全文获取类型
收费全文 | 3304篇 |
免费 | 201篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 25篇 |
综合类 | 3篇 |
化学工业 | 694篇 |
金属工艺 | 38篇 |
机械仪表 | 42篇 |
建筑科学 | 267篇 |
矿业工程 | 2篇 |
能源动力 | 171篇 |
轻工业 | 728篇 |
水利工程 | 23篇 |
石油天然气 | 8篇 |
无线电 | 141篇 |
一般工业技术 | 608篇 |
冶金工业 | 229篇 |
原子能技术 | 16篇 |
自动化技术 | 514篇 |
出版年
2023年 | 28篇 |
2022年 | 20篇 |
2021年 | 47篇 |
2020年 | 44篇 |
2019年 | 61篇 |
2018年 | 124篇 |
2017年 | 118篇 |
2016年 | 112篇 |
2015年 | 109篇 |
2014年 | 122篇 |
2013年 | 227篇 |
2012年 | 166篇 |
2011年 | 224篇 |
2010年 | 167篇 |
2009年 | 131篇 |
2008年 | 166篇 |
2007年 | 174篇 |
2006年 | 179篇 |
2005年 | 108篇 |
2004年 | 94篇 |
2003年 | 120篇 |
2002年 | 95篇 |
2001年 | 75篇 |
2000年 | 70篇 |
1999年 | 67篇 |
1998年 | 116篇 |
1997年 | 68篇 |
1996年 | 46篇 |
1995年 | 42篇 |
1994年 | 40篇 |
1993年 | 32篇 |
1992年 | 18篇 |
1991年 | 18篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 22篇 |
1984年 | 28篇 |
1983年 | 23篇 |
1982年 | 15篇 |
1981年 | 20篇 |
1980年 | 22篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 8篇 |
1974年 | 12篇 |
1973年 | 13篇 |
排序方式: 共有3509条查询结果,搜索用时 953 毫秒
11.
Intensive fertilizer use has led to nitrate contamination of groundwater in many areas. This article examines the possibility of removing nitrates through the construction of artificial wetlands. A pilot study conducted in Denmark has found that the method is effective and economical, at least for small waterworks, though further treatment is necessary before an acceptable microbiological water quality is attained. 相似文献
12.
Summary Small oscillations of a rotating elasticum with a mass at the free end are investigated with Poincaré-Lindstedt series. It is shown that the mass moves on a figure-eight shaped curve in a direction determined by the sign of the angular velocity and hence that the Coriolis force influences the motion. 相似文献
13.
The paper describes a new boundary-layer wind tunnel at the Danish Maritime Institute in Lyngby. The wind tunnel is of the open-circuit type and is integrated into a building raised for the purpose. The design was constrained by the need to provide a simulation of the atmospheric boundary layer (without thermal stratification) and alternatively a uniform flow without excessive turbulence.The wind tunnel has a working section of principal dimensions: length 20.8 m, width 2.6 m and height 1.8 m (adjustable from 1.8 to 2.3 m). The maximum wind speed in the working section when empty is about 26 m s?1.Data acquisition, analysis and instrumentation in relation to the new wind tunnel are discussed and, finally, an example of a simulated natural wind is presented. 相似文献
14.
K. Lefmann B. Lake G. Aeppli S.-W. Cheong N. B. Christensen K. N. Clausen S. Hayden T. E. Mason D.F. McMorrow H. A. Mook H. M. Rønnow H. Takagi 《Journal of Low Temperature Physics》2004,135(5-6):621-664
One important area of modern condensed matter research is the investigation of the nature of the superconducting cuprates. Much progress in this field has been obtained with the technique of neutron scattering. We here present a review of neutron scattering studies of the high-temperature superconductor La2?xSrxCuO4, performed at Risø National Laboratory. We review the work on the mapping of the incommensurate spin fluctuations, the investigation of the gap in the fluctuation spectrum, the magnetic properties of the vortices appearing in an applied field, and the quantum critical behaviour of the system. We discuss our findings in the light of results of neutron scattering from other groups, on other cuprate systems, and results from other experimental methods, e.g. NMR, μSR, STM, X-ray diffraction, and ARPES. We end with a discussion on the implications of the experimental results for the progress in the general understanding of high-temperature superconductivity. PACS numbers: 61.12.Ex, 74.20.Mn, 74.72.Dn, 75.25.+z, 78.70.Nx. 相似文献
15.
