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   2783篇
  免费   46篇
  国内免费   2篇
电工技术   36篇
化学工业   434篇
金属工艺   26篇
机械仪表   59篇
建筑科学   162篇
矿业工程   15篇
能源动力   68篇
轻工业   242篇
水利工程   12篇
石油天然气   12篇
无线电   224篇
一般工业技术   363篇
冶金工业   877篇
原子能技术   16篇
自动化技术   285篇
  2021年   24篇
  2019年   23篇
  2018年   27篇
  2017年   26篇
  2016年   28篇
  2015年   24篇
  2014年   49篇
  2013年   125篇
  2012年   85篇
  2011年   80篇
  2010年   59篇
  2009年   50篇
  2008年   83篇
  2007年   115篇
  2006年   94篇
  2005年   86篇
  2004年   66篇
  2003年   62篇
  2002年   52篇
  2001年   62篇
  2000年   39篇
  1999年   59篇
  1998年   205篇
  1997年   134篇
  1996年   80篇
  1995年   65篇
  1994年   69篇
  1993年   61篇
  1992年   35篇
  1991年   36篇
  1990年   35篇
  1989年   33篇
  1988年   38篇
  1987年   32篇
  1986年   41篇
  1985年   36篇
  1984年   25篇
  1983年   43篇
  1982年   41篇
  1981年   41篇
  1980年   30篇
  1979年   29篇
  1978年   24篇
  1977年   27篇
  1976年   60篇
  1975年   27篇
  1974年   28篇
  1973年   22篇
  1972年   15篇
  1955年   16篇
排序方式: 共有2831条查询结果,搜索用时 296 毫秒
91.
92.
We describe the life and times of a servicing mechanic for cypher equipment for the Royal Air Force during World War II and an opportunity to serve again as a cypher machine restorer for Bletchley Park Museum.  相似文献   
93.
In this paper I make a personal reflection on my research and writings in the field of Project Management over the past 30 years. My research has primarily been about the management of the project-based organization. Within that I have researched governance, organizational behaviour, contingency, marketing, success and shareholder value.  相似文献   
94.
This research explores the dynamics underpinning entrepreneurial project-oriented organizations. Specifically, it focuses on how strategy and execution by projects are managed and how ambidexterity – a firm's ability to exploit old certainties while exploring new possibilities – operates as a logic. The empirical findings from an explorative longitudinal research of supercar maker Pagani Automobili in the period 2007–2019, offer an insight of a complex entrepreneurially led project-oriented organization and suggest three integrative mechanisms that describe the ambidextrous management of the interplay within and between strategy and project levels. Additionally, this research recognizes the critical role of projects also in entrepreneurial environments and suggests that the accomplishment of ambidexterity is unique in nature as it is aimed at reconciling the uniqueness of competitive propositions and that of projects within a unique entrepreneurial environment, opening avenues for more theoretical and empirical studies at the intersection of project management and entrepreneurship.  相似文献   
95.
Abnormal uterine function affects conception rate and embryo development, thereby leading to poor fertility and reproduction failure. Exosomes are a nanosized subclass of extracellular vesicles (EV) that have important functions as intercellular communicators. They contain and carry transferable bioactive substances including micro RNA (miRNA) for target cells. Elements of the cargo can provide epigenetic modifications of the recipient cells and may have crucial roles in mechanisms of reproduction. The dairy industry accounts for a substantial portion of the economy of many agricultural countries. Exosomes can enhance the expression of inflammatory mediators in the endometrium, which contribute to various inflammatory diseases in transition dairy cows. This results in reduced fertility which leads to reduced milk production and increased cow maintenance costs. Thus, gaining a clear knowledge of exosomal epigenetic modifiers is critical to improving the breeding success and profitability of dairy farms. This review provides a brief overview of how exosomal miRNA contributes to inflammatory diseases and hence to poor fertility, particularly in dairy cows.  相似文献   
96.
A smartphone sky camera and associated image analysis algorithm has been developed and validated to determine total cloud cover and the percentage of thick and thin clouds using supervised image classification for a range of cloud types, cloud cover from 4% to 98%, and solar zenith angles between 6° and 49°. Additionally, this system provides the percentage of total, thick, and thin clouds in proximity to the solar disc. The measurement errors were comparable to those associated with values obtained by commercial sky camera systems. The benefits of increasing the availability of cloud fraction measurements include the potential to develop improved local ultraviolet indices and weather forecasts and to provide a better understanding of cloud patterns required for the generation of solar energy.  相似文献   
97.
We have studied the response of mechanically toughened and physically aged polycarbonate primarily using Charpy impact and ultrasonic wave speed measurements. The toughening was conducted through plastic compression on as‐received PC. The Charpy impact tests showed anisotropic toughening, both in the absorbed energy and in the mode of fracture. The amount of toughening with plastic compression, even though anisotropic, is centered around the response of annealed and quenched samples, which represent the response of an unaged PC. There was an anisotropic drop in the toughness of some samples with aging. The time of this drop was uncorrelated in the different directions and disappeared for the highly toughened samples. This transition was bimodal and statistically distributed between either a fully ductile or a fully brittle failure. As the samples were prepared in a manner to remove induced residual stresses, this drop in toughening may be associated with an intrinsic anisotropic thermal aging of the deformed material. POLYM. ENG. SCI., 54:794–804, 2014. © 2013 Society of Plastics Engineers  相似文献   
98.
The nature of home automation is introduced. It is argued that end users should be able to define how the home system reacts to changing circumstances. Policies are employed as user-defined rules for how this should happen. The architecture of the Homer home automation system is briefly overviewed. The Homer policy system and the Homeric policy language it supports are explained. A technique is described for offline conflict analysis among policies (the analogue of the feature interaction problem). A substantial worked example shows how conflict detection is performed on a range of sample home policies.  相似文献   
99.
100.
In this work, an on-line process for pressurised hot water extraction (PHWE) of antioxidants from plants as well as drying of the extract in one step by particle formation based on the use of supercritical carbon dioxide (SC-CO2) has been developed. This process has been called WEPO®, water extraction and particle formation on-line. With this process, dried extracts from onion with the same composition of quercetin derivatives as non-dried extracts have been obtained as a fine powder with spherical particles from 250 nm to 4 μm in diameter. The major compounds present in the extract were quercetin-3,4′-diglucoside, quercetin-4′-glucoside and quercetin. An auxiliary inert gas (hot N2) was used to enhance the drying process. Parameters such as temperature (120 °C), SC-CO2 and N2 pressures (80 and 12.5 bar, respectively) and flow rate of SC-CO2 (10 ml/min), have been settled by trial-and-error in order to achieve a fine and constant spray formation. Water content, size and morphology, antioxidant capacity and quercetin content of the particles were studied to evaluate the efficiency of the WEPO process. Results were compared with the ones from extracts obtained by continuous flow PHWE followed by freeze-drying. Results showed that both processes gave similar results in terms of antioxidant capacity, concentration of quercetin derivatives and water content, while only WEPO was able to produce defined spherical particles smaller than 4 μm.  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