全文获取类型
收费全文 | 1752篇 |
免费 | 124篇 |
出版年
2023年 | 8篇 |
2022年 | 11篇 |
2021年 | 21篇 |
2020年 | 17篇 |
2019年 | 21篇 |
2018年 | 28篇 |
2017年 | 26篇 |
2016年 | 36篇 |
2015年 | 41篇 |
2014年 | 67篇 |
2013年 | 106篇 |
2012年 | 107篇 |
2011年 | 81篇 |
2010年 | 55篇 |
2009年 | 42篇 |
2008年 | 85篇 |
2007年 | 103篇 |
2006年 | 76篇 |
2005年 | 65篇 |
2004年 | 68篇 |
2003年 | 71篇 |
2002年 | 59篇 |
2001年 | 49篇 |
2000年 | 71篇 |
1999年 | 43篇 |
1998年 | 15篇 |
1997年 | 12篇 |
1996年 | 14篇 |
1995年 | 13篇 |
1992年 | 43篇 |
1991年 | 42篇 |
1990年 | 44篇 |
1989年 | 43篇 |
1988年 | 44篇 |
1987年 | 27篇 |
1986年 | 24篇 |
1985年 | 20篇 |
1984年 | 17篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1974年 | 6篇 |
1972年 | 6篇 |
1971年 | 10篇 |
1969年 | 9篇 |
1968年 | 10篇 |
1967年 | 6篇 |
1966年 | 8篇 |
排序方式: 共有1876条查询结果,搜索用时 15 毫秒
51.
A stable Escherichia coli-mycobacteria shuttle vector 'pSO246' in Mycobacterium bovis BCG 总被引:1,自引:0,他引:1
Sohkichi Matsumoto Mikio Tamaki Hideharu Yukitake Takemitu Matsuo Manko Naito Hiroshi Teraoka Takeshi Yamada 《FEMS microbiology letters》1996,135(2-3):237-243
Abstract The most widely used plasmid vector system in mycobacteria is based on pAL5000 from Mycobacterium fortuitum . The derivatives of the pAL5000-based shuttle vectors between Escherichia coli and mycobacteria, which we have utilized to secrete recombinant antigens, were generated. The stability of the vectors was assessed in Mycobacterium bovis BCG (BCG). The plasmid vector pSO246 was stable in BCG for at least 50 generations. 相似文献
52.
Conversion of the Salmonella phase 1 flagellin gene fliC to the phase 2 gene fljB on the Escherichia coli K-12 chromosome. 总被引:5,自引:2,他引:3 下载免费PDF全文
The Escherichia coli-Salmonella typhimurium-Salmonella abortus-equi hybrid strain EJ1420 has the two Salmonella flagellin genes fliC (antigenic determinant i) and fljB (determinant e,n,x) at the same loci as in the Salmonella strains and constitutively expresses the fliC gene because of mutations in the genes mediating phase variation. Selection for motility in semisolid medium containing anti-i flagellum serum yielded 11 motile mutants, which had the active fliC(e,n,x) and silent fljB(e,n,x) genes. Genetic analysis and Southern hybridization indicated that they had mutations only in the fliC gene, not in the fljB gene or the control elements for phase variation. Nucleotide sequence analysis of the fliC(e,n,x) genes from four representative mutants showed that the minimum 38% (565 bp) and maximum 68% (1,013 bp) sequences of the fliC(i) gene are replaced with the corresponding sequences of the fljB(e,n,x) gene. One of the conversion endpoints between the two genes lies somewhere in the 204-bp homologous sequence in the 5' constant region, and the other lies in the short homologous sequence of 6, 8, or 38 bp in the 3' constant region. The conversions include the whole central variable region of the fljB gene, resulting in fliC(e,n,x) genes with the same number of nucleotides (1,503 bp) as the fljB gene. We discuss the mechanisms for gene conversion between the two genes and also some intriguing aspects of flagellar antigenic specificities in various Salmonella serovars from the viewpoint of gene conversion. 相似文献
53.
54.
Sakaba Tomoka Soejima Akiko Fujii Shinji Ikeda Hajime Iwasaki Takaya Saito Hiroaki Suyama Yoshihisa Matsuo Ayumi Kozhevnikov Andrey E. Kozhevnikova Zoya V. Wang Hongfeng Wang Siqi Pak Jae-Hong Fujii Noriyuki 《Journal of plant research》2023,136(4):437-452
Journal of Plant Research - A group of temperate grassland plant species termed the “Mansen elements” occurs in Japan and is widely distributed in the grasslands of continental East... 相似文献
55.
