全文获取类型
收费全文 | 194篇 |
免费 | 20篇 |
国内免费 | 1篇 |
出版年
2021年 | 4篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 1篇 |
2015年 | 10篇 |
2014年 | 7篇 |
2013年 | 7篇 |
2012年 | 19篇 |
2011年 | 9篇 |
2010年 | 9篇 |
2009年 | 14篇 |
2008年 | 6篇 |
2007年 | 9篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 6篇 |
2002年 | 1篇 |
2001年 | 10篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1991年 | 6篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1959年 | 1篇 |
1955年 | 1篇 |
1953年 | 1篇 |
排序方式: 共有215条查询结果,搜索用时 15 毫秒
1.
Summary The use of reticulated polyurethane foam as a support material for the immobilization of methanogenic associations and its application to the anaerobic treatment of fine particulate solid wastes was investigated. The colonization of polyurethane support particles in a continuous upflow reactor fed on a mixture of acetate, propionate and butyrate, was both rapid and dense. The combination of rumen microorganisms and colonized support particles in a two-phase digester resulted in an efficient anaerobic decomposition of papermill sludge. 相似文献
2.
Differential maintenance of penile responses and copulatory behavior by gonadal hormones in castrated male rats 总被引:4,自引:2,他引:2
Sexually experienced male rats were castrated and immediately received implants of Silastic tubing containing either testosterone (T), dihydrotestosterone (DHT), estradiol (E), or nothing (blank). The ability of these hormone treatments to maintain precastration levels of copulatory behavior and ex copula penile responses was assessed for 40 days after castration. Throughout the study T- and E-treated males, but not males with DHT or blank implants, maintained normal copulatory behavior. In contrast males treated with T and DHT, but not E or blanks, maintained penile responses ex copula. In blank-treated males, penile-response latencies increased more rapidly than did intromission latencies. These results, together with those of previous studies, appear to rule out a role for estradiol and reinforce the role of androgens in the activation of rats' penile-response potential ex copula. Similarly, the results support the conclusion that in castrated male rats estradiol treatment is sufficient for the activation of masculine copulatory behavior, and that the penile actions necessary for intromission are not dependent on androgen. Thus, the evocability of penile actions and their relative androgen dependence are context sensitive. 相似文献
3.
Selected and counterselected oligodeoxynucleotide sequences were identified in the total sequence of bacteriophage T7 DNA using a statistical criterion derived for a probability model of the Markov chain type. All extremely rare tetra- and pentadeoxynucleotides are (or contain) recognition sequences for the Escherichia coli DNA methylases dam or dcm. Most of the 37 hexadeoxynucleotides absent from T7 DNA are recognition sequences for type II modification/restriction enzymes of E. coli or related species. In contrast to most restriction sites counterselected during evolution, the EcoP1 site GGTCT occurs 126 times in the T7 genome, and phage T7 replication is severely repressed in P1-lysogenic host cells. We demonstrate that the frequency of the EcoP1 site is determined by that of the overlapping recognition sites for T7 primase, an essential phage enzyme. The recognition site of a type III enzyme, EcoP15, is also not counterselected. In T7 DNA all 36 EcoP15 sites are arranged in such a manner that the sequence CAGCAG is confined to the H strand, the complementary sequence CTGCTG to the L strand. This "strand bias" is highly significant and, therefore, very probably selected. A functional relation between this strand bias and the refractive behaviour of phage T7 to EcoP15 restriction is suspected. 相似文献
4.
Photobilirubin II, a stereoisomer of bilirubin, binds to human serum albumin at a single binding site (K = 2.2 x 10(6)M-1), presumably the high-affinity bilirubin-binding site. Binding in the secondary (class II) binding sites is of minor importance. The results are discussed with respect to photometabolism of bilirubin and as a possible source of error in the determination of bilirubin unbound to albumin. 相似文献
5.
Epitope mapping of antibodies directed against hypervariable region 1 in acute self-limiting and chronic infections due to hepatitis C virus. 总被引:8,自引:0,他引:8 下载免费PDF全文
Epitopes of hypervariable region 1 (HVR1) were mapped by enzyme-linked immunosorbent assay using follow-up sera of patients, all of whom were infected with the same isolate of hepatitis C virus (HCV). Our results suggest that (i) an early appearance (up to month 13 postinfection) of antibodies directed to the N terminus of HVR1 is associated with acute self-limiting infections of HCV and (ii) isolate-independent antibodies which are mainly directed to the C terminus of HVR1 seem to persist in chronically infected patients. The relevance of HVR1-specific antibodies for neutralization was evaluated by characterization of a rabbit serum. 相似文献
6.
7.
The method of determination of Redox potentials of radicals, using the pulse radiolysis technique, is outlined. The method is based on the determination of equilibrium constants of electron transfer reactions between the radicals and appropriate acceptors. The limitations of this technique are discussed. The redox potentials of several quinones-semiquinones are calculated, as well as the standard redox potential of the peroxy radical. EO2/O2=-0.33 V and the redox oxidation properties of the peroxy radical in various systems and pH are discussed. The value determined for the redox potentials of O2/O2 is higher by more than 0.2 V than earlier estimates, which has important implications on the possible role of O2 in biological processes of O2 fixation. 相似文献
8.
9.
We analyzed the evolution of height in Colombia of cohorts born in the period 1965–1990 by ethnic groups. We found that Afro-Colombian men and women were the tallest: 6 cm taller than indigenous people and 2 cm taller than the rest of the population. We also found that the height gap between Afro-Colombians and others decreased during the period under study by 0.7 cm for both men and women. While improvements were noticeable among the Afro-Colombians and those who chose not to be classified by ethnicity, in the case of the indigenous population only female cohorts registered an average-height increase of 1.5 cm. Moreover, we found that indigenous Colombians were more likely than other ethnic groups to experience an increase in biological well-being as a consequence of an improvement in their socio-economic status, thereby reducing the average-stature gap between them and the rest of the population by 2.1 and 3.6 cm for men and women, respectively. 相似文献
10.