全文获取类型
收费全文 | 53845篇 |
免费 | 5135篇 |
国内免费 | 3389篇 |
专业分类
电工技术 | 6123篇 |
综合类 | 4670篇 |
化学工业 | 4636篇 |
金属工艺 | 2628篇 |
机械仪表 | 6381篇 |
建筑科学 | 3127篇 |
矿业工程 | 1399篇 |
能源动力 | 1744篇 |
轻工业 | 1698篇 |
水利工程 | 1099篇 |
石油天然气 | 1575篇 |
武器工业 | 745篇 |
无线电 | 8236篇 |
一般工业技术 | 6781篇 |
冶金工业 | 1849篇 |
原子能技术 | 1058篇 |
自动化技术 | 8620篇 |
出版年
2024年 | 186篇 |
2023年 | 696篇 |
2022年 | 1191篇 |
2021年 | 1447篇 |
2020年 | 1596篇 |
2019年 | 1284篇 |
2018年 | 1284篇 |
2017年 | 1786篇 |
2016年 | 1909篇 |
2015年 | 2177篇 |
2014年 | 3289篇 |
2013年 | 3031篇 |
2012年 | 3795篇 |
2011年 | 4125篇 |
2010年 | 3009篇 |
2009年 | 3159篇 |
2008年 | 3187篇 |
2007年 | 3653篇 |
2006年 | 3307篇 |
2005年 | 2763篇 |
2004年 | 2425篇 |
2003年 | 2140篇 |
2002年 | 1753篇 |
2001年 | 1460篇 |
2000年 | 1279篇 |
1999年 | 1088篇 |
1998年 | 868篇 |
1997年 | 911篇 |
1996年 | 661篇 |
1995年 | 548篇 |
1994年 | 495篇 |
1993年 | 392篇 |
1992年 | 303篇 |
1991年 | 236篇 |
1990年 | 206篇 |
1989年 | 131篇 |
1988年 | 124篇 |
1987年 | 86篇 |
1986年 | 66篇 |
1985年 | 46篇 |
1984年 | 50篇 |
1983年 | 31篇 |
1982年 | 33篇 |
1981年 | 22篇 |
1980年 | 16篇 |
1979年 | 10篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1973年 | 9篇 |
1959年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
介绍了如何将改造后的全站仪应用于直升机悬停性能测试的方法。经真实飞行试验检验,该方法理论严密,方案合理,改装简单,操作方便,成本低廉。较之原始的摄影测量法有无法替代的优点。 相似文献
12.
13.
测定钠中杂质的手动阻塞计的研究 总被引:1,自引:1,他引:0
文章介绍了测定钠中杂质浓度的手动阻塞计的原理、装置和实验结果。为了减少测量误差,我们研究了影响准确测定阻塞温度的因素,并且找到了减少测量误差的办法。在同样的杂质饱和温度下,该阻塞计测得的高、低阻塞温度所对应的杂质浓度差是很接近的。对氧其差值为1.03ppm;对氢为0.0763ppm。 相似文献
14.
15.
介绍了天线近场测量的基本原理和HD-1型平面近场测试系统,并对近场测量在实际天线测试中的应用情况、发展方向和应用前景等作了简单的描述。 相似文献
16.
B. Bereqvist 《Strain》1987,23(1):7-13
The design and performance of precision bending equipment for testing straight beams with constant rectangular section under a pure bending moment is described. Part 1 deals with the loading arrangements and Part 2 with the rig for measuring beam deflection. The methods for recording deflection of strain gauges applied on the beam have been described elsewhere.1–4
The reactions to the deadweight gravity loads are taken via ball bearings. The total bending moment inaccuracy, i.e. the sum of estimated systematic errors and random errors, the latter expressed as the 2Ga confidence interval about the mean (2Gcim ), is about ± 25 x. 10-4% , for 23 tests with a steel beam with 15 mm × 75 mm cross sectional dimensions, loaded to 1-1.5 mm/m strain.
The measuring rig stands on the beam via hardened and polished spherical segment feet and uses a capacitive transducer system with less than 5nm resolution. Various application tasks are described. The total inaccuracy of the measured deflection, i.e. apart from bending moment inaccuracy, is about ± 35 times 104% for about 10 reproduced, not repeated, tests with the same steel beam. The deflection for such a beam is of the order of 2 to 4 mm. 相似文献
The reactions to the deadweight gravity loads are taken via ball bearings. The total bending moment inaccuracy, i.e. the sum of estimated systematic errors and random errors, the latter expressed as the 2Ga confidence interval about the mean (2G
The measuring rig stands on the beam via hardened and polished spherical segment feet and uses a capacitive transducer system with less than 5nm resolution. Various application tasks are described. The total inaccuracy of the measured deflection, i.e. apart from bending moment inaccuracy, is about ± 35 times 10
17.
In optical microscopic measurement of internal blood-vessel diameters, the effect of refraction must be taken into account to ensure accuracy of the result. This effect is discussed and an analytical correction formula derived. Phantom blood vessels with known internal and external diameters were used to test the validity of the correction formula. The errors obtained prior to correction were reduced significantly after correction. 相似文献
18.
A numerical solution of the inverse problem of the gravitational field at a single point is obtained using six field elements
for a point, a spherical cap, a differential spherical sector and a vertical segment. In the system of six equations obtained,
the unknowns are the mass of the body, the depth of its center, and the second, third, and fourth degree moments. The accuracy
of the solution of this system is ten times higher than when using three field elements.
__________
Translated from Izmeritel’naya Tekhnika, No. 5, pp. 3–8, May, 2007. 相似文献
19.
M. Loidl E. Leblanc T. Branger H. Rotzinger T. Daniyarov M. Linck A. Fleischmann C. Enss 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,520(1-3):73-75
We report on a feasibility study on precise determination of mass-specific activity of low-energy emitting radioisotopes. Conventional methods of activity measurement suffer from source self-absorption and a strong decrease in detection efficiency for low-energy electrons and photons. We propose a new method based on metallic magnetic microcalorimeters with the source embedded in the detector target in a 4π geometry. First results with a 55Fe source show that electrons and photons are detected with a detection efficiency close to unity and with little loss of energy for electrons. The aim of this study is to provide standards of activity with very low uncertainties in the framework of radiation metrology. 相似文献
20.
O. Khamman 《Materials Letters》2007,61(3):639-643
The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase nickel niobate (NiNb2O6) powders. The formation of the NiNb2O6 phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that the minor phases of unreacted NiO and Nb2O5 precursors and the Ni4Nb2O9 phase tend to form together with the columbite NiNb2O6 phase, depending on calcination conditions. More importantly, it is seen that optimization of calcination conditions can lead to a single-phase NiNb2O6 in an orthorhombic phase. 相似文献