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In an ecosystem under simultaneous threat from multiple alien species, one invader may buffer the impact of another. Our surveys on a remote floodplain in the Kimberley region of north western Australia show that invasive chinee apple trees (Ziziphus mauritiana) provide critical refuge habitat for native rodents (pale field rats, Rattus tunneyi). Feral horses (Equus caballus) have trampled most of the remaining floodplain, but are excluded from the area around each chinee apple tree by thorny foliage. Although chinee apple trees constituted <10% of trees along our transects, they represented >50% of trees that harboured rat burrows. The mean number of burrows under each chinee apple tree was twice as high as under most other tree species, and we trapped more than seven times as many rats under chinee apple trees as under other types of trees. The extensive burrow systems under chinee apple trees contained female as well as male rats, whereas we only captured males around the smaller burrow systems under other tree species. Our data suggest that this invasive tree plays a critical role in the persistence of pale field rat populations in this degraded ecosystem, and that managers should maintain these trees (despite their alien origins) at least until feral horses have been removed.  相似文献   
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Conventionally flood mapping typically includes only a static water level (e.g. peak of a storm tide) in coastal flood inundation events. Additional factors become increasingly important when increased water-level thresholds are met during the combination of a storm tide and increased mean sea level. This research incorporates factors such as wave overtopping and river flow in a range of flood inundation scenarios of future sea-level projections for a UK case study of Fleetwood, northwest England. With increasing mean sea level it is shown that wave overtopping and river forcing have an important bearing on the cost of coastal flood events. The method presented converts inundation maps into monetary cost. This research demonstrates that under scenarios of joint extreme surge-wave-river events the cost of flooding can be increased by up to a factor of 8 compared with an increase in extent of up to a factor of 3 relative to “surge alone” event. This is due to different areas being exposed to different flood hazards and areas with common hazard where flood waters combine non-linearly. This shows that relying simply on flood extent and volume can under-predict the actual economic impact felt by a coastal community. Additionally, the scenario inundation depths have been presented as “brick course” maps, which represent a new way of interpreting flood maps. This is primarily aimed at stakeholders to increase levels of engagement within the coastal community.  相似文献   
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The divergent TGF-β superfamily member, macrophage inhibitory cytokine-1 (MIC-1/GDF15), is overexpressed by most cancers, including prostate cancer (PCa). Whilst its circulating levels are linked to cancer outcome, the role MIC-1/GDF15 plays in cancer development and progression is incompletely understood. To investigate its effect on PCa development and spread, we have used TRAMP prostate cancer prone mice bearing a germline deletion of MIC-1/GDF15 (TRAMPMIC-/-). On average TRAMPMIC-/- mice died about 5 weeks earlier and had larger prostatic tumors compared with TRAMP mice that were wild type for MIC-1/GDF15 (TRAMPMIC+/+). Additionally, at the time of death or ethical end point, even when adjusted for lifespan, there were no significant differences in the number of mice with metastases between the TRAMPMIC+/+ and TRAMPMIC-/- groups. However, consistent with our previous data, more than twice as many TRAMP mice overexpressing MIC-1/GDF15 (TRAMPfmsmic-1) had metastases than TRAMPMIC+/+ mice (p<0.0001). We conclude that germ line gene deletion of MIC-1/GDF15 leads to increased local tumor growth resulting in decreased survival consistent with an overall protective role for MIC-1/GDF15 in early primary tumor development. However, in advancing disease, as we have previously noted, MIC-1/GDF15 overexpression may promote local invasion and metastatic spread.  相似文献   
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Measurement and regulation of thyroidal status in teleost fish   总被引:5,自引:0,他引:5  
Summary We have reviewed the stages in teleost thyroid function and its regulation, from the initial biosynthesis of the TH to their eventual interaction with putative receptors.TH biosynthesis depends on an adequate plasma iodide level, determined partly by dietary iodide and partly by active branchial iodide uptake from the water, Pulse-injected radioiodide can be used to evaluate thyroidal iodide uptake, aspects of TH biosynthesis and TH thyroidal secretion. However, owing to variable plasma iodide levels, care is required in interpretating these parameters. TH biosynthesis, thyroglobulin properties and intrathyroidal secretion mechanisms have received limited recent attention. Histological indices of thyroid tissue changes, while useful in many situations, do not always correlate with more direct estimates of thyroidal secretion and can be misleading.Thyroid function is regulated by the hypothalamo-pituitary-thyroid axis, but neither the identities of the hypothalamic factors nor a reliable immunoassay for TSH have been established. Currently, activity of the hypothalamic-pituitary axis is usually determined by pituitary thyrotrope histological appearance or bioassay of