全文获取类型
收费全文 | 562篇 |
免费 | 26篇 |
国内免费 | 21篇 |
出版年
2024年 | 3篇 |
2023年 | 3篇 |
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 21篇 |
2016年 | 18篇 |
2015年 | 20篇 |
2014年 | 28篇 |
2013年 | 40篇 |
2012年 | 17篇 |
2011年 | 19篇 |
2010年 | 24篇 |
2009年 | 42篇 |
2008年 | 46篇 |
2007年 | 31篇 |
2006年 | 19篇 |
2005年 | 21篇 |
2004年 | 25篇 |
2003年 | 20篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 14篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 2篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1978年 | 2篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1964年 | 1篇 |
1963年 | 2篇 |
排序方式: 共有609条查询结果,搜索用时 31 毫秒
481.
Efficient families of ratio and product-type estimators 总被引:1,自引:0,他引:1
482.
Otto Wildi 《Plant Ecology》1980,41(2):95-100
Summary Recognition of noda is performed in a point cloud of n-space using grid analysis. The input data represent coordinates, preferably component scores, to reduce dimensionality. The exact position of the noda is approximated in an iterative search procedure which allows the user-defined space segments to drift into regions of high point density. The results are independent of group size and shape and they tend to compensate for uneven sampling in the different types of the survey site. The method gives flexibility in group recognition at different resolutions and provides a practical means to handling large data sets, while at the same time producing an optimal solution. The method, suitable to be used in the place of divisive clustering algorithms, has been applied to vegetation data with success. Results from two such applications are presented.The author expresses his thanks to Dr. L. Orlóci for discussions and critical review, and to the University of Western Ontario for computer time. 相似文献
483.
484.
We have characterized a macronuclear gene of the ciliate protozoan Euplotes raikovi, which encodes an acidic ribosomal protein of the P protein family. This gene shows the typical organization of the hypotrich ciliate macronuclear "gene-sized" molecules with Euplotes telomeres at the ends. The longest open reading frame encodes a conceptual protein of 113 amino acid residues, with a molecular mass and pI value of 11.45 kDa and 3.97, respectively. By using sequence homology analysis, the protein was found to belong to the ribosomal P2 protein family and was named Er P2, where Er stands for Euplotes raikovi. These proteins, generally called A (acidic/alanine rich) proteins in prokaryotes and P (phosphorylated) proteins in eukaryotes, in which they are divided into P1 and P2 families, play a role in the elongation step of protein synthesis. Approximately 40% amino acid sequence identity was found between the cloned protein and other known protozoan ribosomal P2 proteins. Within its N-terminal half, this protein contains several potential kinase phosphorylation sites. Protein Er P2 differs markedly from the consensus P protein sequence in its C-terminal region, usually highly conserved among eukaryotic ribosomal P proteins, and shows similarities with the C-terminus of the archaebacterial ribosomal A proteins. To our knowledge, this E. raikovi protein represents the first demonstration of a ribosome-associated protein of the P2 family in a ciliate protozoan. 相似文献
485.
大麦DNA导入小麦产生抗白粉病变异的遗传研究 总被引:12,自引:1,他引:11
阎新甫刘文轩 王胜军王西成 王锡锋YAN Xin-Pu LIU Wen-Xuan WANG Sheng-Jun WANG Xi-Cheng WANG Xi-Feng 《遗传》1994,16(1):26-30
本研究将抗白粉病的大麦DNA通过花粉管途径直接导入感病的小麦品种花76中,后代出现13株抗白粉病变异株。其中5株在以后的世代中抗性稳定,另8株则继续分离。第2带分离株系的抗病株形成的第3代株系(或株行)中,抗性有分离的株行与无分离的株行比例为1.9:1,而分离株行内抗病株与不抗病株之比为3.35:1。抗性稳定株系与感病亲本杂交,F1表现高抗病,再与感病亲本回交,后代抗感病株比例为1:1,自交F2的比例为2.8:1。说明所获得的抗白粉病性受一对完全显性基因控制,抗病为显性。与已知抗白粉病基因的比较表明,这个抗病基因可能是来自大麦的一个新基因。13 Variant plants with immunity and high-resistance to powdery mildew were found in D1 generation from introducing resistant barley DNA into susceptible wheat cultivar, through pollen tube pathway after self pollination.Of the variants, 5 plants for the resistance had been stable and the other 8 plants segregated insuccessive generation.The ratio of segregating and stable plant-rows was 1.9:1 in D3 plant-rows derived from resistant plants of segregating D2-lines,and the ratio of resistant plants and susceptible plants was 3.35:1 among the segregating D3 plant-rows.The F1 -plants from crosses between stable resistant variants and susceptible parents were higgh resistant to powdery mildew.The ratio of resistant and susceptible plants was 1:1 in progenies of backcross of the F1 and susceptible parents, and this ratio was 2.8:1 in the F2 generation from the F1 selfing. Thus it can be seen that the resistance obtained is camtrolled by a pair of genes, the resistance is dominant. The results in comparison with known powdery mildew resistance genes in wheat indicated that the resistant gene obtained would be a new one from barley. 相似文献
486.
