全文获取类型
收费全文 | 2632篇 |
免费 | 275篇 |
国内免费 | 1篇 |
出版年
2021年 | 40篇 |
2020年 | 22篇 |
2019年 | 26篇 |
2018年 | 46篇 |
2017年 | 39篇 |
2016年 | 59篇 |
2015年 | 70篇 |
2014年 | 98篇 |
2013年 | 102篇 |
2012年 | 150篇 |
2011年 | 123篇 |
2010年 | 98篇 |
2009年 | 74篇 |
2008年 | 94篇 |
2007年 | 117篇 |
2006年 | 106篇 |
2005年 | 106篇 |
2004年 | 99篇 |
2003年 | 82篇 |
2002年 | 75篇 |
2001年 | 81篇 |
2000年 | 77篇 |
1999年 | 69篇 |
1998年 | 43篇 |
1997年 | 31篇 |
1996年 | 33篇 |
1995年 | 29篇 |
1994年 | 24篇 |
1993年 | 23篇 |
1992年 | 56篇 |
1991年 | 38篇 |
1990年 | 38篇 |
1989年 | 51篇 |
1988年 | 34篇 |
1987年 | 37篇 |
1986年 | 44篇 |
1985年 | 38篇 |
1984年 | 43篇 |
1983年 | 31篇 |
1982年 | 23篇 |
1981年 | 19篇 |
1980年 | 25篇 |
1979年 | 27篇 |
1978年 | 25篇 |
1976年 | 22篇 |
1975年 | 23篇 |
1974年 | 25篇 |
1973年 | 21篇 |
1972年 | 36篇 |
1971年 | 20篇 |
排序方式: 共有2908条查询结果,搜索用时 31 毫秒
101.
M J McDonald R W Noble V S Sharma H M Ranney J H Crookston J M Schwartz 《Journal of molecular biology》1975,94(2):305-310
Lepore hemoglobins result from crossovers between normal beta and delta chain genes. Structural investigation of two newly discovered examples of Lepore hemoglobins revealed one of them to be structurally identical to hemoglobin Lepore Hollandia α2Aδ22 -x- β50, a rarely occurring Lepore variant, while the second had the structure of hemoglobin Lepore Boston α2Aδ87 -x- β116. Studies of the equilibrium and kinetic properties of the liganding reactions of these two Lepore hemoglobins, which differ only in three amino acid residues, and comparison of these with the known properties of hemoglobin A1 (α2β2) and hemoglobin A2 (α2δ2) have been carried out. A high value of n, the Hill coefficient, indicating normal heme-heme interaction, was observed in each hemoglobin along with a normal Bohr effect. However, a slight but definite increase in oxygen affinity was observed for each Lepore hemoglobin. Furthermore, kinetic studies indicated a slight but consistently increased rate of ligand combination and a somewhat decreased rate of oxygen dissociation for hemoglobins Lepore Hollandia and Lepore Boston at pH 7 and 20 °C. Apparently, the higher oxygen affinity of these Lepore hemoglobins over those of the normal hemoglobins A1 and A2 reflects changes of sequence that are common to both types of hemoglobin Lepore. 相似文献
102.
I C McDonald D E Overland R A Leopold M E Degrugillier P B Morgan H C Hofmann 《The Journal of heredity》1975,66(3):137-140
Genetic data were used to compare the structure of native house fly populations collected in North Dakota, Texas, and Florida. Recombination studies with mutant markers on chromosomes 3 and 4 indicated a lack of inversion polymorphism among the three populations in those areas of the genetic map studied. Significant differences were observed among flies from the three regions with regard to the frequency of 1) females that produced only male progeny, and 2) male-determining 3rd chromosomes (IIIm chromosomes). However, the North Dakota and Texas flies were more similar to each other than to the Florida flies since populations from the two former areas possessed a low frequency of both male-producing females and IIIm chromosomes; in contrast, the Florida population was void of females that produced males only and a high percentage if not all Florida males appeared to possess the IIIm male-determining mechanism. Tests for recessive lethal 3rd chromosomes showed that there was no significant difference in the frequency of lethal factors recovered from the North Dakota and Texas flies; the presence of IIIm chromosomes in Florida males precluded the recovery of lethal factors from this population by the method employed. The data suggest that house fly strains to be employed in genetic control programs should 1) originate from target control areas to avoid possible behavioral differences existing among flies from different locales, 2) be initiated with as many flies as possible to provide a background for the maintenance of variability, and 3) be renewed periodically with field-collected material since the genotype may be capable of rapid reorganization in response to laboratory selection pressures. 相似文献
103.
104.
105.
106.
107.
108.
109.
Plasmid transformation of Bacillus sphaericus 1593 总被引:3,自引:0,他引:3
Plasmids pUB110 and pBC16 were introduced by protoplast transformation into the entomocidal bacterium Bacillus sphaericus 1593. Transformants expressed the antibiotic resistance determinants present on the plasmid and exhibited sporulation frequencies and larvicidal toxicities which were equivalent to those characteristic of the parent strain. These transformations constitute the first report of genetic transfer in B. sphaericus. 相似文献
110.