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   1161篇
  免费   70篇
  国内免费   2篇
电工技术   3篇
化学工业   389篇
金属工艺   16篇
机械仪表   17篇
建筑科学   57篇
能源动力   13篇
轻工业   213篇
水利工程   12篇
石油天然气   2篇
无线电   41篇
一般工业技术   160篇
冶金工业   160篇
原子能技术   6篇
自动化技术   144篇
  2024年   6篇
  2023年   18篇
  2022年   81篇
  2021年   79篇
  2020年   38篇
  2019年   58篇
  2018年   29篇
  2017年   34篇
  2016年   45篇
  2015年   41篇
  2014年   42篇
  2013年   70篇
  2012年   64篇
  2011年   68篇
  2010年   49篇
  2009年   47篇
  2008年   57篇
  2007年   56篇
  2006年   34篇
  2005年   21篇
  2004年   22篇
  2003年   32篇
  2002年   38篇
  2001年   14篇
  2000年   14篇
  1999年   20篇
  1998年   19篇
  1997年   10篇
  1996年   17篇
  1995年   9篇
  1994年   11篇
  1993年   9篇
  1992年   8篇
  1991年   4篇
  1990年   6篇
  1989年   9篇
  1988年   8篇
  1987年   5篇
  1986年   3篇
  1985年   6篇
  1984年   4篇
  1983年   4篇
  1981年   2篇
  1980年   5篇
  1979年   2篇
  1977年   4篇
  1974年   4篇
  1973年   2篇
  1972年   1篇
  1969年   1篇
排序方式: 共有1233条查询结果,搜索用时 0 毫秒
161.
The objective of the present study was to evaluate the interrelationship between the cuticular and postpharyngeal glands' hydrocarbons, both in the individual ant and during its interaction with nestmates. In vivo radiochemical assays were employed to monitor the de novo hydrocarbon biosynthesis from acetate in the ant's body. The newly synthesized hydrocarbons appeared first internally and after 24 hr they accumulated in the postpharyngeal gland and on the cuticular surface. Blocking the possibility of external transfer of hydrocarbons between cuticle and postpharyngeal gland led to a significant decrease of labeled hydrocarbons in the postpharyngeal gland. In addition, during encounters between labeled and unlabeled ants, newly synthesized hydrocarbons were transferred, mainly via trophallaxis, but also by allo-grooming and physical contact. In view of these results, we propose as a model for their dynamics that hydrocarbons are synthesized in tissues associated with the integument. Through self-grooming, there is a constant exchange of hydrocarbons between the cuticular surface and the postpharyngeal gland. Furthermore, in encounters between nestmates, hydrocarbons are exchanged among them mostly by trophallaxis, with the mediation of the postpharyngeal gland. Thus, this gland acts as a pool for mixing colonial hydrocarbons and may serve to attain a unified colony odor.  相似文献   
162.
In recent years the use of inactive dry yeast (IDY) preparations such as inactive yeast, yeast autolysates, yeast extracts and yeast hulls or walls have been widely used within the oenological industry to improve either technological processes or the sensory characteristics of wines. Some of these preparations have very specific applications and there are currently many of these products in the market under different brands that promise different ways of improving wine characteristics. Nevertheless, scientific information about the chemistry beyond their use and their action mode is still scarce.The objective of this review is to revise the different applications of specific IDY preparations in winemaking, on the basis of their action mechanisms taking into consideration the scientific information available, underlining the necessity of more scientific work in order to better characterize their chemical composition, their action mechanisms, and the establishment of better criteria for their oenological use.  相似文献   
163.
BACKGROUND: A strategy to supply Ca directly to fruits as a tool for improving peach quality has been devised and tested under field conditions. Since peaches in the area of study (Calanda, Spain) are routinely bagged shortly after thinning, a method based on the application of Ca gels to the fruit surface was introduced. The effect of surface treatments was assessed in terms of quality, nutrient balance and surface deposition. RESULTS: Application of Ca‐containing formulations increased mesocarp and exocarp Ca concentrations, providing evidence for the penetration of Ca through the peach skin. Surface Ca treatments had a particular mode of deposition and in some instances improved the shelf life of fruits without affecting their quality. CONCLUSION: Surface treatment with Ca‐containing gels appears to be a viable approach to increase fruit Ca, quality and storability of bagged peach cultivars and should be optimised in future studies. Copyright © 2009 Society of Chemical Industry  相似文献   
164.
