全文获取类型
收费全文 | 7977篇 |
免费 | 672篇 |
国内免费 | 1篇 |
专业分类
8650篇 |
出版年
2023年 | 33篇 |
2022年 | 89篇 |
2021年 | 178篇 |
2020年 | 77篇 |
2019年 | 117篇 |
2018年 | 135篇 |
2017年 | 116篇 |
2016年 | 247篇 |
2015年 | 377篇 |
2014年 | 448篇 |
2013年 | 520篇 |
2012年 | 680篇 |
2011年 | 661篇 |
2010年 | 454篇 |
2009年 | 436篇 |
2008年 | 539篇 |
2007年 | 527篇 |
2006年 | 470篇 |
2005年 | 459篇 |
2004年 | 434篇 |
2003年 | 416篇 |
2002年 | 370篇 |
2001年 | 73篇 |
2000年 | 51篇 |
1999年 | 67篇 |
1998年 | 81篇 |
1997年 | 62篇 |
1996年 | 50篇 |
1995年 | 41篇 |
1994年 | 52篇 |
1993年 | 55篇 |
1992年 | 33篇 |
1991年 | 37篇 |
1990年 | 25篇 |
1989年 | 26篇 |
1988年 | 26篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 14篇 |
1984年 | 13篇 |
1983年 | 19篇 |
1982年 | 10篇 |
1981年 | 16篇 |
1980年 | 7篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1972年 | 4篇 |
排序方式: 共有8650条查询结果,搜索用时 0 毫秒
51.
The environmental contexts of the karstic hominin sites in South Africa have been established largely by means of faunal associations; taken together these data suggest a trend from relatively closed and more mesic to open, drier environments from about 3 to 1.5 Ma. Vrba argued for a major shift within this trend ca. 2.4-2.6 Ma, an influential proposal that posited links between bovid (and hominin) radiation in Africa and the intensification of Northern Hemisphere Glaciation. Yet faunal approaches often rely on habitat and feeding preferences of modern taxa that may differ from those of their extinct predecessors. Here we explore ways of extending 13C/12C data from fossil mammals beyond denoting “presence” or “absence” of C4 grasses using the evolution of open environments in South Africa as a case study. To do so we calculated the relative proportions of C3-, mixed-, and C4-feeding herbivores for all the hominin sites for which we have sufficient data based on 13C/12C analyses of fossil tooth enamel. The results confirm a general trend towards more open environments since 3 Ma, but they also emphasize a marked change to open grassy habitats in the latest Pliocene/early Pleistocene. Mean 13C/12C for large felids also mirrored this trend. 相似文献
52.
Julie M. Bianchini Khameeka N. Kitt Martijn Gloerich Sabine Pokutta William I. Weis W. James Nelson 《The Journal of cell biology》2015,210(7):1065-1074
As part of the E-cadherin–β-catenin–αE-catenin complex (CCC), mammalian αE-catenin binds F-actin weakly in the absence of force, whereas cytosolic αE-catenin forms a homodimer that interacts more strongly with F-actin. It has been concluded that cytosolic αE-catenin homodimer is not important for intercellular adhesion because E-cadherin/αE-catenin chimeras thought to mimic the CCC are sufficient to induce cell–cell adhesion. We show that, unlike αE-catenin in the CCC, these chimeras homodimerize, bind F-actin strongly, and inhibit the Arp2/3 complex, all of which are properties of the αE-catenin homodimer. To more accurately mimic the junctional CCC, we designed a constitutively monomeric chimera, and show that E-cadherin–dependent cell adhesion is weaker in cells expressing this chimera compared with cells in which αE-catenin homodimers are present. Our results demonstrate that E-cadherin/αE-catenin chimeras used previously do not mimic αE-catenin in the native CCC, and imply that both CCC-bound monomer and cytosolic homodimer αE-catenin are required for strong cell–cell adhesion. 相似文献
53.
54.
Julie M. Old 《PloS one》2015,10(12)
The thylacine (Thylacinus cynocephalus) was Australia’s largest marsupial carnivore until its extinction within the last century. There remains considerable interest and debate regarding the biology of this species. Studies of thylacine biology are now limited to preserved specimens, and parts thereof, as well as written historical accounts of its biology. This study describes the development of the immune tissues of a pouch young thylacine, one of only eleven in existence, and the only specimen to be histologically sectioned. The appearance of the immune tissue of the developing pouch young thylacine is compared to the immune tissues of extant marsupials, providing insights into the immunity, biology and ecology of the extinct thylacine. 相似文献
55.
