全文获取类型
收费全文 | 3888篇 |
免费 | 459篇 |
国内免费 | 244篇 |
专业分类
耳鼻咽喉 | 30篇 |
儿科学 | 39篇 |
妇产科学 | 11篇 |
基础医学 | 366篇 |
口腔科学 | 50篇 |
临床医学 | 259篇 |
内科学 | 316篇 |
皮肤病学 | 24篇 |
神经病学 | 142篇 |
特种医学 | 174篇 |
外科学 | 163篇 |
综合类 | 548篇 |
一般理论 | 1篇 |
预防医学 | 437篇 |
眼科学 | 39篇 |
药学 | 686篇 |
中国医学 | 1259篇 |
肿瘤学 | 47篇 |
出版年
2024年 | 20篇 |
2023年 | 88篇 |
2022年 | 146篇 |
2021年 | 194篇 |
2020年 | 148篇 |
2019年 | 168篇 |
2018年 | 137篇 |
2017年 | 155篇 |
2016年 | 167篇 |
2015年 | 167篇 |
2014年 | 266篇 |
2013年 | 293篇 |
2012年 | 295篇 |
2011年 | 336篇 |
2010年 | 262篇 |
2009年 | 175篇 |
2008年 | 200篇 |
2007年 | 187篇 |
2006年 | 169篇 |
2005年 | 137篇 |
2004年 | 104篇 |
2003年 | 102篇 |
2002年 | 81篇 |
2001年 | 72篇 |
2000年 | 52篇 |
1999年 | 46篇 |
1998年 | 42篇 |
1997年 | 41篇 |
1996年 | 22篇 |
1995年 | 24篇 |
1994年 | 28篇 |
1993年 | 22篇 |
1992年 | 32篇 |
1991年 | 14篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 6篇 |
1985年 | 17篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1973年 | 4篇 |
排序方式: 共有4591条查询结果,搜索用时 46 毫秒
31.
We present a theoretical model of gas transport through the dead space during high-frequency ventilation (HFV) with volumes
less than dead space volume. The analysis is based on the axial distribution of transit times of gas moving through the dead
space. The model predicts that for tidal volumes (V) much less than dead space (Vd), gas exchange will be proportional to the product of frequency (f) and V2. If gas transport is analyzed in terms of Fick's law, then the effective diffusion coefficient (Deff) can be shown to be equal to fV2 times a constant, whose value equals the square of the coefficient of dispersion of axial transit times through the dead
space
. Experimental results in straight tubes fit the predictions of this model quite well. A
through the entire dead space of about 30% is more than sufficient to account for gas exchange during HFV in physical models
or in intact animals. An axial dispersion of this magnitude can be measured directly from a typical Fowler dead space determination
in healthy subjects. 相似文献
32.
Yasuhiko Tomino Kazuhiko Funabiki Isao Shirato Hikaru Koide Kazuhiko Eguchi Mitsunori Yagame Hideto Sakai 《Pathology international》1989,39(5):296-305
Computer imaging analysis was used for quantitative evaluation of the extents, amounts and distributions of glomerular extracellular components, such as the 7S and NC 1 domains of type IV collagen, laminin (LN), fibronectin (FN) and IgA, in glomeruli from patients with IgA nephropathy. Renal biopsy specimens from 13 patients with IgA nephropathy were incubated with mouse monoclonal antibodies against the FN or non collagenous (NC 1) domain of type IV collagen or polyclonal antiserum against the LN or 7S domain of human type IV collagen, and then stained with appropriate dilutions of FITC labeled anti mouse Ig antisera. Marked staining of the 7S or NC 1 domain of type IV collagen, LN or FN was detected in the glomerular capillary walls and/or mesangial areas in patients with IgA nephropathy. In particular, a prominent increase of FN was observed in the subendothelial regions of glomerular capillary walls, i.e. mesangial interposition, in the moderate or advanced stage of IgA nephropathy. Therefore, computer imaging analysis was shown to be useful for the quantitative determination of such components distributed in glomeruli from patients with IgA nephropathy. Acta Pathol Jpn 39: 296 305, 1989. 相似文献
33.
34.
