全文获取类型
收费全文 | 365169篇 |
免费 | 33731篇 |
国内免费 | 18611篇 |
专业分类
电工技术 | 24514篇 |
技术理论 | 42篇 |
综合类 | 32835篇 |
化学工业 | 43222篇 |
金属工艺 | 33830篇 |
机械仪表 | 18413篇 |
建筑科学 | 51717篇 |
矿业工程 | 17516篇 |
能源动力 | 12030篇 |
轻工业 | 24742篇 |
水利工程 | 13241篇 |
石油天然气 | 20295篇 |
武器工业 | 4359篇 |
无线电 | 24747篇 |
一般工业技术 | 31312篇 |
冶金工业 | 29504篇 |
原子能技术 | 3242篇 |
自动化技术 | 31950篇 |
出版年
2024年 | 1623篇 |
2023年 | 4934篇 |
2022年 | 9384篇 |
2021年 | 11847篇 |
2020年 | 12219篇 |
2019年 | 9524篇 |
2018年 | 8935篇 |
2017年 | 11404篇 |
2016年 | 13095篇 |
2015年 | 14122篇 |
2014年 | 24313篇 |
2013年 | 21623篇 |
2012年 | 26515篇 |
2011年 | 29048篇 |
2010年 | 21325篇 |
2009年 | 21680篇 |
2008年 | 19407篇 |
2007年 | 24189篇 |
2006年 | 21893篇 |
2005年 | 18857篇 |
2004年 | 15693篇 |
2003年 | 13811篇 |
2002年 | 11622篇 |
2001年 | 9812篇 |
2000年 | 8355篇 |
1999年 | 6672篇 |
1998年 | 4753篇 |
1997年 | 4189篇 |
1996年 | 3508篇 |
1995年 | 2772篇 |
1994年 | 2361篇 |
1993年 | 1656篇 |
1992年 | 1382篇 |
1991年 | 996篇 |
1990年 | 837篇 |
1989年 | 735篇 |
1988年 | 457篇 |
1987年 | 314篇 |
1986年 | 250篇 |
1985年 | 285篇 |
1984年 | 206篇 |
1983年 | 163篇 |
1982年 | 107篇 |
1981年 | 115篇 |
1980年 | 144篇 |
1979年 | 46篇 |
1978年 | 34篇 |
1977年 | 29篇 |
1975年 | 26篇 |
1959年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Poly(L-ornithine)s having various azo-contents in the side chains were synthesized by the water-soluble carbodiimide procedure. The photochemical properties of the polypeptides poly[Nδ-p-(phenylazo)benzoyl-L-ornithine] (PPABLO) containing 3–77 mol% azobenzene were investigated by absorption and circular dichroism spectroscopy in hexafluoro-2-propanol (HFIP) or water, and in HFIP-water or methanol-water solvent mixtures. The photochromism of the dichroic bands of the PPABLOs containing 20–77 mol% azobenzene in the visible and ultraviolet wavelength regions was found to be mostly reversible as a function of irradiation time at different wavelengths due to the photostationary state (above 80% trans-cis photoisomerization) of the azo aromatic moieties. The PPABLO containing 3.2 mol% azobenzene in water exhibited conformational changes from random coil to helix by the addition of methanol or sodium dodecyl sulphate (SDS). The photo-induced conformational change was observed in HFIP-water-SDS solvent mixtures, while no conformational change was seen in water and HFIP-water solvent mixtures. 相似文献
44.
The pyrolysis of tertiarybutylphosphine (TBP) has been studied in the low pressure conditions used for chemical beam epitaxy
(CBE). The pyrolysis studies were carried out in low pressure reactors of two different configurations, one of which is a
cracker cell designed for use in a CBE system. The reaction products were studied using a quadrupole mass spectrometer. The
products observed are accounted for by a reaction mechanism involving homolysis of the parent TBP molecule to produce PH2 and C4H9 radicals. These undergo subsequent reactions to form the stable products C4H8, PH3 and H2, with smaller amounts of P and P2 being produced. The production of the sub-hydride PH2 using this cracker cell design indicates that the use of partially cracked TBP may be a promising technique for reducing
the amount of carbon incorporated into the growing epitaxial layer. 相似文献
45.
aneta Polkowska Jacek Namienik Jacek Czerwiski & Bogdan Zygmunt 《International Journal of Food Science & Technology》1996,31(5):387-395
Applicability of thin-layer headspace (TLHS) procedure giving an aqueous concentrate and also classical purge and trap (PT) in off-line mode to isolate and enrich volatile organohalogen compounds in common beverages was tested. Both enrichment tech-niques were used in combination with gas chromatography – electron capture detection (GC-ECD). TLHS, combined with direct aqueous injection (DAI)-GC-ECD, proved applicable in the determination of volatile organohalogen compounds in all studied beverages, while the PT in a version with no preliminary sample pre-treatment was of limited applicability. Detection limits of the TLHS-based procedure were in the order of 1 ppt. Content of volatile organohalogen compounds in a number of beverages available on the Polish market including mineral waters, beers, juices, carbonated and non-carbonated soft drinks, etc. was determined by means of TLHS-DAI-GC-ECD. 相似文献
46.
A finite element formulation and the solution of a set of nonlinear coupled heat and mass transfer equations for a two-phase system with a moving evaporation interface is presented. The interface condition takes into account the moisture transfer balance at the moving boundary. The finite element results were compared with existing results for a single phase system for model validation. In the two-phase system, the movement of evaporation front has an appreciable effect on the temperature and moisture distribution inside the porous medium during drying. The effect of the nondimensional heat of vapourization parameter γ on the evaporation front, temperature and moisture distribution in porous medium was studied. The higher the value of γ, the slower is the movement of the evaporation front. The temperature decreased and the moisture content increased as the nondimensional vapourization parameter γ increased. This model has potential applications in studying the heat and mass transfer characteristics in food and biomaterials. 相似文献
47.
48.
《西安建筑科技大学学报(自然科学版)》1994,(4)
论述复合脱氧剂的一般化学特性,并以碳化硅和硅铝铁两种复合脱氧剂为例,讨论其对改善钢的质量,进行纯净钢生产的影响。 相似文献
49.
A new principle and arrangement for directly determining the angle of incidence of an optical beam on an object are proposed and demonstrated. The novelty of the approach lies in the realization of a ‘smart object’, which extracts a portion of the incident beam's power into an optical waveguide attached to the object's surface or embedded in its body for converting the angle of incidence into the position of a guided beam with finite lateral extent. This ‘integrated optical light pointer’ beam is accomplished by means of creating additional degrees of freedom on the target in two different ways. While a first type is based on introducing spatial variations of the waveguide thickness, a second type makes use of a chirp of the grating periodicity. The feasibility for practical applications has been experimentally demonstrated by a direct comparison with a commercial high-resolution encoder, resulting in an r.m.s. error of <30′'. Measurements have been performed for chips fabricated based on replicated polycarbonate substrates and with no external optics, showing the great potential of this approach for realizing low-cost yet high-performance miniature goniometers. 相似文献
50.