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   9545篇
  免费   193篇
  国内免费   27篇
电工技术   146篇
综合类   9篇
化学工业   1474篇
金属工艺   153篇
机械仪表   169篇
建筑科学   380篇
矿业工程   26篇
能源动力   218篇
轻工业   620篇
水利工程   62篇
石油天然气   22篇
武器工业   1篇
无线电   851篇
一般工业技术   1269篇
冶金工业   3263篇
原子能技术   92篇
自动化技术   1010篇
  2022年   66篇
  2021年   81篇
  2020年   53篇
  2019年   65篇
  2018年   109篇
  2017年   90篇
  2016年   98篇
  2015年   106篇
  2014年   145篇
  2013年   478篇
  2012年   231篇
  2011年   277篇
  2010年   232篇
  2009年   240篇
  2008年   293篇
  2007年   276篇
  2006年   255篇
  2005年   255篇
  2004年   225篇
  2003年   202篇
  2002年   187篇
  2001年   181篇
  2000年   170篇
  1999年   202篇
  1998年   827篇
  1997年   463篇
  1996年   374篇
  1995年   258篇
  1994年   248篇
  1993年   236篇
  1992年   157篇
  1991年   139篇
  1990年   140篇
  1989年   126篇
  1988年   133篇
  1987年   134篇
  1986年   142篇
  1985年   143篇
  1984年   133篇
  1983年   105篇
  1982年   115篇
  1981年   118篇
  1980年   95篇
  1979年   91篇
  1978年   89篇
  1977年   121篇
  1976年   171篇
  1975年   70篇
  1974年   61篇
  1973年   68篇
排序方式: 共有9765条查询结果,搜索用时 15 毫秒
31.
子午线轮胎出现不久,就采用钢丝带束层代替了纤维带束层,这对于实现子午线轮胎提高使用寿命和改善操纵性能的潜能是必要的。  相似文献   
32.
The human plasma high density lipoproteins (HDL) are a heterogeneous ensemble of five proteins associated with both neutral and polar lipids. The sequences of all five proteins are known. ApoA-I and apoA-II are the major protein components; apoC-I, apoC-II and apoC-III are the minor protein components. All these apoproteins spontaneously recombine with phospholipids to give stable lipid-protein complexes and freely exchange between the two major HDL subclasses, HDL2 and HDL3. In addition, ApoC-I, apoC-II, and apoC-III exchange between HDL and very low density lipoproteins. Furthermore, certain HDL apoproteins are activators for plasma enzymes that are important in lipid metabolism. ApoA-I and apoC-I activate lecithin/cholesterol acyltransferase; apoC-II is an activator of lipoprotein lipase. The regions of apoC-I and apoC-II that are involved in the activation of these enzymes have been localized with synthetic peptides. Studies of synthetic and native fragments of apoA-II, apoC-I, apoC-II, and apoC-III as well as model lipid-binding peptides have identified specific regions with structural features common to lipid-binding proteins. These special properties, which include helical potential, sequences with a critical amphipathic length, and high hydrophobicity of the nonpolar side of the amphipathic helix, are the determinants of HDL structure and metabolism.  相似文献   
33.
Most heterogeneous catalysts are either supported on some kind of porous material or the catalyst itself is porous. To satisfy practical constraints such as pressure drop, handling, and separation from products, these catalysts are generally pelletized. Very often the overall chemical reaction rates within these catalyst pellets are determined by a complicated interaction of internal and external transport effects with the intrinsic kinetic rate at the active surface.  相似文献   
34.
Scanning tunnelling microscopy (STM) has been applied to the topographical study of tungsten carbide (with 6% Co) ball bearings in air. It is shown that, for this material, scanning tunnelling microscopy can provide not only general topographical information on the surface microtexture with a resolution of nearly 0.1 nm if required, but also quantitative information for the measurement of surface roughness. Thus, scanning tunnelling microscopy has utility as a quality control tool of particular relevance in the submicron range. The STM topographical results from specific tungsten carbide ball bearings are presented, and the limitations and applicability of the STM technique when used as a quality control tool are discussed.  相似文献   
35.
The unprecedented water scarcity in Australia coincides with the adoption of a new urban water rhetoric. The 'Security through Diversity' strategy has been adopted in a number of Australian cities as a new and innovative approach to urban water management. Although this strategy offers a more holistic approach to urban water management, in practice, the Security through Diversity strategy is largely being interpreted and implemented in a way that maintains the historical dependence on large scale, centralised water infrastructure and therefore perpetuates existing urban water vulnerabilities. This research explores the implementation of Security through Diversity as the new water scarcity response strategy in the cities of Perth and Melbourne. Through a qualitative study with over sixty-five urban water practitioners, the results reveal that the practitioners have absorbed the new Security through Diversity language whilst maintaining the existing problem and solution framework for urban water management. This can be explained in terms of an entrenched technological path dependency and cognitive lock-in that is preventing practitioners from more comprehensively engaging with the complexities of the Security through Diversity strategy, which is ultimately perpetuating the existing vulnerability of our cities. This paper suggests that greater engagement with the underlying purpose of the security though diversity strategy is a necessary first step to overcome the constraints of the traditional technological paradigm and more effectively reduce the continued vulnerability of Australian cities.  相似文献   
36.
SimpleTreat 3.1 predicts the distribution and elimination of chemicals by sewage treatment. The model is used as the default calculation in EUSES 2.0 to estimate exposure concentration in the receiving water, soil and air. A sensitivity analysis was performed to rank input parameters according to their influence on model predictions. Triclosan was selected for the base case. The sewage flow, degradation rates and parameters describing the raw sewage were shown to be the most sensitive inputs. The pH and dissociation constant are very sensitive parameters when working with ionisable compounds. Variation in certain input parameters was propagated through the model to yield greater variation in output parameters with a maximum ratio of 4.0. SimpleTreat 3.1 is a steady state model describing a highly non-steady system. A large variability in the most sensitive parameters is expected within a single sewage plant and parameters should therefore be selected to cover this variability.  相似文献   
37.
This paper examines the dynamics of entrepreneurial acquisitions undertaken by UK high growth small and medium enterprises (SMEs). While entrepreneurial acquisitions are increasingly deployed by SMEs, little is known about their antecedents, motivational drivers and organisational outcomes. Drawing on detailed case study evidence from Scotland, the key factor found to be driving these acquisitions was the desire to augment and exploit technological complementarities between the acquiring and acquired firms. Acquisition can therefore be conceptualised as an advanced stage of the outside-in ‘open innovation’ strategies proactively used within these innovative SMEs. Firms executing this strategy typically have an acute propensity for risk, a desire for close customer engagement, effective business models and strong external orientation. The work suggests that greater attention should be paid within M&A theory to the dynamics of these types of smaller scale entrepreneurial acquisitions.  相似文献   
38.
ABSTRACT

