全文获取类型
收费全文 | 30670篇 |
免费 | 3346篇 |
国内免费 | 2660篇 |
专业分类
电工技术 | 984篇 |
技术理论 | 3篇 |
综合类 | 3024篇 |
化学工业 | 4451篇 |
金属工艺 | 2330篇 |
机械仪表 | 977篇 |
建筑科学 | 4069篇 |
矿业工程 | 756篇 |
能源动力 | 503篇 |
轻工业 | 1027篇 |
水利工程 | 408篇 |
石油天然气 | 608篇 |
武器工业 | 209篇 |
无线电 | 2233篇 |
一般工业技术 | 3984篇 |
冶金工业 | 3177篇 |
原子能技术 | 219篇 |
自动化技术 | 7714篇 |
出版年
2024年 | 121篇 |
2023年 | 616篇 |
2022年 | 1091篇 |
2021年 | 1282篇 |
2020年 | 1292篇 |
2019年 | 1190篇 |
2018年 | 1110篇 |
2017年 | 1292篇 |
2016年 | 1237篇 |
2015年 | 1330篇 |
2014年 | 1779篇 |
2013年 | 1864篇 |
2012年 | 2021篇 |
2011年 | 2333篇 |
2010年 | 1819篇 |
2009年 | 1851篇 |
2008年 | 1815篇 |
2007年 | 1876篇 |
2006年 | 1646篇 |
2005年 | 1494篇 |
2004年 | 1277篇 |
2003年 | 1142篇 |
2002年 | 914篇 |
2001年 | 737篇 |
2000年 | 533篇 |
1999年 | 442篇 |
1998年 | 348篇 |
1997年 | 304篇 |
1996年 | 227篇 |
1995年 | 204篇 |
1994年 | 171篇 |
1993年 | 139篇 |
1992年 | 106篇 |
1991年 | 86篇 |
1990年 | 101篇 |
1989年 | 58篇 |
1988年 | 43篇 |
1987年 | 38篇 |
1986年 | 43篇 |
1985年 | 29篇 |
1984年 | 31篇 |
1980年 | 32篇 |
1979年 | 27篇 |
1966年 | 28篇 |
1965年 | 31篇 |
1964年 | 49篇 |
1963年 | 39篇 |
1959年 | 29篇 |
1958年 | 30篇 |
1955年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
71.
A feasibility analysis methodology adopted from reactive distillation is applied to membrane reactors. A model is formulated to depict the reactive liquid phase composition on the retentate side of a continuous type membrane reactor. The effects of both the chemical reaction kinetics and the membrane mass transfer kinetics on the feasible products are elucidated by means of retentate phase diagrams and bifurcation analysis. The proposed method can be applied to various membrane processes, independent of the specific structure of the membrane. Two quaternary reaction systems are considered to illustrate the methodology. In the first hypothetical system, it is shown how selective membranes can influence the sequence of effective volatilities which in turn affects the feasible products of the system. In the second example of practical importance, i.e. the heterogeneously catalysed synthesis of propyl acetate coupled with permeation through a porous polycarbonate membrane, the dusty gas model is applied to describe the component fluxes through the membrane. For the latter reaction system, the existence of reactive arheotrope is demonstrated. Arheotropes represent mass transfer controlled feasible products of membrane separation process. 相似文献
72.
A prospective investigation of the impact of childhood sexual abuse on the development of sexuality.
Noll Jennie G.; Trickett Penelope K.; Putnam Frank W. 《Canadian Metallurgical Quarterly》2003,71(3):575
The sexual attitudes and activities of 77 sexually abused and 89 comparison women (mean age=20.41, SD=3.38) were assessed 10 years after disclosure in a longitudinal, prospective study of the long-term effects of childhood sexual abuse. Abused participants were more preoccupied with sex, younger at first voluntary intercourse, more likely to have been teen mothers, and endorsed lower birth control efficacy than comparison participants. When psychological functioning earlier in development was examined, sexual preoccupation was predicted by anxiety, sexual aversion was predicted by childhood sexual behavior problems, and sexual ambivalence (simultaneous sexual preoccupation and sexual aversion) was predicted by pathological dissociation. Findings also indicate that biological father abuse may be associated with greater sexual aversion and sexual ambivalence. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
73.
The diffusional behavior of multi-arm star-shaped p(tBMA) was investigated in a concentration range from dilute to semidilute region with 1H pulsed field gradient spin-echo NMR (PFGSE-NMR). An 142-arm star-shaped p(tBMA) showed two diffusional mode, which reflected the coexistence of liquid ordering phase and liquid phase near the ordering transition. On the other hand, for star-shaped p(tBMA) with 55 arms showed a single diffusional relaxation in all concentration ranges during observation time. In the semidilute region, the relationship between the diffusion coefficient against the polymer concentration was affected strongly not only the arm number but also liquid ordering structure. 相似文献
74.
75.
