全文获取类型
收费全文 | 355538篇 |
免费 | 30209篇 |
国内免费 | 14273篇 |
专业分类
耳鼻咽喉 | 3763篇 |
儿科学 | 6319篇 |
妇产科学 | 3954篇 |
基础医学 | 59230篇 |
口腔科学 | 8375篇 |
临床医学 | 26983篇 |
内科学 | 56484篇 |
皮肤病学 | 6947篇 |
神经病学 | 23723篇 |
特种医学 | 7861篇 |
外国民族医学 | 155篇 |
外科学 | 27536篇 |
综合类 | 50224篇 |
现状与发展 | 65篇 |
一般理论 | 6篇 |
预防医学 | 14126篇 |
眼科学 | 5374篇 |
药学 | 43084篇 |
73篇 | |
中国医学 | 12598篇 |
肿瘤学 | 43140篇 |
出版年
2024年 | 842篇 |
2023年 | 6024篇 |
2022年 | 12197篇 |
2021年 | 15585篇 |
2020年 | 12522篇 |
2019年 | 11292篇 |
2018年 | 11221篇 |
2017年 | 11540篇 |
2016年 | 11924篇 |
2015年 | 13733篇 |
2014年 | 20658篇 |
2013年 | 22954篇 |
2012年 | 20041篇 |
2011年 | 22967篇 |
2010年 | 19138篇 |
2009年 | 19019篇 |
2008年 | 19086篇 |
2007年 | 18408篇 |
2006年 | 16557篇 |
2005年 | 14828篇 |
2004年 | 12793篇 |
2003年 | 11203篇 |
2002年 | 9053篇 |
2001年 | 7606篇 |
2000年 | 6374篇 |
1999年 | 5760篇 |
1998年 | 5362篇 |
1997年 | 4922篇 |
1996年 | 4398篇 |
1995年 | 3885篇 |
1994年 | 3482篇 |
1993年 | 2980篇 |
1992年 | 2446篇 |
1991年 | 2311篇 |
1990年 | 1852篇 |
1989年 | 1648篇 |
1988年 | 1563篇 |
1987年 | 1282篇 |
1986年 | 1181篇 |
1985年 | 1688篇 |
1984年 | 1563篇 |
1983年 | 1098篇 |
1982年 | 1142篇 |
1981年 | 908篇 |
1980年 | 779篇 |
1979年 | 611篇 |
1978年 | 406篇 |
1977年 | 332篇 |
1976年 | 286篇 |
1975年 | 161篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
991.
Chromaffin cells of the adrenal medulla and their tumor counterparts, the pheochromocytoma (PC12) cells, are well-established
model systems in neurobiology. The development of sympathoadrenal progenitor cells to chromaffin cells can be studied with
regard to developmental signals which trigger the differentiation. With regard to potential treatments of neurological disorders
like Parkinson’s disease chromaffin cell grafting can be used as one therapeutical approach. The beneficial effect of chromaffin
cell grafts is possibly not only related to the release of dopamine but may also be linked to the release of growth factors.
One of the growth factors that is synthesized by chromaffin and PC12 cells is basic fibroblast growth factor (FGF-2). The
experimental data available so far, are in agreement with different functional roles of FGF-2. This article summarizes the
putative physiological functions of FGF-2 in the adrenal medulla. Three differential functional roles of FGF-2 are discussed:
(1) as a differentiation factor for sympathoadrenal progenitor cells; (2) as a target-derived neurotrophic factor for preganglionic
sympathetic neurons which innervate adrenal medullary cells; (3) as an auto-/paracrine factor in the adrenal medulla.
Accepted: 21 August 1996 相似文献
992.
