全文获取类型
收费全文 | 3710篇 |
免费 | 323篇 |
国内免费 | 1篇 |
专业分类
4034篇 |
出版年
2023年 | 16篇 |
2022年 | 40篇 |
2021年 | 70篇 |
2020年 | 52篇 |
2019年 | 50篇 |
2018年 | 48篇 |
2017年 | 41篇 |
2016年 | 94篇 |
2015年 | 142篇 |
2014年 | 182篇 |
2013年 | 209篇 |
2012年 | 314篇 |
2011年 | 305篇 |
2010年 | 182篇 |
2009年 | 193篇 |
2008年 | 244篇 |
2007年 | 198篇 |
2006年 | 190篇 |
2005年 | 213篇 |
2004年 | 209篇 |
2003年 | 188篇 |
2002年 | 178篇 |
2001年 | 21篇 |
2000年 | 23篇 |
1999年 | 28篇 |
1998年 | 38篇 |
1997年 | 27篇 |
1996年 | 29篇 |
1995年 | 29篇 |
1994年 | 36篇 |
1993年 | 23篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1985年 | 15篇 |
1984年 | 34篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 28篇 |
1979年 | 15篇 |
1978年 | 25篇 |
1977年 | 27篇 |
1976年 | 15篇 |
1975年 | 14篇 |
1974年 | 22篇 |
1973年 | 16篇 |
排序方式: 共有4034条查询结果,搜索用时 0 毫秒
21.
22.
Total starch, amylose content and amylose-included lipid phosphorus and lysophosphatidylcholine (LPC) were measured in normal Glacier (G) and Hi Amylose Glacier (HA) barley varieties during germination. From days three to six, alkaline and acidic lysophospholipase (LPL) activities in the starchy endosperm were measured and the distribution of these activities between a soluble and particulate form determined. During germination the amylose content of the starches increases as the total starch levels decline. The starch-bound LPC and lipid phosphorus disappear at the same rate between days three and six in both barley varieties, indicating no discrimination among the different lipid-included amylose population for degradation. However, both lipid phosphorus and LPC disappear more rapidly in the G than in the HA variety. This is presumably due to the slightly larger content of LPC per mg amylose of the G than of the HA variety, equivalent to 134 and 150 anhydroglucose residues per lipid molecule in G and HA, respectively. There is no increase in starch-bound lipid phosphorus or LPC expressed as nmol of phosphorus or LPC per mg amylose as amylose content declines, indicating no selective resistance of lipid-included amylose to degradation. The alkaline and acidic LPC activities in each variety increase 2–4-fold between days four and five. In both varieties ca 30% of the acidic LPL and ca 50–60% of the alkaline LPL is particulate from days three to six. No correlation can be made between the content of amylose or amylose-included lipid and particulate LPL activity. However, the possibility that particulate LPL activity is associated with specific populations of residual amylose-included lipid molecules cannot be excluded. 相似文献
23.
Jakob Vinther Derek E. G. Briggs Julia Clarke Gerald Mayr Richard O. Prum 《Biology letters》2010,6(1):128-131
Investigation of feathers from the famous Middle Eocene Messel Oil Shale near Darmstadt, Germany shows that they are preserved as arrays of fossilized melanosomes, the surrounding beta-keratin having degraded. The majority of feathers are preserved as aligned rod-shaped eumelanosomes. In some, however, the barbules of the open pennaceous, distal portion of the feather vane are preserved as a continuous external layer of closely packed melanosomes enclosing loosely aligned melanosomes. This arrangement is similar to the single thin-film nanostructure that generates an iridescent, structurally coloured sheen on the surface of black feathers in many lineages of living birds. This is, to our knowledge, the first evidence of preservation of a colour-producing nanostructure in a fossil feather and confirms the potential for determining colour differences in ancient birds and other dinosaurs. 相似文献
24.
