全文获取类型
收费全文 | 36069篇 |
免费 | 3283篇 |
国内免费 | 5376篇 |
专业分类
44728篇 |
出版年
2024年 | 126篇 |
2023年 | 524篇 |
2022年 | 1202篇 |
2021年 | 1921篇 |
2020年 | 1391篇 |
2019年 | 1789篇 |
2018年 | 1615篇 |
2017年 | 1254篇 |
2016年 | 1690篇 |
2015年 | 2463篇 |
2014年 | 2949篇 |
2013年 | 3059篇 |
2012年 | 3676篇 |
2011年 | 3333篇 |
2010年 | 2139篇 |
2009年 | 1898篇 |
2008年 | 2120篇 |
2007年 | 1912篇 |
2006年 | 1672篇 |
2005年 | 1361篇 |
2004年 | 1121篇 |
2003年 | 1053篇 |
2002年 | 883篇 |
2001年 | 552篇 |
2000年 | 477篇 |
1999年 | 439篇 |
1998年 | 287篇 |
1997年 | 265篇 |
1996年 | 231篇 |
1995年 | 185篇 |
1994年 | 179篇 |
1993年 | 127篇 |
1992年 | 135篇 |
1991年 | 107篇 |
1990年 | 78篇 |
1989年 | 77篇 |
1988年 | 64篇 |
1987年 | 42篇 |
1986年 | 51篇 |
1985年 | 61篇 |
1984年 | 23篇 |
1983年 | 30篇 |
1982年 | 30篇 |
1981年 | 23篇 |
1980年 | 10篇 |
1979年 | 20篇 |
1978年 | 9篇 |
1974年 | 8篇 |
1973年 | 11篇 |
1971年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
941.
Organic carbon availability limiting microbial denitrification in the deep vadose zone 总被引:5,自引:0,他引:5 下载免费PDF全文
Shuaimin Chen Fenghua Wang Yuming Zhang Shuping Qin Shoucai Wei Shiqin Wang Chunsheng Hu Binbin Liu 《Environmental microbiology》2018,20(3):980-992
Microbes in the deep vadose zone play an essential role in the mitigation of nitrate leaching; however, limited information is available on the mechanisms of microbial denitrification due to sampling difficulties. We experimentally studied the factors that affect denitrification in soils collected down to 10.5 meters deep along the soil profile. After an anoxic pre‐incubation, denitrification rates moderately increased and the N2O/(N2O + N2) ratios declined while the microbial abundance and diversity did not change significantly in most of the layers. Denitrification rate was significantly enhanced and the abundance of the denitrification genes was simultaneously elevated by the increased availability of organic carbon in all studied layers, to a greater extent in the subsurface layers than in the surface layers, suggesting the severe scarcity of carbon in the deep vadose zone. The genera Pseudomonas and Bacillus, which are made up of a number of species that have been previously identified as denitrifiers in soil, were the major taxa that respond to carbon addition. Overall, our results suggested that the limited denitrification in the deep vadose zone is not because of the lack of denitrifiers, but due to the low abundance of denitrifiers which is caused by low carbon availability. 相似文献
942.
943.
944.
Optimal data partitioning,multispecies coalescent and Bayesian concordance analyses resolve early divergences of the grape family (Vitaceae) 下载免费PDF全文
945.
Jing Shen Zhangang Xiao Qijie Zhao Mingxing Li Xu Wu Lin Zhang Wei Hu Chi H. Cho 《Cell proliferation》2018,51(4)
Tumour necrosis factor alpha (TNFα) and interferon gamma (IFNγ) were originally found to be produced by inflammatory cells and play important roles in the immune system and surveillance of tumour growth. By activating distinct signalling pathways of nuclear factor‐κB (NF‐κB), mitogen‐activated protein kinase (MAPK), and JAK/STAT, TNFα and IFNγ were reported to effectively trigger cell death and perform powerful anti‐cancer effects. In this review, we will discuss the new advancements of TNFα and IFNγ in anti‐cancer therapy. 相似文献
946.
Wei Tang Chao Li Zengguo He Fen Pan Shuo Pan Yanping Wang 《Probiotics and antimicrobial proteins》2018,10(3):523-533
Lactobacillus plantarum MA2 was isolated from traditional Chinese Tibetan kefir grains. Its antioxidant properties had been demonstrated in vitro and in vivo previously. In the present study, the probiotic characteristics of this strain were further evaluated by investigating its acid and bile salt tolerances, cell surface hydrophobicity, and autoaggregation, respectively. In addition, the cellular antioxidant activity (CAA) assay was applied to test the antioxidant capacity of the isolate in different growth phases. Same method was also used to evaluate the antioxidant capacity of its fermentation supernatant, cell-free extract, and intact cell quantitatively. The results of probiotic characteristic tests showed that MA2 could survive at pH 2.5 and 0.3% bile salt. Meanwhile, the measurements of cell surface hydrophobicity and autoaggregation were 45.29?±?2.15 and 6.30?±?0.34%, respectively. The results of cellular antioxidant activity tests indicated that MA2 had high antioxidant potential. The CAA value of logarithmic phase cell-free extract of MA2 (39,450.00?±?424.05 μmol quercetin equivalents/100 g sample) was significantly higher than that in stationary phase cell-free extract (3395.98?±?126.06 μmol quercetin equivalents/100 g sample) and that of fermentation supernatant in logarithmic phase (2174.41?±?224.47 μmol quercetin equivalents/100 g sample) (p?<?0.05). The CAA method was successively applied to evaluate the antioxidant capacity of MA2 in this study, which suggests that it could be used as a useful method for lactic acid bacteria antioxidant potential evaluation. 相似文献
947.
Zhang Z Qun J Cao C Wang J Li W Wu Y Du L Zhao P Gong K 《Molecular biology reports》2012,39(4):4445-4454
Circulating endothelial progenitor cells (EPCs) have a critical role in endothelial maintenance and repair. Apolipoprotein
A-I mimetic peptide D-4F has been shown to posses anti-atherogenic properties via sequestration of oxidized phospholipids,
induction of remodeling of high density lipoprotein and promotion of cholesterol efflux from macrophage-derived foam cells.
In this study, we test the effects of D-4F on EPC biology. EPCs were isolated from the peripheral venous blood of healthy
male volunteers and characterized by 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine-labeled acetylated LDL uptake
and ulex europaeus agglutinin binding and flow cytometry. Cell proliferation, migration, adhesion, nitric oxide production
and endothelial nitric oxide synthase (eNOS) expression in the absence and presence of D-4F or simvastatin (as a positive
control), were assayed. We demonstrated that D-4F significantly enhanced EPC proliferation, migration and adhesion in a dose-dependent
manner compared with vehicle. However, all of the favorable effects of D-4F on EPCs were dramatically attenuated by preincubation
with NOS inhibitor L-NAME. Further, D-4F also increased nitric oxide production in culture supernatant and the levels of eNOS
expression and phosphorylation. The stimulatory effects of D-4F (10 μg/ml) on EPC biology were comparable to 0.5 μM simvastatin.
These results suggest that eNOS/NO pathway mediates the functional modulation of EPC biology in response to D-4F treatment
and support the notion that the beneficial role of D-4F on EPCs may be one of the important components of its anti-atherogenic
potential. 相似文献
948.
949.
950.