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21.
Metabolism of nitric oxide and nitrous oxide during nitrification and denitrification in soil at different incubation conditions 总被引:1,自引:0,他引:1
Abstract NO production and consumption rates as well as N2 O accumulation rates were measured in a loamy cambisol which was incubated under different conditions (i.e. soil moisture content, addition of nitrogen fertilizer and/or glucose, aerobic or anaerobic gas phase). Inhibition of nitrification with acetylene allowed us to distinguish between nitrification and denitrification as sources of NO and N2 O. Under aerobic conditions untreated soil showed very low release of NO and N2 O but high consumption of NO. Fertilization with NH4 + or urea stimulated both NO and N2 O production by nitrification. Addition of glucose at high soil moisture contents led to increased N2 and N2 O production by denitrification, but not to increased NO production rates. Anaerobic conditions, however, stimulated both NO and N2 O production by denitrification. The production of NO and N2 O was further stimulated at low moisture contents and after addition of glucose or NO3 − . Anaerobic consumption of NO by denitrification followed Michaelis-Menten kinetics and was stimulated by addition of glucose and NO3 − . Aerobic consumption of NO followed first-order kinetics up to mixing ratios of at least 14 ppmv NO, was inhibited by autoclaving but not by acetylene, and decreased with increasing soil moisture content. The high NO-consumption activity and the effects of soil moisture on the apparent rates of anaerobic and aerobic production and consumption of NO suggest that diffusional constraints have an important influence on the release of NO, and may be a reason for the different behaviour of NO release vs N2 O release. 相似文献
22.
The ability of two enantiomeric fluoro-analogues of D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] to mobilize intracellular Ca2+ stores in SH-SY5Y neuroblastoma cells has been investigated. (-)-D-2,2-difluoro-2-deoxy-myo-Ins(1,4,5)P3 [D-2,2-F2-Ins(1,4,5)P3] was a full agonist [EC50 0.21 microM] and slightly less potent than D-Ins(1,4,5)P3 [EC50 0.13 microM]. (+)-L-2,2-F2Ins(1,4,5)P3 was a very poor agonist, confirming the stereospecificity of the Ins(1,4,5)P3 receptor. D-2,2-F2-Ins(1,4,5)P3 mobilized Ca2+ with broadly similar kinetics to Ins(1,4,5)P3 and was a substrate for Ins(1,4,5)P3 3-kinase inhibiting Ins(1,4,5)P3 phosphorylation (apparent Ki = 10.2 microM) but was recognised less well than Ins(1,4,5)P3. L-2,2-F2-Ins(1,4,5)P3 was a potent competitive inhibitor of 3-kinase (Ki = 11.9 microM). Whereas D-2,2-F2-Ins(1,4,5)P3 was a good substrate for Ins(1,4,5)P3 5-phosphatase, L-2,2-F2Ins(1,4,5)P3 was a relatively potent inhibitor (Ki = 19.0 microM). 相似文献
23.
V. Frankard M. Ghislain I. Negrutiu M. Jacobs 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1991,82(3):273-282
Summary Mutagenesis and the subsequent selection of mesophyll diploid protoplasts ofNicotiana sylvestris on growth inhibitory concentrations of lysine plus threonine has led to the isolation of an LT-resistant mutant. Regeneration of this line (RLT 70) and analysis of its descendants demonstrated the dominant monogenic nuclear character of the resistance gene, further namedak-LT1. When the inhibition properties of aspartate kinase were examined in the homozygous mutant, lysine-sensitive activity could no longer be detected. In comparison, 70%–80% of the wild-type enzyme activity was usually inhibited by lysine, and the rest by threonine. Evidence for the existence of at least two AK isoenzymes was obtained by ion-exchange chromatography, where two peaks of activity could be detected: the first one to be eluted is lysine sensitive, and the second one threonine sensitive. One consequence of the altered regulation of AK in the mutant was the enhanced production of soluble threonine. Threonine accumulation was observed to occur throughout the life cycle of the mutant plant as well as in its different organs. In particular, leaves exhibited a 45-fold increment of soluble threonine, which corresponds to a 13-fold increase in total threonine: almost one-third of the total amino acids was free and proteinbound threonine. In RLT 70 seeds, 20% of the free amino acid pool was in the form of threonine (70-fold accumulation compared to the wild type), and total threonine content was increased five fold. As a general rule, the other amino acids were also more abundant in RLT 70 seeds, such that the total of amino acids present was between two to four times higher, but in contrast with the situation encountered in leaves, this was also due to a higher protein-bound amino acid content. 相似文献
24.
Four new strains of Thiopedia rosea were isolated in pure culture from blooms of platelet-forming purple sulfur bacteria in the top layers of the anoxic hypolimnia of two freshwater lakes. Individual cells of the new strains as well as of T. rosea strain 4211 were spherical to oval, nonmotile and contained gas vesicles in the central part. The predominant photosynthetic pigments were bacteriochlorophyll a and okenone. All strains were strictly anaerobic and obligately phototrophic. Optimal growth occurred at low light intensities of 100 E · m-2 s-1 (tungsten lamp); intensities above 150 E · m-2 s-1 inhibited growth completely. Photoautotrophic growth was possible at sulfide concentrations up to 0.6 mM; higher concentrations were inhibitory. Acetate, butyrate and valerate supported photoorganotrophic growth in the presence of bicarbonate and sulfide concentrations below 1 mM. Sulfide was required as a source of cellular sulfur because assimilatory sulfate reduction is lacking. All strains were assigned to the species Thiopedia rosea with strain 4211 as a neotype.Dedicated to Prof. Dr. H. G. Schlegel on the occasion of his 66th birthday 相似文献
25.
