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   2944篇
  免费   39篇
  国内免费   1篇
电工技术   34篇
化学工业   348篇
金属工艺   34篇
机械仪表   40篇
建筑科学   118篇
矿业工程   6篇
能源动力   49篇
轻工业   266篇
水利工程   43篇
石油天然气   12篇
无线电   200篇
一般工业技术   370篇
冶金工业   1068篇
原子能技术   25篇
自动化技术   371篇
  2021年   18篇
  2019年   25篇
  2018年   25篇
  2017年   21篇
  2016年   29篇
  2015年   23篇
  2014年   41篇
  2013年   111篇
  2012年   79篇
  2011年   92篇
  2010年   73篇
  2009年   100篇
  2008年   92篇
  2007年   89篇
  2006年   93篇
  2005年   67篇
  2004年   79篇
  2003年   81篇
  2002年   70篇
  2001年   72篇
  2000年   61篇
  1999年   57篇
  1998年   259篇
  1997年   175篇
  1996年   124篇
  1995年   96篇
  1994年   73篇
  1993年   80篇
  1992年   47篇
  1991年   37篇
  1990年   49篇
  1989年   40篇
  1988年   34篇
  1987年   36篇
  1986年   29篇
  1985年   42篇
  1984年   39篇
  1983年   31篇
  1982年   29篇
  1981年   24篇
  1980年   24篇
  1979年   18篇
  1978年   14篇
  1977年   32篇
  1976年   68篇
  1975年   21篇
  1974年   18篇
  1973年   22篇
  1972年   16篇
  1970年   16篇
排序方式: 共有2984条查询结果,搜索用时 93 毫秒
71.
River management based solely on physical science has proven to be unsustainable and unsuccessful, evidenced by the fact that the problems this approach intended to solve (e.g., flood hazards, water scarcity, and channel instability) have not been solved and long‐term deterioration in river environments has reduced the capacity of rivers to continue meeting the needs of society. In response, there has been a paradigm shift in management over the past few decades, towards river restoration. But the ecological, morphological, and societal benefits of river restoration have, on the whole, been disappointing. We believe that this stems from the fact that restoration overrelies on the same physical analyses and approaches, with flowing water still regarded as the universally predominant driver of channel form and structural intervention seen as essential to influencing fluvial processes. We argue that if river restoration is to reverse long‐standing declines in river functions, it is necessary to recognize the influence of biology on river forms and processes and re‐envisage what it means to restore a river. This entails shifting the focus of river restoration from designing and constructing stable channels that mimic natural forms to reconnecting streams within balanced and healthy biomes, and so levering the power of biology to influence river processes. We define this new approach as biomic river restoration.  相似文献   
72.
We present results of a fairly complete study on which dopants M result in single-phase U1−xMxPt3 samples. The resulting new samples. M = Y, Lu, Sc, Hf, Zr, have been characterized by low temperature magnetic susceptibility and specific heat for x 0.07. Based on a previously proposed model, the c/a ratios of the present alloys would be expected to result in magnetic behavior as observed in U1−xThxPt3 and U(Pt1−xPdx)3. On the contrary, no magnetism is found; the Sc-doped samples actually show a suppression of spin fluctuations. A new proposal is made to explain which properties are critical for the magnetic behavior of UPt3, as well as its doped derivatives.  相似文献   
73.
74.
75.
The mobility limiting scattering mechanisms for amorphous semiconductors and polar polycrystalline semiconductors are studied in the context of developing new high‐performance thin‐film transistor (TFT) channel layer materials for large‐area electronics. A physics‐based model for carrier transport in an amorphous semiconductor is developed to estimate the mobility limits of amorphous semiconductor TFTs. The model involves band tail state trapping of a diffusive mobility. Simulation reveals a strong dependence on the band tail density of states. This consideration makes it difficult to realize a high‐performance p‐type oxide TFT. A polar crystalline semiconductor may offer a higher mobility but is fundamentally limited by polar optical phonon scattering. Any crystalline TFT channel layer for practical large‐area applications will not be a single crystal but polycrystalline, and therefore, grain size and grain boundary‐dependent scattering will further degrade the transport properties.  相似文献   
76.
