全文获取类型
收费全文 | 4527篇 |
免费 | 323篇 |
国内免费 | 1篇 |
专业分类
4851篇 |
出版年
2024年 | 3篇 |
2023年 | 33篇 |
2022年 | 77篇 |
2021年 | 127篇 |
2020年 | 52篇 |
2019年 | 83篇 |
2018年 | 113篇 |
2017年 | 133篇 |
2016年 | 173篇 |
2015年 | 230篇 |
2014年 | 276篇 |
2013年 | 333篇 |
2012年 | 417篇 |
2011年 | 426篇 |
2010年 | 230篇 |
2009年 | 170篇 |
2008年 | 249篇 |
2007年 | 272篇 |
2006年 | 254篇 |
2005年 | 267篇 |
2004年 | 226篇 |
2003年 | 192篇 |
2002年 | 172篇 |
2001年 | 52篇 |
2000年 | 19篇 |
1999年 | 28篇 |
1998年 | 44篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 21篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1968年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有4851条查询结果,搜索用时 15 毫秒
41.
Ballabio E Regan R Garimberti E Harbott J Bradtke J Teigler-Schlegel A Biondi A Cazzaniga G Giudici G Wainscoat JS Boultwood J Bridger JM Knight SJ Tosi S 《PloS one》2011,6(6):e20607
Leukaemia is often associated with genetic alterations such as translocations, amplifications and deletions, and recurrent chromosome abnormalities are used as markers of diagnostic and prognostic relevance. However, a proportion of acute myeloid leukaemia (AML) cases have an apparently normal karyotype despite comprehensive cytogenetic analysis. Based on conventional cytogenetic analysis of banded chromosomes, we selected a series of 23 paediatric patients with acute myeloid leukaemia and performed whole genome array comparative genome hybridization (aCGH) using DNA samples derived from the same patients. Imbalances involving large chromosomal regions or entire chromosomes were detected by aCGH in seven of the patients studied. Results were validated by fluorescence in situ hybridization (FISH) to both interphase nuclei and metaphase chromosomes using appropriate bacterial artificial chromosome (BAC) probes. The majority of these copy number alterations (CNAs) were confirmed by FISH and found to localize to the interphase rather than metaphase nuclei. Furthermore, the proliferative states of the cells analyzed by FISH were tested by immunofluorescence using an antibody against the proliferation marker pKi67. Interestingly, these experiments showed that, in the vast majority of cases, the changes appeared to be confined to interphase nuclei in a non-proliferative status. 相似文献
42.
Collecting and storing biological material from wild animals in a way that does not deteriorate DNA quality for subsequent analyses is instrumental for research in ecology and evolution. Our aims were to gather reports on the effectiveness of methods commonly used by researchers for the field collection and long‐term storage of blood samples and DNA extracts from wild birds. Personal experiences were collected with an online survey targeted specifically at researchers sampling wild birds. Many researchers experienced problems with blood sample storage but not with DNA extract storage. Storage issues generated problems with obtaining adequate DNA quality and sufficient DNA quantity for the targeted molecular analyses but were not related to season of blood sampling, access to equipment, transporting samples, temperature, and method of blood storage. Final DNA quality and quantity were also not affected by storage time before DNA extraction or the methods used to extract DNA. We discuss practical aspects of field collection and storage and provide some general recommendations, with a list of pros and cons of different preservation methods of avian blood samples and DNA extracts. 相似文献
43.
