全文获取类型
收费全文 | 2724篇 |
免费 | 168篇 |
国内免费 | 159篇 |
出版年
2023年 | 46篇 |
2022年 | 39篇 |
2021年 | 54篇 |
2020年 | 73篇 |
2019年 | 75篇 |
2018年 | 71篇 |
2017年 | 50篇 |
2016年 | 74篇 |
2015年 | 76篇 |
2014年 | 99篇 |
2013年 | 177篇 |
2012年 | 97篇 |
2011年 | 141篇 |
2010年 | 85篇 |
2009年 | 111篇 |
2008年 | 128篇 |
2007年 | 145篇 |
2006年 | 139篇 |
2005年 | 117篇 |
2004年 | 111篇 |
2003年 | 95篇 |
2002年 | 99篇 |
2001年 | 75篇 |
2000年 | 61篇 |
1999年 | 52篇 |
1998年 | 53篇 |
1997年 | 64篇 |
1996年 | 49篇 |
1995年 | 32篇 |
1994年 | 58篇 |
1993年 | 50篇 |
1992年 | 33篇 |
1991年 | 39篇 |
1990年 | 30篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 26篇 |
1986年 | 11篇 |
1985年 | 30篇 |
1984年 | 42篇 |
1983年 | 29篇 |
1982年 | 19篇 |
1981年 | 31篇 |
1980年 | 19篇 |
1979年 | 20篇 |
1978年 | 19篇 |
1977年 | 23篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1973年 | 6篇 |
排序方式: 共有3051条查询结果,搜索用时 873 毫秒
911.
Relevance of Bt toxin interaction studies for environmental risk assessment of genetically modified crops 下载免费PDF全文
Adinda De Schrijver Patrick De Clercq Ruud A. de Maagd Kees van Frankenhuyzen 《Plant biotechnology journal》2015,13(9):1221-1223
In recent years, different Bacillus thuringiensis (Bt) toxin‐encoding genes have been combined or ‘stacked’ in genetically modified (GM) crops. Synergism between Bt proteins may occur and thereby increase the impact of the stacked GM event on nontarget invertebrates compared to plants expressing a single Bt gene. On the basis of bioassay data available for Bt toxins alone or in combination, we argue that the current knowledge of Bt protein interactions is of limited relevance in environmental risk assessment (ERA). 相似文献
912.
The interactions between thioglycolic acid‐capped‐CuInS2/ZnS quantum dots (CuInS2/ZnS/TGA QDs) and tyrosine kinase inhibitor (TKI) were investigated using fluorescence, ultraviolet–visible spectrometry and Fourier transform infrared spectrometry. The results indicated that the fluorescence intensity of CuInS2/ZnS/TGA could be quenched by imatinib, dasatinib, nilotinib, gefitinib and erlotinib, which hinted that CuInS2/ZnS/TGA QDs could be used in the detection of TKI in active pharmaceutical ingredients (API). Calibration curves showed good linear correlation and low detection limits. The average recovery was between 98 and 102%. Moreover, the nature of the fluorescence quenching mechanism of CuInS2/ZnS/TGA QDs by TKI was discussed. A ground state complex was formed by hydrogen bonding between the carboxyl group of CuInS2/ZnS/TGA QDs and the amino group of TKI. This led to an increase in non‐radiative transition and fluorescence quenching of CuInS2/ZnS/TGA QDs. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
913.
914.
雪松(Cedrus deodara)是松科(Pianaceae)雪松属(Cedrus)树种的泛称,为广泛分布于喜马拉雅山脉的常绿树种,包括雪松(C.deodara)、黎巴嫩雪松(C.libani)、短叶雪松(C.brevifolia)和北非雪松(C.atlantica)等。雪松的针叶药用历史悠久,主要化学成分为黄酮类、苯丙素类、有机酸类、三萜类、甾体类、多糖及针叶胶等,具有抗肿瘤、抗氧化、改善记忆、抗菌及抗病毒等多种功效。为了测定雪松不同部位中原花青素的含量,并考察其清除DPPH自由基活性的能力,该研究以Fe3+离子为催化剂,用正丁醇-盐酸法分别测定雪松松针、花序、小枝、木质部、树皮中原花青素的含量,并对不同部位提取液清除DPPH自由基的能力进行测定。结果表明:松针、花序、木质部、树皮、小枝中原花青素的含量分别为12.93%、12.93%、6.41%、12.00%、3.37%,在质量浓度(以生药计)为0.8 mg·m L-1时,其对DPPH自由基的清除率均达到或接近90%。该研究结果提示雪松各个部位的原花青素含量丰富,其提取液的体外抗氧化活性很高,这为雪松的进一步开发利用提供了很好的参考价值。 相似文献
915.
