全文获取类型
收费全文 | 1826813篇 |
免费 | 42223篇 |
国内免费 | 16672篇 |
专业分类
电工技术 | 48454篇 |
技术理论 | 28篇 |
综合类 | 21239篇 |
化学工业 | 315568篇 |
金属工艺 | 78904篇 |
机械仪表 | 61561篇 |
建筑科学 | 66212篇 |
矿业工程 | 19735篇 |
能源动力 | 56580篇 |
轻工业 | 139620篇 |
水利工程 | 20020篇 |
石油天然气 | 54513篇 |
武器工业 | 2021篇 |
无线电 | 223656篇 |
一般工业技术 | 326360篇 |
冶金工业 | 212131篇 |
原子能技术 | 36903篇 |
自动化技术 | 202203篇 |
出版年
2022年 | 16932篇 |
2021年 | 24849篇 |
2020年 | 18949篇 |
2019年 | 20549篇 |
2018年 | 25581篇 |
2017年 | 26300篇 |
2016年 | 29482篇 |
2015年 | 26620篇 |
2014年 | 39940篇 |
2013年 | 101122篇 |
2012年 | 53162篇 |
2011年 | 69668篇 |
2010年 | 59922篇 |
2009年 | 66590篇 |
2008年 | 62075篇 |
2007年 | 59915篇 |
2006年 | 59665篇 |
2005年 | 53724篇 |
2004年 | 50688篇 |
2003年 | 49271篇 |
2002年 | 47307篇 |
2001年 | 43575篇 |
2000年 | 42446篇 |
1999年 | 42730篇 |
1998年 | 60797篇 |
1997年 | 50026篇 |
1996年 | 43455篇 |
1995年 | 36490篇 |
1994年 | 33427篇 |
1993年 | 32307篇 |
1992年 | 28264篇 |
1991年 | 25200篇 |
1990年 | 25241篇 |
1989年 | 24180篇 |
1988年 | 22557篇 |
1987年 | 20550篇 |
1986年 | 19869篇 |
1985年 | 23115篇 |
1984年 | 22913篇 |
1983年 | 20844篇 |
1982年 | 19679篇 |
1981年 | 19768篇 |
1980年 | 18385篇 |
1979年 | 18858篇 |
1978年 | 18046篇 |
1977年 | 18279篇 |
1976年 | 20137篇 |
1975年 | 16242篇 |
1974年 | 15731篇 |
1973年 | 15821篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
本文通过径流还原计算和绘制降水径流深相关图的方法,对天然年径流系列的一致性进行了分析,并通过实例验证了该方法可使水文资料系列更具代表性。 相似文献
42.
It was found that vanadyl porphyrin complexes synthesized from petroleum metal porphyrin concentrates stimulated epoxidation during the olefin oxygenation process. The yields of obtained oxiranes turned out to be 38–75%, depending on the olefin structure. An epoxidation mechanism that suggests the formation of a protonated dioxygen adduct as an intermediate during oxygenation of olefins in the presence of vanadyl porphyrin complexes was proposed. An analogy is drawn between the epoxide formation reaction upon the catalytic oxygenation of olefins and the Prilezhaev reaction. 相似文献
43.
Presented here are details of the development of a novel membrane integrated circuit (IC) probe card structure based on microsystems technology. The device design allows probing of both solder bumps and pads. A self-limiting sensor was integrated to prolong device lifetime. Comparison with and discussion of the use of modelling is made. Possible enhancements to the probing structure are discussed to improve alignment and measurements. Also shown is data using our microsystems probe card to access a simple IC device. Our device has a contact resistance of less than 0.5 Ω for a force of 0.004 N. A method to implement our probing structure for commercial application and the potential developments which can be made to improve its ease of use are then discussed. 相似文献
44.
The Magnitogorsk Metallurgical Combine has conducted a study of the effect of technological factors on the hydrogen content
of chromium-nickel-molybdenum steel after vacuum degassing. It was established that the most important factor is the hydrogen
content of the steel before the degassing operation. The study also determined the effects of the circulation coefficient,
the duration of the degassing operation, and the vacuum used in the treatment.
__________
Translated from Metallurg, No. 7, pp. 68–69, July, 2006. 相似文献
45.
Good requirements practices are neither necessary nor sufficient 总被引:2,自引:2,他引:0
46.
Isolating applied mathematics from computer science harms the profession and those who depend on it. 相似文献
47.
Improved homogenization of Ni in sintered steels through the use of Cr-containing prealloyed powders
The homogenization of Ni in powder metal (PM) steel compacts is usually difficult even after high-temperature sintering at
1250°C. An earlier study by the authors demonstrated that this problem can be alleviated through the addition of 0.5 wt pct
Cr in the form of stainless steel powders. To further improve the microstructure and mechanical properties of Ni-containing
PM steels and to understand the mechanisms, an attempt was made in this study using the Fe-3Cr-0.5Mo prealloyed powder as
the base material. The results showed that the distribution of the Ni additives was significantly improved. As a result, the
tensile strength of the Fe-3Cr-0.5Mo-4Ni-0.5C compact sintered at 1250°C reached 1323 MPa. The elongation was higher than
1 pct. These sinter-hardened properties, which were attained using a slow furnace cooling rate, were comparable to those of
the sinter-hardened alloys reported in the literature using accelerated cooling and were equivalent to those of the best quenched-and-tempered
alloys registered in the Metal Powder Industries Federation (MPIF) standards. These improvements were attributed to the positive
effect of Cr addition on alloy homogenization due to the reduction of the repelling effect between Ni and C, as was demonstrated
through the thermodynamic analysis using the Thermo-Calc program. 相似文献
48.
Based on the current spin density functional theory, a theoretical model of three vertically aligned semiconductor quantum dots is proposed and numerically studied. This quantum dot molecule (QDM) model is treated with realistic hard-wall confinement potential and external magnetic field in three-dimensional setting. Using the effective-mass approximation with band nonparabolicity, the many-body Hamiltonian results in a cubic eigenvalue problem from a finite difference discretization. A self-consistent algorithm for solving the Schrödinger-Poisson system by using the Jacobi-Davidson method and GMRES is given to illustrate the Kohn-Sham orbitals and energies of six electrons in the molecule with some magnetic fields. It is shown that the six electrons residing in the central dot at zero magnetic field can be changed to such that each dot contains two electrons with some feasible magnetic field. The Förster-Dexter resonant energy transfer may therefore be generated by two individual QDMs. This may motivate a new paradigm of Fermionic qubits for quantum computing in solid-state systems. 相似文献
49.
Ohne Zusammenfassung 相似文献
50.
K.P. Pipe R.J. Ram 《Photonics Technology Letters, IEEE》2003,15(4):504-506
By measuring the total energy flow from an optical device, we can develop new design strategies for thermal stabilization. Here we present a comprehensive model for heat exchange between a semiconductor laser diode and its environment that includes the mechanisms of conduction, convection, and radiation. We perform quantitative measurements of these processes for several devices, deriving parameters such as a laser's heat transfer coefficient, and then demonstrate the feasibility of thermal probing for the nondestructive wafer-scale characterization of optical devices. 相似文献