全文获取类型
收费全文 | 27422篇 |
免费 | 1430篇 |
国内免费 | 320篇 |
专业分类
电工技术 | 562篇 |
综合类 | 551篇 |
化学工业 | 5522篇 |
金属工艺 | 593篇 |
机械仪表 | 881篇 |
建筑科学 | 1095篇 |
矿业工程 | 188篇 |
能源动力 | 870篇 |
轻工业 | 3332篇 |
水利工程 | 280篇 |
石油天然气 | 218篇 |
武器工业 | 27篇 |
无线电 | 2852篇 |
一般工业技术 | 3857篇 |
冶金工业 | 3840篇 |
原子能技术 | 225篇 |
自动化技术 | 4279篇 |
出版年
2023年 | 145篇 |
2022年 | 477篇 |
2021年 | 760篇 |
2020年 | 471篇 |
2019年 | 544篇 |
2018年 | 632篇 |
2017年 | 637篇 |
2016年 | 701篇 |
2015年 | 558篇 |
2014年 | 892篇 |
2013年 | 1597篇 |
2012年 | 1268篇 |
2011年 | 1529篇 |
2010年 | 1191篇 |
2009年 | 1254篇 |
2008年 | 1207篇 |
2007年 | 1164篇 |
2006年 | 977篇 |
2005年 | 814篇 |
2004年 | 853篇 |
2003年 | 1057篇 |
2002年 | 1358篇 |
2001年 | 1107篇 |
2000年 | 660篇 |
1999年 | 607篇 |
1998年 | 1398篇 |
1997年 | 894篇 |
1996年 | 671篇 |
1995年 | 469篇 |
1994年 | 344篇 |
1993年 | 376篇 |
1992年 | 218篇 |
1991年 | 165篇 |
1990年 | 161篇 |
1989年 | 152篇 |
1988年 | 143篇 |
1987年 | 119篇 |
1986年 | 126篇 |
1985年 | 166篇 |
1984年 | 102篇 |
1983年 | 96篇 |
1982年 | 99篇 |
1981年 | 112篇 |
1980年 | 109篇 |
1979年 | 69篇 |
1978年 | 59篇 |
1977年 | 110篇 |
1976年 | 194篇 |
1975年 | 57篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
161.
J Barreto J Liljestrand C Palha de Sousa S Bergstr?m B B?ttiger G Biberfeld F De la Cruz 《Canadian Metallurgical Quarterly》1993,25(6):685-688
The seroprevalence of HIV-1 and HIV-2 among pregnant women in Maputo, the capital of Mozambique, was compared between the years 1982/83, 1988 and 1990. None of the 432 serum samples collected in 1982/83 was positive for HIV antibodies whereas in 1988 the HIV-1 and HIV-2 seroprevalence was 0.4% (2/500) and 0.6% (3/500), respectively, and in 1990 0.6% (12/2014) and 0.2% (4/2014), respectively. These results indicate that HIV infection has been introduced recently in Maputo and is spreading at a slow rate among women. 相似文献
162.
163.
F Devlieghere B De Meulenaer P Sekitoleko AA Estrella Garcia A Huyghebaert 《Canadian Metallurgical Quarterly》1997,14(6-7):671-683
In this study several types of bottle materials (glass, PET (polyethylene terephthalate), PC (polycarbonate), HDPE (high density polyethylene), PP (polypropylene) and PVC (polyvinyl chloride)) were evaluated in order to be used as food refillables, comparing the residual chemical contamination after classical caustic washing. Bottles were contaminated with model chemicals (chloroxylenol and d-limonene) and caustic washed with varied process parameters using a simulated laboratory-scale washing procedure. After washing, the chemical-contaminated bottles were filled with water and stored for 28 days at 37 degrees C. The concentrations of the model chemicals in the water after storage were taken as a measure of chemical contamination. The influence of the cleaning parameters (temperature, caustic and commercial additive concentration) was studied using response surface methodology. Washing temperature showed a significant influence on the removal of absorbed chemicals from surfaces compared with the effect of the caustic and especially the additive concentration. Optimization of caustic cleaning for the cleaning process in question led to better cleaning effectiveness, although none of the different washing conditions were able to remove all absorbed chemicals out of the polymeric resins. Commercially available plastic refillables (PET and PC) showed the best chemical rinsability. Glass bottles, however, had in every case the best rinsing characteristics. 相似文献
164.
