全文获取类型
收费全文 | 638篇 |
免费 | 109篇 |
国内免费 | 4篇 |
出版年
2022年 | 9篇 |
2021年 | 12篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 20篇 |
2017年 | 13篇 |
2016年 | 24篇 |
2015年 | 37篇 |
2014年 | 33篇 |
2013年 | 38篇 |
2012年 | 49篇 |
2011年 | 40篇 |
2010年 | 28篇 |
2009年 | 27篇 |
2008年 | 22篇 |
2007年 | 19篇 |
2006年 | 20篇 |
2005年 | 23篇 |
2004年 | 25篇 |
2003年 | 20篇 |
2002年 | 25篇 |
2001年 | 30篇 |
2000年 | 26篇 |
1999年 | 17篇 |
1998年 | 13篇 |
1997年 | 6篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 14篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 12篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1962年 | 1篇 |
1960年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有751条查询结果,搜索用时 15 毫秒
61.
Iwashina T López-Sáez JA Herrero A Kitajima J Matsumoto S 《Biochemical Systematics and Ecology》2000,28(7):665-671
The flavonoids of Asplenium foreziense, A. fontanum subsp. fontanum and subsp. pseudofontanum, A. obovatum subsp. obovatum var. obovatum and var. protobillotii, A. obovatum subsp. lanceolatum, and A. incisum were isolated and identified for chemotaxonomic survey. A major constituent of all taxa was kaempferol 3-O-gentiobioside. As minor compounds, kaempferol 3,7-O-glycoside and/or kaempferol 3-O-glycoside were found in A. fontanum, A. obovatum and A. foreziense, and kaempferol 3-O-gentiobioside-4'-O-glucoside, kaempferol 3-O-glucoside and quercetin 3-O-diglucoside in A. incisum. It was suggested that A. foreziense, A. fontanum including subsp. pseudofontanum and A. obovatum including subsp. lanceolatum are not only morphologically but also chemotaxonomically related. The East Asian A. incisum was chemically and geographically different from these taxa. 相似文献
62.
Cabiscol E Piulats E Echave P Herrero E Ros J 《The Journal of biological chemistry》2000,275(35):27393-27398
We have analyzed the proteins that are oxidatively damaged when Saccharomyces cerevisiae cells are exposed to stressing conditions. Carbonyl groups generated by hydrogen peroxide or menadione on proteins of aerobically respiring cells were detected by Western blotting, purified, and identified. Mitochondrial proteins such as E2 subunits of both pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase, aconitase, heat-shock protein 60, and the cytosolic fatty acid synthase (alpha subunit) and glyceraldehyde-3-phosphate dehydrogenase were the major targets. In addition we also report the in vivo modification of lipoamide present in the above-mentioned E2 subunits under the stressing conditions tested and that this also occurs with the homologous enzymes present in Escherichia coli cells that were used for comparative analysis. Under fermentative conditions, the main protein targets in S. cerevisiae cells treated with hydrogen peroxide or menadione were pyruvate decarboxylase, enolase, fatty acid synthase, and glyceraldehyde-3-phosphate dehydrogenase. Under the stress conditions tested, fermenting cells exhibit a lower viability than aerobically respiring cells and, consistently, increased peroxide generation as well as higher content of protein carbonyls and lipid peroxides. Our results strongly suggest that the oxidative stress in prokaryotic and eukaryotic cells shares common features. 相似文献
63.
Extensor digitorum brevis free flap: anatomic study and further clinical applications 总被引:2,自引:0,他引:2
The extensor digitorum brevis muscle flap is reliable, safe, and can be used either as a pedicle or as a free flap with minimal donor site morbidity. To increase the existing knowledge of this flap and to establish further anatomic basis for the design and elevation of the extensor digitorum brevis flap, 26 specimens from 13 fresh cadavers were dissected under 3.5x loupes. The lateral tarsal artery was found to be the main blood supply to the muscle. It has an average diameter of 1.83+/-0.35 mm and a length of 1.89+/-0.69 cm. The dorsalis pedis artery has, at the level of the lateral tarsal artery takeoff, a diameter of 3.25+/-0.62 mm. From this point to the origin of the deep plantar branch, the dorsalis pedis artery has minimal branching, and the surgeon has available an artery homogeneous in diameter that is 6.77+/-0.99 cm in length. Related neurovascular structures (anterior tibial artery and the venae comitantes, dorsalis pedis and first dorsal metatarsal artery, and deep peroneal nerve) were also studied. A safe and reliable harvesting technique and the "T interposed extensor digitorum brevis" technique for sparing the anterior tibial artery are presented, as are clinical case examples on the use of this flap as a flow-through, extensor digitorum brevis-vascularized nerve graft, a combined extensor digitorum brevis-deep peroneal nerve graft, and a bilobed extensor digitorum brevis-dorsalis pedis fasciosubcutaneous free flap. 相似文献
64.
