全文获取类型
收费全文 | 5604篇 |
免费 | 391篇 |
专业分类
5995篇 |
出版年
2021年 | 48篇 |
2019年 | 55篇 |
2018年 | 58篇 |
2017年 | 59篇 |
2016年 | 82篇 |
2015年 | 101篇 |
2014年 | 126篇 |
2013年 | 302篇 |
2012年 | 263篇 |
2011年 | 191篇 |
2010年 | 141篇 |
2009年 | 122篇 |
2008年 | 233篇 |
2007年 | 237篇 |
2006年 | 246篇 |
2005年 | 210篇 |
2004年 | 246篇 |
2003年 | 246篇 |
2002年 | 257篇 |
2001年 | 233篇 |
2000年 | 217篇 |
1999年 | 180篇 |
1998年 | 68篇 |
1997年 | 60篇 |
1996年 | 47篇 |
1995年 | 40篇 |
1994年 | 54篇 |
1993年 | 53篇 |
1992年 | 138篇 |
1991年 | 113篇 |
1990年 | 137篇 |
1989年 | 140篇 |
1988年 | 114篇 |
1987年 | 105篇 |
1986年 | 98篇 |
1985年 | 84篇 |
1984年 | 80篇 |
1983年 | 62篇 |
1982年 | 50篇 |
1981年 | 44篇 |
1980年 | 37篇 |
1979年 | 72篇 |
1978年 | 53篇 |
1977年 | 47篇 |
1976年 | 36篇 |
1975年 | 41篇 |
1974年 | 42篇 |
1973年 | 38篇 |
1972年 | 45篇 |
1970年 | 33篇 |
排序方式: 共有5995条查询结果,搜索用时 15 毫秒
81.
Cell-free synthesis of ornithine decarboxylase. Changes in mRNA activity in the liver of thioacetamide-treated rats 总被引:1,自引:0,他引:1
T Kameji K Fujita T Noguchi M Takiguchi M Mori M Tatibana S Hayashi 《European journal of biochemistry》1984,144(1):35-39
Ornithine decarboxylase (ODC)mRNA associated with free polysomes of rat liver was translated in a reticulocyte lysate cell-free system. Newly synthesized ODC protein was identified by specific immunoprecipitation, molecular size as determined by polyacrylamide gel electrophoresis with sodium dodecyl sulfate, and competition by excess unlabeled ODC in the immunoprecipitation. A single injection of thioacetamide was found to cause several fold increases in both immunotitratable ODC protein and polysomal ODC-mRNA activity, while it provoked a much larger increase in ODC activity in rat liver. The results indicate that the induction of hepatic ODC activity by thioacetamide treatment is due not only to an increase in the activity of polysomal ODC-mRNA but also to a translational and/or posttranslational control. 相似文献
82.
Two neurotoxins, "toxin B", a long neurotoxin from Naja naja, and "cobrotoxin", a short neurotoxin from Naja naja atra, were compared with respect to their limited hydrolysis by trypsin and chymotrypsin and its effect on their neurotoxicity. Limited hydrolysis of toxin B with trypsin cleaves peptide bonds at Arg68-Lys69 and Arg33-Gly34 in the toxin molecule and causes complete loss of the neurotoxicity yielding des-carboxyl terminal toxin B(1-68) nicked at Arg33-Gly34 in the molecule. On the other hand, the des-carboxyl terminal toxin B(1-67) shows 70% of the native toxin B neurotoxicity. These results indicated that the complete loss of the toxicity may be due to hydrolysis of a specific peptide bond, Arg33-Gly34, in the toxin B molecule. Limited trypsin digestion did not affect the toxicity of cobrotoxin and limited chymotrypsin digestion had no effect on either neurotoxin. 相似文献
83.
84.
High concentration (1.0 M) of KSCN, but not of NaSCN, induced lysis of slightly halophilic Vibrio alginolyticus and moderately halophilic Vibrio costicolus, and the decrease in absorbance of the cell suspension was complete after 30 min at 25 degrees C. Replacement of K+ with Na+ effectively prevented the lysis by SCN-.K+ salts of NO3-, Br- and I-, however, induced no significant lysis. In electron micrographs, a prolonged exposure of the cells of V. alginolyticus to 1.0 M KSCN displaced the nucleoplasm to maintain close contact with the cell membranes. After 40 min of interaction, 50% of the cellular protein, 96% of RNA and 94% of DNA were recovered in the lysed cells. In contrast to lysis in hypotonic conditions, the lysis induced by KSCN is due mainly to a partial release of protein from the cells. V. costicolus was more susceptible to SCN- than V. alginolyticus, whereas nonhalophilic Escherichia coli was resistant to 1.0 M KSCN. Thus, lysis by SCN- is characteristic of halophilic bacteria and cell membranes of more halophilic bacteria are more susceptible to chaotropic anions. The protective effect of Na+ observed here was considered to be manifested by specific interactions of Na+ with components of cell membranes, thereby rendering their structures resistant to the action of chaotropic anions. 相似文献
85.
