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   738篇
  免费   5篇
电工技术   15篇
综合类   2篇
化学工业   157篇
金属工艺   67篇
机械仪表   38篇
建筑科学   10篇
矿业工程   6篇
能源动力   4篇
轻工业   10篇
水利工程   13篇
石油天然气   21篇
无线电   33篇
一般工业技术   171篇
冶金工业   78篇
原子能技术   91篇
自动化技术   27篇
  2022年   14篇
  2021年   28篇
  2020年   12篇
  2019年   14篇
  2018年   21篇
  2017年   19篇
  2016年   22篇
  2015年   12篇
  2014年   22篇
  2013年   19篇
  2012年   29篇
  2011年   28篇
  2010年   19篇
  2009年   19篇
  2008年   18篇
  2007年   28篇
  2006年   21篇
  2005年   17篇
  2004年   16篇
  2003年   10篇
  2002年   14篇
  2001年   13篇
  2000年   13篇
  1999年   7篇
  1998年   8篇
  1997年   9篇
  1996年   22篇
  1995年   10篇
  1994年   15篇
  1992年   11篇
  1991年   14篇
  1990年   6篇
  1989年   7篇
  1988年   17篇
  1987年   11篇
  1985年   7篇
  1984年   12篇
  1983年   7篇
  1982年   10篇
  1981年   12篇
  1980年   11篇
  1978年   9篇
  1977年   10篇
  1976年   14篇
  1975年   10篇
  1974年   16篇
  1973年   9篇
  1972年   10篇
  1967年   4篇
  1965年   4篇
排序方式: 共有743条查询结果,搜索用时 15 毫秒
21.
The Northern Eurasian land mass encompasses a diverse array of land cover types including tundra, boreal forest, wetlands, semi-arid steppe, and agricultural land use. Despite the well-established importance of Northern Eurasia in the global carbon and climate system, the distribution and properties of land cover in this region are not well characterized. To address this knowledge and data gap, a hierarchical mapping approach was developed that encompasses the study area for the Northern Eurasia Earth System Partnership Initiative (NEESPI). The Northern Eurasia Land Cover (NELC) database developed in this study follows the FAO-Land Cover Classification System and provides nested groupings of land cover characteristics, with separate layers for land use, wetlands, and tundra. The database implementation is substantially different from other large-scale land cover datasets that provide maps based on a single set of discrete classes. By providing a database consisting of nested maps and complementary layers, the NELC database provides a flexible framework that allows users to tailor maps to suit their needs. The methods used to create the database combine empirically derived climate–vegetation relationships with results from supervised classifications based on Moderate Resolution Imaging Spectroradiometer (MODIS) data. The hierarchical approach provides an effective framework for integrating climate–vegetation relationships with remote sensing-based classifications, and also allows sources of error to be characterized and attributed to specific levels in the hierarchy. The cross-validated accuracy was 73% for the land cover map and 73% and 91% for the agriculture and wetland classifications, respectively. These results support the use of hierarchical classification and climate–vegetation relationships for mapping land cover at continental scales.  相似文献   
22.
Nanocomposites consisting of one-dimensional (1D) crystals of the cationic conductors CuI, CuBr and AgBr inside single-walled carbon nanotubes, mainly (n, 0), were obtained using the capillary technique. 1D crystal structure models were proposed based on the high resolution transmission electron microscopy performed on a FEI Titan 80-300 at 80 kV with aberration correction. According to the models and image simulations there are two modifications of 1D crystal: hexagonal close-packed bromine (iodine) anion sublattice (growth direction <001>) and 1D crystal cubic structure (growth direction <112>) compressed transversely to the nanotube (D(m) ~1.33 nm) axis. Tentatively this kind of 1D crystal can be considered as monoclinic. One modification of the anion sublattice reversibly transforms into the other inside the nanotube, probably initiated by electron beam heating. As demonstrated by micrographs, copper or silver cations can occupy octahedral positions or are statistically distributed across two tetrahedral positions. A 1DAgBr@SWNT (18, 0; 19, 0) pseudoperiodic 'lattice distortion' is revealed resulting from convolution of the nanotube wall function image with 1D cubic crystal function image.  相似文献   
23.
A mathematical model for estimating the thickness of a coating deposited on the surface of a rotating body having a circular symmetry is proposed. A method has been developed for determining the law of control of the mass flow of a deposited material for the purpose of obtaining coatings homogeneous in thickness. It is shown that, in the case of deposition of a coating on the surface of a circular disk, the optimum mass flow of a deposited material is defined by a linear function. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 6, pp. 149–154, November–December, 2006.  相似文献   
24.
