全文获取类型
收费全文 | 597356篇 |
免费 | 12434篇 |
国内免费 | 4204篇 |
专业分类
电工技术 | 13417篇 |
技术理论 | 6篇 |
综合类 | 4947篇 |
化学工业 | 91139篇 |
金属工艺 | 23785篇 |
机械仪表 | 19959篇 |
建筑科学 | 17843篇 |
矿业工程 | 4673篇 |
能源动力 | 16692篇 |
轻工业 | 51735篇 |
水利工程 | 6213篇 |
石油天然气 | 14597篇 |
武器工业 | 497篇 |
无线电 | 67334篇 |
一般工业技术 | 110725篇 |
冶金工业 | 107272篇 |
原子能技术 | 11292篇 |
自动化技术 | 51868篇 |
出版年
2022年 | 5250篇 |
2021年 | 7774篇 |
2020年 | 5656篇 |
2019年 | 6491篇 |
2018年 | 10076篇 |
2017年 | 10071篇 |
2016年 | 9971篇 |
2015年 | 8223篇 |
2014年 | 12635篇 |
2013年 | 28196篇 |
2012年 | 18890篇 |
2011年 | 24893篇 |
2010年 | 19896篇 |
2009年 | 21571篇 |
2008年 | 21855篇 |
2007年 | 21417篇 |
2006年 | 19246篇 |
2005年 | 17575篇 |
2004年 | 15838篇 |
2003年 | 15416篇 |
2002年 | 14460篇 |
2001年 | 14419篇 |
2000年 | 13631篇 |
1999年 | 14600篇 |
1998年 | 34520篇 |
1997年 | 24278篇 |
1996年 | 18820篇 |
1995年 | 14197篇 |
1994年 | 12221篇 |
1993年 | 11665篇 |
1992年 | 8440篇 |
1991年 | 7840篇 |
1990年 | 7569篇 |
1989年 | 7253篇 |
1988年 | 6684篇 |
1987年 | 5902篇 |
1986年 | 5773篇 |
1985年 | 6357篇 |
1984年 | 5960篇 |
1983年 | 5209篇 |
1982年 | 4941篇 |
1981年 | 4992篇 |
1980年 | 4728篇 |
1979年 | 4620篇 |
1978年 | 4411篇 |
1977年 | 5338篇 |
1976年 | 6979篇 |
1975年 | 3800篇 |
1974年 | 3552篇 |
1973年 | 3665篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
V. B. Baiburin Yu. P. Volkov E. M. Il’in S. V. Semenov 《Technical Physics Letters》2002,28(12):981-982
The surface of a palladium-barium cathode was studied using scanning probe microscopy techniques. Data from the tunneling spectroscopy showed the pattern of the electron work function distribution over a microscopic region on the emitter surface. This pattern is compared to the distribution of various phases in the palladium-barium alloy employed. 相似文献
952.
Tour J.M. Van Zandt W.L. Husband C.P. Husband S.M. Wilson L.S. Franzon P.D. Nackashi D.P. 《Nanotechnology, IEEE Transactions on》2002,1(2):100-109
Molecular electronics seeks to build electrical devices to implement computation - logic and memory - using individual or small collections of molecules. These devices have the potential to reduce device size and fabrication costs, by several orders of magnitude, relative to conventional CMOS. However, the construction of a practical molecular computer will require the molecular switches and their related interconnect technologies to behave as large-scale diverse logic, with input/output wires scaled to molecular dimensions. It is unclear whether it is necessary or even. possible to control the precise regular placement and interconnection of these diminutive molecular systems. This paper describes genetic algorithm-based simulations of molecular device structures in a nanocell where placement and connectivity of the internal molecular switches are not specifically directed and the internal topology is generally disordered. With some simplifying assumptions, these results show that it is possible to use easily fabricated nanocells as logic devices by setting the internal molecular switch states after the topological molecular assembly is complete. Simulated logic devices include an inverter, a NAND gate, an XOR gate and a 1-bit adder. Issues of defect and fault tolerance are addressed. 相似文献
953.
Cluster analysis in industrial market segmentation through artificial neural network 总被引:6,自引:0,他引:6
Market segmentation has commonly applied cluster analysis. This study intends to make the comparison of conventional two-stage method with proposed two-stage method through the simulated data. The proposed two-stage method is the combination of self-organizing feature maps and K-means method. The simulation results show that the proposed scheme is better than the conventional two-stage method based on the rate of misclassification. 相似文献
954.
N. M. Markovich 《Automation and Remote Control》2002,63(4):627-640
Nonparametric estimation of the density of a heavy-tailed probability distribution is investigated. The initial data are transformed to a bounded interval and the distribution density is determined by an inverse transformation of the distribution density estimate of transformed data. An adaptive data transformation is studied, in which the order of decay of the tail of the true distribution density is preserved and stable estimation of the deviation in tail index estimates is guaranteed. In classification, the empirical risk of erroneous classification by the Bayes empirical classifier is used as a measure for the quality of distribution density estimates. 相似文献
955.
956.
H.U. Khan K.M. Agrawal M. Anwar S.P. Nautiyal B.S. Rawat 《Petroleum Science and Technology》1998,16(1):145-166
Lubricating oil base stocks differ greatly in their chemical composition and consequently in their physical properties and applications. Influence of waxes and various hydrocarbon type constituents viz saturates and aromatic components on the viscosity and shear stress as a function of temperature in different lube oil base stocks has been studied in the present paper. 相似文献
957.
Under a set of broadly justified simplifying assumptions, an analytical approach to the problem of cross phase modulation in optical fibers is presented. Simple analytical expressions describing intensity interference caused by cross-phase modulation (XPM) are derived. It turns out that within a physically realizable range of parameters the power penalties induced by XPM have a linear dependence on the power of the interfering signal. Examples of specific systems are presented and discussed 相似文献
958.
聚六亚甲基碳酸酯二醇增韧环氧树脂的结构与性能 总被引:6,自引:0,他引:6
采用羟基封端的脂肪族碳酸酯-聚六亚甲基碳酸酯二醇对环氧树脂进行了增韧,通过扫描隧道显微镜,扫描电子显微镜,差示扫描量热分析以及动态力学性能分析等方法研究了增韧EP的结构与性能的关系。 相似文献
959.
In reference to the above-titled paper by R.A. DeMillo and A.J. Offutt (see ibid., vol.17, no.9, p.900-10, Sept. 1991), the commenter rates that he and M.R. Woodward (1985) implemented a system for FORTRAN-77 programs that integrates weak mutation and data flow analysis. He reports here that experiments have been carried out by them (1986), using the system to compare the error exposing ability of weak mutation, data flow, and control flow testing strategies 相似文献
960.
The paper presents a review of results concerning the aspartic proteinase cathepsin D and its role in tumor invasion and metastasis. Special attention was paid to the clinical prognostic value of cathepsin D determination in the breast cancer cytosol. 相似文献