全文获取类型
收费全文 | 404054篇 |
免费 | 4707篇 |
国内免费 | 1364篇 |
专业分类
电工技术 | 7566篇 |
综合类 | 317篇 |
化学工业 | 59922篇 |
金属工艺 | 16437篇 |
机械仪表 | 13502篇 |
建筑科学 | 8359篇 |
矿业工程 | 2155篇 |
能源动力 | 11533篇 |
轻工业 | 28499篇 |
水利工程 | 4267篇 |
石油天然气 | 7915篇 |
武器工业 | 17篇 |
无线电 | 49263篇 |
一般工业技术 | 83038篇 |
冶金工业 | 75017篇 |
原子能技术 | 9183篇 |
自动化技术 | 33135篇 |
出版年
2022年 | 2562篇 |
2021年 | 3906篇 |
2020年 | 2949篇 |
2019年 | 3809篇 |
2018年 | 6490篇 |
2017年 | 6487篇 |
2016年 | 6930篇 |
2015年 | 4326篇 |
2014年 | 7152篇 |
2013年 | 20045篇 |
2012年 | 11429篇 |
2011年 | 15279篇 |
2010年 | 12154篇 |
2009年 | 13723篇 |
2008年 | 14061篇 |
2007年 | 13822篇 |
2006年 | 12424篇 |
2005年 | 11121篇 |
2004年 | 10516篇 |
2003年 | 10424篇 |
2002年 | 9831篇 |
2001年 | 9737篇 |
2000年 | 9142篇 |
1999年 | 9526篇 |
1998年 | 24339篇 |
1997年 | 16722篇 |
1996年 | 12808篇 |
1995年 | 9526篇 |
1994年 | 8369篇 |
1993年 | 8387篇 |
1992年 | 6061篇 |
1991年 | 5694篇 |
1990年 | 5682篇 |
1989年 | 5321篇 |
1988年 | 5051篇 |
1987年 | 4420篇 |
1986年 | 4300篇 |
1985年 | 4813篇 |
1984年 | 4422篇 |
1983年 | 3996篇 |
1982年 | 3655篇 |
1981年 | 3735篇 |
1980年 | 3431篇 |
1979年 | 3327篇 |
1978年 | 3336篇 |
1977年 | 3752篇 |
1976年 | 4850篇 |
1975年 | 2851篇 |
1974年 | 2664篇 |
1973年 | 2730篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
Catastrophic convolutional codes (CC) cause an infinite number of decoded data bit errors when decoding a finite number of code symbols. A CC displays a catastrophic error propagation if the generating polynomials have a common factor. An efficient algorithm for polynomial factorization in GF(2m) is used for detecting catastrophic CC for any rate n/m and constraint length k. A general formula is derived to calculate the number of catastrophic codes in any (m, n, k) CC. 相似文献
182.
A novel class of narrow-band tunable wavelength filters is proposed and evaluated. Wavelength selectivity of the proposed filters Is derived from the finite time response of an optical nonlinearity. The nonlinearity is gain saturation in semiconductor optical amplifier structures. The filters are shown to have very narrow passbands tunable over the entire semiconductor gain bandwidth. The key to filter implementation is a device configuration in which the wave-mixing products can be isolated from the amplified inputs. Three integrated optics compatible configurations are considered and shown to have high filter throughputs 34 to 180% and subangstrom bandwidths 相似文献
183.
V. A. Arzamastsev N. L. Sardaev A. S. Kochergin 《Metal Science and Heat Treatment》1996,38(11):477-479
The technological process of cold forging applied for the first time in the production of the casing of the internal joint with races is described. The process operations of cold forging and the annealing and carburizing regimes for this part me described. 相似文献
184.
G Chessa Ricotti R Cutrì A De Bernardi M Funis S Frediani 《Canadian Metallurgical Quarterly》1995,17(3):271-273
The authors describe 5 cases, 3 boys and 2 girls, with idiopathic growth hormone deficiency in prepubertal age, treated with human growth hormone. In four of five cases the response to treatment with GH was relevant. Only in one case (F1) the response was negative. The results of this study confirm that rhGH is a safe and effective therapy in children with GHD. 相似文献
185.
