全文获取类型
收费全文 | 1191篇 |
免费 | 68篇 |
国内免费 | 1篇 |
出版年
2024年 | 3篇 |
2023年 | 13篇 |
2022年 | 38篇 |
2021年 | 60篇 |
2020年 | 32篇 |
2019年 | 42篇 |
2018年 | 49篇 |
2017年 | 30篇 |
2016年 | 44篇 |
2015年 | 62篇 |
2014年 | 63篇 |
2013年 | 101篇 |
2012年 | 89篇 |
2011年 | 97篇 |
2010年 | 55篇 |
2009年 | 41篇 |
2008年 | 44篇 |
2007年 | 53篇 |
2006年 | 51篇 |
2005年 | 53篇 |
2004年 | 56篇 |
2003年 | 38篇 |
2002年 | 40篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1968年 | 3篇 |
1928年 | 2篇 |
排序方式: 共有1260条查询结果,搜索用时 625 毫秒
101.
Spinosad is a bioinsecticide with a high degree of selective toxicity towards insects of different orders, but its toxicity
towards the two-spotted spider mite (TSSM), Tetranychus urticae Koch (Acari: Tetranychidae) is under debate. In this study, we compared the acaricidal properties of spinosad with the commercial
bioacaricide abamectin on the life stages of TSSM. Adulticide and ovicide bioassays were performed on a susceptible laboratory
strain using direct spraying of leaf disks with five rates of spinosad (20, 25, 30, 35 and 40 mg/l), five rates of abamectin
(0.125, 0.25, 0.5, 1 and 2.5 mg/l), sublethal concentrations or a combination of spinosad and abamectin. Both adulticidal
and ovicidal effects of spinosad against T. urticae in the laboratory were apparent, based on morality rates of the adults, reduction of female fecundity and death of offspring.
Abamectin was also found to significantly reduce female fecundity and killed offspring when applied directly on the eggs.
Interestingly, sublethal concentrations of spinosad reduced female fecundity stronger than abamectin. When a mixture of spinosad
and abamectin was applied at LC50, mortality was 74%, fecundity reduction was comparable to abamectin alone and egg hatching rate was lower than by either compound
alone. In conclusion, spinosad was more harmful than abamectin for TSSM life stages and the combined application is recommended. 相似文献
102.
Is microbial community composition in boreal forest soils determined by pH,C-to-N ratio,the trees,or all three? 总被引:11,自引:0,他引:11
In Fennoscandian boreal forests, soil pH and N supply generally increase downhill as a result of water transport of base cations
and N, respectively. Simultaneously, forest productivity increases, the understory changes from ericaceous dwarf shrubs to
tall herbs; in the soil, fungi decrease whereas bacteria increase. The composition of the soil microbial community is mainly
thought to be controlled by the pH and C-to-N ratio of the substrate. However, the latter also determines the N supply to
plants, the plant community composition, and should also affect plant allocation of C below ground to roots and a major functional
group of microbes, mycorrhizal fungi. We used phospholipid fatty acids (PLFAs) to analyze the potential importance of mycorrhizal
fungi by comparing the microbial community composition in a tree-girdling experiment, where tree belowground C allocation
was terminated, and in a long-term (34 years) N loading experiment, with the shifts across a natural pH and N supply gradient.
Both tree girdling and N loading caused a decline of ca. 45% of the fungal biomarker PLFA 18:2ω6,9, suggesting a common mechanism,
i.e., that N loading caused a decrease in the C supply to ectomycorrhizal fungi just as tree girdling did. The total abundance
of bacterial PLFAs did not respond to tree girdling or to N loading, in which cases the pH (of the mor layer) did not change
appreciably, but bacterial PLFAs increased considerably when pH increased across the natural gradient. Fungal biomass was
high only in acid soil (pH < 4.1) with a high C-to-N ratio (>38). According to a principal component analysis, the soil C-to-N
ratio was as good as predictor of microbial community structure as pH. Our study thus indicated the soil C-to-N ratio, and
the response of trees to this ratio, as important factors that together with soil pH influence soil microbial community composition. 相似文献
103.
Erdreich LS Van Kerkhove MD Scrafford CG Barraj L McNeely M Shum M Sheppard AR Kelsh M 《Radiation research》2007,168(2):253-261
Epidemiological studies of mobile phone use and risk of brain cancer have relied on self-reported use, years as a subscriber, and billing records as exposure surrogates without addressing the level of radiofrequency (RF) power output. The objective of this study was to measure environmental, behavioral and engineering factors affecting the RF power output of GSM mobile phones during operation. We estimated the RF-field exposure of volunteer subjects who made mobile phone calls using software-modified phones (SMPs) that recorded output power settings. Subjects recruited from three geographic areas in the U.S. were instructed to log information (place, time, etc.) for each call made and received during a 5-day period. The largest factor affecting energy output was study area, followed by user movement and location (inside or outside), use of a hands-free device, and urbanicity, although the two latter factors accounted for trivial parts of overall variance. Although some highly statistically significant differences were identified, the effects on average energy output rate were usually less than 50% and were generally comparable to the standard deviation. These results provide information applicable to improving the precision of exposure metrics for epidemiological studies of GSM mobile phones and may have broader application for other mobile phone systems and geographic locations. 相似文献
104.
