全文获取类型
收费全文 | 608篇 |
免费 | 59篇 |
出版年
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 11篇 |
2014年 | 9篇 |
2013年 | 14篇 |
2012年 | 23篇 |
2011年 | 15篇 |
2010年 | 13篇 |
2009年 | 12篇 |
2008年 | 16篇 |
2007年 | 19篇 |
2006年 | 18篇 |
2005年 | 17篇 |
2004年 | 22篇 |
2003年 | 23篇 |
2002年 | 16篇 |
2001年 | 32篇 |
2000年 | 23篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 5篇 |
1983年 | 16篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1979年 | 11篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 13篇 |
1973年 | 8篇 |
1972年 | 15篇 |
1971年 | 9篇 |
1970年 | 14篇 |
1969年 | 7篇 |
1968年 | 9篇 |
1967年 | 13篇 |
1966年 | 9篇 |
排序方式: 共有667条查询结果,搜索用时 15 毫秒
51.
Vector for pop-in/pop-out gene replacement in Pichia pastoris 总被引:3,自引:0,他引:3
Gene replacement in yeast is often accomplished by using a counterselectable marker such as URA3. Although ura3 strains of Pichia pastoris have been generated, these strains are inconvenient to work with because they grow slowly, even in the presence of uracil. To overcome this limitation, we have developed an alternative counterselectable marker that can be used in any P. pastoris strain. This marker is the T-urf13 gene from the mitochondrial genome of male-sterile maize. Previous work showed that expression of a mitochondrially targeted form of T-urf13 in Saccharomyces cerevisiae rendered the cells sensitive to the insecticide methomyl, and similar results have now been obtained with P. pastoris. We have incorporated T-urf13 into a vector that also contains an ARG4 marker for positive selection. The resulting plasmid allows for pop-in/pop-out gene replacement in P. pastoris. 相似文献
52.
53.
Role of Pseudomonas putida indoleacetic acid in development of the host plant root system 总被引:1,自引:0,他引:1
Many plant-associated bacteria synthesize the phytohormone indoleacetic acid (IAA). While IAA produced by phytopathogenic bacteria, mainly by the indoleacetamide pathway, has been implicated in the induction of plant tumors, it is not clear whether IAA synthesized by beneficial bacteria, usually via the indolepyruvic acid pathway, is involved in plant growth promotion. To determine whether bacterial IAA enhances root development in host plants, the ipdc gene that encodes indolepyruvate decarboxylase, a key enzyme in the indolepyruvic acid pathway, was isolated from the plant growth-promoting bacterium Pseudomonas putida GR12-2 and an IAA-deficient mutant constructed by insertional mutagenesis. The canola seedling primary roots from seeds treated with wild-type P. putida GR12-2 were on average 35 to 50% longer than the roots from seeds treated with the IAA-deficient mutant and the roots from uninoculated seeds. In addition, exposing mung bean cuttings to high levels of IAA by soaking them in a suspension of the wild-type strain stimulated the formation of many, very small, adventitious roots. Formation of fewer roots was stimulated by treatment with the IAA-deficient mutant. These results suggest that bacterial IAA plays a major role in the development of the host plant root system. 相似文献
54.
Agriculture depends heavily on biologically fixed nitrogen from the symbiotic association between rhizobia and plants. Molecular nitrogen is fixed by differentiated forms of rhizobia in nodules located on plant roots. The phytohormone, ethylene, acts as a negative factor in the nodulation process. Recent discoveries suggest several strategies used by rhizobia to reduce the amount of ethylene synthesized by their legume symbionts, decreasing the negative effect of ethylene on nodulation. At least one strain of rhizobia produces rhizobitoxine, an inhibitor of ethylene synthesis. Active 1-aminocyclopropane-1-carboxylate (ACC) deaminase has been detected in a number of other rhizobial strains. This enzyme catalyzes the cleavage of ACC to alpha-ketobutyrate and ammonia. It has been shown that the inhibitory effect of ethylene on plant root elongation can be reduced by the activity of ACC deaminase. 相似文献
55.
The plant hormone ethylene is an essential signaling molecule involved in many plant processes including: germination, flower development, fruit ripening and responses to many environmental stimuli. Moreover, large increases in ethylene levels occur during plant stress responses, fruit ripening and flower wilting. Manipulation of ethylene biosynthesis or perception allows us to modulate these processes and thereby create plants with more robust and/or desirable traits, giving us a glimpse into the role of ethylene in the plant. Here, recent and landmark advances in genetic alteration of members of the ethylene pathway in plants and the physiological consequences of these alterations are examined. 相似文献
56.
