全文获取类型
收费全文 | 132386篇 |
免费 | 5296篇 |
国内免费 | 2532篇 |
专业分类
电工技术 | 3594篇 |
技术理论 | 7篇 |
综合类 | 5450篇 |
化学工业 | 19656篇 |
金属工艺 | 7616篇 |
机械仪表 | 6121篇 |
建筑科学 | 5665篇 |
矿业工程 | 2145篇 |
能源动力 | 2623篇 |
轻工业 | 6647篇 |
水利工程 | 2028篇 |
石油天然气 | 3479篇 |
武器工业 | 463篇 |
无线电 | 14976篇 |
一般工业技术 | 22381篇 |
冶金工业 | 5054篇 |
原子能技术 | 934篇 |
自动化技术 | 31375篇 |
出版年
2024年 | 260篇 |
2023年 | 920篇 |
2022年 | 1537篇 |
2021年 | 2175篇 |
2020年 | 1646篇 |
2019年 | 1354篇 |
2018年 | 15733篇 |
2017年 | 14936篇 |
2016年 | 11365篇 |
2015年 | 2643篇 |
2014年 | 2865篇 |
2013年 | 3356篇 |
2012年 | 6403篇 |
2011年 | 12816篇 |
2010年 | 11166篇 |
2009年 | 8332篇 |
2008年 | 9508篇 |
2007年 | 10353篇 |
2006年 | 2700篇 |
2005年 | 3408篇 |
2004年 | 2666篇 |
2003年 | 2501篇 |
2002年 | 1859篇 |
2001年 | 1254篇 |
2000年 | 1330篇 |
1999年 | 1211篇 |
1998年 | 1014篇 |
1997年 | 846篇 |
1996年 | 807篇 |
1995年 | 595篇 |
1994年 | 506篇 |
1993年 | 339篇 |
1992年 | 279篇 |
1991年 | 225篇 |
1990年 | 175篇 |
1989年 | 136篇 |
1988年 | 120篇 |
1987年 | 59篇 |
1986年 | 63篇 |
1985年 | 34篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1959年 | 37篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
A fully-dense Cu-75 vol pct ZrW2O8 metal matrix composite was fabricated by hot isostatic pressing of Cu-coated ZrW2O8 particles. A small amount of the high-pressure γ-ZrW2O8 phase was created during the cooldown and depressurization following densification; near complete transformation to γ-ZrW2O8 was achieved by subsequent cold isostatic pressing. The thermal expansion behavior of the composite between 25°C and 325°C
was altered by the cold isostatic pressing treatment, and also depended on the length of time that had passed between thermal
cycles. The measured thermal expansion coefficients within specific temperature ranges varied from −6·10−6 K−1 to far above the thermal expansion coefficient of the copper matrix. The complex temperature-dependent expansion/contraction
behavior could be justified by considering the evolution of phase transformations taking place in the ZrW2O8 phase, which were observed by in-situ synchrotron X-ray diffraction measurements. 相似文献
132.
Myung-Sun Baek Hyung-Joon Kook Mi-Jeong Kim Young-Hwan You Hyoung-Kyu Song 《Broadcasting, IEEE Transactions on》2005,51(4):551-559
In this paper, we apply multi-antenna scheme to DAB system for high-rate transmission. In the MIMO-DAB system with a number of transmitting and receiving antennas increases the transmission rate efficiently with low multiplication operations. For channel estimation in the MIMO-DAB system, we propose a new PRS structure and evaluate the channel estimation performance. The proposed PRS structure can estimate multi-channel information based on the semi-blind processing. The performance of proposed PRS is compared with that of conventional training sequence employing Tarokh's transmission matrix. And also we investigate the performance limitation due to the imperfect channel estimation in a MIMO-DAB receiver. It has been shown that the MIMO-DAB system with multi-antennas can achieve the high-rate transmission for multimedia broadcasting and the performance of MIMO-DAB system is impaired by imperfect channel information. 相似文献
133.
This paper considers the axisymmetric steady flow driven by exact counter rotation of two co-axial disks of finite radius.
At the edges of the rotating disks one of three conditions is (typically) imposed: (i) zero velocity, corresponding to a stationary,
impermeable, cylindrical shroud (ii) zero normal velocity and zero tangential fluid traction, corresponding to a (confined)
free surface and (iii) an edge constraint that is consistent with a similarity solution of von Kármán form. The similarity
solution is valid in an infinite geometry and possesses a pitchfork bifurcation that breaks the midplane symmetry at a critical
Reynolds number. In this paper, similar bifurcations of the global (finite-domain) flow are sought and comparisons are made
between the resulting bifurcation structure and that found for the similarity solution. The aim is to assess the validity
of the nonlinear similarity solutions in finite domains and to explore the sensitivity of the solution structure to edge conditions
that are implicitly neglected when assuming a self-similar flow. It is found that, whilst the symmetric similarity solution
can be quantitatively useful for a range of boundary conditions, the bifurcated structure of the finite-domain flow is rather
different for each boundary condition and bears little resemblance to the self-similar flow. 相似文献
134.
市场经济带给企业的是:或是在竞争中被淘汰,或是在竞争中获得发展。这足企业科技实力的竞争,人力资源优势、物力资源优势的竞争。当我们还正在逐渐适应市场经济化的企业发展氛围时,国际市场经济竞争的硝烟已占据我们周围的一切环境。这一切促使每个企业要获得发展,就要锻造自身的能力、素质与品质,增强竞争优势,挖掘培植发展潜力,做大、做强,由内向型企业向外向型企业发展,由国内化的企业走向国际化的跨国企业。国内、国际的煤炭行业的竞争也 相似文献
135.
Solidification time and heat treatment are known to have a large effect on the microstructure of cast aluminum alloys. This
study was conducted to quantify how the fatigue properties of a 319-type aluminum alloy are affected by solidification time
and heat treatment. Both porosity-containing (non-hot isostatically pressed (HIP)) and porosity-free (HIP) samples in the
T6 (“peak aged”) or T7 (“overaged”) heattreated conditions were tested. As the solidification time increased, the average
initiating pore diameter increased and stress-controlled fatigue life decreased. Heat treatment was observed to have a large
effect on fatigue properties of the HIP samples. However, in the non-HIP fatigue samples, heat treatment did not significantly
change the fatigue life or fatigue strength of the cast 319-type alloy. The absence of an influence of heat treatment on fatigue
response is attributed to the predominance of the microporosity in fatigue crack initiation in cast aluminum. 相似文献
136.
Nicolas Clauvelin Basile Audoly Sébastien Neukirch 《Scientific Modeling and Simulation》2007,14(1):95-101
The DNA molecule is modeled as an elastic rod with bending and twisting rigidities, subjected to external tension and twist applied at one end, the other end being clamped. We study the plectonemic equilibrium of such a rod, taking into account the impenetrability constraint. Numerical solutions of this boundary value problem have previously shown that purely elastic models can reproduce the supercoiling response of the DNA molecule. Using a variational approach, we derive analytical formulae for the elastic response of the filament, and extend former numerical results. 相似文献
137.
138.
139.
140.
We show new upper bounds for problems in the W-hierarchy of fixed-parameter complexity. A crucial ingredient of our proofs
is an extension to the W-RAM model, which permits more-powerful operations but remains equivalent to the original. We use
the extended model to give new upper bounds for Subsetsum, Maximum Irredundant Set, and various problems concerning intersection
of finite-state machines. 相似文献