全文获取类型
收费全文 | 27334篇 |
免费 | 2267篇 |
国内免费 | 21篇 |
专业分类
29622篇 |
出版年
2023年 | 87篇 |
2022年 | 190篇 |
2021年 | 451篇 |
2020年 | 266篇 |
2019年 | 339篇 |
2018年 | 425篇 |
2017年 | 349篇 |
2016年 | 601篇 |
2015年 | 1046篇 |
2014年 | 1228篇 |
2013年 | 1465篇 |
2012年 | 1947篇 |
2011年 | 1972篇 |
2010年 | 1281篇 |
2009年 | 1093篇 |
2008年 | 1721篇 |
2007年 | 1763篇 |
2006年 | 1627篇 |
2005年 | 1582篇 |
2004年 | 1610篇 |
2003年 | 1533篇 |
2002年 | 1413篇 |
2001年 | 289篇 |
2000年 | 192篇 |
1999年 | 323篇 |
1998年 | 366篇 |
1997年 | 267篇 |
1996年 | 222篇 |
1995年 | 227篇 |
1994年 | 241篇 |
1993年 | 230篇 |
1992年 | 195篇 |
1991年 | 182篇 |
1990年 | 157篇 |
1989年 | 146篇 |
1988年 | 171篇 |
1987年 | 126篇 |
1986年 | 133篇 |
1985年 | 179篇 |
1984年 | 179篇 |
1983年 | 183篇 |
1982年 | 206篇 |
1981年 | 190篇 |
1980年 | 159篇 |
1979年 | 119篇 |
1978年 | 121篇 |
1977年 | 93篇 |
1976年 | 91篇 |
1975年 | 76篇 |
1974年 | 84篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Stephen J. Traphagen Michael J. Dimarco Margaret E. Silliker 《RNA (New York, N.Y.)》2010,16(4):828-838
Regions of the Didymium iridis mitochondrial genome were identified with similarity to typical mitochondrial genes; however, these regions contained numerous stop codons. We used RT-PCR and DNA sequencing to determine whether, through RNA editing, these regions were transcribed into mRNAs that could encode functional proteins. Ten putative gene regions were examined: atp1, atp6, atp8, atp9, cox1, cox2, cytb, nad4L, nad6, and nad7. The cDNA sequences of each gene could encode a functional mitochondrial protein that was highly conserved compared with homologous genes. The type of editing events and editing sequence features were very similar to those observed in the homologous genes of Physarum polycephalum, though the actual editing locations showed a variable degree of conservation. Edited sites were compared with encoded sites in D. iridis and P. polycephalum for all 10 genes. Edited sequence for a portion of the cox1 gene was available for six myxomycetes, which, when compared, showed a high degree of conservation at the protein level. Different types of editing events showed varying degrees of site conservation with C-to-U base changes being the least conserved. Several aspects of single C insertion editing events led to the preferential creation of hydrophobic amino acid codons that may help to minimize adverse effects on the resulting protein structure. 相似文献
22.
Stephen Gene Sullivan Joseph Dancis Rody P. Cox 《Biochimica et Biophysica Acta (BBA)/General Subjects》1978,539(2):135-141
Hypophysectomy caused a marked but transient increase in branched-chain α-keto acid decarboxylase activities in rat liver mitochondria, peaking at about nine days post-surgery. The magnitude of increase is different for each of the three branched-chain α-keto acids. The activities then fall to a new steady state in three weeks with α-ketoisovalerate decarboxylase activity within the normal range, α-keto-β-methylvalerate decarboxylase activity at twice normal, and α-ketoisocaproate decarboxylase activity decreased to a level too low for accurate measurements. 相似文献
23.
24.
Elliott C. Kulakowski Joseph Maturo Stephen W. Schaffer 《Archives of biochemistry and biophysics》1981,210(1):204-209
Cardiac sarcolemma preparations of both pig and rat ventricles were found to possess two sets of taurine-binding components. The two proteins from pig heart were solubilized with the detergent Ammonyx-Lo. Characterization of these solubilized proteins revealed that both components are glycoproteins and retain the binding properties observed for the membrane isolate. However, the characterization also revealed several differences between the proteins including their binding specificities, their affinities for taurine, their binding isotherms, and their molecular sizes. Possible functions of these two taurine-binding proteins are discussed. 相似文献
25.
26.
27.
