全文获取类型
收费全文 | 88399篇 |
免费 | 1165篇 |
国内免费 | 415篇 |
专业分类
电工技术 | 818篇 |
综合类 | 2317篇 |
化学工业 | 12256篇 |
金属工艺 | 4854篇 |
机械仪表 | 3099篇 |
建筑科学 | 2453篇 |
矿业工程 | 580篇 |
能源动力 | 1226篇 |
轻工业 | 4028篇 |
水利工程 | 1307篇 |
石油天然气 | 374篇 |
武器工业 | 1篇 |
无线电 | 9497篇 |
一般工业技术 | 17095篇 |
冶金工业 | 3648篇 |
原子能技术 | 272篇 |
自动化技术 | 26154篇 |
出版年
2021年 | 80篇 |
2020年 | 75篇 |
2019年 | 66篇 |
2018年 | 14511篇 |
2017年 | 13429篇 |
2016年 | 10064篇 |
2015年 | 684篇 |
2014年 | 380篇 |
2013年 | 536篇 |
2012年 | 3369篇 |
2011年 | 9697篇 |
2010年 | 8472篇 |
2009年 | 5721篇 |
2008年 | 7005篇 |
2007年 | 7974篇 |
2006年 | 305篇 |
2005年 | 1397篇 |
2004年 | 1257篇 |
2003年 | 1300篇 |
2002年 | 667篇 |
2001年 | 176篇 |
2000年 | 245篇 |
1999年 | 137篇 |
1998年 | 162篇 |
1997年 | 139篇 |
1996年 | 126篇 |
1995年 | 87篇 |
1994年 | 71篇 |
1993年 | 82篇 |
1992年 | 88篇 |
1991年 | 68篇 |
1990年 | 49篇 |
1989年 | 52篇 |
1988年 | 59篇 |
1987年 | 49篇 |
1986年 | 56篇 |
1985年 | 73篇 |
1984年 | 58篇 |
1983年 | 68篇 |
1982年 | 49篇 |
1980年 | 46篇 |
1979年 | 63篇 |
1978年 | 46篇 |
1977年 | 48篇 |
1968年 | 47篇 |
1966年 | 46篇 |
1965年 | 56篇 |
1959年 | 40篇 |
1955年 | 68篇 |
1954年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
61.
Chao-Hong Wang Sinn-Wen Chen Chia-Hua Chang Jen-Chin Wu 《Metallurgical and Materials Transactions A》2003,34(2):199-209
A series of Al-Cu-Ni alloys of various compositions were made and annealed at 800 °C. The equilibrium phases were studied
by metallography, X-ray diffraction (XRD) analysis, and electron probe microanalysis. The isothermal section of the ternary
Al-Cu-Ni system at 800 °C was then determined based on these experimental results and the available phase relationship knowledge
of the three constituent binary systems. No ternary compound was found. All three phases, AlNi3, AlNi, and Al3Ni2, have very high ternary solubility, especially the AlNi phase, which almost reaches the binary Al-Cu side. However, no continuous
solid solution was formed between the AlNi phase and any of the binary Al-Cu phases. Interfacial reactions of Al/Ni, Al/Cu,
Al-Cu/Ni, and Al-Ni/Cu at 800 °C were investigated by using reaction couple techniques. The results showed that Al3Ni and Al3Ni2 phases were formed in the Al/Ni couples; β-AlCu4, γ
1-Al4Cu9, and ɛ
2-Al2Cu3 phases were formed in the Al/Cu couples. As for the results in the Al-2 at. pct Ni/Cu, Al-5 at. pct Ni/Cu, and Al-2 at. pct
Cu/Ni, Al-4.5 at. pct Cu/Ni, and Al-6 at. pct Cu/Ni were similar to those in the binary Al/Cu and Al/Ni couples, respectively.
A different reaction path was found in the Al-7.5 at. pct Cu/Ni couples, and an AlNi solid solution layer was formed instead
of the Al3Ni and Al3Ni2 phases. 相似文献
62.
63.
Jon T. Carter Paul E. Krajewski Ravi Verma 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(11):77-81
The hot blow forming of magnesium sheet offers significant opportunity for forming complex, lightweight parts for automotive
applications. This paper characterizes the elevated-temperature formability of AZ31 magnesium sheet materials and the effect
of processing conditions on the performance of these materials. In addition, magnesium sheet application development at General
Motors Corporation is reviewed. 相似文献
64.
Toshihiko Hoshide Junpei Fujita 《Journal of Materials Engineering and Performance》2008,17(5):627-632
Strength of ground ceramics may be affected by residual stress as well as surface flaws induced by grinding. Strength prediction
for ground ceramics is convenient for mechanical design of ceramic components. In this article, a numerical procedure based
on fracture mechanics was proposed to estimate strength distribution of ground ceramics by considering grinding-induced residual
stress. Bending strength and residual stress of ground ceramics were measured for three grinding-conditions. By comparison
of simulated results with experimental ones, it was revealed that strength characteristics in experiments were well simulated
by using the proposed procedure. 相似文献
65.
