全文获取类型
收费全文 | 269篇 |
免费 | 28篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 55篇 |
金属工艺 | 11篇 |
机械仪表 | 2篇 |
建筑科学 | 1篇 |
能源动力 | 2篇 |
轻工业 | 18篇 |
水利工程 | 3篇 |
无线电 | 24篇 |
一般工业技术 | 67篇 |
冶金工业 | 89篇 |
原子能技术 | 3篇 |
自动化技术 | 19篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 14篇 |
2020年 | 5篇 |
2019年 | 17篇 |
2018年 | 18篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 13篇 |
2014年 | 6篇 |
2013年 | 10篇 |
2012年 | 15篇 |
2011年 | 12篇 |
2010年 | 9篇 |
2009年 | 10篇 |
2008年 | 13篇 |
2007年 | 6篇 |
2006年 | 9篇 |
2004年 | 2篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1993年 | 6篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1964年 | 3篇 |
1963年 | 2篇 |
1962年 | 2篇 |
1961年 | 6篇 |
1960年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有297条查询结果,搜索用时 0 毫秒
101.
Garwood S. Gray; Phillips Deborah; Hartman Andrew; Zigler Edward F. 《Canadian Metallurgical Quarterly》1989,44(2):434
This article provides a brief history of federal agency involvement in programs for children and their families, examines factors that affect the development of federal social policy, and suggests what might come next. It includes a brief summary of the existing 93 federal programs operated by various agencies of the federal government. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
102.
Rigidity, negative reaction tendencies, and cosatiation effects in normal and feebleminded children.
"Feebleminded and normal children played three pre-experimental games under two conditions of reinforcement, followed by a two-part experimental task given under a support condition." Ss were allowed to play to satiation under the 2 conditions. Hypotheses were generated based upon the supposition that "cosatiation score is a measure of motivational determinants rather than… of the inherent rigidity of individuals. The results in general supported this." From Psyc Abstracts 36:04:4JI20S. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
Recent criticisms of Head Start have arisen as a result of unrealistic expectations, loosely generalized evidence, and misunderstood, incomplete research. But these criticisms have forced advocates to focus on administrative problems that make Head Start less effective than it could be. This healthy climate of critical discussion has led to plans to improve program services and to proceed with expansion in a more thoughtful manner. The debate has sparked further ideas to optimize the Head Start approach and make the program more responsive to the needs of children and families in poverty. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
104.
105.
PURPOSE: To investigate possible causes and implications of the decrease in glutathione concentration in rat lenses during organ culture. METHODS: Freshly excised lenses were incubated in modified TC-199 medium. Ellman's Reagent or the GSH-400 assay were used to assay glutathione levels in lenses cultured for different times and under a variety of altered culture conditions. RESULTS: In lenses from young rats the glutathione decrease was not ameliorated by reduction of oxygen tension in the incubator, nor by supplementation of the culture medium with various antioxidants or sulfhydryl compounds, nor with the amino acid precursors of glutathione. Addition of 2-mercaptoethanol stimulated cysteine transport into the lens but had only a modest effect in maintaining the level of glutathione. The decrease in glutathione concentration was less in cultured lenses from older rats. Lenses from rhesus monkeys exhibited no decrease in glutathione levels when maintained in organ culture for up to 48 h. CONCLUSIONS: The basis for the decreased glutathione in cultured young rat lenses is still uncertain. The data from the present study indicate a definite relationship between glutathione loss and age for cultured rat lenses, with young lenses being much more susceptible. The resistance of cultured monkey lenses to loss of glutathione demonstrates species differences in this property which may be relevant to previously reported differences in susceptibility to oxidative damage. 相似文献
106.
Programs to reduce or prevent juvenile delinquency have been generally unsuccessful. Apparently the risk factors that make a child prone to delinquency are based in too many systems, including the individual, the family, and community networks, to make isolated treatment methods effective. Surprisingly, longitudinal studies of some early childhood intervention programs suggest they may help to reduce future delinquency. These programs take an ecological approach to enhancing child development by attempting to promote overall social competence in the many systems impacting on children. Not engaging in criminal acts is one indicator of competence that is related to others, such as being successful in school and in personal relationships. Evaluators must gather more data to confirm this unanticipated benefit of comprehensive interventions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
107.
108.
We describe the design of a system for fast and reliable HTTP service which we call Web++. Web++ achieves high reliability
by dynamically replicating web data among multiple web servers. Web++ selects the available server that is expected to provide
the fastest response time. Furthermore, Web++ guarantees data delivery given that at least one server containing the requested
data is available. After detecting a server failure, Web++ client requests are satisfied transparently to the user by another
server. Furthermore, the Web++ architecture is flexible enough for implementing additional performance optimizations. We describe
implementation of one such optimization, batch resource transmission, whereby all resources embedded in an HTML page that
are not cached by the client are sent to the client in a single response. Web++ is built on top of the standard HTTP protocol
and does not require any changes either in existing web browsers or the installation of any software on the client side. In
particular, Web++ clients are dynamically downloaded to web browsers as signed Java applets. We implemented a Web++ prototype;
performance experiments indicate that the Web++ system with 3 servers improves the response time perceived by clients on average
by 36.6%, and in many cases by as much as 59%, when compared with the current web performance. In addition, we show that batch
resource transmission can improve the response time on average by 39% for clients with fast network connections and 21% for
the clients with 56 Kb modem connections.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
109.
George Candea Neoklis Polyzotis Radek Vingralek 《The VLDB Journal The International Journal on Very Large Data Bases》2011,20(2):227-248
Conventional data warehouses employ the query-at-a-time model, which maps each query to a distinct physical plan. When several queries execute concurrently, this model introduces contention and thrashing, because the physical plans??unaware of each other??compete for access to the underlying I/O and computation resources. As a result, while modern systems can efficiently optimize and evaluate a single complex data analysis query, their performance suffers significantly and can be highly erratic when multiple complex queries run at the same time. We present in this paper Cjoin, a new design that substantially improves throughput in large-scale data analytics systems processing many concurrent join queries. In contrast to the conventional query-at-a-time model our approach employs a single physical plan that shares I/O, computation, and tuple storage across all in-flight join queries. We use an ??always on?? pipeline of non-blocking operators, managed by a controller that continuously examines the current query mix and optimizes the pipeline on the fly. Our design enables data analytics engines to scale gracefully to large data sets, provide predictable execution times, and reduce contention. We implemented Cjoin as an extension to the PostgreSQL DBMS. This prototype outperforms conventional commercial systems by an order of magnitude for tens to hundreds of concurrent queries. 相似文献
110.
Current US policy supports neither high-quality infant daycare nor alternatives, such as paid leaves for infant care. Psychologists, on the basis of research showing the importance of quality care for infants, should support measures to protect daycare quality and to help families afford decent care. At the same time, there are compelling child and family health reasons for psychologists to support voluntary, part-paid, 6-mo leaves for infant care. For 4 wks preceding and 6 wks following childbirth, working mothers should be eligible for a fully paid maternity leave. The remainder of the leave would be made available on a part-paid basis to either parent in any combination they chose to facilitate the parent–infant relationship. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献