全文获取类型
收费全文 | 7241篇 |
免费 | 243篇 |
国内免费 | 112篇 |
专业分类
耳鼻咽喉 | 152篇 |
儿科学 | 21篇 |
妇产科学 | 22篇 |
基础医学 | 1479篇 |
口腔科学 | 154篇 |
临床医学 | 327篇 |
内科学 | 319篇 |
皮肤病学 | 6篇 |
神经病学 | 2543篇 |
特种医学 | 228篇 |
外科学 | 1010篇 |
综合类 | 533篇 |
预防医学 | 99篇 |
眼科学 | 77篇 |
药学 | 433篇 |
1篇 | |
中国医学 | 105篇 |
肿瘤学 | 87篇 |
出版年
2023年 | 97篇 |
2022年 | 153篇 |
2021年 | 231篇 |
2020年 | 151篇 |
2019年 | 156篇 |
2018年 | 149篇 |
2017年 | 152篇 |
2016年 | 160篇 |
2015年 | 150篇 |
2014年 | 257篇 |
2013年 | 276篇 |
2012年 | 272篇 |
2011年 | 263篇 |
2010年 | 271篇 |
2009年 | 259篇 |
2008年 | 266篇 |
2007年 | 249篇 |
2006年 | 249篇 |
2005年 | 204篇 |
2004年 | 175篇 |
2003年 | 186篇 |
2002年 | 146篇 |
2001年 | 149篇 |
2000年 | 120篇 |
1999年 | 134篇 |
1998年 | 109篇 |
1997年 | 130篇 |
1996年 | 132篇 |
1995年 | 127篇 |
1994年 | 97篇 |
1993年 | 103篇 |
1992年 | 97篇 |
1991年 | 100篇 |
1990年 | 105篇 |
1989年 | 89篇 |
1988年 | 92篇 |
1987年 | 94篇 |
1986年 | 124篇 |
1985年 | 208篇 |
1984年 | 161篇 |
1983年 | 107篇 |
1982年 | 156篇 |
1981年 | 149篇 |
1980年 | 147篇 |
1979年 | 80篇 |
1978年 | 63篇 |
1977年 | 52篇 |
1976年 | 54篇 |
1975年 | 31篇 |
1973年 | 38篇 |
排序方式: 共有7596条查询结果,搜索用时 0 毫秒
71.
Pituitary morphologic changes in patients with Erdheim-Chester disease have not been described in detail. We report here the
histologic and immunohistochemical findings in the autopsy obtained pituitary of a 35-yr-old woman with extensively disseminated
Erdheim-Chester disease. The posterior lobe was completely replaced by xanthogranulomatous infiltrates, providing an explanation
for the patient’s diabetes insipidus. The anterior lobe was intact and immunohistochemistry demonstrated expression of GH,
TSH, FSH, LH, and alpha subunit within the normal range. A clinically observed decrease of anterior pituitary function was
interpreted as hypothalamic in origin due to massive destruction of the hypophysial stalk and compression of the hypothalamus.
Prolactin immunoreactive cells were numerous, consistent with the view that prolactin cell hyperplasia resulted from the loss
of hypothalamic dopaminergic inhibition. Massive Crooke’s hyalinization in the ACTH-producing cells was considered unrelated
to Erdheim-Chester disease and was the consequence of treatment with pharmacologic doses of glucocorticoid hormones. It can
be concluded that prolactin cell hyperplasia may be the only finding in the adenohypophysis of patients with disseminated
Erdheim-Chester disease. It appears that in our patient the clinically apparent anterior hypopituitarism was not due to the
lack of storage but rather to insufficient release of adenohypophysial hormones caused by the defect in hypothalamic regulation. 相似文献
72.
