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   1279篇
  免费   71篇
  国内免费   2篇
电工技术   8篇
综合类   5篇
化学工业   417篇
金属工艺   29篇
机械仪表   16篇
建筑科学   56篇
矿业工程   1篇
能源动力   24篇
轻工业   232篇
水利工程   14篇
石油天然气   3篇
无线电   53篇
一般工业技术   166篇
冶金工业   176篇
原子能技术   1篇
自动化技术   151篇
  2023年   13篇
  2022年   77篇
  2021年   92篇
  2020年   38篇
  2019年   35篇
  2018年   44篇
  2017年   32篇
  2016年   37篇
  2015年   36篇
  2014年   46篇
  2013年   80篇
  2012年   63篇
  2011年   112篇
  2010年   53篇
  2009年   60篇
  2008年   58篇
  2007年   61篇
  2006年   59篇
  2005年   55篇
  2004年   47篇
  2003年   18篇
  2002年   28篇
  2001年   17篇
  2000年   25篇
  1999年   12篇
  1998年   9篇
  1997年   7篇
  1996年   20篇
  1995年   14篇
  1994年   17篇
  1993年   8篇
  1992年   7篇
  1991年   2篇
  1990年   10篇
  1989年   5篇
  1988年   3篇
  1987年   6篇
  1986年   8篇
  1985年   3篇
  1984年   3篇
  1981年   3篇
  1979年   2篇
  1978年   2篇
  1976年   5篇
  1975年   4篇
  1968年   3篇
  1964年   1篇
  1958年   1篇
  1957年   1篇
  1956年   1篇
排序方式: 共有1352条查询结果,搜索用时 15 毫秒
211.
This study investigated the relationship between coping styles and police recruits' stress responses and performance during a stressful event and the relationship between coping styles and traumatic symptoms. Recruits participated in a simulated stressful policing situation and were scored by expert raters. Distress measures included biological and psychological indicators of stress. Coping styles were associated with subjective and physiological distress but not with performance. Different coping styles were associated with different patterns of traumatic symptoms in the participants. Police recruits appear to rely on their training and skill sets in stressful situations regardless of how they manage their emotional response. Furthermore, the results suggest that different posttraumatic stress disorder manifestations may represent different pathologies, each associated with a different style of coping. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
212.
Single-source molecular precursors were found to produce iron phosphide materials. In a surfactant system of trioctylamine and oleic acid, H2Fe3(CO)9PtBu reacted to form Fe4(CO)12(PtBu)2, which decomposed to give Fe2P nanorods and "bundles." Control of the morphology obtained was possible by varying the surfactant system; addition of increasing amounts of oleic acid resulted in crystal splitting, while the addition of microliter amounts of an alkane enhanced the crystal splitting to give sheaflike structures. The different morphologies seen were attributed to imperfect crystal growth mechanisms.  相似文献   
213.
214.
This study reports on the relationship of therapist competence to the outcome of cognitive-behavioral treatment in the National Institute of Mental Health Treatment of Depression Collaborative Research Program. Outpatients suffering from major depressive disorder were treated by cognitive-behavioral therapists at each of 3 U.S. sites using a format of 20 sessions in 16 weeks. Findings provide some support for the relationship of therapist competence (as measured by the Cognitive Therapy Scale) to reduction of depressive symptomatology when controlling for therapist adherence and facilitative conditions. The results are, however, not as strong or consistent as expected. The component of competence that was most highly related to outcome is a factor that reflects the therapist's ability to structure the treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
215.
The paper presents the results of an empirical study of the Danish and Nordic Publication behaviour and international impact in Clinical and Social Medicine covering the period 1988–96. As indicators are applied the international visibility of Scandinavian research output, the publication activity per capita in SCI journals, the development over time of the national citation impact in an OECD and World context, and the ratio of cited papers relative to the World. Compared toMay's analysis (1997), covering 1981–94, the analysis shows that a certain reshuffle of national positions among the OECD countries in citation impact has occurred. UK and New Zealand as well as Denmark and Sweden have lost in ranking to Finland and Belgium, both countries coming up from behind. The most interesting results concern the opposite research policy strategies displayed by Finland and Denmark which result in similar impact patterns relative to the World impact. The implications are discussed.  相似文献   
216.
