全文获取类型
收费全文 | 1644689篇 |
免费 | 126209篇 |
国内免费 | 3658篇 |
专业分类
耳鼻咽喉 | 21887篇 |
儿科学 | 54907篇 |
妇产科学 | 47793篇 |
基础医学 | 236945篇 |
口腔科学 | 43698篇 |
临床医学 | 145639篇 |
内科学 | 326757篇 |
皮肤病学 | 38378篇 |
神经病学 | 133154篇 |
特种医学 | 62895篇 |
外国民族医学 | 501篇 |
外科学 | 247696篇 |
综合类 | 38773篇 |
现状与发展 | 4篇 |
一般理论 | 611篇 |
预防医学 | 126086篇 |
眼科学 | 37233篇 |
药学 | 115719篇 |
1篇 | |
中国医学 | 3914篇 |
肿瘤学 | 91965篇 |
出版年
2021年 | 12511篇 |
2019年 | 13317篇 |
2018年 | 19229篇 |
2017年 | 14639篇 |
2016年 | 16583篇 |
2015年 | 18541篇 |
2014年 | 25978篇 |
2013年 | 38938篇 |
2012年 | 52134篇 |
2011年 | 55100篇 |
2010年 | 32898篇 |
2009年 | 31238篇 |
2008年 | 50889篇 |
2007年 | 54047篇 |
2006年 | 54515篇 |
2005年 | 52778篇 |
2004年 | 50465篇 |
2003年 | 48059篇 |
2002年 | 46249篇 |
2001年 | 82732篇 |
2000年 | 84561篇 |
1999年 | 70024篇 |
1998年 | 19382篇 |
1997年 | 17581篇 |
1996年 | 17606篇 |
1995年 | 16725篇 |
1994年 | 15230篇 |
1993年 | 14293篇 |
1992年 | 52291篇 |
1991年 | 50191篇 |
1990年 | 48208篇 |
1989年 | 46133篇 |
1988年 | 42121篇 |
1987年 | 41098篇 |
1986年 | 38350篇 |
1985年 | 36669篇 |
1984年 | 27763篇 |
1983年 | 23400篇 |
1982年 | 14235篇 |
1981年 | 12467篇 |
1979年 | 24440篇 |
1978年 | 17306篇 |
1977年 | 14434篇 |
1976年 | 13504篇 |
1975年 | 14082篇 |
1974年 | 16902篇 |
1973年 | 16424篇 |
1972年 | 15359篇 |
1971年 | 14004篇 |
1970年 | 13400篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The quantitative relationship between fractional myocardial thallium uptake and radioactive microsphere-determined flow was studied in 33 open chest dogs under baseline conditions during increased coronary flow (dipyridamole), decreased coronary flow (propranolol and coronary artery stenosis), inhibition of Na-K ATPase (ouabain), and regional infarction. Myocardial contents of thallium and microspheres were compared in left ventricular (LV) biopsies taken 5, 10, 15, 30, and 60 min after thallium injection, expressed as fractions of injected dose. Maximal LV thallium uptake occurred 10 min after injection and the 10-min values were therefore used for subsequent comparisons. Combining all dogs, fractional LV thallium content (% injected dose) correlated well with fractional LV blood flow (% cardiac output) (r = 0.95). However, for fractional LV flows in the low, normal, or moderately elevated range (LV flow/cardiac output less than 9%), thallium content consistently exceeded flow by about 15%. This relationship was not altered by ouabain or regional ischemia or infarction. For greatly elevated fractional LV flows (greater than 9%), thallium content was not significantly different from flow. To explain these differences, myocardial and systemic extraction fractions for thallium were determined in eight dogs with a dual tracer method. At baseline, myocardial extraction fraction was significantly greater than systemic (88 +/- 0.4% compared with 75 +/- 1%, p less than 0.001). During dipyridamole, myocardial extraction fraction decreased and myocardial and systemic values were no longer significantly different (82 +/- 1% compared with 79 +/- 1%). These results show that the fraction of injected thallium dose taken up by the LV myocardium exceeds the delivered fraction of cardiac output over a wide range of LV flows, and is not altered by ouabain-induced inhibition of sodium-potassium ATPase or regional myocardial infarction. This difference is explained by a greater myocardial than systemic extraction fraction for thallium. During high LV flows produced by dipyridamole, fractional LV thallium uptake and flow become similar as myocardial and systemic extraction fractions equalize. 相似文献
992.
993.