The Jackfish Bay Remedial Action Plan is the first of Lake Superior's Areas of Concern (AOCs) to consider recognition as an Area in Recovery (AiR). As a result of a high degree of complexity and uncertainty, ecosystem recovery in Jackfish Bay has been determined using a combination of regulatory policies and scientific evidence and extensive public and expert-based decision making. As a result, the conceptualization of the AiR status in Jackfish Bay has been developed with the adaptive management and the ecosystem approach, which provide the basic principles of assessing, monitoring, and managing the Area of Concern. To determine the status of beneficial use impairments caused by effluent from the Terrace Bay Pulp Inc., three public advisory committees—an academic panel of experts, a government technical review committee, and the Jackfish Bay Public Area in Recovery Review Committee (PARRC)—reviewed relevant scientific data and documents, including peer-reviewed publications, to assess changes in pollution levels in Jackfish Bay and improvements to aquatic, biotic, and benthic environments of the bay. The public decision-making process concluded with recommendations by the PARRC to develop a systematic monitoring program so that the ecosystem recovery process in the bay could be assessed on a continued basis, leading to its eventual delisting as an AOC. The entire process provides an example of blending science and public policies for remediation of a degraded ecosystem on the Great Lakes.  相似文献   
77.
This paper reports on the use of qualitative analysis to inform a risk analysis framework for decentralised water systems. To realise the benefits from these technologies, a methodology is applied to learn from previous difficulties in implementing and managing them. A workshop process was used to capture stories from industry professionals on difficulties they have encountered in planning and implementation. Qualitative analysis of story narratives revealed stages where there was some type of development process failure; as well as failure modes and factors influencing the difficulties encountered. The analysis also generated insights: difficulties in one part of the development process tends to propagate to subsequent stages; system difficulties most often occurred in the policy stage of development due to institutional inertia and lack of adaptive governance; and the best indicator of problems with a decentralised system was complaints of poor water quality. Furthermore, this paper also provides a method to learn from past difficulties by identifying what data needs to be collected in order to populate a risk model which can be used for improving risk assessment of the development process for decentralised systems. This can provide a basis for better decision making, policy and guidelines; an important factor in mainstream acceptance.  相似文献   
78.
Scenarios are possible future states of the world that represent alternative plausible conditions under different assumptions. Often, scenarios are developed in a context relevant to stakeholders involved in their applications since the evaluation of scenario outcomes and implications can enhance decision-making activities. This paper reviews the state-of-the-art of scenario development and proposes a formal approach to scenario development in environmental decision-making. The discussion of current issues in scenario studies includes advantages and obstacles in utilizing a formal scenario development framework, and the different forms of uncertainty inherent in scenario development, as well as how they should be treated. An appendix for common scenario terminology has been attached for clarity. Major recommendations for future research in this area include proper consideration of uncertainty in scenario studies in particular in relation to stakeholder relevant information, construction of scenarios that are more diverse in nature, and sharing of information and resources among the scenario development research community.  相似文献   
79.
Various educational programs have been developed and found to be effective in the self-management of arthritis. This study reexamined the effectiveness of one such program, "Bone Up On Arthritis" (BUOA), when the program was delivered by a community-based service organization to a sample of persons (N = 154) who differed widely in disease type and demographic characteristics. Arthritis Foundation staff implemented BUOA at four national sites; data were collected and analyzed by University of Michigan nurse researchers. Investigators found improved scores on all outcome measures (self-care behavior, helplessness, pain, dysfunction, and depression). These findings suggest that "Bone Up" is an effective nursing intervention in multiple organizational and community environments and for diverse patient populations.  相似文献   
80.
This study explores design alternatives for the purification and possible reuse of low-volume organic solvents waste streams in pharmaceutical manufacturing. Solvent use has a large impact on the life cycle of pharmaceutical processes, as typically 80–90% of the total mass used in the production of an active pharmaceutical ingredient is attributed to solvent use. Solvents are not consumed in pharmaceutical processes so they exit the process as waste. These waste streams are usually disposed of using incineration; therefore, generating significant life cycle emissions from disposal and replacement of virgin solvent. Solvent recovery efforts are generally limited to large-volume waste streams. However, results show that solvents in low-volume streams can also be economically recovered using a versatile multi-campaign solvent recovery skid. Three different solvent waste streams were evaluated, and 85.3% reduction in total emissions and 86.3% reduction in operating costs were achieved. Investment in the solvent recovery system was determined to have a payback period of 4.5 years and a 28% IRR over 10 years. A life cycle impact assessment shows impacts on the human health, ecosystems, and resources categories have been reduced by 82.4, 85.1, and 87.1%, respectively.  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