全文获取类型
收费全文 | 874篇 |
免费 | 64篇 |
国内免费 | 4篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 26篇 |
2020年 | 19篇 |
2019年 | 15篇 |
2018年 | 30篇 |
2017年 | 34篇 |
2016年 | 49篇 |
2015年 | 37篇 |
2014年 | 59篇 |
2013年 | 55篇 |
2012年 | 49篇 |
2011年 | 47篇 |
2010年 | 37篇 |
2009年 | 34篇 |
2008年 | 27篇 |
2007年 | 34篇 |
2006年 | 22篇 |
2005年 | 25篇 |
2004年 | 34篇 |
2003年 | 29篇 |
2002年 | 24篇 |
2001年 | 18篇 |
2000年 | 16篇 |
1999年 | 8篇 |
1998年 | 11篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1992年 | 7篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1969年 | 4篇 |
1968年 | 6篇 |
1966年 | 5篇 |
排序方式: 共有942条查询结果,搜索用时 18 毫秒
901.
Laboratory experiments were performed to determine the potential of dominant spider species in winter wheat in Germany,Erigone atra (Blackwall),Lepthyphantes tenuis (Blackwall) andPardosa agrestis (Westring) adults and youngs, in suppressing the population ofRhopalosiphum padi (L.) on wheat plants and their functional response to different aphid densities. The presence of spiders significantly caused between 34 and 58% reduction in aphid population development on wheat plants compared to the aphid population in the absence of spiders. The functional response curves for these spiders as predators ofR. padi seem to descrive a typical type II functional response with the prey consumed increasing to a plateau as aphid densities increased. Prey killed without eating was linear on prey density. 相似文献
902.
903.
Abdelgawad A. Fahmi Mohamed A. El Raey Abeer Y. Ibrahim Mohamed A.O. Abdelfattah Abeer M Abdelmageed Mansour Sobeh 《Saudi Journal of Biological Sciences》2021,28(5):3117-3125
Cancer is the second leading cause of mortality accounting for one in every six deaths globally. Plant secondary metabolites, among them polyphenols, represent an effective and much safer alternative approach to the currently available medications. In this work, utilizing LC-MS/MS, we characterized the constituents of S. yapa leaves extract and evaluated its antioxidant and anticancer properties. In total, 34 secondary metabolites, mainly flavonoids (Tricin, luteolin, and apigenin and their glucosides as well as sulfated derivatives) were identified. The extract manifested substantial antioxidant activity in DPPH assay, and high total phenolic content determined by Folin Ciocalteu method. The extract was safe up to 4800 mg/kg b.wt. when administered orally in mice and neither affected the hematological parameters nor the liver enzyme levels at the studied dose (LD50, 480 mg, kg b.wt.). In the treated animals, the extract surpassed the reference drug (5-flouro uracil) and significantly reduced the tumor volume and weight by 71.50 and 85.46%, respectively, increased the median survival time to 53.2 days and the lifespan by 116%. The extract improved all the hematological parameters, where it increased the hemoglobin (Hb) concentration, red blood cell (RBC) count, packed cell volume (PVC) and platelets by 58.21, 8.98, 9.89 and 120%, respectively, compared to the untreated EAC bearing animals. Additionally, the extract significantly declined the elevated levels of ALT and AST enzymes by 29.18% and 59.88%, respectively. In molecular docking, the annotated flavonoids displayed appreciable binding affinities to the active sites of VEGFR1 and VEGFR2. In conclusion, Saba yapa is a promising plant that can be introduced to further advanced clinical studies for the development of novel anticancer drugs with lower side effects. 相似文献
904.
905.
906.
Godar Sene Mansour Thiao Ramatoulaye Samba-Mbaye Damase Khasa Aboubacry Kane Mame Samba Mbaye Marie-Ève Beaulieu Anicet Manga Samba Ndao Sylla 《Microbial ecology》2013,65(1):128-144
Several fast-growing and multipurpose tree species have been widely used in West Africa to both reverse the tendency of land degradation and restore soil productivity. Although beneficial effects have been reported on soil stabilization, there still remains a lack of information about their impact on soil microorganisms. Our investigation has been carried out in exotic and native tree plantations of 28 years and aimed to survey and compare the abundance and genetic diversity of natural legume-nodulating rhizobia (LNR). The study of LNR is supported by the phylogenetic analysis which clustered the isolates into three genera: Bradyrhizobium, Mesorhizobium, and Sinorhizobium. The results showed close positive correlations between the sizes of LNR populations estimated both in the dry and rainy seasons and the presence of legume tree hosts. There were significant increases in Rhizobium spp. population densities in response to planting with Acacia spp., and high genetic diversities and richness of genotypes were fittest in these tree plantations. This suggests that enrichment of soil Rhizobium spp. populations is host specific. The results indicated also that species of genera Mesorhizobium and Sinorhizobium were lacking in plantations of non-host species. By contrast, there was a widespread distribution of Bradyrhizobium spp. strains across the tree plantations, with no evident specialization in regard to plantation type. Finally, the study provides information about the LNR communities associated with a range of old tree plantations and some aspects of their relationships to soil factors, which may facilitate the management of man-made forest systems that target ecosystem rehabilitation and preservation of soil biota. 相似文献
907.
908.
Albert Eduardo Silva Martins Norma Lucena-Silva Renan Gomes Garcia Stefan Welkovic Aureliana Barboza Maria Luiza Bezerra Menezes Magda Maruza Terezinha Tenório Ricardo AA Ximenes 《Memórias do Instituto Oswaldo Cruz》2014,109(6):738-747
Human immunodeficiency virus (HIV)-positive patients have a greater prevalence of
coinfection with human papillomavirus (HPV) is of high oncogenic risk. Indeed, the
presence of the virus favours intraepithelial squamous cell lesion progression and
may induce cancer. The aim of this study was to evaluate the prevalence of HPV
infection, distribution of HPV types and risk factors among HIV-positive patients.
Cervical samples from 450 HIV-positive patients were analysed with regard to oncotic
cytology, colposcopy and HPV presence and type by means of polymerase chain reaction
and sequencing. The results were analysed by comparing demographic data and data
relating to HPV and HIV infection. The prevalence of HPV was 47.5%. Among the
HPV-positive samples, 59% included viral types of high oncogenic risk. Multivariate
analysis showed an association between HPV infection and the presence of cytological
alterations (p = 0.003), age greater than or equal to 35 years (p = 0.002), number of
partners greater than three (p = 0.002), CD4+ lymphocyte count <
200/mm3 (p = 0.041) and alcohol abuse (p = 0.004). Although high-risk
HPV was present in the majority of the lesions studied, the low frequency of HPV 16
(3.3%), low occurrence of cervical lesions and preserved immunological state in most
of the HIV-positive patients were factors that may explain the low occurrence of
precancerous cervical lesions in this population. 相似文献
909.
Keramati Hassan Miri Ali Baghaei Mehdi Rahimizadeh Aziz Ghorbani Raheb Fakhri Yadolah Bay Abotaleb Moradi Masoud Bahmani Zohreh Ghaderpoori Mansour Mousavi Khaneghah Amin 《Biological trace element research》2019,188(2):261-273
Biological Trace Element Research - A systematic review, meta-analysis, and non-carcinogenic risk considering fluoride content of drinking water resources of 31 provinces of Iran among some... 相似文献
910.