全文获取类型
收费全文 | 104751篇 |
免费 | 9741篇 |
国内免费 | 5235篇 |
专业分类
电工技术 | 7869篇 |
技术理论 | 22篇 |
综合类 | 15695篇 |
化学工业 | 13953篇 |
金属工艺 | 6392篇 |
机械仪表 | 5497篇 |
建筑科学 | 12866篇 |
矿业工程 | 4038篇 |
能源动力 | 2978篇 |
轻工业 | 5630篇 |
水利工程 | 4571篇 |
石油天然气 | 4258篇 |
武器工业 | 767篇 |
无线电 | 10886篇 |
一般工业技术 | 9011篇 |
冶金工业 | 5126篇 |
原子能技术 | 772篇 |
自动化技术 | 9396篇 |
出版年
2024年 | 394篇 |
2023年 | 1213篇 |
2022年 | 2063篇 |
2021年 | 2390篇 |
2020年 | 2540篇 |
2019年 | 2254篇 |
2018年 | 2133篇 |
2017年 | 2813篇 |
2016年 | 3087篇 |
2015年 | 3567篇 |
2014年 | 7037篇 |
2013年 | 5673篇 |
2012年 | 7117篇 |
2011年 | 7544篇 |
2010年 | 5884篇 |
2009年 | 6611篇 |
2008年 | 6004篇 |
2007年 | 7767篇 |
2006年 | 7257篇 |
2005年 | 6105篇 |
2004年 | 5044篇 |
2003年 | 4446篇 |
2002年 | 3626篇 |
2001年 | 3148篇 |
2000年 | 2763篇 |
1999年 | 2082篇 |
1998年 | 1535篇 |
1997年 | 1307篇 |
1996年 | 1117篇 |
1995年 | 996篇 |
1994年 | 861篇 |
1993年 | 621篇 |
1992年 | 592篇 |
1991年 | 408篇 |
1990年 | 378篇 |
1989年 | 373篇 |
1988年 | 218篇 |
1987年 | 137篇 |
1986年 | 123篇 |
1985年 | 79篇 |
1984年 | 85篇 |
1983年 | 54篇 |
1982年 | 45篇 |
1981年 | 63篇 |
1980年 | 44篇 |
1979年 | 24篇 |
1978年 | 16篇 |
1977年 | 12篇 |
1975年 | 17篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
51.
研究了(Ba1-xSrx)(Zn1/3Nb2/3)O3微波介质陶瓷温度系数的非线性变化以及异常的原因。根据CM公式,随着系统中Sr(Zn1/3Nb2/3)O3的增多,τc的异常是由于氧八面体的畸变导致的相转变(对称性降低)所造成的(晶体结构由无序立方相向有序赝立方相的连续变化)。相转变的发生相应影响了极化以及极化模式,这是造成τc异常的根本原因。 相似文献
52.
The relation between the initial unbalance and the output signal of bridge circuits when acted upon simultaneously by the
physical factor being measured and the temperature of the surroundings when the bridge is supplied from a voltage or current
source is investigated. Analytic relations are obtained which explain the temperature dependence of the useful output voltage
under external physical action.
__________
Translated from Izmeritel’naya Tekhnika, No. 1, pp. 48–49, 2007. 相似文献
53.
The exact magnetization pattern of magnetic films close to a spin-reorientation transition is difficult to analyze due to the intrinsically three-dimensional (3d) variation of the orientation of the local magnetization. We present a technique how this can be performed, based on the analysis of high quality 2d polarization maps from a single scanning electron microscope with polarization analysis (SEMPA) measurement with tilted sample. The key tool is the statistical distribution of all occurring polarization doublets, visualized in a 2d histogram plot. From the shape of the distribution the type of transition—canted-phase, or coexisting phases—can be inferred. For the canted-phase state, the canting angle can be accurately determined from geometrical considerations. With help of the histogram the image data can be analyzed and the three components of the magnetization can be calculated for most points of the image. For a Co/Pt multilayer film we found a cone state. The magnetization forms a complex pattern consisting of out-of-plane domains while the in-plane magnetization shows a maze pattern. 相似文献
54.