The short contact time dissolution of vitrinite and inertinite concentrates of an Australian bituminous coal was studied under isothermal conditions with tetralin as solvent. The reactivity of the two maceral types and the yields and nature of the products were determined for a range of reaction temperatures (400, 420 and 440 °C) and reaction times (2–20 min). The dissolution of vitrinite proceeded at a significantly greater rate than for inertinite and was associated with greater selectivity to soluble non-gaseous products. At very short reaction times (2 min), the vitrinite underwent solubilizing reactions to yield products of higher molecular weight and greater oxygen functionality than was the case for inertinite, for which changes in the chemical nature of the products were negligible over the range of conditions studied. At longer reaction times (5 min), the composition of the vitrinite-derived products was similar to that of the inertinite-derived products. 相似文献
66.
Zirconium(IV) tungstoiodophosphate has been synthesized under a variety of conditions. The most chemically and thermally stable
sample is prepared by adding a mixture of aqueous solutions of 0·5 mol L−1 sodium tungstate, potassium iodate and 1 mol L−1 orthophosphoric acid to aqueous solution of 0·1 mol L−1 zirconium(IV) oxychloride. Its ion exchange capacity for Na+ and K+ was found to be 2·20 and 2·35 meq g−1 dry exchanger, respectively. The material has been characterized on the basis of chemical composition, pH titration, Fourier
transform infrared spectroscopy (FTIR) and thermogravimetric analysis. The effect on the exchange capacity of drying the exchanger
at different temperatures has been studied. The analytical importance of the material has been established by quantitative
separation of Pb2+ from other metal ions. 相似文献
67.
Jonathan P. Belnoue Giang D. Nguyen Alexander M. Korsunsky 《International Journal of Fracture》2007,144(1):53-60
This paper presents a new 1-D non-local damage-plasticity deformation model for ductile materials. It uses the thermodynamic
framework described in Houlsby and Puzrin (2000) and holds, nevertheless, some similarities with Lemaitre’s (1971) approach.
A 1D finite element (FE) model of a bar fixed at one end and loaded in tension at the other end is introduced. This simple
model demonstrates how the approach can be implemented within the finite element framework, and that it is capable of capturing
both the pre-peak hardening and post-peak softening (generally responsible for models instability) due to damage-induced stiffness
and strength reduction characteristic of ductile materials. It is also shown that the approach has further advantages of achieving
some degree of mesh independence, and of being able to capture deformation size effects. Finally, it is illustrated how the
model permits the calculation of essential work of rupture (EWR), i.e. the specific energy per unit cross-sectional area that
is needed to cause tensile failure of a specimen. 相似文献
68.
Airframe riveting is a critical process that requires high levels of process monitoring and quality assurance due to the very
high risk associated with the failure of such joints. This paper describes the development of the enabling technology developed
for a machine vision-based process monitoring system. One of the key factors affecting the performance of a machine vision
system is the quality of the lighting. In the application described in this paper the available lighting was severely limited
by the confined space in which the system had to operate. The problem was also compounded by the reflective nature of the
objects to be examined. The initial images obtained were not suitable for further processing due to the presence of significant
shadows and specular reflections. A novel solution to this problem based on multiple wavelength illumination and signal processing
is presented along with results from experimental trials of the approach. 相似文献
69.
Yewang Su Baohua Ji Yonggang Huang Kehchih Hwang 《Journal of Materials Science》2007,42(21):8885-8893
Wet adhesion is widely adopted in biological adhesion systems in nature. Wet adhesion is studied in this paper with the focus
on the effect of different contact shapes (flat, concave, convex, and ring-like) on the adhesion force. The evolution of the
liquid bridge between a fiber tip and substrate during the detaching process shows two transition points. The first transition
from the radius-controlled to the contact-angle controlled process is critical to influence the strength and robustness of
adhesion. We show that a concave shape is more effective than a flat one, while a convex shape has no advantage. A ring-like
contact shape has advantages in a hydrophobic environment and on a rough surface. 相似文献
70.
Jinting Jiu Seiji Isoda Motonari Adachi Hao Wang 《Journal of Materials Science: Materials in Electronics》2007,18(6):593-597
Nanocrystalline TiO2 with 3–10 nm in diameter was prepared with a surfactant-template method. Dye-sensitized solar cells were assembled using
the prepared nanocrystalline TiO2 with large surface area and high crystallinity, which achieved significant higher Jsc when compared to cells fabricated with
bigger particles of 25 nm in diameter. In the cells with nanocrystalline TiO2, the sintering temperature drastically affected the conversion performance of the cells. 相似文献