全文获取类型
收费全文 | 281814篇 |
免费 | 3683篇 |
国内免费 | 1015篇 |
专业分类
电工技术 | 4232篇 |
综合类 | 2458篇 |
化学工业 | 40334篇 |
金属工艺 | 12690篇 |
机械仪表 | 9048篇 |
建筑科学 | 6971篇 |
矿业工程 | 1853篇 |
能源动力 | 6242篇 |
轻工业 | 20885篇 |
水利工程 | 3524篇 |
石油天然气 | 4382篇 |
武器工业 | 8篇 |
无线电 | 32176篇 |
一般工业技术 | 55786篇 |
冶金工业 | 39781篇 |
原子能技术 | 5328篇 |
自动化技术 | 40814篇 |
出版年
2021年 | 1692篇 |
2019年 | 1613篇 |
2018年 | 16767篇 |
2017年 | 15765篇 |
2016年 | 12594篇 |
2015年 | 2418篇 |
2014年 | 3331篇 |
2013年 | 9191篇 |
2012年 | 8163篇 |
2011年 | 16221篇 |
2010年 | 13700篇 |
2009年 | 11799篇 |
2008年 | 13114篇 |
2007年 | 14131篇 |
2006年 | 5734篇 |
2005年 | 6403篇 |
2004年 | 6105篇 |
2003年 | 6023篇 |
2002年 | 5070篇 |
2001年 | 4759篇 |
2000年 | 4750篇 |
1999年 | 4785篇 |
1998年 | 11423篇 |
1997年 | 8147篇 |
1996年 | 6453篇 |
1995年 | 4685篇 |
1994年 | 4289篇 |
1993年 | 4085篇 |
1992年 | 3238篇 |
1991年 | 3099篇 |
1990年 | 2874篇 |
1989年 | 2952篇 |
1988年 | 2836篇 |
1987年 | 2399篇 |
1986年 | 2309篇 |
1985年 | 2716篇 |
1984年 | 2506篇 |
1983年 | 2345篇 |
1982年 | 2092篇 |
1981年 | 2204篇 |
1980年 | 2030篇 |
1979年 | 2124篇 |
1978年 | 2120篇 |
1977年 | 2366篇 |
1976年 | 3188篇 |
1975年 | 1833篇 |
1974年 | 1761篇 |
1973年 | 1772篇 |
1972年 | 1443篇 |
1971年 | 1339篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
We studied experimentally the influence of the degree of water emulsification ofM-40 mazut heated to the water boiling point on the self-ignition time with its pulsed high-pressure injection into heated air. It is shown that water addition does not change the chemistry of the reaction and heating the water-fuel emulsion leads to the disappearance of differences in the ignition character of the emulsion and the moisture-free fuel. It is confirmed that the features of selfignition are determined mostly by conditions of mixture formation. Indirect evidence is obtained that the dynamic tensile strength of the fluid strongly influences the primary dispersion of the jet during its outflow from the sprayer nozzle.Institute of Theoretical and Applied Mechanics, Novosibirsk 630090. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 4, pp. 20–25, July–August, 1995. 相似文献
992.
993.
Multilayer coatings have been produced using unbalanced magnetron physical vapour deposition in which discrete layers of TiN and ZrN were co-deposited. It has been shown that the multilayers exhibited two-fold periodicity having values of 13 and 2.8 nm. This periodicity, measured both by cross-sectional transmission electron microscopy and low-angle X-ray diffraction, has been precisely related to the process parameters used. Analysis has shown that a third, previously unreported, phase existed within the coating having a lattice parameter comparable to that of TiN and a well-defined orientation relationship with the primary phases. The existence of this phase has been explained in terms of variations in the stoichometry of the coating due to non-uniform metal to nitrogen deposition rates within the chamber. Textural studies revealed that preferred orientation existed in the coating; the degree of which was greater in the ZrN layers than the TiN layers. 相似文献
994.
Oommen B.J. Zgierski J.R. 《IEEE transactions on pattern analysis and machine intelligence》1993,15(2):185-192
Let Λ be a finite plaintext alphabet and V be a cypher alphabet with the same cardinality as Λ. In all one-to-one substitution cyphers, there exists the property that each element in V maps onto exactly one element in Λ and vice versa. This mapping of V onto Λ is represented by a function T *, which maps any v ∈V onto some λ∈Λ (i.e., T *(v )=λ). The problem of learning the mapping of T * (or its inverse (T *)-1) by processing a sequence of cypher text is discussed. The fastest reported method to achieve this is a relaxation scheme that utilizes the statistical information contained in the unigrams and trigrams of the plaintext language. A new learning automaton solution to the problem called the cypher learning automaton (CLA) is given. The proposed scheme is fast, and the advantages of the scheme in terms of time and space requirements over the relaxation method have been listed. Simulation results comparing both cypher-breaking techniques are presented 相似文献
995.
The analysis and scanning characteristics of an infinite array of rectangular microstrip patches each loaded with a varactor diode is presented. The analysis is based on full-wave moment method theory and uses attachment modes to accurately model the current through the feed and the diode. The effect of the biased varactor diode on the scan performance is presented, and it is shown that the impedance mismatch caused by a scan blindness can be eliminated. Other characteristics are also given such as: the active element gain, the efficiency of each loaded microstrip element, and the level of cross polarization generated by the loading of the patch. The effect of the diode biasing level as well as the position of the diode on each radiating element on these scan characteristics is also considered 相似文献
996.
The data recovered from compact discs are contaminated with errors that exhibit a bursty behavior. A channel model is developed to characterize the error bursts and good-data gaps that occur in actual data recovered from compact discs. The probability of having m erroneous symbols in a data block of length n symbols is calculated using the channel model. This probability can be used to evaluate the performance of the error-correction code (ECC) used in the compact disc system 相似文献
997.
Yu. B. Afanas’ev E. V. Mokrushina A. A. Nechitailov V. V. Prokof’ev 《Technical Physics Letters》1997,23(3):181-183
The parameters of Bi12TiO20 crystals grown with bismuth oxide of different degrees of purity were measured by a holographic recording technique in an
external ac electric field and were compared with a crystal specially doped with chromium. Various crystal parameters such
as the diffusion length of the photoexcited carriers and the Debye screening length were determined. It was found that the
absorption spectrum of the material and the holographic recording efficiency were strongly influenced by light chromium doping
and by insufficient purity of the starting mixture.
Pis’ma Zh. Tekh. Fiz. 23, 27–32 (March 12, 1997) 相似文献
998.
Energy Value of Resistant Starch 总被引:23,自引:0,他引:23
Resistant starch was evaluated for energy value using fine silica and normal starch as controls and young rats as a test model. The net increase in rats' carcass energy due to the test materials fed over a 3-wk period formed the basis for assessing energy value. Rats fed normal starch deposited about twice as much fat and significantly more protein in the carcass than those fed either resistant starch or silica. Rats fed resistant starch or silica showed similar growth responses and increases in components of body composition and carcass energy content. This suggested that resistant starch provided, like silica, no energy. 相似文献
999.
1000.