全文获取类型
收费全文 | 24217篇 |
免费 | 1632篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 444篇 |
综合类 | 73篇 |
化学工业 | 5322篇 |
金属工艺 | 719篇 |
机械仪表 | 570篇 |
建筑科学 | 1256篇 |
矿业工程 | 151篇 |
能源动力 | 446篇 |
轻工业 | 3200篇 |
水利工程 | 177篇 |
石油天然气 | 36篇 |
无线电 | 1644篇 |
一般工业技术 | 6193篇 |
冶金工业 | 1422篇 |
原子能技术 | 189篇 |
自动化技术 | 4031篇 |
出版年
2023年 | 311篇 |
2022年 | 199篇 |
2021年 | 576篇 |
2020年 | 498篇 |
2019年 | 433篇 |
2018年 | 824篇 |
2017年 | 854篇 |
2016年 | 934篇 |
2015年 | 814篇 |
2014年 | 1009篇 |
2013年 | 1895篇 |
2012年 | 1274篇 |
2011年 | 1513篇 |
2010年 | 1301篇 |
2009年 | 1140篇 |
2008年 | 1243篇 |
2007年 | 1219篇 |
2006年 | 884篇 |
2005年 | 727篇 |
2004年 | 594篇 |
2003年 | 574篇 |
2002年 | 598篇 |
2001年 | 472篇 |
2000年 | 415篇 |
1999年 | 332篇 |
1998年 | 455篇 |
1997年 | 371篇 |
1996年 | 306篇 |
1995年 | 273篇 |
1994年 | 213篇 |
1993年 | 195篇 |
1992年 | 157篇 |
1991年 | 130篇 |
1990年 | 117篇 |
1989年 | 105篇 |
1988年 | 105篇 |
1987年 | 107篇 |
1986年 | 86篇 |
1985年 | 175篇 |
1984年 | 190篇 |
1983年 | 119篇 |
1982年 | 126篇 |
1981年 | 150篇 |
1980年 | 121篇 |
1979年 | 103篇 |
1978年 | 96篇 |
1977年 | 90篇 |
1976年 | 133篇 |
1975年 | 106篇 |
1974年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
51.
Electro-organic synthesis without supporting electrolyte: Possibilities of solid polymer electrolyte technology 总被引:1,自引:0,他引:1
J. Jörissen 《Journal of Applied Electrochemistry》2003,33(10):969-977
The application of ion exchange membranes as solid polymer electrolytes (SPE) in fuel cells is state-of-the-art. This technology needs no supporting electrolyte; consequently it can be applied for electro-organic syntheses in order to save process steps. In this case the process is not predetermined to a maximized energy efficiency so that the selection of the cell design, of the electrode materials and of the operating conditions can be focused on a high selectivity of the electrode reactions. The electro-osmotic stream, which is caused by the solvation shells of the ions during their migration through the membrane, and hence is a typical property of SPE technology, has a significant effect on the electrode reactions. It generates enhanced mass transfer at the electrodes, which is beneficial for reaction selectivity. It can be influenced by the choice of, and possibly by the preparation of, the membrane. An additional remarkable advantage of SPE technology is the exceptional long durability of oxide coated electrodes. By combination of several process engineering methods stable operation of SPE cells has been realized, even for examples of non-aqueous reaction systems. Experiments up to 6000 h duration and in cells of up to 250 cm2 membrane area show the potential for industrial application. 相似文献
52.
Björn Täljsten 《International Journal of Fracture》1996,82(3):253-266
This paper presents the use of fracture mechanics for the plate bonding technique. Plates of steel or carbon-fibre reinforced
plastic are bonded with an epoxy adhesive to rectangular concrete prisms and loaded in shear up to failure, what is normally
known in fracture mechanics as mode II failure. In this special application a linear and a nonlinear approach are presented.
The nonlinear equation derived for a realistic shear-deformation curve can only be used for numerical calculations. However,
for simplified shear-deformation curves, the derived formula can be solved analytically. Results from tests, which are compared
with the theory, are also presented. 相似文献
53.
Depletion and hillock formation were examined in-situ in a scanning electron microscope (SEM) during electromigration of bamboo
Al interconnect segments. Hillocks formed directly at the anode ends of the segments by epitaxial addition of Al at the bottom
Al/TiN interface. Depletion occurred nonuniformly from the cathode end and stopped once the distance between the leading void
and the hillock reached the critical length for electromigration at the given current density. A modified equation for the
drift velocity is proposed, which includes the effect of nonuniform depletion and predicts that interconnects with nonuniform
depletion are more reliable than those with uniform depletion. 相似文献
54.
M Fern? PO Bendahl A Brisfors K Byman M Ekeberg L Ferraud K Grankvist B Hjalmers A Nilsson G Sellberg L Skoog O St?l I Wingmo 《Canadian Metallurgical Quarterly》1997,36(8):793-798
Estrogen and progesterone receptor analysis results were compared within and between six laboratories in Sweden using frozen breast cancer cytosol samples, and the same technique (enzyme immunoassay, Abbott Laboratories). The concordance in receptor status (positive vs. negative) was excellent (98.4% (571/580)). The discordant results were attributable to values near cut-off (n = 4) or outliers (n = 5), the latter probably being due to analytical errors. One laboratory reported significantly higher ER concentrations than the others; thus caution should be observed when comparing absolute values from different centers. For PgR there were similar differences between the laboratories. However, the intra- and inter-laboratory differences were small compared with the overall variability in ER and PgR content between different samples in a large database. The range of the median intra-laboratory coefficient of variation was 11-23% for ER and 12-19% for PgR, indicating that there is room for improvement in the quality of assay performance. 相似文献
55.
T. Herrmannsdörfer J. Friebel F. Pobell J. Mrachkov M. Kirov E. Leyarovski 《Journal of Low Temperature Physics》1997,107(1-2):209-224
We have measured the 16 Hz susceptibility of the diluted Van Vleck paramagnets Pr1−x
Y
x
Ni5 withx=0.00, 0.05, 0.10. 0.20 at temperatures 1.5 K≤T≤50 K and magnetic fields up to 15T. Their Van Vleck type magnetic susceptibility χ(T, B, x) strongly depends on the field atB≥6 T. The temperatureT
max(B, x) of the maximum of χ(T, B, x) decreases at increasing the field from zero to 15 T by approximately one order of magnitude for all Pr1−x
Y
x
Ni5 compounds. Changing the dilutionx from zero to 0.20, the field whereT
max(B, x) strongly drops is increased from 9 T to 11 T. Our data agree qualitatively with the predictions of a point charge model
which considers the Zeeman term in addition to the electronic exchange and the dominating crystal field contributions. 相似文献
56.
57.
Summary Starting with Z-2, 3-diamino-2-butenedinitrile as diamine component the synthesis of the low molecular N,N,O,O-chelate 3.Co and its ligand 3 is optimized. An easy synthesis of the chelate 8.Co covalently bound on macroreticular resins is presented. The chelates 8.Co are the most active heterogenous catalysts for the valence isomerization of quadricyclane to norbornadiene today. 相似文献
58.
59.
60.
Dr. G. Pönisch 《Computing》1987,39(1):1-17
A direct method is described for computing a hysteresis point (double turning point) corresponding to a cusp point of a system ofn nonlinear equations inn variables depending on two parameters. By addition of two equations a minimally extended system ofn+2 nonlinear equations is constructed for which the hysteresis point is an isolated solution. An efficient implementation of Newton's method is presented not requiring evaluations of second derivatives of the original problem. Two numerical examples show the efficiency of theQ-quadratically convergent method. 相似文献