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   15694篇
  免费   1039篇
  国内免费   1359篇
林业   896篇
农学   1397篇
基础科学   132篇
  821篇
综合类   5119篇
农作物   1213篇
水产渔业   708篇
畜牧兽医   4227篇
园艺   2662篇
植物保护   917篇
  2024年   35篇
  2023年   206篇
  2022年   402篇
  2021年   615篇
  2020年   642篇
  2019年   753篇
  2018年   557篇
  2017年   706篇
  2016年   955篇
  2015年   897篇
  2014年   966篇
  2013年   911篇
  2012年   1219篇
  2011年   1330篇
  2010年   1057篇
  2009年   1059篇
  2008年   950篇
  2007年   1034篇
  2006年   767篇
  2005年   668篇
  2004年   445篇
  2003年   375篇
  2002年   241篇
  2001年   207篇
  2000年   201篇
  1999年   159篇
  1998年   108篇
  1997年   92篇
  1996年   87篇
  1995年   56篇
  1994年   52篇
  1993年   57篇
  1992年   35篇
  1991年   34篇
  1990年   19篇
  1989年   30篇
  1988年   24篇
  1987年   19篇
  1986年   23篇
  1985年   13篇
  1984年   10篇
  1983年   4篇
  1982年   5篇
  1981年   18篇
  1980年   10篇
  1979年   3篇
  1976年   4篇
  1962年   6篇
  1956年   13篇
  1955年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Choi YJ  Yoon JH  Cha SW  Lee SG 《Fitoterapia》2011,82(6):911-919
Ginsenoside Rh1 has been reported to possess antiallergic and anti-inflammatory activities, but its effects on monocytes remain to be determined. Herein, we investigated the effects of Rh1 on the expression of MCP-1 and CCR2, activation of MAPK signaling, and chemotaxis of monocytes. Treatment of Rh1 decreased the levels of MCP-1 and CCR2 and the expression of VLA5 and activated β1 integrin on the cell surface, and attenuated the phosphorylation of MAPKs. Based on these results, the inhibitory effects of Rh1 on monocyte function should be regarded as a promising new anti-inflammatory response with a potential therapeutic role against inflammation-dependent diseases.  相似文献   
992.
A new diterpenoid, 15-angeloyloxy-16,17-epoxy-19-kauronic acid (1), along with five known metabolites, 16-kauren-19-oic acid (2), 6′-hydroxy-2′,3′,4,4′-tetramethoxychalcone (3), isosakuranetin (4), acacetin (5), and kaempferide (6) was isolated from the organic extracts of the roots of Chromoleana odorata. Their structures were determined by spectroscopic evidences. The structures of 1 and 2 were further confirmed by single-crystal X-ray diffraction studies. Compound 2 exhibited significant α-glucosidase inhibitory and antibacterial activities against Escherichia coli and Bacillus subtilis.  相似文献   
993.
Processed aconite drugs are widely used in Eastern medicine as painkillers and antirheumatic agents. It is known that the traditional processing of aconite drugs increases the amount of lipo-alkaloids. In order to obtain information about the pharmacological potential of these compounds, semisynthesis of 9 aconitine-derived lipo-alkaloids was carried out and their COX-1, COX-2 and LTB4 formation inhibitory activities were investigated. It was found that compounds esterified with unsaturated fatty acids demonstrated significant COX-2 inhibitory effects, while in the COX-1 assay only 14-benzoylaconine-8-O-eicosapentaenoate exerted remarkable activity. The inhibition of LTB4 formation was pronounced in cases of long chain fatty acid derivatives.  相似文献   
994.
Niu L  Qiao W  Hu Z  Li N  Huang Q  Gong J  Li Q  Zhu W  Li J 《Fitoterapia》2011,82(3):323-330
Berberine was reported to protect against the intestinal injury and improve the survival rate in sepsis, and glutamine deficiency was considered to be correlated with mortality in sepsis. We found that berberine pretreatment ameliorated lipopolysaccharide-induced direct intestinal injury and mucosal hypoplasia and attenuated impairments of intestinal glutamine transport and glutaminase activity, B0AT1 mRNA and protein expressions, and glutaminase protein expression. These findings showed the first time that berberine pretreatment could improve intestinal recovery and attenuate the impairment of glutamine transport and glutaminase activity in rat sepsis. This might be one of the mechanisms for the beneficial effect of berberine on sepsis.  相似文献   
995.
Zhou W  Di LQ  Shan JJ  Bi XL  Chen LT  Wang LC 《Fitoterapia》2011,82(3):375-382
Shuang-Huang-Lian (SHL), a traditional Chinese formula containing Lonicerae japonicae flos (LJF), Scutellariae radix (SR) and Forsythiae fructus (FF), is commonly used to treat acute upper respiratory tract infection, acute bronchitis and light pneumonia. Forsythoside A is one of the main active ingredients in Forsythiae fructus, a key herb in SHL. In the present study, effects of different compositions in SHL on the intestinal absorption of forsythoside A were investigated. The observations from in situ intestinal circulation model showed that A/%(h− 1) of forsythoside A in FF + LSF, FF + SR and SHL were all reduced greatly compared with that in FF. However, in pharmacokinetics study, Cmax and AUC0 → 1440 of forsythoside A all increased and T1/2 prolonged in SHL, FF + LJF and FF + SR compared with FF. The results indicated that the different compositions of SHL decreased absorption but increased bioavailability of forsythoside A, which may be related to its metabolism inhibited in intestine or liver.  相似文献   
996.
