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   2116篇
  免费   138篇
  国内免费   59篇
电工技术   23篇
技术理论   1篇
综合类   146篇
化学工业   423篇
金属工艺   80篇
机械仪表   44篇
建筑科学   110篇
矿业工程   77篇
能源动力   15篇
轻工业   585篇
水利工程   26篇
石油天然气   82篇
武器工业   8篇
无线电   27篇
一般工业技术   93篇
冶金工业   517篇
原子能技术   25篇
自动化技术   31篇
  2024年   18篇
  2023年   29篇
  2022年   81篇
  2021年   87篇
  2020年   71篇
  2019年   42篇
  2018年   29篇
  2017年   37篇
  2016年   46篇
  2015年   54篇
  2014年   75篇
  2013年   76篇
  2012年   101篇
  2011年   142篇
  2010年   128篇
  2009年   115篇
  2008年   113篇
  2007年   123篇
  2006年   156篇
  2005年   136篇
  2004年   125篇
  2003年   102篇
  2002年   86篇
  2001年   81篇
  2000年   38篇
  1999年   35篇
  1998年   34篇
  1997年   25篇
  1996年   26篇
  1995年   20篇
  1994年   16篇
  1993年   16篇
  1992年   9篇
  1991年   9篇
  1990年   9篇
  1989年   5篇
  1988年   6篇
  1987年   3篇
  1986年   1篇
  1985年   2篇
  1984年   2篇
  1982年   1篇
  1977年   1篇
  1976年   2篇
排序方式: 共有2313条查询结果,搜索用时 31 毫秒
1.
2.
Carriers for targeted delivery and controlled release of poorly water-soluble active substances (PWSAS) are facing three challenges: (a) the encapsulation issues, (b) limitations of PWSAS water solubility, and (c) burst drug release which can be pharmacologically dangerous and economically inefficient. The present study brings a novel strategy for encapsulation and controlled release of PWSAS—caffeine in concentrations which are higher than its maximal water solubility without the possibility of burst effect. The modification of hydrophilic carrier based on poly(methacylic acid) was done using casein and liposomes. To further increase the maximal caffeine loading inside the carrier nicotinamide was used. The release study of the encapsulated PWSAS was elaborated with respect to morphology of the carriers and interactions that could be established between its structural components. The carriers swelling and the release of caffeine and nicotinamide were also investigated depending on caffeine concentration, the presence of different liposomal formulations and the volume ratio of liposomal formulation, in three media with different pH simulating the path of the carrier through the human gastrointestinal tract. The synthesized carriers are promising candidates for encapsulation of PWSAS in concentrations which are higher than its maximal water solubility and for the targeted delivery of those dosages.  相似文献   
3.
用土壤含水层处理系统去除水库微污染有机物的试验研究   总被引:10,自引:2,他引:8  
本文针对当前中国饮用水源污染以微污染为主的特点,以北京三家店水库原水和永定河河道砂为研究对象,设计了用于表征土壤含水层处理系统的一维土柱,进行污水净化效果的试验研究。结果表明,土壤含水层处理系统对三家店水库微污染水中的有机物有一定的去除效果,在0.12m/d的水力负荷条件下,对CODMo去除率虽然仅为15%,但是出水达到了地表水Ⅱ类水质标准;对BOD5的去除率达到了55%,可以被有效地去除。渗透速率相同时,水力负荷周期对去除效果的影响不明显,但在保证一定水力负荷的情况下,可适当延长落干期,恢复土壤的渗透能力,达到较好的处理效果。同时,土壤含水层处理系统的净化能力主要发生在土层50cm以内。  相似文献   
4.
Although continuing care is strongly related to positive treatment outcomes for substance use disorder (SUD), participation rates are low and few effective interventions are available. In a randomized clinical trial with 150 participants (97% men), 75 graduates of a residential Veterans Affairs Medical Center SUD program who received an aftercare contract, attendance prompts, and reinforcers (CPR) were compared to 75 graduates who received standard treatment (STX). Among CPR participants, 55% completed at least 3 months of aftercare, compared to 36% in STX. Similarly, CPR participants remained in treatment longer than those in STX (5.5 vs. 4.4 months). Additionally, CPR participants were more likely to be abstinent compared to STX (57% vs. 37%) after 1 year. The CPR intervention offers a practical means to improve adherence among individuals in SUD treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
5.
