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101.
Effect of ethylene on the gibberellic Acid-enhanced synthesis and release of amylase by isolated barley aleurone layers 总被引:7,自引:7,他引:0 下载免费PDF全文
Methods were developed and extended to enable the incubation of isolated barley (Hordeum vulgare cv. Himalaya) aleurone layers under carefully controlled conditions for studies on effects of ethylene on amylase synthesis and release. When layers in medium containing gibberellic acid were exposed to ethylene, the synthesis and release of amylase were altered relative to layers maintained in an ethylene-free environment. These ethylene effects were detected at the smallest concentration used, 0.041 nl/ml, indicating a very low threshold value. During the initial 24 h, ethylene accelerated both the appearance of total amylase activity, and the release of this activity from the aleurone layers. On the other hand, ethylene reduced the total amount of amylase activity that was recovered from samples after 48 and 72 h. 相似文献
102.
The relationship between the temperature at which germination of 50% of the seeds is inhibited in the light (GT50 Light) and secondary dormancy was investigated in three cultivars of Lactuca sativa L. Seeds were incubated for varying periods under non-germinating conditions and subsequent germination in response to red light (R) was determined over a wide range of temperatures. Dark incubation at 32 C reduced the GT50 Light of cv. New York but did not affect germination at temperatures below 24 C. Dark, 32 C incubation had no effect on the GT50 Light of cv. Great Lakes. In cv. Grand Rapids, dark incubation at 15, 24, 32, or 35 C initially reduced the GT50 Light. However, longer incubations induced a secondary dormancy, i.e., the seeds became unable to germinate at all temperatures in response to R given after the high temperature incubation. A single exposure to R at the beginning of a 32 C incubation slowed the induction of secondary dormancy. Repeated exposures to R prevented the induction of secondary dormancy, but did not prevent a decline in the GT50 Light. GA3 mimicked the effect of repeated R. 相似文献
103.
ATPase Activity of Pea Cotyledon Submitochondrial Particles: ACTIVATION, SUBSTRATE SPECIFICITY, AND ANION EFFECTS 总被引:30,自引:22,他引:8 下载免费PDF全文
Submitochondrial particles freshly prepared by sonication from pea cotyledon mitochondria showed low ATPase activity. Activity increased 20-fold on exposure to trypsin. The pea cotyledon submitochondrial particle ATPase was also activated by “aging” in vitro. At pH 7.0 addition of 1 millimolar ATP prevented the activation. ATPase of freshly prepared pea cotyledon submitochondrial particles had a substrate specificity similar to that of the soluble ATPase from pea cotyledon mitochondria, with GTPase > ATPase. “Aged” or trypsin-treated particles showed equal activity with the two substrates. NaCl and NaHCO3, which stimulate the ATPase but not the GTPase activity of the soluble pea enzyme, were stimulatory to both the ATPase and GTPase activities of freshly prepared submitochondrial particles. However, they were stimulatory only to the ATPase activity of trypsin-treated or “aged” submitochondrial particles. In contrast, the ATPase activity of rat liver submitochondrial particles was stimulated by HCO3−, but inhibited by Cl−, indicating that Cl− stimulation is a distinguishing property of the pea mitochondrial ATPase complex. 相似文献
104.
There are nine “giant vertical” neurons in the lobula plate of the fly optic lobe. Intracellular recordings were obtained from the three most peripheral of these cells. These cells respond to a light flash with graded changes in the membrane potential. The response consists of an “on” transient, a sustained depolarization, an increase in membrane potential fluctuations, and an “off” transient. Signal averaging showed that only the “on” and “off” transients are correlated to the stimulus. A pattern of horizontally oriented stripes moving in the vertical direction evokes a response larger than the response to a stationary pattern. The response is most sensitive to vertical movement; motion in the downward direction evokes a net membrane potential depolarization, and upward motion results in a net hyperpolarization. We conclude that the giant vertical cells function primarily as vertical motion detectors and that the direction of the motion is encoded in the polarity of the shift in the membrane potential. 相似文献
105.
Origin of hydrogen in methane produced by Methanobacterium thermoautotrophicum. 总被引:6,自引:1,他引:5 下载免费PDF全文
The production of deuterated methane by Methanobacterium thermoautotrophicum in H2O-D2O mixtures was examined by high-resolution mass spectrometry. The hydrogen in the methane arose solely from water and not from hydrogen gas. Hydrogen gas served only as an electron source in methanogenesis. A whole-cell product isotope discrimination of 1.5 favoring hydrogen over deuterium was observed in methane production in 81 atom% deuterated water. The distribution of deuterated methane species is described by a simple model of the overall reaction. 相似文献
106.
1. Qualitative studies on the stability of rabbit erythrocyte purine nucleoside phosphorylase showed a marked decrease in the susceptibility of the enzyme to thermal inactivation and digestion by proteinases of different specificities in response to certain of its substrates. 2. The extent to which inosine stabilizes the enzyme against thermal and proteolytic inactivation is related in a quantitative manner to the concentration of this substrate; it is proposed that differences in the rates of inactivation of the enzyme may reflect substrate-induced conformational changes in the enzyme structure that could alter the binding properties of the enzyme in a kinetically significant way. 3. A synergistic effect in the stabilization of the enzyme is observed in response to both substrates, inosine and phosphate, when the enzyme is inactivated with Pronase. 4. In the presence of substrate an increased rate of inactivation after reaction with 5,5'-dithiobis-(2-nitrobenzoic acid) is reported. 5. Differential-inactivation studies were also carried out with calf spleen purine nucleoside phosphorylase, and the results are discussed in relation to the kinetic properties displayed by this enzyme. 相似文献
107.