Ian W Boucher Andrzej M Brzozowski James A Brannigan Claudia Schnick Derek J Smith Sue A Kyes Anthony J Wilkinson 《BMC structural biology》2006,6(1):20-10
Background
Superoxide dismutases (SODs) are important enzymes in defence against oxidative stress. In Plasmodium falciparum, they may be expected to have special significance since part of the parasite life cycle is spent in red blood cells where the formation of reactive oxygen species is likely to be promoted by the products of haemoglobin breakdown. Thus, inhibitors of P. falciparum SODs have potential as anti-malarial compounds. As a step towards their development we have determined the crystal structure of the parasite's cytosolic iron superoxide dismutase. 相似文献25.
26.
Daphnia pulex is quickly becoming an attractive model species in the field of ecological genomics due to the recent release of its complete genome sequence, a wide variety of new genomic resources, and a rich history of ecological data. Sequences of the mitochondrial NADH dehydrogenase subunit 5 and cytochrome c oxidase subunit 1 genes were used to assess the global phylogeography of this species, and to further elucidate its phylogenetic relationship to other members of the Daphnia pulex species complex. Using both newly acquired and previously published data, we analyzed 398 individuals from collections spanning five continents. Eleven strongly supported lineages were found within the D. pulex complex, and one lineage in particular, panarctic D. pulex, has very little phylogeographical structure and a near worldwide distribution. Mismatch distribution, haplotype network, and population genetic analyses are compatible with a North American origin for this lineage and subsequent spatial expansion in the Late Pleistocene. In addition, our analyses suggest that dispersal between North and South America of this and other species in the D. pulex complex has occurred multiple times, and is predominantly from north to south. Our results provide additional support for the evolutionary relationships of the eleven main mitochondrial lineages of the D. pulex complex. We found that the well-studied panarctic D. pulex is present on every continent except Australia and Antarctica. Despite being geographically very widespread, there is a lack of strong regionalism in the mitochondrial genomes of panarctic D. pulex – a pattern that differs from that of most studied cladocerans. Moreover, our analyses suggest recent expansion of the panarctic D. pulex lineage, with some continents sharing haplotypes. The hypothesis that hybrid asexuality has contributed to the recent and unusual geographic success of the panarctic D. pulex lineage warrants further study. 相似文献
27.
Genetic mapping at 3-kilobase resolution reveals inositol 1,4,5-triphosphate receptor 3 as a risk factor for type 1 diabetes in Sweden 下载免费PDF全文
Roach JC Deutsch K Li S Siegel AF Bekris LM Einhaus DC Sheridan CM Glusman G Hood L Lernmark A Janer M;Swedish Childhood Diabetes Study Group;Diabetes Incidence in Sweden Study Group 《American journal of human genetics》2006,79(4):614-627
We mapped the genetic influences for type 1 diabetes (T1D), using 2,360 single-nucleotide polymorphism (SNP) markers in the 4.4-Mb human major histocompatibility complex (MHC) locus and the adjacent 493 kb centromeric to the MHC, initially in a survey of 363 Swedish T1D cases and controls. We confirmed prior studies showing association with T1D in the MHC, most significantly near HLA-DR/DQ. In the region centromeric to the MHC, we identified a peak of association within the inositol 1,4,5-triphosphate receptor 3 gene (ITPR3; formerly IP3R3). The most significant single SNP in this region was at the center of the ITPR3 peak of association (P=1.7 x 10(-4) for the survey study). For validation, we typed an additional 761 Swedish individuals. The P value for association computed from all 1,124 individuals was 1.30 x 10(-6) (recessive odds ratio 2.5; 95% confidence interval [CI] 1.7-3.9). The estimated population-attributable risk of 21.6% (95% CI 10.0%-31.0%) suggests that variation within ITPR3 reflects an important contribution to T1D in Sweden. Two-locus regression analysis supports an influence of ITPR3 variation on T1D that is distinct from that of any MHC class II gene. 相似文献
28.
29.
30.
Stark JH Sharma R Ostroff S Cummings DA Ermentrout B Stebbins S Burke DS Wisniewski SR 《PloS one》2012,7(3):e34245