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   1907篇
  免费   98篇
  国内免费   3篇
电工技术   18篇
综合类   3篇
化学工业   473篇
金属工艺   40篇
机械仪表   46篇
建筑科学   46篇
矿业工程   4篇
能源动力   58篇
轻工业   367篇
水利工程   12篇
石油天然气   4篇
无线电   158篇
一般工业技术   297篇
冶金工业   187篇
原子能技术   14篇
自动化技术   281篇
  2023年   20篇
  2022年   57篇
  2021年   59篇
  2020年   42篇
  2019年   31篇
  2018年   60篇
  2017年   64篇
  2016年   72篇
  2015年   54篇
  2014年   73篇
  2013年   130篇
  2012年   119篇
  2011年   117篇
  2010年   93篇
  2009年   87篇
  2008年   100篇
  2007年   85篇
  2006年   76篇
  2005年   45篇
  2004年   36篇
  2003年   61篇
  2002年   53篇
  2001年   34篇
  2000年   30篇
  1999年   28篇
  1998年   65篇
  1997年   55篇
  1996年   28篇
  1995年   28篇
  1994年   16篇
  1993年   25篇
  1992年   14篇
  1991年   11篇
  1990年   18篇
  1989年   13篇
  1988年   10篇
  1987年   5篇
  1986年   8篇
  1985年   10篇
  1983年   8篇
  1982年   4篇
  1981年   10篇
  1980年   9篇
  1979年   5篇
  1978年   8篇
  1977年   4篇
  1976年   4篇
  1973年   5篇
  1971年   3篇
  1966年   4篇
排序方式: 共有2008条查询结果,搜索用时 9 毫秒
31.
Rapid urbanization, climate change and energy security warrant a more detailed understanding of how cities today consume energy. Agent-based, integrated microsimulation models of urban systems provide an excellent platform to accomplish this task, as they can capture both the short- and long-term decisions of firms and households which directly affect urban energy consumption. This paper presents the current effort towards developing an urban energy model for the Integrated Land Use, Transportation, Environment (ILUTE) modelling system.  相似文献   
32.
We report the synthesis and characterization of three half-sandwich Ru(II) arene complexes [(η6-arene)Ru(N,N′)L][PF6]2 containing arene = p-cymene, N,N′ = bipyridine, and L = pyridine meta- with methylenenaphthalimide (C1), methylene(nitro)naphthalimide (C2), or methylene(piperidinyl)naphthalimide (C3). The naphthalimide acts as an antenna for photoactivation. After 3 h of irradiation with blue light, the monodentate pyridyl ligand had almost completely dissociated from complex C3, which contains an electron donor on the naphthalimide ring, whereas only 50% dissociation was observed for C1 and C2. This correlates with the lower wavelength and strong absorption of C3 in this region of the spectrum (λmax = 418 nm) compared with C1 and C2 (λmax = 324 and 323 nm, respectively). All the complexes were relatively non-toxic towards A549 human lung cancer cells in the dark, but only complex C3 exhibited good photocytoxicity towards these cancer cells upon irradiation with blue light (IC50 = 10.55 ± 0.30 μM). Complex C3 has the potential for use in photoactivated chemotherapy (PACT).  相似文献   
33.
The milling time evolution of magnetic anisotropy of ball milled powders can be described considering two regimes. First, for short milling times, the main factor affecting the magnetic behavior of the alloy is the accumulation of internal stresses. Second, for long milling times, magnetic anisotropy can be explained using three contributions: long-range magnetoelastic, averaged short-range magnetoelastic and averaged magnetocrystalline anisotropies.  相似文献   
34.
The barley chloroplast mutator (cpm) is a nuclear gene mutant that induces a wide spectrum of cytoplasmically inherited chlorophyll deficiencies. Plastome instability of cpm seedlings was determined by identification of a particular landscape of polymorphisms that suggests failures in a plastome mismatch repair (MMR) protein. In Arabidopsis, MSH genes encode proteins that are in charge of mismatch repair and have anti-recombination activity. In this work, barley homologs of these genes were identified, and their sequences were analyzed in control and cpm mutant seedlings. A substitution, leading to a premature stop codon and a truncated MSH1 protein, was identified in the Msh1 gene of cpm plants. The relationship between this mutation and the presence of chlorophyll deficiencies was established in progenies from crosses and backcrosses. These results strongly suggest that the mutation identified in the Msh1 gene of the cpm mutant is responsible for the observed plastome instabilities. Interestingly, comparison of mutant phenotypes and molecular changes induced by the barley cpm mutant with those of Arabidopsis MSH1 mutants revealed marked differences.  相似文献   
35.