While selective laser melting (SLM) offers design freedom of metal parts with much less material consumption, there exist several limitations, including high surface roughness, low-dimensional accuracy, and high tensile residual stresses. To make functional parts with high form accuracy and superior surface integrity, an as-SLM part needs finishing to remove the deposited surface material. The integration of machining and SLM creates a hybrid manufacturing route to overcome the inherited limitations of SLM. However, little study has been done to characterise surface integrity of an as-SLM part followed by machining (e.g. hybrid SLM-milling). In this paper, surface, integrity including surface roughness, microstructure, and microhardness, have been characterised for IN718 samples processed by the hybrid process. It has been found that microhardness varies with the scan direction and the use of coolant in the subsequent milling, and surface integrity can be significantly improved by the hybrid SLM-milling route.  相似文献   
39.
Motorcycle protective clothing can be uncomfortably hot during summer, and this experiment was designed to evaluate the physiological significance of that burden. Twelve males participated in four, 90-min trials (cycling 30 W) across three environments (25, 30, 35 °C [all 40% relative humidity]). Clothing was modified between full and minimal injury protection. Both ensembles were tested at 25 °C, with only the more protective ensemble investigated at 30 and 35 °C. At 35 °C, auditory canal temperature rose at 0.02 °C min?1 (SD 0.005), deviating from all other trials (p < 0.05). The thresholds for moderate (>38.5 °C) and profound hyperthermia (>40.0 °C) were predicted to occur within 105 min (SD 20.6) and 180 min (SD 33.0), respectively. Profound hyperthermia might eventuate in ~10 h at 30 °C, but should not occur at 25 °C. These outcomes demonstrate a need to enhance the heat dissipation capabilities of motorcycle clothing designed for summer use in hot climates, but without compromising impact protection.

Practitioner’s Summary:

Motorcycle protective clothing can be uncomfortably hot during summer. This experiment was designed to evaluate the physiological significance of this burden across climatic states. In the heat, moderate (>38.5 °C) and profound hyperthermia (>40.0 °C) were predicted to occur within 105 and 180 min, respectively.  相似文献   

40.
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