
2009年 | 27416篇 |
2008年 | 42318篇 |
2007年 | 45466篇 |
2006年 | 45348篇 |
2005年 | 43503篇 |
2004年 | 40828篇 |
2003年 | 39572篇 |
2002年 | 38273篇 |
2001年 | 67217篇 |
2000年 | 68416篇 |
1999年 | 58312篇 |
1998年 | 16566篇 |
1997年 | 15458篇 |
1996年 | 14380篇 |
1995年 | 13621篇 |
1994年 | 12714篇 |
1992年 | 43842篇 |
1991年 | 42255篇 |
1990年 | 41439篇 |
1989年 | 40364篇 |
1988年 | 37686篇 |
1987年 | 37038篇 |
1986年 | 35486篇 |
1985年 | 33568篇 |
1984年 | 25227篇 |
1983年 | 21366篇 |
1982年 | 12944篇 |
1979年 | 24148篇 |
1978年 | 17290篇 |
1977年 | 15074篇 |
1976年 | 13596篇 |
1975年 | 15408篇 |
1974年 | 18275篇 |
1973年 | 17730篇 |
1972年 | 16962篇 |
1971年 | 15864篇 |
1970年 | 15043篇 |
1969年 | 14472篇 |
1968年 | 13564篇 |
排序方式: 共有10000条查询结果,搜索用时 353 毫秒
961.
Creativity and problem solving are closely related in the learning and practice of nursing. The problem underlying this study concerns the attitudes of professors of nursing in 321 French language community colleges in Quebec toward the creative characteristics of their students. However, given the absence of a valid and reliable French instrument, this study focused on the validation of a French version of Torrance's Ideal Pupil Checklist. Content, construct and criteria validity were all verified, as well as the stability and homogeneity aspects of reliability. 相似文献
962.
Zia Hossein Ma Joseph K. H. O'Donnell John P. Luzzi Louis A. 《Pharmaceutical research》1991,8(4):502-504
Dimethyl isosorbide (DMI), which is currently under investigation for its potential use as a pharmaceutical vehicle and drug permeation enhancer, is a water-miscible liquid with relatively low viscosity. The solubilization behavior of DMI as a cosolvent for nonpolar drugs was characterized via dielectric constant measurements of binary solvent systems containing DMI and either water, propylene glycol (PG), or polyethylene glycol (PEG). Evidence from the dielectric constant profiles and NMR studies suggest that DMI undergoes complexation with water and PG, but not with PEG, through hydrogen bonding interactions. The solvent complexation exhibited a major effect on the solubilities of prednisone, dexamethasone, and prednisolone in the mixed solvent systems. Maximum solubility of each drug was found to occur near a DMI/water or DMI/PG concentration ratio of 1:2. In the DMI–PEG mixed system, while there is no apparent interaction between DMI and PEG molecules, the solubility of prednisone was found to increase with decreasing dielectric constant. 相似文献
963.
Cerebral infarction is rare in premature newborns and is most commonly the result of arterial embolization from the placenta. A focal echodense area was identified on prenatal cranial ultrasonography (US) in a premature infant (34 weeks of gestation). After birth, cerebral infarction was confirmed by magnetic resonance imaging (MRI). The clinical findings, imaging findings and pathogenesis are discussed. New diagnostic methods such as MRI show to be a useful approach in the neonatal period facilitating recognition of cerebrovascular accidents also in low-birth-weight infants. 相似文献
964.
Intraventricular hemorrhage (IVH) in preterm infants is well known to be associated with the high morbidity and mortality of this group. Previous studies have suggested altered cerebral blood flow (CBF) as an important pathologic factor. We measured the CBF in nearterm rabbit fetuses using the hydrogen clearance technique. The local CBF of the rabbit fetuses was significantly low compared with that of the maternal rabbits. The response of CBF to changes in PaCO2 was observed in rabbit fetuses. The CO2 reactivity index of the fetal rabbit was lower than that of the maternal rabbit. This low CO2 reactivity might reflect the immaturity of the fetal brain and its low CBF. We were unable to monitor the fetal blood pressure, but the fetal CBF remained stable when the maternal blood pressure was altered. It is well known that IVH in preterm infants originates from the subependymal germinal matrix and that this has many fragile vessels. Our observation suggests that even a small increase of CBF during hypercapnia might have a large effect towards producing hemorrhage. 相似文献
965.
