全文获取类型
收费全文 | 3521960篇 |
免费 | 266768篇 |
国内免费 | 6887篇 |
专业分类
耳鼻咽喉 | 49736篇 |
儿科学 | 112178篇 |
妇产科学 | 94702篇 |
基础医学 | 495850篇 |
口腔科学 | 103154篇 |
临床医学 | 320804篇 |
内科学 | 681484篇 |
皮肤病学 | 74909篇 |
神经病学 | 286263篇 |
特种医学 | 136582篇 |
外国民族医学 | 1084篇 |
外科学 | 531151篇 |
综合类 | 84028篇 |
现状与发展 | 5篇 |
一般理论 | 1397篇 |
预防医学 | 278521篇 |
眼科学 | 84239篇 |
药学 | 262511篇 |
12篇 | |
中国医学 | 7497篇 |
肿瘤学 | 189508篇 |
出版年
2018年 | 37614篇 |
2017年 | 28735篇 |
2016年 | 31806篇 |
2015年 | 36030篇 |
2014年 | 51205篇 |
2013年 | 76982篇 |
2012年 | 104854篇 |
2011年 | 110835篇 |
2010年 | 65634篇 |
2009年 | 61970篇 |
2008年 | 104198篇 |
2007年 | 110984篇 |
2006年 | 111925篇 |
2005年 | 108580篇 |
2004年 | 104591篇 |
2003年 | 100353篇 |
2002年 | 98123篇 |
2001年 | 166771篇 |
2000年 | 172019篇 |
1999年 | 144806篇 |
1998年 | 41130篇 |
1997年 | 36683篇 |
1996年 | 36347篇 |
1995年 | 35165篇 |
1994年 | 32830篇 |
1993年 | 30427篇 |
1992年 | 114845篇 |
1991年 | 111173篇 |
1990年 | 107280篇 |
1989年 | 103625篇 |
1988年 | 95686篇 |
1987年 | 93986篇 |
1986年 | 88851篇 |
1985年 | 84757篇 |
1984年 | 63816篇 |
1983年 | 54379篇 |
1982年 | 32216篇 |
1981年 | 28772篇 |
1979年 | 58791篇 |
1978年 | 41067篇 |
1977年 | 34894篇 |
1976年 | 32654篇 |
1975年 | 34468篇 |
1974年 | 42428篇 |
1973年 | 40480篇 |
1972年 | 37896篇 |
1971年 | 34991篇 |
1970年 | 32877篇 |
1969年 | 30590篇 |
1968年 | 28087篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Interaction between free radicals and excitatory amino acids in the formation of ischemic brain edema in rats 总被引:6,自引:0,他引:6
Both oxygen free radicals and excitatory amino acids have been implicated as important cellular toxins in ischemic brain. Recent in vitro studies suggest that there may be a mutual interaction between these two mediators. We explored the relation between oxygen free radicals and excitatory amino acids in the development of ischemic brain edema in vivo. Male Sprague-Dawley rats were treated with the free radical scavenger dimethylthiourea 1 hour before ischemia or with the excitotoxin antagonist MK-801 30 minutes before ischemia produced by occlusion of the middle cerebral artery. Groups of seven or eight animals were treated with vehicle, low-dose (375 mg/kg) dimethylthiourea, high-dose (750 mg/kg) dimethylthiourea, low-dose (0.5 mg/kg) MK-801, high-dose (2.0 mg/kg) MK-801, or both high-dose dimethylthiourea and low-dose MK-801. After 4 hours of ischemia, brain water content was determined. In eight vehicle-treated controls, mean +/- SEM water content of tissue in the center of the ischemic zone was 83.29 +/- 0.18%. A significant reduction of brain edema was observed in all drug-treated groups: for example, 50.2% (p less than 0.001) in the high-dose dimethylthiourea group, 53.7% (p less than 0.001) in the low-dose MK-801 group, and 66.4% (p less than 0.001) in the combined dimethylthiourea and MK-801 group. Combined treatment with dimethylthiourea and MK-801 provided no significant additive effect over that resulting from treatment with MK-801 alone.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
992.