Syukur Syukur Joanna Richmond Marwan E. Majzoub Jadranka Nappi Suhelen Egan Torsten Thomas 《Environmental microbiology》2024,26(1):e16564
Different marine seaweed species have been shown to harbour specific bacterial communities, however, the extent to which vertical symbiont transmission from parents to offspring contributes to host-specificity is unclear. Here we use fluorescence and electron microscopy as well as 16S rRNA gene-based community analysis to investigate symbiont transmission in members of the three major seaweed groups (green Chlorophyta, red Rhodophyta and brown Phaeophyceae). We found seaweeds employ diverse strategies to transfer symbionts to their progeny. For instance, the green Ulva australis does not appear to have the capacity for vertical transmission. In contrast, the brown Phyllospora comosa adopts a non-selective vertical transmission. The red Delisea pulchra demonstrates weak selectivity in symbiont transmission, while the brown Hormosira banksii exhibits a strongly selective symbiont transfer. Mucilage on the gametes appears to facilitate vertical transmission and transferred bacteria have predicted properties that could support early development of the seaweeds. Previous meta-analysis has indicated that vertical transmission is rare in aquatic compared to terrestrial environments, however, our results contribute to the growing evidence that this might not be the case and that instead vertical transmission with various degrees of symbiont selection occurs in the ecologically important group of seaweeds. 相似文献
44.
45.
Using miniaturized radiotelemetry to discover the breeding grounds of the endangered New Zealand Storm Petrel Fregetta maoriana 下载免费PDF全文
Matt J. Rayner Chris P. Gaskin Neil B. Fitzgerald Karen A. Baird Martin M. Berg David Boyle Leigh Joyce Todd J. Landers Graeme G. Loh Sue Maturin Lyndon Perrimen R. Paul Scofield Joanna Simm Ian Southey Graeme A. Taylor Alan J. D. Tennyson Bruce C. Robertson Megan Young Richard Walle Stefanie M. H. Ismar 《Ibis》2015,157(4):754-766
Identification of breeding sites remains a critical step in species conservation, particularly in procellariiform seabirds whose threat status is of global concern. We designed and conducted an integrative radiotelemetry approach to uncover the breeding grounds of the critically endangered New Zealand Storm Petrel Fregetta maoriana (NZSP), a species considered extinct before its rediscovery in 2003. Solar‐powered automated radio receivers and hand‐held telemetry were used to detect the presence of birds on three island groups in the Hauraki Gulf near Auckland, New Zealand. At least 11 NZSP captured and radiotagged at sea were detected at night near Te Hauturu‐o‐Toi/Little Barrier Island with the detection of an incubating bird leading to the discovery of the first known breeding site for this species. In total, four NZSP breeding burrows were detected under mature forest canopy and three adult NZSP and two NZSP chicks were ringed. Telemetry data indicated NZSP showed strong moonlight avoidance behaviour over the breeding site, had incubation shifts of approximately 5 days and had a breeding season extending from February to June/July, a different season from other Procellariiformes in the region. Radiotelemetry, in combination with rigorously collected field data on species distribution, offers a valuable technique for locating breeding grounds of procellariiform seabirds and gaining insights into breeding biology while minimizing disturbance to sensitive species or damage to fragile habitat. Our study suggests an avenue for other breeding ground searches in one of the most threatened avian Orders, and highlights the general need for information on the location of breeding sites and understanding the breeding biology in data‐deficient birds. 相似文献
46.
Joanna Kubler-Kielb Evgeny Vinogradov Vince Pozsgay John B. Robbins 《Carbohydrate research》2010,345(11):1600-1608
There is no licensed vaccine for the prevention of shigellosis. Our approach to the development of a Shigella vaccines is based on inducing serum IgG antibodies to the O-specific polysaccharide (O-SP) domain of their lipopolysaccharides (LPS). We have shown that low molecular mass O-SP-core (O-SPC) fragments isolated from Shigella sonnei LPS conjugated to proteins induced significantly higher antibody levels in mice than the full length O-SP conjugates. This finding is now extended to the O-SPC of Shigella flexneri 2a and 6, and Shigella dysenteriae type 1. The structures of O-SPC, containing core plus 1-4 O-SP repeat units (RUs), were analyzed by NMR and mass spectroscopy. The first RUs attached to the cores of S. flexneri 2a and 6 LPS were different from the following RUs in their O-acetylation and/or glucosylation. Conjugates of core plus more than 1 RU were necessary to induce LPS antibodies in mice. The resulting antibody levels were comparable to those induced by the full length O-SP conjugates. In S. dysenteriae type 1, the first RU was identical to the following RUs, with the exception that the GlcNAc was bound to the core in the β-configuration, while in all other RUs the GlcNAc was present in the α-configuration. In spite of this difference, conjugates of S. dysenteriae type 1 core with 1, 2, or 3 RUs induced LPS antibodies in mice with levels statistically higher than those of the full size O-SP conjugates. O-SPC conjugates are easy to prepare, characterize, and standardize, and their clinical evaluation is planned. 相似文献
47.