Cindy Pfeiffer-Linn Raymon M. Glantz 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1991,168(3):373-381
1. | The actions of GABA on three classes of visual interneurons in crayfish, Procambarus clarkii, medulla externa are examined. The effect of GABA on the visual response is compared to GABA's action on agonist-elicited responses purported to mediate the visual response. |
2. | GABA produces a shunting type of inhibition in medullary amacrine cells which is associated with a small depolarization (Figs. 2, 3), a large increase in input conductance (Gn) and a reversal potential close to rest (Fig. 4). GABA is a potent antagonist to the depolarizing action of acetylcholine (ACh) (Fig. 5). |
3. | GABA depolarizes dimming fibers (Fig. 2), and the response is mediated by an increase in Gn (Fig. 6). GABA antagonizes the light-elicited IPSP and the hyperpolarizing action of ACh (Fig. 7). |
4. | Sustaining fibers (SF) do not appear to have GABA receptors but GABA inhibits the excitatory visual input pathway to the SFs (Fig. 8). Conversely, the GABA antagonist, bicuculline, potentiates the SF light response (Fig. 9). |
5. | GABA has at least three different modes of antagonist action in the medulla: i) Increased conductance and depolarization in dimming fibers and medullary amacrine neurons; ii) Decreased chloride conductance in tangential cells; and iii) An inhibitory action on the visual pathway which drives SFs. |
26.
Acetylene inhibition technique underestimates in situ denitrification rates in intact cores of freshwater sediment 总被引:5,自引:0,他引:5
Abstract Denitrification in intact sediment cores was measured by the acetylene inhibition technique and compared with the nitrate flux between water and sediment. Less than half of the nitrate-N consumed by the sediment could be recovered as nitrous oxide-N. The low recovery rate of nitrous oxide from intact sediment cores indicated losses of nitrous oxide by diffusion down to nitrate-free sediment layers, where reduction of nitrous oxide may take place. In sediment slurries 100% of nitrate-N could be recovered as nitrous oxide-N as long as the nitrate concentration in the liquid phase was above 10 μM. Nitrous oxide added to nitrate-free sediment slurries was reduced regardless of whether acetylene was present or not. Therefore denitrification may be significantly underestimated by this method. 相似文献
27.
The in vivo amounts of UDPG, UTP, UDP and UMP, metabolites known to influence the activity of sucrose phosphate synthase (SPS) and sucrose synthase (SS), were measured throughout 5 hr incubations of scutellum slices in fructose or water, i.e. under conditions of sucrose synthesis or breakdown. Cytosolic concentrations were estimated assuming that these metabolites were confined to the cytosol. Within the estimated in vivo concentration ranges, UDPG, UTP and UDP had little effect on the in vitro SS activity, but glucose (100 mM) inhibited SS in the synthesis direction by 63–70% and in the breakdown direction by 86–93%. Glucose inhibition of SS was considerably less when saturating levels of substrates were used. Sucrose did not inhibit SS. It is concluded that during germination the glucose produced from starch breakdown in the maize endosperm enters the scutellum and inhibits SS, preventing a futile cycle and limiting SS participation in sucrose synthesis. 相似文献
28.
Adventitious buds on embryos of Picea abies (L.) Karst. developed after a pulse treatment with 250 μ M benzyladenine (BA) of pH 5.5 for 2 h. Light and temperature regimes were not critical during the initial stages. Adventitious buds developed faster after a pulse treatment and the variation among different experiments was lower compared to when the embryos were cultured on media supplemented with BA. Various stages of the differentiation of adventitious buds were identified: stage 1 - appearance of meristematic centres (approximately the first two weeks); stage 2 - development of adventitious bud primordia (approximately the third week); stage 3 - adventitious bud development (from approximately the 4th to the 8th week). This system may be used for further studies on bud differentiation. 相似文献
29.
Bernhard Knig Patricia A. DiNitto Peter M. Blumberg 《Journal of cellular biochemistry》1985,29(1):37-44
The major phorbol ester receptor is the Ca++-activated, phospholipid-dependent protein kinase C. Diacylglycerol stimulates protein kinase C in a fashion similar to the phorbol esters. Likewise, it inhibits phorbol ester binding competitively. Both results suggest that diacylglycerol is the/an endogenous phorbol ester analogue. Alternatively, the diacylglycerol might simply be acting to modify the phospholipid environment of the protein. If diacylglycerol were indeed functioning as an analogue, it should interact with the receptor stoichiometrically. This interaction can be quantitated by measuring the perturbation in apparent diacylglycerol binding affinity as a function of the ratio of diacylglycerol to receptor. We report here that 1,2-dioleoylglycerol interacts with the receptor with the predicted stoichiometry. 相似文献
30.
In the caterpillar Trichoplusia ni (Lepidoptera: Noctuidae) it has been demonstrated by allatectomy that the appearance of juvenile hormone during the prepupal stage is crucial for the successful larval-pupal ecdysis of most larvae. Application of juvenile hormone or juvenile hormone esterase inhibitors at key times disrupted normal development as well. Thus the subsequent disappearance of juvenile hormone is regulated by degradation by juvenile hormone esterase in addition to a hypothetical reduction in biosynthesis. This reduction in juvenile hormone titer in the prepupa is just as critical for normal development as was its previous appearance. These observations on the critical role of juvenile hormone in the prepupa are in contrast to observations in some other species. For instance, in the case of Manduca sexta (Lepidoptera: Sphingidae), juvenile hormone is considered only supplementary to the action of prothoracicotropic hormone in the postwandering stage and primarily is required for normal pupal development. It thus appears that even within the Lepidoptera the role of juvenile hormone in prepupal development can vary dramatically. 相似文献