全文获取类型
收费全文 | 7387篇 |
免费 | 598篇 |
国内免费 | 398篇 |
专业分类
耳鼻咽喉 | 65篇 |
儿科学 | 65篇 |
妇产科学 | 100篇 |
基础医学 | 2074篇 |
口腔科学 | 109篇 |
临床医学 | 428篇 |
内科学 | 1359篇 |
皮肤病学 | 124篇 |
神经病学 | 562篇 |
特种医学 | 206篇 |
外国民族医学 | 1篇 |
外科学 | 413篇 |
综合类 | 895篇 |
现状与发展 | 5篇 |
预防医学 | 204篇 |
眼科学 | 119篇 |
药学 | 755篇 |
中国医学 | 203篇 |
肿瘤学 | 696篇 |
出版年
2024年 | 13篇 |
2023年 | 73篇 |
2022年 | 116篇 |
2021年 | 147篇 |
2020年 | 118篇 |
2019年 | 136篇 |
2018年 | 127篇 |
2017年 | 165篇 |
2016年 | 204篇 |
2015年 | 239篇 |
2014年 | 369篇 |
2013年 | 488篇 |
2012年 | 435篇 |
2011年 | 487篇 |
2010年 | 446篇 |
2009年 | 536篇 |
2008年 | 498篇 |
2007年 | 504篇 |
2006年 | 464篇 |
2005年 | 412篇 |
2004年 | 362篇 |
2003年 | 350篇 |
2002年 | 270篇 |
2001年 | 242篇 |
2000年 | 169篇 |
1999年 | 163篇 |
1998年 | 144篇 |
1997年 | 127篇 |
1996年 | 104篇 |
1995年 | 97篇 |
1994年 | 77篇 |
1993年 | 69篇 |
1992年 | 31篇 |
1991年 | 29篇 |
1990年 | 16篇 |
1989年 | 24篇 |
1988年 | 14篇 |
1987年 | 19篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1972年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有8383条查询结果,搜索用时 9 毫秒
71.
72.
Laser Doppler flowmetry with optical-fibre beam transmission is a sensitive fast and convenient method of measuring tissue
blood flow. However, its sensitivity can also be a problem because of movement artefacts. This study applies some basic considerations
of fibre optics and Rayleigh light scattering to the field of laser Doppler blood flow meters. Practical suggestions are given
by which movement arterfacts can be reduced by choice of optical fibres, attention to probe geometry, cladding the fibres
to reduce their movements and in the method of application. Experiments which test the normalisation circuitry of laser Doppler
instruments are described and the effects of movement artefacts on the interpretation of the pulsatile component of laser
Doppler records are also discussed. Probe and fibre line movements cause high-frequency intensity fluctuations due to speckle
movement. The intensity fluctuations produce an apparent Doppler shift much greater than the Doppler shift produced by the
relative movements of probe and tissue. It has been found that it is important to ensure that the fields of view of the illuminating
and detecting fibres do not overlap at the skin surface and that probe contact with the skin surface should be maintained. 相似文献
73.
目的:从蛋白质可逆磷酸化修饰的角度初步勾勒出CCKB型受体介导的胞内信号转导途径。方法:培养的小鼠大脑皮质神经元分为实验组、对照组和受体拮抗剂组,在无磷培养基加入 [32P]-NaH2PO4标记细胞中的磷蛋白后,刺激组给予CCK8(10-7 mol/L),对照组加入等量的无磷培养基,受体拮抗剂组在分别加入CCKA型、CCKB型受体拮抗剂L364 718、L365 260以及L364 718+L365 260,浓度均为10-8 mol/L,孵育10 min后,再加入10-7 mol/L CCK8,37 ℃作用60 min,液氮中终止磷酸化反应。裂解细胞提取蛋白质,双向电泳分离,放射自显影7d后,获得磷酸化蛋白的放射自显影双向电泳图谱。采用PDQuest 2D分析软件对图谱进行差异分析,并在Swiss-Prot蛋白质数据库和自建磷蛋白数据库中查询定性。结果:CCK8作用60 min后,小鼠神经元CCK8信号转导相关磷酸化蛋白有:多种蛋白激酶、细胞信号分子、生长因子受体、转录因子等。加入L364 718后,神经元中PKCδ、P55G等的磷酸化水平降低,加入L365 260后, PKCα、PKGβ、OGFR、EGFR等的磷酸化水平呈现不同程度的降低,表明皮质神经元中CCKB受体介导的信号转导更复杂。结论:CCKA型、GGKB型受体均可介导CCK8在神经元的信号转导,但CCKB型受体可能发挥了更重要的作用,其介导的信号途径可能包括:肌醇磷脂信使系统、cAMP-PKA途径、MAPK途径、JNK途径、PI3K-PKB途径和cGMP-PKG途径。 相似文献
74.
