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   129240篇
  免费   10029篇
  国内免费   10558篇
  149827篇
  2024年   275篇
  2023年   1665篇
  2022年   3822篇
  2021年   6488篇
  2020年   4432篇
  2019年   5568篇
  2018年   5313篇
  2017年   3859篇
  2016年   5485篇
  2015年   7896篇
  2014年   9318篇
  2013年   9940篇
  2012年   11821篇
  2011年   10736篇
  2010年   6594篇
  2009年   5958篇
  2008年   6889篇
  2007年   6176篇
  2006年   5342篇
  2005年   4221篇
  2004年   3578篇
  2003年   3291篇
  2002年   2736篇
  2001年   2292篇
  2000年   2099篇
  1999年   2034篇
  1998年   1257篇
  1997年   1212篇
  1996年   1158篇
  1995年   1010篇
  1994年   971篇
  1993年   753篇
  1992年   994篇
  1991年   770篇
  1990年   575篇
  1989年   528篇
  1988年   430篇
  1987年   408篇
  1986年   298篇
  1985年   328篇
  1984年   178篇
  1983年   186篇
  1982年   114篇
  1981年   100篇
  1980年   67篇
  1979年   82篇
  1977年   59篇
  1975年   56篇
  1974年   52篇
  1973年   56篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
鹿衔草化学成分的研究:羟基肾叶鹿蹄草甙的结构鉴定   总被引:9,自引:0,他引:9  
从鹿衔草(Pyrola calliantha H.Andres)分离得到两个化合物。经光谱分析,确定其中1个化合物为新化合物,命名为羟基肾叶鹿蹄草甙(1, hydroxylrenifolin),另一化合物为儿茶素(3)。  相似文献   
992.
Wu D  Li G  Qin C  Ren X 《PloS one》2011,6(8):e23058
The purpose of the current study was to identify potential ligands and develop a novel diagnostic test to highly pathogenic avian influenza A virus (HPAI), subtype H5N1 viruses using phage display technology. The H5N1 viruses were used as an immobilized target in a biopanning process using a 12-mer phage display random peptide library. After five rounds of panning, three phages expressing peptides HAWDPIPARDPF, AAWHLIVALAPN or ATSHLHVRLPSK had a specific binding activity to H5N1 viruses were isolated. Putative binding motifs to H5N1 viruses were identified by DNA sequencing. In terms of the minimum quantity of viruses, the phage-based ELISA was better than antiserum-based ELISA and a manual, semi-quantitative endpoint RT-PCR for detecting H5N1 viruses. More importantly, the selected phages bearing the specific peptides to H5N1 viruses were capable of differentiating this virus from other avian viruses in enzyme-linked immunosorbent assays.  相似文献   
993.
A Gram-stain negative, aerobic, motile by flagella, rod-shaped strain (THG-T16T) was isolated from rhizosphere of Hibiscus syriacus. Growth occurred at 10–40 °C (optimum 28–30 °C), at pH 6.0–8.0 (optimum 7.0) and at 0–1.0% NaCl (optimum 0%). Based on 16S rRNA gene sequence analysis, the near phylogenetic neighbours of strain THG-T16T were identified as Nibribacter koreensis KACC 16450T (98.6%), Rufibacter roseus KCTC 42217T (94.7%), Rufibacter immobilis CCTCC AB 2013351T (94.5%) and Rufibacter tibetensis CCTCC AB 208084T (94.4%). The DNA G+C content of strain THG-T16T was determined to be 46.7 mol%. DNA–DNA hybridization values between strain THG-T16T and N. koreensis KACC 16450T, R. roseus KCTC 42217T, R. immobilis CCTCC AB 2013351T, R.tibetensis CCTCC AB 208084T were 33.5?±?0.5% (31.7?±?0.7% reciprocal analysis), 28.1?±?0.2% (25.2?±?0.2%), 17.1?±?0.9% (10.2?±?0.6%) and 8.1?±?0.3% (5.2?±?0.1%). The polar lipids were identified as phosphatidylethanolamine, two unidentified aminophospholipids, an unidentified aminolipid and three unidentified lipids. The quinone was identified as MK-7 and the polyamine as sym-homospermidine. The major fatty acids were identified as C16:1 ω5c, C17:1 ω6c, iso-C15:0, summed feature 3 (C16:1 ω7c and/or C16:1 ω6c) and summed feature 4 (iso-C17:1 I and/or anteiso-C17:1 B). On the basis of the phylogenetic analysis, chemotaxonomic data, physiological characteristics, and DNA–DNA hybridization data, strain THG-T16T represents a novel species of the genus Nibribacter, for which the name Nibribacter flagellatus sp. nov. is proposed. The type strain is THG-T16T(=?KACC 19188T?=?CCTCC AB 2016246T).  相似文献   
994.