966.
Cloning and characterization of Ca(2+)-dependent and Ca(2+)-independent PKCs expressed in Aplysia sensory cells 总被引:2,自引:0,他引:2
K E Kruger W S Sossin T C Sacktor P J Bergold S Beushausen J H Schwartz 《The Journal of neuroscience》1991,11(8):2303-2313
We isolated cDNA clones from an Aplysia sensory-cell library encoding two isoforms of protein kinase C (PKC). Several isozyme-specific regions are conserved in the Aplysia kinases, notably the variable regions V5 in the Ca(2+)-dependent PKC (Apl I) and V1 in the Ca(2+)-independent PKC (Apl II). Neuronal proteins with the properties expected of these two isoforms can be identified with antibodies raised against peptides synthesized from the amino acid sequences deduced from the clones. Sacktor and Schwartz (1990) measured the proportion of kinase activity that can be translocated to membrane in Aplysia sensory neurons and ganglia by stimuli that produce the presynaptic facilitation underlying behavioral sensitization. Much less Apl I and Apl II are translocated, suggesting that still other isoforms of PKC exist in these cells. 相似文献
967.
J M Darby E M Nemoto H Yonas J Melick 《Journal of cerebral blood flow and metabolism》1991,11(3):522-526
Stable xenon (Xe)-enhanced computed tomography is a potentially valuable tool for high resolution, three-dimensional measurement of CBF in patients. However, reports that Xe causes cerebrovascular dilation and increases intracranial pressure (ICP) have tempered enthusiasm for its use. The effects of 5 min of 33% Xe inhalation on ICP (right and left hemispheres) were studied in eight fentanyl-anesthetized Rhesus monkeys after right-sided cortical freeze injury. ICP, CBF, and physiological variables were monitored for up to 6 h postinsult. The preinjury (control) right hemispheric ICP was 8 +/- 5 mm Hg (mean +/- SD) and left hemispheric ICP was 5 +/- 2 mm Hg. Postinjury observations were classified into low (less than 15 mm Hg) and high ICP (greater than or equal to 15 mm Hg) groups. Both right and left ICP values averaged 9 +/- 3 mm Hg in the low ICP group. In the high ICP group, the right ICP was 20 +/- 4 mm Hg and left ICP was 21 +/- 6 mm Hg. ICP was unchanged by Xe inhalation under control conditions as well as in both low and high ICP groups postinjury. Postinjury, the MABP decreased 10-15 mm Hg in the low ICP group and 10-17 mm Hg in the high ICP group 2-3 min after the start of Xe inhalation (p less than 0.05). These results show that 33% Xe inhalation does not increase ICP in fentanyl-anesthetized monkeys but could decrease MABP in stressed states, presumably because of the anesthetic effects of Xe. 相似文献
968.
M A Warner K H Neill J V Nadler B J Crain 《Journal of cerebral blood flow and metabolism》1991,11(4):600-610
This study compared the ability of three N-methyl-D-aspartate (NMDA) receptor antagonists to prevent neuronal degeneration in an animal model of global cerebral ischemia. The model employed is characterized by damage to the striatum, hippocampus, and neocortex. Antagonists were administered to gerbils either before or after a 5-min bilateral carotid occlusion. The intraischemic rectal temperature was either maintained at 36-37 degrees C or allowed to fall passively to 28-32 degrees C. Antagonists and doses tested were 1 and 10 mg/kg of MK-801 (pre- or postischemia), 30 mg/kg of CGS 19755 preischemia, four 25 mg/kg doses of CGS 19755 administered between 0.5 and 6.5 h postischemia, and 40 mg/kg of MDL 27,266 (pre- or postischemia). All three NMDA receptor antagonists exhibited some degree of neuroprotective activity when the carotid occlusion was performed under normothermic conditions. Most of the treatments with antagonist markedly reduced striatal damage. CA1 hippocampal and neocortical pyramidal cells were spared by only three of the treatments, however, and the extent of neuroprotection varied widely from case to case. Toxic doses of antagonist were required to protect CA1 pyramidal cells from ischemic damage. Ischemic damage to hippocampal areas CA2-CA3a and CA4 appeared to be resistant to all of these treatments. Most CA1 pyramidal cells that were protected from degeneration by an NMDA receptor antagonist were histologically abnormal. The neuroprotective effects of MK-801 and intraischemic hypothermia appeared to be additive. MK-801 (10 mg/kg) consistently reduced the postischemic brain temperature, but only the magnitude of hypothermia produced soon after reperfusion correlated with its neuroprotective action. These results suggest that NMDA receptor antagonists are relatively poor neuroprotective agents against a moderately severe ischemic insult. 相似文献
969.