A method of posterior mitral annulus remodeling is presented. The posterior annulus is divided into three segments, each segment encircled by a suture that is passed in a tourniquet. Coaptation of the leaflets can be achieved by tightening the tourniquets while the ventricle is being filled. This technique is simple and quick, avoids the use of foreign material, and requires less expertise and judgment than traditional annuloplasties. 相似文献
165.
D. J. Strike N. F. De Rooij M. Koudelka-Hep M. Ulmann J. Augustynski 《Journal of Applied Electrochemistry》1992,22(10):922-926
The oxidation of methanol on gold electrodes modified with polypyrrole and platinum is reported. These electrodes were characterized by cyclic voltammetry and by 12h polarizations in methanol solutions. They were found to give higher currents and lower rates of drift than electrodes of platinum and platinized gold. The effect of varying the amount of platinum deposited is also discussed. 相似文献
166.
A. Witvrouw K. Maex W. De Ceuninck G. Lekens J. D'Haen L. De Schepper 《Microelectronics Reliability》1998,38(6-8)
The degradation due to stress induced voiding of nitride passivated Al-1 wt.% Si and Ti/TN/ Al-1wt.% Si-0.5 wt. % Cu/Ti/TN interconnects with widths ranging between 0.4 and 1.2 μm was studied by in-situ conventional
high resolution resistance measurements (HRRM) during storage at temperatures between 168 and 240°C. The conventional measurements on Al-Si lines, which lasted more than one year, clearly showed that the interconnect lifetime decreases with decreasing line width. With HRRM the degradation due to stress induced voiding can be detected much sooner and with much more detail. From the HRRM it is clear that the resistance changes during storage often happen in jumps and that the degradation has a rather complex alloy, line width and temperature dependence. Both for 0.4 and 0.6 μm wide Al---Si lines more degradation occurred for storage at 175 °C compared to storage at 200 °C. For the Al---Si---Cu stacks the degradation of 0.4 μm wide lines was worse for storage at 240°C compared to storage at 200 °C, but the opposite was true for the 0.6 μm wide lines. 相似文献
167.
Wrinkling is a well known phenomenon experimented by tension membranes in Civil Engineering applications. This paper will
present an efficient numerical technique for the computational simulation of such wrinkles in a prestressed membrane. In particular,
the relaxed energy approach (Pipkin in IMA J Appl Math 36:85–99, 1986) is particularized for prestressed membranes (Gil in
Textile composites and inflatable structures, CIMNE, 2003) undergoing moderate strains. Wrinkling conditions in terms of the
Euler-Lagrange finite deformation tensor along principal directions will be obtained. This will provide a framework to describe
properly the initial instant when wrinkles start to be encountered in a prestressed Saint Venant–Kirchhoff hyperelastic membrane.
Subsequently, a modified Helmholtz’s free energy functional will be introduced with the purpose of describing the modified
constitutive behaviour of the continuum after the onset of wrinkling. Consistent derivations of the stress tensor as well
as the constitutive tensor will de depicted. The results will be particularized for membranes and cables in a Finite Element
discretization basis. Some numerical examples will prove the accuracy and robustness of the described algorithm. 相似文献
168.
Weikle R.M. II Kim M. Hacker J.B. De Lisio M.P. Popovic Z.B. Rutledge D.B. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1992,80(11):1800-1809
Although quasi-optical techniques are applicable to a large variety of solid-state devices, special attention is given to transistors, which are attractive because they can be used as either amplifiers or oscillators. Experimental results for MESFET bar-grid and planar grid oscillators are presented. A MESFET grid amplifier that receives only vertically polarized waves at the input and radiates horizontally polarized waves at the output is discussed. These planar grids can be scaled for operation at millimeter- and submillimeter-wave frequencies. By using modern IC fabrication technology, planar grid oscillators and amplifiers containing thousands of devices can be built, thereby realizing an efficient means for large-scale power combining 相似文献
169.
170.
Balasa F. Catthoor F. Hugo De Man 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》1995,3(2):157-172
Memory cost is responsible for a large amount of the chip and/or board area of customized video and image processing system realizations. In this paper, we present a novel technique-founded on data-flow analysis which allows one to address the problem of background memory size evaluation for a given nonprocedural algorithm specification, operating on multidimensional signals with affine indexes. Most of the target applications are characterized by a huge number of signals, so a new polyhedral data-flow model operating on groups of scalar signals is proposed. These groups are obtained by a novel analytical partitioning technique, allowing to select a desired granularity, depending on the application complexity. The method incorporates a way to tradeoff memory size with computational and controller complexity 相似文献