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51.
52.
Jan Petr Jan Kybic Michael Bock Sven Müller Václav Hlavác 《Magnetic resonance in medicine》2007,58(3):582-591
A new reconstruction method for parallel MRI called PROBER is proposed. The method PROBER works in an image domain similar to methods based on Sensitivity Encoding (SENSE). However, unlike SENSE, which first estimates the spatial sensitivity maps, PROBER approximates the reconstruction coefficients directly by B-splines. Also, B-spline coefficients are estimated at once in order to minimize the reconstruction error instead of estimating the reconstruction in each pixel independently (as in SENSE). This makes the method robust to noise in reference images. No presmoothing of reference images is necessary. The number of estimated parameters is reduced, which speeds up the estimation process. PROBER was tested on simulated, phantom, and in vivo data. The results are compared with commercial implementations of the algorithms SENSE and GRAPPA (Generalized Autocalibrating Partially Parallel Acquisitions) in terms of elapsed time and reconstruction quality. The experiments showed that PROBER is faster than GRAPPA and SENSE for images wider than 150x150 pixels for comparable reconstruction quality. With more basis functions, PROBER outperforms both SENSE and GRAPPA in reconstruction quality at the cost of slightly increased computational time. 相似文献
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The capacity for short-term adaptation is a well-established property of the horizontal (H) and vertical (V) components of saccades. It allows these directional components, which clearly serve the goal of foveation, to maintain their precision even under changing circumstances. Torsional (T) saccade components, on the other hand, which deal with the orientation of the target on the fovea, have hardly been investigated in adaptation experiments. They appear to be severely restricted by Listing's law during fixations and saccades. The main purpose of Listing's law is far from obvious but could be visual or oculomotor. Better knowledge of the adaptive capacity of the saccadic system in the torsional direction could throw new light on the functional significance of this interesting neural strategy. To study short-term plasticity in the torsional components of saccades, binocular 3D-eye positions were measured, using magnetic search foils. Five normal human subjects were instructed to make uni-directional refixation saccades, while they viewed a large visual scene. To induce a change in the torsional component, the complete stimulus was rapidly rotated during these saccades. We thoroughly investigated the torsional responses of the saccadic system, to see if any short-term adaptive response in torsional direction was induced, in which case the notion of a visual purpose for Listing's law would be strengthened. In none of our experiments, however, did we find any clear adaptive response in torsional direction. To further investigate the reliability of this result and to ascertain that our experimental conditions allowed classical gain adaptation, we also did experiments designed to achieve a combination of torsional adaptation and classic gain shortening in one of the directional components. While gain adaptation was very obvious, none of the experiments provided evidence for a short-term effect in torsion. We conclude that our experiments do not support a purely visual basis for Listing's law. 相似文献
56.
We have investigated Ca2+ mobilization in single T cells stimulated with their physiological ligand, i.e. antigenic peptide bound to major histocompatibility complex (MHC) molecules on antigen-presenting cells (APC). Fibroblasts expressing I-Ed class II molecules were pulsed with a peptide derived from the λ2315 immunoglobulin light chain. Onto such antigen-pulsed fibroblasts were sedimented cloned Th1 cells loaded with Fura-2. Changes in cytosolic Ca2+ concentration in single T cells were continually monitored by use of an imaging system based on fluorometry. Ca2+ mobilization was both peptide-specific and MHC-restricted. Within seconds of the initial APC-T cell contact, a Ca2+ spike could be observed. The Ca2+ response gradually declined over a 25-min period, during which oscillations were noted. Various parameters characterizing the magnitude of the Ca2+ response (latency, increase rate, max and mean Ca2+ increase, frequency and period of oscillations) all correlated with the amount of peptide used for pulsing the fibroblasts. Thus, Ca2+ mobilization in single T cells appears not to be an all or none phenomenon. Rather, activation is incremental (analog signaling), the degree of Ca2+ mobilization probably being related to the number of stimulatory peptide-MHC complexes on the surface of the APC. The extent of calcium mobilization and lymphokine production (interleukin (IL)-2, IL-3, interferon-γ) correlated, at least at the population level. 相似文献
57.
