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   811篇
  免费   45篇
综合类   1篇
化学工业   228篇
金属工艺   8篇
机械仪表   11篇
建筑科学   36篇
矿业工程   2篇
能源动力   13篇
轻工业   140篇
水利工程   5篇
石油天然气   8篇
无线电   31篇
一般工业技术   89篇
冶金工业   214篇
原子能技术   6篇
自动化技术   64篇
  2023年   9篇
  2022年   32篇
  2021年   39篇
  2020年   23篇
  2019年   25篇
  2018年   21篇
  2017年   22篇
  2016年   21篇
  2015年   14篇
  2014年   22篇
  2013年   45篇
  2012年   35篇
  2011年   36篇
  2010年   38篇
  2009年   42篇
  2008年   38篇
  2007年   43篇
  2006年   36篇
  2005年   22篇
  2004年   30篇
  2003年   19篇
  2002年   22篇
  2001年   16篇
  2000年   9篇
  1999年   21篇
  1998年   14篇
  1997年   18篇
  1996年   19篇
  1995年   10篇
  1994年   8篇
  1993年   13篇
  1992年   6篇
  1991年   2篇
  1990年   9篇
  1989年   6篇
  1988年   6篇
  1987年   6篇
  1986年   7篇
  1985年   9篇
  1984年   7篇
  1983年   3篇
  1982年   7篇
  1981年   3篇
  1980年   2篇
  1979年   2篇
  1978年   6篇
  1976年   5篇
  1974年   2篇
  1973年   3篇
  1962年   1篇
排序方式: 共有856条查询结果,搜索用时 15 毫秒
41.
The conventional sonicator/shaker bath method for phenolic extraction was compared with a less traditional one using a homogenizer. The homogenizer proved to be both more efficient and consistent in extracting phenolics from tender, as well as tough, leaves. We propose that adoption of the homogenizer technique will increase phenolic yield and efficiency.  相似文献   
42.
The intertidal pulmonate limpetTrimusculus reticulatus, which is found in caves or crevices along the California coast, was previously reported to contain two novel diterpenoids, 6-isovaleroxylabda-8,13-dien-7,15-diol (1) and 2,7-diacetoxy-6-isovaleroxylabda-8,13-dien-15-ol (2). Dissection of the animals prior to extraction revealed that the diterpenoids were concentrated in the mantle, foot, and mucus, but not in the viscera. The presence ofT. reticulatus or its mucus was toxic to veliger larvae of the sabellariid reef-building tube wormPhragmatopoma californica. The major diterpenoid1 was responsible for the observed larvicidal activity. Protection against overgrowth by settling invertebrate larvae is important for the survival of this sessile filter-feeding pulmonate. A related pulmonate,T. conica, which was found in similar intertidal habitats in New Zealand, contained 6-acetoxy-7-isovaleroxylabda-8,13-dien-15-oic acid (3) and 1,7,12,18-tetraacetoxy-cholest-5-en-3-ol (4). The diterpene3 was also localized in the foot, mantle, and mucus ofT. conica but was not larvicidal toP. californica.  相似文献   
43.
Phragmites australis is considered the most invasive plant in marsh and wetland communities in the eastern United States. Although allelopathy has been considered as a possible displacing mechanism in P. australis, there has been minimal success in characterizing the responsible allelochemical. We tested the occurrence of root-derived allelopathy in the invasiveness of P. australis. To this end, root exudates of two P. australis genotypes, BB (native) and P38 (an exotic) were tested for phytotoxicity on different plant species. The treatment of the susceptible plants with P. australis root exudates resulted in acute rhizotoxicity. It is interesting to note that the root exudates of P38 were more effective in causing root death in susceptible plants compared to the native BB exudates. The active ingredient in the P. australis exudates was identified as 3,4,5-trihydroxybenzoic acid (gallic acid). We tested the phytotoxic efficacy of gallic acid on various plant systems, including the model plant Arabidopsis thaliana. Most tested plants succumbed to the gallic acid treatment with the exception of P. australis itself. Mechanistically, gallic acid treatment generated elevated levels of reactive oxygen species (ROS) in the treated plant roots. Furthermore, the triggered ROS mediated the disruption of the root architecture of the susceptible plants by damaging the microtubule assembly. The study also highlights the persistence of the exuded gallic acid in P. australis’s rhizosphere and its inhibitory effects against A. thaliana in the soil. In addition, gallic acid demonstrated an inhibitory effect on Spartina alterniflora, one of the salt marsh species it successfully invades. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   
44.