995.
Insect resistance management in GM crops: past, present and future   总被引:33,自引:0,他引:33  
Transgenic plants expressing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) were first commercialized in 1996 amid concern from some scientists, regulators and environmentalists that the widespread use of Bt crops would inevitably lead to resistance and the loss of a 'public good,' specifically, the susceptibility of insect pests to Bt proteins. Eight years later, Bt corn and cotton have been grown on a cumulative area >80 million ha worldwide. Despite dire predictions to the contrary, resistance to a Bt crop has yet to be documented, suggesting that resistance management strategies have been effective thus far. However, current strategies to delay resistance remain far from ideal. Eight years without resistance provides a timely opportunity for researchers, regulators and industry to reassess the risk of resistance and the most effective strategies to preserve Bt and other novel insect-resistant crops in development.  相似文献   
996.
Lanthanide (Ln)-doped upconversion nanoparticles (UCNPs) with appropriate surface modification can be used for a wide range of biomedical applications such as bio-detection, cancer therapy, bio-labeling, fluorescence imaging, magnetic resonance imaging and drug delivery. The upconversion phenomenon exhibited by Ln-doped UCNPs renders them tremendous advantages in biological applications over other types of fluorescent materials (e.g., organic dyes, fluorescent proteins, gold nanoparticles, quantum dots, and luminescent transition metal complexes) for: (i) enhanced tissue penetration depths achieved by near-infrared (NIR) excitation; (ii) improved stability against photobleaching, photoblinking and photochemical degradation; (iii) non-photodamaging to DNA/RNA due to lower excitation light energy; (iv) lower cytotoxicity; and (v) higher detection sensitivity. Ln-doped UCNPs are therefore attracting increasing attentions in recent years. In this review, we present recent advances in the synthesis of Ln-doped UCNPs and their surface modification, as well as their emerging applications in biomedicine. The future prospects of Ln-doped UCNPs for biomedical applications are also discussed.  相似文献   
997.
环境污染物对巨噬细胞的影响及生物监测意义   总被引:1,自引:0,他引:1  
随着工农业的发展,环境污染问题日趋严重。作为常见的环境污染物,二氧化硫经呼吸道转化为亚硫酸盐能引起多种呼吸系统疾病,并可能有促癌作用;重金属汞能引起中枢神经系统和多种器官损害,同时具有一定的免疫毒性,其危害已引起人们广泛关注。生物监测(bi0H10nitoring)是使用活  相似文献   
998.
不同来源的甘露聚糖酶在组成、结构形式、理化性质以及催化功能等方面表现出丰富的多样性,其原因主要在于底物多样性的选择、编码基因的差异、翻译后加工修饰的差异以及酶作用微环境的影响,对此进行了综述.  相似文献   
999.
参照Ty1-copia类逆转座子逆转录酶的保守区设计简并引物,分别从10个不结球白菜(Brassica campestris ssp.chinensis)品种的全基因组中均扩增出260 bp左右的目标条带. 将目的条带回收、克隆和测序后进行分析,DNAstar分析发现,这些序列存在高度的异质性,28个核苷酸序列变化范围为224~278 bp,同源性范围为16.7%~83.0%.28条序列通过核苷酸聚类分为8个家族.推导氨基酸序列有移框突变、终止子突变或二者兼有;与已登录的不同物种同一类型逆转录酶氨基酸系统进化树分析表明,不结球白菜Ty1-copia类逆转座子与芥菜型油菜、拟南芥、芜菁、甜菜可能有共同的起源.半定量和实时定量PCR检测表明,水杨酸(salicylic acid)和Peronospora parasitica均能激活不结球白菜Ty1-copia类逆转座子,逆转座子在不结球白菜叶片中的表达特征说明它可能参与寄主对病原菌的抗性.  相似文献   
1000.
我国生物多样性保护与减贫协同发展模式探索   总被引:1,自引:0,他引:1  
生物多样性和贫困是全球关注的热点论题,生物多样性保护与减贫是关乎我国可持续发展、人民生活水平提高和2020年能否全面实现小康社会的重要问题。近年来,生态环境保护特别是生物多样性保护与贫困地区区域整体协调发展越来越受到社会各界的关注。本文对我国生物多样性保护与减贫的积极和消极影响关系进行了梳理和分析,采用态势分析法对我国现行的生物多样性保护与减贫的宏观政策在未来二者协同发展过程中的优势、劣势、机会和威胁进行了深入探讨。并在此基础上对以生物多样性可持续利用为核心的保护与减贫协调发展的途径进行了探索,提出了促进二者协同发展的生态移民、绿色资本带动、生态旅游、绿色考评等模式,以期对我国推进生物多样性保护与减贫协同发展提供借鉴。  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