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   1454篇
  免费   78篇
  国内免费   1篇
电工技术   10篇
综合类   8篇
化学工业   373篇
金属工艺   14篇
机械仪表   20篇
建筑科学   68篇
矿业工程   6篇
能源动力   27篇
轻工业   236篇
水利工程   30篇
石油天然气   9篇
无线电   105篇
一般工业技术   191篇
冶金工业   302篇
原子能技术   6篇
自动化技术   128篇
  2023年   15篇
  2022年   45篇
  2021年   63篇
  2020年   32篇
  2019年   24篇
  2018年   50篇
  2017年   32篇
  2016年   39篇
  2015年   38篇
  2014年   42篇
  2013年   74篇
  2012年   66篇
  2011年   86篇
  2010年   58篇
  2009年   57篇
  2008年   63篇
  2007年   57篇
  2006年   48篇
  2005年   26篇
  2004年   35篇
  2003年   38篇
  2002年   22篇
  2001年   20篇
  2000年   18篇
  1999年   27篇
  1998年   66篇
  1997年   39篇
  1996年   45篇
  1995年   23篇
  1994年   27篇
  1993年   17篇
  1992年   11篇
  1991年   17篇
  1990年   12篇
  1989年   14篇
  1988年   11篇
  1986年   8篇
  1985年   7篇
  1984年   11篇
  1983年   7篇
  1982年   10篇
  1981年   7篇
  1980年   13篇
  1979年   7篇
  1978年   11篇
  1977年   8篇
  1976年   11篇
  1975年   8篇
  1968年   6篇
  1967年   5篇
排序方式: 共有1533条查询结果,搜索用时 0 毫秒
991.
Different approaches for quantification of pollution loads discharged from combined sewer networks into surface water bodies have been observed over the last few years and decades, but a large number of unresolved problems still remain. Many monitoring campaigns have been based on manual or automated spot sampling - with the long known limitations of this method such as sampling errors and errors due to sample conservation, transport and preparation. On the other hand, only recently have sensors became available which are suitable for continuous application in sewer networks. A large number of practical problems still have to be solved before continuous monitoring in sewer networks will be successful. Additionally, most of the applicable sensors are based on surrogate methods which results in a considerable effort for reference measurements for sensor calibration. Finally, it has to be considered that, depending on the sewer network topography, deposition and remobilisation of pollutants varies considerably, which limits the generality of monitoring results and, subsequently, their applicability as a base for the design of storm water tanks or combined sewer overflows (CSO). A monitoring station for continuous monitoring of load discharges from a CSO has been installed and operated for more than one year. The design and equipment of the measurement station, operational experiences and results are given in this paper.  相似文献   
992.
This work covers an advanced investigation of the single crystal growth process for fullerenic materials and the contribution of Raman and IR spectroscopy to the understanding of the fcc high temperature rotor phase and the low temperature sc ratchet phase of pristine C60. In addition substantial research contributions to the understanding of alkali metal doped fullerenes are presented.

Alkali metal doped crystals are studied with particular attention to the line broadening in the superconducting A3C60 phase and to the phases with stoichiometry A1C60. For the former electron-phonon coupling constants could be determined for all fivefold degenerated gerade modes and a total coupling strenght of λ = 0.90 was found. For the latter the different experimental conditions for obtaining the phase separated intermediate state or alternatively the orthorhombic polymeric state are analysed. Vibrational spectra for the polymeric state obtained from phototransformation and from mono alkali metal doping are found to be characteristically different, mainly with respect to the intensity of the Raman or IR response. Finally, research results obtained from the single crystals by various other techniques like thermal expansion or low frequency elastic deformation are summarized.  相似文献   
993.
Collision-free object movement using vector fields   总被引:1,自引:0,他引:1  
Presents a technique for automatically providing animation and collision avoidance in a general-purpose computer graphics system. The technique, which relies on an expanded notion of vector fields, allows users to set up and animate objects easily, then prevents objects from colliding as the animation proceeds. This technique automatically generates volume octree vector fields around objects in a scene. These vector fields affect object motion and animation, and also provide for automatic collision avoidance for arbitrary objects. Applications of collision avoidance in an animation system encompass any scene containing object movement above or around other objects  相似文献   
994.
Seven long-tailed macaques (Macaca fascicularis) were trained by threes not to drink from a juice nipple as long as an experimenter was facing them. However, they were allowed to drink when the experimenter was standing with his or her back turned. During transfer tests, the monkeys had a choice between 2 juice nipples, one uncovered and the other hidden from the experimenter by a wooden screen, while the experimenter was facing them. We tested whether the monkeys would then prefer to drink behind the screen, thus demonstrating that they transferred knowledge acquired during training. Results did not yield a significant outcome, suggesting that the macaques did not transfer the observable "experimenter's visible open eyes" and that they did not take the experimenter's perspective. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
995.
