全文获取类型
收费全文 | 6701篇 |
免费 | 449篇 |
国内免费 | 177篇 |
专业分类
耳鼻咽喉 | 52篇 |
儿科学 | 23篇 |
妇产科学 | 13篇 |
基础医学 | 1119篇 |
口腔科学 | 19篇 |
临床医学 | 197篇 |
内科学 | 637篇 |
皮肤病学 | 2篇 |
神经病学 | 4267篇 |
特种医学 | 26篇 |
外科学 | 139篇 |
综合类 | 184篇 |
预防医学 | 37篇 |
眼科学 | 102篇 |
药学 | 380篇 |
1篇 | |
中国医学 | 69篇 |
肿瘤学 | 60篇 |
出版年
2024年 | 13篇 |
2023年 | 52篇 |
2022年 | 157篇 |
2021年 | 270篇 |
2020年 | 175篇 |
2019年 | 125篇 |
2018年 | 133篇 |
2017年 | 153篇 |
2016年 | 164篇 |
2015年 | 207篇 |
2014年 | 272篇 |
2013年 | 337篇 |
2012年 | 286篇 |
2011年 | 348篇 |
2010年 | 322篇 |
2009年 | 358篇 |
2008年 | 425篇 |
2007年 | 312篇 |
2006年 | 306篇 |
2005年 | 271篇 |
2004年 | 278篇 |
2003年 | 206篇 |
2002年 | 180篇 |
2001年 | 150篇 |
2000年 | 102篇 |
1999年 | 116篇 |
1998年 | 137篇 |
1997年 | 150篇 |
1996年 | 135篇 |
1995年 | 85篇 |
1994年 | 79篇 |
1993年 | 80篇 |
1992年 | 70篇 |
1991年 | 79篇 |
1990年 | 69篇 |
1989年 | 53篇 |
1988年 | 47篇 |
1987年 | 45篇 |
1986年 | 71篇 |
1985年 | 115篇 |
1984年 | 86篇 |
1983年 | 63篇 |
1982年 | 73篇 |
1981年 | 72篇 |
1980年 | 58篇 |
1979年 | 19篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1972年 | 2篇 |
排序方式: 共有7327条查询结果,搜索用时 15 毫秒
41.
为了研究NMDA受体活性对Aβ引发的海马神经元突触蛋白表达变化的影响,本文运用免疫细胞化学方法检测不同浓度NMDA受体激动剂以及拮抗剂对Aβ诱导的海马神经元突触蛋白变化的影响。结果显示:NMDA可浓度依赖性地缓解Aβ25-35引起的突触蛋白synaptophysin与PSD-95的减少。抑制突触内NMDA受体,NMDA缓解Aβ减少突触蛋白的作用减弱;抑制突触外NMDA受体,对抗Aβ的作用无显著变化。本研究结果提示NMDA受体活性改变影响Aβ诱导的突触蛋白减少,突触内NMDA受体激活可对抗Aβ的毒性作用。突触内NMDA受体活性减弱可能在谷氨酸兴奋毒性中发挥作用。 相似文献
42.
Molecular determinants of human uveal melanoma invasion and metastasis 总被引:19,自引:0,他引:19
Seftor EA Meltzer PS Kirschmann DA Pe'er J Maniotis AJ Trent JM Folberg R Hendrix MJ 《Clinical & experimental metastasis》2002,19(3):233-246
The molecular analysis of cancer has benefited tremendously from the sequencing of the human genome integrated with the science
of bioinformatics. Microarray analysis technology has the potential to classify tumors based on the differential expression
of genes. In the current study, a collaborative, multidisciplinary approach was utilized to study the molecular determinants
of human uveal melanoma invasion and metastasis. Uveal melanoma is considered the most common primary intraocular cancer in
adults, resulting in the death of approximately 50% of patients affected. Unfortunately, at the time of diagnosis, many patients
already harbor microscopic metastases, thus underscoring a critical need to identify prognostic markers indicative of metastatic
potential. The investigative strategy consisted of isolating highly invasive vs. poorly invasive uveal melanoma cells from
a heterogeneous tumor derived from cells that had metastasized from the eye to the liver. The heterogeneous tissue explant
MUM-2 led to the derivation of two clonal cell lines: MUM-2B and MUM-2C. Further morphological and functional analyses revealed
that the MUM-2B cells were epithelioid, interconverted (expressing mesenchymal and epithelial phenotypes) highly invasive,
and demonstrated vasculogenic mimicry. The MUM-2C cells were spindle-like, expressed only a vimentin mesenchymal phenotype,
poorly invasive, and were incapable of vasculogenic mimicry. The molecular analysis of the MUM-2B vs. the MUM-2C clones resulted
in the differential expression of 210 known genes. Overall, the molecular signature of the MUM-2B cells resembled that of
multiple phenotypes – similar to a pluripotent, embryonic-like genotype. Validation of select genes that were upregulated
and down-regulated was conducted by semiquantitative RT-PCR measurement. This study provides a molecular profile that will
hopefully lead to the development of new molecular targets for therapeutic intervention and possible diagnostic markers to
predict the clinical outcome of patients with uveal melanoma.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
43.
