全文获取类型
收费全文 | 10163篇 |
免费 | 1327篇 |
国内免费 | 899篇 |
专业分类
电工技术 | 424篇 |
综合类 | 881篇 |
化学工业 | 1081篇 |
金属工艺 | 454篇 |
机械仪表 | 600篇 |
建筑科学 | 1138篇 |
矿业工程 | 568篇 |
能源动力 | 322篇 |
轻工业 | 324篇 |
水利工程 | 834篇 |
石油天然气 | 916篇 |
武器工业 | 126篇 |
无线电 | 1740篇 |
一般工业技术 | 1064篇 |
冶金工业 | 291篇 |
原子能技术 | 265篇 |
自动化技术 | 1361篇 |
出版年
2024年 | 38篇 |
2023年 | 169篇 |
2022年 | 326篇 |
2021年 | 380篇 |
2020年 | 359篇 |
2019年 | 382篇 |
2018年 | 350篇 |
2017年 | 423篇 |
2016年 | 469篇 |
2015年 | 504篇 |
2014年 | 639篇 |
2013年 | 683篇 |
2012年 | 697篇 |
2011年 | 708篇 |
2010年 | 499篇 |
2009年 | 527篇 |
2008年 | 515篇 |
2007年 | 565篇 |
2006年 | 522篇 |
2005年 | 462篇 |
2004年 | 457篇 |
2003年 | 445篇 |
2002年 | 385篇 |
2001年 | 331篇 |
2000年 | 276篇 |
1999年 | 203篇 |
1998年 | 164篇 |
1997年 | 114篇 |
1996年 | 110篇 |
1995年 | 110篇 |
1994年 | 89篇 |
1993年 | 68篇 |
1992年 | 59篇 |
1991年 | 56篇 |
1990年 | 51篇 |
1989年 | 39篇 |
1988年 | 32篇 |
1987年 | 21篇 |
1986年 | 22篇 |
1985年 | 34篇 |
1984年 | 31篇 |
1983年 | 22篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1964年 | 3篇 |
1963年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
We consider the class of unbounded fan-in depth three Boolean circuits, for which the bottom fan-in is limited by k and the top gate is an OR. It is known that the smallest such circuit computing the parity function has gates (for k = O(n
1/2)) for some , and this was the best lower bound known for explicit (P-time computable) functions. In this paper, for k = 2, we exhibit functions in uniform NC
1 that require size depth 3 circuits. The main tool is a theorem that shows that any circuit on n variables that accepts a inputs and has size s must be constant on a projection (subset defined by equations of the form x
i
= 0, x
i
= 1, x
i
= x
j
or x
i
= ) of dimension at least log(a/s)log n.
Received: April 1, 1997. 相似文献
83.
84.
A procedure relying on linear programming techniques is developed to compute (regression) quantile regions that have been defined recently. In the location case, this procedure allows for computing halfspace depth regions even beyond dimension two. The corresponding algorithm is described in detail, and illustrations are provided both for simulated and real data. The efficiency of a Matlab implementation of the algorithm1 is also investigated through extensive simulations. 相似文献
85.
提出了基于形态学微分的车牌字符分割算法。首先运用形态学微分算法获取车的边界,然后通过巧妙选择连通区域进行深度搜索即可直接获得车牌每个字符的矩形区域。本方法省去了一般车牌识别中的车牌定位部分,对有一定倾角的车牌也有一定的适应能力。 相似文献
86.
87.
88.
HSV-tk基因/GCV系统治疗肿瘤的旁观者效应与缝隙连接关系的研究 总被引:1,自引:0,他引:1
目的 探讨单纯疱疹病毒胸苷激酶(HSV-tk)基因/丙氧鸟苷(GCV)系统杀伤肿瘤细胞时旁观者效应与细胞间缝隙连接的关系。方法 用PA317细胞包装STK质粒(逆转录病毒载体介导的HSV-tk基因),形成假逆转录病毒颗粒,转染有缝隙连接的大鼠胶质瘤细胞C6和无缝隙连接的入宫颈癌细胞 Hela,制成 C6 tk+和 Helatk+细胞,将不同比例的C6和 C6 tk+、Hela和 Hela tk+细胞混合,每种比例8孔,培养 24h后 4孔加入含0.5μg/mlGCV的培养基,4孔作对照,6d后用MTT法测量细胞存活率。在两个培养皿中放入周围粘有33mm高滤纸的载玻片,分别接种 C6、C6 tk+细胞。细胞 80%汇合后将载玻片互换,并加入含0.5μg/ml GCV的培养基,6d后观察细胞形态。结果C6细胞组存在旁观者效应,Heal细胞组不存在旁观者效应。培养皿中tk+细胞大部分被杀死,tk-细胞无变化。结论HSV-tk基因/GCV系统杀伤肿瘤细胞时旁观者效应与细胞间缝隙连接有关。 相似文献
89.
NOTE The Application of Surface Analysis Techniques in the Adhesive Bonding of Oily Automotive Steel
There are fewer papers on the adhesive bonding of steel for structural applications than for aluminum and titanium alloys. However, the approach to the adhesive bonding of all three adherends has been similar, that is, the surfaces are pretreated prior to bonding. Trawinski, et al.1,2,3 reviewed several conversion coatings or etching processes used for steel. Haak and Smith4 selected two surface treatments among nineteen based on minimal cost, simplicity and good durability. Smith5 has reported work on stainless steel-epoxy bonds under hydrothermal stress. Bischof, et al.6 investigated the effect of surface pretreatment of steel on bonding strength obtained with polyvinyl chloride. Ziane, et al.7 identified four fracture zones resulting from shear loading of epoxy bonded galvanized steel following four different surface pretreatments. But in some cases, as in the automotive industry, there is a need to bond oily steel directly without surface pretreatment. Rosty, et al.8 have reported a study of the role of fillers and cure temperature on the shear strength of oily steel bonded with epoxy. None of the reported research utilizes both microscopic and spectroscopic techniques to analyze the fracture surfaces. 相似文献
90.
Kenneth T. Leong James C. Booth J. H. Claassen 《Journal of Superconductivity and Novel Magnetism》2006,19(7-8):637-648
We introduce a novel transmission-line method for determining the penetration depth in thin high-temperature superconducting
(HTS) films. The method is based on the accurate measurement of the inductance per unit length of a superconducting coplanar-waveguide
(CPW) transmission line fabricated on the HTS sample. Using the experimentally obtained inductance per unit length, we interpolate
the penetration depth from a table of numerically determined values of inductance (per unit length) as a function of penetration
depth, calculated from a coupled transmission-line model. A novelty of our procedure is the utilization of the multiline thru-reflect-line
(TRL) method and the calibration-comparison method to accurately determine the inductance per unit length of the superconducting
transmission line. By measuring different CPW geometries patterned onto the same thin-film sample, we can verify our penetration
depth values. We demonstrate this technique by extracting the penetration depth for several different HTS films at 76 K. Estimated
uncertainties in the extracted penetration depth are also provided.
Contribution of an agency of the US government not subject to copyright. 相似文献