首页 | 官方网站   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   962篇
  免费   55篇
工业技术   1017篇
  2023年   14篇
  2022年   13篇
  2021年   75篇
  2020年   26篇
  2019年   28篇
  2018年   30篇
  2017年   37篇
  2016年   35篇
  2015年   18篇
  2014年   30篇
  2013年   58篇
  2012年   55篇
  2011年   54篇
  2010年   53篇
  2009年   50篇
  2008年   60篇
  2007年   35篇
  2006年   23篇
  2005年   23篇
  2004年   22篇
  2003年   24篇
  2002年   26篇
  2001年   12篇
  2000年   7篇
  1999年   12篇
  1998年   12篇
  1997年   8篇
  1996年   16篇
  1995年   13篇
  1994年   12篇
  1993年   8篇
  1992年   13篇
  1991年   5篇
  1990年   10篇
  1989年   8篇
  1988年   7篇
  1987年   9篇
  1986年   7篇
  1985年   8篇
  1984年   8篇
  1983年   7篇
  1982年   4篇
  1981年   5篇
  1979年   3篇
  1978年   6篇
  1977年   3篇
  1976年   3篇
  1974年   3篇
  1970年   3篇
  1964年   2篇
排序方式: 共有1017条查询结果,搜索用时 16 毫秒
41.
42.
欧洲化学品管理局(ECHA)现已将重铬酸盐列入了高关注物质(SVHC)的名单.用含有重铬酸钾和重铬酸钠等的媒介染料染制羊毛的工厂正面临着越来越大的压力.这意味着采用这种技术的染厂未来可能要得到特别授权才能使用这种化学品.  相似文献   
43.
This article reviews the current bibliographic knowledge on early neurobehavioral development and milestones in Fragile X syndrome (FraX), with emphasis on males affected by the condition. Three broad areas of early development were examined: (1) gross and fine motor, (2) speech and language, and (3) social. The result of the current review indicates very limited information on the developmental milestones in all three areas. The scarce literature on motor development shows that in FraX there is an early developmental delay. Research on speech and language demonstrates pervasive deficits in conversational skills and severe developmental delay, with increasing discrepancy between language level and chronological age in young males with FraX. Finally, deficits in social development in FraX include abnormal gaze, approach and avoidance conflict, and high incidence of autistic spectrum disorders.  相似文献   
44.
45.
The isolation and purification of polyphenol oxidase from purple eggplant (Solanum melongena L.) is described. A 15-fold purified preparation has been obtained with 15% yield by a procedure involving (NH4)2SO4 precipitation, DEAE cellulose chromatography and Sephadex G 100 gel filtration.The enzyme has an optimum pH of 6·4 and a molecular weight of 79 000 ± 5000.Inhibition studies with sodium diethyl dithiocarbamate and potassium cyanide and dialysis against the latter show that the enzyme requires copper.Eggplant polyphenol oxidase exhibits only a catecholase activity and presents a great affinity for catechol and caffeic acid. This latter compound is no doubt its natural substrate.These results show that conversely to tomato, where a polyphenol oxidase activity was tightly bound to the peroxidase, in the case of eggplant there is a true polyphenol oxidase enzyme.  相似文献   
46.
Pharmaceuticals are designed and used because of their specific biological effects. Over the past decade, compounds from various classes of pharmaceuticals have been detected in the environment. Concern has grown about the adverse effects pharmaceuticals in the environment might potentially have on human and ecological health. A sound risk assessment is therefore urgently needed for pharmaceuticals. Standardized tests for assessing the effects of chemicals on environmental organisms are widely used for this purpose. However it is questionable whether classical standardized tests give reliable data needed for environmental risk assessment. In this study we investigated the suitability of the respiration inhibition test OECD 209 for the assessment of the effects of antibiotics, disinfectants and cytotoxics on sewage sludge bacteria. We found that inhibition concentrations can strongly depend on the test period and the type of compound. We conclude that tests to assess the effects of pharmaceuticals on environmental organisms such as bacteria have to be evaluated before their results can be used in environmental risk assessment.  相似文献   
47.