165.
When cooling a melt the cooling rate in different layers varies due to differences in heat transfer. These changes in cooling rate were determined experimentally for the As2S3 melt in a quartz ampoule with diameter of 17 mm. The cooling rate at air quenching varies from 1.36 K/s in the bulk middle to 2.11 K/s in the border layers, and from 3.54 to 38.80 K/s for water quenching, respectively. Further, the corresponding changes in the density, microhardness, glass-transition temperature and electrical conductivity in dependence on the choice of the measured sample from various parts of the bulk were found. The anomalous behaviour of these parameters in dependence on the cooling rate corresponds to the polymeric structure of the glass.  相似文献   
166.
At diagnosis, 59 breast cancer patients reported on their overall optimism about life; 1 day presurgery, 10 days postsurgery, and at 3-, 6-, and 12-mo follow-ups, they reported their recent coping responses and distress levels. Optimism related inversely to distress at each point, even controlling for prior distress. Acceptance, positive reframing, and use of religion were the most common coping reactions; denial and behavioral disengagement were the least common reactions. Acceptance and the use of humor prospectively predicted lower distress; denial and disengagement predicted more distress. Path analyses suggested that several coping reactions played mediating roles in the effect of optimism on distress. Discussion centers on the role of various coping reactions in the process of adjustment, the mechanisms by which dispositional optimism vs pessimism appears to operate, third variable issues, and applied implications. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
167.
The main objective of this work is to determine what anthropometric method to use under field conditions, given the kind of mainutrition to be detected. In the first part of the work some criteria and procedures are given by which to compare the field perfomance characteristics (i.e. transportability, facility of use, etc.), of the most commonly used instruments. Then we extrapolate these characteristics to the respective methods like weight for age, weight for height, height for age, etc. In the second part we present a correlation matrix among the various methods and analyze it in order to associate with each method a specific typology of malnutrition.  相似文献   
168.
Examined imitative recall for sentences conforming to the grammatical rules of standard English vs those suggested for nonstandard (black) English. Ss were a total of 87 black and 51 white low- and middle-income children in Grades 3 and 4. Low-income blacks showed better recall than middle-income whites for nonstandard sentences and poorer recall for standard sentences. School integration influenced the performance of low-income blacks: Those who had attended an integrated school were both better on standard and poorer on nonstandard sentences than those who had attended a segregated school. For middle-income Ss, both black and white, there were no evident linguistic effects of integration. Although dialect clearly affected recall, results do not support a conception of black dialect as a separate linguistic system with totally consistent rules. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
169.
A national survey of 1,000 psychologists, to which 223 responded, assessed professionals' clinical practices and beliefs about the treatment of adult survivors of childhood sexual abuse (CSA), personal CSA history, and the phenomenon of clients remembering CSA in therapy. Results indicated that over 25% of therapists reported using guided imagery, dream interpretation, bibliotherapy regarding sexual abuse, referral to sexual abuse survivors' group, and free association of childhood memories as memory retrieval techniques with clients who had no specific memory of CSA. However, the majority of therapists reported that they had not seen any cases of adult clients entering therapy with no memory of CSA and subsequently recalling abuse in the course of therapy. A personal history of CSA was not associated with most clinical practices related to treating sexual abuse survivors. The implications for training and establishing scientific standards of psychological practice are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
170.
Studied data from 194 adult outpatients in a private medical center to determine whether the Minnesota Multiphasic Personality Inventory (MMPI) or a utilization prediction scale (UPS) predicted decrease in outpatient medical utilization following psychotherapy. Although none of the 13 MMPI scales discriminated differences, a UPS cutoff score correctly categorized 75% of the original sample. When the UPS was applied to a cross-validation sample, two-thirds were correctly identified. (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