全文获取类型
收费全文 | 25935篇 |
免费 | 1484篇 |
国内免费 | 130篇 |
学科分类
工业技术 | 27549篇 |
出版年
2023年 | 171篇 |
2022年 | 228篇 |
2021年 | 656篇 |
2020年 | 479篇 |
2019年 | 501篇 |
2018年 | 664篇 |
2017年 | 675篇 |
2016年 | 746篇 |
2015年 | 635篇 |
2014年 | 910篇 |
2013年 | 1561篇 |
2012年 | 1413篇 |
2011年 | 2374篇 |
2010年 | 1397篇 |
2009年 | 1230篇 |
2008年 | 1266篇 |
2007年 | 1200篇 |
2006年 | 1046篇 |
2005年 | 906篇 |
2004年 | 1207篇 |
2003年 | 1030篇 |
2002年 | 931篇 |
2001年 | 614篇 |
2000年 | 471篇 |
1999年 | 563篇 |
1998年 | 463篇 |
1997年 | 343篇 |
1996年 | 310篇 |
1995年 | 280篇 |
1994年 | 250篇 |
1993年 | 231篇 |
1992年 | 180篇 |
1991年 | 116篇 |
1990年 | 185篇 |
1989年 | 172篇 |
1988年 | 114篇 |
1987年 | 130篇 |
1986年 | 135篇 |
1985年 | 148篇 |
1984年 | 140篇 |
1983年 | 119篇 |
1982年 | 136篇 |
1981年 | 134篇 |
1980年 | 108篇 |
1979年 | 116篇 |
1978年 | 81篇 |
1977年 | 120篇 |
1976年 | 97篇 |
1975年 | 71篇 |
1974年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
91.
We report a case of early Wegener's disease mimicking tuberculosis in a 36 year old man. Lungs are solely affected for 6 months. Unusual appearance of radiographic features with large apical excavations explain the delai for the diagnosis. We discuss morphological features in the lungs and kidney. 相似文献
92.
93.
Tony Maillet Jacques Barbier Jr. Daniel Duprez 《Applied catalysis. B, Environmental》1996,9(1-4):251-266
A 1% Pd catalyst (38% dispersion) was prepared by impregnating a γ-alumina with palladium acetylacetonate dissolved in acetone. The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated. Temperature-programmed reactions of C3H8 with O2 or with O2 + H2O were carried out with different stoichiometric ratios S(S =[O2]/5[C3H8]). The conversion profiles of C3H8 for the reaction carried out in substoichiometry of O2 (S < 1) showed two discrete domains of conversion: oxidation at temperatures below 350°C and SR at temperatures above 350°C. The presence of steam in the inlet gases is not necessary for SR to occur: there is sufficient water produced in the oxidation to form H2 and carbon oxides by this reaction. Contrary to what was observed with Pt, an apparent deactivation between 310 and 385°C could be observed with Pd in oxidation. This is due to a reduction of PdOx into Pd0, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdOx into Pd0. Compared to Pt and to Rh, Pd has a higher thermal resistance: no deactivation occurred after treatment up to 700°C and limited deactivation after treatment up to 900°C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling. 相似文献
94.
Microllular plastics are cellular polymers characterized by cell densities greater than 109 cells/cm3 and cells smaller than 10 μm. One of the critical steps in the continuous production of microcellular plastics is the promotion of high cell nucleation rates in a flowing polymer matrix. These high nucleation rates can be achieved by first forming a polymer/gas solution followed by rapidly decreasing the solubility of gas in the polymer. Since, in the processing range of interest, the gas solubility in the polymer decreases as the pressure decreases, a rapid pressure drop element, consisting of a nozzle, has been employed as a continuous microcellular nucleation device. In this paper, the effects of the pressure drop rate on the nucleation of cells and the cell density are discussed. The experimental results indicate that both the magnitude and the cell density are discussed. The experimental results indicate that both the magnitude and the rate of pressure drop play a strong role in microcellular processing. The pressure phenomenon affects the thermodynamic instability induced in the polymer/gas solution and the competition between cell nucleation and growth. 相似文献
95.
长25-29井在完井阶段通井过程中发生粘附卡钻事故,在处理卡钻过程中又发生卡套铣筒、井漏、溢流等事故及复杂情况。通过对井下情况的认真分析,采取先堵漏后循环再解卡的处理方案,顺利地解除了该次卡钻事故,大大地减少了经济损失。 相似文献
96.
97.
98.
太钢4号高炉喷煤站从1990年起采用MFD-Ⅲ型脉动反吹式布袋除尘器。这种除尘器采用脉动式反吹清灰设施,合理布置布袋间距,布袋支撑骨架及选用针呢材质的布袋,过滤面积大,反吹清灰效果好,设备运行平稳,除尘效率高达99.8%,排放浓度小于10mg/m^3,故障率低。 相似文献
99.
The coupling of the changes in bacterial quantitative and metabolic aspects during Microcystis aeruginosa bloom conditions together with several environmental parameters was studied in the hypereutrophic Villerest reservoir, France. Bacterial abundance varied from 5.20 to 21.28 × 106 bacteria-mL?1, while bacterial biomass ranged between 75 and 507 μg C mL?1. These results confirmed the highly eutrophic status of the Villerest reservoir. The relative quantitative importance of attached bacteria increased as Microcystis proliferated. Methyl-3H incorporation and D-(U-14C) glucose uptake varied from 8.99 to 60.57 × 106 cells-mL?1, and 0.016 to 1.587 μg CL?1 h?1, respectively. Correlations between several abiotic and biotic parameters showed that phytoplankton regulated bacterial growth by releasing organic carbon which is directly uptaken by heterotrophic bacteria. In the hypolimnion, the sedimentation of decaying algae represented a substantial substrate for bacterial growth. 相似文献
100.
John P. Wikswo Jr. Nestor G. Sepulveda Yu Pei Ma W. Patrick Henry Daniel J. Staton Duane Crum 《Journal of Nondestructive Evaluation》1993,12(2):109-119
A SQUID magnetometer can be used to measure the magnetic field produced by flaws in a two-dimensional, conducting plate carrying a current. Identification of the flaw-induced magnetic field is difficult because of the large magnetic field associated with the edges of the plate and the current in the leads that connect the plate to the power supply. We have developed a technique by which the wire and edge fields can be cancelled prior to mapping the magnetic field. In this technique, a similar unflawed conducting sheet is placed adjacent to the flawed plate, with a connection between the sheet and the plate at one edge, and with the opposite edges of the sheet and of the plate connected to the two conductors of a coaxial cable. Thus, an applied current will flow along one conductor of the cable, across the cancelling sheet, cross into the flawed plate, return along the plate, and then return to the power supply along the other conductor of the coaxial cable. As a result of this geometry, there is no magnetic field from the lead-in wires because they are coaxial, and the magnetic field due to the edges of the plate is cancelled by the opposing magnetic field of the edges in the adjacent sheet. The extent of cancellation is determined primarily by the separation between the plate and the cancelling sheet, by the thickness of the plate, and by macroscopic inhomogeneities in their electrical conductivities. 相似文献