全文获取类型
收费全文 | 1308454篇 |
免费 | 101845篇 |
国内免费 | 2059篇 |
专业分类
耳鼻咽喉 | 18704篇 |
儿科学 | 45277篇 |
妇产科学 | 35697篇 |
基础医学 | 187327篇 |
口腔科学 | 33930篇 |
临床医学 | 114290篇 |
内科学 | 265397篇 |
皮肤病学 | 28708篇 |
神经病学 | 103390篇 |
特种医学 | 52141篇 |
外国民族医学 | 686篇 |
外科学 | 200367篇 |
综合类 | 27135篇 |
现状与发展 | 1篇 |
一般理论 | 383篇 |
预防医学 | 98055篇 |
眼科学 | 28392篇 |
药学 | 97001篇 |
2篇 | |
中国医学 | 2489篇 |
肿瘤学 | 72986篇 |
出版年
2019年 | 9674篇 |
2018年 | 14109篇 |
2017年 | 10657篇 |
2016年 | 11566篇 |
2015年 | 13207篇 |
2014年 | 18083篇 |
2013年 | 27611篇 |
2012年 | 38440篇 |
2011年 | 40411篇 |
2010年 | 23982篇 |
2009年 | 22764篇 |
2008年 | 38777篇 |
2007年 | 41399篇 |
2006年 | 41506篇 |
2005年 | 40543篇 |
2004年 | 39611篇 |
2003年 | 38298篇 |
2002年 | 37602篇 |
2001年 | 64612篇 |
2000年 | 67098篇 |
1999年 | 56959篇 |
1998年 | 15320篇 |
1997年 | 13895篇 |
1996年 | 14323篇 |
1995年 | 13569篇 |
1994年 | 12881篇 |
1993年 | 11892篇 |
1992年 | 44848篇 |
1991年 | 43757篇 |
1990年 | 42505篇 |
1989年 | 40367篇 |
1988年 | 37139篇 |
1987年 | 36461篇 |
1986年 | 33831篇 |
1985年 | 32476篇 |
1984年 | 24303篇 |
1983年 | 20391篇 |
1982年 | 11816篇 |
1981年 | 10763篇 |
1979年 | 21441篇 |
1978年 | 14889篇 |
1977年 | 12601篇 |
1976年 | 11763篇 |
1975年 | 12685篇 |
1974年 | 14749篇 |
1973年 | 14179篇 |
1972年 | 13006篇 |
1971年 | 11798篇 |
1970年 | 11118篇 |
1969年 | 10107篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
841.
Ticlopidine and clopidogrel (SR 25990C) selectively neutralize ADP inhibition of PGE1-activated platelet adenylate cyclase in rats and rabbits 总被引:1,自引:0,他引:1
G Defreyn C Gachet P Savi F Driot J P Cazenave J P Maffrand 《Thrombosis and haemostasis》1991,65(2):186-190
Ticlopidine and its potent analogue, clopidogrel, are powerful inhibitors of ADP-induced platelet aggregation. In order to improve the understanding of this ADP-selectivity, we studied the effect of these compounds on PGE1-stimulated adenylate cyclase and on the inhibition of this enzyme by ADP, epinephrine and thrombin. Neither drug changed the basal cAMP levels nor the kinetics of cAMP accumulation upon PGE1-stimulation in rat or rabbit platelets, which excludes any direct effect on adenylate cyclase or on cyclic nucleotide phosphodiesterase. However, the drop in cAMP levels observed after addition of ADP to PGE1-stimulated control platelets was inhibited in platelets from treated animals. In contrast, the drop in cAMP levels produced by epinephrine was not prevented by either drug in rabbit platelets. In rat platelets, thrombin inhibited the PGE1-induced cAMP elevation but this effects seems to be entirely mediated by the released ADP. Under these conditions, it was not surprising to find that clopidogrel also potently inhibited that effect of thrombin on platelet adenylate cyclase. In conclusion, ticlopidine and clopidogrel selectively neutralize the ADP inhibition of PGE1-activated platelet adenylate cyclase in rats and rabbits. 相似文献
842.