C Walsh J Fisher R Spencer D W Graham W T Ashton J E Brown R D Brown E F Rogers 《Biochemistry》1978,17(10):1942-1951
The chemical and enzymatic properties of 26 analogues of riboflavin are presented. These analogues include both endo- and exocyclically substituted isoalloxazines with redox potentials from -370 to -128 mV. Physical and chemical data such as the electronic absorption spectra, pKas, and redox potentials of the analogues are presented and are discussed with respect to preferred tautomeric and resonance forms. Like riboflavin, most of the analogues are shown to be catalytic oxidants of dihydro-5-deazaflavins. Analogue binding to egg white binding apoprotein has been quantitated and serves to determine the origins of binding site specificity for this protein. Nearly all of the analogues that possess D-ribityl groups are found to be processed to the FAD level by the flavokinase/FAD synthetase system of Brevibacterium ammoniagenes. Most extensively studied are the reactivities of the analogues with the NAD(P)H:flavin oxidoreductase of Beneckea harveyi. Many of the analogues are substrates in this enzymatic redox reaction, and a linear free energy-rate relation (log Vmax vs. E0' of the analogue) is seen that parallels similar relationships in the nonenzymatic oxidation of dihydro-5-deazaflavins. This suggests a common mechanism for the reactions of such diverse flavins as riboflavin, 5-deazariboflavin, and 1-deazariboflavin. 相似文献
108.
Lymphoma induced by herpesvirus: Resistance associated with a major histocompatibility gene 总被引:1,自引:1,他引:0
B. M. Longenecker F. Pazderka J. S. Gavora J. L. Spencer R. F. Ruth 《Immunogenetics》1976,3(1):401-407
Studies with crosses of inbred chicken lines demonstrate that resistance to Marek's disease, a herpesvirus-induced lymphoma of chickens, is associated with an allele (B
21) of the major histocompatibility locus (theB locus). TheB
21 allele is thus the first genetic marker for resistance to herpesvirus-induced neoplastic disease, and our studies suggest the means whereby similar associations might be found in man. 相似文献
109.
J Jesty A K Spencer Y Nakashima Y Nemerson W Konigsberg 《The Journal of biological chemistry》1975,250(12):4497-4504
Bovine Factor X can be activated by two alternative pathways. The first, favored at high concentrations of the complex of tissue factor and Factor VII, is initiated by the action of Factor VII on Factor X to cleave an activation peptide from the NH2 terminus of the heavy chain, to produce alpha-Xa. This is then converted autocatalytically to another form of Factor Xa, beta-Xa, by the loss of a 17-residue glycopeptide from the COOH terminus of the heavy chain, in a lipid-dependent reaction. The alternative pathway, favored at lower activator concentrations, is initiated by the action of Factor Xa on Factor X, in the presence of lipid, to release the same COOH-terminal peptide as is produced in the conversion of alpha-Xa to beta-Xa. The intermediate produced by the loss of this peptide from Factor X,I1, can be activated directly to beta-Xa by the tissue factor-Factor VII complex, with the loss of the same NH2-terminal peptide as is produced in the conversion of Factor X to alpha-Xa. The autocatalytic activation of Factor X by Factor Xa described previously occurs to a marked extent only at very low activator concentrations, and has been shown to proceed largely by the loss of the normal NH2-terminal peptide from the heavy chain of I1-Initial experiments show that neither peptide affects the rate of coagulation by either the extrinsic or intrinsic pathways. The amino acid sequences have been determined on both sides of the peptide cleavages, and it has been shown that the cleavage sites are the same, regardless of the pathway of activation. The amino acid sequence and carbohydrate composition of the COOH-terminal peptide have been determined. The carbohydrate moiety is attached via an O-glycosidic linkage at a threonine residue, and contains galactosamine but no glucosamine. 相似文献
110.
Ehrlich ascites-tumour cells were investigated with regard to their stability to transport L-lactate by measuring either the distribution of [14C]lactate or concomitant H+ ion movements. The movement of lactate was dependent on the pH difference across the cell membrane and was electroneutral, as evidenced by an observed 1:1 antiport for OH- ions or 1:1 symport with H+ ions. 2. Kinetic experiments showed that lactate transport was saturable, with an apparent Km of approx. 4.68 mM and a Vmax. as high as 680 nmol/min per mg of protein at pH 6.2 and 37 degrees C. 3. Lactate transport exhibited a high temperature dependence (activation energy = 139 kJ/mol). 4. Lactate transport was inhibited competitively by (a) a variety of other substituted monocarboxylic acids (e.g. pyruvate, Ki = 6.3 mM), which were themselves transported, (b) the non-transportable analogues alpha-cyano-4-hydroxycinnamate (Ki = 0.5 mM), alpha-cyano-3-hydroxycinnamate (Ki = 2mM) and DL-p-hydroxyphenyl-lactate (Ki = 3.6 mM) and (c) the thiol-group reagent mersalyl (Ki = 125 muM). 5. Transport of simple monocarboxylic acids, including acetate and propionate, was insensitive to these inhibitors; they presumably cross the membrane by means of a different mechanism. 6. Experiments using saturating amounts of mersalyl as an "inhibitor stop" allowed measurements of the initial rates of net influx and of net efflux of [14C]lactate. Influx and efflux of lactate were judged to be symmetrical reactions in that they exhibited similar concentration dependence. 7. It is concluded that lactate transport in Ehrlich ascites-tumour cells is mediated by a carrier capable of transporting a number of other substituted monocarboxylic acids, but not unsubstituted short-chain aliphatic acids. 相似文献