Xiang MA Rybczynski PJ Patel M Chen RH McComsey DF Zhang HC Gunnet JW Look R Wang Y Minor LK Zhong HM Villani FJ Demarest KT Damiano BP Maryanoff BE 《Bioorganic & medicinal chemistry letters》2007,17(23):6623-6628
We have continued to explore spirobenzazepines as vasopressin receptor antagonists to follow up on RWJ-339489 (2), which had advanced into preclinical development. Further structural modifications were pursued to find a suitable backup compound for human clinical studies. Thus, we identified carboxylic acid derivative 3 (RWJ-676070; JNJ-17158063) as a potent, balanced vasopressin V(1a)/V(2) receptor antagonist with favorable properties for clinical development. Compound 3 is currently undergoing human clinical investigation. 相似文献
105.
Papenbrock J Riemenschneider A Kamp A Schulz-Vogt HN Schmidt A 《Plant biology (Stuttgart, Germany)》2007,9(5):582-588
Due to the clean air acts and subsequent reduction of emission of gaseous sulfur compounds sulfur deficiency became one of the major nutrient disorders in Northern Europe. Typical sulfur deficiency symptoms can be diagnosed. Especially plants of the Cruciferae family are more susceptible against pathogen attack. Sulfur fertilization can in part recover or even increase resistance against pathogens in comparison to sulfur-deficient plants. The term sulfur-induced resistance (SIR) was introduced, however, the molecular basis for SIR is largely unknown. There are several sulfur-containing compounds in plants which might be involved in SIR, such as high levels of thiols, glucosinolates, cysteine-rich proteins, phytoalexins, elemental sulfur, or H2S. Probably more than one strategy is used by plants. Species- or even variety-dependent differences in the development of SIR are probably used. Our research focussed mainly on the release of H2S as defence strategy. In field experiments using different BRASSICA NAPUS genotypes it was shown that the genetic differences among BRASSICA genotypes lead to differences in sulfur content and L-cysteine desulfhydrase activity. Another field experiment demonstrated that sulfur supply and infection with PYRENOPEZIZA BRASSICA influenced L-cysteine desulfhydrase activity in BRASSICA NAPUS. Cysteine-degrading enzymes such as cysteine desulfhydrases are hypothesized to be involved in H2S release. Several L- and D-cysteine-specific desulfhydrase candidates have been isolated and partially analyzed from the model plant ARABIDOPSIS THALIANA. However, it cannot be excluded that H2S is also released in a partial back reaction of O-acetyl-L-serine(thiol)lyase or enzymes not yet characterized. For the exact determination of the H2S concentration in the cell a H2S-specific microsensor was used the first time for plant cells. The transfer of the results obtained for application back on BRASSICA was initiated. 相似文献
106.
Mona Hoppenrath Malte Elbrächter Hannelore Halliger Reinoud P. T. Koeman Alexander Krakhmalnyy Barbara Surek Katrin Erler Bernd Luckas 《Helgoland Marine Research》2007,61(3):157-165
Thecadinium yashimaense was recorded for the first time in France, Great Britain, The Netherlands, and Germany. The invasion and establishment of
the species in the German Bight was documented reliably and is presented here. The geographic expansion of the species from
the North Pacific to the North Atlantic Ocean is discussed. This bloom-forming, marine, sand-dwelling dinoflagellate was shown
to be non-toxic. Also Thecadinium kofoidii, the type species of the genus, was analyzed for potential toxin production and turned out to be non-toxic as well. 相似文献
107.
Hassan Mona M. Taha Rania A. Abd El-Aziz M. E. Shaaban Esam A. Ibrahim Eman A. 《Plant Cell, Tissue and Organ Culture》2022,148(1):73-80
Plant Cell, Tissue and Organ Culture (PCTOC) - Leaf chlorosis is often a problem in micropropagated Rubus idaeus, which makes successful acclimatization difficult. We found that... 相似文献
108.
Dawood Mona F. A. Zaid Abbu Latef Arafat Abdel Hamed Abdel 《Journal of Plant Growth Regulation》2022,41(5):1919-1942
Journal of Plant Growth Regulation - Under the present era of changing climate, plants face simultaneous abiotic pressures rather than single stress. Under these unprecedented and joint... 相似文献
109.
Yu Zhao Mona C Majid Jennifer M Soll Joshua R Brickner Sebastian Dango Nima Mosammaparast 《The EMBO journal》2015,34(12):1687-1703
Repair of DNA alkylation damage is critical for genomic stability and involves multiple conserved enzymatic pathways. Alkylation damage resistance, which is critical in cancer chemotherapy, depends on the overexpression of alkylation repair proteins. However, the mechanisms responsible for this upregulation are unknown. Here, we show that an OTU domain deubiquitinase, OTUD4, is a positive regulator of ALKBH2 and ALKBH3, two DNA demethylases critical for alkylation repair. Remarkably, we find that OTUD4 catalytic activity is completely dispensable for this function. Rather, OTUD4 is a scaffold for USP7 and USP9X, two deubiquitinases that act directly on the AlkB proteins. Moreover, we show that loss of OTUD4, USP7, or USP9X in tumor cells makes them significantly more sensitive to alkylating agents. Taken together, this work reveals a novel, noncanonical mechanism by which an OTU family deubiquitinase regulates its substrates, and provides multiple new targets for alkylation chemotherapy sensitization of tumors. 相似文献
110.