Basic fibroblast growth factor prevents thalamic degeneration after cortical infarction 总被引:10,自引:0,他引:10
K Yamada A Kinoshita E Kohmura T Sakaguchi J Taguchi K Kataoka T Hayakawa 《Journal of cerebral blood flow and metabolism》1991,11(3):472-478
In the focal infarction model of the rat middle cerebral artery (MCA), the thalamus of the occluded side becomes gradually atrophic, mainly because of retrograde degeneration. We determined whether basic fibroblast growth factor (bFGF) administered intracisternally could prevent this thalamic atrophy. We occluded the left MCA through a small cranial opening, and animals were then divided into two groups. One group received intracisternal injections of recombinant bFGF (1 microgram dissolved in 0.1 ml of saline with 2% rat serum) starting 1 day after occlusion and repeated once a week to a total dose of 4 micrograms by four injections. The other group received vehicle solution by the same schedule. The animals were perfused and fixed at 28 days after occlusion, and histological examination was made at the level of the caudoputamen and thalamus. In the bFGF-treated rats, the area of the posterior ventral thalamus of the occluded side was 93% of that of the contralateral side, i.e., significantly larger than in the normal saline-treated rats (75%, p less than 0.01). The infarction size was not statistically different in the two groups. Microscopic observation indicated that normal-saline-treated animals showed shrinkage and disappearance of thalamic neurons, whereas bFGF-treated groups showed preservation of thalamic neurons. Computerized analysis of the cell size substantiated this observation. To assess the effect of bFGF on astrocytes, bFGF or vehicle solution was injected into normal rats, and their histology was evaluated at 1, 2, and 4 weeks after injection. The bFGF-injected group showed a significant increase in glial fibrillary acidic protein-positive astrocytes in the brain tissue facing the ventriculocisternal system.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
993.
C Peabody J Van Norman L Hollister D Warner 《Progress in neuro-psychopharmacology & biological psychiatry》1991,15(1):63-70
1. Twenty-two patients hospitalized for treatment of depression were treated under conditions simulating those of home treatment. 2. Full doses of nortriptyline, from 100 to 150 mg/day, were started after baseline observations were made. 3. Two patients were dropped from the study, one for orthostatic hypotension, one for an aberrant response to nortriptyline. Two additional patients developed orthostasis which was easily managed. Otherwise no unusual side effects were noted. 4. After six days of treatment, 9 of 20 patients showed significant improvement with an overall reduction in scores on the Hamilton Depression Scale of 49% for the entire group. 5. Using the weight-adjusted dosage schedule, 18 of the 21 patients attained plasma concentrations of nortriptyline within the presumed therapeutic range; however, no clear relationship could be established between plasma concentrations and clinical response. 6. With proper selection of patients, it should be possible to treat at home some patients who currently are considered to require hospitalization. 相似文献
994.
The involvement of excitatory amino acid (EAA) receptors in mediation of the toxic effects of cocaine was studied in male ICR mice. Cocaine HCl (90 mg/kg, IP) induced seizures in 95% and death within 24 h in 68% (n = 135) of the animals. There was a significant correlation (r = .54) between the time to onset of convulsions and the time to death in mice which died within 30 min of injection (n = 84). Pretreatment with selected EAA receptor antagonists 15 min prior to cocaine differentially blocked cocaine toxicity. Selective N-methyl-D-aspartic acid (NMDA) receptor antagonists (MK-801, dextrorphan, CPP) decreased both the incidence of seizures and mortality. A nonselective EAA antagonist, kynurenic acid, decreased lethality in doses which did not reduce convulsions. A similar action was observed following pretreatment with the selective kainic acid/AMPA receptor antagonist, GDEE. Antagonists at EAA receptors can provide significant protection against cocaine-induced toxicity. Moreover, the data provide evidence for the involvement of both NMDA and non-NMDA receptor subtypes in aspects of cocaine toxicity. 相似文献
995.
D J Jenden 《Neuroscience and biobehavioral reviews》1991,15(1):105-107
Variation among species in their response to xenobiotic agents depends upon two sets of factors: pharmacokinetic and pharmacodynamic. Pharmacokinetic factors, of which the rate of metabolic transformation is the most important, determine the concentration of the agent in plasma and tissues as a function of time after it is administered, while pharmacodynamic factors define the tissue response to a given concentration. Both are subject to considerable uncertainty when dealing with a new compound, so that it is not in general possible to predict reliably the response of human subjects to a new compound solely from studies on experimental animals. This uncertainty can be reduced substantially by understanding its mechanisms of action. Greater accuracy in predicting the metabolism of foreign compounds in man is also likely to be achieved by studies of the species variation of cytochrome P450s, and by the use of human hepatocytes and other cell lines to study xenobiotic metabolism. 相似文献
996.
D J Kupfer B G Pollock J M Perel D B Jarrett A B McEachran J M Miewald 《Psychiatry research》1991,36(3):279-289
An i.v. challenge dose of clomipramine (12.5 mg) was given to eight outpatients with major depression. The procedure facilitated the examination of all-night sleep and sleep-related neuroendocrine changes (cortisol, growth hormone, and prolactin). In comparison to baseline saline nights, the patients experienced a profound suppression of rapid eye movement (REM) sleep throughout the night with no rebound recovery in the second half of the night. Furthermore, REM-suppressing effects were noted on the following no-drug night. In contrast, little effect on delta wave sleep was found, except for increased consolidation of delta waves within stage 3 and 4 sleep. Delta sleep measures were significantly correlated with levels of cortisol and growth hormone. 相似文献
997.