'Gliosarcomas' have long been considered to be mixed gliomas and sarcomas. The present study failed to define criteria which clearly delineate 'gliosarcomas' from glioblastoma multiforme and suggests that 'gliosarcomas' should be considered as spindle cell glioblastomas. A total of six cases originally diagnosed as 'gliosarcomas' were compared with four cases of glioblastoma multiforme. No clinical or prognostic features were defined which would clearly separate 'gliosarcomas' from glioblastoma multiforme. Macroscopically, biopsies from 'gliosarcomas' ranged from firm, apparently well-circumscribed tumours to poorly circumscribed lesions with a soft consistency resembling glioblastoma multiforme. Histology revealed a continuous spectrum in which 'gliosarcomas' with large reticulin-rich areas of spindle cells merged with typical glioblastomas containing only small islands of spindle cells and reticulin staining. Immunocytochemistry for glial fibrillary acidic protein (GFAP); S100 protein and alpha-smooth muscle actin (ASMA) showed that the majority of cells in reticulin-poor areas of 'gliosarcoma' and glioblastomas expressed S100 protein and GFAP; many expressed ASMA and some expressed both GFAP and ASMA. Spindle cells in reticulin-rich areas of 'gliosarcomas' and glioblastomas most frequently expressed ASMA but many cells also expressed S100 protein and GFAP; some cells expressed both GFAP and ASMA. The results of this study and a review of the literature suggests that there is a clinical, radiological and pathological continuum with glioblastoma and 'gliosarcoma' at different ends of the spectrum. It is suggested, therefore, that most, if not all, 'gliosarcomas' be redesignated as spindle cell glioblastomas and not be considered as a mixture of glioma and sarcoma. 相似文献
970.
The effects of maternal ethanol exposure on neurotransmission and second messenger systems were examined in rats using histochemistry and in vitro autoradiography. Thirty % ethanol was administered to pregnant rats from gestational day 7 to the day of delivery. Quantitative autoradiography was used to map muscarinic cholinergic, dopamine D2, adenosine A1, and inositol 1,4,5-trisphosphate binding sites, as well as to localize adenylate cyclase and protein kinase C. We found no difference in the patterns of staining with acetylcholinesterase and Timm's stain between control and prenatally ethanol-exposed rats on postnatal day (PN) 30. In the ethanol-exposed rats, [3H]forskolin binding sites were increased during early development in the CA1 subfield of the hippocampus and the occipital cortex; [3H]phorbol ester binding sites were increased in the cortex, striatum, and hippocampus; hippocampal muscarinic cholinergic sites were increased on PN4 and 30; adenosine A1 binding was reduced on PN10 in most regions examined, but was increased in the CA1 subfield on PN30; dopamine D2 receptor levels were significantly reduced on PN30 in the striatum; and IP3 receptors were decreased in most regions studied, but particularly in the cerebellum. Thus, some of these changes were transient and others were long-lasting. Although histopathological abnormalities were minimal, the alterations of binding sites in the cerebellum (the coordination center) and in the hippocampus (related to memory and learning) that were detected may contribute to the behavioral and mental deterioration seen in the fetal alcohol syndrome. 相似文献