全文获取类型
收费全文 | 20442篇 |
免费 | 916篇 |
国内免费 | 659篇 |
专业分类
耳鼻咽喉 | 93篇 |
儿科学 | 103篇 |
妇产科学 | 208篇 |
基础医学 | 4169篇 |
口腔科学 | 202篇 |
临床医学 | 892篇 |
内科学 | 2374篇 |
皮肤病学 | 217篇 |
神经病学 | 4497篇 |
特种医学 | 247篇 |
外国民族医学 | 1篇 |
外科学 | 901篇 |
综合类 | 1315篇 |
现状与发展 | 3篇 |
预防医学 | 280篇 |
眼科学 | 134篇 |
药学 | 5294篇 |
中国医学 | 157篇 |
肿瘤学 | 930篇 |
出版年
2023年 | 96篇 |
2022年 | 164篇 |
2021年 | 306篇 |
2020年 | 282篇 |
2019年 | 291篇 |
2018年 | 288篇 |
2017年 | 331篇 |
2016年 | 356篇 |
2015年 | 457篇 |
2014年 | 713篇 |
2013年 | 1101篇 |
2012年 | 766篇 |
2011年 | 991篇 |
2010年 | 834篇 |
2009年 | 1004篇 |
2008年 | 1117篇 |
2007年 | 955篇 |
2006年 | 900篇 |
2005年 | 832篇 |
2004年 | 814篇 |
2003年 | 767篇 |
2002年 | 607篇 |
2001年 | 521篇 |
2000年 | 464篇 |
1999年 | 427篇 |
1998年 | 521篇 |
1997年 | 507篇 |
1996年 | 442篇 |
1995年 | 443篇 |
1994年 | 397篇 |
1993年 | 377篇 |
1992年 | 345篇 |
1991年 | 313篇 |
1990年 | 279篇 |
1989年 | 279篇 |
1988年 | 219篇 |
1987年 | 238篇 |
1986年 | 179篇 |
1985年 | 308篇 |
1984年 | 432篇 |
1983年 | 246篇 |
1982年 | 319篇 |
1981年 | 230篇 |
1980年 | 166篇 |
1979年 | 126篇 |
1978年 | 74篇 |
1977年 | 62篇 |
1976年 | 47篇 |
1975年 | 20篇 |
1974年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
81.
ALUN M. DAVIES 《Journal of anatomy》1997,191(4):483-491
The accessibility of the primary sensory neurons of the trigeminal system at stages throughout their development in avian and mammalian embryos and the ease with which these neurons can be studied in vivo has facilitated investigation of several fundamental aspects of neurotrophin biology. Studies of the timing and sequence of action of neurotrophins and the expression of neurotrophins and their receptors in this well characterised neuronal system have led to a detailed understanding of the functions of neurotrophins in neuronal development. The concepts of neurotrophin independent survival, neurotrophin switching and neurotrophin cooperativity have largely arisen from work on the trigeminal system. Moreover, in vitro studies of trigeminal neurons provided some of the first evidence that the neurotrophin requirements of sensory neurons are related to sensory modality. The developing trigeminal system has been studied most extensively in mice and chickens, each of which has particular advantages for understanding different aspects of neurotrophin biology. In this review, I will outline these advantages and describe some of the main findings that have arisen from this work. 相似文献
82.
Functional effects of the σ ligand, (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine ((+)-3PPP), were explored in perfused rat tail and rabbit ear arteries in vitro. In the rat tail artery (+)-3PPP inhibited contractile responses to adrenergic nerve stimulation, an effect which was reversed to potentiation by the dopamine D2 receptor antagonist sulpiride. In the rabbit ear artery, however, (+)-3PPP potentiated contractile responses to nerve stimulation, an effect which was unchanged by sulpiride. In the rat tail artery, blockade of norepinephrine uptake by cocaine and deoxycorticosterone in the presence of sulpiride revealed two additional actions of (+)-3PPP. First, an inhibitory action on the monoamine uptake site was confirmed by direct measurement of [3H]norepmephrine accumulation. Second, at higher concentrations, an action to inhibit contractile responses to adrenergic nerve stimulation was manifested at a still unidentified site. These studies demonstrate that the observed functional effect of (+)-3PPP results from its combined actions on three individual sites with the net effect dependent on the relative densities of these different receptor sites in each type of vessel. 相似文献
83.
