全文获取类型
收费全文 | 30762篇 |
免费 | 2882篇 |
国内免费 | 1526篇 |
专业分类
电工技术 | 2053篇 |
技术理论 | 2篇 |
综合类 | 2108篇 |
化学工业 | 4972篇 |
金属工艺 | 1522篇 |
机械仪表 | 2056篇 |
建筑科学 | 3075篇 |
矿业工程 | 850篇 |
能源动力 | 890篇 |
轻工业 | 2497篇 |
水利工程 | 543篇 |
石油天然气 | 1397篇 |
武器工业 | 234篇 |
无线电 | 3715篇 |
一般工业技术 | 3548篇 |
冶金工业 | 1212篇 |
原子能技术 | 441篇 |
自动化技术 | 4055篇 |
出版年
2024年 | 152篇 |
2023年 | 577篇 |
2022年 | 1065篇 |
2021年 | 1466篇 |
2020年 | 1059篇 |
2019年 | 869篇 |
2018年 | 941篇 |
2017年 | 1047篇 |
2016年 | 985篇 |
2015年 | 1221篇 |
2014年 | 1576篇 |
2013年 | 1820篇 |
2012年 | 2051篇 |
2011年 | 2190篇 |
2010年 | 2046篇 |
2009年 | 1911篇 |
2008年 | 1752篇 |
2007年 | 1660篇 |
2006年 | 1599篇 |
2005年 | 1348篇 |
2004年 | 901篇 |
2003年 | 846篇 |
2002年 | 827篇 |
2001年 | 748篇 |
2000年 | 677篇 |
1999年 | 709篇 |
1998年 | 497篇 |
1997年 | 475篇 |
1996年 | 471篇 |
1995年 | 374篇 |
1994年 | 316篇 |
1993年 | 210篇 |
1992年 | 162篇 |
1991年 | 114篇 |
1990年 | 84篇 |
1989年 | 82篇 |
1988年 | 63篇 |
1987年 | 44篇 |
1986年 | 36篇 |
1985年 | 24篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1977年 | 4篇 |
1962年 | 42篇 |
1961年 | 39篇 |
1960年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
A semi-Markov model is constructed that describes an arbitrarily structured multicomponent technological system and takes
into account its calendar maintenance. Using an aggregation algorithm, approximate values of stationary reliability characteristics
and an optimal term of maintenance work are determined for the system.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 69–86, March–April 2006. 相似文献
112.
113.
采用隔壁精馏塔分离苯-甲苯-对二甲苯物系,用Aspen Plus软件模拟了隔壁精馏塔内温度分布及液相组成分布,考察了汽相和液相分配比对产品纯度的影响。对隔壁精馏塔模拟得到的优化操作条件为:隔壁精馏塔的理论板数为30块,侧线采出在第14块理论板,进料段为15块理论板,在进料段的第7块理论板进料,进料组成n(苯)∶n(甲苯)∶n(对二甲苯)为1∶3∶1,回流比为8.8,液相分配比为2.96,汽相分配比为0.83。在此条件下,各组分的摩尔分数大于98.5%,与实验结果基本吻合。当进料组成n(苯)∶n(甲苯)∶n(对二甲苯)为1∶3∶1时,采用隔壁精馏塔可比常规两塔流程节能27.18%。 相似文献
114.
Ye Yuan Yanfang Li Cameron B.D. Relue P. 《IEEE journal of selected topics in quantum electronics》2007,13(6):1671-1679
In this study, we wanted to see if fluorescence anisotropy could be used to detect changes in metabolism in cells with significant light scattering and absorption properties. Fluorescence anisotropy measurements of nicotinamide adenine dinucleotide (NADH) were performed with human melanocytes and melanoma cell lines. To demonstrate the feasibility of using fluorescence anisotropy for detecting metabolic changes, the electron transport chain was blocked using rotenone, inducing an accumulation of intracellular NADH. Total fluorescence increased in all cells as a result of rotenone treatment. Fluorescence anisotropy decreased in the rotenone-treated cells relative to the controls, suggesting an increased ratio of free to protein-bound NADH in the treated cells. In general, the fluorescence anisotropy of the melanocytes was significantly higher than that of the melanoma cell lines. Reflectance spectroscopy showed that the differences in fluorescence anisotropy between the cell types were not due to differences in scattering and absorption properties. Intrinsic cellular NADH fluorescence was experimentally extracted by ratioing polarized fluorescence to polarized reflectance. NADH binding, measured as the ratio of fluorescence intensity at 430 and 465 nm, showed more protein-bound NADH in the melanocytes than in the melanoma cells, consistent with the fluorescence anisotropy measurements. 相似文献
115.
116.
Understanding how the structure of the unit-cell affects the cryogenic performance of a Si power Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is an important step toward optimizing of the device for cryogenic operations. In this paper, numerical simulations of the Si power Double Diffused MOSFET’ (DMOS) are performed at room temperature and cryogenic temperatures. Physically based models for temperature dependent silicon properties are employed in the simulations. The performances of power DMOS’ with various unit-cell structures are compared at both room temperature and low temperatures. The effect of the cell structure on the on-resistance and breakdown voltage of the device are analyzed. The simulation results suggest that the device optimized for room temperature operation can be further optimized at cryogenic temperatures. 相似文献
117.
This paper presents a new method for the direct and accurate evaluation of strongly singular integrals in the sense of Cauchy principal values and weakly singular integrals over quadratic boundary elements in three-dimensional stress analysis and quadratic internal cells in two-dimensional elastoplastic analysis by the boundary element method. A quadratic triangle polar co-ordinate transformation technique is applied to reduce the order of singularity of the singular integrals. Next, a form of Stokes' theorem is introduced in order to remove the singularity in the Cauchy principal value integrals; therefore, the evaluation of these integrals can be carried out by standard Gaussian quadrature. Numerical examples of 2-D elastoplastic problems and a 3-D elastic problem show the effectiveness and efficiency of the method. 相似文献
118.
119.
A coupled-mode equation for anisotropic waveguide systems of arbitrary cross section and general dielectric distribution is derived. Numerical results comparing the exact calculations to those of the method of Hardy et al. (Opt. Lett., vol.11, 742-4, 1986) show that the same accuracy can be obtained not only for TE, but also for TM mode coupling in the case of anisotropic waveguides, and the improved coupled-mode theory is applicable to the situation when moderately strong coupling occurs under the condition where the edge-to-edge separation of two coupled guides D 2 is about 0.1 μm 相似文献
120.