In order to evaluate the pump output control based on the oxygen delivery to peripheral tissues, arterial and mixed venous hemoglobin content ([Hb]) and oxygen saturation (SO2) were continuously monitored in three biventricular bypass animals (3-, 6-, and 40-day experiments) with fibrillating ventricles. The specially developed oxygen sensors were mounted in the outflow ports of the artificial hearts to measure [Hb] and SO2. One animal was exercised on the treadmill at 2.0 mile/h for 15 min with pump flows fixed to deliver oxygen of (a) above 13 cc/min/kg, (b) 10, and (c) 9. In (a), the mixed venous saturation (SvO2) dropped to approximately 25% with no increase in the blood lactate level. In (b) and (c), the SvO2 decreased to approximately 10-15% with increase in blood lactate levels from 4 to 10-30 mg/dl. Also, the recovery of the SvO2 in these groups following the termination of the exercise was slower in comparison to (a). The lower limit of the SvO2 level that would create oxygen debt situation in the peripheral tissues was approximately 25-30% for the exercise of 2.0 mile/h. The SvO2 reflects changes in respiratory status, pump output, hemoglobin level, and metabolism, and is thus a useful indicator to diagnose quickly the circulatory status as well as possibly to control the artificial heart output. 相似文献
993.
本文报道给C57小鼠腹腔注射不同剂量1-甲基-4-苯基-1,2,3,6-四氢吡啶(MPTP)后,发现组3(MPTP35 mg/kg,每天一次,共7天)鼠肝匀浆、线粒体和微粒体的膜丙二醛含量明显增加,与对照组相比分别增加70.5%,67%和51.4%(P<0.01),而组1(MPTP 35mg/kg,每4小时一次,共3次)和组2(MPTP35mg/kg,每天一次,共4天)鼠肝丙二醛含量与对照组相近。结果表明MPTP有明显地促进鼠肝脂质过氧化的作用,并与其剂量有关。 相似文献
994.
Rajabi-Siahboomi Ali R. Bowtell Richard W. Mansfield Peter Davies Martyn C. Melia Colin D. 《Pharmaceutical research》1996,13(3):376-380
Purpose. The purpose of this study was to characterise the water mobility in the gel layer of hydrating HPMC tablets. Water mobility in the gel layer of different HPMCs was studied.
Methods. NMR imaging, a non-invasive technique, has been used to measure the spatial distribution of self-diffusion coefficient (SDC) and T2 relaxation times across the gel layer.
Results. It has been shown that there is a water mobility gradient across the gel layer of HPMC tablets. Although SDC and T2 relaxation times in the outer parts of the gel layer approached that of free water, in the inner parts they decreased progressively. Water mobility and SDC in the gel layer of different HPMCs appeared to vary with degree of substitution of the polymer and the lowest values were obtained across the gel layer of K4M tablets.
Conclusions. Water mobility varies across the gel layer of hydrating HPMC tablets and it is dependent on the degree of substitution of the polymer. 相似文献
995.
High Cell-Density Culture System of Hepatocytes Entrapped in a Three-Dimensional Hollow Fiber Module with Collagen Gel 总被引:2,自引:0,他引:2
Kazuyoshi Takeshita Haruaki Ishibashi Masayuki Suzuki Takumi Yamamoto Toshihiro Akaike Masashi Kodama 《Artificial organs》1995,19(2):191-193
Abstract: A compact three-dimensional (3D) module is needed for hepatocyte culture in order to develop an effective hybrid artificial liver system that can retain hepa-tocellular structure and differentiated functions. We treated the 3D module with collagen gel to entrap rat hepatocytes. This method yielded a high hepatocellular density (2 times 107 cells/ml) over a period of 14 days and maintained the secretion of albumin and ureogenesis at the same level as the control monolayer method. The ammonia removal remained at 43% of the Day 0 value over 8 days of perfusion. Our data show that this approach may be useful for liver support therapy in an ex-tracorporeal circuit. 相似文献
996.
ystein Bruserud Ingrid Aasen Per Espen Akselsen Jann Bergheim Gro Rasmussen Ingrid Nesthus 《European journal of haematology》1996,57(1):87-95
Abstract: Blast cells derived from peripheral blood of patients with acute myelogenous leukaemia (AML) were cultured in vitro and interleukin 1 receptor antagonist (IL1RA) concentrations determined in culture supernatants. AML blasts derived from patients classified as AML-M4 and AML-M5 subtype showed an increased release of IL1RA. IL1α and IL1β caused a similar increase in AML blast release of IL1RA, and addition of anti-ILl antibodies decreased IL1RA release. IL1RA release from AML blasts was also increased by stem cell factor, tumour necrosis factor α (TNFα), granulocyte-macrophage colony-stimulating factor and macrophage colony-stimulating factor, whereas interleukin 3, interleukin 6, leukaemia inhibitory factor and granulocyte colony- stimulating factor did not significantly alter IL1RA release. When investigating IL1RA serum levels, serum concentrations were decreased in acute leukaemia patients with chemotherapy-induced cytopenia compared with healthy controls. Serum levels of both IL1RA as well as IL1β and soluble TNFα receptors increased when the leucopenic patients developed complicating bacterial infections. 相似文献
997.
