全文获取类型
收费全文 | 8181篇 |
免费 | 564篇 |
国内免费 | 5篇 |
专业分类
8750篇 |
出版年
2024年 | 12篇 |
2023年 | 37篇 |
2022年 | 116篇 |
2021年 | 179篇 |
2020年 | 118篇 |
2019年 | 149篇 |
2018年 | 257篇 |
2017年 | 210篇 |
2016年 | 330篇 |
2015年 | 516篇 |
2014年 | 513篇 |
2013年 | 604篇 |
2012年 | 782篇 |
2011年 | 663篇 |
2010年 | 429篇 |
2009年 | 361篇 |
2008年 | 495篇 |
2007年 | 497篇 |
2006年 | 407篇 |
2005年 | 365篇 |
2004年 | 329篇 |
2003年 | 300篇 |
2002年 | 228篇 |
2001年 | 155篇 |
2000年 | 141篇 |
1999年 | 106篇 |
1998年 | 43篇 |
1997年 | 37篇 |
1996年 | 20篇 |
1995年 | 23篇 |
1994年 | 15篇 |
1993年 | 16篇 |
1992年 | 27篇 |
1991年 | 29篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 19篇 |
1987年 | 19篇 |
1986年 | 8篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1975年 | 8篇 |
1973年 | 7篇 |
排序方式: 共有8750条查询结果,搜索用时 0 毫秒
21.
22.
Hyung-Jun Kwon Young Bae Ryu Young-Min Kim Naaleum Song Cha Young Kim Mun-Chual Rho Jae-Ho Jeong Kyoung-Oh Cho Woo Song Lee Su-Jin Park 《Bioorganic & medicinal chemistry》2013,21(15):4706-4713
Despite the prepdominat agent causing severe entero-pathogenic diarrhea in swine, there are no effective therapeutical treatment of porcine epidemic diarrhea virus (PEDV). In this study, we evaluated the antiviral activity of five phlorotannins isolated from Ecklonia cava (E. cava) against PEDV. In vitro antiviral activity was tested using two different assay strategies: (1) blockage of the binding of virus to cells (simultaneous-treatment assay) and (2) inhibition of viral replication (post-treatment assay). In simultaneous-treatment assay, compounds 2–5 except compound 1 exhibited antiviral activities of a 50% inhibitory concentration (IC50) with the ranging from 10.8 ± 1.4 to 22.5 ± 2.2 μM against PEDV. Compounds 1–5 were completely blocked binding of viral spike protein to sialic acids at less than 36.6 μM concentrations by hemagglutination inhibition. Moreover, compounds 4 and 5 of five phlorotannins inhibited viral replication with IC50 values of 12.2 ± 2.8 and 14.6 ± 1.3 μM in the post-treatment assay, respectively. During virus replication steps, compounds 4 and 5 exhibited stronger inhibition of viral RNA and viral protein synthesis in late stages (18 and 24 h) than in early stages (6 and 12 h). Interestingly, compounds 4 and 5 inhibited both viral entry by hemagglutination inhibition and viral replication by inhibition of viral RNA and viral protein synthesis, but not viral protease. These results suggest that compounds isolated from E. cava have strong antiviral activity against PEDV, inhibiting viral entry and/or viral replication, and may be developed into natural therapeutic drugs against coronavirus infection. 相似文献
23.
24.
Lee JY Lim JM Kim DK Zheng YH Moon S Han BK Song KD Kim H Han JY 《Molecular reproduction and development》2008,75(1):184-190
Members of the Pumilio (Pum) family of RNA-binding proteins act as translational repressors and are required for germ cell development and asymmetric division. We identified the chicken Pum1 and Pum2 genes and analyzed their expression patterns in various tissues. Comparative sequence analysis of the Pum1 and Pum2 proteins from the drosophila, chicken, mouse, and human revealed a high degree of evolutionary conservation in terms of the levels of homology of the peptide sequences and the structure of Pumilio homology domain (PUM-HD), C-terminal RNA-binding domain, with similar spacing between the adjacent Pum eight tandem repeats. In addition, phylogenetic patterns of pumilio family showed that Pum 1 and 2 of chicken are more closely related to those of mouse and human than other species and Pum1 is more conserved than Pum2. Using real-time RT-PCR, the expression levels of the Pum1 and Pum2 genes were found to be highest in hatched female gonads, and high-level expression of Pum2 was detected in 12-day and hatched gonads among the various chicken embryonic tissues tested. In adult tissues, the expression levels of Pum1 and Pum2 were expressed at higher levels in the testis and muscle than in any other tissue. The characteristics of the tissue-specific expression of Pum genes suggest that Pum1 and Pum2 have effects crucially in particular stage during development of chicken gonads depending on sexual maturation. 相似文献
25.