OBJECTIVES: A myocardial calcium-independent PLA2 has been described that is activated during myocardial ischemia and this enzyme may modulate ATP-sensitive potassium channels (KATP). The aim of this study was to determine the effect of an inhibitor of this enzyme, a bromoenol lactone, in isolated globally ischemic rat hearts. METHODS: Isolated rat hearts were treated for 10 min with 0.3-6 microM bromoenol lactone and then subjected to 25 min ischemia and 30 min reperfusion. RESULTS: The bromoenol lactone significantly increased coronary flow in nonischemic myocardium, and slightly reduced cardiac function at 6 microM. During global ischemia, time to contracture was significantly increased from vehicle group values in the presence of the bromoenol lactone (EC50 = 1.2 microM). During reperfusion, a concentration-dependent increase in function and a reduction in LDH release were observed for the PLA2 inhibitor. The concentrations of the PLA2 inhibitor which were significantly cardioprotective, inhibited this enzyme in membrane fractions of rat myocardium (IC50 = 0.87 microM). The KATP blocker sodium 5-hydroxydecanoate (5-HD) inhibited the increase in time to contracture observed for the bromoenol lactone. During reperfusion, 5-HD abolished the protective effects of the bromoenol lactone on cardiac function and LDH release. Glyburide had similar effects on the cardioprotective activity of the bromoenol lactone, although it only partially abolished the LDH reducing effect of this agent. CONCLUSIONS: The bromoenol lactone protects ischemic myocardium at concentrations which also inhibit calcium-independent PLA2. This cardioprotection can be attenuated by blockers of KATP, suggesting a potential mechanism for modulation of myocardial KATP.  相似文献   
996.
Bridged monobactams are novel, potent, mechanism-based inhibitors of class C beta-lactamases, designed using X-ray crystal structures of the enzymes. They stabilize the acyl-enzyme intermediate by blocking access of water to the enzyme-inhibitor ester bond. Bridged monobactams are selective class C beta-lactamase inhibitors, with half-inhibition constants as low as 10 nM, and are less effective against class A and class B enzymes (half-inhibition constants > 100 microM) because of the different hydrolysis mechanisms in these classes of beta-lactamases. The stability of the acyl-enzyme complexes formed with class C beta-lactamases (half-lives up to 2 days were observed) enabled determination of their crystal structures. The conformation of the inhibitor moiety was close to that predicted by molecular modeling, confirming a simple reaction mechanism, unlike those of known beta-lactamase inhibitors such as clavulanic acid and penam sulfones, which involve secondary rearrangements. Synergy between the bridged monobactams and beta-lactamase-labile antibiotics could be observed when such combinations were tested against strains of Enterobacteriaceae that produce large amounts of class C beta-lactamases. The minimal inhibitory concentration of the antibiotic of more than 64 mg/L could be decreased to 0.25 mg/L in a 1:4 combination with the inhibitor.  相似文献   
997.
998.
999.
Purity testing of recombinant DNA (rDNA) proteins using slab gel electrophoresis in conjunction with scanning densitometry is time consuming and labor intensive and is difficult to reproduce because the dyes used for visualizing proteins do not bind in a stoichiometric fashion for all proteins. The present report describes a micellar capillary zone electrophoresis (MCZE) procedure that overcomes these difficulties. The MCZE method was evaluated to estimate protein purity of hydrophobic cytomegalovirus proteins, expressed E. coli, and highly glycosylated hepatitis C virus proteins, expressed in Chinese hamster ovary cells. The results obtained by the MCZE procedure correlated very well with the purity results quantitated by the conventional slab gel electrophoresis method using purified Coomassie Brilliant Blue dye to reduce anomalies. MCZE may serve as an alternative method for in-process and purity testing of rDNA proteins.  相似文献   
1000.
Rats were trained on an appetitive Pavlovian conditioning task in which the conditioned stimulus (CS) was either localized (a light in the food tray) or nonlocalized (an increase in the general level of illumination). The conditioned response (CR) of approaching the site of food delivery in the presence of the CS was monitored. Presession treatment with the 5-HT1A agonist 8-OH-DPAT (subcutaneous injections at a dose of 0.15 mg/kg) retarded acquisition of the CR, but only when the localized CS was used. The results confirm the general proposal that serotonergic processes are involved in learning. The selective effect of the drug is not to be explained in terms of its motor effects and is consistent with the specific suggestion that systemic administration of 8-OH-DPAT is especially effective in disrupting learning tasks mediated by hippocampal mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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