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991.
Rape seedlings ( Brassica napus L. cv. Brink) were exposed to repeated water-deficit stress. The water-stress program started after 19 days of growth and consisted of three 24 h stress periods interspersed with 24 h rewatering periods. After the third stress period the seedlings were harvested and the membrane lipids of the roots were extracted, isolated and quantified. The stress caused an increased ratio of dry weight roots/shoot. Furthermore, the total amount of acyl lipids as well as phospholipids decreased drastically. However, the relative distribution of individual phospholipids was constant and independent of stress. Free and esterified sterols showed only a small decrease in response to water stress. As a consequence the ratio free sterols/phospholipids increased from 0.07 in the control root cells to 0.15 in the stressed cells. The lipid changes are discussed in relation to membrane activity.  相似文献   
992.
Treatment of melon leaves or seedlings with elicitors of Colletotrichum lagenarium, a fungal pathogen of melon, increases chitinase activity. In treated leaves, chitinase is enhanced within the first 6 hours and becomes 2 to 10 times higher than in control leaves after 24 hours. Ethylene is increased simultaneously and is correlated with chitinase elicitation. In the presence of aminoethoxyvinylglycine, an inhibitor of ethylene synthesis, both elicitor-induced ethylene and elicitor-induced chitinase are inhibited. This inhibition is overcome by added exogenous ethylene. On the other hand, 1-aminocyclopropane-1-carboxylic acid the direct precursor of ethylene, triggers chitinase activity. Chitinase elicitation is thought to be a protein synthesis dependent process, as it does not occur in the presence of cycloheximide.  相似文献   
993.
A commercial beta-glucuronidase (beta-GUR) test for the rapid and economical identification of Escherichia coli was evaluated. A total of 762 clinical strains and 228 environmental isolates were studied. More than 95% of the E. coli strains were found to be beta-GUR positive. Thirty-one clinical isolates of Shigella sonnei, 10 of Enterobacter cloacae, eight of Enterobacter aerogenes, nine of Citrobacter freundii and one of Salmonella enteritidis also gave positive results. The enzyme beta-GUR was also detected in two environmental strains of E. cloacae and one C. freundii. A comparative study between the beta-GUR test and the conventional identification system was carried out in 233 consecutive isolates of lactose positive enterobacteria. Agreement was observed in 223 cases and 190 E. coli strains were correctly identified using this test. Discrepancies were found in 10 cases: nine E. coli were beta-GUR negative and one C. freundii was beta-GUR positive. Escherichia coli was the only species positive for both beta-GUR and indole tests. This procedure permits a rapid, easy, precise and inexpensive identification of E. coli. beta-GUR positive Enterobacter strains have not previously been described.  相似文献   
994.
Report of a family with dominant hereditary multicentric osteolysis. The review of the literature proves the clinical and genetic heterogeneity of the disease.  相似文献   
995.
Starting from a crystal-negative parental strain of Bacillus thuringiensis, we isolated certain bacteriophage-resistant mutants which showed decreased virulence in pupae of the cecropia moth (Hyalophora cecropia). These strains (class I mutants) were highly pleiotropic and showed resistance to seven or eight different phages, sensitivity to methicillin, and loss of flagella. They were also more sensitive to cecropia immune hemolymph in vitro. In addition, the export of at least three proteins was reduced. Revertants (class II mutants) were sensitive to phages, virulent, and resistant to penicillin derivatives. One class II mutant was a complete revertant in all properties examined. The other class II mutant was an incomplete revertant still susceptible to immune hemolymph and with repressed export of proteins. Virulence was not coupled to phage resistance as such or to lack of flagella because other mutants affected in these properties were virulent. Other factors which could be excluded as causes of virulence were production of extracellular protease and hemolysin.  相似文献   
996.
Lycorine: a eukaryotic termination inhibitor?   总被引:1,自引:0,他引:1  
The effect of the alkaloid lycorine on viral protein synthesis was studied in poliovirus-infected HeLa cells. The incorporation of [3H]leucine was inhibited by lycorine in a dose-dependent way, although lycorine never completely abolished translation. Using polyacrylamide gel electrophoresis, the viral proteins were identified as derived from the P1 (5' terminal), P2 (middle), or P3 (3' terminal) region of the poliovirus translation unit. The residual labeling of viral proteins in the presence of lycorine was mainly due to synthesis of P1 proteins and slightly less to P2 proteins, while virtually no P3-derived proteins were made. It is suggested that lycorine may act at the level of termination.  相似文献   
997.
