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   1997篇
  免费   123篇
  国内免费   9篇
林业   151篇
农学   117篇
基础科学   38篇
  461篇
综合类   145篇
农作物   266篇
水产渔业   188篇
畜牧兽医   440篇
园艺   75篇
植物保护   248篇
  2023年   19篇
  2022年   57篇
  2021年   76篇
  2020年   95篇
  2019年   125篇
  2018年   142篇
  2017年   130篇
  2016年   133篇
  2015年   71篇
  2014年   85篇
  2013年   213篇
  2012年   111篇
  2011年   131篇
  2010年   105篇
  2009年   68篇
  2008年   121篇
  2007年   57篇
  2006年   45篇
  2005年   38篇
  2004年   33篇
  2003年   32篇
  2002年   24篇
  2001年   17篇
  2000年   27篇
  1999年   16篇
  1998年   15篇
  1997年   12篇
  1996年   14篇
  1995年   13篇
  1994年   7篇
  1993年   4篇
  1992年   8篇
  1991年   6篇
  1990年   8篇
  1989年   6篇
  1988年   3篇
  1987年   7篇
  1986年   4篇
  1985年   5篇
  1984年   9篇
  1983年   4篇
  1982年   2篇
  1981年   4篇
  1979年   5篇
  1975年   3篇
  1973年   3篇
  1972年   2篇
  1971年   3篇
  1967年   3篇
  1955年   1篇
排序方式: 共有2129条查询结果,搜索用时 234 毫秒
51.
Kumar A  Ali M 《Fitoterapia》2000,71(2):101-104
A new steroidal alkaloid, named antidysentericine, has been isolated from the seeds of Holarrhena antidysenterica and characterized as 3 beta-dimethylaminocon-5-enin-18-one (1).  相似文献   
52.
Tropical Animal Health and Production - This study was conducted to evaluate the male effect on the manifestation of estrus and feeding behavior of Afshari ewes during their breeding season. The...  相似文献   
53.
Inhibins are members of the TGFβ superfamily and act as suppressors of follicle stimulating hormone (FSH) secretion from pituitary glands via a negative feedback mechanism to regulate folliculogenesis. In this study, the INHBB gene was knocked down by three RNAi-Ready pSIREN-RetroQ-ZsGreen vector- mediated recombinant plasmids to explore the effects of INHBB silencing on granulosa cell (GC) cell cycle, apoptosis and steroid production in vitro. Quantitative real-time polymerase chain reaction, Western blot, flow cytometry and ELISA were performed to evaluate the role of INHBB in the mouse GC cell cycle, apoptosis and steroid production in vitro. The results showed that the relative mRNA and protein expression of INHBB in mouse GCs can be significantly reduced by RNAi with pshRNA-B1, pshRNA-B2 and pshRNA-B3 plasmids, with pshRNA-B3 having the best knockdown efficiency. Downregulation of the expression of INHBB significantly arrests cells in the G1 phase of the cell cycle and increases the apoptosis rate in GCs. This was further confirmed by downregulation of the protein expressions of Cyclin D1, Cyclin E and Bcl2, while the protein expression of Bax was upregulated. In addition, specific downregulation of INHBB markedly decreased the concentration of estradiol and progesterone, which was further validated by the decrease in the mRNA levels of CYP19A1and CYP11A1. These findings suggest that inhibin βB is important in the regulation of apoptosis and cell cycle progression in granulosa cells. Furthermore, the inhibin βB subunit has a role in the regulation of steroid hormone biosynthesis. Evidence is accumulating to support the concept that inhibin βB is physiologically essential for early folliculogenesis in the mouse.  相似文献   
54.
