全文获取类型
收费全文 | 13482篇 |
免费 | 414篇 |
国内免费 | 64篇 |
专业分类
电工技术 | 277篇 |
综合类 | 16篇 |
化学工业 | 2343篇 |
金属工艺 | 382篇 |
机械仪表 | 382篇 |
建筑科学 | 239篇 |
矿业工程 | 74篇 |
能源动力 | 722篇 |
轻工业 | 1237篇 |
水利工程 | 196篇 |
石油天然气 | 85篇 |
无线电 | 1709篇 |
一般工业技术 | 2932篇 |
冶金工业 | 1625篇 |
原子能技术 | 199篇 |
自动化技术 | 1542篇 |
出版年
2024年 | 39篇 |
2023年 | 185篇 |
2022年 | 521篇 |
2021年 | 524篇 |
2020年 | 427篇 |
2019年 | 426篇 |
2018年 | 578篇 |
2017年 | 528篇 |
2016年 | 495篇 |
2015年 | 294篇 |
2014年 | 457篇 |
2013年 | 921篇 |
2012年 | 538篇 |
2011年 | 712篇 |
2010年 | 565篇 |
2009年 | 556篇 |
2008年 | 488篇 |
2007年 | 407篇 |
2006年 | 352篇 |
2005年 | 277篇 |
2004年 | 262篇 |
2003年 | 225篇 |
2002年 | 187篇 |
2001年 | 158篇 |
2000年 | 156篇 |
1999年 | 163篇 |
1998年 | 379篇 |
1997年 | 251篇 |
1996年 | 262篇 |
1995年 | 230篇 |
1994年 | 196篇 |
1993年 | 191篇 |
1992年 | 154篇 |
1991年 | 168篇 |
1990年 | 119篇 |
1989年 | 114篇 |
1988年 | 137篇 |
1987年 | 120篇 |
1986年 | 95篇 |
1985年 | 126篇 |
1984年 | 102篇 |
1983年 | 115篇 |
1982年 | 109篇 |
1981年 | 98篇 |
1980年 | 90篇 |
1979年 | 60篇 |
1978年 | 52篇 |
1977年 | 67篇 |
1976年 | 88篇 |
1975年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
Metallurgical and Materials Transactions A - The design of high entropy alloys (HEAs) can be accelerated using machine learning (ML) algorithms. In the current study, the design parameter’s... 相似文献
32.
R. P. Singh 《Polymer Bulletin》1981,6(3-4):175-181
An investigation of the photo-oxidative degradation and stabilization of IIR and SBR in the temperature range of 258 to 313°K in air with a monochromatic light of 366 nm in the absence and presence of various concentrations of the different copper chelates has been described. The stabilizer performance in IIR and SBR was accessed by carbonyl index and quantum yield measurements. The changes of IIR and SBR during the irradiation with an ultra-violet light (366 nm) have been conducted by viscometrically and actinometric techniques. Irradiations were conducted on the films at 0, 2, 4, 6, 8, 10, 12 and 14 hours and various parameters were obtained. 相似文献
33.
Thermal behaviour of starch-graft-polyacrylamide (S-g-PAM) copolymers was evaluated. Grafting of polyacrylamide onto starch lowers the initial decomposition temperature. However, the over-all stability as assessed by the shape of thermogravimetric curve and integral procedural decomposition temperature increased with an increase in % graft-on. 相似文献
34.
The group-contribution method for vapor pressures of hydrocarbons and organic compounds containing nitrogen or sulfur, based on the kinetic theory of fluids, is revised and extended to include new groups containing nitrogen or sulfur. Good representation is obtained for vapor pressure data in the region 1.30-270 kPa. The method may be used to estimate vapor pressures and enthalpies of vaporization for those organic fluids containing nitrogen or sulfur, where no experimental data are available. 相似文献
35.
Responses of ZnSO4, Zn3 (PO4)2 · 4H2O, ZnO, ZnNH4PO3 · 2H2O and zincated superphosphate were studied on wheat (Triticum aestivum) and pearl-millet (Pennistem americanum) in Balsamand sand (Ustipsament) and Ladwa fine loam (Typic Camborthids). In Balsamand sand all Zn fertilizers increased wheat and pearl-milllet grain yield significantly over control but ZnNH4 PO4 · 2H2O and zincated super were the best sources. Straw yield was also highest due to zincated super and ZnNH4PO4 · 2H2O applications. Zinc sulphate was significantly inferior to zincated super and ZnNH4PO4 · 2H2O. In Ladwa fine loam, all fertilizers gave significantly higher grain yield of wheat and pearl-millet than control except ZnO in pearl-millet. Highest yield in this soil was obtained by ZnSO4 · 7H2O followed by ZnNH4 PO4 · 2H2O and then zincated super.In Balsamand sand, the Zn fertilizers significantly increased the Zn concentration and Zn uptake of wheat grain. In pearl-millet, only Zn uptake was increased significantly with Zn fertilizers. Zincated super gave highest Zn uptake.The concentration of P in wheat grain was increased by Zn fertilizers in Balsamand sand, and also in pearl-millet where zincated super and ZnNH4PO4 were most effective in increasing the P content.When Zn fertilizers were applied to preceding pearl-millet the effect on succeeding wheat crop were in the same order as direct application of Zn fertilizers. Zincated super was the best and ZnO worst with respect to wheat grain and straw yield and uptake of Zn and P. 相似文献
36.
