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   339篇
  免费   16篇
电工技术   8篇
化学工业   59篇
金属工艺   17篇
机械仪表   8篇
建筑科学   27篇
能源动力   36篇
轻工业   17篇
石油天然气   3篇
无线电   27篇
一般工业技术   95篇
冶金工业   22篇
原子能技术   3篇
自动化技术   33篇
  2024年   1篇
  2023年   3篇
  2022年   11篇
  2021年   10篇
  2020年   9篇
  2019年   9篇
  2018年   13篇
  2017年   10篇
  2016年   9篇
  2015年   7篇
  2014年   9篇
  2013年   17篇
  2012年   27篇
  2011年   23篇
  2010年   22篇
  2009年   30篇
  2008年   35篇
  2007年   26篇
  2006年   20篇
  2005年   16篇
  2004年   13篇
  2003年   6篇
  2002年   13篇
  2001年   4篇
  2000年   3篇
  1998年   2篇
  1997年   2篇
  1995年   1篇
  1992年   1篇
  1991年   2篇
  1989年   1篇
排序方式: 共有355条查询结果,搜索用时 15 毫秒
11.
Ultra-dense deuterium D(?1) is expected to be both a superfluid and a superconductor as shown by recent theoretical research. Condensed D(?1) can be deposited on surfaces by a source which produces a stream of clusters. A magnetic field strongly influences the type of material formed. Very little of D(?1) and of the form D(1), which is strongly coupled to D(?1), exists on the magnet surface or within several mm from the magnet surface. Even the formation of D(?1) on the source emitter is strongly influenced by a magnetic field, with a critical field strength in the range 0.03?C0.07 T. Higher excitation levels D(2) and D(3) dominate in a magnetic field. The excitation level D(2) is now observed for the first time. The removal of D(?1) and D(1) in strong magnetic fields is proposed to be due to a Meissner effect in long D(?1) clusters by large-orbit electron motion. The lifting of long D(?1) clusters above the magnet surface is slightly larger than expected, possibly due to the coupling to D(1). The previously reported oscillation between D(?1) and D(1) in an electric field is proposed to be due to destruction of D(?1).  相似文献   
12.
13.
14.
During the past 20 years, findings have indicated that nature plays an active role in helping people recover from stress and fatigue. Two of the most cited theories in this field are Rachel and Stephen Kaplan's theory of recovery from Directed Attention Fatigue in nature and Roger Ulrich's theory of aesthetic and affective responses to natural environments and stress recovery. One aim of the present study is to test whether being outdoors in a green recreational environment causes people to be more focused, compared to being in a room indoors (in line with hypotheses suggested by the Kaplans). Another aim is to test whether people experience stress reduction, i.e. as evidenced by changes in blood pressure and heart rate, if they are placed in an environment with many green elements (in line with hypotheses suggested by Ulrich). The overall study design is that of an intervention study. Fifteen elderly persons living at a home for very elderly people participated. Their powers of concentration, blood pressure and heart rate were measured before and after an hour of rest in a garden or in an indoor setting. Seven elderly people were randomly chosen to have their first series of tests in a garden, while eight elderly people had their first series of tests indoors. The results indicate that powers of concentration increase for very elderly people after a visit to a garden outside the geriatric home in which they live, compared to that after resting indoors in their favourite room. The results did not show any effects on blood pressure or heart rate. It is suggested that having a one-hour rest outdoors in a garden setting plays a role in elderly people's powers of concentration, and could thereby affect their performance of activities of daily living. One important factor in this study was that both the outdoor environment and the indoor environment at the home were highly valued by participants.  相似文献   
15.
Simulations and designs are presented of conventional and periodic SO2 absorption from exhaust gases using salt water as absorption solvent. Operating conditions resemble those of a maritime operation, involving relatively small amounts of SO2, so the separation is in the linear region. The advantages of periodic operation, as already demonstrated for conventional distillation remain valid for absorption processes: Less tall towers, than staged towers are possible, or substantially less salt water is required for the process employing periodic cycling.  相似文献   
16.
