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971.
Pascal Coorevits Lieven Danneels Dirk Cambier Herman Ramon Hans Druyts J Stefan Karlsson Georges De Moor Guy Vanderstraeten 《Journal of electromyography and kinesiology》2008,18(4):637-644
The aims of the current study were to examine the stationarities of surface electromyographic (EMG) signals obtained from eight bilateral back and hip muscles during a modified Biering-Sørensen test, and to investigate whether short-time Fourier (STFT) and continuous wavelet transforms (CWT) provided similar information with regard to EMG spectral parameters in the analysis of localized muscle fatigue. Twenty healthy subjects participated in the study after giving their informed consent. Reverse arrangement tests showed that 91.6% of the EMG signal epochs demonstrated no significant trends (all p > 0.05), meaning 91.6% of the EMG signal epochs could be considered as stationary signals. Pearson correlation coefficients showed that STFT and CWT in general provide similar information with respect to the EMG spectral variables during isometric back extensions, and as a consequence STFT can still be used. 相似文献
972.
Jos Vanrenterghem Maarten F Bobbert L J Richard Casius Dirk De Clercq 《Journal of electromyography and kinesiology》2008,18(1):108-115
This paper presents a simulation study that was conducted to investigate whether the stereotyped motion pattern observed in human sub-maximal jumping can be interpreted from the perspective of energy expenditure. Human sub-maximal vertical countermovement jumps were compared to jumps simulated with a forward dynamic musculo-skeletal model. This model consisted of four interconnected rigid segments, actuated by six Hill-type muscle actuators. The only independent input of the model was the stimulation of muscles as a function of time. This input was optimized using an objective function, in which targeting a specific sub-maximal height value was combined with minimizing the amount of muscle work produced. The characteristic changes in motion pattern observed in humans jumping to different target heights were reproduced by the model. As the target height was lowered, two major changes occurred in the motion pattern. First, the countermovement amplitude was reduced; this helped to save energy because of reduced dissipation and regeneration of energy in the contractile elements. Second, the contribution of rotation of the heavy proximal segments of the lower limbs to the vertical velocity of the centre of gravity at take-off was less; this helped to save energy because of reduced ineffective rotational energies at take-off. The simulations also revealed that, with the observed movement adaptations, muscle work was reduced through improved relative use of the muscle's elastic properties in sub-maximal jumping. According to the results of the simulations, the stereotyped motion pattern observed in sub-maximal jumping is consistent with the idea that in sub-maximal jumping, subjects are trying to achieve the targeted jump height with minimal energy expenditure. 相似文献
973.
Vanrenterghem J Lees A Clercq DD 《Journal of strength and conditioning research / National Strength & Conditioning Association》2008,22(3):708-714
It is commonly accepted that vertical jump performance is a good indicator of maximal joint power. Some studies, however, have indicated that knee joint power output in the vertical jump is limited due to forward trunk inclination early in the push-off. The aim of this experimental study was to investigate the effect of forward trunk inclination on joint power output in vertical jumping. A group of 20 male subjects performed maximal vertical countermovement jumps from stance while minimizing the contribution of arm swing by holding their hands on their hips (arms akimbo). They also performed maximal jumps while holding the trunk as upright as possible throughout the jump, still holding the arms akimbo. Jump height, joint kinematics (angles), and joint kinetics (torque, power) were calculated. Jump height of vertical jumps while holding the trunk upright was 10% less than in normal jumps. Hip joint power was decreased by 37% while knee joint power was increased by 13%. Ankle joint power did not change. These results demonstrated that maximal jump performance does not necessarily represent maximal power of each individual joint. The implication is that jump performance may well be a good representation of overall joint power; it is, however, not an accurate measure to evaluate maximal individual joint power as part of contemporary training and rehabilitation methods. 相似文献
974.