E D Endean S K Mukhopadhyay L K Fung J L Cronenwett J C Stanley S M Lindenauer 《The Journal of surgical research》1986,40(1):49-54
Basal isolated canine paw blood flow was equally distributed between arteriovenous anastomosis (AVA) and capillary circulations. Norepinephrine decreased AVA flow by 92% and capillary flow by 41%. Dopamine significantly reduced AVA flow by 94% compared to baseline with a 37% reduction in capillary flow. However, with alpha-adrenergic blockade dopamine decreased AVA flow 66% while capillary flow increased 42%. Isoproterenol increased capillary flow almost twofold and appeared to decrease AVA flow, although the latter was statistically insignificant. Differential effects of adrenergic and dopaminergic agonists on canine paw AVA and capillary blood flow suggest the existence of independent regulation of these components of the microcirculation. 相似文献
994.
David S. Ball D.O. Arnold C. Friedman David S. Hartman Paul D. Radecki Dina F. Caroline 《Urologic radiology》1986,8(1):46-48
This case report illustrates the magnetic resonance imaging (MRI) appearance of a typically asymptomatic renal oncocytoma as a homogeneous mass of medium signal with a stellate central region of decreased signal, representing the central scar. The MRI was correlated with computed tomography (CT), ultrasound (US), and gross pathologic appearance. The appearance of a central scar is not specific for oncocytoma and does not exclude renal cell carcinoma, as illustrated by a second case. 相似文献
995.
Mitogen responsiveness of lymphocytes from the BB/W rat 总被引:3,自引:0,他引:3
The response of BB diabetes-prone (DP) and W-line non-diabetes-prone rats to the T-cell mitogen concanavalin A (ConA) was measured. The W line was a good responder to ConA, whereas the DP was relatively unresponsive. This unresponsiveness could not be reversed with exogenous interleukin 2 (IL-2). The response of DP rats was enhanced by removing adherent cells. To directly test the response of BB T-cells, they were isolated by flow sorting. These experiments demonstrated that BB T-cells could mount a normal ConA response. The normal function of isolated BB T-cells suggested that they were under suppression. Suppressor activity could not be found in the OX8+ population but was found in the DP-adherent cell population. Adherent cells from the W line were not suppressive at the concentrations used. These results showed that the decreased mitogen responsiveness of BB T-cells was not due to an intrinsic T-cell abnormality but was due, in part, to suppression by adherent cells. 相似文献
996.
G Bussone L La Mantia E A Parati F Frediani E Lamperti A Boiardi C Peccarisi A M Tortorano M A Viviani 《European neurology》1986,25(4):256-261
A case of cryptococcal meningoencephalitis, as presented by a hypertensive hydrocephalus, is described. To our knowledge, this is the 24th case described in Italy since 1953. The diagnosis was made with ventricular fluid examination: the patient was successfully treated with amphotericin B and 5-fluorocytosine, thus avoiding the risks of surgical treatment of hydrocephalus. Early diagnosis and proper therapy are necessary in order to decrease the high lethality of cryptococcosis. 相似文献
997.
Osteomalacia and bone disease arising from aluminum 总被引:2,自引:0,他引:2
998.
999.
N. R. Galloway J. Tolia C. Barber 《Documenta ophthalmologica. Advances in ophthalmology》1986,63(1):31-36
The pattern evoked electroretinogram (PERG) was investigated in 11 patients with unilateral optic nerve disease and in a series of age-matched controls. The visually evoked potential (VEP) was also measured. The PERG showed a similar reduction to the VEP in optic nerve disease. Serial studies indicate that the PERG may not be affected immediately in some instances but may show a gradual decline over several months. 相似文献
1000.
K Tamazawa H Arima T Kojima Y Isomura M Okada S Fujita T Furuya T Takenaka O Inagaki M Terai 《Journal of medicinal chemistry》1986,29(12):2504-2511
Four enantiomers (3a-d) of the title compound, YM-09730 (3), were synthesized by the reaction of (-)- or (+)-5-(methoxycarbonyl)-2, 6-dimethyl-4-(m-nitrophenyl)-1,4-dihydropyridine-3-carboxylic acid (1a or 1b) with (S)- or (R)-1-benzyl-3-pyrrolidinol (2a or 2b). [3H]Nitrendipine binding affinity and coronary vasodilating activity of these compounds were evaluated. The absolute configuration of the most potent enantiomer (3a) with the longest duration was unequivocally determined to be (S)-1,4-dihydropyridine-C4 and (S)-pyrrolidine-C3 (S,S) by X-ray crystallographic study on 3a X HBr as well as 3a X HCl. The configuration of 1a corresponds to R, and the other enantiomers of 3 were respectively determined by chemical correlation. The potency order of the four enantiomers was (S,S)-3a greater than (S,R)-3b greater than (R,R)-3d greater than (R,S)-3c. Latent chiral characters of nifedipine derivatives with the identical ester groups were assigned by comparison of their puckering modes of 1,4-dihydropyridine (DHP) rings with those found in 3a X HCl or 3a X HBr. On the basis of the assignment, it has been revealed that the (S)-DHP nifedipine derivatives possess the synperiplanar carbonyl group at C5. The conformational restriction may be a factor causing stereoselectivity of antagonism. 相似文献