全文获取类型
收费全文 | 3038篇 |
免费 | 274篇 |
国内免费 | 2篇 |
出版年
2022年 | 9篇 |
2021年 | 29篇 |
2020年 | 11篇 |
2019年 | 25篇 |
2018年 | 47篇 |
2017年 | 24篇 |
2016年 | 31篇 |
2015年 | 55篇 |
2014年 | 67篇 |
2013年 | 159篇 |
2012年 | 155篇 |
2011年 | 165篇 |
2010年 | 103篇 |
2009年 | 92篇 |
2008年 | 175篇 |
2007年 | 145篇 |
2006年 | 159篇 |
2005年 | 150篇 |
2004年 | 155篇 |
2003年 | 148篇 |
2002年 | 112篇 |
2001年 | 88篇 |
2000年 | 133篇 |
1999年 | 98篇 |
1998年 | 47篇 |
1997年 | 41篇 |
1996年 | 30篇 |
1995年 | 33篇 |
1994年 | 36篇 |
1993年 | 43篇 |
1992年 | 95篇 |
1991年 | 80篇 |
1990年 | 75篇 |
1989年 | 64篇 |
1988年 | 72篇 |
1987年 | 42篇 |
1986年 | 45篇 |
1985年 | 54篇 |
1984年 | 40篇 |
1983年 | 32篇 |
1982年 | 12篇 |
1981年 | 20篇 |
1980年 | 14篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 17篇 |
1976年 | 13篇 |
1973年 | 8篇 |
1971年 | 7篇 |
1968年 | 6篇 |
排序方式: 共有3314条查询结果,搜索用时 187 毫秒
51.
Tomoko Ohta 《Journal of molecular evolution》1984,20(3-4):274-280
Summary The previous simple model for treating concerted evolution of multigene families has been revised to be compatible with various new observations on the immunoglobulin variable region family and other families. In the previous model, gene conversion and unequal crossing-over were considered, and it was assumed that genes are randomly arranged on the chromosome; neither subdivision nor correlation of gene identity and chromosomal distance were considered. Although this model satisfactorily explains the observed amino acid diversity within and between species, it fails to predict the very ancient branching of the mouse immunoglobulin heavy chain V-gene family. By incorporating subdivided structure and genetic correlation with chromosomal distance into the simple model, the data of divergence may be satisfactorily explained, as well as the rate of nucleotide substitution and the amino acid diversity. The rate at which a V-gene is duplicated or deleted by conversion or by unequal crossing-over is estimated by the new model to be on the order of 10–6 per year. The model may be applicable to other multigene families, such as those coding for silkmoth chorion or mammalian kallikrein.Contribution no. 1560 from the National Institute of Genetics, Mishima, 411 Japan 相似文献
52.
K Tojo Y Kato Y Kabayama H Ohta T Inoue H Imura 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1986,181(4):517-522
Intracerebroventricular (icv) injection of neurotensin (NT) (2 micrograms/rat) suppressed prolactin (PRL) release induced by L-5-hydroxytryptophan (1 mg/100 g body wt, iv), prostaglandin E2(1 microgram/rat, icv), and FK33-824 (10 micrograms/100 g body wt, iv), a Met5-enkephalin analog, in urethane-anesthetized or conscious rats. In contrast, NT did not suppress elevated plasma PRL levels sustained by a large dose of domperidone (10 micrograms/100 g body wt, iv), a peripheral dopamine antagonist. In in vitro experiments, NT (10(-5) M) stimulated dopamine release from perifused rat hypothalamic fragments. These results suggest that central NT inhibits PRL secretion by stimulating dopamine release from the hypothalamus into hypophysical portal blood in the rat. 相似文献
53.
An 8-year-old girl with meningococcal meningitis lacked serum complement activity. The seventh component of complement (C7) could not be detected in her serum by either functional or immunochemical analysis. The levels of the other components were within the normal range. Her serum complement activity was restored by the addition of purified C7. Her fresh serum showed a total absence of bactericidal activity against Neisseria meningitidis, group Y, but her serum bactericidal activity was restored by the addition of purified C7. The restoration of her serum bactericidal activity was completely inhibited in the presence of Mg2+ EGTA. These findings suggest that restoration of the bactericidal activity of her serum against N. meningitidis might be mediated by the specific antibody against N. meningitidis and the reconstituted complement system in her serum. Heterozygous deficiency of C7 was found in 10 of her family members. Genetic studies showed that the mode of inheritance might be an autosomal codominant trait. No genetic linkage between deficiency of C7 and the HLA system was found. 相似文献
54.
Amphibian metallothionein. Induction in the frogs Rana japonica, R. nigromaculata and Rhacophorus schlegelii 总被引:1,自引:0,他引:1
K T Suzuki N Itoh K Ohta H Sunaga 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1986,83(2):253-259
Cadmium (Cd) was injected intramuscularly into three species of frogs to examine the number of isoforms in the induced metallothionein (MT). The induced MT was shown to consist of a single isoform in the three species of frogs Rana japonica, R. nigromaculata and Rhacophorus schlegelii. Native MT in the livers of R. japonica and R. nigromaculata was copper (Cu)-MT and the induced MT in the three species was Cd, Cu-MT, the Cd/Cu ratio in the induced MT being different from species to species. The effect of Cd injections on the concentrations of 10 elements in the livers and kidneys of the Rana species was not significant except for Cu. 相似文献
55.