Mitochondrial bioenergetics reprogramming is an essential response of cells to stress. Platelets, an accessible source of mitochondria, have a crucial role in cancer development; however, the platelet mitochondrial function has not been studied in urothelial carcinoma (UC) patients. A total of 15 patients with UC and 15 healthy controls were included in the study. Parameters of platelet mitochondrial respiration were evaluated using the high-resolution respirometry method, and the selected antioxidant levels were determined by HPLC. In addition, oxidative stress was evaluated by the thiobarbituric acid reactive substances (TBARS) concentration in plasma. We demonstrated deficient platelet mitochondrial respiratory chain functions, oxidative phosphorylation (OXPHOS), and electron transfer (ET) capacity with complex I (CI)-linked substrates, and reduced the endogenous platelet coenzyme Q10 (CoQ10) concentration in UC patients. The activity of citrate synthase was decreased in UC patients vs. controls (p = 0.0191). γ-tocopherol, α-tocopherol in platelets, and β-carotene in plasma were significantly lower in UC patients (p = 0.0019; p = 0.02; p = 0.0387, respectively), whereas the plasma concentration of TBARS was increased (p = 0.0022) vs. controls. The changes in platelet mitochondrial bioenergetics are consistent with cell metabolism reprogramming in UC patients. We suppose that increased oxidative stress, decreased OXPHOS, and a reduced platelet endogenous CoQ10 level can contribute to the reprogramming of platelet mitochondrial OXPHOS toward the activation of glycolysis. The impaired mitochondrial function can contribute to increased oxidative stress by triggering the reverse electron transport from the CoQ10 cycle (Q-junction) to CI.  相似文献   
17.
Abstract. This article considers a mean zero stationary first‐order autoregressive (AR) model. It is shown that the least squares estimator and t statistic have Cauchy and standard normal asymptotic distributions, respectively, when the AR parameter ρn is very near to one in the sense that 1 ? ρn = o(n?1).  相似文献   
18.
Since any firearm injury is potentially lethal, it is of great interest to prevent firearm incidents. This study investigated such incidents during hunting and Swedish hunters’ safety behaviour. A 48-item questionnaire was posted to a random sample of 1000 members of the Swedish Association for Hunting and Wildlife Management. The questions considered demographics, hunting experience/hunting habits/safety behaviour/attitudes and experience of careless weapon handling, hunters’ weapons and safety behaviour relating to weapons, health status, firearm incidents and their preventability, and personal comments on the questionnaire. The response rate was almost 50%. The mean age of the responders was 54 years; 5% were females. Almost none (1%) reported hunting under the influence of alcohol. Young age and male sex were positively associated with risk behaviour, although the presence of multiple risk behaviours in the same responder was not common. A very high degree of compliance with Swedish laws regarding weapon storage was reported. One-quarter of the responders had witnessed a firearm incident caused by another hunter, which in most situations did not result in human injury or death. An unsafetied weapon was the most common reported “cause” of these incidents. Experience of a firearm incident was not uncommon and the majority of the responders considered the incident in question to be preventable. This study provides a picture of the possible risk behaviour among hunters and the results suggest that future prevention work should target safer weapon handling.  相似文献   
19.
20.
High-density atomic hydrogen, which is believed to be a quantum liquid, can be formed by heterogeneous catalysis at the surface of hydrogen-transfer metal oxide catalysts. Extensive studies have been made of the hydrogen phase named H(1), with interatomic distance of 150 pm found by Coulomb explosion measurements. This bond distance corresponds to a material density of 0.5–0.7 kg dm−3. The use of this material as fusion target for inertial confinement fusion (ICF) is proposed in J Fusion Energy 2008;27:296–300. A much denser hydrogen (deuterium) material D(−1) also exists with an interatomic distance of 2.3 pm. This material is probably the inverse of metallic D(1), where nuclei and electrons exchange their roles. The ICF process would be greatly simplified if the intended initial multi-laser compression stage was not necessary. The close-packed density of D(−1) is calculated from the bond distance as >130 kg cm−3. This is much higher than that required for “fast ignition” laser-driven fusion (>0.3 kg cm−3). It may mean that a method already exists to prepare dense hydrogen fuel for small-scale laser-driven fusion. The high energy particles observed experimentally (up to 150 keV/atomic mass unit in the peak or 109 K) indicate that high energy processes exist at relatively low laser intensities.  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