Hye Suck An Myung Mo Nam Jeong In Myeong Chul Min An 《Molecular biology reports》2014,41(11):7281-7292
The Korean starry flounder, Platichthys stellatus, is economically valuable coastal resident fish species. However, the annual catch of this fish has fluctuated and suffered major declines in Korea. We examined the genetic diversity and population structure for four wild populations and three hatchery stocks of Korean starry flounder to protect its genetic integrity using nine microsatellites. A group of 339 genotypes belonging to seven populations were screened. High degrees of polymorphism at the microsatellite loci were observed within both the wild and hatchery populations. Compared to the wild populations, genetic changes, including reduced genetic diversity and highly significant differentiation, have occurred in cultured stocks. Significant population differentiation was also observed in wild starry flounder populations. Similar degrees of inbreeding and significant Hardy–Weinberg equilibrium deviations were detected in both the wild and the hatchery populations. The genetic connectivity pattern identified four distinct metapopulations of starry flounder in Korea by clustering in the phylogenetic tree, Bayesian analyses, molecular variance analysis, PCA and multidimensional scaling analysis. A pattern of isolation-by-distance was not significant. This genetic differentiation may be the result of the co-effects of various factors, such as historic dispersal, local environment or anthropogenic activities. These results provide useful information for the genetic monitoring of P. stellatus hatchery stocks, for the genetic improvement of this species by selective breeding and for designing suitable management guidelines for the conservation of this species. 相似文献
26.
Electron transport system (ETS) activity was measured in Chirocephalus croaticus from the intermittent lake, Petelinjsko Jezero. The ETS activities were measured at 5, 10, 15, 20, and 25 °C, and were studied separately in juveniles, females and males. Juveniles had significantly higher activity than adults at a standard temperature of 20 °C. The mass-specific ETS activity decreased with increasing size of the animals; the value b was 0.787. Respiration rates (R) were determined at 20 °C and the ratio ETS/R (±standard deviation) for C. croaticus was 1.43±0.46 (n=38). ETS activity increased with temperature. Females had higher Q10 than males in higher temperature range (t-test; t=2.50; d.f.=8; p<0.05). Activation energy Ea was higher for females than males (t-test; t=2.35; d.f.=8; p<0.05). Females exhibited lower ETS activity than males over the lower temperature range, but their ETS could function more efficient at higher temperature. 相似文献
27.
Guillermo López Marcos López-Parra Germán Garrote Leonardo Fernández Teresa del Rey-Wamba Rafael Arenas-Rojas Maribel García-Tardío Gema Ruiz Irene Zorrilla Manuel Moral Miguel A. Simón 《European Journal of Wildlife Research》2014,60(2):359-366
The conservation of endangered species requires accurate data, and knowledge of cause-specific mortality rates is one of the most important issues. In recent years, conservation programs for the critically endangered Iberian lynx Lynx pardinus have been developed on the basis of mortality data derived 30 years ago from the small Doñana population. Thus, there is an urgent need for an update of mortality rates and causes in both populations (Sierra Morena and Doñana). Here we use radio-tracking information from the whole range of the Iberian lynx to quantify mortality rates and identify their causes. Between 2006 and 2011, we radio-tagged 78 Iberian lynxes from its two remaining populations (39 from Sierra Morena and 39 from Doñana). Mortality events were evaluated to identify causes, and cause-specific annual mortality rates (AMR) were obtained using the nonparametric cumulative incidence function estimator. Overall, AMR was estimated at 0.16?±?0.05 (0.19?±?0.09 in Sierra Morena and 0.12?±?0.07 in Doñana). Disease was the main cause of mortality both for the whole population and the Doñana population. Poaching was the main cause of mortality in Sierra Morena. Our results suggest that the best strategy for conserving this species is to focus action on decreasing the fatal effect of disease and poaching. Given the possible existence of an underlying inbreeding-mediated immunosuppression, genetic management aimed at increasing the genetic diversity of this population is also recommended. 相似文献
28.
29.
30.
Seung Jea Shin Kwang Jin Ko Tae Sun Kim Hyun Soo Ryoo Hyun Hwan Sung Hwang Gyun Jeon Byong Chang Jeong Seong Il Seo Hyun Moo Lee Han Yong Choi Seong Soo Jeon 《PloS one》2015,10(11)