Tropical upper montane forests usually comprise trees of small stature with a relatively low aboveground productivity. In
contrast to this rule, in the Cordillera de Talamanca (Costa Rica), tall trees (>35 m in height and more than 60 cm in diameter)
are characteristic for the upper montane old-growth oak forests which are growing at an altitude of almost 3,000 m close to
the alpine timberline. For these exceptional forests, productivity data are not yet available. In this study, we analyzed
litterfall and its components (tree leaves, litter of epiphytic vascular and non-vascular plants, mistletoes, twigs and other
canopy debris) in three forest stands belonging to different successional stages and related seasonal changes in litterfall
to micrometeorological variables. The studied stands were early-successional forest (10–15-year-old), mid-successional forest
(40-year-old), and old-growth forest. The stands are dominated by Quercus copeyensis and are located at 2,900-m altitude. Total litterfall was highest in the mid-successional forest (1,720 g m−2 y−1), and reached 1,288 g m−2 y−1 in the old-growth forest and 934 g m−2 y−1 in the early-successional forest. Litter mass was dominated by leaves in all stages (56–84% of total litterfall). In the old-growth
forest, however, twigs and small canopy debris particles (33%), epiphytes (6%), and mistletoes (5%) also contributed substantially
to litter mass. Leaf litterfall showed a clear seasonal pattern with a negative correlation to monthly precipitation and highest
values in the dry season (January–April). However, the strongest correlation existed with minimum air temperature (negative),
probably because temperatures already dropped at the end of the rainy season, when precipitation had not yet declined and
leaf shedding already increased. In contrast, litterfall of epiphyte mass, and twigs and other debris was mostly dependent
on occasional strong winds. We conclude that the upper montane oak forests of the Cordillera de Talamanca are exceptional
with respect to the large tree size and the relatively high productivity as indicated by litterfall. Litter mass was especially
high in the mid-successional and old-growth forests, where the observed annual totals are among the highest recorded for tropical
forests so far. 相似文献
975.
976.
Kaiser PO Riess T Wagner CL Linke D Lupas AN Schwarz H Raddatz G Schäfer A Kempf VA 《Cellular microbiology》2008,10(11):2223-2234
Human pathogenic Bartonella henselae cause cat scratch disease and vasculoproliferative disorders (e.g. bacillary angiomatosis). Expression of Bartonella adhesin A (BadA) is crucial for bacterial autoagglutination, adhesion to host cells, binding to extracellular matrix proteins and proangiogenic reprogramming via activation of hypoxia inducible factor (HIF)-1. Like the prototypic Yersinia adhesin A, BadA belongs to the class of trimeric autotransporter adhesins and is constructed modularly consisting of a head, a long and repetitive neck-stalk module and a membrane anchor. Until now, the exact biological role of these domains is not known. Here, we analysed the function of the BadA head by truncating the repetitive neck-stalk module of BadA (B. henselae badA(-)/pHN23). Like B. henselae Marseille wild type, B. henselae badA(-)/pHN23 showed autoagglutination, adhesion to collagen and endothelial cells and activation of HIF-1 in host cells. Remarkably, B. henselae badA(-)/pHN23 did not bind to fibronectin (Fn) suggesting a crucial role of the deleted stalk domain in Fn binding. Additionally, the recombinantly expressed BadA head adhered to human umbilical vein endothelial cells and to a lesser degree to epithelial (HeLa 229) cells. Our data suggest that the head represents the major functional domain of BadA responsible for host adhesion and angiogenic reprogramming. 相似文献
977.
978.
Raúl Pérez-Ruiz Olga Hinze J?rg-M Neud?rfl Dirk Blunk Helmut G?rner Axel G Griesbeck 《Photochemical & photobiological sciences》2008,7(7):782-788
The solution photochemistry of the ortho allyloxy-substituted benzophenone has been investigated in detail. Product analysis revealed formation of a diastereomeric mixture of dihydrobenzofuran derivatives by cyclization via a short-lived intermediate 1,5-biradical and an unusual acetal by a pseudo-Paternò-Büchi rearrangement. The latter reaction pathway was supported by means of laser flash photolysis, where a long-lived intermediate with a maximum absorption band at 380 nm was observed. Besides, theoretical calculations (TD-DFT) of this UV-transient resulted in a band with maximum intensity at 390 nm showing a good correlation between experimental results and theoretical calculations. For comparison, the meta-substituent substrate was also investigated showing preferred triplet-triplet energy transfer. 相似文献
979.
Koczan D Drynda S Hecker M Drynda A Guthke R Kekow J Thiesen HJ 《Arthritis research & therapy》2008,10(3):R50
Introduction
About 30% of rheumatoid arthritis patients fail to respond adequately to TNFα-blocking therapy. There is a medical and socioeconomic need to identify molecular markers for an early prediction of responders and nonresponders. 相似文献980.
Libnow S Methling K Hein M Michalik D Harms M Wende K Flemming A Köckerling M Reinke H Bednarski PJ Lalk M Langer P 《Bioorganic & medicinal chemistry》2008,16(10):5570-5583
The first indirubin-N'-glycosides were prepared based on reactions of isatin-N'-glycosides with indoxyls. The products show a significant anti-proliferative activity against various human cancer cell lines. Good results were observed for an indirubin-N'-mannoside which was shown to have medium to high anti-proliferative activity against all investigated cell lines. The highest activities and selectivities against the MCF-7 breast cancer cell line were observed for indirubin-N'-rhamnosides. 相似文献