全文获取类型
收费全文 | 19390篇 |
免费 | 2029篇 |
国内免费 | 1611篇 |
专业分类
电工技术 | 1028篇 |
技术理论 | 1篇 |
综合类 | 2369篇 |
化学工业 | 2550篇 |
金属工艺 | 1212篇 |
机械仪表 | 1379篇 |
建筑科学 | 1887篇 |
矿业工程 | 888篇 |
能源动力 | 1023篇 |
轻工业 | 489篇 |
水利工程 | 1395篇 |
石油天然气 | 1926篇 |
武器工业 | 612篇 |
无线电 | 1093篇 |
一般工业技术 | 2769篇 |
冶金工业 | 628篇 |
原子能技术 | 444篇 |
自动化技术 | 1337篇 |
出版年
2024年 | 43篇 |
2023年 | 218篇 |
2022年 | 454篇 |
2021年 | 495篇 |
2020年 | 550篇 |
2019年 | 496篇 |
2018年 | 506篇 |
2017年 | 631篇 |
2016年 | 790篇 |
2015年 | 727篇 |
2014年 | 982篇 |
2013年 | 1343篇 |
2012年 | 1244篇 |
2011年 | 1337篇 |
2010年 | 1033篇 |
2009年 | 1104篇 |
2008年 | 1013篇 |
2007年 | 1286篇 |
2006年 | 1206篇 |
2005年 | 1018篇 |
2004年 | 909篇 |
2003年 | 784篇 |
2002年 | 693篇 |
2001年 | 592篇 |
2000年 | 503篇 |
1999年 | 467篇 |
1998年 | 400篇 |
1997年 | 305篇 |
1996年 | 321篇 |
1995年 | 324篇 |
1994年 | 279篇 |
1993年 | 182篇 |
1992年 | 180篇 |
1991年 | 138篇 |
1990年 | 101篇 |
1989年 | 91篇 |
1988年 | 62篇 |
1987年 | 52篇 |
1986年 | 38篇 |
1985年 | 31篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 19篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1961年 | 2篇 |
1959年 | 14篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
51.
横向各向同性介质中的初至波旅行时计算 总被引:1,自引:0,他引:1
本文直接采用Thomsen导出的横向各向同性介质中的相速度、群角与相角、群速度与相速度的精确函数关系,提出了一种新的具有任意各向异性强度的横向各向同性介质中的初至波旅行时计算方法,它不同于Faria等人给出的采用群速度近似公式(Byun)的仅适应弱各向异性的初至波旅行时计算方法。该新算法在计算具有任意各向异性强度的横向各向同性介质中的初至波旅行时时,并不显著地增大计算时间。分析对比由新算法得到的初至波旅行时的等值线图和由交错网格有限差分波场模拟得到的波场快照表明,无论是对弱各向异性还是对强弱各向异性,新算法都具有较高的精度;随着各向异性强度的增大,新算法的计算结果与采用近似公式计算结果的差值也随之增大。 相似文献
52.
53.
The transit time of the coolant, and thus its velocity, has been measured using the temperature fluctuation at the outlet of a reactor core. An impulse response function estimation is introduced, which substitutes the widely used cross-correlation measurement technique. It is shown in theory and practice that the time delay estimation is improved when using the impulse response function instead of the cross-correlation function in parameter estimation. Extremely low velocities (down to 2 cm/sec) have been measured in a natural circulation regime in a research reactor. 相似文献
54.
《Particulate Science and Technology》2007,25(1):77-89
The removal of particulate contamination is a critical issue for many manufacturing processes. It is particularly critical to the electronics industry in which small pieces of microscopic debris remaining after chemical mechanical planarization (cmp) using submicron polishing particles can cause device failure. One way to enhance particle removal following the cmp process is to utilize surfactants. Recent research has shown ways to model the effect of surfactants on enhanced particle removal. However, previous research has not demonstrated the effect of ionic strength on enhanced particle removal associated with surfactant use. Past research has also not shown the combined effects of ionic strength and surfactant concentration on enhanced particle removal using surfactants. This article summarizes the parameters affecting particle removal, and it provides data and analysis on the effect of ionic strength as well as the combined effects of ionic strength and surfactant concentration on particle removal following cmp processing. 相似文献
55.
