全文获取类型
收费全文 | 787篇 |
免费 | 29篇 |
国内免费 | 79篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 15篇 |
2016年 | 26篇 |
2015年 | 19篇 |
2014年 | 21篇 |
2013年 | 84篇 |
2012年 | 22篇 |
2011年 | 24篇 |
2010年 | 24篇 |
2009年 | 35篇 |
2008年 | 38篇 |
2007年 | 35篇 |
2006年 | 38篇 |
2005年 | 39篇 |
2004年 | 30篇 |
2003年 | 25篇 |
2002年 | 29篇 |
2001年 | 27篇 |
2000年 | 28篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 23篇 |
1996年 | 21篇 |
1995年 | 15篇 |
1994年 | 13篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1974年 | 2篇 |
1973年 | 5篇 |
排序方式: 共有895条查询结果,搜索用时 15 毫秒
731.
Changes in Isozyme Patterns During in Vitro Regeneration from Cotyledon Explants of Brassica Species
High frequency shoot regeneration from cotyledons excised from 4-d-old seedlings of Brassica campestris L. cv. M 27 and Brassica
juncea (L.) Czern. cv. Pusabold was achieved on Murashige and Skoog's (MS) medium supplemented with 1.0 mg dm-3 N6-benzyladenine (BA) and 3 % (m/v) saccharose. Rooting occurred simultaneously with shoot formation on the medium containing
1.0 mg dm-3 BA and 0.5 mg dm-3 1-naphthaleneacetic acid. Cultures of cotyledon, cotyledon derived non-differentiating calli and differentiated calli with
shoots and/or roots were analysed at different intervals for isozyme patterns of esterase and peroxidase. With the BA-induced
development of shoot and/or root from non-differentiating callus, some conspicuous isozymes appeared which indicates the involvement
of these isozymes in root and shoot development rather than in induction of morphogenesis in callus.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
732.
在从胡萝卜愈伤组织细胞中分离出两个与重力作用相关的酯酶(grEST1 和grEST2)后( 蔡伟明等1998) ,对这两个酯酶的性质作了进一步研究。发现它们具有非常独特的抗SDS的特性。脱氧胆酸盐对它们的活力有部分的抑制作用。β苯丙酸、AgNO3 和CuSO4 对它们的活力没有抑制作用。抗坏血酸和半胱氨酸对它们的活力有抑制,特别是半胱氨酸有明显的影响。分别加去污剂脱氧胆酸盐、Triton X100 和SDS的非变性电泳测得grEST1 和grEST2 的分子量分别在49 ~66 kD 和43 ~59 kD 范围附近。它们的等电点分别约为pH5 .4 和4 .9 。它们可以在40 % 硫酸铵饱和度时沉淀,并可以用这个方法将它们部分纯化 相似文献
733.
Jinfu Wang 《Insect Science》1999,6(3):271-276
Abstract The stability of resistance in the organophosphate resistant strain of Culex pipiens pallens with amplification of single gene coding for esterase B2 was determined under relaxation of insecticide selection. Insecticide resistance and amplification of esterase were both lost when strains were not homozygous for the presence of amplified gene, probably due to biological disadvantage of the esterase gene. LC50 and LC95 of chlorpyrifos for this strain were 0. 2099 mg/L and 0.9036 mg/L in the F0 generation respectively, but 0. 0207 mg/L and 2. 8027 mg/L respectively in the F16 generation. In the homozygous strain, insecticide resistance was still stable and amplification of esterase remained after 16 generations under relaxation of insecticide selection, which indicated that copy of esterase gene was not lost in the offspring of this strain. The evolution of insecticide resistance in mosquitoes is discussed. 相似文献
734.
Harry W. Eckerson Allen Oseroff Oksana Lockridge Bert N. La Du 《Biochemical genetics》1983,21(1-2):93-108
Antiserum prepared against highly purified usual human serum cholinesterase (the most common phenotype) cross-reacted identically
with the atypical serum cholinesterase. The level of circulating atypical enzyme protein, determined immunologically, was
about 30% lower when the enzyme came from an atypical rather than a usual phenotype, and the level of enzyme activity measured
enzymatically atV
max with eithero-nitrophenylbutyrate or benzoylcholine as substrate showed approximately the same degree of reduction. The average specific
activity (activity atV
max per microgram of enzyme protein) in sera from 28 usual and 20 atypical individuals did not differ significantly. These findings
suggest that the atypical enzyme not only has altered catalytic properties (K)mbut also might be synthesized more slowly, or clearedin vivo more rapidly, than the usual enzyme.
This work was supported by U.S. Public Health Service Grants NS 15871 and GM 27028 and by a grant from the Hoffmann-La Roche
Foundation. 相似文献
735.
Ralf G. Berger Friedrich Drawert Christa Kunz 《Plant Cell, Tissue and Organ Culture》1988,15(2):137-147
The time course of the activities of esterase, -galactosidase, and -glucosidase in cell sap and nutrient medium in in vitro cultured apple cells (Malus sylvestris Mill.) was studied. The corresponding isozyme patterns and the intracellular and extracellular isozyme patterns of acid phosphatase and polyphenol oxidase were compared using isozyme visualization methods adapted to ultra-thin-layer isoelectric focusing. Neither quantitative (total activity) nor qualitative (isozyme pattern) data were congruent for cell saps and nutrient media. Malate dehydrogenase, malic enzyme, and glutamate dehydrogenase occurred in cell sap only. The extracellular activities probably originate to a great part from a programmed release by intact cells. Nutrient media of plant cell cultures constitute a rich source of active plant isozymes. 相似文献
736.