H Ohta 《Folia primatologica; international journal of primatology》1983,40(4):256-267
In primates, learning set formation has been reported in various simian species, but in only few prosimian species. The formation of visual discrimination learning set was tested on a nocturnal prosimian species, slow lorises (Nycticebus coucang). Their performance was higher than that of some New World monkeys. This confirmed the suggestion from the data on black lemurs (Lemur macaco) that there is an overlap between prosimians and simians in learning set ability. 相似文献
56.
Phenotypic and chemotaxonomic characteristics of five isolates of acetylenereducing (nitrogen-fixing) oligotrophic bacteria from a paddy soil were investigated. They showed similar phenotypic characteristics: they were aerobic, asporogenous, gram-negative, motile by a polar flagellum, and irregular rods. On full strength nutrient broth (NB) growth was severely suppressed, but well supported on 10-to 10000-fold diluted NB. They consumed glucose but produced no acid, and also utilized phenolic acids such as ferulic acid or p-coumaric acid. The cellular fatty acid composition, quinone system and DNA base composition of the isolates were investigated. Cellular fatty acids mainly consisted of straightchain unsaturated C18 : 1 (62–81% of total fatty acids). Ubiquinone Q-10 and a high guanine-plus-cytosine content (65.1–66.0 mol%) were found. The taxonomic status of the isolates is discussed and a new genus, Agromonas, with a single species Agromonas oligotrophica sp. nov., is proposed for these isolates. The type strain of A. oligotrophica is JCM 1494. 相似文献
57.
Role of Tween 80 and Monoolein in a Lipid-Sterol-Protein Complex Which Enhances Ethanol Tolerance of Sake Yeasts 总被引:7,自引:6,他引:1 下载免费PDF全文
An exogenous ternary complex composed of Tween 80, ergosterol, and albumin increased the final ethanol concentration of fermentation by sake yeasts from 17.2 to 19.0% (vol/vol) and reduced the fermentation time from 30 to 25 days. Likewise, a complex of monoolein, albumin, and either ergosterol or ergosteryl oleate increased the final ethanol concentration of fermentation to 19.7 or 19.8% (vol/vol), respectively, and reduced the fermentation time to 25 days. Both Tween 80 and monoolein promoted the fermentative activity (QCO2) of cells, and the effect was enhanced by the presence of ergosterol. 相似文献
58.
A total of 228 pesticides (88 insecticides, 60 fungicides, 62 herbicides, 12 plant-growth regulators, 3 metabolites and 3 other compounds) was tested for mutagenicity in bacterial reversion-assay systems with 5 strains (TA100, TA98, TA1535, TA1537 and TA1538) of Salmonella typhimurium and a strain (WP2 hcr) of Escherichia coli. 50 pesticides (25 insecticides, 20 fungicides, 3 herbicides, 1 plant-growth regulator and 1 other compound) were found to be mutagenic. 5 of them required metabolic activation (S9 mix) for their activities. Among various chemical groups, organic phosphates, halogenated alkanes and dithiocarbamates showed higher ratios of mutagens. Although 22 of the pesticides tested have been reported to be carcinogenic, 7 of them, i.e., captain, DBCP, EDB, EDC, ETU, HEH and nitrofen, were detected as mutagens in the present assay. Most of the other 15 non-mutagenic carcinogens were organochlorine pesticides such as alpha-BHC, chlorobenzilate, p,p'-DDT, dieldrin and quintozene. 相似文献
59.
Antimutagenic effects of cinnamaldehyde on mutagenesis by chemical agents were investigated in Escherichia coli WP2 uvrA- trpE-. Cinnamaldehyde, when added to agar medium, greatly reduced the number of Trp+ revertants induced by 4-nitroquinoline 1-oxide (4-NQO) without any decrease of cell viability. This antimutagenic effect could not be explained by inactivation of 4-NQO caused by direct interaction with cinnamaldehyde. Mutagenesis by furylfuramide (AF-2) was also suppressed significantly. Mutations induced by methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS) were slightly inhibited. However, cinnamaldehyde was not at all effective on the mutagenesis of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Two derivatives of cinnamaldehyde, cinnamyl alcohol and trans-cinnamic acid, did not have as strong antimutagenic effects on 4-NQO mutagenesis as cinnamaldehyde had. Because cinnamaldehyde showed marked antimutagenic effects against mutations induced by UV-mimic mutagens but not those induced by MNNG or EMS, it seems that cinnamaldehyde might act by interfering with an inducible error-prone DNA repair pathway. 相似文献
60.
On the constancy of the evolutionary rate of cistrons 总被引:32,自引:0,他引:32
Summary The variations of evolutionary rates in hemoglobins and cytochrome c among various lines of vertebrates are analysed by estimating the variance. The observed variances appear to be larger than expected purely by chance.If the amino acid substitutions in evolution are the result of random fixation of selectively neutral or nearly neutral mutations, the evolutionary rate of cistrons can be represented by the integral of the product of mutation rate and fixation probability in terms of selective values around the neutral point. This integral is called the effective neutral mutation rate.The influence of effective population number and generation time on the effective neutral mutation rate is discussed. It is concluded that the uniformity of the rate of amino acid substitutions over diverse lines is compatible with random fixation of neutral or very slightly deleterious mutations which have some chance of being selected against during the course of substitution. On the other hand, definitely advantageous mutations will introduce significant variation in the substitution rate among lines. Approximately 10% of the amino acid substitutions of average cistrons might be adaptive and create slight but significant variations in evolutionary rate among vertebrate lines, although the uniformity of evolutionary rate is still valid as a first approximation.Contribution No. 813 from the National Institute of Genetics, Mishima, Shizuokaken 411 Japan. Aided in part by a grant-in-aid from the Ministry of Education, Japan. 相似文献