全文获取类型
收费全文 | 52644篇 |
免费 | 2857篇 |
国内免费 | 48篇 |
专业分类
电工技术 | 383篇 |
综合类 | 30篇 |
化学工业 | 10667篇 |
金属工艺 | 914篇 |
机械仪表 | 1122篇 |
建筑科学 | 1578篇 |
矿业工程 | 107篇 |
能源动力 | 1100篇 |
轻工业 | 8816篇 |
水利工程 | 542篇 |
石油天然气 | 192篇 |
武器工业 | 6篇 |
无线电 | 2071篇 |
一般工业技术 | 8781篇 |
冶金工业 | 11588篇 |
原子能技术 | 223篇 |
自动化技术 | 7429篇 |
出版年
2024年 | 118篇 |
2023年 | 477篇 |
2022年 | 562篇 |
2021年 | 1266篇 |
2020年 | 1101篇 |
2019年 | 1168篇 |
2018年 | 2192篇 |
2017年 | 2156篇 |
2016年 | 2255篇 |
2015年 | 1676篇 |
2014年 | 1993篇 |
2013年 | 4275篇 |
2012年 | 3142篇 |
2011年 | 2881篇 |
2010年 | 2403篇 |
2009年 | 2118篇 |
2008年 | 2133篇 |
2007年 | 1967篇 |
2006年 | 1364篇 |
2005年 | 1127篇 |
2004年 | 1018篇 |
2003年 | 975篇 |
2002年 | 893篇 |
2001年 | 657篇 |
2000年 | 600篇 |
1999年 | 657篇 |
1998年 | 3599篇 |
1997年 | 2380篇 |
1996年 | 1536篇 |
1995年 | 892篇 |
1994年 | 702篇 |
1993年 | 769篇 |
1992年 | 272篇 |
1991年 | 259篇 |
1990年 | 210篇 |
1989年 | 216篇 |
1988年 | 220篇 |
1987年 | 192篇 |
1986年 | 170篇 |
1985年 | 210篇 |
1984年 | 183篇 |
1983年 | 123篇 |
1982年 | 157篇 |
1981年 | 194篇 |
1980年 | 203篇 |
1979年 | 107篇 |
1978年 | 101篇 |
1977年 | 353篇 |
1976年 | 750篇 |
1973年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Peter Eaton Andrea Ragusa Caroline Clavel Cristina T Rojas Paul Graham Raúl V Durán Soledad Penadés 《IEEE transactions on nanobioscience》2007,6(4):309-318
Glyconanoparticles which present carbohydrate and amino groups motifs at their surface were produced. These particles were highly stable and soluble in aqueous solutions. The presence of the carbohydrate groups also allowed the inclusion of more strongly binding groups, without affecting solubility. The binding of a model DNA, plasmid by these nanoparticles was studied by atomic force microscopy, transmission electron microscopy, and gel electrophoresis. Significant differences between the nanoparticles based on their affinities for the DNA were found, with implications for their potential use as nonviral gene delivery agents. 相似文献
102.
103.
Talita Moreira de Oliveira Nilda de Fátima Ferreira Soares Rodrigo Magela Pereira Kátia de Freitas Fraga 《Packaging Technology and Science》2007,20(2):147-153
Conservation of food products depends on product quality and packaging suitability. The objective of this work was to develop and evaluate the antimicrobial efficiency of natamycin‐incorporated film in the production process of Gorgonzola cheese. It aims to optimize the production process and increase shelf‐life and food safety for the consumer. Films with different concentrations of natamycin were produced and tested in Gorgonzola cheeses to evaluate its efficiency against Penicillium roqueforti on the cheese surface. Films with 2 and 4% natamycin presented satisfactory results for fungus inhibition and the amount of natamycin released to the cheese was below that allowed by the legislation. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
104.
András Ványolos Balázs Dóra Attila Virosztek 《Journal of Superconductivity and Novel Magnetism》2007,20(7-8):643-645
We report of a theoretical study on quasi-one dimensional unconventional charge density wave (UCDW) driven by electron–phonon
interaction. Within mean field theory, we find that the wavevector dependence of the coupling leads to a momentum dependent
single particle gap on the Fermi surface. The presence of small energy single particle excitations around the gap nodes significantly
changes the optical conductivity compared to the conventional CDW result. In addition to that, the collective phase excitation
arising from fluctuation of the order parameter leads to further qualitative changes of the conductivity and results in an
effective mass that is nonmonotonic in temperature.
相似文献
105.
106.