This experiment was conducted to evaluate the effects of different levels of sweet orange (Citrus sinensis) peel extract (SOPE) on humoral immune system responses in broiler chickens. Three hundred 1‐day broilers (Ross‐308) were randomly allocated to treatments varying in supplemental SOPE added in the drinking water. The experimental groups consisted of three treatments fed for 42 days as follows: a control treatment without feed extract, a treatment containing 1000 ppm of SOPE and a treatment containing 1250 ppm of SOPE. All treatments were isocaloric and isonitrogenous. Broilers were vaccinated with Newcastle disease virus (NDV), avian influenza (AI), infectious bursal disease (IBD) and infectious bronchitis virus (IBV) vaccines. Antibody titer response to sheep red blood cells (SRBC) was higher in the group fed 1250 ppm of SOPE (P < 0.05) as well as for immunoglobulin G (IgG) and IgM. Similarly, antibody titer responses to all vaccines were constantly elevated (P < 0.05) by SOPE enrichment in a dose‐dependent manner. Relative weights of spleen and bursa of Fabricius were unaffected by treatments. Dietary SOPE supplementation may improve the immune response and diseases resistance, indicating that it can constitute a useful additive in broiler feeding. Thus, supplying SOPE in rations may help to improve relative immune response in broiler chickens.  相似文献   
55.
The effect of a combination of (-)-epigallocatechin-3-gallate (EGCG) with fish oil on intestinal tumorigenesis in Apc (Min/+) mice fed a high-fat diet was investigated in the present study. The combined treatment of EGCG and fish oil for 9 weeks reduced the tumor number by 53% as compared to controls while neither agent alone had a significant effect. Apoptosis was significantly increased in all treatment groups. beta-Catenin nuclear positivity in adenomas from the combination group was lower than control mice, implicating the modulation of Wnt signaling by the combination. Fish oil and the combination significantly reduced prostaglandin E 2 (PGE 2) levels in small intestinal tumors as compared to controls, suggesting modulation of aberrant arachidonic acid metabolism by fish oil. Akt phosphorylation in adenomas was significantly reduced in all treatment groups, which may have contributed to the observed increase in apoptosis. The results indicate that a combination of low doses of EGCG and fish oil can inhibit tumor multiplicity in Apc (Min/+) mice.  相似文献   
56.
BACKGROUND: Spodoptera litura (F.) causes enormous losses in many economically important crops. The genetics of insecticide resistance has been extensively studied in several insect pests, but there is a lack of information on S. litura. Therefore, the genetics and mechanisms of the resistance of S. litura to deltamethrin were investigated. RESULTS: Bioassays at generation G1 gave resistance ratios of 9, 5, 41, 52 and 49 for deltamethrin, cypermethrin, profenofos, chlorpyrifos and triazofos respectively, when compared with the susceptible Lab-PK strain. Bioassays at G4 with a deltamethrin-selected population (Delta-SEL) showed that selection gave resistance ratios of 63 and 7 for deltamethrin when compared with the Lab-PK and UNSEL strains respectively. Cross-resistance to other insecticides tested was observed in the selected population. A notable feature of the Delta-SEL strain was that resistance to deltamethrin, cypermethrin, profenofos and chlorpyrifos did not decline over the course of five generations. Synergism tests with microsomal oxidase (MO) and esterase-specific inhibitors indicated that the deltamethrin resistance was associated with MO and, possibly, esterase activity. Reciprocal crosses between the Delta-SEL and Lab-PK strains indicated that resistance was autosomal and incompletely dominant. A direct test of monogenic inheritance suggested that resistance to deltamethrin was controlled by more than one locus. CONCLUSION: Stability and dominance of resistance and cross-resistance suggest that insecticides with different modes of action should be recommended to reduce pyrethroid selection pressure.  相似文献   
57.
