全文获取类型
收费全文 | 105篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
系统科学 | 1篇 |
教育与普及 | 1篇 |
现状及发展 | 35篇 |
研究方法 | 10篇 |
综合类 | 51篇 |
自然研究 | 8篇 |
出版年
2017年 | 3篇 |
2016年 | 1篇 |
2014年 | 2篇 |
2013年 | 1篇 |
2012年 | 3篇 |
2011年 | 14篇 |
2010年 | 2篇 |
2009年 | 1篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 1篇 |
1998年 | 1篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1972年 | 6篇 |
1970年 | 4篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1965年 | 2篇 |
1964年 | 2篇 |
排序方式: 共有106条查询结果,搜索用时 312 毫秒
21.
Mourning Doves are the most commonly hunted game bird in New Mexico based on hunter harvest data collected by New Mexico Department of Game and Fish. Research is limited on the influence of rangeland ecological condition on Mourning Dove ( Zenaida macroura ) populations in the Chihuahuan Desert of New Mexico. Mourning Dove numbers were evaluated periodically (1988-1989) on ranges in late- and mid-seral conditions in south central New Mexico based on the Dyksterhuis quantitative climax procedure. Strip transect procedures were used to estimate Mourning Dove populations. Concurrently, vegetation canopy cover was determined by line intercept. On the basis of percent cover, grasses were the most abundant group on late-seral range while shrubs dominated mid-seral range. Mourning Dove sightings did not differ ( P > 0.05) between late- and mid-seral ranges, nor did they differ ( P > 0.05) among grassland, shrubland, and shrub-grass mosaic communities. Mourning Dove populations showed seasonal differences ( P < 0.05), with numbers highest in summer and fall and lowest in winter and spring. Data from our study indicate that Chihuahuan Desert ranges in either mid- or late-seral stages provide equally suitable habitat for Mourning Doves. 相似文献
22.
23.
Alpha-helical coiled coils in muscle exemplify simplicity and economy of protein design: small variations in sequence lead to remarkable diversity in cellular functions. Myosin II is the key protein in muscle contraction, and the molecule's two-chain alpha-helical coiled-coil rod region--towards the carboxy terminus of the heavy chain--has unusual structural and dynamic features. The amino-terminal subfragment-2 (S2) domains of the rods can swing out from the thick filament backbone at a hinge in the coiled coil, allowing the two myosin 'heads' and their motor domains to interact with actin and generate tension. Most of the S2 rod appears to be a flexible coiled coil, but studies suggest that the structure at the N-terminal region is unstable, and unwinding or bending of the alpha-helices near the head-rod junction seems necessary for many of myosin's functional properties. Here we show the physical basis of a particularly weak coiled-coil segment by determining the 2.5-A-resolution crystal structure of a leucine-zipper-stabilized fragment of the scallop striated-muscle myosin rod adjacent to the head-rod junction. The N-terminal 14 residues are poorly ordered; the rest of the S2 segment forms a flexible coiled coil with poorly packed core residues. The unusual absence of interhelical salt bridges here exposes apolar core atoms to solvent. 相似文献
24.
Summary The essentiality of (-6) and (-3) fatty acids in mammals is well known. Nevertheless, some important points remain unclear concerning their implication in physiology. After a short discussion about the definition of essential fatty acids deficiency, this brief overview deals with some of these points, pointing out some of the unresolved questions. Different subjects are approached concerning the (-6) and (-3) fatty acids metabolism: desaturases, eicosanoids, production, as well as some of their metabolic effects on cell membranes, intestinal function, glucose and lipid metabolism, haemorheology. 相似文献
25.
A phenylalanine in DGAT is a key determinant of oil content and composition in maize 总被引:9,自引:0,他引:9
Zheng P Allen WB Roesler K Williams ME Zhang S Li J Glassman K Ranch J Nubel D Solawetz W Bhattramakki D Llaca V Deschamps S Zhong GY Tarczynski MC Shen B 《Nature genetics》2008,40(3):367-372
Plant oil is an important renewable resource for biodiesel production and for dietary consumption by humans and livestock. Through genetic mapping of the oil trait in plants, studies have reported multiple quantitative trait loci (QTLs) with small effects, but the molecular basis of oil QTLs remains largely unknown. Here we show that a high-oil QTL (qHO6) affecting maize seed oil and oleic-acid contents encodes an acyl-CoA:diacylglycerol acyltransferase (DGAT1-2), which catalyzes the final step of oil synthesis. We further show that a phenylalanine insertion in DGAT1-2 at position 469 (F469) is responsible for the increased oil and oleic-acid contents. The DGAT1-2 allele with F469 is ancestral, whereas the allele without F469 is a more recent mutant selected by domestication or breeding. Ectopic expression of the high-oil DGAT1-2 allele increases oil and oleic-acid contents by up to 41% and 107%, respectively. This work provides insights into the molecular basis of natural variation of oil and oleic-acid contents in plants and highlights DGAT as a promising target for increasing oil and oleic-acid contents in other crops. 相似文献
26.
Gunsalus KC Ge H Schetter AJ Goldberg DS Han JD Hao T Berriz GF Bertin N Huang J Chuang LS Li N Mani R Hyman AA Sönnichsen B Echeverri CJ Roth FP Vidal M Piano F 《Nature》2005,436(7052):861-865
Although numerous fundamental aspects of development have been uncovered through the study of individual genes and proteins, system-level models are still missing for most developmental processes. The first two cell divisions of Caenorhabditis elegans embryogenesis constitute an ideal test bed for a system-level approach. Early embryogenesis, including processes such as cell division and establishment of cellular polarity, is readily amenable to large-scale functional analysis. A first step toward a system-level understanding is to provide 'first-draft' models both of the molecular assemblies involved and of the functional connections between them. Here we show that such models can be derived from an integrated gene/protein network generated from three different types of functional relationship: protein interaction, expression profiling similarity and phenotypic profiling similarity, as estimated from detailed early embryonic RNA interference phenotypes systematically recorded for hundreds of early embryogenesis genes. The topology of the integrated network suggests that C. elegans early embryogenesis is achieved through coordination of a limited set of molecular machines. We assessed the overall predictive value of such molecular machine models by dynamic localization of ten previously uncharacterized proteins within the living embryo. 相似文献
27.
28.
Prawitt D Enklaar T Gärtner-Rupprecht B Spangenberg C Lausch E Reutzel D Fees S Korzon M Brozek I Limon J Housman DE Pelletier J Zabel B 《Nature genetics》2005,37(8):785-6; author reply 786-7
29.
B Cherruau M Mangeot J F Demelier C Charpentier C Pelletier A Lemonnier 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1979,289(5):469-472
After administering sodium dipropylacetate to normal rats and biotin-deficient rats, we observed a slight hyperglycinemia, significant constant hyperglycinuria, but no accumulation of propionic acid in the blood or significant urinary elimination. Hepatic propionyl-CoA carboxylase activity, in vivo and in vitro, did not change, neither did sodium dipropylacetate inhibit propionyl-CoA carboxylase nor induce propionic acidemia resulting from a deficiency in this enzyme. 相似文献
30.
卡尔·兰斯泰纳(Karl.landsteiner)于1901年发现了人类血型抗原,并把人类血液分为A、B、O和AB型,从而开创了现代输血的新纪元。血型的研究,对认识迄今输血失败的原因起到了至关重要的作用。 相似文献