全文获取类型
收费全文 | 116040篇 |
免费 | 5909篇 |
国内免费 | 138篇 |
专业分类
耳鼻咽喉 | 1771篇 |
儿科学 | 5196篇 |
妇产科学 | 3928篇 |
基础医学 | 16053篇 |
口腔科学 | 2901篇 |
临床医学 | 8306篇 |
内科学 | 21964篇 |
皮肤病学 | 3355篇 |
神经病学 | 8973篇 |
特种医学 | 5043篇 |
外国民族医学 | 32篇 |
外科学 | 19014篇 |
综合类 | 1595篇 |
一般理论 | 29篇 |
预防医学 | 5803篇 |
眼科学 | 3390篇 |
药学 | 8041篇 |
中国医学 | 323篇 |
肿瘤学 | 6370篇 |
出版年
2018年 | 889篇 |
2017年 | 776篇 |
2016年 | 1094篇 |
2015年 | 1220篇 |
2014年 | 1601篇 |
2013年 | 2363篇 |
2012年 | 3094篇 |
2011年 | 3143篇 |
2010年 | 1969篇 |
2009年 | 1927篇 |
2008年 | 3250篇 |
2007年 | 3486篇 |
2006年 | 3630篇 |
2005年 | 3746篇 |
2004年 | 3689篇 |
2003年 | 3554篇 |
2002年 | 3504篇 |
2001年 | 7013篇 |
2000年 | 6957篇 |
1999年 | 5857篇 |
1998年 | 1622篇 |
1997年 | 1559篇 |
1996年 | 1335篇 |
1995年 | 1201篇 |
1994年 | 1091篇 |
1993年 | 1119篇 |
1992年 | 3765篇 |
1991年 | 3575篇 |
1990年 | 3561篇 |
1989年 | 3348篇 |
1988年 | 2985篇 |
1987年 | 2894篇 |
1986年 | 2803篇 |
1985年 | 2617篇 |
1984年 | 1943篇 |
1983年 | 1594篇 |
1982年 | 927篇 |
1981年 | 915篇 |
1980年 | 765篇 |
1979年 | 1822篇 |
1978年 | 1346篇 |
1977年 | 1111篇 |
1976年 | 936篇 |
1975年 | 1178篇 |
1974年 | 1212篇 |
1973年 | 1198篇 |
1972年 | 1040篇 |
1971年 | 975篇 |
1970年 | 880篇 |
1969年 | 787篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
Facilitation and depression in the responses of spinal Renshaw cells to random stimulation of motor axons 总被引:1,自引:0,他引:1
Windhorst U.; Rissing R.; Meyer-Lohmann J.; Laouris Y.; Kuipers U. 《Journal of neurophysiology》1988,60(5):1638-1652
1. We investigated the responses of cat lumbosacral Renshaw cells to pseudo-Poison stimulus sequences (of three different mean rates) delivered to motor axons in ventral roots or various muscle nerves. The Renshaw cell responses were evaluated by computation of peristimulus time histograms (PSTHs). 2. PSTHs computed with respect to all the stimuli showed, before the reference time, near-constant bin contents corresponding to the mean firing probability (rate), and an initial excitatory component (increase in discharge probability) after the reference time, followed by a small but longer-lasting reduction of firing rate. These two response components were strongly correlated linearly. It is suggested that the postexcitatory rate reduction is predominantly due to afterhyperpolarization. 3. In general, Renshaw cell responses to any stimulus in a stimulus train depended upon the stimulation history. In the averaged record, the response to the second of a pair of stimuli was affected by the first stimulus independently of intervening (random) stimuli. Very often, the second response showed a long-lasting depression (from 25 to greater than 250 ms). In a number of cases a briefer facilitating effect preceded the depression. 4. These conditioning effects were largely homosynaptic, i.e., confined to the particular input channel that was stimulated. This was shown by stimulating two different nerves (or nerve branches) with independent random patterns of similar mean rates and determining the cross-conditioning exerted by one input channel on the excitatory effects of the other. At small intervals between conditioning and test stimuli of some tens of milliseconds, a facilitatory effect could often be seen, which almost certainly reflected spatial summation. However, the subsequent depressant effect was largely accounted for by the postexcitatory rate reduction consequent to the conditioning stimulus in the parallel channel. Autoconditioning was still present. 5. The amount of facilitation and depression as well as their balance depended on the average Renshaw cell response. This in turn depended, at each mean stimulus rate, on the strength of synaptic coupling between an input channel and the cell, and on the mean stimulus rate, declining with an increase in mean rate. That is, the facilitation increased and the depression decreased with decreasing synaptic coupling and increasing mean stimulus rate. 6. Several factors may contribute to facilitation and depression; these are discussed with respect to their relative quantitative significance.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
922.
923.
Neuroimmunologic aspects of skin inflammation involve several interacting systems. The modulating influence of autonomic and sensory nerves has been known for a long time. Neurokinines derived from these nerves have recently been shown to interact with antigen presentation in dermal Langerhans cells and other key functions of allergic skin disease. While some mechanisms of afferent function and local reflex are known, the nature of efferent effects (from brain to periphery) remains to be elucidated. New aspects include involvement of the brain-derived neurotrophic factor in addition to the autonomic nervous system in mental stress response and insight in the immunomodulation by proopiomelanocortins. Novel strategies for therapy and prevention of chronicity may also result from understanding the role of increased secretion of nerve growth factor in atopic eczema and psoriasis. 相似文献
924.
Only target-conformal treatment allows one to exploit the advantages of ion beams (the increased dose and high biological efficiency at the end of the particle range) to a maximum extent. Up to now, target-conformal treatments such as spot scanning or intensity-controlled raster scanning have used fast magnetic lateral deflection in one or two directions perpendicular to the beam axis and a slow range variation in the longitudinal axis by active or passive energy variation. The present paper describes a new method for conformal irradiation with a fast intensity-controlled longitudinal scan in the beam direction, called 'depth scanning'. Its advantages and disadvantages will be discussed. First experimental results from depth scanning will be presented. 相似文献
925.