Goto F Straka H Dieringer N 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2002,147(3):374-386
Postlesional reorganization of vestibular afferent and commissural inputs onto second-order vestibular neurons was studied
in the isolated brain after unilateral section of the N.VIII, of the ramus anterior (RA) of N.VIII, of the utricular (UT)
or of the anterior vertical and horizontal canal nerves in combination. RA nerve section eliminated the inputs from utricular,
anterior vertical and horizontal canal organs. In the first set of experiments we recorded field potentials on the operated
side of the vestibular nuclei 2 months after RA nerve section. These responses were evoked by electrical stimulation of the
RA nerve or of the posterior vertical canal nerve on the operated or on the intact side. The amplitudes of afferent field
potentials evoked by stimulation of the spared posterior vertical canal nerve were increased. The amplitudes of afferent field
potentials evoked by stimulation of the axotomized RA nerve remained unaltered. After N.VIII section the commissural, but
not the afferent, field potentials increased significantly on the operated side following stimulation of N.VIII on the intact
and on the operated side, respectively. After UT nerve section no change in commissural but an increase in the amplitude of
afferent field potentials from each of the three intact canal nerves was observed on the operated side. In the context of
earlier results these findings imply that second-order vestibular neurons, disfacilitated due to afferent nerve section, became
receptive to additional, excitatory synaptic inputs, preferentially from intact vestibular nerve afferent fibers. The reduced
excitation via afferent nerve inputs was thereby replaced by other afferent nerve inputs from spatially inadequate vestibular
end-organs. The synaptic terminals of inactivated afferent nerve fibers were maintained and not repressed. The process of
central reorganization after vestibular nerve lesion was activity related, the expansion of signals restricted to inputs from
intact fibers, its extent graded and its onset delayed with respect to the onset of corresponding spinal changes and to the
onset of postural recovery after the same type of nerve lesion. After the section of RA nerve or of an individual nerve branch
the labyrinthine end-organs remained intact and were not removed as after unilateral labyrinthectomy (UL). Peripheral reinnervation
of the end-organs was thus excluded after UL, but expected after one of the former types of lesion. Functional reinnervation
of the utricular macula was mirrored behaviorally by the reappearance of severe postural deficits following a second RA nerve
section. These lesion-induced postural deficits began to reappear if the repeated RA nerve section was delayed with respect
to the first by about 3 months. We therefore studied postlesional reorganization in the brainstem 3 months after the first
RA nerve section. Reinnervation of the utricular macula was accompanied by a rapid decline of the increased amplitudes of
afferent and commissural vestibular field potentials towards control values, suggesting the reversibility of the lesion-induced
central reorganization.
Electronic Publication 相似文献
44.
The hypothalamic arcuate nucleus (ARCN) was examined ultrastructurally 3 weeks after the complete deafferentation of the medial basal hypothalamus (MBH) with the island isolation technique in ovariectomized aged female rats (720-930 days of age). The mean numbers of axodendritic and axosomatic synapses in the ARCN decreased to about one-third of those in the intact controls. However, the treatment with estradiol benzoate (2 micrograms/day) during the 3 weeks following the day of brain surgery brought about a marked increase in the numbers of these synapses. The data suggest that the ARCN neurons of aged female rats still retain plasticity to react to deafferentation under influences of estrogen. 相似文献
45.
A naive, sexually matureD. melanogaster male tested with a young, sexually immature male will perform vigorous courtship, but the mature male will perform much less courtship if he is subsequently tested with a second young male. This phenomenon is called experience-dependent courtship modification (EDCM). We have shown that exposure to either or both of the two courtship-stimulating pheromones that immature males synthesize is sufficient to induce EDCM. 相似文献
46.
Ricardo A. Maselli Hélio van der Linden Jr Michael Ferns 《American journal of medical genetics. Part A》2020,182(7):1744-1749
Defects in the gene encoding synaptotagmin 2 (SYT2) have been linked to a presynaptic congenital myasthenic syndrome (CMS) and motor neuropathies. However, to date only dominant forms of the disease have been described. We report here a consanguineous patient with a severe recessive form of presynaptic CMS and denervation atrophy caused by the homozygous mutation c.1191delG, p.Arg397Serfs*37 in SYT2. The affected 2‐year‐old girl had profound weakness and areflexia with moderate bulbar deficit. Repetitive nerve stimulation revealed an extreme reduction of compound muscle action potential amplitudes at rest, with a striking facilitation followed by a progressive decline at fast stimulation rates. These findings were reminiscent, but not identical to those seen in the Lambert–Eaton myasthenic syndrome. 3,4 diaminopyridine and pyridostigmine were effective to ameliorate muscle fatigue, but albuterol was ineffective. Modeling of the mutation using the rat Syt1 C2B x‐ray structure revealed that Arg397Serfs*37 disrupts a highly conserved amino acid sequence at the bottom face of the C2B domain not directly involved in calcium binding, but crucial for synaptotagmin‐SNARE interaction and exocytosis. Thus, this report describes a recessive form of synaptotagmin 2‐CMS and highlights the importance of the synaptotagmin C‐terminal on synaptic vesicle fusion and exocytosis. 相似文献
47.