Butler Emily A.; Egloff Boris; Wlhelm Frank H.; Smith Nancy C.; Erickson Elizabeth A.; Gross James J. 《Canadian Metallurgical Quarterly》2003,3(1):48
At times, people keep their emotions from showing during social interactions. The authors' analysis suggests that such expressive suppression should disrupt communication and increase stress levels. To test this hypothesis, the authors conducted 2 studies in which unacquainted pairs of women discussed an upsetting topic. In Study 1, one member of each pair was randomly assigned to (a) suppress her emotional behavior, (b) respond naturally, or (c) cognitively reappraise in a way that reduced emotional responding. Suppression alone disrupted communication and magnified blood pressure responses in the suppressors' partners. In Study 2, suppression had a negative impact on the regulators' emotional experience and increased blood pressure in both regulators and their partners. Suppression also reduced rapport and inhibited relationship formation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
76.
采用差示扫描量热仪研究了5种具有不同取代基的苯甲酸钠盐作为结晶成核剂对聚对苯二甲酸乙二醇酯(HET)结晶和熔融行为的影响,并同滑石粉进行了对比。结果表明,成核剂的加入能明显改变PET的结晶和熔融行为。苯甲酸钠、对苯二甲酸甲酯单羧酸钠和对羟基苯甲酸钠提高既汀的熔融结晶温度(Tc)分别达22.93、21.7和19.37℃,但使PET降解严重;对苯酚钠甲酸钠能够提高Tc达17.75℃且对PET相对分子质量影响很小;对苯二甲酸二钠成核作用最差。低于滑石粉。此外,成核剂的成核能力越强,PET双熔融峰中的低温峰顶温度就越高。 相似文献
77.
Lean philosophy: implementation in a forging company 总被引:2,自引:2,他引:0
Ajit Kumar Sahoo N. K. Singh Ravi Shankar M. K. Tiwari 《The International Journal of Advanced Manufacturing Technology》2008,36(5-6):451-462
This research addresses the implementation of lean philosophy in a forging company with a focus on radial forging production
flow lines. Here, the prime motive is to evolve and test several strategies to eliminate waste on the shop floor. In this
research, a systematic approach is suggested for the implementation of lean principles. This paper describes an application
of value stream mapping (VSM). Consequently, the present and future states of value stream maps are constructed to improve
the production process by identifying waste and its sources. Furthermore, Taguchi’s method of design of experiments is pursued
here to minimize the forging defects produced due to imperfect operating conditions. A noticeable reduction in set-up time
and work-in-process (WIP) inventory level is substantiated. Finally, we conclude with a discussion of managerial implications
and the future scope of research. 相似文献
78.
Two studies are presented. The first aimed to identify possible barriers to the uptake and use of commonly available telephony features and to determine whether greater knowledge of features/access codes and availability of user manuals could increase feature usage under certain conditions. Results showed that feature-usage patterns were not affected by any of the manipulations, but that they were determined by specific job demands. Using Constantine and Lockwood's (1999) conceptualization of user roles, a method to support feature bundling decisions for specific target markets was developed and tested in the second study. The method - Strategic User Needs Analysis (SUNA) - was shown to yield a useful balance between high- and low-level information about selected roles. SUNA provided sufficient information to distinguish between PDA feature usage patterns of two similar target user groups as well as to suggest additional features each of the two target groups would find useful. The development of SUNA and observational findings of actual PDA usage are reported. 相似文献
79.
建立了水驱强度影响下的水驱油渗流数学模型,在获得数学模型解的基础上,计算了考虑井筒储存、表皮效应以及水驱强度影响下油井的压力及压力导数典型曲线,分析了压力动态特征,通过这些研究为水驱油藏的试井分析提供了理论基础,为水驱油藏的识别提供了一种新的手段。 相似文献
80.
[Correction Notice: An erratum for this article was reported in Vol 31(2) of Canadian Psychology Psychologie Canadienne (see record 2007-08913-001). In the October 1989 issue (Vol. 30, No. 4, p. 697), Arnold Rincover's affiliation with the Ontario Institute for Studies in Education was incorrectly given as Associate Professor. He has been an Extramural Instructor at O.I.S.E.] Reviews the book, The parent-child connection by Arnold Rincover (1988). The parent-child connection is a well written book that offers valuable advice to help parents of young children evaluate and understand their children's behaviour. It also offers useful suggestions on managing child behaviour, although these parenting tips are most likely to be useful to those parents who least need them (i.e., those with numerous personal and social resources, whose children are presenting only minor behavioural difficulties). The two general themes of the book, child behaviour as communication and developmental norms as guidelines for deciding if behaviour is problematic, are well-suited to the purposes of a parent reference book. They offer an appropriate framework for discussing specific child behaviours and helping parents to determine if these behaviours are problematic in their children. This book is a welcome addition to the list of available parenting books, and may prove particularly useful for younger parents in need of accurate and understandable information about normal child development and behaviour. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献