The control of retinogeniculate transmission in the mammalian lateral geniculate nucleus 总被引:13,自引:0,他引:13
S. M. Sherman C. Koch 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1986,63(1):1-20
Summary In the mammalian visual system, the lateral geniculate nucleus is commonly thought to act merely as a relay for the transmission of visual information from the retina to the visual cortex, a relay without significant elaboration in receptive field properties or signal strength. However, many morphological and electrophysiological observations are at odds with this view. Only 10–20% of the synapses found on geniculate relay neurons are retinal in origin. Roughly half of all synapses derive from cells in layer VI of visual cortex; roughly one third are inhibitory and GABAergic, derived either from interneurons or from cells of the nearby perigeniculate nucleus. Most of the remaining synapses probably derive from cholinergic, noradrenergic, and serotonergic sites within the brainstem reticular formation. Moreover, recent biophysical studies have revealed several ionic currents present in virtually all thalamic neurons. One is a Ca2+-dependent K+ current underlying the afterhyperpolarization (or the IAHP), which may last up to 100–200 ms following an action potential. Activation of the IAHP leads to spike frequency adaptation in response to a sustained, suprathreshold input. Intracellular recordings from other neuronal preparations have shown that the IAHP can be blocked by noradrenalin or acetylcholine, leading to an increased cellular excitability. Another ionic current results from a voltage- and time-dependent Ca2+ conductance that produces a low threshold spike. Activation of this conductance transforms a geniculate neuron from a state of faithful relay of information to one of bursting behavior that bears little relationship to the activity of its retinal afférents. We propose that state-dependent gating of geniculate relay cells, which may represent part of the neuronal substrate involved in certain forms of selective visual attention, can be effected through at least three different mechanisms: (1) conventional GABAergic inhibition, which is largely controlled via brainstem and cortical afferents through interneurons and perigeniculate cells; (2) the IAHP, which is controlled via noradrenergic and cholinergic afferents from the brainstem reticular formation; and (3) the low threshold spike, which may be controlled by GABAergic inputs, cholinergic inputs, and/or the corticogeniculate input, although other possibilities also exist. Furthermore, it seems likely that gating functions involving the corticogeniculate pathway are suited to attentional processes within the visual domain (e.g., saccadic suppression), whereas brain-stem inputs seem more likely to have more global effects that switch attention between sensory systems. In any case, it is now abundantly clear that geniculate circuitry and the intrinsic electrophysiological properties of geniculate neurons are no longer compatible with the notion that the lateral geniculate nucleus serves as a simple relay. 相似文献
73.
Cortical and hippocampal EEG were correlated with behavior in rats before and after bilateral hypothalamic (LH) damage. In Stage 1 of recovery (aphagia and adipsia), the neocortex showed continuous large amplitude slow activity. It did not desynchronize during spontaneous acts such as grooming as well as during tail pinch-induced struggling or orienting, even though a slow form of hippocampal theta accompanied these acts. However, during Stage 2 (anorexia), the neocortical EEG did desynchronize when such theta appeared. Therefore, as behavioral recovery progresses after LH damage, there appears to be a concomitant recovery of cortical participation in such behavior. Early in recovery, LH rats, unlike normals, showed slow (3–4.5 Hz) atropine-sensitive hippocampal theta during automatisms such as grooming as well as during immobility. Thus, LH damage, while temporarily abolishing fast. noncholinergic theta, appears to release slow cholinergic theta. Later in recovery, faster atropine-resistant (noncholinergic) theta becomes functional again. 相似文献
74.
Mel'nikova VI Lavrent'eva AV Kudrin VS Raevskii KS Ugryumov MV 《Neuroscience and behavioral physiology》2005,35(8):809-813
The aim of the present work was to verify the hypothesis that non-dopaminergic neurons expressing individual complementary dopamine synthesis enzymes can perform the co-located synthesis of dopamine. According to this hypothesis, neurons expressing tyrosine hydroxylase use L-tyrosine for the synthesis of L-dihydroxyphenylalanine (L-DOPA), which then enters neurons expressing aromatic amino acid decarboxylase, which converts L-DOPA to dopamine. Experiments were performed using the mediobasal hypothalamus of rat fetuses, which mostly contains single-enzyme neurons (>99%) and occasional double-enzyme neurons (<1%). Controls were obtained from the fetal substantia nigra, which is enriched with dopaminergic neurons. High-performance liquid chromatography was used to measure levels of dopamine and L-DOPA in cell extracts and the incubation medium after incubation in the presence and absence of exogenous L-tyrosine. Addition of L-tyrosine to the medium led to increases in the level of synthesis and release of L-DOPA in the mediobasal hypothalamus and substantia nigra. In addition, L-tyrosine increased dopamine synthesis in the substantia nigra and decreased dopamine synthesis in the mediobasal hypothalamus. This regional difference in levels of dopamine synthesis is probably due to inhibition of the uptake of L-DOPA from the intercellular medium by neurons in the mediobasal hypothalamus containing aromatic amino acid decarboxylase, due to the competitive binding of the L-DOPA transporter by L-tyrosine. Thus, these results provide the first evidence for the co-located synthesis of dopamine by non-dopaminergic neurons expressing single complementary enzymes involved in the synthesis of this neurotransmitter.__________Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 90, No. 7, pp. 825–832, July, 2004. 相似文献
75.