Fragmentation is frequently observed in animal and human embryosobtained via in-vitro fertilization (IVF), and is known to beassociated with decreased pregnancy rates and poor survivalfollowing cryopreservation. We postulate that embryo fragmentationis a consequence of activated programmed cell death (PCD) andsubsequent apoptosis and discuss evidence of morphological,histological and biochemical features compatible with the occurrenceof PCD in preimplantation embryos. If PCD is an underlying causeof the high incidence of the fragmentation seen in human pre-embryos,it remains to be determined whether this is reflective of thenatural incidence of lethal chromo somes in the human populationor due to the IVF procedure and culture conditions. 相似文献
998.
Rodney Harrison Michael J. Bronskill R. Mark Henkelman 《Magnetic resonance in medicine》1995,33(4):490-496
T2 relaxation makes an important contribution to tissue contrast in magnetic resonance (MR) imaging. Many tissues are known to exhibit multicomponent T2 relaxation that suggests some compartmental segregation of mobile protons on a T2 timescale. Magnetization transfer (MT) is another relaxation mechanism that can be used to produce tissue contrast in MR imaging. The MT process depends strongly on water-macromolecular interactions. To investigate the relationship between multicomponent T2 relaxation and the MT process, multiecho T2 measurements have been combined with MT measurements for freshly excised samples of cardiac muscle, striated muscle, and white matter. For muscle, short T2 components show greater MT than long T2 components, consistent with the belief that they represent distinct water environments. For white matter, quantitative MT measurements were identical for the two major T2 components, apparently because of exchange between the T2 compartments on a timescale characteristic of the MT experiment. Implications for accurate modeling of MT in tissue and the use of MT for MR image contrast are discussed. 相似文献
999.
The presence of diadenosine polyphosphates (ApxA), diadenosine tetraphosphate (Ap4A), diadenosine pentaphosphate (Ap6A), and diadenosine hexaphosphate (Ap6A), has been described in secretory granules of chromaffin cells, Torpedo synaptic vesicles, and rat brain synaptosomes. The release of these compounds by the action of secretagogues and depolarizing agents, in the presence of calcium, increases their importance as active neurotransmitters. Two high affinity receptors have been described in the three neural models, with Kd values ranging from 0.08 to 0.40 nM for the first binding site and from 5.6 to 18nM for the second lower affinity binding site. Both binding sites exhibit a P2y-like profile in chromaffin cells and Torpedo synaptic terminals and a different pattern in rat brain synaptosomes, suggesting the presence of a novel P2-purinoceptor tentatively named P2d. Studies about the second messenger linked to this receptor, in chromaffin cells, demonstrate the mobilization of calcium from internal stores. ApxA receptors at the extracellular milieu are responsible for the inhibition of catecholamine release stimulated by secretagogues. Finally, all diadenosine polyphosphates are destroyed by the action of an ecto-phosphodiesterase which, in chromaffin cells, shows Km values ranging from 1 to 4 μM. © 1993 Wiley-Liss, Inc. 相似文献
1000.
电针改善硬膜外吗啡用于术后镇痛所引起的免疫抑制 总被引:1,自引:1,他引:0
为观察硬膜外吗啡和电针对术后患者免疫功能的影响,检测自然杀伤细胞(NKcell)活性和PHA诱导白细胞介素2(IL-2)水平在单纯胆囊切除术患者术前和术后第1、3、7天的动态变化情况。结果吗啡组NK活性在术后第1、3、7天抑制,手术组仅在术后第1、3天出现抑制,而抑制率低于同天的吗啡组,电针可拮抗吗啡引起的NK活性抑制加深状况。在术后第1天,手术组和吗啡组IL-2水平均下降,吗啡+电针组无明显变化,术后第7天吗啡+电针组IL-2升高接近正常人水平。表明电针能改善硬膜外吗啡引起的免疫抑制,促进术后机体的恢复。硬膜外吗啡结合电针是值得推荐的术后镇痛方法。 相似文献