全文获取类型
收费全文 | 11690篇 |
免费 | 800篇 |
国内免费 | 258篇 |
出版年
2024年 | 10篇 |
2023年 | 84篇 |
2022年 | 186篇 |
2021年 | 345篇 |
2020年 | 268篇 |
2019年 | 324篇 |
2018年 | 370篇 |
2017年 | 308篇 |
2016年 | 511篇 |
2015年 | 669篇 |
2014年 | 749篇 |
2013年 | 887篇 |
2012年 | 1051篇 |
2011年 | 1005篇 |
2010年 | 654篇 |
2009年 | 509篇 |
2008年 | 736篇 |
2007年 | 628篇 |
2006年 | 547篇 |
2005年 | 492篇 |
2004年 | 513篇 |
2003年 | 359篇 |
2002年 | 340篇 |
2001年 | 179篇 |
2000年 | 145篇 |
1999年 | 151篇 |
1998年 | 86篇 |
1997年 | 88篇 |
1996年 | 65篇 |
1995年 | 62篇 |
1994年 | 48篇 |
1993年 | 32篇 |
1992年 | 54篇 |
1991年 | 32篇 |
1990年 | 24篇 |
1989年 | 26篇 |
1988年 | 26篇 |
1987年 | 23篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 21篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1973年 | 10篇 |
1969年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 687 毫秒
1.
Food availability is important to the dynamics of animal social organizations or populations. However, the role of winter
food availability in animal population dynamics is still controversial. We carried out an experimental study to test Lack’s
hypothesis that reduced food in winter limits survival and spring numbers of breeding individuals of social groups, using
the Mongolian gerbil (Meriones unguiculatus) as model species. We established 24 gerbil social groups in 24, 10 × 10 m, pens in September 2008. We provided wheat seeds
as supplemental food in 12 enclosures from September 2008 to March 2009; the other 12 enclosures, not provided with supplemental
food, served as controls. We live-trapped gerbils at a 2-week interval from September to April. Supplemental food during winter
increased biweekly survival by 10% relative to that in control groups. Only four control social groups survived to the end
of our study whereas all 12 food-supplemented social groups survived through our study period. Supplemental food also increased
cumulative numbers of recruits and group sizes of gerbils. We conclude that winter food availability limits winter survival
and spring social groups or population sizes of Mongolian gerbils. 相似文献
2.
An interspecific somatic hybrid between Actinidia chinensis and Actinidia kolomikta and its chilling tolerance 总被引:2,自引:0,他引:2
Protoplasts isolated from cotyledon-derived callus of Actinidia chinensisPlanch. var. chinensis (2N=2x=58) were fused with mesophyll protoplasts of Actiniadia kolomikta(Maxim. et Rupr.) Maxim (2N=2x=58) using a PEG method. Plantlets were regenerated from the fusion product clone 11. RAPD analyses, chromosome numbers of root tip cells and fluorescence peak position of leaf nuclei confirmed that clone 11 was an interspecific somatic hybrid (2N=4x=116) between A. chinensis and A. kolomikta. The chilling tolerance of the somatic hybrid was tested with in vitro leaves at low temperatures. Based on data of leaf thickness, electroconductivity, proline levels, malondialdehyde content and activity of superoxide dismutase, dendrogram cluster analysis suggested that the interspecific somatic hybrid was similar to A. kolomikta, and might have a higher capacity of cold resistance than A. chinensis. 相似文献
3.