J. W. Constantine W. S. Lebel H. A. Woody 《Naunyn-Schmiedeberg's archives of pharmacology》1990,342(6):722-724
Summary Neurokinin A, neurokinin B and substance P caused concentration-related contractions of rabbit isolated aorta with pD2 values of 8.1, 6.9 and 6.0, respectively. [D-Pro2, D-Trp7,9]-substance P, a competitive tachykinin antagonist, had pA2 values of 5.3 against neurokinin A, 5.1 against neurokinin B and 5.2 against substance P indicating that tachykinin receptors
mediated responses to the agonists. [pGIu5,MePhe8,-McGly9]-substance P 5–11 (DiMe-C7), senktide and septide did not contract the aorta. It is concluded that of the known tachykinin
receptors smooth muscle of the rabbit isolated aorta contains only the NK-2 type.
Send offprint requests to J. W. Constantine at the above address 相似文献
84.
The effect of lithium administration (800 mg daily for 7 days) on the neuroendocrine and temperature responses to the 5-HT1A receptor agonist, gepirone, was studied in eight healthy male volunteers. Gepirone (20 mg orally) significantly increased plasma levels of prolactin, growth hormone, corticotropin and cortisol, and lowered oral temperature. None of these responses was significantly altered by lithium treatment. The results suggest that the ability of short-term lithium treatment to increase 5-HT-mediated neuroendocrine responses in humans is unlikely to be related to changes in the sensitivity of pre- or post-synaptic 5-HT1A receptors. 相似文献
85.
S. M. O. Hourani S. J. Bailey C. R. Johnson J. P. Tennant 《Naunyn-Schmiedeberg's archives of pharmacology》1998,358(4):464-473
The functional effects of adenosine 5’-triphosphate (ATP), uridine 5’-triphosphate (UTP), adenosine 5’-tetraphosphate (AP4) and the diadenosine polyphosphates P1,P3-diadenosine triphosphate (Ap3A), P1,P4-diadenosine tetraphosphate (Ap4A) and P1,P5-diadenosine pentaphosphate (Ap5A) were studied in two isolated smooth muscle preparations thought to contain P2Y (P2Y1) receptors, the guinea-pig taenia caeci (which relaxes to ATP) and the rat colon muscularis mucosae (which contracts to ATP).
In addition, the breakdown of these compounds by the rat colon muscularis mucosae was investigated by high pressure liquid
chromatography. In the guinea-pig taenia caeci all the purine nucleotides caused relaxation with a potency order of Ap3A=Ap4A> ATP>AP4=Ap5A, and these relaxations were antagonised by suramin with apparent pA2 values in the region of 5, consistent with activation of a P2Y1 receptor. In the rat colon muscularis mucosae the nucleotides caused contraction with a potency order of Ap3A = Ap4A>ATP=AP4 =Ap5A >UTP. However, while suramin (100 μM) inhibited responses to ATP and UTP at all concentrations of agonist, it only inhibited
contractions induced by the higher concentrations of AP4, Ap3A and Ap4A and had little effect on contractions induced by Ap5A. A higher concentration of suramin (1 mM) enhanced contractions induced by ATP but greatly inhibited those induced by UTP
and had no effect on responses to the other agonists. The A1 adenosine receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 10 nM) had no effect on responses to ATP or UTP
but inhibited responses to Ap3A, Ap4A, Ap5A and AP4. A combination of suramin (1 mM) and DPCPX (10 nM) almost abolished responses to all the agonists. ATP and UTP were rapidly
degraded by the rat colon muscularis mucosae while AP4, Ap3A, Ap4A and Ap5A were degraded more slowly, and the major product detected after breakdown of the purine nucleotides was inosine rather than
adenosine. The breakdown of all the nucleotides was inhibited by suramin (1 mM), although this inhibition did not achieve
statistical significance in the case of ATP. These results show that while the diadenosine polyphosphates appear to act as
P2 agonists in the taenia caeci, in the rat colon muscularis mucosae their major action is via adenosine A1 receptors rather than via P2 receptors. In addition, although they are more stable than ATP or UTP, their action in this
tissue is clearly affected by their degradation which complicates the effects of suramin.
