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   1629篇
  免费   21篇
  国内免费   63篇
  1713篇
  2022年   17篇
  2021年   23篇
  2020年   18篇
  2019年   29篇
  2018年   34篇
  2017年   24篇
  2016年   29篇
  2015年   18篇
  2014年   27篇
  2013年   76篇
  2012年   32篇
  2011年   60篇
  2010年   50篇
  2009年   33篇
  2008年   51篇
  2007年   36篇
  2006年   31篇
  2005年   38篇
  2004年   41篇
  2003年   30篇
  2002年   41篇
  2001年   23篇
  2000年   38篇
  1992年   39篇
  1991年   49篇
  1990年   44篇
  1989年   50篇
  1988年   54篇
  1987年   49篇
  1986年   40篇
  1985年   46篇
  1984年   37篇
  1983年   24篇
  1982年   17篇
  1981年   18篇
  1980年   17篇
  1979年   23篇
  1978年   24篇
  1977年   21篇
  1976年   25篇
  1975年   23篇
  1974年   30篇
  1973年   26篇
  1972年   32篇
  1971年   19篇
  1970年   19篇
  1969年   20篇
  1968年   21篇
  1967年   17篇
  1966年   24篇
排序方式: 共有1713条查询结果,搜索用时 8 毫秒
71.
Russian Journal of Bioorganic Chemistry - The activity of specific tyrosine protein kinases is known to be associated with the production of oncogenes. A specific inhibitor of tyrosine protein...  相似文献   
72.
The investigation of the inhibitory activity on the membrane bonded ATP-ase of the M(L)2X2 complexes [where M = Pd(II), Pt(II); L = isoxazole(isox), 3,5-dimethylisoxazole(3,5-diMeisox), 3-methyl,5-phenylisoxazole(3-Me,5-Phisox), 3,5-diphenylisoxazole-(3,5-diPhisox), and 4-amino-3,5-dimethylisoxazole(4-ADI); X = Cl, Br] is reported. These results show that the complexes with isox and its methyl and phenyl derivatives have a much stronger inhibitory effect than the corresponding free ligands; in the 4-ADI compounds this activity drops. The Pd(II) complexes have a greater effect than the Pt(II) derivatives. The interaction occurs with SH groups and probably also with other active centers of the enzyme. These conclusions have been correlated with the E.S.C.A. spectra. These measurements show that the electron density of the complexes on the central metal ion and Nring atom or Nring and N-hexocyclic atoms on passing from chloride to bromide derivatives changes slightly.  相似文献   
73.
One hundred decamer primers of random-amplified polymorphic DNA were tested on dioecious Asparagus officinalis plants to identify sex-linked molecular markers. One primer (S368) produced two markers (S368-928 and S368-1178) in female plants. These two DNA markers were identified in 30 male and female plants, respectively, and a S368-928 marker was proved to be linked to the female sex locus. The female-linked S368-928 marker was sequenced and specific primers were synthesized to generate a 928 bp marker of sequence characterized amplified regions (SCAR) in female plants, SCAR928. SCAR928 could be used to correctly screen homozygous mm female plants of A. officinalis. However, results of Southern blot analysis suggest that the hybridization pattern of S368-928 was presented in both sex plants. This text was submitted by the authors in English.  相似文献   
74.

采用时空互代法,以典型侵蚀环境纸坊沟流域生态恢复过程中不同年限的人工刺槐林为研究对象,选取坡耕地和天然侧柏林为参照,分析了植被恢复过程中土壤微生物量、呼吸强度、代谢商及理化性质的演变特征。结果表明,生态恢复过程中刺槐林土壤理化性质得到明显改善,微生物量随恢复年限的增加变化显著,10~15a后达到显著水平;并随年限逐渐增加,在近熟林和成熟林期基本达到稳定,成熟林后期又开始上升,恢复50a的刺槐林微生物量碳、氮、磷较坡耕地增加幅度分别为213%、201%和83%,但仅为天然侧柏林的50.98%、55.17%和61.48%。呼吸强度随恢复年限增加先升高后降低,与有机碳变化规律不同步;qCO2在恢复初期较坡耕地显著升高,随后迅速降低,25a后开始回落到坡耕地以下,50a后达到最低值,与天然侧柏林没有显著差异。相关性分析显示微生物量碳、氮、磷、qCO2与土壤养分和恢复年限相关性最为密切,达到显著(P<0.05)或极显著水平(P<0.01)。人工刺槐林促进生态恢复可以依靠生物的自肥作用恢复土壤肥力和增加微生物量,但要恢复到破坏前该地区顶级群落时的土壤微生物量和理化性状,还需要一个漫长的阶段,这个阶段可能需要上百年的时间。

  相似文献   
75.
Two types of mutants lacking the second purine nucleoside phosphorylase (PNPase 2) activity were isolated using the Escherichia coli K-12 pndR strains with constitutive or inosine-inducible synthesis of the PNPase 2. The mutations of the first type are recessive to the pndR+ allele on the F' episome. They are closely linked to the original pndR+ mutations and therefore affect the pndR gene encoding the activator protein. The mutations of the second type affect the PNPase 2 structural gene (pndA) and are recessive to the pndA+ allele on the F' episome. The nupC-pndR-pndA-ptsH-cysA gene order was established by means of four- and five-factorial transductional crosses.  相似文献   
76.