L. F. M. van Zutphen M. G. C. den Bieman O. von Deimling R. R. Fox 《Biochemical genetics》1987,25(5-6):335-344
Genetic analysis of a polymorphic tissue esterase revealed a new locus (Est-6) with two alleles (Est-6
a andEst-6
b) on linkage group VI of the rabbit.Est-6 is closely linked to theEst-1,2,4 cluster. Esterase ofEst-6 is found in many organs, particularly in liver and small intestine, but not in erythrocytes and serum.Est-6 esterase hydrolyzes -naphthyl acetate and butyrate, naphthol AS-D acetate, indoxyl acetate, and butyrate as well as 5-bromoindoxyl acetate,N-acetyl-l-alanine--naphthyl ester but not 4-methylumbelliferyl acetate and fluorescein diacetate. The enzyme is inhibited by bis-p-nitrophenyl phosphate and eserine but not byp-chloromercuribenzoate. It was classified as a carboxylesterase (EC 3.1.1.1). Based on chromosomal localization, tissue distribution, substrate specificity, inhibitor sensitivity, and range ofpI's, rabbitEst-6 is assumed to be homologous with mouseEs-7.The contribution of Dr. O. von Deimling (No. 59) was supported by the Deutsche Forschungsgemeinschaft (De 315/2-2). 相似文献
737.
738.
小地老虎变态期间马氏管超微结构与酯酶活性的变化 总被引:2,自引:1,他引:1
本实验用光镜和电镜观察了小地老虎Agrotis ypsilon Rottemberg幼虫在变态期间马氏管超微结构的变化及成虫马氏管的重组过程,同时还研究了变态期马氏管酯酶的活性.结果表明:(1)变态期间马氏管外形完整,除至预蛹期隐肾复合体解体外,其余无明显变化.(2)变态期间管壁细胞变化显著.幼虫6龄末期马氏管细胞结构开始变化,主要特点为:细胞质电子密度高,充满了核糖体颗粒,微绒毛萎缩,线粒体从萎缩的微绒毛中退出进入细胞质,基膜内褶破坏.进入预蛹期幼虫马氏管细胞解体:基膜内褶、顶端微绒毛、线粒体及细胞质内的其它细胞器消失,并形成自体吞噬泡,细胞质内仅存细胞核及各种类型的液泡.但是在变态期间因底膜始终存在,故马氏管外形不变;至蛹后期,成虫马氏管细胞在原位重组,基膜内褶由浅变深,微绒毛由短变长,线粒体内嵴从无到有.(3)变态过程中羧酸酯酶和酸性磷酸酯酶的活性变化趋势基本相同,以六龄幼虫最强,预蛹期次之,蛹期最低. 相似文献
739.
Biochemical and molecular analyses of genetic variation were evaluated to address the taxonomic status of Nacobbus aberrans. Isolates from Mexico, Peru, and Argentina, cultured on tomato in the greenhouse, were analyzed with respect to isozyme and DNA marker variation. Although acid phosphatase and malate dehydrogenase revealed distinct profiles for each isolate, non-specific esterases revealed possible affinities between the Peruvian isolates and between the isolates from Mexico and Peru. Two of l 0 RAPD primers revealed affinities suggested by esterase profiles. RFLP analysis of the rDNA repeating unit with six restriction enzymes revealed identical cleavage patterns between the Peru isolates and a distinct profile shared by isolates from Mexico and Argentina. Nucleotide sequence analysis of the 5.8S rRNA coding region revealed differences among the four isolates at eight of 157 positions; sequences of the Peruvian isolates differed from each other at only one position, whereas the Mexican and Argentine isolates were identical and could be distinguished from the Peruvian isolates. A distance matrix from unweighted pairwise comparisons of the 5.8S rDNA revealed apparent elevated intraspecific divergence in N. aberrans comparable to intergeneric divergence between Heterodera and Globodera. Analysis of additional N. aberrans isolates from throughout the distribution range should help determine the full extent of intraspecific genetic variation that underlies the phenotypic and morphologic diversity of the genus. 相似文献
740.
Ferulic andp-coumaric acid can be separated from their corresponding aliphatic methyl esters by capillary zone electrophoresis, which allows the convenient determination of feruloyl andp-coumaroyl esterase activities using synthetic esters as substrates. A feruloyl-containing sugar ester from wheat bran was also efficiently separated and used as substrate for the enzyme assays.Penicillium expansum was shown to produce feruloyl/p-coumaroyl esterase activity when grown on wheat bran in solid-state culture.The authors are with the Food Microbiology Research Division, Department of Agriculture for Northern Ireland, Newforge Lane, Belfast BT9 5PX, UK; A.M. McKay is also affiliated with the Department of Food Science (Microbiology), The Queen's University of Belfast, Newforge Lane, Belfast BT9 5PX, UK. 相似文献