全文获取类型
收费全文 | 1006篇 |
免费 | 108篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2017年 | 8篇 |
2016年 | 15篇 |
2015年 | 44篇 |
2014年 | 43篇 |
2013年 | 58篇 |
2012年 | 81篇 |
2011年 | 57篇 |
2010年 | 57篇 |
2009年 | 30篇 |
2008年 | 63篇 |
2007年 | 66篇 |
2006年 | 62篇 |
2005年 | 48篇 |
2004年 | 50篇 |
2003年 | 51篇 |
2002年 | 49篇 |
2001年 | 13篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 14篇 |
1997年 | 17篇 |
1996年 | 16篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 14篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 6篇 |
排序方式: 共有1114条查询结果,搜索用时 15 毫秒
1.
2.
Frédéric Boccard Jean-Luc Pernodet Annick Friedmann Michel Guérineau 《Molecular & general genetics : MGG》1988,212(3):432-439
Summary
Streptomyces ambofaciens strain ATCC23877 contains the 11.1 kb plasmid pSAM2 stably integrated into its chromosome. This plasmidic sequence is able to loop out and to be transferred at high frequency to S. lividans where it is found simultaneously as both free and integrated plasmid. When a UV derivative of strain ATCC23877 (strain ATCC15154) is used, the resident copy of pSAM2 can be transferred to S. lividans, but only the integrated form is found in this strain. In both cases, the integration occurs at a unique chromosomal region through the same plasmidic integration site as that in strain ATCC23877. The resident copy of strain ATCC15154 can also be transferred at low frequency to S. ambofaciens DSM40697 (devoid of any pSAM2 sequence). In this case, as several copies of pSAM2 are integrated, the integration pattern is complicated. Integration of a complete pSAM2 sequence in this strain occurs in a region that hybridizes with the integration zones of S. lividans and of S. ambofaciens strain ATCC23877. Comparison of the cloned integration zone of S. lividans before and after the integration event showed that the restriction pattern of the resident pSAM2 in strain ATCC15154 is similar to that of the free form of pSAM2 found naturally in another UV derivative of strain ATCC23877 (strain JI3212). 相似文献
3.
Groups of male Alderley Park rats were dosed concomitantly with 2-acetylaminofluorene (2AAF) by gavage at doses between 0.01 mg/kg and 40 mg/kg, and livers sampled 2-72 h later. The liver of one group of animals was perfused to yield hepatocytes which were assayed in vitro for unscheduled DNA synthesis (UDS) via incorporation of tritiated thymidine and autoradiography. DNA was extracted from the livers of the other group and DNA adduct levels determined using the 32P-postlabelling technique. The major C-8 2-aminofluorene/guanosine adduct and 3 minor adducts were quantitated, enabling the relative sensitivity of the 2 techniques to be compared. A dose- and time-related UDS response was observed, which, at the most sensitive time-point (12 h) enabled DNA repair to be discerned at a dose level of 0.1-1 mg/kg of 2AAF, a response classified as formally positive at 5 mg/kg 2AAF. Only the C-8 adduct, as determined by 32P-postlabelling, was discernible at 0.01 mg/kg of 2AAF, although other adducts were visible on autoradiograms at higher dose levels. It is concluded that as part of a well-defined dose response, UDS can be discerned with confidence for doses of 2AAF between approximately 0.1 and 5 mg/kg, and DNA adducts for doses of 2AAF between approximately 0.01 and 1 mg/kg. Discernible UDS for 2AAF in the rat liver is apparent at approximately 13 DNA (total) adducts/10(8) nucleotides, or approximately 8 DNA (C-8) adducts/10(8) nucleotides. The presumed C-8 2-acetylaminofluorene/guanosine adduct, prepared by reaction of 2-acetoxy-2-acetylaminofluorene (2AAAF) with DNA, was a significant but unreliable marker of 2AAF/DNA adducts in the rat liver in vivo. DNA repair did not appear to remove DNA adducts selectively, and adducts remained in DNA when discernible DNA repair had ceased. 相似文献
4.
Summary Semi-thin sections of three-dimensional reaggregates from adult female rat pituitary, cultured in serum-free defined medium, were stained for prolactin, gonadotropin, thyrotropin, growth hormone and S-100, using the double immunolabelling technique. The frequency of juxtaposition between lactotrophs and gonadotrophs was enumerated and compared with the expected frequency at random distribution of polygonal cell profiles in a hexagonal configuration. The proportions of lactotrophs and gonadotrophs in the aggregate sections were determined using stereometrical analysis. The observed frequency of juxtaposition did not differ significantly from the expected frequency. Hence, no reason was found to assume a selective adhesion between lactotrophs and gonadotrophs in adult female rat pituitary reaggregates. A constant proportion of lactotrophs was found to meet the criteria of a cup-shaped morphology, and 70%±9% (mean ±S.D.) of these so-called cupshaped lactotrophs were found to be juxtaposed at their concave side to gonadotrophs. Administration of 0.01 nM 17-oestradiol to the culture medium resulted in a significant reduction of the proportion of cup-shaped lactotrophs but did not affect the selectivity of juxtaposition to gonadotrophs. The selectivity of juxtaposition between cup-shaped lactotrophs and gonadotrophs may be the morphological correlate of the functional relationship between these cells, which are known to be involved in an intra-pituitary paracrine communication system. 相似文献
5.
6.
M E Lefevre D D Joel G Schidlovsky 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1985,179(4):522-528
Conventional and germfree mice ingested a suspension of 2-micron latex particles in drinking water for a 15-day period. Number and distribution of intestinal Peyer's patches did not differ significantly in the two types of mice. Cleared Peyer's patches were compared with regard to size and particle content. The location of particles within Peyer's patch follicles of germfree mice was similar to that of conventional mice, but the latter had significantly larger follicles and greater accumulations of latex particles. Latex concentration varied with patch location. Proximal patches contained the majority of particles in germfree mice, whereas particles were most abundant in distal patches of conventional mice. The results show that particle uptake into Peyer's patches takes place even in the complete absence of bacteria in the gut. 相似文献
7.
Recognition sites for a membrane-derived DNA binding protein preparation in the E. coli replication origin 总被引:11,自引:0,他引:11
Annick Jacq Masamichi Kohiyama Heinz Lother Walter Messer 《Molecular & general genetics : MGG》1983,191(3):460-465
Summary The DNA binding protein B' preparation, isolated from the membrane of E. coli, recognizes two sites, one of which is locatd in the minimum oriC (35–270 bp) and the other between base pairs 417 and 488. Recognition is only possible when restriction fragments containing these sites are in single-stranded state. At the first site the strand reading 3OH-5P in the direction of the E. coli genetic map is recognized, at the second site the 5P-3OH strand. 相似文献
8.
Claude Lefevre 《Bulletin of mathematical biology》1983,45(1):11-20
This paper is concerned with a generalization of the simple epidemic model in which the infective population is partitioned
intom classes, each of specific infectiousness. Attention is restricted, however, to the case where all the meeting rates between
two individuals are equal to each other. Both deterministic and stochastic versions are examined. In either case the development
in time of the epidemic process is investigated by exploiting a connection with the standard simple epidemic model. Finally,
it is shown that the technique used also applies to a similar model for the spread of information. 相似文献
9.
10.