Sung Ho Son Sung Mee Choi Kum Boo Choi Yun Hee Lee Dea Sook Lee Myung Suk Choi Young Goo Park 《Biotechnology and Bioprocess Engineering》1999,4(2):112-118
Calli were induced from 300,000 embryos isolated from immature to mature stage of seeds collected on late September from 14
elite trees. When the embryos were cultured onto plastic Petri-dish containing 20 mL of modified B5 basal medium supplemented
with 3% (w/v) sucrose, 500 mg/L casein hydrolysate, 250 mg/L myo-inositol, 0.5% (w/v) polyvinyl polypyrrolidon (PVPP), 2×MS
vitamins, 0.5 mg/L gibberellic acid, and 10 mg/L 2,4-D after 2 weeks of culture, yellowish-white calli were immediately formed
on the surfaces of embryos, and subcultured for 4 weeks in same culture medium. Because most of calli maintained for more
than 3 months were revealed differences in their colors, surface texture, and growth rate, visual selection was made for first
round screening. When the size of visually selected calli larger than 19 mm in their diameter were inoculated, persistent
proliferation was observed. Among the plating methods tested for the selection of rapid growing cell lines at single cell
and/or small cell aggregate level, 2-layer spread plating revealed as the best for single cell cloning. To enhance cell growth
and maintain high rate of viability for long-term culture of yew cells in bioreactor, final cell volume less than 50% in SCV
seemed to be the best. Time course study revealed that 30% of inoculum density was suitable for fed batch culture. Among the
tested conditional media, the rate of 1∶2 (old medium: fresh medium) was recorded at the best for cell growth. 相似文献
4.
Sabrina Piombo Gode B. Calleja Bong Yul Yoo Byron F. Johnson 《Cell biochemistry and biophysics》1998,29(3):263-279
Distributions of rupture sites of fission yeast cells ruptured by glass beads have been related to a new morphometric analysis.
As shown previously (Johnson et al.,Cell Biophysics, 1995), ruptures were not randomly distributed nor was their distribution dictated by geometry, rather, ruptures at the extensile
end were related to cell length just as the rate of extension is related to cell length. The extension patterns of early log,
mid-log, late log, and stationary phase cells from suspension cultures were found to approximate the linear growth patterns
of Kubitschek and Clay (1986). The median length of cells was found to decline through the log phase in an unbalanced manner. 相似文献
5.
6.
7.
Summary The effects of phosphate on -amylase fermentation byBacillus amyloliquefaciens were investigated. It was observed through batch culture that optimal phosphate level which maximizes -amylase biosynthesis exists. High concentration of phosphate level promotes maltose uptake and growth of the microorganism, while high maltose uptake rate in the microorganism at the same time represses the enzyme biosynthesis presumably due to catabolite repression inside the microorganism. In continuous cultivation, a steady state of -amylase biosynthesis was obtained by maintaining phosphate level at a certain level. In fed-batch culture, by intermittant feeding of phosphate as well as maltose, higher activity of -amylase in the broth was obtained compared to the result from single nutrient feeding. 相似文献
8.
Two subunits of mannose permease, II-PMan and II-MMan, of Escherichia coli mediate coliphage N4 infection 总被引:1,自引:0,他引:1
Mutant strains of Escherichia coli that lack one or all of the intact components of mannose permease do not support the growth of phage N4. Complementation experiments using three recombinant plasmids containing DNA fragments coding for the subunits of mannose permease revealed that among the three component subunits, II-PMan and II-MMan alone are sufficient to confer N4 sensitivity. 相似文献
9.
Summary Citric acid was produced using Aspergillus niger immobilized on polyurethane foam in a bubble column reactor. Most of the adsorbed cells remained on the support and, as a result, high oxygen tension was maintained during the reactor operation. However, uncontrolled growth of the pellets made continuous reactor operation difficult. The citric acid productivity obtained from 15 vol.% foam particles containing immobilized cells was 0.135 g/l per hour. This productivity of immobilized cells was almost the same as that of free cells. The oxygen level dropped to half saturation in 5 days in the immobilized cell culture in contrast to 2 days in the free cell culture. 相似文献
10.
Double-stranded RNA unwinding and modifying activity is detected ubiquitously in primary tissues and cell lines. 总被引:19,自引:4,他引:15
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
R W Wagner C Yoo L Wrabetz J Kamholz J Buchhalter N F Hassan K Khalili S U Kim B Perussia F A McMorris et al. 《Molecular and cellular biology》1990,10(10):5586-5590
A double-stranded RNA unwinding and modifying activity was found to be present in a wide range of tissues and cell types. The level of activity did not vary significantly with respect to the state of cell differentiation, cell cycle, or transformation. Thus, the unwinding and modifying activity, localized in the nucleus in somatic cells and capable of converting many adenosine residues to inosine, appears to be one of the housekeeping genes. 相似文献