926.
927.
Specific and innervation-regulated expression of the intermediate filament protein nestin at neuromuscular and myotendinous junctions in skeletal muscle 总被引:8,自引:0,他引:8 下载免费PDF全文
Vaittinen S Lukka R Sahlgren C Rantanen J Hurme T Lendahl U Eriksson JE Kalimo H 《The American journal of pathology》1999,154(2):591-600
The intermediate filament proteins nestin, vimentin, and desmin show a specific temporal expression pattern during the development of myofibers from myogenic precursor cells. Nestin and vimentin are actively expressed during early developmental stages to be later down-regulated, vimentin completely and nestin to minimal levels, whereas desmin expression begins later and is maintained in mature myofibers, in which desmin participates in maintaining structural integrity. In this study we have analyzed the expression levels and distribution pattern of nestin in intact and denervated muscle in rat and in human. Nestin immunoreactivity was specifically and focally localized in the sarcoplasm underneath neuromuscular junctions (NMJs) and in the vicinity of the myotendinous junctions (MTJs), ie, in regions associated with acetylcholine receptors (AChRs). This association prompted us to analyze nestin in neurogenically and myogenically denervated muscle. Immunoblot analysis disclosed a marked overall increase of accumulated nestin protein. Similar to the extrajunctional redistribution of AChRs in denervated myofibers, nestin immunoreactivity extended widely beyond the NMJ region. Re-innervation caused complete reversion of these changes. Our study demonstrates that the expression levels and distribution pattern of nestin are regulated by innervation, ie, signal transduction into myofibers. 相似文献
928.
Weber C Michaelis M Vogel JU Cinatl J Kreuter J Langer K 《Journal of chromatography. B, Biomedical sciences and applications》1999,736(1-2):299-303
Diethylenetriaminepentaacetic acid (DTPA) is a commonly used chelating agent. Its antiviral, antibacterial and immunomodulatory effects are well documented. DTPA forms a highly stable complex with lead (II) with an increased absorption coefficient and a bathochromic shift of the absorption maximum compared to pure DTPA. Based on this complex a high-performance liquid chromatographic method for the quantitative detection of DTPA in biological fluids was developed. A calibration curve was prepared and linearity was shown in the concentration range between 10 mg l(-1) and 1000 mg l(-1) DTPA. The recovery in water and in human plasma showed the method to be suitable for routine use. 相似文献
929.
Knowledge discovery and knowledge validation in intensive care 总被引:1,自引:0,他引:1
Morik K Imhoff M Brockhausen P Joachims T Gather U Imboff M 《Artificial intelligence in medicine》2000,19(3):225-249
Operational protocols are a valuable means for quality control. However, developing operational protocols is a highly complex and costly task. We present an integrated approach involving both intelligent data analysis and knowledge acquisition from experts that support the development of operational protocols. The aim is to ensure high quality standards for the protocol through empirical validation during the development, as well as lower development cost through the use of machine learning and statistical techniques. We demonstrate our approach of integrating expert knowledge with data driven techniques based on our effort to develop an operational protocol for the hemodynamic system. 相似文献
930.
Srimanote P Ittiprasert W Sermsart B Chaisri U Mahannop P Sakolvaree Y Tapchaisri P Maleewong W Kurazono H Hayashi H Chaicumpa W 《Asian Pacific journal of allergy and immunology / launched by the Allergy and Immunology Society of Thailand》2000,18(1):37-45
Hybridomas secreting monoclonal antibodies (MAbs) to Trichinella spiralis were produced. Myeloma cells were fused with splenocytes of a mouse immunized with excretory-secretory (E-S) antigen of infective larvae. A large percentage of growing hybrids secreted antibodies cross-reactive to many of 23 heterologous parasites tested. Only 6 monoclones (designated 3F2, 5D1, 10F6, 11E4, 13D6 and 14D11) secreted MAbs specific to the E-S antigen and/or a crude extract (CE) of T. spiralis infective larvae. The 6 monoclones secreted IgM, IgG3, IgM, IgG3, IgG3 and IgG3, respectively. Clone 5D1 was selected to mass produce MAbs which were then coupled to CNBr-activated Sepharose CL-4B to prepare an affinity-purified antigen. Dot-blot ELISA with either purified antigen or CE was evaluated. There were 17 patients with acute trichinellosis and 76 individuals convalescing from T. spiralis infection (group 1). Controls were 170 patients with parasitic infections other than trichinellosis (group 2) and 35 healthy parasite-free controls (group 3). CE-ELISA was positive in all group 1 patients. However, sera from many group 2 patients also were reactive (opisthorchiasis-44.2%, schistosomiasis-44%, gnathostomiasis-30%, paragonimiasis-28.6%, taeniasis-27.3%, strongyloidiasis-23.1% and hookworm infections-20%). Affinity-purified antigen was 100% specific, all sera from group 2 and group 3 individuals tested negative. Although 74 of 76 patients (97.4%) with convalescing trichinellosis tested positive, sera from only 3 of 17 patients (17.6%) with acute T. spiralis were reactive. Thus, CE antigen is appropriate when sensitivity is needed, while purified antigen should be used when specificity is required. Dot-blot ELISA is easier to perform, more rapid and less expensive than indirect ELISA. Many samples can be assayed simultaneously, special equipment is not required, and results can be preserved for retrospective analysis. Dot-blot ELISA is therefore the method of choice for the rapid diagnosis of trichinellosis, particularly when more complex laboratory tests are unavailable. 相似文献