Through whole-cell patch recordings in brainstem slices, the effects of histamine on neuronal activity of the lateral vestibular nucleus (LVN) were investigated. Bath application of histamine elicited a concentration-dependent excitation of both spontaneous firing (n = 19) and silent (n = 7) LVN neurons. Moreover, histamine induced a stable inward current in the LVN neurons (n = 5) and the histamine-induced depolarization of membrane potential persisted in the presence of tetrodotoxin (n = 4), indicating a direct post-synaptic effect of the histamine on the LVN neurons. Selective histamine H2 receptor antagonist ranitidine effectively blocked the histamine-evoked excitatory responses on the LVN neurons (n = 4), but selective histamine H1 receptor antagonist triprolidine did not (n = 4). In addition, selective histamine H2 receptor agonist dimaprit (n = 3) rather than 2-pyridylethylamine (n = 4), a selective histamine H1 receptor agonist, mimicked the excitatory action of histamine on LVN neurons. The results demonstrate that histamine excites the LVN neurons via post-synaptic histamine H2 receptors and suggest that the central histaminergic projection arising from the hypothalamus may modulate LVN neurons activity and actively influence the vestibular reflexes and functions. 相似文献
76.
The functional relation between the anterior olfactory area (AO) and the lateral hypothalamic area (LH) was examined in a self-stimulation situation. Bar-pressing responses for AO sitmulation were suppressed by unilateral injection of procaine, and enhanced by glutamate, into LH. Neither procaine nor glutamate injected into AO had any influence upon LH self-stimulation. It is unlikely that the procaine effect was due to motor disturbance because similar injection of procaine into LH did not disturb the performance of a one-way avoidance task. It appears that the rewarding effect of AO stimulation is dependent upon the excitation of the more caudal structures including LH. 相似文献
77.
Electrical stimulation of the medial prefrontal cortex (MC) in rats delivered daily for seven days causes a marked improvement in the rate of acquisition of a self-stimulation response. In the present experiment, we looked at whether we could get the same facilitatory effect on self-stimulation of the MC by delivering pre-training stimulation to other points in the brain anatomically related to the MC. Electrical stimulation of the lateral hypothalamus was without effect. However, electrical stimulation of the sulcal prefrontal cortex (SC) either contralateral or ipsilateral to the MC electrode did facilitate acquisition of self-stimulation of the MC. Thus the SC and MC would appear to be part of the same substrate controlling the development of positive reinforcement in the MC. 相似文献
78.
79.
Steroid hormones regulate sexual behavior primarily by slow, genomically mediated effects. These effects are realized, in part, by enhancing the processing of relevant sensory stimuli, altering the synthesis, release, and/or receptors for neurotransmitters in integrative areas, and increasing the responsiveness of appropriate motor outputs. Dopamine has facilitative effects on sexual motivation, copulatory proficiency, and genital reflexes. Dopamine in the nigrostriatal tract influences motor activity; in the mesolimbic tract it activates numerous motivated behaviors, including copulation; in the medial preoptic area (MPOA) it controls genital reflexes, copulatory patterns, and specifically sexual motivation. Testosterone increases nitric oxide synthase in the MPOA; nitric oxide increases basal and female-stimulated dopamine release, which in turn facilitates copulation and genital reflexes. Serotonin (5-HT) is primarily inhibitory, although stimulation of 5-HT(2C) receptors increases erections and inhibits ejaculation, whereas stimulation of 5-HT(1A) receptors has the opposite effects: facilitation of ejaculation and, in some circumstances, inhibition of erection. 5-HT is released in the anterior lateral hypothalamus at the time of ejaculation. Microinjections of selective serotonin reuptake inhibitors there delay the onset of copulation and delay ejaculation after copulation begins. One means for this inhibition is a decrease in dopamine release in the mesolimbic tract. 相似文献
80.
Ventromedial hypothalamic lesioned rats maintained at preoperative body weight received an equal number of shocks while emitting significantly fewer responses than controls in a lever-pressing free-operant avoidance paradigm, and performed as well as unoperated animals in lever-pressing and shuttle box (both 1- and 2-way) discriminated avoidance tasks. The failure of VMH lesions to facilitate performance in the 2-way avoidance paradigm was probably the result of a ceiling effect. With the exception of the simple one-way avoidance task, obese lesioned rats were markedly impaired in the acquisition of all active avoidance behavior, but escape behavior was not affected. When tested in a free-operant paradigm, the avoidance performance of well trained lesioned animals varied inversely with body weight. As obese rats displayed lower flinch thresholds to shock than controls and similar levels of activity and responding as lean lesioned animals, it was concluded that their impaired avoidance behavior was not due to changes in sensitivity or mobility. The possible relation to other VMH lesion- and/or obesity-induced deficits is discussed. 相似文献