Spinal cord injury (SCI) causes significant mortality and morbidity. Currently, no FDA-approved pharmacotherapy is available for treating SCI. Previously, low doses of estrogen (17β-estradiol, E2) were shown to improve the post-injury outcome in a rat SCI model. However, the range of associated side effects makes advocating its therapeutic use difficult. Therefore, this study aimed at investigating the therapeutic efficacy of Premarin (PRM) in SCI. PRM is an FDA-approved E2 (10%) formulation, which is used for hormone replacement therapy with minimal risk of serious side effects. The effects of PRM on SCI were examined by magnetic resonance imaging, immunofluorescent staining, and western blot analysis in a rat model. SCI animals treated with vehicle alone, PRM, E2 receptor antagonist (ICI), or PRM + ICI were graded in a blinded way for locomotor function by using the Basso–Beattie–Bresnahan (BBB) locomotor scale. PRM treatment for 7 days decreased post-SCI lesion volume and attenuated neuronal cell death, inflammation, and axonal damage. PRM also altered the balance of pro- and anti-apoptotic proteins in favor of cell survival and improved angiogenesis and microvascular growth. Increased expression of estrogen receptors (ERs) ERα and ERβ following PRM treatment and their inhibition by ER inhibitor indicated that the neuroprotection associated with PRM treatment might be E2-receptor mediated. The attenuation of glial activation with decreased inflammation and cell death, and increased angiogenesis by PRM led to improved functional outcome as determined by the BBB locomotor scale. These results suggest that PRM treatment has significant therapeutic implications for the improvement of post-SCI outcome.  相似文献   
45.
Connexin37 (Cx37) and Cx40 form intercellular channels between endothelial cells (EC), which contribute to the regulation of the functions of vessels. We previously documented the participation of both Cx in developmental angiogenesis and have further shown that loss of Cx40 decreases the growth of different tumors. Here, we report that loss of Cx37 reduces (1) the in vitro proliferation of primary human EC; (2) the vascularization of subcutaneously implanted matrigel plugs in Cx37−/− mice or in WT using matrigel plugs supplemented with a peptide targeting Cx37 channels; (3) tumor angiogenesis; and (4) the growth of TC-1 and B16 tumors, resulting in a longer mice survival. We further document that Cx37 and Cx40 function in a collaborative manner to promote tumor growth, inasmuch as the injection of a peptide targeting Cx40 into Cx37−/− mice decreased the growth of TC-1 tumors to a larger extent than after loss of Cx37. This loss did not alter vessel perfusion, mural cells coverage and tumor hypoxia compared to tumors grown in WT mice. The data show that Cx37 is relevant for the control of EC proliferation and growth in different tumor models, suggesting that it may be a target, alone or in combination with Cx40, in the development of anti-tumoral treatments.  相似文献   
46.
Films of Polypyrrole/Montmorillonite (PPy/MT) clays were electropolymerized potentiostatically on aluminium alloy 1100, using sodium dodecylbenzenesulfonate (SDBS) as a dopant. Two clay species were used: Na+-Montmorillonite (MT-Na) and modified-Montmorillonite (MT-M). The characterization of the PPy/MT films performed by XRD and TEM shows that the exfoliation method employed, as well the electrochemical polymerization method used in this work, allow nanocomposite materials to be obtained. The PPy/MT films were found to have less electrical conductivity than pure PPy. The corrosion protection of aluminium alloy 1100 covering PPy/MT was evaluated by electrochemical techniques in 0.05 mol L−1 NaCl medium. The electrochemical parameters derived from the polarization curves, together with the EIS data, revealed that the corrosion resistance of PPy/clay coatings depends on the type and concentration of Montmorillonite employed. The best performance in the corrosion protection of the aluminum was achieved with PPy/MT films containing 1% of clay.  相似文献   
47.
This study examined perceptions of school psychologists regarding their use of evidence-based interventions in school settings after completing a graduate course in school-based psychosocial interventions. Ninety-four individuals who completed the course during the 10 years prior to the study were asked to complete a survey that focused on personal and organizational factors affecting the implementation of evidence-based interventions through assessment of (a) the extent of their use of interventions in professional school psychology practice, (b) perceptions of facilitators to implementation, and (c) perceptions of barriers to implementation. Fifty-four responded (a 57% response rate); analyses were conducted on the responses of 34 individuals who indicated that they were currently school psychologists working in schools. Results indicated that school psychologists’ personal beliefs about the interventions influenced their decisions to implement them. Several evidence-based interventions were less likely to be used in urban practice settings. Training in evidence-based interventions should address the personal and contextual issues that are related to implementation, as well as the procedures of the interventions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
48.
49.
To understand how mammalian herbivores process plant secondary compounds, we examined differences in expression of biotransformation enzyme mRNAs among populations of wild woodrats (Neotoma lepida) and laboratory rats. We compared expression of mRNAs for 10 biotransforming enzymes in five families (CYP, mEH, QOR, GST, and UGT) by using Northern blot analysis. We found significant differences in eight of 10 mRNAs tested. We suggest that the differences in mRNA expression among populations of woodrats and laboratory rats may be due to differences in the secondary compound composition of their diets. Our results provide background for future studies of detoxification strategies in mammalian herbivores that combine pharmacological techniques with an ecological perspective.  相似文献   
50.
In this replication and extension of a national survey of psychotherapists conducted in 1987, American psychologists (n = 219), counselors (n = 191), and social workers (n = 192) reported in 2007 on the processes and outcomes of their personal therapy experiences. Of the 85% who sought therapy at least once, women, men, and members of all three professions were equally as likely to have received personal treatment. Their top reasons for seeking therapy were marital–couple distress (20%), depression (13%), need for self-understanding (12%), and anxiety–stress (10%). Approximately 24% used psychotropic medication in combination with personal therapy. More than 90% of therapists reported positive outcomes across multiple domains. The modal lasting lessons from personal treatment related to therapist reliability, skill, and empathy. The results are tentatively compared with those obtained in 1987, thus chronicling the evolution of personal therapy among psychologists and social workers during the past 20 years. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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