56.
DiDonato M Krishna SS Schwarzenbacher R McMullan D Jaroszewski L Miller MD Abdubek P Agarwalla S Ambing E Axelrod H Biorac T Chiu HJ Deacon AM Elsliger MA Feuerhelm J Godzik A Grittini C Grzechnik SK Hale J Hampton E Haugen J Hornsby M Klock HE Knuth MW Koesema E Kreusch A Kuhn P Lesley SA Moy K Nigoghossian E Okach L Paulsen J Quijano K Reyes R Rife C Spraggon G Stevens RC van den Bedem H Velasquez J White A Wolf G Xu Q Hodgson KO Wooley J Wilson IA 《Proteins》2006,63(1):256-260
57.
G. Gray Eaton Deanne F. Johnson Barbara B. Glick Julie M. Worlein 《Primates; journal of primatology》1986,27(2):141-150
We have quantitatively documented the development of sex differences in the behavior of juvenile Japanese macaques (1 to 2
years of age). Mothers treated their offspring differently by sex, i.e., mothers of males broke contact with them more frequently
than did mothers of females. Juvenile males played more, and mounted other macaques more frequently; juvenile females groomed
their mothers more and were also punished by other group members more frequently than were males. Males showed a pattern of
decreasing interactions with their mothers, but females increased the frequency of their maternal interactions. These patterns
appear to presage the life histories of the sexes. However, comparisons with other species of nonhuman primates indicate that
although sex differences in behavior are common, the variability among species severely limits cross-specific generalizations. 相似文献
58.
Peter G. Walley Gemma Hough Jonathan D. Moore John Carder Marian Elliott Andrew Mead Julie Jones Graham Teakle Guy Barker Vicky Buchanan-Wollaston Paul Hand David Pink Rosemary Collier 《Molecular breeding : new strategies in plant improvement》2017,37(1):4
Domesticated lettuce varieties encompass much morphological variation across a range of crop type groups, with large collections of cultivars and landrace accessions maintained in genebanks. Additional variation not captured during domestication, present in ancestral wild relatives, represents a potentially rich source of alleles that can deliver to sustainable crop production. However, these large collections are difficult and costly to screen for many agronomically important traits. In this paper, we describe the generation of a diversity collection of 96 lettuce and wild species accessions that are amenable to routine phenotypic analysis and their genotypic characterization with a panel of 682 newly developed expressed sequence tag (EST)-linked KASP? single nucleotide polymorphism (SNP) markers that are anchored to the draft Lactuca sativa genome assembly. To exemplify the utility of these resources, we screened the collection for putative sources of resistance to currant-lettuce aphid (Nasonovia ribisnigri) and carried out association analyses to look for potential SNPs linked to resistance. 相似文献
59.
60.
Jér?me Loc'h Magali Blaud Stéphane Réty Simon Lebaron Patrick Deschamps Joseph Bareille Julie Jombart Julien Robert-Paganin Lila Delbos Florian Chardon Elodie Zhang Clément Charenton David Tollervey Nicolas Leulliot 《PLoS biology》2014,12(5)
During biogenesis of the 40S and 60S ribosomal subunits, the pre-40S particles are exported to the cytoplasm prior to final cleavage of the 20S pre-rRNA to mature 18S rRNA. Amongst the factors involved in this maturation step, Fap7 is unusual, as it both interacts with ribosomal protein Rps14 and harbors adenylate kinase activity, a function not usually associated with ribonucleoprotein assembly. Human hFap7 also regulates Cajal body assembly and cell cycle progression via the p53–MDM2 pathway. This work presents the functional and structural characterization of the Fap7–Rps14 complex. We report that Fap7 association blocks the RNA binding surface of Rps14 and, conversely, Rps14 binding inhibits adenylate kinase activity of Fap7. In addition, the affinity of Fap7 for Rps14 is higher with bound ADP, whereas ATP hydrolysis dissociates the complex. These results suggest that Fap7 chaperones Rps14 assembly into pre-40S particles via RNA mimicry in an ATP-dependent manner. Incorporation of Rps14 by Fap7 leads to a structural rearrangement of the platform domain necessary for the pre-rRNA to acquire a cleavage competent conformation. 相似文献