全文获取类型
收费全文 | 1755篇 |
免费 | 160篇 |
国内免费 | 2篇 |
出版年
2022年 | 9篇 |
2021年 | 17篇 |
2020年 | 9篇 |
2019年 | 19篇 |
2018年 | 26篇 |
2017年 | 17篇 |
2016年 | 29篇 |
2015年 | 57篇 |
2014年 | 62篇 |
2013年 | 82篇 |
2012年 | 93篇 |
2011年 | 85篇 |
2010年 | 58篇 |
2009年 | 51篇 |
2008年 | 91篇 |
2007年 | 89篇 |
2006年 | 89篇 |
2005年 | 102篇 |
2004年 | 116篇 |
2003年 | 108篇 |
2002年 | 98篇 |
2001年 | 32篇 |
2000年 | 21篇 |
1999年 | 20篇 |
1998年 | 34篇 |
1997年 | 22篇 |
1996年 | 31篇 |
1995年 | 17篇 |
1994年 | 18篇 |
1993年 | 25篇 |
1992年 | 25篇 |
1991年 | 14篇 |
1990年 | 23篇 |
1989年 | 12篇 |
1988年 | 15篇 |
1987年 | 17篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 18篇 |
1983年 | 13篇 |
1982年 | 24篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1975年 | 10篇 |
1974年 | 18篇 |
1973年 | 17篇 |
1972年 | 12篇 |
排序方式: 共有1917条查询结果,搜索用时 17 毫秒
71.
Community-acquired urinary tract infections (UTIs) are commonly caused by uropathogenic Escherichia coli (UPEC). We hypothesize that chemotaxis toward ligands present in urine could direct UPEC into and up the urinary tract. Wild-type E. coli CFT073 and chemoreceptor mutants with tsr, tar, or aer deletions were tested for chemotaxis toward human urine in the capillary tube assay. Wild-type CFT073 was attracted toward urine, and Tsr and Tar were the chemoreceptors mainly responsible for mediating this response. The individual components of urine including L-amino acids, D-amino acids and various organic compounds were also tested in the capillary assay with wild-type CFT073. Our results indicate that CFT073 is attracted toward some L- amino acids and possibly toward some D-amino acids but not other common compounds found in urine such as urea, creatinine and glucuronic acid. In the murine model of UTI, the loss of any two chemoreceptors did not affect the ability of the bacteria to compete with the wild-type strain. Our data suggest that the presence of any strong attractant and its associated chemoreceptor might be sufficient for colonization of the urinary tract and that amino acids are the main chemoattractants for E. coli strain CFT073 in this niche. 相似文献
72.
73.
Bray Rodney A. Waeschenbach Andrea Littlewood D. Timothy J. Halvorsen Odd Olson Peter D. 《Systematic parasitology》2020,97(3):285-296
Systematic Parasitology - Chimaeras, or ratfishes, are the only extant group of holocephalan fishes and are the sole host group of gyrocotylidean cestodes, which represent a sister group of the... 相似文献
74.
Donald G Newman Ben D Bell Phillip J Bishop Rhys Burns Amanda Haigh Rodney A Hitchmough 《New Zealand journal of zoology.》2013,40(2):121-130
Abstract A reappraisal of the conservation status of the New Zealand frog fauna is presented using the 2008 version of the New Zealand Threat Classification System. Of New Zealand's four extant endemic species, three are judged to be ‘Threatened’ (Leiopelma hamiltoni being ‘Nationally Critical’, and L. pakeka and L. archeyi being ‘Nationally Vulnerable’) and one ‘At Risk’ (L. hochstetteri ‘Declining’). Three Leiopelma species are listed as extinct—they are known from bone deposits in caves throughout the country until some time in the last 1000 years. Three introduced and naturalised Litoria species are abundant in New Zealand although two (L. aurea and L. raniformis) are threatened in their country of origin (Australia). An additional unidentified frog taxon from northern Great Barrier Island is listed as ‘Data Deficient’. 相似文献
75.
Yuri L. Lyubchenko Alexander A. Gall Lyuda S. Shlyakhtenko Rodney E. Harrington Bertram L. Jacobs Patrick I. Oden 《Journal of biomolecular structure & dynamics》2013,31(3):589-606
Abstract A procedure for imaging long DNA and double stranded RNA (dsRNA) molecules using Atomic Force Microscopy (AFM) is described. Stable binding of double stranded DNA molecules to the flat mica surface is achieved by chemical modification of freshly cleaved mica under mild conditions with 3-aminopropyltriethoxy silane. We have obtained striking images of intact lambda DNA, Hind III restriction fragments of lambda DNA and dsRNA from reovirus. These images are stable under repeated scanning and measured contour lengths are accurate to within a few percent. This procedure leads to strong DNA attachment, allowing imaging under water. The widths of the DNA images lie in the range of 20 to 80nm for data obtained in air with commercially available probes. The work demonstrates that AFM is now a routine tool for simple measurements such as a length distribution. Improvement of substrate and sample preparation methods are needed to achieve yet higher resolution. 相似文献
76.