Virulence of Beauveria brongniartii and B. bassiana against Schizonycha affinis white grubs and adults (Coleoptera: Scarabaeidae) 下载免费PDF全文
Two endemic scarab pests, Schizonycha affinis Boheman and Hypopholis sommeri Burmeister (Coleoptera: Melolonthinae) have increased in prevalence in the sugarcane producing regions of the KwaZulu‐Natal Midlands, South Africa. The crop losses associated with their feeding, the failure of chemical insecticides applied for their control, and the recent discovery of Beauveria brongniartii (Sacc.) Petch (Ascomycota: Cordycipitaceae) epizootics on these pests, have generated interest in the development of a mycoinsecticide targeting adults and larvae of these species. Previous research, using microsatellite markers, identified low levels of genetic diversity among isolates of B. brongniartii collected from two field sites where epizootics occurred. The virulence of 21 of these closely related B. brongniartii isolates and two isolates of Beauveria bassiana (Balsamo) Vuillemin was evaluated. Bioassays were conducted against adults and larvae of S. affinis, and adult Tenebrio molitor (L.) (Coleoptera: Tenebrionidae) as a surrogate test insect. The closely related B. brongniartii isolates varied significantly in their virulence towards both S. affinis (50.1–95% mortality) and T. molitor (39–74% mortality), with a number of these not highly virulent against either of these insect species. Those isolates sharing a haplotype did not vary in virulence. Adults of S. affinis were more susceptible than larvae to isolates of B. brongniartii. The median lethal concentration (LC50) required to kill half the adult S. affinis test insects was 7.65 × 106 conidia per millilitre. Schizonycha affinis second instar larvae had a median survival time of 17.5 days when exposed to some B. brongniartii isolates; however, third instars survived significantly longer with a median of 21 days. Third instars exposed to the highest concentration of B. brongniartii isolate HHWG1 survived for a median time of 15 days. Bioassays supported the finding that genetically closely related isolates may vary in their virulence, even if they were obtained from the same field epizootics. 相似文献
916.
917.
918.
《Journal of enzyme inhibition and medicinal chemistry》2013,28(5):846-851
AbstractA novel series of (1,2-benzothiazin-4-yl)acetic acid enantiomers was prepared by chiral resolution, and their absolute configurations were determined using the PGME method. The biological evaluation of the racemate and single enantiomers has shown a remarkable difference for the aldose reductase inhibitory activity and selectivity. The (R)-(?)-enantiomer exhibited the strongest aldose reductase activity with an IC50 value of 0.120?μM, which was 35 times more active than the S-(+)-enantiomer. Thus, the stereocenter at the C4 position of this scaffold was shown to have a major impact on the activity and selectivity. 相似文献
919.
After the initial discovery of intermediate filament (IF)–forming proteins in 1968, a decade would elapse before they were revealed to comprise a diverse group of proteins which undergo tissue-, developmental stage-, differentiation-, and context-dependent regulation. Our appreciation for just how large (n = 70), conserved, complex, and dynamic IF genes and proteins are became even sharper upon completion of the human genome project. While there has been extraordinary progress in understanding the multimodal roles of IFs in cells and tissues, even revealing them as direct causative agents in a broad array of human genetic disorders, the link between individual IFs and cell differentiation has remained elusive. Here, we review evidence that demonstrates a role for IFs in lineage determination, cell differentiation, and tissue homeostasis. A major theme in this review is the function of IFs as sensors and transducers of mechanical forces, intersecting microenvironmental cues and fundamental processes through cellular redox balance. 相似文献
920.