SUMMARY Event-related potential (ERP) recordings were used to investigate the nature of auditory stimulus evaluation during stage 2 sleep. Frequent and rare stimuli, differing in intensity and frequency, were presented to six adult subjects while awake and asleep. The latency and voltage distribution of one of the long-latency components evoked during sleep resembled the P3 component evoked while awake. However, it was attenuated in voltage and superimposed on N3, a large late negative component, most probably the slow potential of the K complex. The identification of a P3-like potential during sleep suggests that the P3 potential is not solely a marker of active cognitive processes, but contains a small component which reflects automatic, pre-attentive evaluation of deviant stimuli. 相似文献
35.
Yutaka Imai Takashi Sato Mitsunori Yamakawa Takeshi Kasajima Akio Suda Yoshihiro Watanabe 《Pathology international》1989,39(2):127-134
Rheumatoid arthritis (RA) is one of the immune complex (IC) diseases in which lymphoid germinal centers (GCs) are found in the synovial tissue. Simultaneously, patients with RA often show swelling of lymph nodes. The morphology and function of the lymph node GCs in patients with RA is not clear. The aim of this study was to evaluate the differences in morphology and immunoreactions to complement (C) components, their receptors, and lgM-rheumatoid factor (RF) between synovial GCs and lymph-node GCs in RA. Furthermore, the relationship between these immuno-reactive substances and follicular dendritic cells (FDCs) in GCs was investigated. The tissues examined were 41 RA synovial specimens, seven RA lymph nodes with massive lymphadenopathy, and 10 non-RA lymph nodes. The number of synovial GCs was relatively decreased in comparison with lymph-node GCs in RA, and the diameter of each synovial GC was smaller than that of each lymph-node GC. The synovial GCs were edematous and less cellular, and moreover, those from RF-seronegative cases were smaller than those from RF seropositive cases. On the other hand, the lymph-node GCs in RA were larger, more cellular and hyperplastic, but contained more tingible-body macro-phages (TBMs) and neutrophils. In the GCs of both synovial tissues and lymph nodes in RA, early C components (C1q, C4, C3c, C3d), IgM RF, and C3b receptor (C3bR) and C3d receptor (C3dR) were expressed as a lacy network by light microscopy, and were demonstrated on the surfaces of FDCs and lymphocytes, and in the intercellular spaces by electron microscopy. Furthermore, immuno-staining for dendritic reticulum cells (DRC, DAKO DRC1) was observed in a lacy pattern by light microscopy and on the cell surface of FDCs by electron microscopy. In the GCs of non-RA lymph nodes, early C components, C3bR, C3dR, and DRC showed a similar reaction pattern, but IgMRF did not. Consequently, no marked difference in immunoreactions in the GCs, except for the immunoreactions of late C components, was found between synovial tissues and lymph nodes in RA. On the basis of these findings, we discuss the possibility of the presence of a RF-IC. 相似文献
36.
P. Valdés J. Bosch R. Grave J. Hernandez J. Riera R. Pascual R. Biscay 《Brain topography》1992,4(4):309-319
The structure of the normal resting EEG crosspectrum SVV(omega) is analyzed using complex multivariate statistics. Exploratory data analysis with Principal Component Analysis (PCA) is followed by hypothesis testing and computer simulations related to possible neural generators. The SVV(omega) of 211 normal individuals (ages 5 to 97) may be decomposed into two types of processes: the xi process with spatial isotropicity reflecting diffuse, correlated cortical generators with radial symmetry, and processes that seem to be generated by more spatially concentrated, correlated sources. The latter are reflected as spectral peaks such as the process. The eigenvectors of the xi process are the Spherical Harmonic Functions which explains the recurring pattern of maps characteristic of the spatial PCA of qEEG data. A new method for estimating sources in the frequency domain which fits dipoles to the whole crosspectrum is applied to explain the characteristics of the localized sources. 相似文献
37.
