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Spermatogonia of the nine-banded armadillo, Dasypus novemcinctus mexicanus, were studied morphologically using light and electron microscopy and examined histochemically using light microscopy. Immature flat type spermatogonia have ovoid or irregular nuclei with loosely condensed chromatin. Free ribosomes are abundant while profiles of rough endoplasmic reticulum are scarce. Smooth endoplasmic reticulum is a prominent feature occasionally taking an unusual cylindrical form. Mature spermatogonia exhibit rounder nuclei with greater degrees of chromatin clumping. Smooth endoplasmic reticulum is no longer prominent whereas profiles of rough endoplasmic reticulum are quite common. Occasional lysosomal configurations are found in mature spermatogonia. The majority of spermatogonial cells exhibit weak to moderate reactivity when stained with the periodic acid-Schiff (PAS) reaction. Certain cells in each tubular cross section stain vividly with this reaction and the PAS positivity is removable with salivary amylase. Because of nuclear characteristics, position of the cell immediately upon the basal lamina, intensity of the PAS reaction and the relative paucity of the vividly staining cells, it is suggested that they are members of the immature spermatogonial cell line, perhaps acting as stem cells. None of the several other histochemical procedures employed was capable of selectively demonstrating these cells. 相似文献
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Nina Elisabeth Nagy Vincent R Franceschi Harald Kvaalen Halvor Solheim 《Trees - Structure and Function》2005,19(6):695-703
In field experiments, clones of Norway spruce [Picea abies (L.) Karst.] showed different degrees of resistance against pathogenic fungi inoculated into the bark that correlate with
differences in polyphenolic parenchyma (PP) cells of the bark. Cells of spruce callus cultures, particularly towards the callus
surface, resemble PP cells and this study looks at changes in callus cells during infection and the relative resistance of
cultures from clones of low (weak) or high (strong) resistance to fungal infection. Callus cultures, initiated from trees
with different resistance, were co-inoculated with Ceratocystis polonica (Siem.) C. Moreau and Heterobasidion annosum (Fr.) Bref. Callus cells from strong clones resemble PP cells of bark tissue from strong clones, having more polyphenolic
bodies, while callus cells from weak clones are more similar to PP cells from those clones, which have less extensive phenolic
bodies. Callus cultures from trees with weak resistance were more quickly overgrown by both species of pathogenic fungi than
cultures from trees with strong resistance. Callus cells of infected cultures showed changes similar to activated PP cells
of bark, including enhanced accumulation of polyphenolics. Phenolic bodies were more numerous and more extensive (larger and
denser) in callus cells of strong versus weak clones under all conditions. Thus, callus cells may perform similar functions
in defense as PP cells in the bark. Callus from trees of varying resistance seem to reflect the relative resistance of the
trees from which they are derived, and this study indicates that some mechanisms of resistance can be studied using callus
from trees of different resistance. 相似文献
37.
Biological soil crusts composed of cyanobacteria, green algae, bryophytes, and lichens colonize soils in arid and semiarid
ecosystems worldwide and are responsible for significant N input to the soils of these ecosystems. Soil crusts also colonize
active sand dunes in more humid regions, but studies of structure and function of such sand dune crusts are lacking. We identified
the cyanobacterial, algal, and bryophytic constituents and N production and leachates of biological soil crusts that colonize
beach dunes at the Indiana Dunes National Lakeshore along southern Lake Michigan in Indiana, USA. To determine the role of
these crusts in this system, we conducted a greenhouse experiment in which intact soil cores with biological crusts were subjected
to artificial rainfall over a full growing season. The volume and N content of leachate from the cores were quantified in
relation to degree of crust development, taxonomic composition, rainfall volume and intensity, light intensity, and the presence
of plant litter. Net N throughput significantly exceeded N inputs to cores in rainwater. Net N outputs from crusts to subsurface
soil ranged from 0. 01 to 0.19 g NH
4
+
-N m−2 yr−1 and 0.01 to 0.61 g NO
3
–
N m−2 yr−1. Thus, total inorganic N inputs associated with biological soil crusts ranged from 0.02 g N m−2 yr−1 to 0.8 g N m−2 yr−1. High volume (≥2 cm) rainfall resulted in more N leaching than low volume events, and plant litter added over the surface
of crusted soil cores significantly increased the amount of N in leachate. Exploratory path analysis revealed direct and indirect
linkages among environmental factors, crust development, and crust composition in regulating the throughput of H2O and N from these intact soil cores. Biological soil crusts at this site, combined with other properties of the soil surface,
substantially increase N inputs to this water- and nutrient-limited sand dune ecosystem. 相似文献
38.
Indicators of physiological stress and the elaboration of sexual traits in the collared flycatcher 总被引:2,自引:1,他引:1
Garamszegi Laszlo Zsolt; Merino Santiago; Torok Janos; Eens Marcel; Martinez Javier 《Behavioral ecology》2006,17(3):399-404
Stress may have consequences for the evolution of condition-dependentsexual traits. For example, stress may be related to sexualtraits through immune function, and sexual traits can reflecthow individuals bear the costs of stress-mediated immunosuppression.However, male traits may be directly associated with stress,and such traits would then indicate stress tolerance. Here,we present initial results for the relationship between physiologicalstress estimated by the levels of heat shock proteins (HSP60and HSP70) and heterophil/lymphocyte ratio and the elaborationof sexual traits, such as forehead and wing patch size and songfeatures in the collared flycatcher Ficedula albicollis. Malesproducing longer and more versatile songs had significantlyhigher levels of HSP70, but other traits were unrelated to stress.In general, effect sizes for the relationship between stressand sexual traits had broad confidence intervals and variedbetween being small and medium effects. Immunoglobulin levels,leukocyte abundance, haemoparasite prevalence, male age, anddate and time effects did not affect the relationship betweenstress and sexual traits. These preliminary results, servinga basis for further experimental studies indicate that the relationshipbetween sexual traits and stress does not seem to be strong,but stress may partially constrain the expression of some sexualtraits. 相似文献
39.
Fanni S. Kálmán Beáta Lizák Szilvia K. Nagy Tamás Mészáros Veronika Zámbó József Mandl Miklós Csala Éva Kereszturi 《Biochimie》2013
NADH cytochrome b5 oxidoreductase (Ncb5or) protects β-cells against oxidative stress and lipotoxicity. The predominant phenotype of lean Ncb5or-null mouse is insulin-dependent diabetes due to β-cell death. This suggests the putative role of NCB5OR polymorphism in human diabetes. Therefore, we aimed to investigate the effect of natural missense mutations on the expression of human NCB5OR. Protein and mRNA levels of five non-synonymous coding variants were analyzed in transfected HEK293 and HepG2 cells. Although the mRNA levels were only slightly affected by the mutations, the amount of Ncb5or protein was largely reduced upon two Glu to Gly replacements in the third exon (p.E87G, p.E93G). These two mutations remarkably and synergistically shortened the half-life of Ncb5or and their effect could be attenuated by proteasome inhibitors. Our results strongly indicate that p.E87G, p.E93G mutations lead to enhanced proteasomal degradation due to manifest conformational alterations in the b5 domain. These data provide first evidence for natural mutations in NCB5OR gene resulting in decreased protein levels and hence having potential implications in human pathology. 相似文献
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