D D Cochrane K J Poskitt M G Norman 《The Canadian journal of neurological sciences. Le journal canadien des sciences neurologiques》1991,18(2):181-195
Cerebral dysgenesis encompasses varied disorders of brain development. Based on the understanding of these conditions provided by histopathologists, embryologists, radiologists and developmental pediatricians, surgeons are able to appropriately assist in the care of these patients. The surgeon can offer assessment of the ventriculomegaly that commonly accompanies cerebral dysgenesis in addition to providing methods to control hydrocephalus, to reconstruct cranial and facial malformations and to remove dysfunctional tissue. For most patients, surgical intervention is only one of the many factors that determine developmental prognosis. Based on the foundation built by other specialists, this review discusses cerebral dysgenesis from the perspective of historical and current surgical interventions. 相似文献
998.
C E Hack J Wagstaff R J Strack van Schijndel A J Eerenberg H M Pinedo L G Thijs J H Nuijens 《Thrombosis and haemostasis》1991,65(5):497-503
Patients treated with high doses of interleukin-2 (IL-2) because of cancer, develop hemodynamic and vasopermeability changes, that resemble those observed in sepsis. These patients thus provide a unique opportunity to study the early events in the development of septic shock. We analysed the changes that occurred in the contact system of coagulation in plasma from 4 patients, who together received seven 12-day cycles of high doses of IL-2. Levels of factor XII and prekallikrein during the cycles progressively fell to 50 and 30% of their initial levels, respectively, whereas significant increases in plasma factor XIIa- and kallikrein-C1-inhibitor complexes were not observed (in 3 out of 211 samples slightly increased levels of both complexes were found). The reductions in factor XII and prekallikrein were only in part due to protein leakage, since levels were still significantly lower, i.e., 80 and 50%, respectively, when corrected for albumin decreases. Levels of high molecular weight kininogen (HMWK) also decreased during IL-2 therapy, however, this decrease paralleled that of albumin. SDS-PAGE analysis of plasma HMWK did not reveal increased cleavage of this protein. The reduction of factor XII and prekallikrein, corrected for protein leakage, significantly correlated with albumin levels and inversely with daily cumulative weight gain in the patients. Thus, we demonstrate that factor XII and prekallikrein decrease during IL-2 therapy. As these decreases, already observed after 1 day treatment, were disproportional to that of albumin, a negative acute phase reactant, and correlated with signs of the vascular leak syndrome, we favor the explanation that they reflected activation rather than a decreased synthesis of the contact system proteins.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
999.
In the present experiments we have investigated the influence of wall shear rate and axial position on platelet and fibrin deposition which results when flowing human non-anticoagulated blood is exposed to either non-procoagulant fibrillar collagen (human type III) or procoagulant subendothelium (rabbit aorta). Platelet adhesion, thrombus volume and fibrin deposition were morphometrically evaluated at axial positions of 1 and 13 mm following perfusions for 5 min at shear rates of 100, 650 and 2,600 s-1. An axially-dependent decrease of platelet adhesion (34-57%, p less than 0.01-0.05) and thrombus volume (57-80%, p less than 0.05) was observed on collagen at all shear rates. On subendothelium, an axially-dependent decrease was observed for platelet adhesion only at 100 s-1 (29%; p less than 0.01) and for thrombus volume at shear rates of 650 s-1 and above (49-58%, p less than 0.01). Deposition of fibrin on subendothelium was axially decreased (16-42%, p less than 0.05) at all shear rates, while no significant axial differences were seen on collagen. However, substantially more fibrin was deposited on the subendothelium (p less than 0.05), and the upstream platelet adhesion and thrombus volume were lower than on collagen (p less than 0.05) at 100 s-1 and 650 s-1. The axially-dependent phenomena on the two surfaces are consistent with the concept of rapid-growing upstream thrombi which deplete the blood layer streaming adjacent ot the surface of platelets, leading to decreased platelet deposition further downstream.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
1000.
H J Schluesener 《Journal of neuroscience research》1991,28(2):310-314
The transforming growth factors type beta 1, beta 2, and beta 1.2 suppress multidrug transport in human pat-1 glioblastoma cells and even in cells that strongly over-express mdr genes and are resistant to inhibition of multidrug transport by chemosensitizers. Thus, inhibition of multidrug transport by cytokines might be a new approach to increase cellular accumulation of chemotherapeutic agents in multidrug resistant glial tumor cells. Interestingly, a member of the more distantly related decapentaplegic subgroup of transforming growth factors, the bone morphogenetic protein BMP 2, did not inhibit multidrug transport. 相似文献