J. Gajdoš Kljusurić 《Sadhana》2003,28(6):991-998
This work is an experimental study of the differential scanning calorimetry characterisation of polymer materials used in
food packaging materials, such as polypropylene (0.03 mm), polyethylene (0.1 and 0.03 mm), poly(D-(-)-Β-hydroxybutyrate) (powder),
two-layered polypropylene (0.064 mm), and two-layered polypropylene with poly-vinylidene-chloride (0.012/0.021). The polymer
stability was checked by simulation of conditions during food preparation in microwave ovens, sterilisation or rapid freezing.
The materials were tested in the temperature range from 40 to 200‡C at different scan rates from 2 to 30°C min−1 during heating or cooling. The enthalpies show a high correlation coefficient (0.964) with scan rate. All samples undergo
phase change in the temperature range from 107 to 173°C during heating and enthalpies are in the range from 31.8 to 71.1Jg−1. Upon subsequent cooling from 200°C, the temperature range of phase changes is shifted to lower temperatures from 86 to 102°C
with enthalpies ranging from 30.4 to 57.8 J g−1.
Experiments with exposure of polymers to microwave radiation and freezing prove that the phase change considering the temperature
range is very similar in all experiments. 相似文献
55.
56.
Michael V. Antony 《Minds and Machines》1991,1(3):321-341
Fodor and Pylyshyn (1988) have argued that the cognitive architecture is not Connectionist. Their argument takes the following form: (1) the cognitive architecture is Classical; (2) Classicalism and Connectionism are incompatible; (3) therefore the cognitive architecture is not Connectionist. In this essay I argue that Fodor and Pylyshyn's defenses of (1) and (2) are inadequate. Their argument for (1), based on their claim that Classicalism best explains the systematicity of cognitive capacities, is an invalid instance of inference to the best explanation. And their argument for (2) turns out to be question-begging. The upshot is that, while Fodor and Pylyshyn have presented Connectionists with the important empirical challenge of explaining systematicity, they have failed to provide sufficient reason for inferring that the cognitive architecture is Classical and not Connectionist. 相似文献
57.
David Mills 《Granular Matter》2004,6(2-3):173-177
For fine powdered materials, capable of being conveyed in dense phase, a conveying region exists in which instability in flow and pipeline blockage can occur if the pressure gradient available is insufficient to maintain a minimum value of solids loading ratio. A reduction in material flow rate can also lead to pipeline blockage in this region. Conveying trials under-taken with cement are used to illustrate the nature of the problem. 相似文献
58.
尺度目标识别中的若干技术问题 总被引:1,自引:0,他引:1
从工程应用的角度阐述了现代鱼雷常用的尺度目标识别原理,讨论了影响识别距离的若干因素和措施,提出了小尺度模拟靶通过亮点延时算法以弥补尺度不足及其试验技术,试验结果表明,该方法可以获得良好效果。 相似文献
59.
On the basis of new concept using a solid disperse phase we have developed an efficient catalytic solid-phase-system for epoxidations of alkenes using urea–hydrogen peroxide (urea–H2O2) complex and cetylpyridinium dodecatungstate ((CetylPy)10[H2W12O42]) catalyst on fluorapatite (FAp). The recovered solid catalyst phase was reused to keep the catalytic activity after several times. In the conceptual idea it is a key point that in situ solid-phase-activation of the catalyst with urea–H2O2 proceeds to form microcrystals of the active species dispersed on the solid phase. The dispersion of the catalyst on FAp in the case of tungstic acid (H2WO4) was suggested by EPMA analysis. We proposed the peroxo type of species keeping the parent polyoxometalate framework as novel active species from FT-IR spectroscopic studies. FAp phase plays important roles of dispersing the active species on its surface to have high catalytic activity and of stabilizing the active species to lead to high reusability. 相似文献
60.
火电厂实施废水零排放的可行性探讨 总被引:1,自引:0,他引:1
对合肥发电厂的用排水现状进行了介绍,并提出了实施废水零排放的可行性方案。 相似文献