A Farmer-based approach to conserving crop germplasm 总被引:1,自引:0,他引:1
Stephen B. Brush 《Economic botany》1991,45(2):153-165
In situ conservation of crop genetic resources from centers of agricultural diversity is considered. This strategy has been rejected for several reasons, but other factors make it an important potential contributor to the overall conservation effort. Case studies of potato agriculture in Peru, maize agriculture in Mexico, and rice agriculture in Thailand indicate that farmers frequently engage in de facto conservation of landraces. Five principles should guide planning of in situ conservation: complementarity with off-site conservation, minimal institutional development, continuity with existing programs, meeting the development goals of increasing income and food, and accepting germplasm as an international public good. Four means to implement on-site conservation are presented: the institutional framework; the information base; the policy framework; and the role of grassroots organizations. 相似文献
28.
29.
Loblolly pine (Pinus taeda L.) produces an induced defensive hypersensitive response in inner bark colonized by the southern pine beetle, Dendroctonus frontalis Zimm. (Coleoptera: Scolytidae), and its associated fungi. Adult beetles forced to colonize the induced response tissue in a laboratory study constructed galleries that were the same length as adults boring in normal phloem. However, each female laid fewer eggs in the induced tissue. Larval and pupal mortality were also higher in this tissue when compared to surrounding phloem. Beetles colonizing trees in response to pheromone baits constructed less gallery and laid fewer eggs in induced tissue than in surrounding normal phloem. These results suggest that the lesions produced by the induced defense system in conifers may not only contain the growth of fungi inoculated into trees during the attack phase of beetle colonization, but may also affect survival of bark beetle progeny.
Résumé Une réaction hypersensible de défense a été induite dans les couches profondes de l'écorce de P. taeda colonisée par D. frontalis et le champignon qui lui est associé. Au laboratoire, des adultes, contraints de coloniser les tissus où une réaction hypersensible e été induite, ont foré des galeries de même longueur que celles creusées dans du phloème sain. Cependant les femelles ont pondu moins d'oeufs dans les tissus induits; les mortalités larvaires et nymphales étaient aussi plus fortes dans ce tissu que dans le phloème voisin. Les scolytes, ayant colonisé les arbres après attraction par des pièges à phéromones, forent moins de galeries et pondent moins d'oeufs dans le tissu induit que dans le phloème sain voisin. Ces résultats suggèrent que les lésions, provoquées par le système de défense induit des conifères, peuvent non seulement limiter la croissance du champignon inoculé dans l'arbre au cours de la colonisation des scolytes, mais aussi affecter la survie des descendants dans l'écorce.相似文献
30.
Patrick F. Carfagna Steven D. Wyrick David J. Holbrook Stephen G. Chaney 《Journal of biochemical and molecular toxicology》1991,6(1):71-80
We have studied the effects of diethyldithiocarbamate (DDTC) on the biotransformations of toxic doses of tetrachloro (d,l-trans)1,2-diaminocyclohexaneplatinum(IV) (tetraplatin) in Fischer 344 rats. In animals not treated with DDTC, tetraplatin was rapidly converted to dichloro(d,I-trans)1,2-diaminocyclohexaneplatinum(II) [PtCl2(dach]. Subsequent biotransformations included the transient formation of the (d,I-trans)1,2-diaminocyclohexane-aquachloroplatinum(II) [Pt(H2O)(Cl)(dach)]+ complex, followed by formation of the platinum (Pt)-methionine and either Pt-cysteine or Pt-ornithine complexes. Significant amounts of free (d,I-trans) 1,2-diaminocyclohexane (dach) were observed in plasma as a result of intracellular trans-labilization reactions. DDTC caused a marked decrease in both total and protein-bound platinum in the circulation. A significant increase in the plasma concentration of free dach was also observed as a result of formation of the Pt(DDTC)2 complex. Some of the free dach could have arisen from intracellular reactions with DDTC, but the displacement of platinum from plasma proteins was more than sufficient to account for the increase in free dach in the circulation. DDTC treatment also decreased plasma concentrations of tetraplatin, PtCl2(dach), [Pt(H2O)(Cl)(dach)]+, the Pt-methionine complex, and one unidentified biotransformation product, but had no effect on the Pt-cysteine (or Pt-ornithine) complex. These effects of DDTC on protein-bound platinum and low-molecular-weight biotransformation products in plasma may contribute to the decrease in tetraplatin toxicity seen in DDTC-treated rats. 相似文献