重复电刺激前肢神经引起成年大鼠运动皮层的可塑性改变 总被引:2,自引:0,他引:2
为了了解成年大鼠运动皮层的功能可塑性,利用皮层内微刺激方法测定MI代表区并观察重复电刺激前肢神经对MI代表区的影响。实验组大鼠(9例)持续1.2-2小时的前肢神经电刺激导致前肢运动区与面部触须运动区边界向VI方向,移动263.3±90.9μm并同时伴有运动阈值的改变;FL内MT降低5.0±13.3μA,而在VI内MT升高9.6±11.6μA对照组大鼠间隔1.5-2小时的两次测定结果,FL-VI边界 相似文献
48.
Pérez-Costas E Meléndez-Ferro M Pérez-García CG Caruncho HJ Rodicio MC 《Journal of chemical neuroanatomy》2004,27(1):7-21
The expression of reelin, a large extracellular matrix glycoprotein, was studied in the brain of pre-spawning adult sea lampreys by immunohistochemistry using two monoclonal antibodies against this protein. Reelin immunoreactive (reln-ir) neurons were observed in the olfactory bulb, and pallial and subpallial regions in the telencephalon. In the diencephalon, reln-ir cells were observed in some hypothalamic nuclei, in the nucleus of Bellonci, and in the habenula. In the mesencephalon, this protein was detected in several nuclei related with the centrifugal visual system, although the optic tectum was devoid of immunoreactivity. The hindbrain showed several nuclei with immunopositive neurons, including the branchiomeric nerve motor nuclei and also some groups of non-giant cells of the reticular formation. The rostral spinal cord showed some immunopositive neurons mainly located in lateral and ventral positions. Overall, the pattern of distribution of reelin in the adult sea lamprey correlates with the previously reported in other adult vertebrates. Furthermore, the wide distribution of reelin in the adult lamprey brain is consistent with a possible existence of different roles for this protein not related with development in the central nervous system (CNS) of vertebrates (i.e. neuronal plasticity and/or maintenance). 相似文献
49.
Peter Anderer Georg Gruber Gerhard Klösch Wolfgang Klimesch Bernd Saletu Josef Zeitlhofer 《Somnologie - Schlafforschung und Schlafmedizin》2002,6(2):54-62
Summary Memory consolidation involves a complex series of molecular, cellular and network-level processes that take place on time scales from millisecond to months. Evidence from a wide range of experimental observations supports the hypothesis that parts of these processes occur during sleep when the brain is not engaged in processing and encoding incoming information. Indeed, sleep seems to be favorable for brain plasticity. Experience-dependent cortical plasticity observed during sleep has been hypothesized to be part of the global process of memory consolidation. Thus, studying task-dependent, regionally specific reactivation of neuronal assemblies during posttraining sleep may make important contributions to elucidating the role of sleep in memory trace processing. A new methodology – low-resolution brain electromagnetic tomography (LORETA) – offers the possibility of localizing electrical activity produced by cortical neuronal generators under normal (undisturbed) sleeping conditions. The high time resolution of brain electrical data can be exploited to produce neuroimages for specific EEG spectral frequency bands (e.g. delta, theta, or spindle bands). This makes it possible to investigate, dependent on the type of memory, when – in which sleep stages (S2 sleep, SWS, REM sleep) – and where – in which cortical brain regions (primary sensory cortex, higher association cortex) – experience-dependent reactivation occurs. 相似文献
50.
Dobel C Pulvermüller F Härle M Cohen R Köbbel P Schönle PW Rockstroh B 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2001,140(1):77-85
A syntactic and a semantic task were performed by German-speaking healthy subjects and aphasics with lesions in the dominant left hemisphere. In both tasks, pictures of objects were presented that had to be classified by pressing buttons. The classification was into grammatical gender in the syntactic task (masculine or feminine gender?) and into semantic category in the semantic task (man- or nature made?). Behavioral data revealed a significant Group by Task interaction, with aphasics showing most pronounced problems with syntax. Brain event-related potentials 300-600 ms following picture onset showed different task-dependent laterality patterns in the two groups. In controls, the syntax task induced a left-lateralized negative ERP, whereas the semantic task produced more symmetric responses over the hemispheres. The opposite was the case in the patients, where, paradoxically, stronger laterality of physiological brain responses emerged in the semantic task than in the syntactic task. We interpret these data based on neuro-psycholinguistic models of word processing and current theories about the roles of the hemispheres in language recovery. 相似文献