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991.
Nitrogen budgets for the Republic of Korea and the Yellow Sea region 总被引:10,自引:2,他引:10
Growing populations in northeast Asia have greatly altered the nitrogencycle, with increases in agricultural production to feed the population, andwith increases in N emissions and transboundary air pollution. For example,during the 1900's over 50% of the N deposition over Republic of Korea wasimported from abroad. In this paper, we present biogeochemical budgets ofN for the South Korean peninsula (the Republic of Korea) and for the YellowSea region. We quantify N inputs from atmospheric deposition, fertilizers,biological fixation, and imports of food, feed, and products. We quantifyoutputs in riverine export, crop uptake, denitrification, volatilization,runoff, sedimentation and sea water exchange. Calculations were conductedusing mean values from 1994–1997. All of the nitrogen budgets werepositive, with N inputs exceeding outputs. The excess N inputs gave rise toincreases in N storage in landfills and in groundwater. Annual accumulationof N in the Yellow sea, including inputs from South Korea and otherdrainage areas, was 1229 kt yr–1 with a residence time for N ofapproximately 1.5 years, thus doubling N content in marine waters every 3years during 1994–1997. The human derived N inputs leads to excessiveeutrophication and pollution of the Yellow Sea. 相似文献
992.
A new isolate of Salmonella, strain MR4, reduced Mn(IV)O2 at 2.3 mM under aerobic conditions by about 83% over 24 h. Direct contact of cells to MnO2 was not necessary as the cell-free spent medium produced a similar amount of Mn(II). Pyruvate (1.6 mM) and oxalate (0.8 mM) were identified in the culture medium and presumed to have a role in Mn(II) production in this microorganism. 相似文献
993.
Dragoi V 《Biological cybernetics》2002,86(6):419-426
Simple exposure to repeatitive stimulation is known to induce short-term learning effects across a wide range of species.
These effects can be both suppressive and facilitatory depending on stimulus conditions: repeatitive presentation of a weak
stimulus decreases the strength of the response (habituation), whereas presentation of a tonic stimulus following a series
of weak stimuli transiently increases the response strength (dishabituation). Although these phenomena have been comprehensively
characterized at both behavioral and cellular levels, most existing models of nonassociative learning focus exclusively on
the suppressive or facilitatory changes in response, and do not attempt to relate cellular events to behavior. I propose here
a feedforward model of habituation effects that explains both suppressive and facilitatory changes in response relying on
the interaction between excitatory and inhibitory processes that develop in parallel on two different timescales. The model's
properties are used to explain the rate sensitivity property of habituation and recovery and stimulus dishabituation.
Received: 1 June 2001 / Accepted in revised form: 4 December 2001 相似文献
994.
995.
996.
Based on NMR spectroscopic information about the allosamidin-hevamine complex, ab initio MO calculations of the ring current effect of the aromatic moieties of Trp255, Tyr183 and Tyr6 of hevamine were carried out to investigate the role of these amino acid residues in binding interactions with allosamidin in solution. In addition, the intermolecular steric compression effect on the 13C chemical shifts of the allosamizoline carbon atoms and the hydrogen bonding to Glu127 was identified. It can be inferred that the binding forces are strongest in the allosamizoline moiety of allosamidin. 相似文献
997.
High rates of deforestation in the Brazilian Amazon have the potential to alter the storage and cycling of carbon (C) and nitrogen (N) across this region. To investigate the impacts of deforestation, we quantified total aboveground biomass (TAGB), aboveground and soil pools of C and N, and soil N availability along a land-use gradient in Rondônia, Brazil, that included standing primary forest, slashed primary and secondary forest, shifting cultivation, and pasture sites. TAGB decreased substantially with increasing land use, ranging from 311 and 399 Mg ha–1 (primary forests) to 63 Mg ha–1 (pasture). Aboveground C and N pools declined in patterns and magnitudes similar to those of TAGB. Unlike aboveground pools, soil C and N concentrations and pools did not show consistent declines in response to land use. Instead, C and N concentrations were strongly related to percent clay content of soils. Concentrations of NO3-N and NH4-N generally increased in soils following slash-and-burn events along the land-use gradient and decreased with increasing land use. Increasing land use resulted in marked declines in NO3-N pools relative to NH4-N pools. Rates of net nitrification and N-mineralization were also generally higher in postfire treatments relative to prefire treatments along the land-use gradient and declined with increasing land use. Results demonstrate the linked responses of aboveground C and N pools and soil N availability to land use in the Brazilian Amazon; steady reductions in aboveground pools along the land-use gradient were accompanied by declines in inorganic soil N pools and transformation rates. 相似文献
998.
