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101.
When we reach out for an object with our hand, we transform visual information about the object's position into muscle contractions that will bring our digits to that position. If we reach out with a tool the transformation is different, because the muscle contractions must bring the critical part of the tool to the object, rather than the digits. The difference between the motion of the hand and that of the tool can be quite large, as when moving a computer mouse across a table to bring a cursor to a position on a screen. We examined the responses to unpredictable visual perturbations during such movements. People responded about as quickly to changes in the position of the target when pointing with the mouse as when doing so with their hand. They also responded about as quickly when the cursor was displaced as when the target was displaced. We show that this is not because the visually perceived separation between target and cursor is transformed into a desired displacement of the hand. Our conclusion is that our actions are controlled by the judged positions of the end-effector and the target, even when the former is quite detached from the muscles and joints that are involved in the action. 相似文献
102.
Saeij JP Groeneveld A Van Rooijen N Haenen OL Wiegertjes GF 《Diseases of aquatic organisms》2003,57(1-2):67-75
Carp Cyprinus carpio macrophages were depleted by intraperitoneal (i.p.) injection of clodronate-liposomes for the in vivo study of the effect of macrophage depletion on the resistance of carp to infection with blood flagellate parasites. Clodronate released inside the cell induces apoptosis of (murine) macrophages. Following i.p. injection of carp with liposomes alone, but not with Trypanoplasma borreli, neutrophilic granulocytes rapidly migrated from the head kidney to the peritoneal cavity. The majority of liposomes in the peritoneal cavity were not taken up by newly arrived neutrophilic granulocytes, however, but by resident macrophages. After 2 i.p. injections of clodronate-liposomes, the percentage of macrophages present in the peritoneal cavity was significantly reduced, as evaluated by flow cytometry. Macrophage-depleted carp that were infected i.p. with T. borreli suffered from high mortality. However, these fish did not show lethal parasitaemia but did show clear bacteraemia. Macrophage-depleted carp that were infected i.p. with Trypanosoma carassii showed a minor increase in parasitaemia. In addition, macrophage-depleted carp, immune to T. borreli as a result of having survived a prior infection, remained immune to i.p. reinfection with T. borreli. Succesful depletion of peritoneal macrophages seemed to have a minor effect on the resistance of carp against blood flagellates. However, carp macrophages are essential as a first line of defence against (bacterial) infection. 相似文献
103.
Pouwels J Moracci M Cobucci-Ponzano B Perugino G van der Oost J Kaper T Lebbink JH de Vos WM Ciaramella M Rossi M 《Extremophiles : life under extreme conditions》2000,4(3):157-164
Sβgly and CelB are well-studied hyperthermophilic glycosyl hydrolases, isolated from the Archaea Sulfolobus solfataricus and Pyrococcus furiosus, respectively. Previous studies revealed that the two enzymes are phylogenetically related; they are very active and stable
at high temperatures, and their overall three-dimensional structure is very well conserved. To acquire insight in the molecular
determinants of thermostability and thermoactivity of these enzymes, we have performed a detailed comparison, under identical
conditions, of enzymological and biochemical parameters of Sβgly and CelB, and we have probed the basis of their stability
by perturbations induced by temperature, pH, ionic strength, and detergents. The major result of the present study is that,
although the two enzymes are remarkably similar with respect to kinetic parameters, substrate specificity, and reaction mechanism,
they are strikingly different in stability to the different physical or chemical perturbations induced. These results provide
useful information for the design of further experiments aimed at understanding the structure–function relationships in these
enzymes.
Received: May 20, 1999 / Accepted: January 10, 2000 相似文献
104.
Physiological Activity of Campylobacter jejuni Far below the Minimal Growth Temperature 总被引:3,自引:0,他引:3
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Wilma C. Hazeleger Jeroen A. Wouters Frank M. Rombouts Tjakko Abee 《Applied microbiology》1998,64(10):3917-3922
The behavior of Campylobacter jejuni at environmental temperatures was examined by determining the physiological activities of this human pathogen. The minimal growth temperatures were found to be 32 and 31°C for strains 104 and ATCC 33560, respectively. Both strains exhibited a sudden decrease in growth rate from the maximum to zero within a few degrees not only near the maximal growth temperature but also near the minimal growth temperature. This could be an indication that a temperature-dependent transition in the structure of a key enzyme(s) or regulatory compound(s) determines the minimal growth temperature. Oxygen consumption, catalase activity, ATP generation, and protein synthesis were observed at temperatures as low as 4°C, indicating that vital cellular processes were still functioning. PCR analysis showed that cold shock protein genes, which play a role in low-temperature adaptation in many bacteria, are not present in C. jejuni. The fact that chemotaxis and aerotaxis could be observed at all temperatures shows that the pathogen is able to move to favorable places at environmental temperatures, which may have significant implications for the survival of C. jejuni in the environment. 相似文献
105.
Salmonella typhimurium Encodes an SdiA Homolog, a Putative Quorum Sensor of the LuxR Family, That Regulates Genes on the Virulence Plasmid 总被引:6,自引:0,他引:6
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106.
