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   4529篇
  免费   320篇
  国内免费   472篇
林业   265篇
农学   209篇
基础科学   218篇
  442篇
综合类   2214篇
农作物   311篇
水产渔业   353篇
畜牧兽医   681篇
园艺   410篇
植物保护   218篇
  2024年   35篇
  2023年   116篇
  2022年   214篇
  2021年   200篇
  2020年   189篇
  2019年   200篇
  2018年   151篇
  2017年   236篇
  2016年   171篇
  2015年   209篇
  2014年   250篇
  2013年   299篇
  2012年   379篇
  2011年   394篇
  2010年   339篇
  2009年   305篇
  2008年   403篇
  2007年   315篇
  2006年   236篇
  2005年   180篇
  2004年   116篇
  2003年   83篇
  2002年   92篇
  2001年   82篇
  2000年   75篇
  1999年   24篇
  1998年   2篇
  1997年   1篇
  1995年   1篇
  1994年   3篇
  1993年   3篇
  1992年   3篇
  1991年   5篇
  1990年   1篇
  1988年   1篇
  1986年   2篇
  1985年   1篇
  1962年   2篇
  1956年   2篇
  1955年   1篇
排序方式: 共有5321条查询结果,搜索用时 15 毫秒
51.
电偶腐蚀和缝隙腐蚀的发生及预防   总被引:2,自引:0,他引:2  
主要介绍了电偶腐蚀和缝隙腐蚀的定义、发生原理、常见形式及相应的预防措施。  相似文献   
52.
为探索由银耳(Tremella fuciformis)子实体、菌丝体胶质化产生的双核酵母状孢子(FBMds)的萌发条件,研究比较了不同来源和不同浓度的香灰菌(Annuloypoxylon stygium)浸提液及不同来源银耳孢子发酵液对银耳Tr21 FBMds萌发率的影响。试验结果表明,香灰菌浸提液和银耳孢子发酵液均有不同程度促银耳Tr21FBMds萌发的作用。不同浓度香灰菌浸提液对FBMds萌发率的试验表明,在一定浓度范围内,高浓度香灰菌浸提液可显著提高银耳FBMds萌发率,最佳浓度为40%;在该浓度下,银耳Tr21的原伴生香灰菌HTW01-5的浸提液对FBMds萌发率作用高达30.34%。银耳孢子T30-CAS、Tr01、Tr21、T8225-CAS的发酵液虽能显著促进银耳Tr21 FBMds的萌发,但效果不如香灰菌浸提液明显。研究所得银耳菌丝为纯菌丝,可稳定传代,为进一步研究银耳二型态转变以及银耳新品种选育奠定了扎实基础。  相似文献   
53.
在重庆市开州区长沙镇选择栽培品种、砧木、定植时间一致的2个果园分别作为对照果园和处理果园。对照果园每年仅土壤施肥3次,株施氮磷钾比例为10-4-8的有机无机复合肥3 kg,分别于3月底、6月底和9月底施0.6、0.6和1.8 kg。处理果园土壤施肥同对照果园,同时根据上一年叶片营养诊断结果进行叶面补镁肥,若缺镁,则分别在5月上旬、5月中旬、9月中旬3次进行叶片喷施0.2%七水硫酸镁。调查结果表明,对照果园叶片镁含量长期处于偏低水平,历年平均叶片缺镁症率4.33%。处理果园叶面喷施0.2%七水硫酸镁可以显著降低大小年结果的产量差和提高单产,7年内产量差为392.86 kg,较对照低19.58%,平均年产量1 860.25 kg/667 m~2,较对照高38.15%,叶片缺镁症率控制在1.58%,较对照低59.69%。  相似文献   
54.
