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121.
Molecular chaperones recognize and bind destabilized proteins. This can be especially important for proteins whose stability
is reduced by mutations. We focused our study on a major chaperone system, RAC-Ssb, which assists folding of newly synthesized
polypeptides in the yeast cytosol. A sensitive phenotypic assay, the red color of Ade2 mutants, was used to screen for variants
with metabolic activity dependent on RAC-Ssb. None of the Ade2 mutants were found to exhibit lower metabolic activity after
inactivation of RAC-Ssb. In order to explicitly test the relationship between protein instability and activity of chaperones,
a series of temperature sensitive Ade2 mutants were tested in the presence or absence of RAC-Ssb. The growth of Ade2(ts) mutants
at elevated temperatures was enhanced if chaperones were missing. Similar pattern was found for thermally sensitive mutants
of several other genes. Because RAC-Ssb normally supports the folding of proteins, it appears paradoxical that catabolic activity
of mutants is reduced when these chaperones are present. We suggest that under non-stressful conditions, molecular chaperones
are tuned to support folding of native proteins, but not that of mutated ones. 相似文献
122.
Luciano S. Pinto Celso S. Nagano Taianá M. Oliveira Tales R. Moura Alexandre H. Sampaio Henri Debray Vicente P. Pinto Odir A. Dellagostin Benildo S. Cavada 《Journal of biosciences》2008,33(3):355-363
A new galactose-specific lectin was purified from seeds of a Caesalpinoideae plant, Bauhinia variegata, by affinity chromatography on lactose-agarose. Protein extracts haemagglutinated rabbit and human erythrocytes (native and
treated with proteolytic enzymes), showing preference for rabbit blood treated with papain and trypsin. Among various carbohydrates
tested, the lectin was best inhibited by D-galactose and its derivatives, especially lactose. SDS-PAGE showed that the lectin,
named BVL, has a pattern similar to other lectins isolated from the same genus, Bauhinia purpurea agglutinin (BPA). The molecular mass of BVL subunit is 32 871 Da, determined by MALDI-TOF spectrometry. DNA extracted from
B. variegata young leaves and primers designed according to the B. purpurea lectin were used to generate specific fragments which were cloned and sequenced, revealing two distinct isoforms. The bvl gene sequence comprised an open reading frame of 876 base pairs which encodes a protein of 291 amino acids. The protein carried
a putative signal peptide. The mature protein was predicted to have 263 amino acid residues and 28 963 Da in size. 相似文献
123.
Hyuk-Sung Kwon Eunyong Chung Junse Oh Chang-Ha Lee Ik-Sung Ahn 《Biotechnology and Bioprocess Engineering》2008,13(1):108-114
Manganese peroxidase (MnP) is a key enzyme involved in the lignolysis of white-rot fungi. The purpose of this study is to
investigate the effect of immobilization and culture conditions on MnP production in cultures of Phanerochaete chrysosporium grown on polyurethane foam. Higher concentrations of foam and lower levels of spore inoculums resulted in the formation of
scattered mycelial pellets, increased autolysis of chlamydospore-like cells (a reservoir of MnP), and a higher activity of
MnP. Even though MnP was a secondary metabolite, the addition of 5 times more glucose and diammonium tartrate, as carbon and
nitrogen sources, resulted in a 4 fold increase in the dry cell mass. However, MnP activity decreased under these conditions
to less than half, due to the formation of increasingly dense pellets and the inhibited lysis of chlamydospore-like cells. 相似文献
124.
The reserve mobilization was analysed in germinating seeds of faba bean (Vicia faba) exposed to treatment with a toxic cadmium concentration for 4 days. When the behaviours of three cultivars were compared with regard to the germination rate, the following order of sensitivity to cadmium was observed: Aguadulce and Luz de otoño showed 59 and 19% of inhibition from controls, respectively, while no effect was observed in the case of the local Féverole. The growth of embryo radicle was also affected in the same pattern. The differential vulnerability to Cd stress cannot be correlated to shortage in water supply of cotyledons. However, Cd-treated germinating seeds of the most sensitive cultivar (Aguadulce) showed restriction in starch mobilization and decrease in availability of soluble sugars and free amino acids. Moreover, glucose, fructose and amino acids were markedly leaked into the germination medium at the expense of the growing embryonic axis during exposure to Cd. These results provide an indication of the way in which cadmium might impair seed germination. 相似文献
125.
The effect of water deficit on chlorophyll fluorescence, sugar content, and growth parameters of strawberry (Fragaria×ananassa Duch. cv. Elsanta) was studied. Drought stress caused significant reductions in leaf water potential, fresh and dry masses,
leaf area, and leaf number. A gradual reduction of photochemical quenching (qP) and quantum efficiency (ΦPS2) was observed under drought stress while non-photochemical quenching (qN) increased. Maximum efficiency of photosystem 2 (Fv/Fm) was not affected by drought stress. 相似文献
126.
Daniel E. Atha 《Brittonia》2008,60(2):185-189
Acalypha gentlei is described, illustrated and mapped. The species is endemic to Belize and adjacent areas of Mexico and Guatemala and restricted
to semi-deciduous moist forests on limestone. The species is referred to Acalypha subgenus Linostachys.
Resumen Se describe, ilustra y grafica la distribución de Acalypha gentlei. Esta especie nueva es endémica a Belice y áreas adyacentes de México y Guatemala, y está restringida a bosques húmedos semi-deciduos sobre caliza. La especie es referida a Acalypha subgénero Linostachys.相似文献
127.