A fiber optic ring network, such as fiber distributed data interface (FDDI), can be operated over multiple wavelengths on its existing fiber plant consisting of point-to-point fiber links. Using wavelength division multiplexing (WDM) technology, FDDI nodes can be partitioned to operate over multiple subnetworks, with each subnetwork operating independently on a different wavelength, and inter-subnetwork traffic forwarding performed by a bridge. For this multiwavelength version of FDDI, which we refer to as wavelength distributed data interface (WDDI), we examine the necessary upgrades to the architecture of a FDDI node, including its possibility to serve as a bridge. The main motivation behind this study is that, as network traffic scales beyond (the single-wavelength) FDDI's information-carrying capacity, its multiwavelength version, WDDI, can gracefully accommodate such traffic growth. A number of design choices exist in constructing a good WDDI network. Specifically, we investigate algorithms using which, based on prevailing traffic conditions, partitioning of nodes into subnetworks can be performed in an optimized fashion. Our algorithms partition the nodes into subrings, such that the total traffic flow in the network and/or the network-wide average packet delay is minimized 相似文献
186.
The magnetization of a melt-texture growth (MTG) HTSC ring has been studied. It is shown that the magnetic field inside the ring is larger than the external field under a certain range of external magnetic fields. We have also investigated the magnetic field dependence of the response of a detective coil near a rotating superconducting ring. The responses of the MTG sample are different for different cooling methods. 相似文献
187.
188.
This article describes a study of delamination growth along 0 °/0 °, 0 °/ 5 °, ± 5 °, and 0 °/90 ° interfaces sandwiched between unidirectional carbon fibre/epoxy composite material. Relationships between damage criticality, growth rate and acoustic emission activity for delamination growth have been studied and the transferability of results from laboratory coupons to composite structural elements has been examined. Two types of coupon tests, conventional delamination beams and rigidly loaded single edge notched strips, have been compared for different mode ratios. Comparative tests have been made on buckling-induced delamination in plates. A graphite crack gauge has been used to measure delamination length and growth rate, ranging from 0.05–2000 m/s. Damage growth was also followed using visual, ultrasonic C-scan, X-ray radiography, macro-video and acoustic emission measurements. Empirical evaluations of interlaminar toughness for delamination beams are made using the Irwin-Kies relation. Unstable growth is analysed using elasto-dynamic moving finite elements. Bucklinginduced delamination is analysed using plate/shell FE methods with growth/remeshing algorithms. 相似文献
189.
Nitric oxide reduction and carbon monoxide oxidation over carbon-supported copper-chromium catalysts 总被引:1,自引:0,他引:1
S. Stegenga R. van Soest F. Kapteijn J. A. Moulijn 《Applied catalysis. B, Environmental》1993,2(4):257-275
Carbon supported copper-chromium catalysts are shown to be very active for both the reduction of nitric oxide with carbon monoxide and the oxidation of carbon monoxide with oxygen. Mixed copper-chromium oxide active phases have good activity in the simultaneous removal of nitric oxide and carbon monoxide from exhaust gases. The influence of several catalyst variables has been investigated. The activity per volume of catalyst increases with increasing loading, while the intrinsic activity shows a maximum around C/M=100−50. An optimum catalyst for nitric oxide reduction and carbon monoxide oxidation has a copper/chromium ratio of 2/1. The apparent activation energy for the carbon monoxide oxidation over carbon supported copper-chromium catalysts is 77 kJ/mol, suggesting that the Cu---O bond rupture is the rate-limiting process. The reduction of nitric oxide takes place at higher temperatures. Since all catalysts have a low selectivity for molecular nitrogen formation at lower temperatures, the dissociation of nitric oxide is probably rate determining, resulting in a slightly reduced catalyst system. In an excess of carbon monoxide the reaction is first-order in nitric oxide and zero-order in carbon monoxide. Moisture inhibits the reaction by reversible competitive adsorption, whereas carbon dioxide does not. Oxygen completely inhibits the reduction of nitric oxide due to the more rapid reoxidation of the catalytic sites compared to nitric oxide. Therefore, the reduction of nitric oxide takes place only when all oxygen has been converted and, hence, is shifted to higher temperatures. As a possible consequence, the production of nitrous oxide is reduced. Nitric oxide and molecular oxygen react preferentially with carbon monoxide, so, in an excess of oxidizing component, gasification of the carbon support occurs at higher temperatures after carbon monoxide has been completely consumed. 相似文献
190.
R.N. ARNOLD K.K. SCHELLER S.C. ARP S.N. WILLIAMS D.M. SCHAEFER 《Journal of food science》1993,58(1):28-33
The effect of long-term feeding (252 days) of three supplemental levels of α-tocopheryl acetate (actual 0, 360 and 1290 IU/head/day) on meat quality was evaluated in Holstein and beef breed steers. Tissue vitamin E concentrations were increased by each increment of supplementation. The color display life of fresh beef under simulated retail conditions was extended 2 to 5 days by vitamin E and lipid oxidation was markedly reduced. Microbial population was not affected by level of supplementation. No deterioration in sensory quality occurred for steaks from supplemented steers that were displayed until the time steaks from unsupplemented steers discolored. 相似文献