Alexander P. Gultyaev F.H.D. van Batenburg Cornelis W.A. Pleij 《Journal of molecular evolution》2002,54(1):1-8
Comparison of the most stable potential hairpins in the sequences of natural ribozymes with those in the randomized sequences
has revealed that the hairpin loop energies are lower than expected by chance. Although these hairpins are not necessarily
parts of functional structures, there is a selective pressure to diminish the destabilizing free energies of the hairpin loops.
In contrast, no significant bias is observed in the stacking values of the most stable stems. In the ribozymes isolated in
vitro the loops of potential hairpins are closer to random values, which can result in less efficient folding rates. Furthermore,
the effects of kinetic traps seem to be more significant in the folding pathways of the in vitro isolates due to a potential
to form stable stacks incompatible with the functional folds. Similarly to natural ribozyme sequences, the untranslated regions
of viral RNAs also form hairpins with relatively low loop free energies. These evolutionary trends suggest ways for efficient
engineering of improved RNA constructs on the basis of analysis of in vitro isolates and approaches for the search of regions
coding for functional RNA structures in large genome sequences.
Received: 12 January 2001 / Accepted: 21 May 2001 相似文献
999.
Bertuzzi A Faretta M Gandolfi A Sinisgalli C Starace G Valoti G Ubezio P 《Bulletin of mathematical biology》2002,64(2):355-384
In the present paper we propose a method of analysis of the cell kinetic characteristics of in vivo experimental tumours, that uses DNA-BrdUrd flow cytometry data at various times after the bromodeoxyuridine (BrdUrd) injection
and mathematical modelling. The model of the cell population takes into account the cell-cell heterogeneity of the progression
rate across cell cycle phases within the tumour, and assumes a strict correlation between the durations of S and G2M phases.
The model also allows for a nonconstant DNA synthesis rate across S phase. In addition, the measurement process is modelled,
considering the possibility of nonimpulsive labelling and providing a representation of the time course of the bivariate DNA-BrdUrd
fluorescence distribution. Sequential DNA-BrdUrd distributions were obtained in vivo from a human ovarian carcinoma transplanted in mice and, for comparison, in vitro from a cell line of the same origin. From these data, that included the fractional density and the mean BrdUrd-fluorescence
of BrdUrd-positive cells as a function of the DNA-fluorescence, kinetic parameters such as the potential doubling time (T
pot) and the mean and variance of the transit times in S and G2M phases, were estimated. This study revealed the presence of
a substantial heterogeneity in S and G2M phases within the in vivo cell population and of a lower heterogeneity in the in vitro population. Moreover, our analysis suggests a nonnegligible effect of the BrdUrd pharmacokinetics in the in vivo cell labelling. 相似文献
1000.
Anderlid BM Schoumans J Annerén G Tapia-Paez I Dumanski J Blennow E Nordenskjöld M 《Human genetics》2002,110(5):439-443
Both cytogenetically visible and cryptic deletions of the terminal region of chromosome 22q are associated with a clinical phenotype including mental retardation, delay in expressive speech development, hypotonia, normal to accelerated growth and minor facial dysmorphic features. The genes responsible for the development of the phenotype have not yet been identified, but a distal localization is probable, since the cytogenetically visible and the cryptic deletions show a similar pattern of symptoms. We report a 33-year-old woman with a submicroscopic 22q13 deletion, mild mental retardation, speech delay, autistic symptoms and mild facial dysmorphic features. The deletion was mapped by FISH using cosmid probes from terminal 22q13, and the size of the deletion was estimated to be 100 kb. Three genes are affected by the deletion in this patient. ACR and RABL2B are deleted and proSAP2 is disrupted. This observation, together with recently published data, supports the notion that proSAP2 is the most important contributor to the 22q13 deletion phenotype. 相似文献