全文获取类型
收费全文 | 721482篇 |
免费 | 63086篇 |
国内免费 | 44223篇 |
专业分类
电工技术 | 50575篇 |
综合类 | 58304篇 |
化学工业 | 93005篇 |
金属工艺 | 46603篇 |
机械仪表 | 44226篇 |
建筑科学 | 43621篇 |
矿业工程 | 25394篇 |
能源动力 | 17906篇 |
轻工业 | 70321篇 |
水利工程 | 21033篇 |
石油天然气 | 25652篇 |
武器工业 | 8765篇 |
无线电 | 75168篇 |
一般工业技术 | 86197篇 |
冶金工业 | 55473篇 |
原子能技术 | 15091篇 |
自动化技术 | 91457篇 |
出版年
2024年 | 3386篇 |
2023年 | 8804篇 |
2022年 | 21698篇 |
2021年 | 27883篇 |
2020年 | 20362篇 |
2019年 | 14828篇 |
2018年 | 17429篇 |
2017年 | 19996篇 |
2016年 | 18458篇 |
2015年 | 25422篇 |
2014年 | 33136篇 |
2013年 | 42732篇 |
2012年 | 49218篇 |
2011年 | 52575篇 |
2010年 | 49433篇 |
2009年 | 47855篇 |
2008年 | 49597篇 |
2007年 | 48610篇 |
2006年 | 41236篇 |
2005年 | 34188篇 |
2004年 | 25533篇 |
2003年 | 18074篇 |
2002年 | 16975篇 |
2001年 | 16006篇 |
2000年 | 13192篇 |
1999年 | 7344篇 |
1998年 | 10996篇 |
1997年 | 7784篇 |
1996年 | 5969篇 |
1995年 | 4539篇 |
1994年 | 3870篇 |
1993年 | 4167篇 |
1992年 | 3275篇 |
1991年 | 3169篇 |
1990年 | 3081篇 |
1989年 | 3081篇 |
1988年 | 3003篇 |
1987年 | 2602篇 |
1986年 | 2662篇 |
1985年 | 2903篇 |
1984年 | 2754篇 |
1983年 | 2612篇 |
1982年 | 2347篇 |
1981年 | 2357篇 |
1980年 | 2512篇 |
1979年 | 2468篇 |
1978年 | 2389篇 |
1977年 | 2489篇 |
1976年 | 2881篇 |
1975年 | 2196篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
H. Yamamoto N. Heyamoto T. Matsui N. Murayama J. Shibata 《International Journal of Thermophysics》2003,24(5):1385-1394
Polyvinylalcohol (PVA) polymer gel is a temperature sensitive polymeric gel, with a critical transition temperature (with H2O) of 310 K. At higher than 310 K, this temperature sensitive polymer gel shrinks because of discharging water, whereas at lower temperatures, the gel swelled because of absorbing water. The reversibility of the gel's volume change was confirmed by temperature swing. The adsorption behavior of an organic compound onto the PVA polymer gel in water was tested at various temperatures. The amount of adsorbed organic compound increased remarkably at temperatures higher than about 310 K. Then, it was confirmed that the organic compound in PVA polymer gel could be reversibly adsorbed and desorbed by a temperature change between 293 and 323 K. The mechanism of adsorption of the organic compound onto the PVA polymer gel could be explained by hydration and dehydration of polymer gel. 相似文献
72.
73.
J.M. Roth T.G. Ulmer N.W. Spellmeyer S. Constantine M.E. Grein 《Photonics Technology Letters, IEEE》2004,16(9):2009-2011
We demonstrate a novel 40-GHz mode-locked fiber laser that utilizes a single active device to provide both gain and mode-locking. The laser produces pulses as short as 2.2 ps, is tunable over a 27-nm band centered at 1553 nm, and exhibits long-term stability without cavity-length feedback control. The pulse train at 1556 nm was used in a 40-Gb/s transmission experiment over 45 km with a low 0.4-dB power penalty. 相似文献
74.