The fatty acid, sn-2 fatty acid, triacyglycerol (TAG), tocopherol, and phytosterol compositions of kernel oils obtained from nine apricot varieties grown in the Malatya region of Turkey were determined ( P<0.05). The names of the apricot varieties were Alyanak (ALY), Cataloglu (CAT), C?loglu (COL), Hacihaliloglu (HAC), Hacikiz (HKI), Hasanbey (HSB), Kabaasi (KAB), Soganci (SOG), and Tokaloglu (TOK). The total oil contents of apricot kernels ranged from 40.23 to 53.19%. Oleic acid contributed 70.83% to the total fatty acids, followed by linoleic (21.96%), palmitic (4.92%), and stearic (1.21%) acids. The s n-2 position is mainly occupied with oleic acid (63.54%), linoleic acid (35.0%), and palmitic acid (0.96%). Eight TAG species were identified: LLL, OLL, PLL, OOL+POL, OOO+POO, and SOO (where P, palmitoyl; S, stearoyl; O, oleoyl; and L, linoleoyl), among which mainly OOO+POO contributed to 48.64% of the total, followed by OOL+POL at 32.63% and OLL at 14.33%. Four tocopherol and six phytosterol isomers were identified and quantified; among these, gamma-tocopherol (475.11 mg/kg of oil) and beta-sitosterol (273.67 mg/100 g of oil) were predominant. Principal component analysis (PCA) was applied to the data from lipid components of apricot kernel oil in order to explore the distribution of the apricot variety according to their kernel's lipid components. PCA separated some varieties including ALY, COL, KAB, CAT, SOG, and HSB in one group and varieties TOK, HAC, and HKI in another group based on their lipid components of apricot kernel oil. So, in the present study, PCA was found to be a powerful tool for classification of the samples.  相似文献   
58.
Agroforestry Systems - Complex agroforestry systems are suggested as a possible solution to reduce the effects of deforestation in the tropics while enhancing the livelihoods of local human...  相似文献   
59.
Desneux  Nicolas  Han  Peng  Mansour  Ramzi  Arn&#;  Judit  Br&#;vault  Thierry  Campos  Mateus R.  Chailleux  Anais  Guedes  Raul N. C.  Karimi  Javad  Konan  Kouassi Arthur J.  Lavoir  Anne-violette  Luna  Mar&#;a G.  Perez-Hedo  Meritxell  Urbaneja  Alberto  Verheggen  Fran&#;ois J.  Zappal&#;  Lucia  Abbes  Khaled  Ali  Abid  Bayram  Yunus  Cantor  Fernando  Cuthbertson  Andrew G. S.  De Vis  Raf  Erler  Fedai  Firake  Dnyaneshwar M.  Haddi  Khalid  Hajjar  M. Jamal  Ismoilov  Khasan  Jaworski  Coline C.  Kenis  Marc  Liu  Hao-tian  Madadi  Hossein  Martin  Thibaud  Mazih  Ahmed  J. Messelink  Gerben  Mohamed  Samira A.  Nofemela  Robert S.  Oke  Abiola  Ramos  C&#;sar  Ricupero  Michele  Roditakis  Emmanouil  Shashank  Pathour R.  Wan  Fang-Hao  Wang  Ming-hui  Wang  Su  Zhang  Yi-Bo  Biondi  Antonio 《Journal of pest science》2022,95(1):17-39
Journal of Pest Science - The South American tomato pinworm, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), has invaded most Afro-Eurasian countries and is threatening worldwide tomato...  相似文献   
60.
【目的】研究荨麻促进消化道平滑肌运动的植株主要部位,分析其可能的受体机制。【方法】用生物信号处理系统监测麻叶荨麻皮刺与内茎(不含皮刺)水提液对小鼠离体小肠平滑肌的影响。【结果】2倍浓度递增(0.1%~3.2%)的皮刺剂量依赖性增加小肠收缩幅度、收缩张力和收缩峰值(P<0.05),但对收缩频率无影响(P>0.05);而内茎浓度达0.4%后使小肠收缩频率减慢(P<0.05)。0.8%皮刺一次性用药后小肠收缩幅度、收缩张力、收缩峰值均显著升高(P<0.05),而同剂量内茎对小肠收缩无影响(P>0.05)。M-受体阻断剂ATr与0.8%皮刺联合用药可使收缩幅度显著减弱(P<0.05)。【结论】荨麻植株的皮刺对消化道平滑肌具有促进作用,且可能部分作用是通过激活M-受体而实现。  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