全文获取类型
收费全文 | 201658篇 |
免费 | 2402篇 |
国内免费 | 618篇 |
专业分类
电工技术 | 3491篇 |
综合类 | 153篇 |
化学工业 | 29455篇 |
金属工艺 | 8094篇 |
机械仪表 | 6117篇 |
建筑科学 | 4850篇 |
矿业工程 | 1310篇 |
能源动力 | 5182篇 |
轻工业 | 17232篇 |
水利工程 | 2304篇 |
石油天然气 | 4064篇 |
武器工业 | 9篇 |
无线电 | 23244篇 |
一般工业技术 | 40631篇 |
冶金工业 | 37286篇 |
原子能技术 | 5116篇 |
自动化技术 | 16140篇 |
出版年
2021年 | 1703篇 |
2019年 | 1630篇 |
2018年 | 2648篇 |
2017年 | 2713篇 |
2016年 | 2846篇 |
2015年 | 1840篇 |
2014年 | 3176篇 |
2013年 | 9078篇 |
2012年 | 5190篇 |
2011年 | 7212篇 |
2010年 | 5676篇 |
2009年 | 6448篇 |
2008年 | 6537篇 |
2007年 | 6622篇 |
2006年 | 5663篇 |
2005年 | 5295篇 |
2004年 | 5077篇 |
2003年 | 4935篇 |
2002年 | 4593篇 |
2001年 | 4680篇 |
2000年 | 4599篇 |
1999年 | 4749篇 |
1998年 | 11400篇 |
1997年 | 8140篇 |
1996年 | 6416篇 |
1995年 | 4683篇 |
1994年 | 4284篇 |
1993年 | 4083篇 |
1992年 | 3232篇 |
1991年 | 3082篇 |
1990年 | 2875篇 |
1989年 | 2954篇 |
1988年 | 2828篇 |
1987年 | 2402篇 |
1986年 | 2309篇 |
1985年 | 2718篇 |
1984年 | 2506篇 |
1983年 | 2347篇 |
1982年 | 2090篇 |
1981年 | 2203篇 |
1980年 | 2029篇 |
1979年 | 2126篇 |
1978年 | 2121篇 |
1977年 | 2367篇 |
1976年 | 3189篇 |
1975年 | 1833篇 |
1974年 | 1761篇 |
1973年 | 1774篇 |
1972年 | 1444篇 |
1971年 | 1339篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
J Byrne S Kienzle D Johnson G Duke V Gannon B Selinger J Thomas 《Water science and technology》2006,53(10):327-334
Long-term trends in alpine and prairie snow pack accumulation and melt are affecting streamflow within the Oldman River Basin in southern Alberta, Canada. Unchecked rural and urban development also has contributed to changes in water quality, including enhanced microbial populations and increased waterborne pathogen occurrence. In this study we look at changing environment within the Oldman River Basin and its impact on water quality and quantity. The cumulative effects include a decline in net water supplies, and declining quality resulting in increased risk of disease. Our data indicates that decreases in the rate of flow of water can result in sedimentation of bacterial contaminants within the water column. Water for ecosystems, urban consumption, recreation and distribution through irrigation is often drawn from waterholding facilities such as dams and weirs, and concern must be expressed over the potential for contaminate build-up and disproportionate potential of these structures to pose a risk to human and animal health. With disruption of natural flow rates for water resulting from environmental change such as global warming and/or human intervention, increased attention needs to be paid to use of best management practices to protect source water supplies. 相似文献
72.
Physically based simulation of human hair is a well studied and well known problem. But the “pure” physically based representation of hair (and other animation elements) is not the only concern of the animators, who want to “control” the creation and animation phases of the content. This paper describes a sketch-based tool, with which a user can both create hair models with different styling parameters and produce animations of these created hair models using physically and key frame-based techniques. The model creation and animation production tasks are all performed with direct manipulation techniques in real-time. 相似文献
73.
M.G. Pujar N. Parvathavarthini Sidhartha S. Jena B.V.R. Tata R.K. Dayal H.S. Khatak 《Journal of Materials Engineering and Performance》2008,17(6):793-801
In the present work 316LN as well as 316 stainless steel (SS) coupons each of dimensions (0.025 × 0.018 × 0.006 m3) in well-polished condition were used as two nominal electrodes which were immersed in the aerated solution of 0.5 M NaCl.
Correlated current and potential electrochemical noise (EN) signals were collected at 1 Hz sampling frequency for 1 h daily
over a period of 30 days. The detrended EN data were used to calculate the noise resistance (R
N) as well as the spectral noise resistance at zero frequency (R
SNo) values and other statistical parameters. To study the nature of pits and distribution of their diameters as well as depths,
extensive observations of the pitted and the blank specimens were carried out using Confocal Laser Scanning Microscopy (CLSM).
The current and the potential records of the two alloys showed distinct differences in their corrosion behavior. It was observed
that within less than 4 h of immersion, 316SS showed signals indicative of unstable pitting and onset of stable pitting was
noticed after 48 h of exposure. However, until about 24 h, 316LN showed just the random signals and unstable pitting was observed
after 28 h. The signals clearly indicated continuous growth of the stable pits in 316SS as against the repassivation of the
unstable pits in 316LN after 7 days exposure. It was observed that R
N values showed a continuous decrease in the case of 316SS, but were quite stable in the case of 316LN over the exposure period.