研制了一种新型微合金非调质钢。通过合理设计合金成分,改善熔炼脱氧过程,控制钢中氧化物的组成、分布、形状和尺寸,在研制钢中形成微细的氧化物夹杂作为晶内铁素体最有利的析出位置。通过晶内铁素体的析出细化了晶粒,提高了钢的强度与韧性。将研制的新型微合金非调质钢用于拖拉机的牵引插销是可行且有效的。  相似文献   
6.
Longitudinal data from a representative sample of 1,978 Black and White adolescents were used to examine the role of personality in multiple risk or problem behaviors. Results indicate that covariation among diverse behaviors (educational underachievement, delinquent behavior, substance use, sexual behavior) can be adequately modeled by a single higher order factor, and that impulsivity and avoidance coping serve as generalized risk factors for involvement in these behaviors. Whereas none of the personality variables examined explained change in problem behaviors once established, avoidance coping prospectively predicted involvement among a subgroup of adolescents with little or no prior involvement. Results suggest that dysfunctional styles of regulating emotions and emotionally driven behaviors are core features of risky or problem behaviors during adolescence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
7.
The goal of the present studies was to construct and validate a short form of the 50-item Smoking Consequences Questionnaire (SCQ; T. H. Brandon & T. B. Baker, 1991), a measure of smoking outcome expectancies. In Study 1, a 21-item short form (S-SCQ) was derived from a sample of 107 young adults previously treated for substance abuse. In Study 2, the measure was cross-validated on 125 adolescents in treatment for substance abuse. Confirmatory factor analyses revealed good model fit and factorial invariance for the 4 S-SCQ subscales across both samples. Validation analyses on each sample found that subscale scores generally correlated significantly with smoking-related variables. The present studies provide initial evidence for the utility of the S-SCQ when used with young adults and adolescents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
8.
探讨肥料中有机质的分析方法。通过对两个肥料标准中有机质的分析方法进行比较,对各标准中有机质检验过程中的影响因素进行了分析,确定了本地区有机肥料中有机质适宜的分析方法。  相似文献   
9.
Reviews the book, The chemically dependent: Phases of treatment and recovery edited by Barbara C. Wallace (see record 1992-98403-000). While this book is ambitious, interesting, educational, and useful, it is also disappointing, repetitious, and incomplete. Because it tries to accomplish so much, it may appear to have succeeded too little. This book is organized around, and explicative of, several basic ideas which might have been controversial if not heretical had this book been published ten years ago. Section I, purporting to link specific "phases of recovery" to particular forms and functions of treatment, will certainly be useful for novice clinicians but falls short of its overstated goals and is thereby disappointing. Section II is a collection of moderately redundant chapters describing the etiology and treatment of substance abusers from the viewpoints of psychoanalytic, psychodynamic, ego psychology, and object-relations theorists and therapists. Section III focuses on cognitive-behavioral, self-help, and relapse-prevention treatments. Section IV is quite uneven in quality of writing and applicability of content, and could have benefited from closer editorial scrutiny or selectivity. The final section focuses on special needs of particular subpopulations of substance abusers: African-Americans, prison inmates, HIV/AIDS patients, persons who are homeless, those who have been sexually and physically abused, and others. According to the reviewer this is not the best book on substance abuse treatment, but it does present some clinically useful ideas and it is worth reading. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
10.
School psychologists are generally not provided with the knowledge and skills to address both educational and psychosocial issues of Asian American and Pacific Islander students. The present study is the first of its kind in examining 36 independent (i.e., demographic, social, cultural, psychological) variables in association with four school outcomes (i.e., grade point average, absences, suspensions, and school infractions) with a large sample of Caucasian, Filipino, Native Hawaiian, Japanese, mixed/non-Hawaiian, and "other" Hawai'i high school students (N = 2,833). Given the relatively unique sample in question and the sheer number of variables, an exploratory approach was utilized with the goal of determining the most robust independent variables, with the unique inclusion of Hawaiian cultural identification. A cross-validation technique was used, whereby stepwise regressions were performed for each of two cross-validation samples; only common variables were retained in a final stepwise model for each of the four school outcomes. The results indicated that, remarkably, substance use accounted for the most variance (i.e., 8.4% -16.1 %) in the four school measures. Further analyses detailed the relationship, including the finding that smoking cigarettes regularly, accounted for the most variance compared to the other five substance use items. Further research and implications of the findings are discussed, including the need for prevention and intervention programs that incorporate substance use as a component, both within and outside of school environments. (PsycINFO Database Record (c) 2011 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