全文获取类型
收费全文 | 303238篇 |
免费 | 6137篇 |
国内免费 | 1202篇 |
专业分类
电工技术 | 5078篇 |
综合类 | 278篇 |
化学工业 | 47315篇 |
金属工艺 | 10072篇 |
机械仪表 | 10109篇 |
建筑科学 | 7852篇 |
矿业工程 | 590篇 |
能源动力 | 9272篇 |
轻工业 | 32338篇 |
水利工程 | 2304篇 |
石油天然气 | 2055篇 |
武器工业 | 6篇 |
无线电 | 41973篇 |
一般工业技术 | 56137篇 |
冶金工业 | 51774篇 |
原子能技术 | 3926篇 |
自动化技术 | 29498篇 |
出版年
2022年 | 1843篇 |
2021年 | 3162篇 |
2020年 | 2297篇 |
2019年 | 2635篇 |
2018年 | 3848篇 |
2017年 | 3877篇 |
2016年 | 4460篇 |
2015年 | 3413篇 |
2014年 | 5595篇 |
2013年 | 15235篇 |
2012年 | 9768篇 |
2011年 | 13316篇 |
2010年 | 10210篇 |
2009年 | 11325篇 |
2008年 | 11585篇 |
2007年 | 11102篇 |
2006年 | 10227篇 |
2005年 | 9171篇 |
2004年 | 8804篇 |
2003年 | 8548篇 |
2002年 | 7997篇 |
2001年 | 8087篇 |
2000年 | 7333篇 |
1999年 | 7840篇 |
1998年 | 18331篇 |
1997年 | 12644篇 |
1996年 | 9631篇 |
1995年 | 7361篇 |
1994年 | 6329篇 |
1993年 | 6154篇 |
1992年 | 4375篇 |
1991年 | 4166篇 |
1990年 | 3863篇 |
1989年 | 3701篇 |
1988年 | 3528篇 |
1987年 | 2810篇 |
1986年 | 2694篇 |
1985年 | 3339篇 |
1984年 | 2950篇 |
1983年 | 2682篇 |
1982年 | 2477篇 |
1981年 | 2495篇 |
1980年 | 2312篇 |
1979年 | 2129篇 |
1978年 | 1961篇 |
1977年 | 2290篇 |
1976年 | 2871篇 |
1975年 | 1653篇 |
1974年 | 1550篇 |
1973年 | 1610篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
A Gopal G Li Mandri DL King C Marboe S Homma 《Canadian Metallurgical Quarterly》1994,105(6):1885-1887
Cardiac papillary fibroelastomas are unusual, frond-like growths typically found on cardiac valves, diagnosed incidentally on autopsy or cardiac surgery, but rarely during life. We report a rare case of an aortic valve papillary fibroelastoma detected by transthoracic echocardiography and confirmed by histologic study. 相似文献
112.
LeeSiewWei 《水利水电快报》2002,23(19):1-5
在英国伦敦多克兰斯轻便铁路刘易舍姆延长线(DLR-LWE)双隧道掘进工程中,在敏感建筑物下进行了补偿灌浆,以防止隧道开挖引起的过度沉降。但是,过度灌浆也会对隧道下部施加超越。介绍了由隧道掘进承包商所编辑的关于地面和建筑物沉降以及由补偿灌浆引起的隧道衬砌变形的详细现场监测数据。 相似文献
113.
We present methods to generate rendering sequences for triangle meshes which preserve mesh locality as much as possible. This is useful for maximizing vertex reuse when rendering the mesh using a FIFO vertex buffer, such as those available in modern 3D graphics hardware. The sequences are universal in the sense that they perform well for all sizes of vertex buffers, and generalize to progressive meshes. This has been verified experimentally. 相似文献
114.
This paper analyzes probability of bit-error (Pe) performance of asynchronous bandlimited direct-sequence code-division multiple-access systems with binary phase-shift keying spreading. The two present methods of Pe analysis under bandwidth-efficient pulse shaping: the often-cited standard Gaussian approximation and the characteristic function (CF) method suffer from either a low accuracy in regions of low Pe (< 10-3) or a prohibitively large computational complexity. The paper presents an alternate method of Pe analysis with moderate computational complexity and high accuracy based on a key observation. A sequence of chip decision statistics (whose sum yields a bit statistic) forms a stationary, m-dependent sequence when conditioned on the chip delay and phase offset of each interfering signal. This observation permits the generalization of the improved Gaussian approximation previously derived for the rectangular pulse and the derivation of a numerically efficient approximation based on the CF method. Numerical examples of systems using the square-root raised-cosine and IS-95 pulses illustrate THE P e performance, user capacity and the accuracy of the proposed method 相似文献
115.
116.
G.D. Wignall R.W. Hendricks W.C. Koehler J.S. Lin M.P. Wai E.L. Thomas R.S. Stein 《Polymer》1981,22(7):886-889
A series of small angle neutron scattering measurements on blends of normal polystyrene (PSH) and labelled (deuterated) polystyrene (PSD) have been made with concentrations of PSD from 5 to 50 mol %. It is shown that the single chain form factor of the polymer in bulk can be obtained from a single concentration measurement for any concentration of labelled molecules, providing the molecular weights of the parent and labelled molecules are the same and the molecular weight distributions are narrow. 相似文献
117.
For flexible manufacturing of short production runs where a large variety of product sizes, component types, and surface reflectance characteristics are encountered, it is desirable to build flexible computer-controlled systems for feeding parts into machine tools or assembly processes that combine maximum flexibility and reliability with minimum cost and cycle-time. This is not a general bin-picking problem; the parts are assumed to be propositioned approximately in totes/pallets/kits with regularly spaced locations. This article presents a machine vision technique based on the principle of retroreflective vision sensing for part-presentation. Since retroreflective material has a distinctive surface reflectance that is not commonly found in natural or man-made objects, the use of retroreflective surfaces enables reliable high object-to-background contrast images to be obtained for a wide variety of objects. Unlike conventional machine vision techniques, which rely on the variance of the surface reflectance of the objects to generate detailed images, retroreflective vision sensing aims at generating a reliable two-dimensional digital object silhouettes so that the location and orientation of the part can be reliably determined. Two application examples, machine loading and assembly, are illustrated. 相似文献
118.
N.C. Knowles 《Nuclear Engineering and Design》1989,116(1)
Geomechanical aspects of the storage of radioactive waste in salt formations have been studied extensively using finite element methods over the last 20 years. In consequence a range of computer programs and associated modelling techniques have been assembled. The paper is based on a benchmark exercise to compare the predictive abilities of a number of these programs and highlights the difficulties of making reliable a-priori estimates of long term behaviour. 相似文献
119.
Experiments showing the frequency and amplitude of the flow induced motion of the gate for a 2- and a 4-in. swing check valve have been performed. The gate motion is due to turbulence in approach flow. We have found the dominant turbulent frequency of the approach flow is about half the natural frequency of the valves. The valves appear to be almost critically damped. Because of this, the valves respond almost as they would to a static force of the magnitude characteristic of the turbulent fluctuation in the flow. Both the dimensionless exciting force and the damping ratio have been found to be independent of valve size so the above statements are true for larger valves also. The recommended valve oscillation amplitudes and frequencies are used to calculate the wear at the shaft and at the stop. For an unpegged check valve, such as one of the 10-in. valves which was used at the San Onofre Nuclear Generation Station, it was found that shaft bearing wear would amount to 0.27 in.3/year and stop wear to 0.03 in.3/year. 相似文献
120.