首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   15125篇
  免费   3763篇
  国内免费   4篇
林业   975篇
农学   778篇
基础科学   63篇
  3762篇
综合类   253篇
农作物   531篇
水产渔业   3151篇
畜牧兽医   7242篇
园艺   145篇
植物保护   1992篇
  2023年   75篇
  2022年   119篇
  2021年   355篇
  2020年   678篇
  2019年   1162篇
  2018年   1258篇
  2017年   1289篇
  2016年   1294篇
  2015年   1079篇
  2014年   1129篇
  2013年   1477篇
  2012年   1132篇
  2011年   1055篇
  2010年   907篇
  2009年   524篇
  2008年   739篇
  2007年   603篇
  2006年   524篇
  2005年   512篇
  2004年   451篇
  2003年   413篇
  2002年   363篇
  2001年   274篇
  2000年   307篇
  1999年   182篇
  1998年   40篇
  1997年   47篇
  1996年   34篇
  1995年   21篇
  1994年   19篇
  1993年   25篇
  1992年   55篇
  1991年   43篇
  1990年   44篇
  1989年   50篇
  1988年   37篇
  1987年   40篇
  1986年   48篇
  1985年   48篇
  1984年   36篇
  1983年   37篇
  1982年   21篇
  1981年   15篇
  1979年   32篇
  1978年   36篇
  1977年   32篇
  1974年   29篇
  1973年   46篇
  1972年   30篇
  1971年   25篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
Extracts of five halophytes from southern Portugal (Arthrocnemum macrostachyum, Mesembryanthemum edule, Juncus acutus, Plantago coronopus and Halimione portulacoides), were studied for antioxidant, anti-inflammatory and in vitro antitumor properties. The most active extracts towards the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical were the methanol extracts of M. edule (IC50 = 0.1 mg/mL) and J. acutus (IC50 = 0.4 mg/mL), and the ether extracts of J. acutus (IC50 = 0.2 mg/mL) and A. macrostachyum (IC50 = 0.3 mg/mL). The highest radical scavenging activity (RSA) against the 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical was obtained in the ether extract of J. acutus (IC50 = 0.4 mg/mL) and H. portulacoides (IC50 = 0.9 mg/mL). The maximum total phenolic content (TPC) was found in the methanol extract of M. edule (147 mg gallic acid equivalents (GAE)/g) and in the ether extract of J. acutus (94 mg GAE/g). Significant decreases in nitric oxide (NO) production were observed after incubation of macrophages with lipopolysaccharide (LPS) and the chloroform extract of H. portulacoides (IC50 = 109 µg/mL) and the hexane extract of P. coronopus (IC50 = 98.0 µg/mL). High in vitro cytotoxic activity and selectivity was obtained with the ether extract of J. acutus. Juncunol was identified as the active compound and for the first time was shown to display selective in vitro cytotoxicity towards various human cancer cells.  相似文献   
992.
As part of our program to identify novel secondary metabolites that target drug-resistant ovarian cancers, a screening of our aquatic-derived actinomycete fraction library against a cisplatin-resistant ovarian cancer cell line (OVCAR5) led to the isolation of novel diaza-anthracene antibiotic diazaquinomycin E (DAQE; 1), the isomeric mixture of diazaquinomycin F (DAQF; 2) and diazaquinomycin G (DAQG; 3), and known analog diazaquinomycin A (DAQA; 4). The structures of DAQF and DAQG were solved through deconvolution of X-Ray diffraction data of their corresponding co-crystal. DAQE and DAQA exhibited moderate LC50 values against OVCAR5 of 9.0 and 8.8 μM, respectively. At lethal concentrations of DAQA, evidence of DNA damage was observed via induction of apoptosis through cleaved-PARP. Herein, we will discuss the isolation, structure elucidation, and biological activity of these secondary metabolites.  相似文献   
993.
Journal of Soils and Sediments - The objective of this study was to examine the pedogenetic evolution occurring in technic hard materials from an iron mine through the characterization of a...  相似文献   
994.
Journal of Soils and Sediments - Dissipation of pharmaceutical compounds entered into the natural environment is an important process minimizing the adverse effects on the living organisms. The aim...  相似文献   
995.
Fu  Zihao  Hong  Zijin  Wei  Junling  Liao  Yukai  You  Songlin  Wang  Yifan  Lv  Jianjing  Feng  Huan  Kolenčík  Marek  Chang  Xuexiu  Qian  Yu 《Journal of Soils and Sediments》2022,22(9):2530-2547
Journal of Soils and Sediments - Sediment phosphorus fractionation, adsorption kinetics, and adsorption isotherm characteristics were studied in two rivers, Muyang River and Lengshui River in...  相似文献   
996.
997.
Plant Foods for Human Nutrition - High-fat/high-fructose diets promote early metabolic disorders in weight and lipid and glucose metabolism. Bioactive compounds such as polyphenols and fiber...  相似文献   
998.
Plant Foods for Human Nutrition - Complementary feeding starts at around six months of age because neither breast milk nor formula assure the proper nutrition of infants. Therefore, along...  相似文献   
999.
Plant Foods for Human Nutrition - There is great interest in the search for new alternatives to antimicrobial drugs, and the use of prebiotics and probiotics is a promising approach to this...  相似文献   
1000.
Pinus pinaster wood samples, obtained at different positions of three healthy trees, were subjected to two sequential extractions using an Accelerated Solvent Extraction instrument. The first extraction was carried out with hexane (to remove lipophilic extractives) and the second one with acetone/water (95:5 v/v) to recover bioactive phenolic compounds, the target compounds of this study. The extracted fractions were assayed for total yield and composition. The extracts contained a spectrum of phenolic compounds (simple phenolics, phenolic stilbenes, flavonoids and lignans) and non-phenolic components (juvabiones, resin and fatty acids, steryl esters and triglycerides). The fractionation effects achieved by consecutive extractions and the recovery of bioactive phenolics are discussed.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号