AIM: In this study, CD147 antibody was used to carry out targeted modification of nanoparticles for protein kinase Cε (PKCε)-siRNA gene therapy to target lung cancer cells. The inhibitory effects of the nanoparticles on the proliferation and invasion of the lung cancer cells were observed. METHODS: The magnetic nanoparticles targeting CD147 protein were assembled as gene vector. The expression of CD147 in the lung cancer cells was observed under laser scanning confocal microscope. The cells were divided into CP group, CN group and LP group as the experimental groups. Targeted nanoparticles were used as CA group. Non-transfected cells were used as control group. The cell transfection was carried out with 250 ng plasmids/well in 6-well plate. The effect of nanocontrast agent on the cell endocytosis was observed under laser scanning confocal microscope. The mRNA expression of PKCε was detected by RT-qPCR. The protein expression of Ki67, MMP3, PKCε, Wnt1 and GAPDH was determined by Western blot. The cell proliferation ability was detected with colony formation assay. The cell invasion ability was detected by Transwell method. RESULTS: The expression of CD147 protein in the human lung cancer A549 cells was confirmed by immunofluorescence staining. The endocytosis of siRNA into the A549 cells in CP group was observed with the highest efficiency as compared with CN group and LP group. The relative mRNA expression of PKCε in the A549 cells of CP group, CN group, LP group and CA group were (9.76±0.18)%, (98.51±0.32)%, (99.17±0.16)% and (99.68±0.11)%, respectively. The difference between CP group and control group was statistically significant (P<0.05). No significant difference among CN group, LP group and control group was observed. The protein expression of PKCε, Ki-67, MMP3 and Wnt1 in CP group was significantly reduced, and the protein expression levels among CN group, LP group and control group had no significant difference. The colony number in CP group was significantly smaller than that in control group (P<0.05). The effective colony numbers in CN group, LP group and CA group had no significant difference as compared with control group. The number of the invading cells in CP group was significantly less than that in control group (P<0.05). The numbers of the invading cells in CN group, LP group and CA group had no significant difference as compared with control group. CONCLUSION: Nanogene vector targeting CD147 can carry PKCε-siRNA to conduct gene therapy efficiently on the lung cancer cells to achieve effective inhibitory effects on the proliferation and invasion of the lung cancer cells.  相似文献   
55.
以酿酒葡萄"赤霞珠"为试验材料,调查了2012—2014年昌黎产区酿酒葡萄"赤霞珠"霜霉病的发生情况。结果表明:葡萄霜霉病在昌黎产区一般从6月下旬开始出现,7—8月是发病高峰期;对葡萄霜霉病的病情指数和气象因子进行相关分析表明,温度、降雨量及空气相对湿度对葡萄霜霉病发生影响较大,昼夜温差和日照时数对该病的发生没有显著影响。  相似文献   
56.
文章主要探讨和阐述了光学系统中的光心如何确定、如何定义、如何计算,并明确指出了确定光心的重要性和实际意义.  相似文献   
57.
为研究SPF鸡感染禽网状内皮组织增生症病毒(REV)后白细胞介素2(IL-2) mRNA表达的动态变化,本研究应用荧光定量RT-PCR方法,对SPF鸡感染REV后主要免疫器官的IL-2 mRNA转录水平进行了初步研究.结果显示,与对照组相比,REV感染组鸡的脾脏、胸腺和法氏囊中IL-2基因的表达量在感染后7d、14d、21d、28 d、35 d、42 d和49 d均呈现升高,而且除21日龄、28日龄鸡的脾脏外,均为差异显著(p<0.05).本研究表明REV感染后可以诱导鸡的机体表达IL-2.  相似文献   
58.
The last step of ethylene biosynthesis in higher plants is to convert 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene by ACC oxidase (ACO). In our investigation, a cross-introns genomic DNA gene encoding ACC oxidase, PsgACO, was isolated from Paeonia suffruticosa. It revealed that PsgACO (FJ855434) has 1281 bases, containing four exons and three introns, encoding 312 amino acids. The four exons stretched from 1 to 105, 217 to 434, 592 to 925 and 1000 to 1281 bases. A splicing junction sequence of all the exon-introns conformed to the GT-AG rule in the cross-intron genomic DNA sequence of the ACO gene. PsgACO showed high homology to many characterized ACC oxidases both at the nucleic acid and amino acid levels. As well, twelve amino acid residues were conserved among many ACOs from other species. A phylogenetic tree analysis indicated that the amino acid of ACOs is quite conserved among the different eudicots. The phylogenetic tree showed that both the tree peony and herbaceous peony are quite isolated taxa. Bioinformatic analysis showed that the molecular weight of ACO is 35.29 kD, with a theoretical pI of 5.25. It is a non-secrete, stable hydrophilic protein, located in the cytoplasm.  相似文献   
59.
对回交转育的中间材料定向选择,选育出了草白色果皮的强雌系Q03苦瓜,其雌花率90%以上,且雌性稳定,以其作母本配制的川苦77,早期产量和总产量杂种优势明显,与适宜的亲本配组表现出正向的强雌性杂种优势。同时便于杂交种子生产。  相似文献   
60.
河南省自1987年开始在孟县、卢氏等县265亩苹果园中进行生物药剂治疗苹果树腐烂病的试验示范。以刮皮法和划刻法用农抗120、S-921和843康复剂涂抹病疤,一年后在发病季节调查。以刮皮法用农抗120处理的病疤,治愈率达100%,无一复发。以划刻法用农抗120处理的病疤治愈率为78-90%,以S-921和843康复剂处理的治疗效果达100%。作者认为这些生物药剂可取代福美砷治疗苹果树腐烂病。  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