Pears (Pyrus communis L cv Blanquilla) were stored at various CO2 concentrations to induce core browning. The severity of core browning and the products and enzymes associated with fermentative and antioxidant metabolisms were determined immediately after harvest and in healthy and damaged fruits after storage. The incidence and severity of brown core increased with CO2 concentration. Acetaldehyde and ethanol concentrations and alcohol dehydrogenase (ADH, EC 1.1.1.1) activity increased in all fruits during storage, but more in fruits with brown core than in healthy fruits. Pyruvate decarboxylase (PDC, EC 4.1.1.1) activity decreased slightly during this time. Ascorbate contents decreased whereas glutathione concentrations increased during storage in fruits with brown core compared to the same fruits at harvest. Superoxide dismutase (SOD, EC 1.15.11) activity increased during storage but was not affected by brown core. In contrast, a significant increase in both ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) activities and a significant decrease in catalase (CAT, EC 1.11.1.6) activity were found in damaged fruits. Malonaldehyde (MDA) and 4‐hydroxyalkenal (4‐HNE) contents increased significantly in the damaged fruits as a result of peroxidation. Collectively, our results suggest that brown core in pears is indirectly correlated with fermentation and involves oxidative damage which may be a causal factor in brown core development. © 2001 Society of Chemical Industry  相似文献   
217.
The use of ceramics as low cost membrane materials for Microbial Fuel Cells (MFCs) has gained increasing interest, due to improved performance levels in terms of power and catholyte production. The catholyte production in ceramic MFCs can be attributed to a combination of water or hydrogen peroxide formation from the oxygen reduction reaction in the cathode, water diffusion and electroosmotic drag through the ion exchange membrane. This study aims to evaluate, for the first time, the effect of ceramic wall/membrane thickness, in terms of power, as well as catholyte production from MFCs using urine as a feedstock. Cylindrical MFCs were assembled with fine fire clay of different thicknesses (2.5, 5 and 10 mm) as structural and membrane materials. The power generated increased when the membrane thickness decreased, reaching 2.1 ± 0.19 mW per single MFC (2.5 mm), which was 50% higher than that from the MFCs with the thickest membrane (10 mm). The amount of catholyte collected also decreased with the wall thickness, whereas the pH increased. Evidence shows that the catholyte composition varies with the wall thickness of the ceramic membrane. The possibility of producing different quality of catholyte from urine opens a new field of study in water reuse and resource recovery for practical implementation.  相似文献   
218.
Polarized Fourier transform infrared (FTIR) transmission and attenuated total reflection (ATR) spectroscopy are well‐known powerful tools to determine the orientation function of polymer materials. Both methods demand a special sample preparation. In our present studies, we used polarized FTIR photoacoustic spectroscopy (PAS) to determine the orientation function of real products from polymer processing without special preparation. We compare the results with those obtained with polarized FTIR transmission spectroscopy. It is demonstrated that polarized FTIR–PAS is useful to describe differences in the orientational behavior of hard and soft segments of thermoplastic poly(ether‐urethane) in different elongated blends with common polypropylene and polypropylene grafted with maleic anhydride. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1194–1204, 2000  相似文献   
219.
Leishmaniasis is a disease caused by parasites of the Leishmania genus that affects 98 countries worldwide, 2 million of new cases occur each year and more than 350 million people are at risk. The use of the actual treatments is limited due to toxicity concerns and the apparition of resistance strains. Therefore, there is an urgent necessity to find new drugs for the treatment of this disease. In this context, enzymes from the polyamine biosynthesis pathway, such as arginase, have been considered a good target. In the present work, a chemical library of benzimidazole derivatives was studied performing computational, enzyme kinetics, biological activity, and cytotoxic effect characterization, as well as in silico ADME-Tox predictions, to find new inhibitors for arginase from Leishmania mexicana (LmARG). The results show that the two most potent inhibitors (compounds 1 and 2) have an I50 values of 52 μM and 82 μM, respectively. Moreover, assays with human arginase 1 (HsARG) show that both compounds are selective for LmARG. According to molecular dynamics simulation studies these inhibitors interact with important residues for enzyme catalysis. Biological activity assays demonstrate that both compounds have activity against promastigote and amastigote, and low cytotoxic effect in murine macrophages. Finally, in silico prediction of their ADME-Tox properties suggest that these inhibitors support the characteristics to be considered drug candidates. Altogether, the results reported in our study suggest that the benzimidazole derivatives are an excellent starting point for design new drugs against leishmanisis.  相似文献   
220.
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