Randall, R. and Ross, G. J. B. 1979. Increasing population of Cape Gannets on Bird Island, Algoa Bay, and observations on breeding success. Ostrich 50:168-175. The South African Gannet Sula capensis on Bird Island has doubled in numbers between 1956 and 1974 and the process is continuing. The increase is similar to that of the two closely related species S. serrator and S. bassana. We estimated from the colony surface area and nest density that the number of birds with nests in 1974/5 was approximately 77 000. Making allowance for non-breeders, there were about 100 000 adults in 1974/5. Guano harvests from 1938–75 show considerable annual fluctuations with an overall downward trend. Poor agreement was found when relating guano harvests to population estimates, when the latter are gauged by colony surface area. We suggest that guano harvests are not good indicators of gannet population trends on Bird Island, primarily because of harvesting methods and environmental conditions. The number of chicks which fledged in the 1976/7 season in a section of the colony was far fewer than expected, even when allowances were made for egg-loss and chick mortality. A combination of heavier-than-usual rainfall and poor management techniques have resulted in high egg-loss and low chick numbers. 相似文献
77.
Chun Jung Chen Jennifer E. Cox Rodney P. Kincaid Angel Martinez Christopher S. Sullivan 《Journal of virology》2013,87(20):11135-11147
Hundreds of virus-encoded microRNAs (miRNAs) have been uncovered, but an in-depth functional understanding is lacking for most. A major challenge for the field is separating those miRNA targets that are biologically relevant from those that are not advantageous to the virus. Here, we show that miRNAs from related variants of the polyomavirus simian vacuolating virus 40 (SV40) have differing host target repertoires (targetomes) while their direct autoregulatory activity on virus-encoded early gene products is completely preserved. These results underscore the importance of miRNA-mediated viral gene autoregulation in some polyomavirus life cycles. More broadly, these findings imply that some host targets of virus-encoded miRNAs are likely to be of little selective advantage to the virus, and our approach provides a strategy for prioritizing relevant targets. 相似文献
78.
Kara A. Bernstein Eleni P. Mimitou Michael J. Mihalevic Huan Chen Ivana Sunjaveric Lorraine S. Symington Rodney Rothstein 《Genetics》2013,195(4):1241-1251
The RecQ helicase family is critical during DNA damage repair, and mutations in these proteins are associated with Bloom, Werner, or Rothmund-Thompson syndromes in humans, leading to cancer predisposition and/or premature aging. In the budding yeast Saccharomyces cerevisiae, mutations in the RecQ homolog, SGS1, phenocopy many of the defects observed in the human syndromes. One challenge to studying RecQ helicases is that their disruption leads to a pleiotropic phenotype. Using yeast, we show that the separation-of-function allele of SGS1, sgs1-D664Δ, has impaired activity at DNA ends, resulting in a resection processivity defect. Compromising Sgs1 resection function in the absence of the Sae2 nuclease causes slow growth, which is alleviated by making the DNA ends accessible to Exo1 nuclease. Furthermore, fluorescent microscopy studies reveal that, when Sgs1 resection activity is compromised in sae2Δ cells, Mre11 repair foci persist. We suggest a model where the role of Sgs1 in end resection along with Sae2 is important for removing Mre11 from DNA ends during repair. 相似文献
79.
Swati P. Mercer Anthony J. Roecker Susan Garson Duane R. Reiss C. Meacham Harrell Kathy L. Murphy Joseph G. Bruno Rodney A. Bednar Wei Lemaire Donghui Cui Tamara D. Cabalu Cuyue Tang Thomayant Prueksaritanont George D. Hartman Steven D. Young Christopher J. Winrow John J. Renger Paul J. Coleman 《Bioorganic & medicinal chemistry letters》2013,23(24):6620-6624
The orexin (or hypocretin) system has been identified as a novel target for the treatment of insomnia due to the wealth of biological and genetic data discovered over the past decade. Recently, clinical proof-of-concept was achieved for the treatment of primary insomnia using dual (OX1R/OX2R) orexin receptor antagonists. However, elucidation of the pharmacology associated with selective orexin-2 receptor antagonists (2-SORAs) has been hampered by the lack of orally bioavailable, highly selective small molecule probes. Herein, the discovery and optimization of a novel series of 2,5-diarylnicotinamides as potent and orally bioavailable orexin-2 receptor selective antagonists is described. A compound from this series demonstrated potent sleep promotion when dosed orally to EEG telemetrized rats. 相似文献
80.
Hassan Mahomed Rodney Ehrlich Tony Hawkridge Mark Hatherill Lawrence Geiter Fazlin Kafaar Deborah Ann Abrahams Humphrey Mulenga Michele Tameris Hennie Geldenhuys Willem Albert Hanekom Suzanne Verver Gregory Dudley Hussey 《PloS one》2013,8(3)