Mitochondrial production of oxygen radicals seems to be involved in many diseases and aging. Recent studies clearly showed that a substantial part of the free radical generation of rodent mitochondria comes from complex I. It is thus important to further localize the free radical generator site within this respiratory complex. In this study, superoxide production by heart and nonsynaptic brain submitochondrial particles from up to seven mammalian species, showing different longevities, were studied under different conditions. The results, taking together, show that rotenone stimulates NADH-supported superoxide generation, confirming that complex I is a source of oxygen radicals in mammals, in general. The rotenone-stimulated NADH-supported superoxide production of the heart and nonsynaptic brain mammalian submitochondrial particles was inhibited both by p-chloromercuribenzoate and by ethoxyformic anhydride. These results localize the complex I oxygen radical generator between the ferricyanide and the ubiquinone reduction site, making iron—sulfur centers possible candidates, although unstable semiquinones can not be discarded. The results also indicate that the previously described inverse correlation between rates of mitochondrial oxygen radical generation and mammalian longevity operates through mechanisms dependent on the presence of intact functional mitochondria. 相似文献
65.
The narA Locus of Synechococcus sp. Strain PCC 7942 Consists of a Cluster of Molybdopterin Biosynthesis Genes 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The narA locus required for nitrate reduction in Synechococcus sp. strain PCC 7942 is shown to consist of a cluster of genes, namely, moeA, moaC, moaD, moaE, and moaA, involved in molybdenum cofactor biosynthesis. The product of the moaC gene of strain PCC 7942 shows homology in its N-terminal half to MoaC from Escherichia coli and in its C-terminal half to MoaB or Mog. Overexpression of the Synechococcus moaC gene in E. coli resulted in the synthesis of a polypeptide of 36 kDa, a size that would conform to a protein resembling a fusion of the MoaC and MoaB or Mog polypeptides of E. coli. Insertional inactivation of the moeA, moaC, moaE, and moaA genes showed that the moeA-moa gene cluster is required for growth on nitrate and expression of nitrate reductase activity in strain PCC 7942. The moaCDEA genes constitute an operon which is transcribed divergently from the moeA gene. Expression of the moeA gene and the moa operon was little affected by the nitrogen source present in the culture medium. 相似文献
66.
In many plant species with multiovulate ovaries, a considerable reduction in the number of ovules takes place. However, the
underlying physiological causes are not clear. In Prunus spp., although flowers present two ovules, usually only one seed is produced. We have followed the development and degeneration
of the two ovules in apricot (Prunus armeniaca L.) and examined the extent to which carbohydrates within the ovule might be involved in determining the fate of the ovule.
While the primary ovule grows in the days following anthesis, growth of the secondary ovule is arrested. Starch distribution
along the different ovular tissues exhibits several changes that are different in the two ovules. Primary ovule growth is
inversely related to starch content and this growth takes place independently of pollination since it occurs in the same way
in pollinated and unpollinated flowers. In the secondary ovule, starch disappears simultaneously from all ovular structures
and callose is layered at the chalazal end of the nucellus. The size of the secondary ovule does not change significantly
from anthesis to degeneration, and callose starts to accumulate 5 days after anthesis. Likewise, this process occurs independently
of pollination. These results are discussed in terms of the implications of the starch content of ovules in fertilization
success and ovule fate.
Received: 26 August 1997 / Revision accepted: 17 December 1997 相似文献
67.
Vctor de Lorenzo Marta Herrero Juan M. Sánchez Kenneth N. Timmis 《FEMS microbiology ecology》1998,27(3):211-224
68.
Laura Corrales-Guerrero Vicente Mariscal Dennis J. Nürnberg Jeff Elhai Conrad W. Mullineaux Enrique Flores Antonia Herrero 《Journal of bacteriology》2014,196(19):3452-3460
In the filamentous cyanobacterium Anabaena sp. strain PCC 7120, heterocysts are formed in the absence of combined nitrogen, following a specific distribution pattern along the filament. The PatS and HetN factors contribute to the heterocyst pattern by inhibiting the formation of consecutive heterocysts. Thus, inactivation of any of these factors produces the multiple contiguous heterocyst (Mch) phenotype. Upon N stepdown, a HetN protein with its C terminus fused to a superfolder version of green fluorescent protein (sf-GFP) or to GFP-mut2 was observed, localized first throughout the whole area of differentiating cells and later specifically on the peripheries and in the polar regions of mature heterocysts, coinciding with the location of the thylakoids. Polar localization required an N-terminal stretch comprising residues 2 to 27 that may represent an unconventional signal peptide. Anabaena strains expressing a version of HetN lacking this fragment from a mutant gene placed at the native hetN locus exhibited a mild Mch phenotype. In agreement with previous results, deletion of an internal ERGSGR sequence, which is identical to the C-terminal sequence of PatS, also led to the Mch phenotype. The subcellular localization in heterocysts of fluorescence resulting from the fusion of GFP to the C terminus of HetN suggests that a full HetN protein is present in these cells. Furthermore, the full HetN protein is more conserved among cyanobacteria than the internal ERGSGR sequence. These observations suggest that HetN anchored to thylakoid membranes in heterocysts may serve a function besides that of generating a regulatory (ERGSGR) peptide. 相似文献
69.
70.