Concurrent to these observations it was observed that 316SS specimen was extensively pitted. The frequency distributions of
pit diameters as well pit depths were observed to be highest at 10-20 μm and 5-10 μm, respectively. However, pits with as
large as 70-80 μm diameter and as deep as 20-25 μm too were observed. No pits were observed in case of 316LN even after 30 days
of exposure, an observation that corroborates well with the stable R
N values. Thus, in the present investigation, the long-term tests using EN technique coupled with CLSM studies conclusively
prove that many unstable pits initiated in 316SS turn into stable ones resulting in insidious localized corrosion attack whereas
the unstable pits initiated in 316LN get passivated in the simulated coastal environment. 相似文献
74.
Oxide films were deposited on different substrates by laser molecular beam epitaxy. Reflection high-energy electron diffraction was performed to in situ investigate the change of growth mode and the lattice relaxation during the growth. An asymmetrical phenomenon was found in the two kinds of strain states, compressive stress and tensile stress of heterostructures with different lattice mismatch. In the case of BaTiO3/SrTiO3 (2.2%), 2D layer-by-layer growth mode without lattice relaxation can be maintained for a longer period for BTO films on STO with compressive stress, comparing to STO films on BTO with tensile stress. When MgO films were deposited on SrTiO3 with a large mismatch of 7.8%, compressive stress leads to rapid lattice relaxation with a very thin wet layer, and 3D strained island were observed. As a comparison, SrTiO3 films on MgO with tensile stress were configured. No RHEED patterns can be observed duo to a large tensile stress. 相似文献
75.
Filled fibrous sorbents modified with transition metal ferro- and ferricyanides capable to recover americium(III) and rare-earth metals(III) from nitric acid solutions were prepared. The most complete and rapid recovery is attained on complex-forming and cation-exchange sorbents (as filled fibrous materials) saturated with nickel ions. The sorbents are characterized by good kinetic properties and can be used for recovery of the above metals. 相似文献
76.
A. A. Man’kov Yu. V. Krasovitskii E. V. Arkhangel’skaya S. L. Kabargin D. B. Troshchenko N. N. Lobacheva V. P. Dobrosotskii 《Refractories and Industrial Ceramics》2008,49(3):225-228
Methods are proposed for designing interpolation models for the preliminary determination and subsequent forecasting of general
and fractional breakthrough coefficients for dust used with granular filters, as employed in energy-saving and high-performance
dust trapping from technological gases and ventilation discharges in refractory production. The models are supplied with nomograms,
which makes them widely suitable for experts working in environmental protection at refractory-producing organizations. The
main factors are identified that influence the performance. The results are of interest to experts in related areas of industry
such as building materials and engineering ceramics and so on.
Translated from Novye Ogneupory, No. 4, pp. 64–67, April, 2008. 相似文献
77.
B. L. Krasnyi V. P. Tarasovskii A. B. Krasnyi A. L. Kuteinikova 《Refractories and Industrial Ceramics》2008,49(1):57-62
Results are presented on the corrosion resistance of chromium-bearing refractories of granular structure acted on by corrosive
molten slags, metals, and glasses. It is possible to recommend these refractories to customers for particular conditions of
use. Chromium-bearing refractories increase the working lives of furnaces considerably.
__________
Translated from Novye Ogneupory, No. 1, pp. 55–61, January, 2008. 相似文献
78.
I. A. Zvereva O. I. Silyukov A. V. Markelov A. B. Missyul’ M. V. Chislov I. A. Rodionov D. -Sh. Li 《Glass Physics and Chemistry》2008,34(6):749-755
The processes of phase formation in the Na2CO3-TiO2 and Na2CO3-TiO2-Nd2O3 systems are investigated in the temperature range 600–900°C. The high-temperature solid-phase reactions underlying the process of formation of complex oxide NaNdTiO4 are studied. It is established that the synthesis of the NaNdTiO4 compound occurs through the reaction of the intermediate product Na8Ti5O14 with neodymium oxide in the temperature range 720–780°C. The optimum method is proposed for synthesizing NaNdTiO4, which makes it possible to reduce the temperature of the synthesis, to avoid the formation of impurities, and to obtain the product in a finely dispersed state. 相似文献
79.
Phase transitions are considered for silicon oxycarbide material between joints in hearth blocks under aluminum electrolyzer
operating conditions. It is established that in the electrolyzer there is formation of aluminum subcarbide, and also there
is conversion of silicon carbide polytypes as a result of impurities of aluminum, sodium, magnesium, copper and iron. Due
to phase transitions there is a reduction in joint strength, and therefore it is undesirable to use material based on corundum
and black silicon carbide in hearth joints between blocks for aluminum electrolyzers. Use of pure α-SiO2 free from impurities is recommended for this purpose.
Translated from Novye Ogneupory, No. 4, pp. 47–52, April 2008. 相似文献
80.
Nanosized (2–8 nm) amorphous powders of the solid solution based on zirconia and hafnia are synthesized through back coprecipitation
upon treatment of gels at temperatures from +20 to −77°C. Heat treatment of these powders at temperatures up to 1000 and above
1100°C leads to the formation of cubic (fluorite type, O
h
5 = Fm3m) and tetragonal phases of the Zr82Hf10Y3Ce5O
x
composition, respectively. It is revealed that a decrease in the synthesis temperature (from +20°C to −6°C) results in a
decrease in the size of gel agglomerates from 30 to 1 μm. Recrystallization processes in the gels prepared using cryochemical
treatment are developed very slowly in the temperature range 500–1200°C (the crystallite size does not exceed 25 nm).
Original Russian Text ? T.I. Panova, V.B. Glushkova, A.E. Lapshin, 2008, published in Fizika i Khimiya Stekla. 相似文献