全文获取类型
收费全文 | 247986篇 |
免费 | 12737篇 |
国内免费 | 6484篇 |
专业分类
电工技术 | 9466篇 |
技术理论 | 9篇 |
综合类 | 10888篇 |
化学工业 | 38242篇 |
金属工艺 | 14627篇 |
机械仪表 | 12972篇 |
建筑科学 | 11898篇 |
矿业工程 | 4474篇 |
能源动力 | 4715篇 |
轻工业 | 12797篇 |
水利工程 | 4386篇 |
石油天然气 | 9846篇 |
武器工业 | 1067篇 |
无线电 | 26485篇 |
一般工业技术 | 42512篇 |
冶金工业 | 13636篇 |
原子能技术 | 5062篇 |
自动化技术 | 44125篇 |
出版年
2024年 | 718篇 |
2023年 | 2326篇 |
2022年 | 4605篇 |
2021年 | 6231篇 |
2020年 | 4681篇 |
2019年 | 4022篇 |
2018年 | 19091篇 |
2017年 | 18548篇 |
2016年 | 14781篇 |
2015年 | 6230篇 |
2014年 | 7514篇 |
2013年 | 9063篇 |
2012年 | 12588篇 |
2011年 | 19373篇 |
2010年 | 16746篇 |
2009年 | 13906篇 |
2008年 | 15013篇 |
2007年 | 15506篇 |
2006年 | 7415篇 |
2005年 | 7405篇 |
2004年 | 5867篇 |
2003年 | 5849篇 |
2002年 | 5269篇 |
2001年 | 4412篇 |
2000年 | 3916篇 |
1999年 | 3369篇 |
1998年 | 2670篇 |
1997年 | 2235篇 |
1996年 | 2017篇 |
1995年 | 1741篇 |
1994年 | 1475篇 |
1993年 | 1250篇 |
1992年 | 1227篇 |
1991年 | 1096篇 |
1990年 | 1090篇 |
1989年 | 1010篇 |
1988年 | 905篇 |
1987年 | 841篇 |
1986年 | 763篇 |
1985年 | 716篇 |
1984年 | 702篇 |
1981年 | 668篇 |
1979年 | 736篇 |
1978年 | 777篇 |
1977年 | 739篇 |
1976年 | 755篇 |
1975年 | 713篇 |
1974年 | 719篇 |
1973年 | 723篇 |
1972年 | 705篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
减压渣油与FCC油浆共炭化的化学组成变化 总被引:6,自引:2,他引:4
考察了齐鲁石化胜利炼油厂催化油浆(FCC)和胜利减压渣油(VR)在490℃,0.8MPa下不同混合比的原料和不同反应时间的中间产物的HS、TS、PS、P及其1h中间产物的HS和TS的^1H-NMR。数据结果反映了体系的反应速度。掺入FCC油浆抑制了VR的反应活性,降低了体系的反应速度,增加了基质的溶解度;1h中间产物的组成结构更接近于原料及反应体系的反应性和基质的溶解度;1h中间产物的芳香度越高,取代基越少,侧链越短,基质对VR中的活性反应组分在炭化早期生成的高度缩合物质的溶解度越大。 相似文献
62.
The crystal structure of [NpO2{OC(NH2)2}5]ClO4·H2O and [NpO2Cl{OC(NH2)2}4] was studied by X-ray diffraction. The electronic absorption spectra of these complexes were recorded. The coordination polyhedron of Np in both complexes is a distorted pentagonal bipyramid. There is no cation-cation interaction of neptunyl cations in these complexes. 相似文献
63.
Androstenedione labeled with tritium at positions 1 and 2 was prepared. The molar radioactivity of the sample prepared using homogeneous catalysts was as high as 1.4-1.5 PBq mol-
1. [1,2-3H]Androst-4-ene-3,17-dione can be converted into the [1-3H]steroid with the molar radioactivity of 0.9 PBq mol-
1. 相似文献
64.
N. A. Sivov A. I. Martynenko G. N. Bondarenko M. P. Filatova E. Yu. Kabanova N. I. Popova A. N. Sivov E. B. Kruts’ko 《Petroleum Chemistry》2006,46(1):41-59
Structures and compositions of the monomers guanidine acrylate and guanidine methacrylate, their homopolymers, and copolymers with diallyldimethylammonium chloride enriched in acrylate comonomer units were determined. It was shown that ampholytic copolymers, owing to their ionic nature, contained comonomeric guanidine acrylate or methacrylate units and diallyldimethylammonium chloride units, as well as the acrylate comonomer with the diallyl counterion and polymeric acrylate and diallyl ion pairs. It follows from IR and 1H NMR data that guanidine methacrylate has the same structure (with two hydrogen bonds) in the solid state and in solutions. Guanidine acrylate structures in the solid state and in dimethylsulfoxide are identical and analogous to guanidine methacrylate structure in this solvent. In water, the guanidine acrylate structure has another type of hydrogen bonding (with one hydrogen bond, where the proton is shifted toward the guanidine group). These features of hydrogen bonding of guanidine acrylate and guanidine methacrylate are also retained in their homopolymers and copolymers with diallyldimethylammonium chloride. It was shown that the thermal stability of the copolymers was higher than that of their homopolymers, confirming the formation of intramolecular ion pairs of oppositely charged units of ampholytic copolymers. Moreover, the thermal stability of guanidine methacrylate-diallyldimethylammonium chloride copolymers is higher than that of guanidine acrylate-diallyldimethylammonium chloride copolymers. 相似文献
65.