Golubev  A. A.  Validov  Sh. Z.  Usachev  K. S.  Yusupov  M. M. 《Molecular Biology》2019,53(4):501-512
Molecular Biology - The protein synthesis in cells occurs in ribosomes, with the involvement of protein translational factors. One of these translational factors is the elongation factor P (EF-P)....  相似文献   
77.
Effect of three- and fivefold intramuscular injections of antibiotics oxytetracyclin hydrochloride and benzylpenicillin sodium (20 mg/kg) on immunophysiological status of juveniles of rainbow trout Parasalmo (=Oncorhynchus) mykiss (pathomorphological evaluation of internal organs, determination of the number of different types of leucocytes in the blood, and electrophoretic investigation of protein profile of the blood serum) was investigated. It was determined that both antibiotics cause neutropenia, removal of albumin fraction in the blood serum, and appearance of lipoid assemblages and different pathologies of internal organs. Taste attractiveness of oxytetracyclin hydrochloride, benzylpenicillin sodium, cefazolin-akos, and neomycin sulfate at the concentration in artificial food pellets of 1, 10, and 100 mg/ml was evaluated. It was determined that neomycin sulfate has more preferable taste for fishes, cefazolin-akos is less attractive, and reaction of fishes to oxytetracyclin hydrochloride and benzylpenicillin sodium depends on their concentration. The presence of two strongly different behavioral stereotypes of testing of food taste was confirmed.  相似文献   
78.
以大决明子为原材料,基于氨基酸比值系数法,对决明子的营养价值进行了分析;并以碱性缓冲液为提取剂,进行决明子蛋白提取工艺研究,探讨了缓冲液浓度及pH值、料液比、浸泡时间对蛋白提取率的影响,最后用正交试验确定大决明子蛋白的最佳提取工艺。结果表明决明子的营养价值高于大豆和紫花苜蓿,与南瓜接近略低于鸡蛋;提取工艺条件最佳为50 mmol/L、pH值=8.0的KH2PO4-NaOH缓冲液,料液比1 g:50 mL,浸泡提取时间12h。此条件下决明子蛋白的提取率为93.3%。  相似文献   
79.
PCR-RFLP analysis was performed for 391 cases and 514 control individuals to analyze the contribution of polymorphisms of the matrix metalloproteinase genes MMP1 (−1607 G>GG, rs1799750; −519 A>G, rs494379), MMP2 (−735 C>T, rs2285053), MMP3 (−1171 5A>6A, rs35068180), MMP9 (−1562 C>T, rs3918242; 2660A>G, rs17576), MMP12 (−82 A>G, rs2276109), the disintegrin and metalloproteinase 33 gene ADAM33 (12418 A>G, rs2280091; 13491 C>G, rs2787094), and tissue inhibitors of metalloproteinase genes TIMP2 (−418 G>C, rs8179090) and TIMP3 (−1296 T>C, rs9619311) to chronic obstructive pulmonary disease. Significant association with increased rick of chronic obstructive pulmonary disease was observed for the 6A6A genotype of the MMP3 −1171 5A>6A polymorphism (OR = 2.49, P adj = 0.003979, P cor = 0.0358 adjusted for age, sex, smoke pack-years, ethnicity) and for the G-G haplotype of ADAM33 polymorphisms 13491 C>G and 12418 A>G (OR = 0.39, P adj = 0.0012, P cor = 0.006). Significant interactions were detected between the smoking status and ADAM33 12418 A >G (P interact = 0.026) and TIMP3 −1296 T>C (P interact = 0.044). The risk of emphysema was increased in GG homozygotes by ADAM33 13491 C>G and a risk of emphysema was found (OR = 1.74, P adj = 0.013, P cor = 0.117). The severity of chronic obstructive pulmonary disease was modified by MMP9 −1562 C>T in the additive model (OR = 1.883, P adj = 0.028, P cor = 0.252). Thus, polymorphisms of MMP3, MMP9, ADAM33, and TIMP3 can be considered important risk factors for the development and progression of chronic obstructive pulmonary disease; in addition, pathogenetically significant gene-environment interactions were identified. These data contribute to the understanding of hereditary predisposition to chronic obstructive pulmonary disease.  相似文献   
80.
黄河三角洲盐碱地条件下不同甘薯品种耐盐性   总被引:1,自引:0,他引:1  
利用北方薯区当前生产上广泛种植的甘薯新品种,在黄河三角洲盐碱地上开展种植试验,以期选育耐盐甘薯品种。对每个测试品种的重要农艺性状及盐离子含量进行分析。结果表明不同甘薯品种的耐盐性存在差异。除叶片数、分枝数、分枝长度无显著性差异外,其他农艺性状如总鲜重、鲜薯产量、薯块干率、薯干产量、薯块数等都在不同品种中达到显著水平,建议耐盐性的评价指标应以鲜薯和薯干产量为主。对甘薯新生叶片、成熟叶片、须根、块根等不同器官进行Cl-、Ca2+、Na+和K+的含量分析,结果表明不同品种其不同器官中各种盐离子含量差异显著,暗示不同基因型耐盐机制存在差异。基于对鲜薯和薯干产量的比较,筛选出耐盐碱的品种,主要有‘泰中9号’、‘苏薯7号’、‘龙薯1号’、‘徐薯18’等。同时,对甘薯种植前后的土壤总盐分和营养成分的分析显示:甘薯收获后,土壤中的含盐量显著降低。本研究为沿海滩涂培育和种植耐盐碱甘薯新品种进行了有益的尝试,同时也为盐碱地改良和生物质能原材料种植提供了思路。  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