Mogelsvang S Gomez-Ospina N Soderholm J Glick BS Staehelin LA 《Molecular biology of the cell》2003,14(6):2277-2291
The budding yeast Pichia pastoris contains ordered Golgi stacks next to discrete transitional endoplasmic reticulum (tER) sites, making this organism ideal for structure-function studies of the secretory pathway. Here, we have used P. pastoris to test various models for Golgi trafficking. The experimental approach was to analyze P. pastoris tER-Golgi units by using cryofixed and freeze-substituted cells for electron microscope tomography, immunoelectron microscopy, and serial thin section analysis of entire cells. We find that tER sites and the adjacent Golgi stacks are enclosed in a ribosome-excluding "matrix." Each stack contains three to four cisternae, which can be classified as cis, medial, trans, or trans-Golgi network (TGN). No membrane continuities between compartments were detected. This work provides three major new insights. First, two types of transport vesicles accumulate at the tER-Golgi interface. Morphological analysis indicates that the center of the tER-Golgi interface contains COPII vesicles, whereas the periphery contains COPI vesicles. Second, fenestrae are absent from cis cisternae, but are present in medial through TGN cisternae. The number and distribution of the fenestrae suggest that they form at the edges of the medial cisternae and then migrate inward. Third, intact TGN cisternae apparently peel off from the Golgi stacks and persist for some time in the cytosol, and these "free-floating" TGN cisternae produce clathrin-coated vesicles. These observations are most readily explained by assuming that Golgi cisternae form at the cis face of the stack, progressively mature, and ultimately dissociate from the trans face of the stack. 相似文献
57.
Tietge UJ Maugeais C Cain W Grass D Glick JM de Beer FC Rader DJ 《The Journal of biological chemistry》2000,275(14):10077-10084
Plasma levels of high density lipoprotein (HDL) cholesterol and its major protein component apolipoprotein (apo) A-I are significantly reduced in both acute and chronic inflammatory conditions, but the basis for this phenomenon is not well understood. We hypothesized that secretory phospholipase A(2) (sPLA(2)), an acute phase protein that has been found in association with HDL, promotes HDL catabolism. A series of HDL metabolic studies were performed in transgenic mice that specifically overexpress human sPLA(2) but have no evidence of local or systemic inflammation. We found that HDL isolated from these mice have a significantly lower phospholipid and cholesteryl ester and significantly greater triglyceride content. The fractional catabolic rate (FCR) of (125)I-HDL was significantly faster in sPLA(2) transgenic mice (4.08 +/- 0.01 pools/day) compared with control wild-type littermates (2.16 +/- 0.48 pools/day). (125)I-HDL isolated from sPLA(2) transgenic mice was catabolized significantly faster than (131)I-HDL isolated from wild-type mice after injection in wild-type mice (p < 0.001). Injection of (125)I-tyramine-cellobiose-HDL demonstrated significantly greater degradation of HDL apolipoproteins in the kidneys of sPLA(2) transgenic mice compared with control mice (p < 0.05). The fractional catabolic rate of [(3)H]cholesteryl ether HDL was significantly faster in sPLA(2)-overexpressing mice (6.48 +/- 0.24 pools/day) compared with controls (4.80 +/- 0.72 pools/day). Uptake of [(3)H] cholesteryl ether into the livers and adrenals of sPLA(2) transgenic mice was significantly enhanced compared with control mice. In summary, these data demonstrate that overexpression of sPLA(2) alone in the absence of inflammation causes profound alterations of HDL metabolism in vivo and are consistent with the hypothesis that sPLA(2) may promote HDL catabolism in acute and chronic inflammatory conditions. 相似文献
58.
King CH Meckler H Herr RJ Trova MP Glick SD Maisonneuve IM 《Bioorganic & medicinal chemistry letters》2000,10(5):473-476
Chemical resolution of racemic 18-methoxycoronaridine (18-MC) was achieved by the formation of its diastereomeric sulfonamides with either (R)-(-)- or (S)-(+)-camphorsulfonyl chloride. Preliminary assessment of (+)-, (-)-, and (+/-)-18-MC x HCl showed similar effects on morphine self-administration in a rat model, and similar affinities at the kappa opioid receptors. 相似文献
59.
A typical vertebrate cell contains several hundred sites of transitional ER (tER). Presumably, tER sites generate elements of the ER-Golgi intermediate compartment (ERGIC), and ERGIC elements then generate Golgi cisternae. Therefore, characterizing the mechanisms that influence tER distribution may shed light on the dynamic behavior of the Golgi. We explored the properties of tER sites using Sec13 as a marker protein. Fluorescence microscopy confirmed that tER sites are long-lived ER subdomains. tER sites proliferate during interphase but lose Sec13 during mitosis. Unlike ERGIC elements, tER sites move very little. Nevertheless, when microtubules are depolymerized with nocodazole, tER sites redistribute rapidly to form clusters next to Golgi structures. Hence, tER sites have the unusual property of being immobile, yet dynamic. These findings can be explained by a model in which new tER sites are created by retrograde membrane traffic from the Golgi. We propose that the tER-Golgi system is organized by mutual feedback between these two compartments. 相似文献
60.