Yanqiu Shao Jiqing Han Ting Liu Yongzhen Zhao 《International Journal of Speech Technology》2007,10(1):45-55
In real speech, not like lexical words (LWs), prosodic words (PWs) are basic rhythmic units. The naturalness of a Text-to-Speech
(TTS) system is directly influenced by the segmentation of the PWs. Most of the PWs are the combination of several LWs. In
this paper, three Lexical Combination Models are proposed to combine LWs into PWs, including a Directed Acyclic Graph Model,
a Segmentation Model and a Markov Model (MM). To cope with the situation where some long LWs should be segmented into two
or more PWs, a Lexical Split Model (LSM) is applied to the long LWs. Experimental results prove that relatively constant results
with various training data can be obtained from a MM. The Transformation-Based Error Driven Learning (TBED) algorithm, for
its high performance of individual property, is applied in combination with the MM to improve the precision of PW segmentation.
Experiments show that among the three proposed models, the MM combined with TBED and LSM, leads to the best performance, in
which a precision of 93.00% and a recall of 93.23% are achieved. The perception test indicates that by using PWs as the lowest
prosodic units a speech sounds more natural and acceptable than by using LWs.
This paper is supported by NSFC Project (60503071); 973 Natural Basic Research Program of China (2004CB318102); Postdoctor
Science Foundation of P. R. China (20070420275). 相似文献
66.
In this paper we describe, from a theoretical point of view, critical configurations for the projective reconstruction of
a set of points, for a single view, i.e. for calibration of a camera, in the case of projections from ℙk to ℙ2 for k ≥ 4. We give first a general result describing these critical loci in ℙk, which, if irreducible, are algebraic varieties of dimension k−2 and degree 3. If k=4 they can be either a smooth ruled surface or a cone and if k = 5 they can be a smooth three dimensional variety, ruled in planes, or a cone. If k≥ 6, the variety is always a cone, the
vertex of which has dimension at least k − 6. The reducible cases are studied in Appendix A.
These results are then applied to determine explicitly the critical loci for the projections from ℙk which arise from the dynamic scenes in ℙ3 considered in [13].
Marina Bertolini is currently Associate Professor of Geometry at the Department of Mathematics at the Università degli Studi di Milano, Italy.
Her main field of research is Complex Projective Algebraic Geometry, with particular interest for the classification of projective
varieties and for the geometry of Grassmann varieties. On these topics M. Bertolini has published more than twenty reviewed
papers on national and international journals. She has been for some years now interested also in applications of Algebraic
Geometry to Computer Vision problems.
Cristina Turrini is Associate Professor of Geometry at the Department of Mathematics of Università degli Studi di Milano, Italy. Her main
research interest is Complex Projective Algebraic Geometry: subvarieties of Grassmannians, special varieties, automorphisms,
classification. In the last two years she has started to work on applications of Algebraic Geometry to problems of Computer
Vision. She is author or co-author of about thirty reviewed papers. She is also involved in popularization of Mathematics,
and on this subject she is co-editor of some books. 相似文献
67.
It is established that the capillary rise of a liquid has an oscillatory character, in contrast to the commonly accepted opinion that a vertical capillary is filled at a monotonically varying velocity. The value of the tangential shear stress arising in an ascending liquid is evaluated for ethyl alcohol and distilled water. 相似文献
68.
A. M. Kozodaev O. V. Shvedov V. N. Konev B. Yu. Sharkov V. V. Vasil'ev E. B. Volkov N. V. Lazarev A. M. Raskopin G. G. Shimchuk P. V. Bogdanov A. I. Kiryushin V. V. Petrunin E. I. Azhnin E. I. Tyurin I. I. Titaev Yu. P. Severgin A. Yu. Konstantinov 《Atomic Energy》2003,94(1):56-60
The purpose and current construction status, at the Institute of Theoretical and Experimental Physics, of an experimental electronuclear setup, combining a pulsed proton linear accelerator (36 MeV, 0.5 mA) and a subcritical blanket thermal-power assembly 100 kW, are discussed. The main equipment is already available or is being built in industry. The setup can be used to investigate the dynamics of the interaction of a linac–driver and a subcritical reactor and problems concerning the accelerator–driver and the target–blanket assembly. The proton beams and neutron fluxes will be used for applied purposes. In the future it will be possible to increase substantially the current and energy of the proton beam. 相似文献
69.
A. D. Pogrebnyak M. V. Il’yashenko V. S. Kshnyakin V. V. Ponaryadov Sh. M. Ruzimov Yu. N. Tyurin 《Technical Physics Letters》2003,29(12):1028-1030
Chromium carbide-nickel coatings were deposited onto a technical grade copper substrate by means of a high-velocity plasma
jet of a plasmatron operating in specially selected regimes. An analysis of the coatings showed evidence of the formation
of a Ni-based solid solution, a complex chromium carbide (Cr7C3), and an fcc crystal phase with a lattice parameter of 3.614 Å. The surface of the coatings exhibits a characteristic relief
resulting from a dynamic interaction between melted and fused particles of the initial powder. The local hardness on some
areas of the surface and in depth of the coating reaches 66±4.5 HRC, while the coating adhesion strength varies from 25 to
300 MPa. 相似文献
70.