pituitary TSH. Plasma free T4 feeds back at both the pituitary and hypothalamic levels and inhibits TSH release. Thyroidal T4 secretory activity is presumably adjusted to maintain a constant plasma T4level according to physiologic state.Plasma T4 is probably the most commonly used index of thyroidal status. However, (1) T4 is probably not the active form of TH, (2) the T4 plasma level may be influenced by the binding properties of plasma proteins, and (3) the T4 concentration alone makes no provision for the rate of T4 turnover in plasma. The most practical way to measure thyroidal T4SR is to determine plasma T4DR, and assuming steady-state conditions, equate it to T4SR. The T4DR is determined from kinetic studies employing*T4, which also enable estimates of sizes of vascular and extravascular T4 pools and their rates of exchange. Excretion of T4 or its derivatives in urine or bile can be determined also. A high proportion of T4 is enzymatically monodeiodinated in liver and other tissues, generating T3 for local (intracellular) and vascular systemic compartments.Bothin vivo andin vitro methods have been used to quantify T4 deiodinase activity, which is highly responsive to physiologic state and environmental variables. T3 production is inhibited by a moderate T3 excess indicating an autoregulatory system, whereby tissue T3 levels are maintained at a set-point appropriate for a particular physiologic state. The rate of T3 production provides an informative measure of thyroidal status in a given tissue. However, other pathways also contribute to the maintenance of T3 homeostasis at a particular set-point. These include the rate of T3 degradation to 3,3-T2, the rate of T4 substrate diversion to rT3 (an inactive isomer) and by the excretion of parent compounds or conjugates in bile and urine. Potential losses across branchial or integumentary surfaces have yet to be evaluated.The most fundamental measure of thyroidal status is represented by the amount of T3 saturably bound to receptors/nucleus for the cell type of interest. This is estimated most accurately in double isotope studies in which T3 contributions from both vascular and intracellular compartments are evaluated. Less satisfactory but meaningful indices of T3 availability to receptor sites may be obtained from the plasma T3 (or free T3) level and from the tissue T3 level. The former is appropriate if the cell type in question obtains its T3 primarily from plasma; the latter should be measured if the cell type derives its T3 mainly through intracellular deiodinase activity. If the proportion of vascular T3/intracellular T3 bound to receptors is known, it may indicate the degree of receptor activation. However, even cytosolic T3 levels may not vary in proportion to nuclear T3 levels.Differences in thyroidal function between teleosts and homeotherms can be attributed to distinctive strategies in iodide economy and to fundamental differences in control of thyroidal status. Owing to more certain iodide availability (branchial iodide pump and plasma iodide-binding proteins), teleosts are probably more liberal in their iodide use and have less efficient mechanisms for recovery and retention of hormonal iodide than homeotherms. Also, primary control of teleost thyroidal function appears peripheral. It is the finely regulated conversion of T4 to T3 in tissues which may largely determine the T4 secretion rate. Thus, T4, as a prohormone, may be produced more to satisfy the substrate needs for T4 conversion rather than to drive T3 production. Because TH are mainly implicated in tissue- or cell-specific processes involved in development, growth and reproduction in teleosts, it may be advantageous for their thyroidal status to be determined locally through T4-to-T3 deiodination. In homeotherms, primary control is mainly central through the hypothalamic-pituitary axis, which regulates thyroidal secretion of T4 and significant amounts of T3. The level of T4 (free T4) is believed to drive the production of T3 in most peripheral tissues. Because TH are extensively involved in the systemically integrated adjustment of basal metabolic rate in homeotherms, it may have been advantageous to evolve a system leaning towards central control by the hypothalamus, the brain centre associated with thermoregulation.  相似文献   
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The effects of near ultraviolet (NUV) light on a NUV chromophore-containing oxidant-sensitive enzyme, dihydroxyacid dehydratase (DHAD), were measured in seven strains of Escherichia coli. The strains differed in production of the oxidant-defense enzymes, superoxide dismutases (Fe-SOD and Mn-SOD), and catalases HPI and HPII. With the stress of aerobic growth but without NUV exposure, the strains lacking either Fe or Mn SOD or both SODs had 57%, 25%, and 12%, respectively, of the DHAD-specific activity of the parent (K12) strain. Under the same conditions, the catalase strains that were wild type, overproducing, and deficient had comparable DHAD-specific activities. When aerobic cultures were exposed for 30 min to NUV with a fluence of 216 J/m2/s at 310–400 nm, the percentage decreases in DHAD-specific activities were similar (ranging from 75% to 89%) in strains with none, either, or both SODs missing, and in the catalase-overproducing strain. However, the decreases were only 58% and 52% in the strain with catalase missing and in its parent, respectively. The NUV-induced loss of DHAD enzyme activity was not accompanied by any detectable loss of the DHAD protein as measured by polyclonal antibody to DHAD.  相似文献   
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