全文获取类型
收费全文 | 215532篇 |
免费 | 2446篇 |
国内免费 | 378篇 |
专业分类
电工技术 | 3182篇 |
综合类 | 754篇 |
化学工业 | 32853篇 |
金属工艺 | 10125篇 |
机械仪表 | 6800篇 |
建筑科学 | 4114篇 |
矿业工程 | 2289篇 |
能源动力 | 3419篇 |
轻工业 | 11936篇 |
水利工程 | 3396篇 |
石油天然气 | 8779篇 |
武器工业 | 18篇 |
无线电 | 16577篇 |
一般工业技术 | 42450篇 |
冶金工业 | 47796篇 |
原子能技术 | 7157篇 |
自动化技术 | 16711篇 |
出版年
2021年 | 1995篇 |
2019年 | 1863篇 |
2018年 | 3709篇 |
2017年 | 4055篇 |
2016年 | 4696篇 |
2015年 | 2647篇 |
2014年 | 3645篇 |
2013年 | 7300篇 |
2012年 | 6763篇 |
2011年 | 8257篇 |
2010年 | 5431篇 |
2009年 | 6035篇 |
2008年 | 5852篇 |
2007年 | 5742篇 |
2006年 | 4928篇 |
2005年 | 7238篇 |
2004年 | 6288篇 |
2003年 | 5653篇 |
2002年 | 4397篇 |
2001年 | 4265篇 |
2000年 | 3712篇 |
1999年 | 3857篇 |
1998年 | 12743篇 |
1997年 | 8671篇 |
1996年 | 6187篇 |
1995年 | 4307篇 |
1994年 | 3617篇 |
1993年 | 3744篇 |
1992年 | 2496篇 |
1991年 | 2597篇 |
1990年 | 2703篇 |
1989年 | 2584篇 |
1988年 | 2589篇 |
1987年 | 2395篇 |
1986年 | 2424篇 |
1985年 | 2453篇 |
1984年 | 2286篇 |
1983年 | 2225篇 |
1982年 | 2112篇 |
1981年 | 2368篇 |
1980年 | 2245篇 |
1979年 | 2328篇 |
1978年 | 2520篇 |
1977年 | 3013篇 |
1976年 | 4338篇 |
1975年 | 2334篇 |
1974年 | 2342篇 |
1973年 | 2385篇 |
1972年 | 2194篇 |
1971年 | 1956篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
An antenna array for wideband operation (up to 70%) is presented. The structure has low windloading area and consists of parallel printed circuit boards (PCB) with microstrip dipoles, feed network and metal fences placed between the PCBs. The low profile, low weight antenna array forms the main beam and three difference patterns for sidelobe cancellation. Experimental results are compared with calculations for both microstrip dipole and array 相似文献
63.
GN Mozhokina GB Sokolova OV Makarova LP Mikha?lova 《Canadian Metallurgical Quarterly》1996,41(7-8):31-33
The effect of lomefloxacin was studied on mice with experimental infection due to Mycobacterium tuberculosis. The antibiotic was administered in doses of 100 and 200 mg/kg. It was shown that the use of lomefloxacin for a month provided a lower death rate of the animals with progressing acute generalized tuberculosis, a lower level of the lesions in the internal organs and a lower number of the Mycobacterium isolates from them. The efficacy of the treatment depended on the drug dose. When lomefloxacin was used in a dose of 200 mg/kg, the survival rate was much higher and the number of the epithelial unicellular granulomas in the tissue of the lung and spleen was markedly decreased while with the lower dose the indices did not differ from those in the control. 相似文献
64.
65.
T P?usa P Górski H Frank-Piskorska M Kowalski J Kruszewski P Kuna M Kurek R Kurzawa W Silny E Zawisza 《Canadian Metallurgical Quarterly》1996,1(4):292-293
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre. 相似文献
66.
V. M. Yakovenko M. V. Burtyka I. V. Yakovenko 《Journal of Infrared, Millimeter and Terahertz Waves》1996,17(3):559-568
The theory of interaction of charged particle beams with 2D electron gas, located in the field of the delta-like potential wallU(y) =U oδ(y) has been developed. The kinetic equation for plasmons in 2D electron gas was obtained; the conditions of arising of their instability are given and the corresponding expressions for the increment of plasmons are found. 相似文献
67.
A.G. Berkovski G. Chiodi J.-P. Fabre A. Frenkel S.V. Golovkin Yu.I. Gubanov G.N. Kislizkai E.N. Kozarenko I.E. Kreslo A.E. Kushnirenko G. Martellotti D. Mazza A.M. Medvedkov G. Penso 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,380(3):537-543
We present the performance of a high-speed gateable vacuum image pipeline, which permits individual images to be delayed and selected from continuous non-repetitive image stream. This device is composed of a vacuum tube equipped with a photocathode at one end, a phosphor screen at the other end, and a system of metal grids in between. Photoelectrons produced by the images focused on the photocathode, are guided by a uniform magnetic field, parallel to the tube axis. By changing the grid potentials, the drift time of the photoelectrons inside the tube can be varied from 0.35 to 1.5 μs. An image can then be selected by an external trigger with a time resolution in the range of 4–30 ns, depending on the delay time. The selected photoelectrons are finally accelerated onto the phosphor screen, set at 10 kV, where they reproduce the desired image. With a magnetic field of 0.1 T, a spatial resolution of 33 lp/mm was obtained. The high spatial and time resolution make this device an interesting tool for high-energy physics and astrophysics experiments, and for high-speed photography. 相似文献
68.
Purified cell-envelope polyphosphatase as well as polyphoshatase activities of cytosol and isolated vacuoles, of nuclei and mitochondria of the yeast Saccharomyces cerevisiae were compared. The polyphosphatases of cell envelope and cytosol are similar, the polyphosphatases of nuclei, vacuoles and mitochondria differ in their kinetic properties, substrate specificity, requirements in divalent cations and in some effector actions both from these and from each other. 相似文献
69.
70.
K Giesen T Hummel A Stollewerk S Harrison A Travers C Kl?mbt 《Canadian Metallurgical Quarterly》1997,124(12):2307-2316
Two classes of glial cells are found in the embryonic Drosophila CNS, midline glial cells and lateral glial cells. Midline glial development is triggered by EGF-receptor signalling, whereas lateral glial development is controlled by the gcm gene. Subsequent glial cell differentiation depends partly on the pointed gene. Here we describe a novel component required for all CNS glia development. The tramtrack gene encodes two zinc-finger proteins, one of which, ttkp69, is expressed in all non-neuronal CNS cells. We show that ttkp69 is downstream of gcm and can repress neuronal differentiation. Double mutant analysis and coexpression experiments indicate that glial cell differentiation may depend on a dual process, requiring the activation of glial differentiation by pointed and the concomitant repression of neuronal development by tramtrack. 相似文献