Received: 23 March 1998 / Accepted: 29 June 1998 相似文献
86.
Critchley Hilary O.D.; Bailey Deborah A.; Au Chak L.; Affandi Biran; Rogers Peter A.W. 《Human reproduction (Oxford, England)》1993,8(10):1632-1639
The bleeding problems experienced by users of subdermal levonorgestrelimplants (Norplant) remain unexplained. The aim of the presentstudy was to investigate the oestrogen (ER) and progesteronereceptor (PR) distribution in levonorgestrel-treated endometrialbiopsies from 31 subjects recruited in Jakarta, Indonesia, andto compare the sex steroid receptor immunostaining with thatof endometrium from 58 normally cycling women from Melbourne,Australia. Sex steroid receptor immunoreactivity was additionallycompared with days of exposure to subdermal levonorgestrel,serum oestradiol and progesterone levels and days of bleedingduring a 90-day reference period. An immunohistochemical techniquewith an alkaline phosphatase anti-alkaline phosphatase (APAAP)detection system for use in formalin-fixed paraffin wax embeddedendometrial tissue was employed. Significantly greater meanimmunostaining scores of stromal PR were observed in Norplantcompared with control endometrium at all stages across the cycle.No significant correlations were demonstrated between sex steroidreceptor immunostaining and days of exposure to subdermal levonorgestrel,serum oestradiol or progesterone concentrations or days of bleedingduring a 90-day reference period. Whether the elevated stromalPR immunostaining in Norplant-treated endometrium is a consequenceof increased synthesis or reduced turnover of receptor remainsunclear. As yet it is undetermined whether increased PR immunoreactivitycorresponds to an increase in number of functional PR. 相似文献
87.
Jordi Ortiz Lawrence W. Fitzgerald Maura Charlton Sarah Lane Louis Trevisan Xavier Guitart William Shoemaker Ronald S. Duman Eric J. Nestler 《Synapse (New York, N.Y.)》1995,21(4):289-298
In previous studies, we have demonstrated that chronic administration of morphine or cocaine produces some common biochemical adaptations in the ventral tegmental area (VTA) and nucleus accumbens (NAc), components of the mesolimbic dopamine system implicated in the reinforcing actions of these and other drugs of abuse. Since this neural pathway is also implicated in the reinforcing actions of ethanol, it was of interest to determine whether chronic ethanol exposure results in similar biochemical adaptations. Indeed, as seen for chronic morphine and cocaine treatments, we show here that chronic ethanol treatment increased levels of tyrosine hydroxylase and glial fibrillary acidic protein immunoreactivity, and decreases levels of neurofilament protein immunoreactivity, in the VTA. Also like morphine and cocaine, ethanol increases levels of cyclic AMP-dependent protein kinase activity in the NAc. These actions of ethanol required long-term exposure to the drug, and were in most cases not seen in the substantia nigra or caudate-putamen, components of the nigrostriatal dopamine system studied for comparison. Altered levels of tyrosine hydroxylase in catecholaminergic cells frequently reflect altered states of activation of the cells. Moreover, increasing evidence indicates that ethanol produces many of its acute effects on the brain by regulating NMDA glutamate and GABA receptors. We therefore examined the influence of chronic ethanol treatment on levels of expression of specific glutamate and GABA receptor subunits in the VTA. It was found that long-term, but not short-term, ethanol exposure increased levels of immunoreactivity of the NMDARl subunit, an obligatory component of NMDA glutamate receptors, and of the Glu Rl subunit, a component of many AMPA glutamate receptors; but at the same time, long-term ethanol exposure decreased immunoreactivity levels of the α1 subunit of the GABAA receptor complex. These changes are consistent with an increased state of activation of VTA neurons inferred from the observed increase intyrosine hydroxylase (TH) expression. These results demonstrate that chronic ethanol exposure results in several biochemical adaptations in the mesolimbic dopamine system, which may underlie prominent changes in the structural and functional properties of this neural pathway related to alcohol abuse and alcoholism. © 1995 Wiley-Liss, Inc. 相似文献
88.