优质抗裂金丝小枣新品种‘沧金1号’选育研究   总被引:1,自引:0,他引:1  
‘沧金1号’由沧州市农林科学院选育。果实圆形,个大,纵横径平均为2.61 cm×2.58 cm,成熟果实紫红色,平均单果重8.3 g,最大单果重12.7 g,制干率60%,鲜果含可溶性固形物32.08%,Vc451 mg/100 g,干枣含糖量73.5%;味甘甜微酸,品质上等,可食率97%,肉厚核小,制干率60%,适于鲜食和制干。株行距3 m×5m,嫁接后连续3 a开甲,株产鲜枣20.5 kg,产量13.84 t/hm2;较普通金丝小枣增产10%;连续4 a开甲,株产鲜枣21.5 kg,产量14.51 t/hm2,较普通金丝小枣增产13%;连续5 a开甲,株产鲜枣23.5 kg,产量15.86 t/hm2,较普通金丝小枣增产12%;耐瘠薄,抗盐碱,抗病能力强,抗裂果,裂果率低于3%;2010年12月通过河北省林木品种审定委员会审定。  相似文献   
997.
土壤数据库在土壤学研究工作中作为一种存储、分析工具的重要性是不言而喻的.本研究利用ArcGIS和Visual FoxPro建立了包括8 830个图斑、269个土壤剖面数据的无锡和常州市1:5万土壤数据库,根据“土壤质量演变规律与持续利用‘973'项目”的土壤肥力质量指标(pH、速效磷和速效钾)和全国养分分级标准(全氮)编制出土壤表层(0~15 cm)pH、全氮、速效磷和速效钾的空间分异图,从中表明pH 1~2级的土壤占整个研究区面积90%左右;土壤养分全氮、速效磷和速效钾的空间分布有明显共同特征-太滆平田区养分含量要显著高于其他地区.对不同母质和不同土壤类型(亚类级别)间的土壤表层容重、粘粒、pH、有机质、全氮、全磷、全钾、速效磷和速效钾进行了方差分析,结果显示,除全氮之外,其他属性均有显著差异.在1:5万尺度范围内,成土母质对pH、容重、全磷、有机质和速效钾起到主导作用,土壤类型对pH起到主导作用,成土母质对土壤属性的影响程度要大于土壤类型.  相似文献   
998.
Despite the lack of universal concepts for species and speciation, both sexual and asexual organisms are expected to diversify into discrete genotypic and morphological clusters. Species-rich clusters of parthenogenetic oribatid mites likely evolved in the absence of sexual reproduction. We used nucleotide sequences of the large and small rDNA genes (18S and 28S) and the coding genes for heat shock protein 82 (hsp82) and elongation factor-1 alpha (ef-1α) for phylogenetic analyses of three morphotypes of the parthenogenetic oribatid mite genus Tectocepheus. DNA sequence divergences of the different morphotypes were similar to those of sexual species in other organisms. Maximum likelihood analyses of single genes and combined data sets were largely congruent in reconstructing the phylogeny of the Tectocepheus species. The results suggest that the different morphotypes of Tectocepheus indeed evolved in the absence of sexual reproduction, and that Tectocepheus minor, Tectocepheus velatus and Tectocepheus sarekensis are best considered distinct species. Further, the results suggest that 18S rDNA, hsp82 and ef-1α are powerful markers for resolving phylogenetic relationships of oribatid mites. Saturation plots indicated that the D3-region of 28S is much more saturated than all other examined genes. This indicates that the D3-region is unsuitable for resolving ancient splits in oribatid mites.  相似文献   
999.
In this study, we used Herbaspirillum sp. B501gfp1 (B501gfp1), an isolate from wild rice, to investigate the interaction between a non-host nitrogen-fixing endophytic bacterium and micropropagated sugarcane plants under aseptic condition. Two Japanese sugarcane plants (Saccharum sp.) cultivars (cvs) NiF8 and Ni15 were inoculated using B501gfp1 in two inoculum doses of 108 and 102 bacterial-cells-per-milliliter suspension. The results showed that bacterial cells colonized both the root and stem tissues, and colonization was apparent in the intercellular spaces. Higher bacterial numbers were detected in plant tissues inoculated with the higher inoculum concentration treatment. Bacterial numbers also varied between the two cultivars, with the higher values determined in cv Ni15. This study provides evidence that Herbaspirillum sp. B501gfp1, a rice isolate, could colonize sugarcane tissues, suggesting non-specificity of host plant among endophytes.  相似文献   
1000.
ABSTRACT

Root-knot nematodes (RKN; Meloidogyne spp.) cause enormous yield reductions in vegetable crops. While nematicides are the most effective method for controlling RKN in carrot (Dacatus carota), the efficacy of non-fumigant nematicides, compared to fumigants, is still not fully understood. The objective of this study was to evaluate the effect of 1,3-dichloropropene, a fumigant nematicide, and fluensulfone, a non-fumigant nematicide, on RKN control and yield of fresh market and processing carrot. Field experiments were conducted in a commercial farm in Lenox, GA. A randomized complete block design (r = 4) was used in a factorial arrangement of 3 nematicide treatments and 2 carrot cultivars. Nematicide treatments were the application of 1,3-dichloropropene, fluensulfone, and untreated control. Carrot cultivars were Baltimore (fresh marketing) and Belgrado (processing). In general, RKN population was low early season, averaging 0.8 RKN 100 cm?3 of soil. RKN populations increased with crop development and there were significant differences among nematicide treatments. At harvest, RKN populations were lower for fluensulfone (1.1 RKN 100 cm?3 of soil) and 1,3-dichloropropene (3.2 RKN 100 cm?3 of soil) compared to Control (26.4 RKN 100 cm?3 of soil); however, fluensulfone (91,278 kg ha?1) had higher yield than 1,3-dichloropropene (64,154 kg ha?1) and Control (61,908 kg ha?1). Carrot cultivars were similar for RKN population and yield. Overall, the non-fumigant nematicide was more beneficial for carrot production than the fumigant nematicide.  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