Molecular diffusivity of a solute in a solvent may be determined by measuring the extent of dispersion of solute in solvent flowing in a straight circular tube under the conditions of laminar flow. This simple and rapid method for determination of molecular diffusivity in aquous polymer solutions is discussed. Experimental results show a substantial reduction in the solute diffusivity with increase in polymer concentration. 相似文献
37.
For Tanzanian soils dominant in hydrous oxides of iron and amorphous ferri-alumino silicate, a 48-hour (hr) mixing period with the sulphate (SO4) solution was adequate for a near-equilibrium condition. Although differing in their SO4 sorption capacity, all the soils sorbed SO4 at or beyond 1µg ml–1 sulphur (S) concentration in the supernatant. Hydroxyl (OH) ions were displaced during SO4 sorption as indicated by a significant positive correlation between the amount of sorbed SO4 and the difference in pH values determined in 0.1N K2 SO4 and 0.1N KCl, i.e. the dpH values.In a greenhouse experiment, alfalfa was grown on eight soils at six adjusted S concentrations. Sulphur deficiency symptoms appeared in the control pots of those soils which were low in native sorbed SO4, SO4 sorption capacity and initial soil solution S concentration. Sulphur fertilization increased dry matter (DM) yield as well as response to applied S. The external S concentration, i.e. adjusted S concentration required for 95% of the maximum DM yield, ranged from 0.8 to 8.2µg S ml–1 with values less than 2.0 on most of the soils. The external S concentration decreased hyperbolically as the SO4 sorption capacity of the soils increased. The total amount of fertilizer S required to obtain the external S concentration in solution, and at the same time satisfy the SO4 sorption capacity of the soil at the external S concentration (determined from the sorption isotherm) was defined as the external S requirement for the specified yield level of alfalfa. The external S requirement for 95% of the maximum yield of alfalfa varied from soil to soil due to differences in their capacity and intensity for S nutrition.Part of a thesis by the senior author for the MSc (Agric) degree of the University of Dar es Salaam 相似文献
38.
Megh Singh J. R. Orsenigo D. O. Shah 《Journal of the American Oil Chemists' Society》1984,61(3):596-600
Contact angle and surface tension were measured for distilled and hard water solutions of adjuvants, Ortho X-77, Span-20,
Sterox-NJ. Surfactant-WK, Triton B-1956, Triton X-114, Tween-20, and Sun Oil 11E. The same parameters were measured for suspensions
of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and ametryne [2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine] with and without each adjuvant. All adjuvants reduced surface tension and contact angle of distilled water; Surfactant-WK
was most effective and Tween-20 was least effective. Increasing concentration of surfactants from 0 to 0.1% (v/v) gave progressive
reduction in surface tension and contact angle while higher concentrations, 0.1 to 2.0% (v/v), had no further effect. Surfactant-WK
at 0.1% (v/v) in distilled water reduced the surfact tension from 72.8 dynes/cm to 27 dynes/cm and contact angle from 110°
to 41°. An additional increase in Surfactant-WK concentration from 0.1% (v/v) to 2% (v/v) did not further reduce surface tension
and contact angle. Sun Oil 11E was identical in behavior except that it was less effective than the surfactants. Water hardness
up to 1,000 ppm as Ca ions did not affect surface tension and contact angle in surfactant solutions. An aqueous solution of
atrazine had a higher surface tension and contact angle than ametryne in the absence of surfactants. However, these differences
were not observed when surfactants were added to either herbicide. 相似文献
39.
Lime-induced chlorosis is a potential problem on most calcareous soils particularly in arid and semi-arid climates affecting most of the plants grown on them. Bicarbonates, phosphates, calcium, iron inactivation in plant tissue and organic anions have been held responsible as the mechanism leading to the disorder which is still not fully understood, and there is a lack of agreement as to the primary factor responsible for lime-induced chlorosis. To date, no hypothesis has adequately explained why chlorosis occurs on some high lime soils and not on others. Likewise, the nutrient ratios, K/Ca, P/Fe and Fe/Mn considered as diagnostic criteria for lime-induced chlorosis, have shown inconsistency. The presence of calcium carbonate, bicarbonate, calcium and imbalance of nutrient cations in the growth medium, injudicious addition of phosphates, quality of irrigation water, and other soil and plant factors have been held responsible for the disorder. Amelioration of lime-induced chlorosis by (i) acidification of calcareous soils, (ii) use of iron salts, (iii) use of synthetic iron chelates, and (iv) by management practices including the selection and development of varieties resistant to lime-induced iron chlorosis, is discussed. Suggestions for future research work are made. 相似文献
40.
Alok Singh Sitaram Dash Mohammed Kamruddin Puthupparampil K. Ajikumar Ashok K. Tyagi Vinjamoor S. Raghunathan Baldev Raj 《Journal of the American Ceramic Society》2002,85(4):927-932
Formation of nanocrystalline calcia from calcite has been studied in situ via transmission electron microscopy. The crystallographic transformation occurred via two mechanisms: the first is by distortion of the cleaved rhombohedron of calcite, formed by {104} planes in hexagonal coordinates, into a cube. This produced a microstructure of oriented, elongated nanocrystals of calcia with planar boundaries. In the second mechanism, the micrometer-sized parent calcite particles broke up into nano-sized grains as the decomposition began, leading to irregularly shaped, randomly oriented nanocrystals of calcia. 相似文献