全文获取类型
收费全文 | 1183篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
系统科学 | 5篇 |
理论与方法论 | 5篇 |
现状及发展 | 687篇 |
研究方法 | 105篇 |
综合类 | 386篇 |
自然研究 | 1篇 |
出版年
2018年 | 16篇 |
2017年 | 13篇 |
2016年 | 14篇 |
2014年 | 12篇 |
2013年 | 14篇 |
2012年 | 45篇 |
2011年 | 52篇 |
2010年 | 31篇 |
2009年 | 14篇 |
2008年 | 55篇 |
2007年 | 50篇 |
2006年 | 48篇 |
2005年 | 51篇 |
2004年 | 33篇 |
2003年 | 35篇 |
2002年 | 42篇 |
2001年 | 26篇 |
2000年 | 25篇 |
1999年 | 16篇 |
1994年 | 11篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1980年 | 12篇 |
1979年 | 22篇 |
1978年 | 15篇 |
1977年 | 19篇 |
1976年 | 16篇 |
1975年 | 20篇 |
1974年 | 18篇 |
1973年 | 27篇 |
1972年 | 13篇 |
1971年 | 25篇 |
1970年 | 28篇 |
1969年 | 28篇 |
1968年 | 20篇 |
1967年 | 21篇 |
1966年 | 29篇 |
1965年 | 14篇 |
1962年 | 11篇 |
1961年 | 11篇 |
1960年 | 8篇 |
1959年 | 9篇 |
1957年 | 9篇 |
1956年 | 9篇 |
1955年 | 16篇 |
1947年 | 9篇 |
排序方式: 共有1189条查询结果,搜索用时 0 毫秒
121.
Maize HapMap2 identifies extant variation from a genome in flux 总被引:3,自引:0,他引:3
Chia JM Song C Bradbury PJ Costich D de Leon N Doebley J Elshire RJ Gaut B Geller L Glaubitz JC Gore M Guill KE Holland J Hufford MB Lai J Li M Liu X Lu Y McCombie R Nelson R Poland J Prasanna BM Pyhäjärvi T Rong T Sekhon RS Sun Q Tenaillon MI Tian F Wang J Xu X Zhang Z Kaeppler SM Ross-Ibarra J McMullen MD Buckler ES Zhang G Xu Y Ware D 《Nature genetics》2012,44(7):803-807
Whereas breeders have exploited diversity in maize for yield improvements, there has been limited progress in using beneficial alleles in undomesticated varieties. Characterizing standing variation in this complex genome has been challenging, with only a small fraction of it described to date. Using a population genetics scoring model, we identified 55 million SNPs in 103 lines across pre-domestication and domesticated Zea mays varieties, including a representative from the sister genus Tripsacum. We find that structural variations are pervasive in the Z. mays genome and are enriched at loci associated with important traits. By investigating the drivers of genome size variation, we find that the larger Tripsacum genome can be explained by transposable element abundance rather than an allopolyploid origin. In contrast, intraspecies genome size variation seems to be controlled by chromosomal knob content. There is tremendous overlap in key gene content in maize and Tripsacum, suggesting that adaptations from Tripsacum (for example, perennialism and frost and drought tolerance) can likely be integrated into maize. 相似文献
122.
P Milner V Ralevic A M Hopwood E Fehér J Lincoln K A Kirkpatrick G Burnstock 《Experientia》1989,45(2):121-125
Substance P and choline acetyltransferase have been localised in a small proportion of endothelial cells of rat coronary arteries using electron microscopic immunocytochemistry. During a hypoxic period of 1 min, coronary vasodilatation was produced in the Langendorff heart preparation and increased levels of substance P and acetylcholine were released into the perfusate. The possibility that these substances are released from endothelial cells during hypoxia and contribute to the hyperaemic response is discussed. 相似文献
123.
Zusammenfassung
3H-Oestradiol wurde Mäusen injiziert und nachher autoradiographisch verfolgt, wobei Ag-Körnchen über den Chromosomen der Granulosazellen des Ovariums festgestellt werden konnten. 相似文献
124.
125.
D. Reinhardt J. Wagner H. J. Schümann 《Cellular and molecular life sciences : CMLS》1973,29(7):830-832
Zusammenfassung Am Kaninchen-Ileum besteht die durch Temperaturerhöhung bedingte Rechtsverschiebung der Dosis-Wirkungs-Kurven von Isoprenalin und Th 1165a aus einem reversiblen und einem irreversiblen Anteil. 相似文献
126.
The effect of dynorphin A-(1-13) (Dyn A-(1-13] and other opioids on the cytosolic free calcium concentration [(Ca2+]i) in rat anterior pituitary cells was examined using the fluorescent indicator fura-2. A commercial synthetic Dyn A-(1-13) preparation elevated [Ca2+]i. Results, which were obtained with receptor antagonists, and in LHRH receptor radioligand binding studies as well as by HPLC combined with LHRH radioimmunoassay, strongly suggest that this effect of the dynorphin preparation was due to contamination with a LHRH-like compound. Dyn A-(1-13), purified by HPLC, as well as Dyn A-(2-13), [Leu5]enkephalin, beta-endorphin, morphine, or U50,488H had no effect on [Ca2+]i. LHRH caused a rapid increase in [Ca2+]i by about 50 nM which was blocked by the LHRH antagonist, [D-pGlu1,D-Phe2,D-Trp3,6] LHRH. 相似文献
127.
H. -D. Jakubke H. Däumer A. Könnecke P. Kuhl J. Fischer 《Cellular and molecular life sciences : CMLS》1980,36(9):1039-1040
Summary The affinity of N-acyl-L-phenylalanine 4-nitroanilides for chymotrypsin is enhanced as the hydrophobicity of non-amino acid residues in the P2-position of the substrates increases, whereas kcat remains nearly constant. On the other hand, if alanine or leucine is in the P2-position kcat increases with decreasing KM. 相似文献
128.
The stimulatory effect of nitro-compounds on arterial and hepatic guanylate cyclase became significantly depressed at 0.2 microM and higher concentrations of free Ca2+. The basal enzyme activity proved to be Ca2+-independent. 相似文献
129.
130.
The RNA required in the first step of chlorophyll biosynthesis is a chloroplast glutamate tRNA 总被引:27,自引:0,他引:27
A molecule of chlorophyll is synthesized from eight molecules of delta-aminolevulinate (DALA), the universal precursor of porphyrins. The light-regulated conversion of glutamate to delta-aminolevulinate in the stroma of greening plastids involves the reduction of glutamate to glutamate-1-semialdehyde and its subsequent transamination. The components performing this conversion have been isolated from barley and Chlamydomonas and separated into three fractions by serial affinity chromatography on Blue Sepharose and haem- or chlorophyllin-Sepharose. The complete reaction can be performed in vitro in a reconstituted assay by combining all three fractions. An RNA is the essential component of the chlorophyllin-Sepharose-bound fraction. By nucleotide sequence analysis, we have now identified this RNA as a chloroplast glutamate acceptor RNA. Glutamate attached by an aminoacyl bond to the 3'-terminal adenosine of this RNA is a substrate for the enzyme(s) which perform the subsequent reactions. This reaction represents a novel role for transfer RNA: participation in the metabolic conversion of its cognate amino acid into another metabolite of low relative molecular mass which subsequently is not used in peptide bond synthesis. 相似文献