全文获取类型
收费全文 | 468900篇 |
免费 | 4033篇 |
国内免费 | 930篇 |
专业分类
电工技术 | 8581篇 |
综合类 | 289篇 |
化学工业 | 68125篇 |
金属工艺 | 25633篇 |
机械仪表 | 17307篇 |
建筑科学 | 8797篇 |
矿业工程 | 4597篇 |
能源动力 | 8721篇 |
轻工业 | 24015篇 |
水利工程 | 6233篇 |
石油天然气 | 14918篇 |
武器工业 | 35篇 |
无线电 | 49327篇 |
一般工业技术 | 106526篇 |
冶金工业 | 77695篇 |
原子能技术 | 14257篇 |
自动化技术 | 38807篇 |
出版年
2021年 | 3764篇 |
2019年 | 3746篇 |
2018年 | 12252篇 |
2017年 | 12628篇 |
2016年 | 10934篇 |
2015年 | 4606篇 |
2014年 | 7516篇 |
2013年 | 17134篇 |
2012年 | 12651篇 |
2011年 | 19245篇 |
2010年 | 16526篇 |
2009年 | 16908篇 |
2008年 | 17700篇 |
2007年 | 18701篇 |
2006年 | 11363篇 |
2005年 | 12220篇 |
2004年 | 11446篇 |
2003年 | 11035篇 |
2002年 | 10046篇 |
2001年 | 9777篇 |
2000年 | 9484篇 |
1999年 | 9260篇 |
1998年 | 22154篇 |
1997年 | 15571篇 |
1996年 | 11924篇 |
1995年 | 9094篇 |
1994年 | 8145篇 |
1993年 | 8290篇 |
1992年 | 6286篇 |
1991年 | 6244篇 |
1990年 | 6325篇 |
1989年 | 6041篇 |
1988年 | 5684篇 |
1987年 | 5157篇 |
1986年 | 5128篇 |
1985年 | 5570篇 |
1984年 | 5227篇 |
1983年 | 4882篇 |
1982年 | 4599篇 |
1981年 | 4781篇 |
1980年 | 4561篇 |
1979年 | 4657篇 |
1978年 | 4845篇 |
1977年 | 5157篇 |
1976年 | 6329篇 |
1975年 | 4346篇 |
1974年 | 4381篇 |
1973年 | 4384篇 |
1972年 | 3849篇 |
1971年 | 3481篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
M. M. Stadnyk 《Materials Science》2007,43(6):764-768
We deduce the theoretical formula taking into account the influence of biaxial loading of a plate weakened by a crack on the
stress intensity factor K
I. This enables us to compute the characteristic of crack resistance K
c according to the known boundary forces.
__________
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 6, pp. 14–16, November–December, 2007. 相似文献
992.
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
993.
The paper describes an experimental investigation of the diamond-like carbon deposition process from methane precursor with an innovative high-density inductively coupled plasma source. It appears that a high plasma density allows a fast growth of diamond-like carbon coatings exhibiting a high hardness. In contrast to what is usually found in the literature, it seems that the ion species participate significantly to the growth of the carbon film when exposed to a high ion flux. 相似文献
994.
Ya. O. Shablovskii 《Inorganic Materials》2007,43(12):1345-1349
The pyroelectric properties of lithium sulfate have been studied theoretically on the hypothesis of a pseudosymmetry of the structure of its polar phase. Analytical expressions are proposed for the temperature dependences of its pyroelectric polarization and pyroelectric coefficient at low temperatures and near the polymorphic transformation. The pyroelectric and piezoelectric coefficients of a polar crystal are shown to be in direct proportion. 相似文献
995.
M. V. Zagidullin V. D. Nikolaev M. I. Svistun N. A. Khvatov 《Journal of Engineering Physics and Thermophysics》2007,80(3):555-562
The results of parametric tests of a centrifugal bubble singlet-oxygen generator based on the reaction of chlorine with an
alkaline hydrogen peroxide solution have been given. The utilization of chlorine grows with bubble-layer height, whereas the
relative content of O2(1Δ) remains constant. Growth in centrifugal acceleration leads to a more efficient utilization of chlorine. A specific oxygen
output of more than 1 mmole·cm−2·sec−1 from the bubble layer for a degree of chlorine utilization of ∼95% and a singlet-oxygen yield of more than 50% has been attained.
It has been shown that a centrifugal bubble singlet-oxygen generator is an efficient energy source for an oxygen-iodine laser.
__________
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 3, pp. 121–128, May–June, 2007. 相似文献
996.
Unit commitment (UC) of a large system is a complex puzzle with integer/continuous variables and numerous inter-temporal constraints. After deregulation, price offers submitted by GenCos are predominantly in the form of linear price quantity (PQ) pairs. A fuzzy UC formulation that uses price offers modeled as PQ pairs. This fuzzy linear optimisation formulation of UC is solved using a mixed integer linear programming (MILP) routine. In this formulation, start up cost is modelled using linear variables. The fuzzy formulation provides modeling flexibility, relaxation in constraint enforcement and allows the method to seek a practical solution. The use of MILP technique makes the proposed solution method rigorous and fast. The method is tested on a 24 h, 104-generator system demonstrating its speed and robustness gained by using the LP technique. A five-generator system is additionally used to create a see-through example demonstrating advantages of using the fuzzy optimisation model. 相似文献
997.
M. V. Yurkov 《Atomic Energy》2003,94(2):108-112
The program for developing free-electron x-ray lasers at TESLA started in 1994. The plan is to use the TESLA test accelerator to develop an x-ray laser with minimum wavelength 0.1–6 nm. The first phase of the project was successfully completed in 2001. At saturation, the laser produces ultrashort 30–100 fsec, gigawatt, radiation pulses. The wavelength can be tuned smoothly over the range 80–120 nm. 相似文献
998.
Kubat M. Hafez A. Raghavan V.V. Lekkala J.R. Wei Kian Chen 《Knowledge and Data Engineering, IEEE Transactions on》2003,15(6):1522-1534
Association mining techniques search for groups of frequently co-occurring items in a market-basket type of data and turn these groups into business-oriented rules. Previous research has focused predominantly on how to obtain exhaustive lists of such associations. However, users often prefer a quick response to targeted queries. For instance, they may want to learn about the buying habits of customers that frequently purchase cereals and fruits. To expedite the processing of such queries, we propose an approach that converts the market-basket database into an itemset tree. Experiments indicate that the targeted queries are answered in a time that is roughly linear in the number of market baskets, N. Also, the construction of the itemset tree has O(N) space and time requirements. Some useful theoretical properties are proven. 相似文献
999.
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
1000.
Awareness of the construction environment can be improved by automatic three-dimensional (3D) sensing and modeling of job sites in real time. Commercially available 3D modeling approaches based on range scanning techniques are capable of modeling static objects only, and thus cannot model dynamic objects in real time in an environment comprised of moving humans, equipment, and materials. Emerging prototype video range cameras offer an alternative by facilitating affordable, wide field of view, dynamic object tracking at frame rates better than 1?Hz (real time). This paper describes a methodology to model, detect, and track the position of static and moving objects in real time, based on data obtained from video range cameras. Experiments with this technology have produced results that indicate that video rate 3D data acquisition and analysis of construction environments can support effective modeling, detection, and tracking of project resources. This approach to job site awareness has inherent value and broad application. In combination with effective management practices and other sensing techniques, this technology has the potential to significantly improve safety on construction job sites. 相似文献