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1.
Masaru Kubota Ying-Wei Lin Keigo Hamahata Machiko Sawada Seiji Koishi Haruyo Hirota Yoshihiro Wakazono 《Mutation Research - Genetic Toxicology and Environmental Mutagenesis》2000,470(2):21
The occurrence of a second neoplasm is one of the major obstacles in cancer chemotherapy. The elucidation of the genotoxic effects induced by anti-cancer drugs is considered to be helpful in identifying the degree of cancer risk. Numerous investigations on cancer patients after chemotherapy have demonstrated: (i) an increase in the in vivo somatic cell mutant frequency (Mf) at three genetic loci, including hypoxanthine–guanine phosphoribosyl-transferase (hprt), glycophorin A (GPA), and the T-cell receptor (TCR), and (ii) alterations in the mutational spectra of hprt mutants. However, the time required for and the degree of such changes are quite variable among patients even if they have received the same chemotherapy, suggesting the existence of underlying genetic factor(s). Accordingly, some cancer patients prior to chemotherapy as well as patients with cancer-prone syndrome have been found to show an elevated Mf. Based on the information obtained from somatic cell mutation assays, an individualized chemotherapy should be considered in order to minimize the risk of a second neoplasm. 相似文献
2.
Eleven temperature-sensitive mutants of adenovirus type 12, capable of forming plaques in human cells at 33 C but not at 39.5 C, were isolated from a stock of a wild-type strain after treatment with either nitrous acid or hydroxyl-amine. Complementation tests in doubly infected human cells permitted a tentative assignment of eight of these mutants to six complementation groups. Temperature-shift experiments revealed that one mutant is affected early and most of the other mutants are affected late. Only the early mutant, H12ts505, was temperature sensitive in viral DNA replication. Infectious virions of all the mutants except H12ts505 and two of the late mutants produced at 33 C, appeared to be more heat labile than those of the wild type. Only H12ts505 was temperature sensitive for the establishment of transformation of rat 3Y1 cells. One of the late mutants (H12ts504) had an increased transforming ability at the permissive temperature. Results of temperature-shift transformation experiments suggest that a viral function affected in H12ts505 is required for “initiation” of transformation. Some of the growth properties of H12ts505-transformed cells were also temperature dependent, suggesting that a functional expression of a gene mutated in H12ts505 is required to maintain at least some aspects of the transformed state. 相似文献
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The enzyme activity of dephosphorylation of thymidine triphosphate was found in microsomal fraction of rat liver. The enzyme activity decreased at the time when [3H]thymidine incorporation into DNA of regenerating liver increased. When the [3H]thymidine incorporation was suppressed by 1,3-diaminopropane, the enzyme activity remained elevated. These results suggest that the enzyme activity appears to be closely linked to DNA synthesis. 相似文献
6.
Toru Shimizu Masahiro Hatano Seiji Nagao Yoshinori Nozawa 《Biochemical and biophysical research communications》1982,106(4):1112-1118
43Ca NMR spectra of Ca2+-Tetrahymena calmodulin(Tet. CaM.) complexes have been observed under various conditions. Off-rate of Ca2+ from Tet. CaM. is estimated to be approx. 2.7 × 103 s?1 under a certain assumption. Relaxation rates of 43Ca NMR of Ca2+-Tet. CaM. are remarkably increased(by one order in magnitude) by adding trifluoperazine(TFP), a potent calmodulin antagonist. Relaxation parameters estimated suggest that Ca2+ mobility is reduced by the TFP binding. A stoichiometry of TFP is two moles per Tet. CaM. molecule. The relaxation rates of 43Ca NMR signals are increased by adding excessive Mg2+ to the Ca2+-Tet. CaM. solutions. The addition of Mg2+ to the Ca2+-Tet. CaM. complex decreases apparent pKa value of the complex as well. 相似文献
7.
Isao Matsui Masaharu Kamei Shuzo Otani Seiji Morisawa Anthony E. Pegg 《Biochemical and biophysical research communications》1982,106(4):1155-1160
Spermidine acetylase activity was detected in extracts prepared from and there was a marked increase in activity over the early period of growth. This increase reached a maximum 3 h after inoculation and was followed by an increase in ornithine decarboxylase activity. The acetylase was also able to use spermine as a substrate, but not putrescine. With spermidine and acetyl-CoA as substrate, the product formed was exclusively N1-acetyl-spermidine. This is the first evidence for the occurrence in bacteria of spermidine-N1-acetyltransferase, an enzyme which has previously been described in mammalian cells. These results suggest that acetylation of spermidine may be involved in the growth of and in the regulation of its polyamine content. 相似文献
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9.
Phenylalanine Transport Across the Blood-Brain Barrier as Studied with the In Situ Brain Perfusion Technique 总被引:6,自引:5,他引:1
Seiji Momma Masaki Aoyagi Stanley I. Rapoport Quentin R. Smith 《Journal of neurochemistry》1987,48(4):1291-1300
Unidirectional L-phenylalanine transport into six brain regions of pentobarbital-anesthetized rats was studied using the in situ brain perfusion technique. This technique allows both accurate measurements of cerebrovascular amino acid transport and complete control of perfusate amino acid composition. L-Phenylalanine influx into the brain was sodium independent and could be described by a model with a saturable and a nonsaturable component. Best-fit values for the kinetic constants in the parietal cortex equaled 6.9 X 10(-4) mumol/s/g for Vmax, 0.011 mumol/ml for Km, and 1.8 X 10(-4) ml/s/g for KD during perfusion with fluid that did not contain competing amino acids. D-Phenylalanine competitively inhibited L-phenylalanine transport with a Ki approximately 10-fold greater than the Km for L-phenylalanine. There were no significant regional differences in Km, KD, or Ki, whereas Vmax was significantly greater in the cortical lobes than in the other brain regions. L-Phenylalanine influx during plasma perfusion was only 30% of that predicted in the absence of competing amino acids. Competitive inhibition increased the apparent Km during plasma perfusion by approximately 20-fold, to 0.21 mumol/ml. These data provide accurate new estimates of the kinetic constants that describe L-phenylalanine transport across the blood-brain barrier. In addition, they indicate that the cerebrovascular transfer site affinity (1/Km) for L-phenylalanine is three- to 12-fold greater than previously estimated in either awake or anesthetized animals. 相似文献
10.
Kinetics of Neutral Amino Acid Transport Across the Blood-Brain Barrier 总被引:20,自引:8,他引:12
Quentin R. Smith Seiji Momma Masaki Aoyagi Stanley I. Rapoport 《Journal of neurochemistry》1987,49(5):1651-1658
Neutral amino acid (NAA) transport across the blood-brain barrier was examined in pentobarbital-anesthetized rats with an in situ brain perfusion technique. Fourteen of 16 plasma NAAs showed measurable affinity for the cerebrovascular NAA transport system. Values of the transport constants (Vmax, Km, KD) were determined for seven large NAAs from saturation studies, whereas Km values for five small NAAs were estimated from inhibition studies. These data, together with our previous work, provide a complete set of constants for prediction of NAA influx from plasma. Among the NAAs, Vmax varied at least fivefold and Km varied approximately 700 fold. The apparent affinity (1/Km) of each NAA was related linearly (r = 0.910) to the octanol/water partition coefficient, a measure of NAA side-chain hydrophobicity. Predicted influx values from transport constants and average plasma concentrations agree well with values measured using plasma perfusate. These results provide accurate new estimates of the kinetic constants that determine NAA transport across the blood-brain barrier. Furthermore, they suggest that affinity of a L-alpha-amino acid for the transport system is determined primarily by side-chain hydrophobicity. 相似文献