Loss of the Plasma Membrane-Bound Protein Gas1p in Saccharomyces cerevisiae Results in the Release of β1,3-Glucan into the Medium and Induces a Compensation Mechanism To Ensure Cell Wall Integrity
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Arthur F. J. Ram Johan C. Kapteyn Roy C. Montijn L. Heleen P. Caro Jeroen E. Douwes Walter Baginsky Paul Mazur Herman van den Ende Frans M. Klis 《Journal of bacteriology》1998,180(6):1418-1424
Deletion of GAS1/GGP1/CWH52 results in a lower β-glucan content of the cell wall and swollen, more spherical cells (L. Popolo, M. Vai, E. Gatti, S. Porello, P. Bonfante, R. Balestrini, and L. Alberghina, J. Bacteriol. 175:1879–1885, 1993; A. F. J. Ram, S. S. C. Brekelmans, L. J. W. M. Oehlen, and F. M. Klis, FEBS Lett. 358:165–170, 1995). We show here that gas1Δ cells release β1,3-glucan into the medium. Western analysis of the medium proteins with β1,3-glucan- and β1,6-glucan-specific antibodies showed further that at least some of the released β1,3-glucan was linked to protein as part of a β1,3-glucan–β1,6-glucan–protein complex. These data indicate that Gas1p might play a role in the retention of β1,3-glucan and/or β-glucosylated proteins. Interestingly, the defective incorporation of β1,3-glucan in the cell wall was accompanied by an increase in chitin and mannan content in the cell wall, an enhanced expression of cell wall protein 1 (Cwp1p), and an increase in β1,3-glucan synthase activity, probably caused by the induced expression of Fks2p. It is proposed that the cell wall weakening caused by the loss of Gas1p induces a set of compensatory reactions to ensure cell integrity. 相似文献
107.
Jeroen Poels Miloš R. Spasić Patrick Callaerts Koenraad K. Norga 《BioEssays : news and reviews in molecular, cellular and developmental biology》2009,31(9):944-952
AMP‐activated protein kinase (AMPK) is an evolutionarily conserved cellular switch that activates catabolic pathways and turns off anabolic processes. In this way, AMPK activation can restore the perturbation of cellular energy levels. In physiological situations, AMPK senses energy deficiency (in the form of an increased AMP/ATP ratio), but it is also activated by metabolic insults, such as glucose or oxygen deprivation. Metformin, one of the most widely prescribed anti‐diabetic drugs, exerts its actions by AMPK activation. However, while the functions of AMPK as a metabolic regulator are fairly well understood, its actions in neuronal cells only recently gained attention. This review will discuss newly emerged functions of AMPK in neuroprotection and neurodegeneration. Additionally, recent views on the role of AMPK in autophagy, an important catabolic process that is also involved in neurodegeneration and cancer, will be highlighted. 相似文献
108.
Differential Responses to Woodland Character and Landscape Context by Cryptic Bats in Urban Environments 总被引:1,自引:0,他引:1
Paul R. Lintott Nils Bunnefeld Jeroen Minderman Elisa Fuentes-Montemayor Rebekah J. Mayhew Lena Olley Kirsty J. Park 《PloS one》2015,10(5)
Urbanisation is one of the most dramatic forms of land use change which relatively few species can adapt to. Determining how and why species respond differently to urban habitats is important in predicting future biodiversity loss as urban areas rapidly expand. Understanding how morphological or behavioural traits can influence species adaptability to the built environment may enable us to improve the effectiveness of conservation efforts. Although many bat species are able to exploit human resources, bat species richness generally declines with increasing urbanisation and there is considerable variation in the responses of different bat species to urbanisation. Here, we use acoustic recordings from two cryptic, and largely sympatric European bat species to assess differential responses in their use of fragmented urban woodland and the surrounding urban matrix. There was a high probability of P. pygmaeus activity relative to P. pipistrellus in woodlands with low clutter and understory cover which were surrounded by low levels of built environment. Additionally, the probability of recording P. pygmaeus relative to P. pipistrellus was considerably higher in urban woodland interior or edge habitat in contrast to urban grey or non-wooded green space. These results show differential habitat use occurring between two morphologically similar species; whilst the underlying mechanism for this partitioning is unknown it may be driven by competition avoidance over foraging resources. Their differing response to urbanisation indicates the difficulties involved when attempting to assess how adaptable a species is to urbanisation for conservation purposes. 相似文献
109.
Objective
To investigate the differences in breathing pattern and effort in infants at birth who failed or succeeded on continuous positive airway pressure (CPAP) during the first 48 hours after birth.Methods
Respiratory function recordings of 32 preterm infants were reviewed of which 15 infants with a gestational age of 28.6 (0.7) weeks failed CPAP and 17 infants with a GA of 30.1 (0.4) weeks did not fail CPAP. Frequency, duration and tidal volumes (VT) of expiratory holds (EHs), peak inspiratory flows, CPAP-level and FiO2-levels were analysed.Results
EH incidence increased <6 minutes after birth and remained stable thereafter. EH peak inspiratory flows and VT were similar between CPAP-fail and CPAP-success infants. At 9-12 minutes, CPAP-fail infants more frequently used smaller VTs, 0-9 ml/kg and required higher peak inspiratory flows. However, CPAP-success infants often used large VTs (>9 ml/kg) with higher peak inspiratory flows than CPAP-fail infants (71.8 ± 15.8 vs. 15.5 ± 5.2 ml/kg.s, p <0.05). CPAP-fail infants required higher FiO2 (0.31 ± 0.03 vs. 0.21 ± 0.01), higher CPAP pressures (6.62 ± 0.3 vs. 5.67 ± 0.26 cmH2O) and more positive pressure-delivered breaths (45 ± 12 vs. 19 ± 9%) (p <0.05)Conclusion
At 9-12 minutes after birth, CPAP-fail infants more commonly used lower VTs and required higher peak inspiratory flow rates while receiving greater respiratory support. VT was less variable and larger VT was infrequently used reflecting early signs of fatigue. 相似文献110.
Freek?Cox Eirikur?SaelandEmail author Matthijs?Baart Martin?Koldijk Jeroen?Tolboom Liesbeth?Dekking Wouter?Koudstaal Karin?L?vgren Bengtsson Jaap?Goudsmit Katarina?Rado?evi? 《Virology journal》2015,12(1):210