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   3662篇
  免费   237篇
  国内免费   148篇
电工技术   70篇
综合类   236篇
化学工业   862篇
金属工艺   290篇
机械仪表   548篇
建筑科学   128篇
矿业工程   50篇
能源动力   133篇
轻工业   195篇
水利工程   27篇
石油天然气   145篇
武器工业   14篇
无线电   226篇
一般工业技术   577篇
冶金工业   221篇
原子能技术   13篇
自动化技术   312篇
  2024年   26篇
  2023年   152篇
  2022年   138篇
  2021年   163篇
  2020年   133篇
  2019年   125篇
  2018年   103篇
  2017年   103篇
  2016年   151篇
  2015年   127篇
  2014年   172篇
  2013年   227篇
  2012年   149篇
  2011年   205篇
  2010年   160篇
  2009年   163篇
  2008年   144篇
  2007年   204篇
  2006年   199篇
  2005年   156篇
  2004年   155篇
  2003年   123篇
  2002年   105篇
  2001年   105篇
  2000年   67篇
  1999年   51篇
  1998年   63篇
  1997年   45篇
  1996年   46篇
  1995年   43篇
  1994年   44篇
  1993年   21篇
  1992年   19篇
  1991年   25篇
  1990年   15篇
  1989年   17篇
  1988年   11篇
  1987年   12篇
  1986年   17篇
  1985年   4篇
  1984年   13篇
  1983年   8篇
  1982年   11篇
  1980年   4篇
  1979年   4篇
  1978年   2篇
  1975年   2篇
  1965年   2篇
  1964年   3篇
  1955年   2篇
排序方式: 共有4047条查询结果,搜索用时 0 毫秒
11.
The relationship between treatment outcome and the extent to which participants completed homework assignments was evaluated among 60 cocaine-dependent individuals assigned to cognitive-behavioral therapy (CBT). Homework was assigned in 72% of all sessions and initiated by participants in 48% of the sessions in which it was assigned. Completion of homework was unrelated to participants' baseline characteristics and several indicators of treatment compliance. Participants who completed more homework assignments demonstrated significantly greater increases in the quantity and quality of their coping skills and used significantly less cocaine during treatment and through a 1-year follow-up. These data suggest that the extent to which participants are willing to complete extrasession assignments may be an important mediator of response to CBT. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
12.
Although it is widely accepted that control mechanisms are necessary for human behavior to be adapted, very little is known about how such mechanisms are recruited. A suggestion to fill the gap was put forward by M. M. Botvinick, T. S. Braver, C. S. Carter, D. M. Barch, and J. D. Cohen (2001), who proposed the conflict-loop theory. This theory has been successful in accounting for the reduction of compatibility effects after an incompatible trial: The level of conflict being, on average, higher during an incompatible trial, more control occurs after such a trial. The authors have tested this prediction by sorting the trials on the basis of amount of conflict (quantified by the electromyographic activity) they presented. A reduction of the compatibility effect was observed after incompatible trials, but it was independent of the level of conflict on previous trials, suggesting that the conflict does not trigger changes in executive control. Consequences for the conflict monitoring model are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
13.
Electronic commerce has been one of the traditional arenas for agent technology. The complexity of these applications has been a challenge for researchers that have developed methodologies, products, and systems, having in mind the specificities of trade, the interaction particularities of commerce, the strict notion of commitment and contract, and the clearly shaped conventions and norms that structure the field. In this paper I survey some key areas for agent technology which, although general, are of special importance in electronic commerce, namely, solid development methodologies, negotiation technologies and trust-building mechanisms. I give examples of systems in which I have directly participated, although I also try to refer to the work of other AgentLink Special Interest Group members over the last few years.  相似文献   
14.
The author reviews selected experimental results which have contributed to improved understanding of sliding wear processes. The emphasis is on the chemical and structural changes which occur at and near the surface of metallic materials during sliding in different environments. The importance of plastic deformation, fracture, transfer, mechanical mixing, phase transformations and oxidation is discussed. Examples of transitions are described, and interesting correlations noted. In selecting the content of this paper, the author includes controversial results and conclusions and raises questions about the development of wear equations, interpretations of the wear coefficient, the importance of adhesion, the roles of hardness, the causes of transitions and the location of debris-producing cracks.  相似文献   
15.
Reviews the book, Evolution, culture and the human mind edited by M. Schaller, et al. (see record 2009-20004-000). This current volume, Evolution, culture and the human mind, follows the lead of Wundt where an attempt is made to provide a synthesis of theory and data across psychological subfields into a holistic framework. Norenzayan, Schaller, and Heine begin the volume with an overview of the scope and themes that arose from their 2004 conference at the University of British Columbia on “Mind, Culture and Evolution.” Explicit throughout this volume is an effort to bridge the “yawning chasm” between perspectives of evolutionary determinism and cultural constructionism. In doing so, there is interest in providing a rigorous multidisciplinary scientific effort to solve this foundational problem for psychology. As such this volume provides an interesting and insightful examination of the evolution of consciousness, cognition, decision-making, actions, and cultural norms in terms of collective consequences and genetic mechanisms. The volume is divided into three sections where several dialectical themes (theory/data, top-down/bottom-up, ecological/social, diversification/integration) are woven throughout. Overall the volume offers nice flow from one collection of essays to the next as themes are picked up and let go, only to return later on. This volume shows a dominance of natural science (cross-cultural) inclinations where some readers may call for more voice given to phenomenological and hermeneutical (cultural) human science contributions. Other critics may challenge the reliance upon correlational, comparative, and post hoc data to bolster claims of causality in support of various theoretical suppositions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
16.