Ohsaki Y Sugimoto Y Suzuki M Kaidoh T Shimada Y Ohno-Iwashita Y Davies JP Ioannou YA Ohno K Ninomiya H 《Histochemistry and cell biology》2004,121(4):263-272
-Toxin (perfringolysin O) binds to cell surface cholesterol and forms oligomeric pores that cause membrane damage. Both in cytotoxicity and cell survival assays, a mutant Chinese hamster ovary cell line NPC1(–) that lacked Niemann-Pick C1 showed reduced sensitivity to -toxin, compared with wild-type (wt) cells. BC is a derivative of -toxin that retains cholesterol-binding activity but lacks cytotoxicity. Confocal and electron microscopy revealed the presence of multiple vesicles which bound BC, both on the cell surface and in the extracellular space of these cells. BC binding to raft microdomains was verified by its resistance to 1% Triton X-100 at 4°C and recovery of bound BC in floating low-density fractions on sucrose density gradient fractionation. BC-labeled vesicles were abolished when NPC1(–) cells were depleted of lipoproteins and also when treated with a Rho-associated kinase inhibitor Y-27632. In addition, similar vesicles were observed in wt cells treated with progesterone. In parallel with these results, -toxin sensitivity of NPC1(–) cells was increased when cells were depleted of lipoproteins or treated with Y-27632, whereas that of wt cells was decreased by progesterone. Our findings suggest that sequestration of toxin to raft-enriched cell surface vesicles may underlie reduced sensitivity of NPC1-deficient cells to -toxin. 相似文献
48.
49.
50.
Wei Su Sergey V. Slepenkov Michael K. Slevin Shawn M. Lyons Marcin Ziemniak Joanna Kowalska Edward Darzynkiewicz Jacek Jemielity William F. Marzluff Robert E. Rhoads 《RNA (New York, N.Y.)》2013,19(1):1-16
Metazoan replication-dependent histone mRNAs are only present in S-phase, due partly to changes in their stability. These mRNAs end in a unique stem–loop (SL) that is required for both translation and cell-cycle regulation. Previous studies showed that histone mRNA degradation occurs through both 5′→3′ and 3′→5′ processes, but the relative contributions are not known. The 3′ end of histone mRNA is oligouridylated during its degradation, although it is not known whether this is an essential step. We introduced firefly luciferase reporter mRNAs containing the histone 3′ UTR SL (Luc-SL) and either a normal or hDcp2-resistant cap into S-phase HeLa cells. Both mRNAs were translated, and translation initially protected the mRNAs from degradation, but there was a lag of ∼40 min with the uncleavable cap compared to ∼8 min for the normal cap before rapid decay. Knockdown of hDcp2 resulted in a similar longer lag for Luc-SL containing a normal cap, indicating that 5′→3′ decay is important in this system. Inhibition of DNA replication with hydroxyurea accelerated the degradation of Luc-SL. Knockdown of terminal uridyltransferase (TUTase) 4 but not TUTase 3 slowed the decay process, but TUTase 4 knockdown had no effect on destabilization of the mRNA by hydroxyurea. Both Luc-SL and its 5′ decay intermediates were oligouridylated. Preventing oligouridylation by 3′-deoxyadenosine (cordycepin) addition to the mRNA slowed degradation, in the presence or absence of hydroxyurea, suggesting oligouridylation initiates degradation. The spectrum of oligouridylated fragments suggests the 3′→5′ degradation machinery stalls during initial degradation, whereupon reuridylation occurs. 相似文献