Per Karlsson Lars Farde Christer Halldin Carl-Gunnar Swahn Göran Sedvall Christian Foged Kristian Tage Hansen Birte Skrumsager 《Psychopharmacology》1993,113(2):149-156
The benzazepines NNC 687 and NNC 756 have in animal studies been described as selective D1-dopamine receptor antagonists. Both compounds have been labeled with11C for examination by positron emission tomography (PET). In the present study central receptor binding was studied in monkeys and healthy men. After IV injection of both radioligands in Cynomolgus monkeys radioactivity accumulated markedly in the striatum, a region with a high density of D1-dopamine receptors. This striatal uptake was displaced by high doses of the selective D1-antagonist SCH 23390 (2 mg/kg) but not by the 5HT2-antagonist ketanserin (1.5 mg/kg) or the selective D2-antagonist raclopride (3 mg/kg). The cortical uptake after injection of [11C]NNC 687 was not reduced in displacement experiments with ketanserin. The cortical uptake of [11C]NNC 756 was reduced in displacement and protection experiments with ketanserin by 24–28% (1.5 mg/kg), whereas no reduction could be demonstrated on striatal uptake. In healthy males both compounds accumulated markedly in the striatum. For [11C]NNC 687 the ratio of radioactivity in the putamen to cerebellum was about 1.5. For [11C]NNC 756 the ratio was about 5. This ratio of 5 for [11C]NNC 756 is the highest obtained so far for PET radioligands for the D1-dopamine receptor. 相似文献
89.
Elizabeth Z. Bordayo John R. Fawcett Sarita Lagalwar Aleta L. Svitak William H. Frey 《Journal of molecular neuroscience : MN》1996,27(2):185-194
Arachidonic acid (AA), released in response to muscarinic acetylcholine receptor (mAChR) stimulation, previously has been
reported to function as a reversible feedback inhibitor of the mAChR. To determine if the effects of AA on binding to the
mAChR are subtype specific and whether AA inhibits ligand binding to other G protein-coupled receptors (GPCRs), the effects
of AA on ligand binding to the mAChR subtypes (M1, M2, M3, M4, and M5) and to the μ-opioid receptor, β2-adrenergic receptor (β2-AR), 5-hydroxytryptamine receptor (5-HTR), and nicotinic receptors were examined. AA was found to inhibit ligand binding
to all mAChR subtypes, to the β2-AR, the 5-HTR, and to the μ-opioid receptor. However, AA does not inhibit ligand binding to the nicotinic receptor, even
at high concentrations of AA. Thus, AA inhibits several types of GPCRs, with 50% inhibition occurring at 3–25 μM, whereas the nicotinic receptor, a non-GPCR, remains unaffected. Further research is needed to determine the mechanism by
which AA inhibits GPCR function. 相似文献
90.
Katherine Wiegmann Shylaja Muthyala Duk Hwan Kim Barry G. W. Arnason Ewa Chelmicka-Schorr 《Journal of neuroimmunology》1995,56(2)
Chronic/relapsing experimental allergic encephalomyelitis (CREAE) serves as an animal model for relapsing/remitting multiple sclerosis. Treatment with the β-adrenergic agonist isoproterenol or the β2-adrenergic agonist terbutaline significantly suppressed both the first acute attack and the number of relapses in CREAE Lewis rats. The number of relapses was decreased even when treatment with β-adrenergic agonist was started after the onset of the first acute attack of CREAE. β-adrenergic receptor number was increased significantly on splenocytes from CREAE rats as compared to healthy controls or CFA-injected rats. Terbutaline treatment of CREAE rats lowered the splenocyte receptor number to normal values. 相似文献