高抗挤厚壁套管的性能及应用效果评价 总被引:1,自引:1,他引:0
中原油田套管损坏的主要原因是现有套管强度不够,无法抵抗盐膏层段的巨大外挤力。开发了TP130TT型高抗挤厚壁套管,其强度能很好地抵抗盐膏层巨大外挤力。实验室试验表明,各项性能指标达到了设计要求,现场使用取得了很好的效果,解决了中原油田盐膏层段套管强度不足的难题。 相似文献
75.
在实际应用中常常需要将人像从照片的背景中有效地分割出来,通常的做法是通过提取照片中人像各部分特征来实现分割,其缺陷是计算复杂度较大,分割效果受各种干扰因素影响很大。现提出了一种基于主体外部轮廓信息的照片分割算法,通过梯度锐化、边缘保护、临近像素点相似度比较来确定图像的边界,该算法对于具有相对均匀背景的照片具有较高的计算效率。 相似文献
76.
The hydrocarbon-group composition and distribution of naphthenoaromatic hydrocarbons of West Siberian oils were studied by the technique of mass spectrometry. Naphthenoaromatic hydrocarbons of the general formula CnH2n?z , where z is 8, 10, 12, 14, 16, or 18, containing from one to six saturated cycles are present in oils in significant concentrations. Naphthenomonoarenes with one saturated cycle dominate in all oils. An increase in the amount of compounds containing 3–6 saturated cycles in their molecule with the occurrence depth was noted. Naphthenobiarenes of the general formula CnH2n?z , where z is 14, 16, 18, 20, 22, or 24 containing from one to six saturated cycles are present in oils in concentrations from 20.0 to 54.0 wt % of the biaromatic fraction. Most oils are characterized by the prevalence of structures with one and two saturated cycles in their molecule. The dependence of the number of cycles in naphthenobiarenes on the nature of original organic matter (OM) was not traced. The lack of correlation between the number of cycles and the OM type is presumably due to the fact that, for the most part, fused polycyclic naphthenobiarenes reflect the degree of catagenetic alteration of organic matter. 相似文献
77.
78.
Mutoh N. Nakashima J. Kanesaki M. 《Industrial Electronics, IEEE Transactions on》2003,50(6):1085-1094
Electromagnetic interference (EMI) noises generated in power converters are diffused on the surface of conductors. This means influences occur from radiated EMI noises emitted from power transmission lines as well as conducted EMI noises transmitted from them. EMI noises diffusing on the surface of conductors are generally difficult to control using conventional concentrated constant theory. Thus, a new approach based on distributed constant circuit theory is needed in order to control EMI noises. A power converter structure to control EMI noises using multilayer power printed circuit technology is studied in this paper. A structure which can control EMI noises should simultaneously satisfy two conditions, i.e., one to shut down and one to attenuate EMI noises. The structure satisfying these conditions is studied through simulations using the Transmission-Line Modeling Method. The simulations show that the diffusion of EMI noises is controlled by dividing the flow of currents produced by EMI noises into the horizontal and perpendicular directions. That is, the horizontal current flow is controlled inside using the differences in the resistance produced from differences between inner and outer diameter of power transmission lines and the perpendicular current flow can be controlled by properly designing the thickness of the dielectric layer sandwiched between P-and N-power transmission lines with the symmetrical structure. Moreover, it is confirmed by simulations and experiments that the attenuation of EMI noises is affected by the width of the power transmission lines. It is expected that the results obtained in this paper can provide important rules when designing power converters with EMI noise control functions which use the multilayer power printed circuit technology. 相似文献
79.
The studies show that in the combined use of biological and chemisorption stages of treatment, a deeper degree of removal of industrial pollutants from wastewaters is attained. The chemisorption stage allows stabilizing the treatment process in different concentration-temperature drops and increasing the degree of removal of synthetic surfactants (SSF), petroleum products, and nitrogen compounds. The possibility of regulating the selectivity of the treatment process by varying the composition of the chemisorption material is demonstrated. 相似文献
80.