A dynamic mutation in exon 1 of the FMR1 gene causes Fragile X-related Disorders (FXDs), due to the expansion of an unstable CGG repeat sequence. Based on the CGG sequence size, two types of FMR1 alleles are possible: “premutation” (PM, with 56-200 CGGs) and “full mutation” (FM, with >200 triplets). Premutated females are at risk of transmitting a FM allele that, when methylated, epigenetically silences FMR1 and causes Fragile X syndrome (FXS), a very common form of inherited intellectual disability (ID). Expansions events of the CGG sequence are predominant over contractions and are responsible for meiotic and mitotic instability. The CGG repeat usually includes one or more AGG interspersed triplets that influence allele stability and the risk of transmitting FM to children through maternal meiosis. A unique mechanism responsible for repeat instability has not been identified, but several processes are under investigations using cellular and animal models. The formation of unusual secondary DNA structures at the expanded repeats are likely to occur and contribute to the CGG expansion. This review will focus on the current knowledge about CGG repeat instability addressing the CGG sequence expands.  相似文献   
17.
Differential evolution of apoptosis, programmed necrosis, and autophagy, parthanatos is a form of cell death mediated by poly(ADP-ribose) polymerase 1 (PARP1), which is caused by DNA damage. PARP1 hyper-activation stimulates apoptosis-inducing factor (AIF) nucleus translocation, and accelerates nicotinamide adenine dinucleotide (NAD+) and adenosine triphosphate (ATP) depletion, leading to DNA fragmentation. The mechanisms of parthanatos mainly include DNA damage, PARP1 hyper-activation, PAR accumulation, NAD+ and ATP depletion, and AIF nucleus translocation. Now, it is reported that parthanatos widely exists in different diseases (tumors, retinal diseases, neurological diseases, diabetes, renal diseases, cardiovascular diseases, ischemia-reperfusion injury...). Excessive or defective parthanatos contributes to pathological cell damage; therefore, parthanatos is critical in the therapy and prevention of many diseases. In this work, the hallmarks and molecular mechanisms of parthanatos and its related disorders are summarized. The questions raised by the recent findings are also presented. Further understanding of parthanatos will provide a new treatment option for associated conditions.  相似文献   
18.
Isoflavonoids such as genistein (GE) are well known antioxidants. The predictive biological activity of structurally new compounds such as thiogenistein (TGE)–a new analogue of GE–becomes an interesting way to design new drug candidates with promising properties. Two oxidation strategies were used to characterize TGE oxidation products: the first in solution and the second on the 2D surface of the Au electrode as a self-assembling TGE monolayer. The structure elucidation of products generated by different oxidation strategies was performed. The electrospray ionization mass spectrometry (ESI-MS) was used for identifying the product of electrochemical and hydrogen peroxide oxidation in the solution. Fourier transform infrared spectroscopy (FT-IR) with the ATR mode was used to identify a product after hydrogen peroxide treatment of TGE on the 2D surface. The density functional theory was used to support the experimental results for the estimation of antioxidant activity of TGE as well as for the molecular modeling of oxidation products. The biological studies were performed simultaneously to assess the suitability of TGE for antioxidant and antitumor properties. It was found that TGE was characterized by a high cytotoxic activity toward human breast cancer cells. The research was also carried out on mice macrophages, disclosing that TGE neutralized the production of the LPS-induced reactive oxygen species (ROS) and exhibits ABTS (2,2′-azino-bis-3-(ethylbenzothiazoline-6-sulphonic acid) radical scavenging ability. In the presented study, we identified the main oxidation products of TGE generated under different environmental conditions. The electroactive centers of TGE were identified and its oxidation mechanisms were proposed. TGE redox properties can be related to its various pharmacological activities. Our new thiolated analogue of genistein neutralizes the LPS-induced ROS production better than GE. Additionally, TGE shows a high cytotoxic activity against human breast cancer cells. The viability of MCF-7 (estrogen-positive cells) drops two times after a 72-h incubation with 12.5 μM TGE (viability 53.86%) compared to genistein (viability 94.46%).  相似文献   
19.
实体肿瘤的缺氧严重影响着基于氧气的光动力疗法(PDT)的效果.另外,单一治疗模式通常难以达到满意的治疗效果.为此,我们设计合成了一种多功能纳米复合材料Pt-Ce6用于克服肿瘤乏氧,实现PDT/PTT协同治疗.在该体系中,我们使用多孔Pt纳米粒子作为过氧化氢纳米酶、近红外二区(NIR-Ⅱ)光热转换剂和光敏剂二氢卟吩e6(...  相似文献   
20.
High concentrations of defects are introduced into nanoscale ZnO through non‐equilibrium processes and resultant blue emissions are comprehensively analyzed, focusing on defect origins and broad controls. Some ZnO nanoparticles exhibit very strong blue emissions, the intensity of which first increase and then decrease with annealing. These visible emissions exhibit strong and interesting excitation dependences: 1) the optimal excitation energy for blue emissions is near the bandgap energy, but the effective excitation can obviously be lower, even 420 nm (2.95 eV < Eg = 3.26 eV); in contrast, green emissions can be excited only by energies larger than the bandgap energy; and, 2) there are several fixed emitting wavelengths at 415, 440, 455 and 488 nm in the blue wave band, which exhibit considerable stability in different excitation and annealing conditions. Mechanisms for blue emissions from ZnO are proposed with interstitial‐zinc‐related defect levels as initial states. EPR spectra reveal the predominance of interstitial zinc in as‐prepared samples, and the evolutions of coexisting interstitial zinc and oxygen vacancies with annealing. Furthermore, good controllability of visible emissions is achieved, including the co‐emission of blue and green emissions and peak adjustment from blue to yellow.  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