Titanium Dioxide, TiO2, is a photocatalyst with a unique characteristic. A surface coated with TiO2 exhibits an extremely high affinity for water when exposed to UV light and the contact angle decreases nearly to zero. Inversely, the contact angle increases when the surface is shielded from UV. This superhydrophilic nature gives a self-cleaning effect to the coated surface and has already been applied to some construction materials, car coatings and so on. We applied this property to the enhancement of boiling heat transfer. An experiment involving the pool boiling of pure water has been performed to make clear the effect of high wettability on heat transfer characteristics. The heat transfer surface is a vertical copper cylinder of 17 mm in diameter and the measurement has been done at saturated temperature and in a steady state. Both TiO2-coated and non-coated surfaces were used for comparison. In the case of the TiO2-coated surface, it is exposed to UV light for a few hours before experiment and it is found that the maximum heat flux (CHF) is about two times larger than that of the uncoated surface. The temperature at minimum heat flux (MHF) for the superhydrophilic surface is higher by 100 K than that for the normal one. The superhydrophilic surface can be an ideal heat transfer surface. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
56.
A vibrating Kelvin probe in form of a platinum wire loop is used to measure the surface potential Us on electron-irradiated free-floating metal and insulator specimens as a function of electron energy E. This allows an accurate measurement of the critical electron energy E2 for no charging. At energies below E2, the positive charging increases with decreasing energy to Us=2–5 eV at E=0.5 keV and switching off the collector bias of the Everhart-Thornley detector. A two-to threefold increase of Us is observed when the bias is switched on. For E > E2, the strong increase of a negative surface potential can be measured. Insulating films free-supported on a conductive substrate show a steep decrease to small positive and negative Us when the film thickness becomes lower than the electron range at a critical energy E3 > E2. At insulating specimen the temporal decrease of charging can be measured when the electron beam is switched off. 相似文献
57.
一种新的含水率校正方法 总被引:2,自引:0,他引:2
从研究流体流动规律出发,结合模拟井实验结果,建立了多参数、非线性的半理论和半实验含水率校正模型,提出了反映两相滑脱效应的滑动比概念,其计算方法物理意义清晰并具有明确的收敛边界。与模拟井实验结果进行对比,使用平方法降低了含水率校正误差。 相似文献
58.
Xu You-heng Dong Li-yun Huang Dong-qun Fudan University Shanghai P. R. China 《水动力学研究与进展(B辑)》1998,(3)
In this paper,the oscillation amplitude of the free end of a group of threecylinders are studied.The three cylinders are erected at the vertices of an equilateral trian-gle,and three arrangements are made in this study.One of the three cylinders is served asa working cylinder which is mounted by a flexible cantilever and two accelerometers areattached on the free end in two directions.The results of the three-cylinder arrangementare compared with those of two cylinders in tandem/side-by-side arrangement in the samecondition.The experimental results show that the rear cylinder of a group of three cylin-ders is affected more seriously than that of the corresponding two cylinders in the contrastarrangement.The main direction of oscillation is changed.The transversal oscillation isstronger than the longitudinal oscillation in the three-cylinder arrangement.On the con-trary,the transversal oscillation is much weaker than the longitudinal oscillation in two-cylinder arrangement.The largest transversal oscillat 相似文献
59.
文章论述了井塔拆除爆破中,把框架承重立柱的裸露钢筋骨架失稳看作为压杆失稳以及井塔在倾斜撞地时下部不解体破坏的估算。 相似文献
60.
本文围绕基因枪技术中用高速微粒向植物细胞中导入外源基因的速度条件,分析了其中的三个动力学过程:发射宏弹、加速微弹、侵入细胞.提出了气动撞击发射式基因枪中弹簧刚度应满足的条件;得到了一种用理论分析与试验测试相结合确定微弹出射速度的方法;找到了微弹侵入植物细胞的最小速度条件。从而为基因枪的设计提供了理论依据。 相似文献