目的: 旨在研究银杏叶提取物(Ginkgo Biloba Extract,EGB761)对大鼠主动脉平滑肌细胞(RVSMC)血红素氧合酶-1(HO-1)蛋白的影响,并探讨其中涉及的细胞信号通路。方法: 大鼠主动脉平滑肌细胞株复苏、传代培养到第6代,再复孔培养用于实验,分别给予空白对照、单纯EGB761、EGB761+锌原卟啉Ⅸ(ZnPPⅨ)或不同的细胞内信号途径特异性阻断剂进行处理,采用Western blotting法定量检测HO-1蛋白表达。结果: EGB761能呈剂量依赖性诱导HO-1蛋白表达,加用ZnPPⅨ(血红素氧合酶特异性阻断剂)及酪氨酸蛋白激酶(TPK)阻断剂木黄酮均能显著抑制EGB761诱导的HO-1蛋白表达(均P<0.01),但calphostin-C(蛋白激酶C阻断剂)、LY294002(磷脂酰肌醇-3激酶阻断剂)及Bay11-7082(核因子-κB阻断剂)对EGB761诱导的HO-1蛋白表达无明显影响(均P>0.05)。结论: (1) EGB761能显著诱导RVSMC中HO-1蛋白的表达,并且这种诱导作用能被血红素氧合酶的特异性阻断剂ZnPPⅨ所阻断。(2)EGB761通过TPK途径介导大鼠主动脉平滑肌细胞HO-1蛋白的表达。 相似文献
75.
76.
Joshua S. Newton Jin Li Zhi-Qiang Ning Diana E. Schoendorf John D. Norton John J. Murphy 《European journal of immunology》1996,26(4):811-816
B lymphocytes are activated following antigen stimulation of the B cell receptor but require co-stimulation with accessory molecules provided by interleukin (IL)-4/CD40 ligand for cell cycle progression and proliferation. By analyzing a panel of 11 early response genes induced by cross-linking of surface immunoglobulin, we show that CD40 signaling alone induces only 2 genes, c-myc together with an anonymous gene, 3L3, and that these are distinct from the set of genes induced in response to IL-4. Co-stimulation with the proliferative combination of anti-μ, IL-4 + CD40 signaling led to a fourfold enhancement of egr-2/krox20 expression over that seen with anti-μ alone. Egr-2 expression/activity was selectively inhibited by the immunosuppressive drug cyclosporin A, and antisense oligonucleotide blockade of Egr-2 activity elicited a dose-dependent inhibition of B cell proliferation. Taken together, these observations show that the early gene regulatory programs coupled to different surface receptors on B cells are largely distinct from each other, but that certain genes, exemplified by egr-2, may represent a point of convergence in the integration of different signaling pathways into the B cell proliferative response. 相似文献
77.
脑缺血性损伤早期小胶质细胞即被激活。激活的小胶质细胞既有细胞毒性又有神经营养作用。小胶质细胞行使免疫功能的信号转导受体之一是TLR4(toll-like receptor 4)。TLR4在脑内主要表达在小胶质细胞,是一种模式识别受体(pattern recognition receptor,PRR), 识别一些外源性和内源性的配体。最近的研究表明,TLR4信号通路在脑缺血再灌注损伤中起重要作用。TLR4通过激活小胶质细胞,大量表达炎症因子,加重脑缺血性损伤。 相似文献
78.
Independent Component Analysis (ICA) is a promising tool for the analysis of functional magnetic resonance imaging (fMRI) time series. In these studies, mostly assumed is a spatially independent component map of fMRI data (spatial ICA). In this paper, we assume that the temporal courses of the signal and noises are independent within a Tiny spatial domain (temporal ICA). Then with fast-ICA algorithm, spatially neighboring fMRI data were blindly separated into several temporal courses and were preassumed to be formed by a signal time course and several noise time courses where the signal has the largest correlation coefficient with the reference signal. The final functional imaging was completed for the signals obtained from each voxel. Simulations showed that compared with the spatial ICA method, the new temporal ICA method is more effective than the spatial ICA in detecting weak signal in a fMRI dataset. As background noise, the simulations include simulated Gaussian noise and fMRI data without stimulation. Finally, vivo fMRI tests showed that the excited areas evoked by a visual stimuli are mainly in the region of the primary visual cortex and that evoked by auditory stimuli are mainly in the region of the primary temporal cortex. 相似文献
79.
This paper describes the development of a digitized, real-time, microcomputer-based signal processing system which records the following variables: systolic and diastolic blood pressure, heart rate, pulse transit time, blood volume pulse, and R-, S-, and T-wave amplitudes of EKG signals. Forty-eight healthy subjects participated in a three-task stress response study in order to gather initial data for evaluating the reliability and validity of this monitoring system. The three tasks represented replications of earlier studies: 1) reading aloud of a monotonous neutral text (Reading Only, RO); 2) mental arithmetic without vocalization (Arithmetic Quiet, AQ); and 3) mental arithmetic with vocalization (Arithmetic Aloud, AA). The findings provided support for the reliability and validity of the new monitoring system given that few data were lost, and resting values as well as differential task responses were found to be comparable with earlier data sets derived via similar experimental protocols. 相似文献
80.
The purpose of the experiment was to test the hypothesis of a systematic change in perceptual performance within a single cardiac cycle due to the activity of the baroreceptors in carotid sinus. As an index of perceptual performance the ds-parameter from signal detection theory (TSD) was used. A 1000 Hz sine tone had to be detected in a background of white noise. Each of 4 subjects received on the average 4605 noise or noise plus tone stimuli distributed over 10 experimental sessions. When comparing performance during time intervals before and after baroreceptor activity onset no significant difference was found. Also, when tracing perceptual performance over the whole cardiac cycle in steps of 66,100, and 200 msec, no systematic variation could be detected. For steps of 33 msec a rhythmic pulsation of perceptual performance of about 8 Hz appeared. An influence of electrical activity of the brain on perceptual performance was postulated. This activity would have to be time-locked to carotid sinus baroreceptor activity. 相似文献