Many invasive alien plants occur in large populations with abundant flowers which are highly attractive to pollinators, and
thus might affect pollination of co-occurring native species. This study focuses on the invasive Heracleum mantegazzianum and distance-dependent effects on pollination of Mimulus guttatus in abandoned grassland over 2 years. First, we examined pollinator abundance in yellow traps at 0, 10, 30 and 60–200 m from
H. mantegazzianum. We then placed M. guttatus plants at the same distances to monitor effects of the invasive species on pollinator visitation and seed set of neighbouring
plants. Finally, we conducted a garden experiment to test if deposition of H. mantegazzianum pollen reduces seed set in M. guttatus. No distance effect was found for the number of bumblebees in traps, although the invasive species attracted a diverse assemblage
of insects, and visitation of M. guttatus was enhanced close to H. mantegazzianum. This positive effect was not reflected by seed set of M. guttatus, and heterospecific pollen decreased seed set in these plants. Overall there is little evidence for negative effects of the
invasive species on pollination of neighbouring plants, and flower visitation even increases close to the invaded patches.
The functional role of the invader and suitable control strategies need further clarification, since removal of H. mantegazzianum may actually damage local pollinator populations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
128.
The Influence of Landscape Position and Catchment Characteristics on Aquatic Biogeochemistry in High-Elevation Lake-Chains 总被引:2,自引:0,他引:2
To examine the influence of landscape characteristics and landscape position on aquatic biogeochemistry, we sampled a total
of 76 lakes within 14 different lake-chains spanning the latitudinal extent of the high-elevation Sierra Nevada (California).
We measured water chemistry, dissolved organic matter (DOM), nutrients, and biotic variables in study catchments that encompassed
representative ranges of area (3–22 km2), elevation (2,200–3,700 m.a.s.l), elevation change (50–700 m), and average slope (13°–26°). Hierarchical models were used
to account for variability in biogeochemistry because they explicitly maintain the framework of lakes within individual lake-chains
while accounting for variation among lake-chains. Unconditional means models, where lake-chain was a random effect, revealed
significant differences among lake-chains for nearly all biogeochemical variables. Models explained 42–95% of this variability,
with the majority of the variation (70%) explained by the among lake-chain component. To explore the amount of additional
variation explained by lake landscape position, we added lake network number (LNN) to models. LNN explained a significant
amount of additional variation (7% average) in 8 of 23 biogeochemical parameters. However, it explained more variability within
individual lake-chains (75%), where among lake-chain differences did not obscure patterns. Patterns of increase with LNN were
found for dissolved organic carbon and nitrogen, fluorescence of DOM, alkalinity, and bacterioplankton abundance, whereas
nitrate and nitrogen to phosphorus nutrient ratios decreased. LNN explained variation because it served as a proxy for underlying
catchment characteristics that changed consistently along downstream flow paths. To characterize the amount of variation explained
by catchment characteristics alone, we fit a third model that included lake-chain as a random effect and landscape or lake
morphometry attributes as fixed effects. Catchment characteristics explained about as much additional variation (6%) as LNN,
but for substantially more biogeochemical parameters (18 out of 23). The catchment characteristics most predictive of biogeochemistry
were land-cover factors delineating alpine and subalpine zones (elevation, slope, or proportions of rock or shrub cover).
In general, catchment characteristics were stronger predictors of biogeochemistry than characteristics of lake morphometry,
emphasizing the relative importance of landscape processes in snowmelt-dominated lake ecosystems. 相似文献
129.
Since the late 1960s, researchers have observed that starch in the chloroplasts of the guard cells breaks down during the
day and accumulates in the dark. Based on this, carbohydrates have historically been regarded as the primary osmotica modulating
stomatal opening. However, the discovery of an important role for potassium uptake has led to the replacement of that starch-sugar
hypothesis. Current research now focuses mainly on how K+ is transported in and out of cells when the stomata open or close. However, questions remain concerning photoreceptors, and
the functioning of guard cell chloroplasts is still disputed. Coincidentally, some recent study results have again suggested
that sucrose may play a major role in guard cell osmoregulation, thus supporting the original theory of starch-sugar involvement. 相似文献
130.
Luciana Dini 《Apoptosis : an international journal on programmed cell death》2010,15(9):1147-1164
It is becoming evident that failure in the removal of dying cells causes and/or promotes the onset of chronic diseases. Impairment
of phagocytosis of apoptotic cells can be due not only to genetic or molecular malfunctioning but also to external/environmental
factors. Two of these environmental factors have been recently reported to down regulate the clearance of apoptotic cells:
cigarette smoke and static magnetic fields. Cigarette smoke contains highly reactive carbonyls that modify proteins which
directly/indirectly affects cellular function. Human macrophages interacting with carbonyl or cigarette smoke modified extracellular
matrix (ECM) proteins dramatically down regulated their ability to phagocytose apoptotic neutrophils. It was postulated that
changes in the ECM environment as a result of cigarette smoke affect the ability of macrophages to remove apoptotic cells.
This decreased phagocytic activity was as a result of sequestration of receptors involved in the uptake of apoptotic cells
towards that of recognition of carbonyl adducts on the modified ECM proteins leading to increased macrophage adhesion. Downregulation
of the phagocytosis of apoptotic cells was also described when performed in presence of static magnetic fields (SMFs) of moderate
intensity. SMFs have been reported to perturb distribution of membrane proteins and glycoproteins, receptors, cytoskeleton
and trans-membrane fluxes of different ions, especially calcium [Ca2+]i, that in turn, interfere with many different physiological activities, including phagocytosis. The effects of cigarette
smoke and SMF on the phagocytosis of dying cells will be here discussed. 相似文献