Capillary electrophoresis (CE) was coupled to ICPMS in order to combine the good performance of this separation technique with the high sensitivity of the ICPMS for the analysis of plutonium and neptunium oxidation states. The combination of a fused-silica capillary with a MicroMist AR 30-I-FM02 nebulizer and a Cinnabar small-volume cyclonic spray chamber yielded the best separation results. With this setup, it was possible to separate a model element mixture containing neptunium (NpO2(+)), uranium (UO2(2+)), lanthanum (La3+), and thorium (Th4+) in 1 M acetic acid. The same conditions were also suitable for the separation of various oxidation states of plutonium and neptunium in different aqueous samples. All separations were obtained within less than 15 min. A detection limit of 50 ppb identical with 2 x 10(-7) M (3-fold standard deviation of a blank) was achieved. To prove the negligible disturbance of the plutonium and neptunium redox equilibria during the CE separations, plutonium and neptunium speciation by CE-ICPMS in acidic solutions was compared with the results of UV/visible absorption spectroscopy and was found to be in good agreement. The CE-ICPMS system was also applied to study the reduction of Pu(VI) in a humic acid-containing groundwater at different pH values.  相似文献   
48.
This study compared patterns of self-disclosure in psychotherapy and marriage. Participants (48 married, current psychotherapy patients, mean age = 42) completed a 101-item Disclosure to Therapist Inventory and a companion measure, a 101-item Disclosure to Spouse Inventory. Results indicated a pattern of greater disclosure to one's therapist in regard to issues involving despair (e.g., feelings of depression), and to one's spouse in regard to procreation and body concerns (e.g., birth control) and values (e.g., feelings about religion, race, or politics). Issues involving sex were infrequently discussed in either context. Discrepancy scores (differences between extent of disclosure and perceived importance) were greater in the spouse condition. Outcome predictors varied by situation, with overall disclosure predicting therapeutic outcome and both overall disclosure and discrepancy scores predicting marital satisfaction. Findings suggest that although there is substantial overlap in issues discussed in these two contexts, certain intimate disclosures are perceived as situation-specific. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
49.
Less is known about depression in children than in adults. This study integrates fields by combining cognitive and interpersonal research investigating childhood depression symptoms through the use of a genetic framework. Three research questions are addressed. First, what are the associations among interpersonal cognitions, anxiety, and depression? Second, what are the relative magnitudes of genetic and environmental influences on interpersonal cognitions? Third, to what extent do genetic and environmental influences explain associations between interpersonal cognitions and depression? Three hundred pairs of 8-year-old twins reported on symptoms of depression and anxiety by completing the Children's Depression Inventory and the Screen for Childhood Anxiety-Related Emotional Disorders. The authors examined interpersonal cognitions with the Children's Expectation of Social Behaviors and the Perceptions of Peers and Self Questionnaires. Interpersonal cognitions were more strongly correlated with depression (mean r = .35) than with anxiety (mean r = .13). Genetic influence on interpersonal cognitions was small (M = 3%), and associations between interpersonal cognitions and depression were mainly explained by environmental influences. These latter findings may result from interpersonal cognitions in young children, reflecting life experiences as opposed to trait-like cognitive biases. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
50.
Childhood depressive conditions have been explored from multiple theoretical approaches but with few empirical attempts to address the interrelationships among these different domains and their combined effects. In the present study, the authors examined different pathways through which social, cognitive, and genetic risk factors may be expressed to influence depressive symptoms in 300 pairs of child twins from a longitudinal study. Path analysis supported several indirect routes. First, risks associated with living in a step- or single-parent family and punitive parenting did not directly influence depressive outcome but were instead mediated through maternal depressive symptoms and child negative attributional style. Second, the effects of negative attributional style on depressive outcome were greatly exacerbated in the presence of precipitating negative life events. Third, independent of these social and cognitive risk mechanisms, modest genetic effects were also implicated in symptoms, with some indication that these risks are expressed through exposure to negative stressors. Together, these routes accounted for approximately 13% of total phenotypic variance in depressive symptoms. Theoretical and analytical implications of these results are discussed in the context of several design-related caveats. (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-23

京公网安备 11010802026262号