When methylmercury was incubated in the presence of selenite and reduced glutathione (GSH), the mercury which was extracted into benzene under acidic condition decreased gradually with the elapse of time. This decrease was due to the cleavage of mercury-carbon bond of methylmercury. The reaction did not proceed when selenite or GSH was singly added to the reaction mixture. L-Cysteine, 2-mercaptoethanol and sodium sulfide in place of GSH also were effective for decomposition of methylmercury in combination with selenite, but oxidized glutathione (GSSG) and L-cystine were not. This suggests that reduction of selenite is needed for the degradation of methylmercury. Thus, the effect of reduced metabolites of selenite produced by GSH was investigated. Glutathione selenotrisulfide (GSSeSG) requierd GSH for the degradation of methylmercury, whereas H2Se possessed a strong activity even in the absence of GSH. This may indicate that H2Se is involved directly in the conversion of methylmercury to inorganic mercury. This phenomenon found in experiments is discussed in relation to the biotransformation of methylmercury. 相似文献
86.
T M Larsen R C Miller G B Spiegelman S Hayashi G M Tener D A Sinclair T A Grigliatti 《Molecular & general genetics : MGG》1982,185(3):390-396
Summary Transfer RNA was extracted from 50–300 mg of adult flies and specifically labeled in vitro. The level of individual isoacceptors was quantitated by efficient annealing to Drosphila tRNA genes carried on recombinant DNA plasmids immobilized on nitrocellulose filters. The level of tRNA
3b
Val
in the tRNA isolated from flies deficient in the major tRNA
3b
Val
loci has been examined. The results show that deletion of the major tRNA
3b
Val
loci resulted in a reduction of approximately 50% in the level of tRNA
3b
Val
but did not produce the Minute phenotype; furthermore the effects of deficiencies at two loci were approximately additive. 相似文献
87.
Kozo Hayashi Kazuo Yamada Keiji Ohe Akima Miyoshi Takashi Kawasaki 《生物化学与生物物理学报:生物膜》1980,596(3):414-419
The effect of amytal on energy metabolism and acid secretion in an isolated gastric mucosa of the guinea-pig were studied. Determination of adenine nucleotides, creatine phosphate, pyruvate and lactate in the gastric mucosa showed that amytal depressed the levels of ATP, creatine phosphate and energy charge with elevation of the AMP and pyruvate levels. This treatment inhibited concomitantly acid secretion and active chloride transport detected by short circuit current. The addition of menadione with ascorbate to the medium in the presence of amytal partially restored ATP and energy charge levels and also induced a partial recovery of acid secretion and active chloride transport. These results suggest that ATP is a direct energy donor for acid secretion in the gastric mucosa of the guinea-pig. 相似文献
88.
Jun-Ichi Hayashi Osamu Gotoh Yusaku Tagashira 《Archives of biochemistry and biophysics》1980,205(1):27-35
Previous studies showed that stimulation of mouse mitochondrial ATPase activity of tumor cells, fetal liver, and adult brain by the uncoupler 2,4-dinitrophenol was markedly suppressed during incubation of the mitochondria with the uncoupler (J.-I. Hayashi et al., 1980, Biochem. Biophys. Res. Commun.92, 261–267). The present work showed the reason for this suppression. More than half the endogenous Mg2+ leaked from mitochondria of all tumor cells tested, and of fetal liver and adult brain during incubation with the uncoupler, while only about 30% of the endogenous Mg2+ leaked from mitochondria of other normal tissues. The effect of the uncoupler on Mg2+ leakage from liver mitochondria changed from the fetal to the adult type within about 30 min after birth. In hypotonic medium, normal liver mitochondria also lost more than half their total Mg2+ and concomitantly stimulation of their ATPase activity by uncoupler was considerably reduced. Exogenously added Mg2+ could reverse this reduced effect of the uncoupler on ATPase activity of mitochondria from normal tissues and tumor cells. These results show that the endogenous Mg2+ content of mitochondria directly affects the stimulation by uncoupler of ATPase activity of mitochondria from both normal tissues and tumor cells. Thus, mitochondria of all tumor cells tested, and of fetal liver and adult brain are leaky to Mg2+ during incubation with uncoupler and as a result of the leakage, the stimulatory effect of the uncoupler on their ATPase activity is greatly reduced. 相似文献
89.
90.
M Hayashi 《Journal of biochemistry》1978,84(6):1363-1372
A large-scale purification of monkey brain arylamidase was carried out. Amino acid analyses indicate that the enzyme is rich in acidic amino acids and is poor in cystine. The amino terminal residue was determined to be alanine by dansylation. The enzyme was activated by sulfhydryl compounds. Dithiothreitol was more effective than beta-mercaptoethanol. Bestatin competitively inhibited the enzyme activity and the Ki value was calculated to be 2.5 x 10(-7) M, which was of the same order as that of puromycin. The inhibitions by puromycin and bestatin were reversible. The enzyme hydrolyzed di-, tri-, and oligopeptides including physiologically active peptides. Of physiologically active peptides, enkephalins and Met-Lys-bradykinin, which possess a neutral amino acid at the N-terminal position, were more rapidly hydrolyzed by the enzyme. Peptides such as LH-RH and TRH, which possess a pyrrolidonecarboxylyl group at the N-terminal position, and substance P and bradykinin, which possess a proline residue adjacent to the N-terminal residue, were not hydrolyzed by the enzyme. The Km values for various peptides indicate that the enzyme has higher affinity for oligopeptides than di- and tripeptides. The aminopeptidase activity of the enzyme was also competitively inhibited by puromycin and bestatin. Analyses of the hydrolysis products of various peptides by the dansylation method indicate that the enzyme has both kinin-converting activity and angiotensinase activity. 相似文献