998.
Two proteins of Mr = 58,000 and 59,000, respectively, were purified from 4 M guanidinium chloride extracts of articular cartilage by dissociative CsCl-density gradient centrifugation followed by gel chromatography on Sephadex G-200 and ion exchange chromatography on DEAE-cellulose. The two proteins differ in ionic properties and only the one with Mr = 59,000 bound to the ion exchanger. Although the two proteins showed dissimilar peptide patterns after proteolysis, their amino acid composition was similar, with very high contents of leucine and aspartic acid/asparagine. The two proteins showed no cross-reactivity in radioimmunoassays. By use of these assays, the proteins were demonstrated in extracts of most connective tissues, with high contents of about 0.1% of tissue wet weight determined in several types of cartilage. Among the non-cartilage connective tissues, tendon and sclera had the highest contents of the proteins, i.e. about 0.1% of the tissue wet weight. Bone extracts, on the other hand, contained insignificant amounts of the proteins. Only the Mr = 59,000 protein was detected in serum, its concentration being about 33 micrograms/l. Both proteins were shown to be localized in the extracellular matrix of cartilage, predominantly in the territorial matrix, by using indirect immunofluorescence.  相似文献   
999.
Equilibrium binding of insulin to rat white fat cells at 15 degrees C   总被引:1,自引:0,他引:1  
Equilibrium binding of insulin to isolated rat epididymal fat cells was investigated. A temperature of 15 degrees C was chosen for the study to minimize lysosomal degradation of insulin. Indeed, medium insulin lost only 1% of its precipitability in trichloroacetic acid during the 4-h incubation required to approach equilibrium. Binding was measured by a method that did not perturb the equilibrium of the system. A new formalism for analyzing binding data in general was introduced. A correction for trapping of insulin in the interstitial space of cell pellets was both necessary and sufficient to derive specific binding data from raw observations. Thus, so-called "nonspecific binding" was unmasked as a misnomer, and the expression "correction for trapping" was proposed as a substitute. Equations for one and two independent classes of binding sites were fit to the data by the method of maximum likelihood, and the best fit was selected based on Akaike's information criterion, as adapted for a constant fractional error. More than 99.7% of the binding sites were found to be describable by a simple binding isotherm with Kd,app = 8.8 multiplied by over divided by 1.3 nM. Less than 0.3% sites had a higher affinity (Kd approximately equal to 8 multiplied by over divided by 3 pM). There were 99,000 x/divided by 1.6 binding sites/cell. These equilibrium parameters are in agreement with values derived from a kinetic analysis, presented in the subsequent paper (Lipkin, E. W., Teller, D. C., and de Ha?n, C. (1986) J. Biol. Chem. 260, 1702-1711).  相似文献   
1000.
The accumulation in large amounts of bisnucleoside polyphosphates (Ap4X) after heat shock in Xenopus laevis oocytes or cultured hepatoma cells (HTC cells) is observed after exposure to temperatures of 45 degrees C or higher. The accumulation is a transient phenomenon, with the collapse in cellular ATP concentration severely affecting the rate of synthesis of Ap4X, allowing degrading activities to empty the pool of these compounds under prolonged heat shock. This accumulation of Ap4X to high levels, compared to the basic content, is only observed under conditions leading to irreversible damage, ultimately resulting in the death of the cell. It is shown that the increase in Ap4X after hyperthermia is due to the partial or almost complete inhibition of their degradation pathways, rather than to a stimulation of their rate of synthesis. Finally, the synthesis of heat-shock proteins could be observed under conditions which do not lead to important accumulation of Ap4X, therefore ruling out the possibility that these adenylylated nucleotides would behave as chemical signals ("alarmones") triggering the synthesis of heat-shock proteins. Nevertheless, on the basis of our earlier results (Guédon, G., Sovia, D., Ebel, J. P., Befort, D., and Remy, P. (1985) Embo J. 4, 3743-3749), it cannot be excluded that Ap4X might play a role in the regulation of the heat-shock response; this would, however, rely on variations in Ap4X concentrations which do not exceed a factor of 2.  相似文献   
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