H. Ikezawa K. Tameishi A. Yamada H. Tamura K. Tsukamoto Y. Matsuo K. Nishikawa 《Amino acids》1995,9(3):293-298
Summary Chemical modifications suggested that acidic amino acids such as aspartic and glutamic acids are involved in the active sites ofBacillus cereus sphingomyelinase. Among aspartic acid residues in the conserved regions of this enzyme, Asp-126, Asp-156, Asp-233 and Asp-295 were converted to glycine by site-directed mutagenesis. According to prediction on structural similarity to pancreatic DNase I, His-151 and His-296 were also converted to alanine. The Asp and His mutants, D126G, D156G, D233G, D295G, H151A and H296A, were produced inBacillus brevis 47, a protein-hyperproducing strain. The catalytic activities of D295G, H151A and H296A were completely abolished, and sphingomyelin-hydrolyzing activity of D126G or D156G was reduced by more than 50%. The activity of D126G towardp-NPPC was comparable to that of the wild-type, while D156G catalyzed the hydrolysis of HNP andp-NPPC more efficiently than the wild-type. Hemolytic activities of the mutants were parallel to their sphingomyelin-hydrolyzing activities. 相似文献
56.
Carbon dioxide treatment of persimmon fruit (Diospyros KakiL., cv. "Hiratanenashi" astringent type) at 20?C for 24 hr,at 30?C for 12 hr, or at 40?C for 6 hr followed by storage inair at 30?C for 3 days produced de-astringent fruit of excellentquality without abnormal softening. The induction process inthe anaerobic atmosphere had a Q10 of ca. 2.0 and the subsequentde-astringency process, which proceeded either in air or carbondioxide, had Q10 of ca. 1.4. During the short gas treatment(at 40?C for 6 hr) the ethanol content increased rapidly andreached a maximum of 28.0 mg and the acetaldehyde content graduallyreached 0.443 mg per fruit, whereas the soluble tannin(s) contentdecreased rapidly to two-thirds of its initial level. Therewas a lag period of 3 hr in the decrease of soluble tannin(s).Dimedon and sodium bisulfite, as well as sodium fluoride, inhibitedde-astringency. The mechanisms of removing astringency in thisfruit are discussed. (Received June 3, 1976; ) 相似文献
57.
Matsuo Tsukasa 《Journal of plant research》1983,96(2):127-133
The late-glacial logistic decline of spruce (Picea) populations (the intrinsic growth rate,r in yr?1=?0.0015) was progressively delayed toward cooler sites in Japan; spruce populations expanded asymptotically (r=0.0040?0.0045) in Sakhalin early in the Holocene. Such a time-transgressive range shift in spruce distribution, covering a wide latitudinal range (ca. 35–50°N), implies that the regional temperature rise was not instantaneous, but was rapid, being 0.0015–0.0025 C yr?1 from 13,000 to 10,000 years B.P. Spruce populations increased in response to Neoglacial cooling only at the margin of its distribution (r=0.0036), but then declined logistically 1,000 years B.P. (r=?0.0022). 相似文献
58.
Protein kinase C (PKC) from a human megakaryoblastic leukemic cell line (MEG-01) was resolved into two fractions by hydroxyapatite column chromatography, which are indistinguishable from the brain type II (beta I/beta II) and type III (alpha) subspecies, by biochemical and immunoblot analysis. In the presence of both phosphatidylserine and diacylglycerol, several free unsaturated fatty acids (FFA's), such as arachidonic, oleic, linoleic and linolenic acids, further enhanced the enzyme activation, and allowed the enzyme to exhibit almost full activity at nearly basal levels of Ca2+ concentration. The concentration of unsaturated FFA's giving rise to the maximum enzyme activation was around 2 x 10(-5) M. Palmitic and stearic acids were inactive. The result implies that, in addition to diacylglycerol, the receptor-mediated release of unsaturated FFA's from membrane phospholipids may also take part in the activation of PKC. 相似文献
59.
M Nakazato S Ikeda K Shiomi S Matsukura K Yoshida H Shimizu T Atsumi K Kangawa H Matsuo 《FEBS letters》1992,306(2-3):206-208
A novel variant transthyretin which contains a leucine-for-valine substitution at position 30 was isolated and identified in the serum of a patient with familial amyloidotic polyneuropathy (FAP). The amino acid substitution was proven to result from a guanine-to-cytosine change at the first base of codon 30 located in exon 2 in the mutated transthyretin gene by restriction fragment length analysis on the amplified transthyretin gene using Cfr13 I. The study indicates that the point mutation of the transthyretin gene is a cause of the disorder. 相似文献
60.
Toshiaki Nagafuji Tohru Koide Tatsuo Miyauchi Michiaki Takato 《Journal of neurochemistry》1992,58(1):362-368
In search of factors mitigating the final outcome of ischemic and epileptic brain damage, we tested a novel dibenzoxazepine derivative (BY-1949), as the compound has been shown to be effective under these two conditions. First, using rat brain, we assessed whether or not BY-1949 affects the Na+,K(+)-ATPase activity. Although in vitro applications of either BY-1949 or its three major metabolites did not cause any apparent effects, both acute and chronic oral administrations of the compound (10 mg/kg) invariably increased the Na+,K(+)-ATPase activity in the synaptosomal plasma membranes by increasing Vmax values. Second, it was shown by this study that the drug treatment caused marked increases in the uptake of both glutamic acid and gamma-aminobutyric acid into the synaptosomes. These results suggest that the activity against ischemic/epileptic brain damage by BY-1949 is explicable, at least partly, in terms of improvement of ionic derangements across the neural membranes via Na+,K(+)-ATPase activation. 相似文献