The isochoric heat capacity of pure methanol in the temperature range from 482 to 533 K, at near-critical densities between 274.87 and 331.59 kg· m−3, has been measured by using a high-temperature and high-pressure nearly constant volume adiabatic calorimeter. The measurements were performed in the single- and two-phase regions including along the coexistence curve. Uncertainties of the isochoric heat capacity measurements are estimated to be within 2%. The single- and two-phase isochoric heat capacities, temperatures, and densities at saturation were extracted from experimental data for each measured isochore. The critical temperature (Tc = 512.78±0.02K) and the critical density (ρc = 277.49±2 kg · m−3) for pure methanol were derived from the isochoric heat-capacity measurements by using the well-established method of quasi-static thermograms. The results of the CVVT measurements together with recent new experimental PVT data for pure methanol were used to develop a thermodynamically self-consistent Helmholtz free-energy parametric crossover model, CREOS97-04. The accuracy of the crossover model was confirmed by a comprehensive comparison with available experimental data for pure methanol and values calculated with various multiparameter equations of state and correlations. In the critical and supercritical regions at 0.98TcT ≤ 1.5Tc and in the density range 0.35ρc ≤ ρ leq 1.65 ρc, CREOS97-04 represents all available experimental thermodynamic data for pure methanol to within their experimental uncertainties.  相似文献   
25.
The GIT-32 current generator was developed for experiments with current carrying pulsed plasma. The main parts of the generator are capacitor bank, multichannel multigap spark switches, low inductive current driving lines, and central load part. The generator consists of four identical sections, connected in parallel to one load. The capacitor bank is assembled from 32 IEK-100-0.17 (0.17 microF, 40 nH, 100 kV) capacitors, connected in parallel. It stores approximately 18 kJ at 80 kV charging voltage. Each two capacitors are commuted to a load by a multigap spark switch with eight parallel channels. Switches operate in ambient air at atmospheric pressure. The GIT-32 generator was tested with 10, 15, and 20 nH inductive loads. At 10 nH load and 80 kV of charging voltage it provides 1 MA of current amplitude and 490 ns rise time with 0.8 Omega damping resistors in discharge circuit of each capacitor and 1.34 MA530 ns without resistors. The net generator inductance without a load was optimized to be as low as 12 nH, which results in extremely low self-impedance of the generator ( approximately 0.05 Omega). It ensures effective energy coupling with low impedance loads like Z pinch. The generator operates reliably without any adjustments in 40-80 kV range of charging voltage. Maximum jitter (relative to a triggering pulse) at 40 kV charging voltage is about 7 ns and lower at higher charging voltages. Operation and handling are very simple, because no oil and no purified gases are required for the generator. The GIT-32 generator has dimensions of 3200 x 3200 x 400 mm(3) and total weight of about 2500 kg, thus manifesting itself as a simple, robust, and cost effective apparatus.  相似文献   
26.
The objective of this work was to evaluate the quality of sterilised canned pea and corn in electro‐activated brine solutions at moderate temperatures. The lowest change in vitamin C was associated with the lowest heat treatment, while the short treatment time resulted in significant changes in texture and colour of vegetables. Best texture profile was obtained with the acid electro‐activated brine solution for pea and corn. The neutral electro‐activated brine solution resulted in a less firm texture for pea and corn. The green colour and brightness of canned pea were higher when neutral solution was used (a* = ?8.4 ± 0.3) than for the acidic one (a* = ?3.7 ± 0.6). The yellowness of corn was better with the neutral electro‐activated brine solution (b* = 36.32 ± 1.24) than with the acidic one (b* = 28.44 ± 2.39). Thirty‐three percent decrease of energy consumption was obtained using the electro‐activation technology.  相似文献   
27.
The primary standard for the unit of pressure, the pascal, its constituent parts, ranges of application, and the results of key comparisons are described.  相似文献   
28.
High-purity single-crystal W and W??Nb?? have been prepared using chemical vapor transport. The impurity composition of the materials has been determined using spark source mass spectrometry and high-temperature vacuum extraction. The radial Nb profile in the alloy has been investigated by electron microscopy.  相似文献   
29.
The Am volatility from 4 M NaOH solutions in the course of their ozonation at 80°C was studied. The formation of volatile Am compounds under these conditions was proved by α-ray spectrometry. The whole set of data on the volatility and kinetics of reduction of ozonized Am solutions suggest possible formation of short-lived hydroxo complexes of Am in higher oxidation state, including Am(VIII), along with Am(VI) hydroxo complexes, with AmO4 possibly existing in equilibrium with these Am(VIII) species. No Cm volatility was detected under the same conditions. The observed differences in the behavior of Pu and Am, on the one hand, and Np and Cm, on the other hand, under identical ozonation conditions are attributed to the ability of Pu and Am to be oxidized under these conditions to unstable octavalent state, responsible for their volatility.  相似文献   
30.
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