全文获取类型
收费全文 | 403754篇 |
免费 | 4687篇 |
国内免费 | 1364篇 |
专业分类
电工技术 | 7565篇 |
综合类 | 317篇 |
化学工业 | 59837篇 |
金属工艺 | 16429篇 |
机械仪表 | 13491篇 |
建筑科学 | 8348篇 |
矿业工程 | 2154篇 |
能源动力 | 11530篇 |
轻工业 | 28458篇 |
水利工程 | 4267篇 |
石油天然气 | 7913篇 |
武器工业 | 19篇 |
无线电 | 49238篇 |
一般工业技术 | 82986篇 |
冶金工业 | 74959篇 |
原子能技术 | 9181篇 |
自动化技术 | 33113篇 |
出版年
2022年 | 2553篇 |
2021年 | 3893篇 |
2020年 | 2943篇 |
2019年 | 3812篇 |
2018年 | 6492篇 |
2017年 | 6478篇 |
2016年 | 6921篇 |
2015年 | 4316篇 |
2014年 | 7136篇 |
2013年 | 20025篇 |
2012年 | 11416篇 |
2011年 | 15262篇 |
2010年 | 12139篇 |
2009年 | 13712篇 |
2008年 | 14051篇 |
2007年 | 13812篇 |
2006年 | 12416篇 |
2005年 | 11111篇 |
2004年 | 10505篇 |
2003年 | 10416篇 |
2002年 | 9828篇 |
2001年 | 9733篇 |
2000年 | 9133篇 |
1999年 | 9522篇 |
1998年 | 24326篇 |
1997年 | 16710篇 |
1996年 | 12799篇 |
1995年 | 9516篇 |
1994年 | 8362篇 |
1993年 | 8380篇 |
1992年 | 6054篇 |
1991年 | 5694篇 |
1990年 | 5680篇 |
1989年 | 5318篇 |
1988年 | 5043篇 |
1987年 | 4420篇 |
1986年 | 4299篇 |
1985年 | 4812篇 |
1984年 | 4422篇 |
1983年 | 3994篇 |
1982年 | 3654篇 |
1981年 | 3730篇 |
1980年 | 3429篇 |
1979年 | 3326篇 |
1978年 | 3334篇 |
1977年 | 3750篇 |
1976年 | 4847篇 |
1975年 | 2850篇 |
1974年 | 2663篇 |
1973年 | 2730篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
An extended logistic model with a varying asymptotic upper bound for long-range peak demand forecasting is described. The model has been applied to a typical fast growing system, the Saudi Consolidated Electric Company. The forecasts are compared with actual demands and with those obtained from classical forecasting methods. The model gave relatively accurate peak demand forecasts compared with other classical methods. The model with a single load observation is capable of producing several peak demand forecasts corresponding to different levels of maximum temperature and various levels of social activity. The forecasts produced by the model were also stable irrespective of the length of the ex-post simulation period 相似文献
92.
Y Furuya Y Yoshida T Katayama S Yamamoto A Kawamura 《Canadian Metallurgical Quarterly》1993,31(6):1637-1640
Polymerase chain reaction (PCR) with nested primer pairs was used to diagnose scrub typhus and identify the Rickettsia tsutsugamushi serotype. The primer pairs used for PCR were designed on the basis of the nucleotide sequence of the gene that encodes the 56-kDa antigen. Serotype-specific primers were used in the second PCR amplification. Five serovariants, the Gilliam, Karp, Kato, Kawasaki, and Kuroki strains of R. tsutsugamushi, were identified by nested PCR. In addition, the serotype identified by PCR with DNA from blood clots was the same as that of the strain isolated from five patients with scrub typhus. These findings indicate that this method is useful for diagnosis and identification of the rickettsial serotype in infected patients. 相似文献
93.
94.
Studies static-state feedback control of discrete-event systems under partial observation. The authors present a necessary and sufficient condition for the existence of a static-state feedback controller. A static controller is a special case of a dynamic controller studied by Kumar et al. The authors' condition, however, has computational advantage in contrast to those obtained by Kumar et al. The authors also present a necessary and sufficient condition under which the modular feedback synthesis is possible 相似文献
95.
96.
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
97.
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
98.
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
99.
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
100.
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