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排序方式: 共有8106条查询结果,搜索用时 15 毫秒
41.
Frequency-domain analysis of cerebral autoregulation from spontaneous fluctuations in arterial blood pressure 总被引:4,自引:0,他引:4
Dr. R. B. Panerai J. M. Rennie A. W. R. Kelsall D. H. Evans 《Medical & biological engineering & computing》1998,36(3):315-322
The dynamic relationship between spontaneous fluctuations of arterial blood pressure (ABP) and corresponding changes in crebral
blood flow velocity (CBFV) is studied in a population of 83 neonates. Static and dynamic methods are used to identify two
subgroups showing either normal (group A, n=23) or impaired (group B, n=21) cerebral autoregulation. An FFT algorithm is used
to estimate the coherence and transfer function between CBFV and ABP. The significance of the linear dependence between these
two variables in demonstrated by mean values of squared coherence >0.50 for both groups in the frequency range 0.02–0.50 Hz.
However, group A has significanlty smaller coherences than group B in the frequency ranges 0.02–0.10 Hz and 0.33–0.49 Hz.
The phase response of group A is also significantly more positive than that of group B, with slopes of 9.3±1.05 and 1.80±1.2
rad Hz−1, respectively. The amplitude frequency response is also significantly smaller for group A in relation to group B for the
frequency range 0.25–0.43 Hz. These results suggest that transfer function analysis may be able to identify different components
of cerebral autoregulation and also provide a deeper understanding of recent findings by other investigators. 相似文献
42.
Righetti-Veltema M Conne-Perréard E Bousquet A Manzano J 《Journal of affective disorders》2002,70(3):291-306
Background: This paper is part of a prospective, epidemiologic study concerning postpartum depression (PPD). The women were first examined during pregnancy; after delivery they were seen with their infants at 3 and 18 months. The present study focuses on the 3-months-postpartum results. Methods: A sample of 570 women and their infants were examined 3 months after delivery. Using the EPDS (Edinburgh Postnatal Depression Scale; Cox et al., 1987. Br. J. Psychiatry 150:782–786), 10.2% of these new mothers presented PPD. The focus of the study concerned the effects of this neurotic disorder on the mother, the infant and on the mother–infant relationship. Results: The deleterious effects concerning the infant were functional disorders such as eating or sleeping difficulties. The ‘depressed’ dyads presented less vocal and visual communications, less corporal interactions and less smiling. Conditions surrounding delivery and tiredness at 3 months are linked to difficulties in mother–infant relationship for the non-depressed mothers. Logistic models showed that primiparous PPD mothers have difficulties bathing their infants, whereas multiparous PPD mothers are more tired. Limitation: This study did not take into account either protective factors or the effects of the infant himself. Clinical relevance: Knowledge of the mothers’ and infants’ difficulties may help caregivers to detect these at-risk dyads and initiate therapeutic measures. 相似文献
43.
Dr. Joel M. Price 《Annals of biomedical engineering》1984,12(5):481-496
This study examines the effect of length on the dose-response (D-R) relationship and the effect of agonist concentration on
the length-tension (L-T) relationship in vascular smooth muscle. The experiments used 2-mm rings from isolated segments of
the dog anterior tibial artery. In D-R experiments the length (internal ring circumference) for maximum active force (Lmax) was determined first. D-R relationships were obtained from cumulative responses to increasing concentrations of norepinephrine
(NE) or potassium (K+). L-T relationships were obtained from individual responses to a specific concentration of agonist as the ring was stretched
in increments of L0 (the initial length for resting force). Dimensions of the arterial rings were measured with a video caliper. For NE and K+ stimulations at lengths equal to and less than Lmax: (a) The concentration for half maximal response (ED50) was lowest (most sensitive) at Lmax and increased significantly as length decreased from Lmax; (b) When the direction of length change was reversed, the direction of change in ED50 was reversed; and (c) The ED50 of repeated dose-response experiments at Lmax was not significantly different. For NE: (a) the ED50 decreased significantly when length was increased from Lmax; and (b) the ED50 increased significantly when length was decreased to Lmax. The results of L-T experiments show Lmax is significantly longer for a low concentration of NE (10−6 M) than for a high concentration (10−5 M). With force normalized to the maximum force, the L-T curve is significantly lower, and the initial length for an active
response was 80% longer for 10−6 M than for 10−5 M NE. It may be concluded that vascular smooth muscle has a length-dependent dose-response relationship and a concentration-dependent
length-tension relationship. 相似文献
44.
