全文获取类型
收费全文 | 259873篇 |
免费 | 3437篇 |
国内免费 | 822篇 |
专业分类
电工技术 | 5130篇 |
综合类 | 330篇 |
化学工业 | 37224篇 |
金属工艺 | 10252篇 |
机械仪表 | 8486篇 |
建筑科学 | 6101篇 |
矿业工程 | 1076篇 |
能源动力 | 6389篇 |
轻工业 | 22880篇 |
水利工程 | 2561篇 |
石油天然气 | 3908篇 |
武器工业 | 68篇 |
无线电 | 34721篇 |
一般工业技术 | 50062篇 |
冶金工业 | 46542篇 |
原子能技术 | 5418篇 |
自动化技术 | 22984篇 |
出版年
2021年 | 2037篇 |
2019年 | 2034篇 |
2018年 | 3467篇 |
2017年 | 3532篇 |
2016年 | 3728篇 |
2015年 | 2320篇 |
2014年 | 4047篇 |
2013年 | 11285篇 |
2012年 | 6562篇 |
2011年 | 8874篇 |
2010年 | 6981篇 |
2009年 | 7850篇 |
2008年 | 8676篇 |
2007年 | 8617篇 |
2006年 | 7802篇 |
2005年 | 7140篇 |
2004年 | 6885篇 |
2003年 | 6733篇 |
2002年 | 6370篇 |
2001年 | 6472篇 |
2000年 | 6169篇 |
1999年 | 6253篇 |
1998年 | 14243篇 |
1997年 | 10270篇 |
1996年 | 8113篇 |
1995年 | 6413篇 |
1994年 | 5711篇 |
1993年 | 5583篇 |
1992年 | 4553篇 |
1991年 | 4213篇 |
1990年 | 4049篇 |
1989年 | 3779篇 |
1988年 | 3624篇 |
1987年 | 3170篇 |
1986年 | 3066篇 |
1985年 | 3613篇 |
1984年 | 3386篇 |
1983年 | 3032篇 |
1982年 | 2852篇 |
1981年 | 2953篇 |
1980年 | 2761篇 |
1979年 | 2651篇 |
1978年 | 2500篇 |
1977年 | 2945篇 |
1976年 | 3555篇 |
1975年 | 2317篇 |
1974年 | 2314篇 |
1973年 | 2320篇 |
1972年 | 1849篇 |
1971年 | 1745篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015. 相似文献
82.
Metallurgist - Kinetics of austenite grain growth within a heat-affected zone is studied for low carbon low-alloy steels of different alloying composition. The effect of Ti/N ratio on the metal... 相似文献
83.
Palmitoleic acid has been classified as an insulin-sensitizing lipokine, but evidence for this from human studies has been inconsistent. We hypothesized that this is related to either the types of samples or conditions under which samples are collected. We measured plasma palmitoleic acid and total free fatty acids (FFA) using ultra-performance liquid chromatography in blood samples collected from 34 adults under a variety of conditions. We collected duplicate samples of adipose (n = 10), FFA (n = 9), and very low density lipoprotein triacylglycerol (VLDL-TAG) (n = 7) to measure the palmitoleic acid as a percentage of total fatty acids. We tested whether the percentage of palmitoleic acid was correlated with insulin resistance, as measured by homeostatic model of insulin resistance (HOMA-IR). Adipose stearoyl-coenzyme A desaturase 1 (SCD-1) protein was measured by capillary Western blotting. FFA-palmitoleic acid percentage increased as a function of total FFA and was greater (p < 0.005) in females than males. Adipose palmitoleic acid percentage was greater in females than males (p < 0.001), as was adipose SCD-1. Palmitoleic acid was greater in femoral fat than in abdominal fat in both females and males (p < 0.001), and correlated positively with HOMA-IR only in females. The test–retest reliability values for percentage palmitoleic acid were 7 ± 10% for adipose, 24 ± 26% for VLDL, and 53 ± 31% for FFA. Because FFA-palmitoleic acid percentage varies as a function of total FFA, investigators should re-evaluate how palmitoleic acid data is presented. The positive relationship between adipose palmitoleic acid and HOMA-IR in females suggests that it is not a potent insulin-sensitizing lipokine in humans. 相似文献
84.
85.
86.
87.
Shchelkunov E. B. Vinogradov S. V. Shchelkunova M. E. Pronin A. I. Buravitsyn D. A. 《Russian Engineering Research》2020,40(5):367-371
Russian Engineering Research - The theoretically possible reconfigurable parallel mechanisms are classified, in terms of the layout of guides on the base. Formulas are derived for the... 相似文献
88.
89.
90.
This study addresses the thermo‐diffusion and the diffusion‐thermo phenomena in a semi‐infinite absorbent channel whose walls are contracting/expanding, with heat source/sink effects. The governing partial differential equations with suitable boundary conditions are transformed to a system of dimensionless ordinary differential equations. An analytic solution of the problem has been found using a technique called homotopy analysis method (HAM). HAM gives consistently valid answers to the problem over an extensive variety of parameters and also provides better accuracy. To validate the analytical results, a comparison has been presented with a numerical solution calculated by using the parallel shooting method. The effects of dimensionless parameters, that is, deformation parameter, Reynolds number, Soret and Dufour numbers, and heat source/sink parameter on the expressions of velocity, temperature, and concentration profiles are analyzed graphically to understand the physics of the deformable channel. It has been noted that the velocity across the channel is higher for the expanding channel, as compared to that for the contracting channel. Also the Soret and Dufour number increases the temperature of the fluid, and decreases the concentration. The temperature profile has an increasing behavior in the case of heat source, and a decreasing behavior in the case of heat sink. 相似文献