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   230篇
  免费   10篇
电工技术   3篇
化学工业   93篇
金属工艺   3篇
建筑科学   5篇
矿业工程   1篇
能源动力   3篇
轻工业   25篇
水利工程   1篇
石油天然气   5篇
无线电   9篇
一般工业技术   27篇
冶金工业   50篇
原子能技术   7篇
自动化技术   8篇
  2024年   1篇
  2023年   1篇
  2022年   3篇
  2021年   2篇
  2020年   1篇
  2018年   4篇
  2017年   7篇
  2016年   4篇
  2015年   2篇
  2014年   19篇
  2013年   11篇
  2012年   7篇
  2011年   5篇
  2010年   7篇
  2009年   7篇
  2008年   16篇
  2007年   7篇
  2006年   14篇
  2005年   2篇
  2004年   6篇
  2003年   7篇
  2002年   3篇
  2001年   2篇
  2000年   2篇
  1999年   4篇
  1998年   13篇
  1997年   2篇
  1996年   3篇
  1995年   1篇
  1994年   4篇
  1993年   5篇
  1992年   1篇
  1991年   3篇
  1990年   1篇
  1989年   7篇
  1988年   2篇
  1987年   10篇
  1986年   5篇
  1985年   4篇
  1984年   6篇
  1982年   3篇
  1981年   3篇
  1980年   2篇
  1979年   4篇
  1978年   5篇
  1977年   4篇
  1976年   3篇
  1975年   5篇
排序方式: 共有240条查询结果,搜索用时 15 毫秒
51.
52.
A technique for mass-labeling was developed to study sex pheromone biosynthesis in the red-banded leafroller moth,Argyrotaenia velutinana. With this technique, the pheromone components and all fatty acyl groups in the pheromone gland were analyzed for incorporation of label in the same analytic ran with gas chromatography-mass spectrometry, using chemical ionization and selected ion monitoring (GC-SIM-CI-MS). Sex pheromone glands were incubated with fatty acids or triacylglycerols labeled with at least three deuterium atoms or carbon-13 atoms. The results of these incubations support an interpretation in which hexadecanoate is chain shortened to tetradecanoate, which is desaturated to produce (E)- and (Z)-11-tetradecenoate precursors for the sex pheromone components (E)- and (Z)-11-tetradecen-1-yl acetate. Labeled (E)- and (Z)-11-tetradecenoyl groups in synthetic triacylglycerols were not incorporated into the sex pheromone components, perhaps indicating that this lipid class is not a donor of the immediate fatty acyl precursors in sex pheromone biosynthesis.  相似文献   
53.
以钛片为催化剂,通过乙炔气体在750℃下热解制备了规则螺旋的碳管,这些规则的螺旋碳管直径约为200nm,规则螺旋碳管的形成与钛片的预处理有关,在盐酸处理过的钛片表面上所生长的碳管几乎都是规则螺旋形状的。  相似文献   
54.
In the present study male redbanded leafroller (Argyrotaenia velutinana), cabbage looper (Trichoplusia ni), and Oriental fruit moths, (Grapholita molesta), were tested in a flight tunnel to (1) the major pheromone component, (2) theZ/E pheromone component mixtures for Oriental fruit moth and redbanded leafroller, (3) and the female-released blends, over a series of dosages. Experiments were designed to test the hypothesis that male response downwind of a female is initiated by the major component and that minor components function only to elicit behaviors close to the female during close-range approach and courtship. The results did not support this hypothesis, but rather showed that males initiated upwind flight in significantly higher percentages to the complete blends of components, at all dosages, compared to single components or partial blends. Addition of minor components also signficantly enhanced male perception of the major component at lower dosages, resulting in completed flights to dosages of the major component that alone did not elicit any upwind flight. Our results support the concept that minor components function to enhance male sensitivity to the pheromone, and the specificity of the signal. Our results also support the hypothesis that the active space of the pheromone is a function of the upper and lower concentration thresholds for the blend of components, and not simply for the major component.  相似文献   
55.
56.
BACKGROUND: Fibrosis of serosa, along with smooth muscle (SM) cell hypertrophy, has been shown to occur in the rabbit bladder after partial outflow obstruction. Identification of cells involved in the serosal thickening can be of primary interest to elucidate the functional changes that this organ undergoes. EXPERIMENTAL DESIGN: Cytoskeletal protein composition of cells present in the thickened serosa at different times from the onset of obstruction (7, 15, 30 and 60 days) was evaluated. This was accomplished by means of a panel of monoclonal antibodies specific for a number of differentiation markers of mesenchymal cells (vimentin, desmin, alpha-actin of SM type, nonmuscle (NM) and SM myosins), and by immunocytochemical and immunochemical techniques. RESULTS: The immunocytochemical study revealed that cells in serosal thickening follow a two-step maturation process from pre-existing vimentin-positive cells. In the first time period (7 to 15 days of obstruction), these cells predominantly achieved an immunophenotype corresponding to that of a specific myofibroblast subtype (i.e., containing vimentin, NM myosin, and SM alpha-actin). After 30 days from the onset of obstruction, the cytoskeletal protein content of serosal cells, as also revealed by Western blotting experiments, shifted towards that of fetal-type SM cells (i.e., presence of vimentin, NM myosin, SM alpha-actin, and SM myosin isoforms). Distribution of vimentin, desmin, SM alpha-actin, and SM myosin in tissue culture as well as the ultrastructure in vivo very closely resembled that of SM cells. Bromodeoxyuridine incorporation studies indicated that cells accumulated in the serosa of obstructed bladders did not derive, at least initially, from SM cells of the detrusor muscle. CONCLUSIONS: These findings are consistent with the existence of a differentiation process in which resident mesenchymal cells of bladder serosa may transform to myofibroblasts and, subsequently, in fetal-type SM cells during experimental outflow obstruction.  相似文献   
57.