In large structures it is often necessary to estimate the reliability of the system by use of parallel systems. Optimality criteria-based algorithms for calculation of the joint design point in a parallel system are described and efficient active set strategies are developed. Three possible algorithms are tested in two examples against well-known general non-linear optimization algorithms. Especially one of the suggested algorithms seems to be stable and fast. 相似文献
16.
Two different generators for ozone were tested, a traditional electrical discharge generator and a generator based upon UV–irradiation of air at 150–180 nm. It was demonstrated that the traditional generator gave slightly higher reductions in levels of color for equivalent ozone dosages. Both gases affected the molecular weight distribution in the way that the bigger molecules were broken down to smaller ones. No significant difference between the molecular weight reduction efficiency of the gases was found. 相似文献
17.
Summary
We report the synthesis of some new backbone fluorinated
polymers of the poly(phenylenevinylene) type. The new polymers
were characterised by NMR, SEC and X-ray powder diffraction. The
charge carrier mobilities were determined using pulse radiolysis
time resolved microwave conductivity (PR-TRMC) and the carrier
mobilities were compared to the similar non-fluorinated
analogues. The changes in charge carrier mobilities as a
function of molecular substitution pattern is discussed in terms
of other materials properties such as electronic structure and
absorption properties. The major result is that it was found
possible for this type of material to alter the electronic
energy levels by molecular substitution without imparting
significant changes in the magnitude of the charge carrier
mobilities and the optical properties. 相似文献
18.
It is well known that horizontal surfaces of high strength concrete (HSC) are susceptible to cracking in the time before and
during setting. It appears that there are two critical time periods for such cracking: An early period ranging from placing
to an hour or two, and a late period that covers the setting time and early hardening. The latter is considered here. In this
period, the cracking risk may be assessed from the ratio between strain (the volume change) and tensile strain capacity, or
from the ratio between stress generated from the volume change at restraint, and the tensile strength. All these parameters
were measured. It is shown that relatively moderate volume changes of HSC-surfaces caused by drying plus cooling, generate
restraining stress that may exceed the tensile strength, and thus, generate failure. The results indicate that crack risk
assessment from stress/strength is more reliable than using strain/strain capacity. The starting point of tensile strength
evolution of hardened concrete seems to coincide fairly well with the initial setting time. Also, the tensile strain capacity
reaches a low level at this point, but continues descending for another hour or more. 相似文献
19.
An executable subset of VDM-SL in an SA/RT framework 总被引:2,自引:2,他引:0
In this article we present the executable specification language IPTES Meta-IV based on the formal specification language VDM-SL. The language has been fitted to work in an SA/RT framework and the article presents how it supports the specification of the data transformation part of SA/RT. Furthermore we present some of the advanced constructs of the language seen as an executable specification language in its own right. Finally we present how an IPTES Meta-IV interpreter is used in combination with a high-level timed Petri net executor to execute SA/RT models. 相似文献
20.
A. K. Dahle P. A. Tøndel C. J. Paradies L. Arnberg 《Metallurgical and Materials Transactions A》1996,27(8):2305-2313
The effect of grain refinement on the fluidity of AlSi7Mg and AlSi11Mg has been investigated by spiral tests. Two different
types of grain refiners have been evaluated. An AlTi5Bl master alloy was added to different Ti contents. Since the commercial
alloys had a high initial content of titanium, model alloys were made to investigate the fluidity at low grain refiner additions.
Commercial alloys grain refined only by boron additions have also been investigated. The results from the fluidity measurements
have been verified by measuring the dendrite coherency point of the different cast alloys. Although different, the two methods
show similar trends. The spirals from each fraction grain refiner cast were subsequently investigated metallographically at
the tip of the spirals and at a reference point a distance behind, but no obvious difference in structure was observed. For
both alloys, an increase in fluidity is observed as the content of grain refiner increases above 0.12 pct Ti, while the fluidity
is impaired with increased grain refinement below 0.12 pct Ti. The alloys grain refined with ~0.015 pct B show the highest
fraction solid at dendrite coherency, the smallest grain size, and the best fluidity. 相似文献