843.
Brain opioids modulate the activity of the hypothalamo-pituitary complex by binding to specific receptors which have been subdivided at least into 3 subclasses (mu, kappa, delta, etc). mu-Receptors and their ligands seem to be particularly involved in the control of gonadotropin and prolactin release. It is known that the neuroendocrine system, as well as the brain opioid systems and their receptors, are not fully mature at birth; it is also known that the postnatal maturation of many brain machineries is under the control of androgens secreted by the developing testes. Consequently, it has been investigated whether the presence or the absence of testosterone at time of birth may induce changes of the binding characteristics of hypothalamic mu-opioid receptors. The experiments have been performed by evaluating the maximal binding capacity (Bmax, an index of the number of receptors), and the affinity constant (Ka) of the specific mu-ligand dihydromorphine in hypothalamic plasma membrane preparations derived from normal male rats, normal female rats, male rats orchidectomized 2 days after birth and female rats treated 2 days after birth with 1.25 mg of testosterone propionate. Animals belonging to the 4 groups were killed at days 16, 26 and 60 of age. The results obtained show that, at 16 days of age, in the 4 groups of rats the number of hypothalamic mu receptors is identical. At 26 days a significant increase in the number of mu-receptors occurs in normal female animals, while their levels remain similar to those found at 16 days in the other 3 groups of animals. At 60 days of age, the number of mu-receptors in normal females remains elevated, while the number of mu-receptors increases to reach normal female levels in the hypothalamus of neonatally castrated males. At 60 days, there were no changes in normal males or in androgenized females. The variations here reported took place without any change of the Ka of dihydromorphine for the mu-receptors. These data show a sexual dimorphism of hypothalamic mu-receptors and suggest that their ontogenetic development may be linked to the presence or the absence of androgens at time of birth. 相似文献
844.
P Riekkinen M Riekkinen H Lahtinen J Sirvi? A Valjakka P Riekkinen 《Brain research bulletin》1991,27(5):587-594
The present study examines whether tetrahydroaminoacridine (THA) can improve the deterioration in passive avoidance (PA) retention performance induced by medial septal (MS) and fimbria-fornix (FF) lesions in young rats or by aging. Retention of young MS-lesioned rats was improved by pretraining injection of THA at 3 mg/kg, but not by THA at 1 mg/kg or by either of the posttraining doses of THA (1 and 3 mg/kg). Pretraining injections of THA at 1 or 3 mg/kg had no effect on the PA retention performance of FF-lesioned rats. Age-induced PA failure was alleviated by pretraining administration of THA at 1 and 3 mg/kg. Posttraining injections of THA (1 or 3 mg/kg) had no effect on PA retention performance of aged rats. These results demonstrate that 1) THA may improve hippocampal cholinergic denervation-induced functional deficits and 2) some of the age-related PA deficits may be due to a cholinergic deficit and can be reversed with THA. 相似文献
845.
P A Rittenhouse E A Bakkum L D Van de Kar 《The Journal of pharmacology and experimental therapeutics》1991,259(1):58-65
DOI [(+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCI] is a serotonin (5-HT1C/5-HT2) agonist, with potent cardiovascular effects. The purpose of the present studies was to determine the identity and location of the 5-HT receptor subtype(s) mediating the renin and blood pressure responses to DOI. Injection (i.p.) of DOI to conscious male rats elevated plasma renin activity in a dose-dependent manner. The 5-HT1C/5-HT2 antagonist ritanserin completely blocked the DOI-induced increase in plasma renin activity. In order to distinguish the 5-HT2- from the 5-HT1C- mediated effect of DOI, spiperone was administered before DOI. Low doses of spiperone (0.01 and 0.1 mg/kg, s.c.) significantly reduced the renin response to DOI. Because spiperone has a higher affinity for 5-HT2 than 5-HT1C receptors, these data suggest that DOI stimulates renin secretion through 5-HT2 receptors. To separate central from peripheral 5-HT receptors, we injected DOI into rats pretreated with saline or xylamidine, a 5-HT2 antagonist which does not cross the blood-brain barrier. Xylamidine produced a shift to the right and suppression of the maximal effect of DOI on plasma renin activity, suggesting a role for peripheral 5-HT2 receptors in the effect of DOI. On the other hand, i.c.v. administration of DOI, using doses lower than the peripherally effective doses, caused a significant elevation of plasma renin activity at 200 micrograms/kg. These experiments suggest that DOI's elevation of plasma renin activity has both peripheral and central sites of action.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
846.