Substitution of nine hydrogens by nine fluorines in the butyl terminus of (Z)-7-dodecenyl acetate, the major component of the pheromone blend of the cabbage looper,Trichoplusia ni (Lepidoptera: Noctuidae), produces a highly volatile analog that is significantly less active as a replacement for the natural pheromone component, either alone or substituted in the sixcomponent pheromone blend of this species. When 9,9,10,10,11,11,12,12, 12-nonafluoro-(Z)-7-dodecenyl acetate (nf-Z7-12: OAc) was tested in a wind tunnel as a single component or as part of the six-component blend, males exhibited preflight activation, but they did not orient in the pheromone plume and fly upwind over a five-decade range of doses at levels comparable with those of the natural component and blend. Addition of large amounts of nf-Z7-12:OAc to the optimal dose of the natural blend also did not effect flight arrestment as when increased amounts of Z7-12:OAc were added. The nonafluoro (nf) analog of (Z)-9-tetradecenyl acetate, a minor component in theT. ni blend, did not affect male behavior when substituted in the sixcomponent blend, and substitution of both nf analogs in the natural blend produced the same results as observed for blends containing nf-Z7-12:OAc. The lack of an effect with substitution of nf-Z9-14:OAc is discussed in relation to the reported redundancy in the action of minor components inT. ni.  相似文献   
58.
Identification of the California red scale sex pheromone   总被引:2,自引:0,他引:2  
Pheromone components of female California red scale,Aonidiella aurantii (Maskell) were isolated from airborne collections and found to be 3-methyl-6-isopropenyl-9-decen-1-yl acetate and (Z)-3-methyl-6-isopropenyl-3,9-decadien-1-yl acetate. Both enantiomers of the latter compound as well as the corresponding enantiomers of theE isomer were prepared from (S)- or (R)-carvone. Bioassays with each of the four isomers showed that only theR,Z isomer attracted male red scale. Aonidiella aurantii (Maskell) (Homoptera: Diaspididae).This research was supported by a USDA Cooperative Research Grant.  相似文献   
59.
Identification of the sex pheromone of the yellow scale   总被引:1,自引:0,他引:1  
The sex pheromone of the yellow scale,Aonidiella citrina (Coquillett), was isolated from airborne collections and found to be (E)-3,9-dimethyl-6-isopropyl-5,8-decadien-1-yl acetate. Aonidiella citrina (Coquillett) (Homoptera: Diaspididae).This research was supported by a USDA cooperative research grant.  相似文献   
60.
Males of the redbanded leafroller,Argyrotaenia velutinana (Walker) (Lepidoptera: Tortricidae), were studied for their behavioral responses in laboratory olfactometers and in the field to the 3 components of the female-produced sex pheromone:cis-11-tetradecenyl acetate (c11–14Ac),trans-11-tetradecenyl acetate (t11–14Ac), and dodecyl acetate (12Ac). Dodecyl acetate, when evaporated with c11–14Ac (8%trans) in the field, modified the behavior of feral males nearby the chemical source, causing an increase in the frequency of landing and close approach to the pheromone dispenser. Apparently, an inflight behavioral modification concerning landing or not landing occurs within 60 cm of the source and is mediated by 12Ac. In laboratory olfactometers, c11–14Ac (8%trans) demonstrated a lower threshold for male activation than pure c11- and t11–14Ac and blends of the two isomers. Additionally, over a wide range of dosages, males responded with optimum wing-fanning response to c11–14Ac (8%trans) compared to pure c11–14Ac, c11–14:Ac (30%trans), and pure t11–14Ac, suggesting that thecistrans ratio rather than absolute amounts of either isomer, is a crucial factor in eliciting male response. When presented with c11–14Ac (8%trans) (11), dodecyl acetate caused a significant prolongation of wing-fanning over c11–14Ac (8%trans) alone and resulted in a greater percentage of males moving upwind to the source. Since the increase in wing-fanning and orientation occurred at higher concentrations of the 3-component mixture, the effect of 12Ac in the laboratory may reflect the close-range role of 12Ac in the field.  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