Effective haemostasis during cardiac surgery 总被引:2,自引:0,他引:2
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59.
The effect of sodium lauryl sulphate (SLS) on cytokeratin (CK) gene expression in hamster cheek pouch epithelium was studied with a hybridohistochemical technique. Using specific human anti-sense RNA probes, the plausible hamster mRNA counterparts for these human CK mRNAs were localized by detection of heterologous hybrids. In comparison with normal epithelium, the expression and distribution pattern of CK mRNAs in the hamster cheek pouch were obviously changed after application of SLS. There was a decreased expression of CK mRNAs in the hyperplastic basal layer, and increased expression in the hypertrophic granular layer. Strikingly, hybridization with the human CK 18 cRNA probe revealed an additionally expressed CK mRNA in the SLS-treated epithelium that was not found in the untreated epithelium. The present study indicates that cRNA probes for human CK mRNAs can be used successfully, not only to distinguish between different hamster CK mRNAs but also to investigate changes in CK gene expression upon the induction of non-neoplastic and neoplastic alterations in the hamster cheek pouch model. This may help elucidate the molecular changes involved in epithelial pathologies. 相似文献
60.
Helmut Seidel Barbara Harazin Kristina Pavlas Christine Sroka Jörg Richter Ralph Blüthner Udo Erdmann Jan Grzesik Barbara Hinz Reinhard Rothe 《International archives of occupational and environmental health》1988,61(1-2):95-106
Summary This study was carried out in order: (1) to examine the effects of isolated and combined prolonged exposures to noise and whole-body vibration on hearing, vision and subjectively experienced strain, and (2) to check the combined effects with repeated exposures. Six male subjects were exposed twice to noise (N) at 92 dBA, whole-body vibration (V) in the Z-axis at 4 Hz and 1.0 ms–2 rms, and noise and vibration (NV) for 90 min with each condition. Temporary threshold shifts of hearing (TTS) and their integrals (ITTS) were measured at 4, 6, 10, and 12 kHz. Visual acuity was examined by means of a very sensitive test. Cross-modality matching (CMM) of the handgrip force was used to judge the subjectively experienced strain. NV induced a clear tendency of higher TTS and ITTS than N, with several significant differences most pronounced at 10 kHz. With repeated exposures, the effect of NV decreased, while the reactions to N and V remained unchanged. The individual reactions to NV differed. The influence of the duration of exposures on vision depended on the condition; N caused time-dependent changes, whereas V did not. CMM-data increased with the duration of the exposure during V and NV. N was generally judged to be more straining than V; NV caused higher strain than V during the first 30 min of exposure only. Correlations between different effects suggest certain links between them. Additionally, less motivation — daily obtained by a questionnaire — often correlated with higher ITTS during N and NV. The results also illustrate the combined effects on the individual susceptibility, repetition of exposure, the kind of response, and, possibly, the actual psychic state.Abbreviations CMM
cross-modality matching
- MVC
maximum voluntary contraction force
- N
exposure condition: noise level 92dBA, no whole-body vibration
- NV
exposure condition: combined exposure to noise with a level of 92 dBA and wholebody vibration with 4 Hz, 1 ms–2 rms
- V
exposure condition: whole-body vibration with 4 Hz, 1 ms–2 rms
- TTS
temporary threshold shift
- ITTS
integral of temporary threshold shift
- WBV
whole-body vibration in the common sense
This work was done in the Temporary International Research Team on Combined Effects of Noise and Vibration of the Council of Mutual Economic Assistance of the Socialist Countries. The authors gratefully acknowledge the help and assistance of L.-M. Brumm, Y. Bening, M. Godau, G. Weber, and R. Vizcaino. 相似文献