B. Bromm R. -D. Treede 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1987,67(1):153-162
Summary Brief radiant heat pulses, generated by a CO2 laser, were used to activate slowly conducting afferents in the hairy skin in man. In order to isolate C-fibre responses a preferential A-fibre block was applied by pressure to the radial nerve at the wrist. Stimulus estimation and evoked cerebral potentials (EP), as well as reaction times, motor and sudomotor activity were recorded in response to each stimulus. With intact nerve, the single supra-threshold stimulus induced a double pain sensation: A first sharp and stinging component (mean reaction time 480 ms) was followed by a second burning component lasting for seconds (mean reaction time 1350 ms). Under A-fibre block only one sensation remained with characteristics and latencies of second pain. The heat pulse evoked potential consisted of a late vertex negativity at 240 ms (N240) followed by a prominent late positive peak at 370 ms (P370). Later activity was not reliably present. Under A-fibre block this late EP was replaced by an ultralate EP beyond 1000 ms, which in the conventional average looked like a slow halfwave of 800 ms duration. This potential was distinct from eye movements, skin potentials or muscle artefacts. With cross-correlation methods waveforms similar to the N240/P370 were detected in the latency range from 900 to 1500 ms during A-fibre block, indicating a much greater latency jitter of the ultralate EP. Latency corrected averaging with a modified Woody filter yielded a grand mean ultralate EP (N1050/P1250), the shape of which was surprisingly similar to the late EP (N240/P370). The similarity of these components indicates that both EPs may be secondary responses to afferent input into neural centers, onto which myelinated and unmyelinated fibres converge. Such convergence may also explain through the known mechanisms of short term habituation and selective attention, why ultralate EPs are not reliably present without peripheral nerve block. 相似文献
38.
Frank H. Duffy Kenneth Jones Peter Bartels Gloria McAnulty Marilyn Albert 《Brain topography》1992,4(4):291-307
Summary Principal components analysis (PCA) was performed on the 1536 spectral and 2944 evoked potential (EP) variables generated by neurophysiologic paradigms including flash VER, click AER, and eyes open and closed spectral EEG from 202 healthy subjects aged 30 to 80. In each case data dimensionality of 1500 to 3000 was substantially reduced using PCA by magnitudes of 20 to over 200. Just 20 PCA factors accounted for 70% to 85% of the variance. Visual inspection of the topographic distribution of factor loading scores revealed complex loadings across multiple data dimensions (time-space and frequency-space). Forty-two non-artifactual factors were successful in classifying age, gender, and a separate group of 60 demented patients by linear discriminant analysis. Discrimination of age and gender primarily involved EP derived factors, whereas dementia primarily involved EEG derived factors. Thirty-eight artifactual factors were identified which, alone, could not discriminate age but were relatively successful in discriminating gender and dementia. The need to parsimoniously develop real neurophysiologic measures and to objectively exclude artifact are discussed. Unrestricted PCA is suggested as a step in this direction.Acknowledgements: This work was supported in part by NIA program project PO1AG049853 to M. Albert and the Mental Retardation Program Project P30HD18655 to J.J. Volpe. We thank our qEEG technologists Adele Mirabella, Susan Katz, Ellen Belles, and Marianne McGaffigan as well as our research secretaries for their unflagging support. 相似文献
39.
【目的】 在全面推进“中国科技期刊卓越行动计划”实施的背景下,探索科技期刊提升学术服务能力的有效方法。通过提升卓越期刊的学术服务能力,使其为科技创新及学术交流提供多元化的支撑。【方法】 以《中国电机工程学报》为例,采用方法创新与实践相结合的形式,对提升学术服务能力的方法进行深入挖掘并积极开展实践。【结果】 根据不同的期刊服务对象有针对性地实施新举措,使得期刊学术服务的深度及广度不断延伸,服务能力显著提升。【结论】 培养卓越的学术服务能力是“中国科技期刊卓越行动计划”资助期刊建设的重要内容。采用有效的方法可以使期刊学术服务能力得到快速提升,所提出的方法及办刊实践可为同行提供参考与借鉴。 相似文献
40.
肝毒性中药及其与药性和有效成分的关系——对55种中药肝毒性文献资料的分析报告 总被引:13,自引:0,他引:13
目的 :研究有关文献资料中中药肝毒性的报告及其与四气、五味、归经、有效成分之间的关系。方法 :应用文献研究方法 ,对 55种具有肝毒性的中药进行统计归类分析研究。结果 :中药四气、五味、归经及其有效成分与肝毒性有一定相关性。肝毒性主要集中在寒、热类 ,苦、辛类 ,归肝、脾、肾经类和有效成分中碱、甙类药物方面。结论 :中药药性理论及有效成分均与肝毒性有一定的关系 ,应用归类分析的方法对文献资料进行分析研究是中药毒性研究中确实可行的方法。 相似文献