The MEGAPIE project aimed to design, build and operate a liquid metal spallation neutron target of about 1 MW beam power in the SINQ facility at the Paul Scherrer Institut (Villigen, Switzerland). This project is an important step in the roadmap towards the demonstration of the accelerator driven system (ADS) concept and high power liquid metal targets in general. Following the design phase, an experimental program was defined to provide a complete characterization of the facility by performing a “mapping” of the neutron flux at different points, from the center of the target to the beam lines. The neutronic performance of the target was studied using different experimental techniques with the goals of validating the Monte Carlo codes used in the design of the target; additionally, the performance was compared with the solid lead targets used before and after the MEGAPIE experiment.  相似文献   
36.
The starch granules remaining after enzymatic hydrolysis were analyzed. Enzymatic corrosion efficiency was related to granule diameter. The intrinsic viscosity of enzymatically treated cassava and corn starches was gradually lowered by hydrolysis. X-ray analysis and observation under a polarizing microscope suggested that enzymatic corrosion must occur in amorphous areas of the granules. Scanning electron microscopy showed that, for cassava granules, enzymatic corrosion occured mainly at the surface. Corn starch granules displayed considerable surface corrosion, as well as deep radial corrosion channels.  相似文献   
37.
In this article, a Z‐shaped antenna is designed for 2.45 GHz ISM band applications. The proposed antenna is surrounded by metasurface‐based unit cells. The unit cells are designed to reflect for the proposed frequency. Each of this unit cells are activated with the help of a diode. Unit cell is considered active by switching on the diode of respective unit cell. According to the activation of unit cell the pattern of the antenna will be reconfigured. The 2.45 GHz ISM band pattern reconfigurable microstrip antenna is presented. The radiation pattern of the antenna can be steered toward a desired direction by activating appropriate metasurface unit cell, minimizing the interference and optimizing medium usage. The proposed antenna performance is presented with the help of reflection coefficient and the pattern steerable capability by activating metasurface unit cells. The proposed antenna is having azimuth‐pattern reconfigurable capability around 360°.  相似文献   
38.
A thorough analysis of the behavior of error‐correcting codes over space links affected by solar scintillation is presented. The relevant channel parameters are fixed through the development of a model based on real missions' data. Both telecommand and telemetry links are considered in fast and slow fading conditions. Besides classical coherent modulation schemes, the possibility to use noncoherent modulation schemes is considered, to eliminate the problem of phase tracking. For the case of channels with very slow fading, the use of external interleavers or erasure coding is proposed to cope with error bursts.  相似文献   
39.
If one needs to cancel the effects of the anisotropy of the sample in a EELS experiment in the TEM, a particular couple of values for the collection and convergence angle must be used, called magic angle conditions (MAC). Recent developments in the theory have shown that a full relativistic treatment is mandatory to correctly describe this effect and that the MAC are strongly dependent on the acceleration voltage. We show how the analytical formula can be derived and give the exact analytical solution for the MAC which can then be easily applied to every practical case. We show the consequences of the energy dependence of the magic angle and that the parallelity of the beam will be the limiting factor for high acceleration voltages while for low acceleration voltages the contribution coming from Bragg spots may make it impossible to reach MAC.  相似文献   
40.
聚氨酯胶粘剂水解问题的有效解决途径   总被引:1,自引:0,他引:1  
聚合物有几种主要的降解机理:热降解、化学物降解、氧化降解、微生物降解以及水解降解。其中,水解是缩聚反应生成的聚合物最致命的弱点,聚氨酯粘合剂也不例外。水解使聚合物的力学性能在一段时间后丧失殆尽,严重影响了其使用性能和应用范围。碳化二亚胺(Stabaxol~(?))是为解决酯类聚合物水解问题而研制的高效抗水解剂。文章描述了碳化二亚胺抗水解剂在聚酯型聚氨酯粘合剂中的水解保护机理及效果。  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