Frank Queisser Ralph Blüthner Dieter Bräuer Helmut Seidel 《European journal of applied physiology》1994,68(1):92-101
A group of 12 healthy men volunteered for the experiment. Electromyograms (EMG) were obtained from semispinalis capitis, splenius capitis, levator scapulae, and trapezius muscles. The flexion angle of the cervical spine was precisely adjusted to 0°, 10°, 20°, and 30° relative to the horizontal, with a constant angle of the atlanto-occipital joint. The subjects made eight short (about 2 s) vertical extension forces (6%, 12%,18%, 24%, 30%, 36%, 42%, and 48% of maximal voluntary peak contraction force). For each position, the centre of pressure under the head was determine as the basis for the calculation of the external lever arm. The presence of motor endplate regions was ascertained by multiple surface electrodes. The slopes of individual linear regression lines for the root mean square (rms)-values were dependent on the existence of endplates in the area of the electrodes — endplates caused smaller rms values per Newton metres of external torque. Significant intersubject differences between regression equations could not be eliminated by the normalization of EMG-parameters and/or torques. The elimination of gravity, the continuous monitoring of positions, and the consideration of localization of motor endplate regions were essential prerequisites for the acquisition of reliable relationships between EMG of different neck muscles and external torques. Two important conclusions were derived for the prediction of torques from EMG measurements: firstly, individual regression equations which take into account the position of the head and neck should be used; secondly, normalization procedures do not justify the application of average regressions to a group of subjects. 相似文献
45.
de Koning F. L. Binkhorst R. A. Vos J. A. van 't Hof M. A. 《European journal of applied physiology》1985,54(1):89-94
Summary The force-velocity curve (FVC) of arm flexion was established in 123 untrained males and 110 untrained females aged from 15 to 36 years, and 48 arm-trained athletes competing in different sport disciplines. The FVC was described by Hill's equation and defined by the parameters: maximal static moment (M0), maximal angular velocity (0), maximal power (P0) and the concavity of the FVC (H). Within the given age range the level of the curve parameters of both untrained men and women was independent of age.On average, H was the same in all three groups. As compared to M0 of the untrained males, M0 of the athletes was 33% higher and M0 of the females was 38% lower; with regard to P0 these differences were +30% and –43% respectively. 0 was the same for trained and untrained males, wherease 0 of the women was 10% lower than 0 of the men. 相似文献
46.
应用模糊极小极大神经网络研究了化合物复杂结构和性能(QSAR)之间的关系,用该法进行几组化合物致癌的识别,结果优于线性回归的方法,对此作出一些分析。 相似文献
47.
Infectious full-length cDNA clones from the genomic RNAs of a subgroup II cucumber mosaic cucumovirus strain (Trk7) were obtained. Sequence analysis of the whole genome revealed strong homology (99%) to the genome of Q-CMV, the only subgroup II strain whose entire genomic nucleotide sequence had been available in the database, and an overall 75% homology to those of subgroup I strains. We provide sequence comparisons of different parts of 1a, 2a and 2b proteins of Cucumovirus species, and propose phylogenetic trees based on these protein sequences. 相似文献
48.
Six men and four women performed, in separate trials, maximal dynamic knee extensions with loads of 15%, 30%, 45% and 60%
of maximal isometric knee extension peak torque (MVC). The dynamic extensions were done after postactivation potentiation
(PAP) had been induced with a 10-s MVC, and in a control trial without PAP. PAP, measured as the increase in evoked twitch
torque, was 53 (4)% (SE) and 43 (3)% at the time of the first and second extensions with each load. PAP failed to increase
the attained peak velocity with any load; on the contrary, there was a trend for peak velocity to decrease in the first extension,
which occurred ≅15 s after the 10-s MVC. The results suggest that fatigue produced by the 10-s MVC suppressed any benefit
that could be derived from the induced PAP. A surface electromyogram (EMG) recorded from one muscle of quadriceps femoris
gave no indication of activation failure in the first knee extension; however, activation impairment specific to the rate
of force development cannot be ruled out. It is concluded that the strategy employed, namely of having knee extensions performed
soon after the 10-s MVC to maximize PAP at the time of performance, was unsuccessful because there had been insufficient time
for recovery from fatigue. It is possible that a longer recovery time, even at the cost of a diminished PAP, may have proved
beneficial.
Accepted: 27 July 2000 相似文献
49.
A linear mathematical model of the electromyogram (e.m.g.) has been developed for the biceps muscle. The number of motor units (and therefore muscle fibres) contributing to the resultant e.m.g. at any stage of movement has been found from the force analysis of elbow flexion. The depths of various motor units and the phase difference between the recruitment of any two motor units have been formulated using a spiral spread of recruitment sequence. The attenuation of individual motor-unit action potentials due to varying depths has been taken into consideration, and due regard has been taken of the length-tension diagram of a muscle while performing the force analysis. Attention has been focused on the flexion of the elbow joint, in which a method of finding the individual contribution of the biceps and brachialis muscles has been developed and applied. The results predicted by the model have been verified by experiments. The model can also be extended to the e.m.g. of other fast skeletal muscles. The conditions and limitations for such generalisations have been stated and discussed. 相似文献
50.
Adult rats emit 22 kHz ultrasonic vocalizations (USVs) in response to aversive stimuli, and these sounds are suggested to have communicative information among conspecifics. It is conceivable that social environment during development of rats has relevance to the emission of 22 kHz USVs. To examine the effects of social environment after weaning on production of stress-induced USVs, we compared the amount of emission of USVs among three groups of rats reared under different conditions after weaning. One group of rats was housed individually, and the other two groups were housed in pairs, in which social hierarchy of the pair was determined by social dominance-subordination relationships. The USVs were induced by acute mild somatic stimuli on the back and neck. Individually reared rats emitted much fewer USVs than pair-reared rats. In addition, socially subordinate rats emitted more USVs compared with socially dominant ones. These results suggest that not only social interaction but also the status in social hierarchy may play an important role in the process of the development of USVs induced by somatic stimuli. 相似文献