V. Ocelík V. Z. Bengus E. B. Korolkova K. Csach J. Miškuf P. Duhaj 《Journal of Materials Science》1991,26(24):6699-6705
The fracture stress and the critical stress intensity factor of the Fe40Ni40B20 amorphous metallic ribbons 20 μm thick were measured in the temperature range 4.2–300 K and at deformation rates from 3.3×10−6 to 1.25×10−3 m−1 with the aim to obtain more information on the condition for the onset and development of the inhomogeneous plastic deformation
and fracture. 相似文献
107.
The Role of Network Topologies in the Optical Core of IP-over-WDM Networks with Static Wavelength Routing 总被引:3,自引:0,他引:3
Freire Mário M. Rodrigues Joel J.P.C. Coelho Rui M.F. 《Telecommunication Systems》2003,24(2-4):111-122
In this paper, we present a performance analysis of network topologies for the optical core of IP-over-WDM networks with static wavelength routing. The performance analysis is focused on regular degree four topologies, and, for comparison purposes, degree three topologies are also considered. It is shown that the increase of the nodal degree from three (degree three topology with smallest diameter) to four (degree four topology with smallest diameter) improves the network performance if a larger number of wavelengths per link is available. However, the influence of wavelength interchange on the nodal degree gain is small. The performance of regular degree four topologies with smallest diameter is also compared with the performance of mesh–torus topologies (which are also degree four topologies), and it is shown that the blocking probability of degree four topologies with smallest diameter is about two orders of magnitude lower than the blocking probability of mesh–torus topologies. It is also presented a performance comparison of WDM-based networks with nodal degrees ranging from two to five and it is shown that the increase of the nodal degree from two to three leads to high nodal degree gains, while de increase of the nodal degree from four to five leads to low nodal degree gains. These results show that degree three and degree four topologies are very attractive for use in the optical core of IP-over-WDM networks. 相似文献
108.
In this paper, a new approach for powder cold compaction simulations is presented. A density-dependent plastic model within
the framework of finite strain multiplicative hyperelastoplasticity is used to describe the highly nonlinear material behaviour;
the Coulomb dry friction model is used to capture friction effects at die-powder contact; and an Arbitrary Lagrangian–Eulerian
(ALE) formulation is used to avoid the (usual) excessive distortion of Lagrangian meshes caused by large mass fluxes. Several
representative examples, involving structured and unstructured meshes are simulated. The results obtained agree with the experimental
data and other numerical results reported in the literature. It is shown that, contrary to other Lagrangian and adaptive h-remeshing approaches recently reported for this type of problems, the present approach verifies the mass conservation principle
with very low relative errors (less than 1% in all ALE examples and exactly in the pure Lagrangian examples). Moreover, thanks
to the use of an ALE formulation and in contrast with other simulations, the presented density distributions do not present
spurious oscillations.
Received: 20 March 2002 / Accepted: 15 October 2002
The partial financial support of the Ministerio de Ciencia y Tecnología (grant number DPI 2001-2204) is gratefully acknowledged. 相似文献
109.
Jefferson Fabrício Cardoso Lins Hugo Ricardo Z. Sandim Hans-Jürgen Kestenbach 《Journal of Materials Science》2007,42(16):6572-6577
The present paper reports the experimental results on the microstructural and textural characterization of a hot-rolled IF
steel. The IF steel was hot-rolled in multiple passes in the austenitic field (1,070 °C) followed by air-cooling. SEM, TEM,
and LOM were used to image the microstructure of the material. The global texture was determined by X-ray diffraction (XRD)
technique. The mesotexture of selected regions was investigated by electron backscatter diffraction (EBSD). Results show the
presence of a diffuse (nearly random) and weak texture in the hot-band that consists of recrystallized polygonal grains and
subgrains. The fraction of boundaries with misorientations comprised in the interval 2° ≤ ψ < 15° was found to be lower than
5%. It can be concluded that these low angle boundaries and the presence of subgrains can be associated to the existence of
a few areas softened by recovery during or after hot rolling in austenitic field. 相似文献
110.
Synthesis of oleyl oleate as a jojoba oil analog 总被引:2,自引:0,他引:2
N. Sánchez M. Martinez J. Aracil A. Corma 《Journal of the American Oil Chemists' Society》1992,69(11):1150-1153
Synthesis of a wax ester analog of jojoba oil was accomplished from oleic acid and oleyl alcohol with a zeolite as catalyst.
A full 23 factorial design at two levels has been used in the synthesis. The variables selected were temperature, reduced pressure
and initial catalyst concentration. The most important variable within the range studied was temperature. Reduced pressure
had a negative influence, and initial catalyst concentration showed a positive influence on the process. A response equation
has been determined for the yield of ester. The properties of the synthesized product are similar to those of natural jojoba
oil. 相似文献