847.
Opsoclonus in organophosphate poisoning 总被引:1,自引:0,他引:1
Transient opsoclonus was observed in a patient who attempted suicide with the organophosphate insecticide Malathion (diethyl[dimethoxyphosphinothioyl]thiobutanedioate). Several toxins can cause opsoclonus, and these must be considered in its differential diagnosis. Eye movement disorders are one of the more common manifestations of organophosphate intoxication, and opsoclonus should now be included among these. Acetylcholine may be a neurotransmitter in the ocular motor pathway. 相似文献
848.
Linkage mapping of a mouse gene, iv, that controls left-right asymmetry of the heart and viscera. 总被引:1,自引:0,他引:1 下载免费PDF全文
M Brueckner P D''''Eustachio A L Horwich 《Proceedings of the National Academy of Sciences of the United States of America》1989,86(13):5035-5038
Inherited single gene defects have been identified in both humans and mice that lead to loss of developmental control over the left-right asymmetry of the heart and viscera. In mice the recessively inherited mutation iv leads to such apparent loss of control over situs: 50% of iv/iv mice exhibit situs inversus and 50% exhibit normal situs. The affected gene product has not been identified in these animals. To study the normal function of iv, we have taken an approach directed to the gene itself. As a first step, we have mapped iv genetically, by examining its segregation in backcrosses with respect to markers defined by restriction fragment length polymorphisms. The iv locus lies 3 centimorgans (cM) from the immunoglobulin heavy-chain constant-region gene complex (Igh-C) on chromosome 12. A multilocus map of the region suggests the gene order centromere-Aat (alpha 1-antitrypsin gene complex)-(11 cM)-iv-(3 cM)-Igh-C-(1 cM)-Igh-V (immunoglobulin heavy-chain variable-region gene complex). 相似文献
849.
C P Baveja D Chattopadhya S Kumari K K Dutta S Sehgal 《The Journal of communicable diseases》1989,21(1):59-61
Sixty drinking water samples collected from various sources in different areas of Delhi during epidemic of cholera and gastroenteritis were analysed for bacteriological standards. Only 27 (45 per cent) samples were found to be satisfactory for human consumption. Remaining thirty-three (55 per cent) samples showed presence of coliform organisms with MPN value ranging from 10 to 1800+ per 100 ml. Among these positive samples, 31 (93.9 per cent) samples contained faecal coli. Twenty out of thirty (66.6 per cent) Hand pump, 9 out of 21 (42.8 per cent) Taps 2 out of 4 (50 per cent) Tube well and 2 out of 5 (40 per cent) of miscellaneous sources showed contamination with coliform organisms. 相似文献
850.
The action of papain and bromelain, prepared over a pH range from 4.6 to 8.6, was evaluated for the ability to render red cells agglutinable by five incomplete antibodies of differing blood group specificities using a two-stage technique. The optimal pH for treatment of red cells by activated papain or bromelain was between 5.4 and 5.8. Above this pH range, a fall in serological sensitivity was apparent which was much more pronounced with papain than with bromelain. The optimal pH for enzyme treatment of red cells can be achieved in two-stage techniques, but not in one-stage techniques due to the buffering effect of serum proteins. 相似文献