全文获取类型
收费全文 | 420篇 |
免费 | 46篇 |
出版年
2021年 | 10篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2017年 | 6篇 |
2016年 | 11篇 |
2015年 | 10篇 |
2014年 | 16篇 |
2013年 | 28篇 |
2012年 | 20篇 |
2011年 | 31篇 |
2010年 | 14篇 |
2009年 | 13篇 |
2008年 | 25篇 |
2007年 | 17篇 |
2006年 | 31篇 |
2005年 | 24篇 |
2004年 | 19篇 |
2003年 | 18篇 |
2002年 | 19篇 |
2001年 | 12篇 |
2000年 | 14篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1971年 | 2篇 |
1968年 | 3篇 |
1966年 | 2篇 |
1965年 | 3篇 |
排序方式: 共有466条查询结果,搜索用时 31 毫秒
1.
2.
Hadar Kless Yaron Sitrit Ilan Chet Amos B. Oppenheim 《Molecular & general genetics : MGG》1989,217(2-3):471-473
Summary A λ phage DNA library ofSerratia marcescens was constructed and a clone carrying the gene coding for chitobiase (E.C.3.2.1.29) was isolated and characterized. Deletion
analysis limited the cloned region to 4.5 kb that is capable of efficient expression of chitobiase.Escherichia coli cells harboring a plasmid carrying the cloned gene express chitobiase constitutively. The molecular weight of the protein
is about 95000 daltons. In exponentially growingE. coli cells the chitobiase enzyme was found to be secreted into the periplasm. 相似文献
3.
Sequence of gonadal events and oestradiol levels in Sparus aurata (L.) under two photoperiod regimes
Individually tagged Sparus aurata were kept in tanks with running sea water (21°± 2°C) during their second and third years of life. Gonads were biopsied and blood was sampled at monthly intervals. Thirteen of 50 fish in the second year and 24 of 35 fish in the third year were phenotypically females. Fish kept under 16L/8D photoperiod from July 1981 to August 1982 did not reach maturation; waves of initial ovarian growth alternated with waves of atresia. When photoperiod was shortened as from August 1982, gonadal development commenced within a month and proceeded at a rate higher than that of the control fish reared under natural photoperiod. Under natural photoperiod oestradiol serum levels (E2 ) were relatively low during the resting phase, May-October (108 ± 11 pg ml−1 ), and during the late vitellogenic phase (502 ± 76 pg ml−1 ). High levels (1669 ± 312 and 1240 ± 172pg ml−1 ) occurred during the early vitellogenic and the maturational phases. The high level of E2 during the spawning season of S. aurata is explained by earlier reports indicating a prolonged breeding season with daily release of eggs, and alternating daily surges of E2 and 17α, 20β, dihydroxy-4-pregnen-3-one, possibly a 'maturational progestin' in this fish. In phenotypic males, E2 was highest during early spermatogenic phases (745 ± 142pg ml−1 ) but was low (155 ± 11 pg ml−1 ) in males with running sperm. 相似文献
4.
The potato tuber moth (PTM),Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is a major pest of processing tomatoes,Lycopersicon esculentum Mill. (Solanaceae), in Israel. The larvae penetrate the tomato fruit through the stem end and present a serious threat to
crop quality. Foliage and fruit samples were taken in nine commercial tomato fields located in Israel's three main tomato
growing areas, two of which are potato growing areas as well. PTM was not found where potatoes were absent. Potato harvest
in nearby fields was found to be the most significant factor affecting seasonal trends in PTM population density in tomatoes.
All four larval instars were found in foliage on all sampling dates. Significantly higher proportions of first instars were
found during the population density increase which followed potato harvest. Damaged fruits did not contain first instar larvae,
indicating that PTM never undergoes complete development within tomato fruit. Fruit damage levels at harvest were positively
correlated to the peak mean population densities on foliage and the date they were observed. In tomato fields not adjacent
to potatoes, infestation was first observed at the edge of the field. Both before and after the potato harvest in nearby fields,
population density at the edge of the field was significantly higher than at the center. In tomato fields adjacent to potatoes,
no significant differences were found between population densities at the edge and center before the potatoes were harvested.
After the potato harvest, population density at the center of tomato fields was higher than at the edge.
Deceased, October 1988 相似文献
5.
6.
Role of intron-contained sequences in formation of moloney murine leukemia virus env mRNA. 总被引:24,自引:5,他引:19
Formation of the Moloney murine leukemia virus envelope mRNA involves the removal of a 5,185-base pair-long intron. Deletion analysis of two Moloney murine leukemia virus-derived expression vectors revealed the existence of two short regions within the viral intron which are required for the efficient formation of the spliced RNA species. One region was present upstream from the 3' splice junction, extended at least 85 nucleotides beyond the splice site, and was not more than 165 nucleotides long. As yeast polymerase II introns, the Moloney murine leukemia virus intron contains the sequence 5'-TACTAAC-3' 15 nucleotides upstream from the 3' splice site. A second region located in the middle of the intron, within a 560-nucleotide-long sequence, was also essential for formation of the spliced RNA species. The efficient splicing of the env mRNA in the absence of expression of viral genes raises the possibility that similar mechanisms are used to remove introns of (some) cellular genes. 相似文献
7.
Ruth Melamud Martin Risk H. Gilboa 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,678(3):311-315
Relaxation time measurements T1 and T2 of sodium in Halobacterium halobium pellets were carried out at two frequencies. From those measurements, combined with intensity measurements of the sodium in the system, estimation of the properties of the sodium ions in the system was carried out. It is suggested that three types of sodium ions are present in the bacterial pellet. (A) The extracellular sodium with properties of free solution and (B) sodium which is in the pericellular volume between the cell wall and the cell membrane. There is an exchange between type A and type B sodium. The type B sodium has (e2qQ)/h = 3.7 · 107 rad/s, τcB = 5.2 · 10−6 s and τB = 1 · 10−3 s. The sodium of type C is bound inside the cell and undetected. It's concentration inside the cell is assumed to be 1.9 M. 相似文献
8.
A detailed model of reverse transcription and tests of crucial aspects 总被引:48,自引:0,他引:48
9.
10.
Gingold-Belfer Rachel Levy Sigal Layfer Olga Pakanaev Lea Niv Yaron Dickman Ram Perets Tsachi Tsadok 《Probiotics and antimicrobial proteins》2020,12(1):112-118
Probiotics and Antimicrobial Proteins - Lactose intolerance is a common condition caused by lactase deficiency and may result in symptoms of lactose malabsorption (bloating, flatulence, abdominal... 相似文献