Plants and plant derived ingredients are common and of major importance in the fields of pharmacy, food and cosmetics. The
cosmetic industry is a fast moving market. Products have short life-cycles and the industry has to come up with innovative
products constantly. Most cosmetic products and their applications are defined by active ingredients. These active ingredients
may derive from either synthetic sources or from plant sources. Beside this, no other origin like human or animal are accepted
or allowed in cosmetics nor are genetically modified plant sources. The whole cosmetic research and development society is
therefore desperately seeking for new innovative plant ingredients for cosmetic application. Unfortunately, new plant derived
ingredients are limited because several plants of cosmetic interest are not to be used due to following facts: the plants
contain toxic metabolites, the plants grow too slow and a seasonal harvesting is not possible, the concentration of plant
constituents differ from harvest to harvest or the plant is endangered and not allowed to harvest. With the plant cell culture
technology we bring complete new aspects in the development of novel cosmetic plant derived actives. Due to all these findings,
we decided to risk the step into plant cell culture derived cosmetic active ingredient production. This article describes
the successful
establishment of an apple suspension culture producing a high yield of biomass, cultured in disposable, middle-scale bioreactors.
The use of a bioactive extract out of these cells for cosmetic application and the efficacy of this extract on mammalian stem
cells is also outlined in this article. To obtain a suitable cosmetic product we used the high pressure homogenization technique
to decompose the plant cells and release all the beneficial constituents while encapsulating these components at the same
time in liquid Nanoparticles. With the plant cell culture technology we bring complete new aspects in the development of novel
cosmetic plants derived actives. 相似文献
487.
As part of the joint Finnish-Russian research and development project “Assessment of the ecological state of the transboundary waters”, seasonal and spatial variations in the phytoplankton communities of Lake Pyhäjärvi were studied in order to identify possible long-term (1963–2002) changes and to present recent data (since 2002) on phytoplankton biomass and species composition. Some changes in both phytoplankton biomass and species composition, particularly in the littoral zone and northern basins of the lake, were obvious at the end of the 1980s; in particular, the density of blue-greens increased during that period. Biomasses increased five-fold in 1980, decreased after 1990 and have remained low (0.14 mg l?l) to the present time. The effective water protection measures applied, especially reducing the phosphorus load from municipal wastewaters and airborne pollution, can now be seen to have improved the water quality. Although no significant temporal differences were found in phytoplankton biomass during the intensive biweekly sampling in 2002, considerable spatial variation was seen within the lake. An obvious change in the species composition of phytoplankton and an increase in biomass were seen even in the loaded parts of the lake. Despite the spatial differences in phytoplankton biomass and community structure, the changed species composition in the northern part of the lake indicated a clear recovery from the blue-green and Chrysophyceae dominated high biomass of the 1980s. 相似文献
488.
Hongmei Wu Duxue Cheng Lixian Wang 《遗传学报》2008,35(2):91-95
The present research was designed to study the association of polymorphism of natural resistance-associated macrophage proteinl (Nrampl) with some immune function and the production performance in Large White pig. The PCR-RFLP technique was applied to analyze the correlation between the polymorphisms of Nrampl gene and immune function [value of Polymorphonuclear Leukocytes (PMN) obtained by Nitroblue Tetrazolium (NBT) Reduction and effect of Cytotoxin in Monocyte] and production performance in 165 Large White pigs. The results showed that there was one Nde I restriction locus in Large White pig, and both values of PMN by NBT Reduction and effect of Cytotoxin in Monocyte in genotype BB were higher than those in genotype AB (P〈0.05). Simultaneously, the weight of 180-day-old pigs with genotype BB was higher than that with genotype AB (P〈0.05). The results indicated that there was a significant correlation between different genotypes of Nrampl gene and Immune function and production performance, and it can be regarded as a candidate gene of disease resistance. All these results provide valuable reference to further studies of pig disease resistance. 相似文献
489.
490.
目的 从血管形成角度探索青春型双歧杆菌预防大肠癌生长的途径。方法 建立大肠癌裸鼠移植瘤模型,以免疫组化法检测大肠癌组织血管内皮生长因子(VEGF)的蛋白表达水平及其微血管密度(MVD)。结果 双歧杆菌预防组大肠癌VEGF的阳性细胞密度及MVD的数量均明显低于肿瘤对照组(P〈0.01)。结论 青春型双歧杆菌能下调大肠癌VEGF的表达,进而抑制其血管形成,这可能是它预防大肠癌生长的途径之一。 相似文献