全文获取类型
收费全文 | 93161篇 |
免费 | 1492篇 |
国内免费 | 420篇 |
专业分类
电工技术 | 875篇 |
综合类 | 2320篇 |
化学工业 | 13508篇 |
金属工艺 | 4953篇 |
机械仪表 | 3209篇 |
建筑科学 | 2475篇 |
矿业工程 | 586篇 |
能源动力 | 1381篇 |
轻工业 | 4633篇 |
水利工程 | 1360篇 |
石油天然气 | 376篇 |
武器工业 | 6篇 |
无线电 | 9936篇 |
一般工业技术 | 18107篇 |
冶金工业 | 4245篇 |
原子能技术 | 331篇 |
自动化技术 | 26772篇 |
出版年
2023年 | 62篇 |
2022年 | 113篇 |
2021年 | 200篇 |
2020年 | 185篇 |
2019年 | 167篇 |
2018年 | 14594篇 |
2017年 | 13549篇 |
2016年 | 10209篇 |
2015年 | 805篇 |
2014年 | 535篇 |
2013年 | 848篇 |
2012年 | 3605篇 |
2011年 | 9967篇 |
2010年 | 8664篇 |
2009年 | 5939篇 |
2008年 | 7296篇 |
2007年 | 8223篇 |
2006年 | 529篇 |
2005年 | 1562篇 |
2004年 | 1451篇 |
2003年 | 1460篇 |
2002年 | 786篇 |
2001年 | 261篇 |
2000年 | 324篇 |
1999年 | 235篇 |
1998年 | 358篇 |
1997年 | 257篇 |
1996年 | 256篇 |
1995年 | 184篇 |
1994年 | 185篇 |
1993年 | 157篇 |
1992年 | 113篇 |
1991年 | 99篇 |
1990年 | 76篇 |
1989年 | 88篇 |
1988年 | 79篇 |
1987年 | 47篇 |
1986年 | 61篇 |
1985年 | 80篇 |
1984年 | 68篇 |
1981年 | 60篇 |
1977年 | 55篇 |
1976年 | 53篇 |
1969年 | 52篇 |
1968年 | 63篇 |
1967年 | 45篇 |
1966年 | 58篇 |
1965年 | 54篇 |
1955年 | 66篇 |
1954年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
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
72.
Xueming Huang Gordon I. McCalla Jim E. Greer Eric Neufeld 《User Modeling and User-Adapted Interaction》1991,1(1):87-115
A user/student model must be revised when new information about the user/student is obtained. But a sophisticated user/student model is a complex structure that contains different types of knowledge. Different techniques may be needed for revising different types of knowledge. This paper presents a student model maintenance system (SMMS) which deals with revision of two important types of knowledge in student models: deductive knowledge and stereotypical knowledge. In the SMMS, deductive knowledge is represented by justified beliefs. Its revision is accomplished by a combination of techniques involving reason maintenance and formal diagnosis. Stereotypical knowledge is represented in the Default Package Network (DPN). The DPN is a knowledge partitioning hierarchy in which each node contains concepts in a sub-domain. Revision of stereotypical knowledge is realized by propagating new information through the DPN to change default packages (stereotypes) of the nodes in the DPN. A revision of deductive knowledge may trigger a revision of stereotypical knowledge, which results in a desirable student model in which the two types of knowledge exist harmoniously. 相似文献
73.
In optical microscopic measurement of internal blood-vessel diameters, the effect of refraction must be taken into account to ensure accuracy of the result. This effect is discussed and an analytical correction formula derived. Phantom blood vessels with known internal and external diameters were used to test the validity of the correction formula. The errors obtained prior to correction were reduced significantly after correction. 相似文献
74.
This paper sets out to share BT's leadership and experience by determining the identity management opportunities and issues,
then document the lessons learnt in previous deployments and recommend strategies for all types and sizes of organisation.
Today's ICT environment has created a mixed approach to access management across sectors. Browser-based any time, anywhere,
anyone access, coupled with the business need to access more systems and services across a changing infrastructure of distributed
platforms and networked services, has changed the administrative landscape. Enterprises are being forced to add administrative
support staff or invest in technology-driven process change. At the same time, users are undergoing significant change, creating
new expectations in service quality. Moreover, regulatory bodies are demanding confirmation that processes granting access
are controlled and documented. In this world of increasing demands, complexity and expectation, the service management tools,
techniques and options available to improve user access management are as varied and numerous as the issues faced by management
in their deployment.
Identity management is widely heralded as an opportunity to improve the end user experience, reduce costs, improve security
and deliver regulatory compliance — but is often misunderstood. Projects regularly fail to achieve the expected benefits.
These failures are the result of expectations being inappropriately set, deployment of solutions turning out to be more complex
or taking longer than expected, and/or products selected before required functionality has been determined.
For the larger more mature organisations, or those organisations that are the amalgamation of mergers and acquisitions, the
dilemma is where to start and what approach to take. 相似文献
75.
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
76.
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
77.
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
78.
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
79.
Irine Banu Lucy 《Journal of Materials Science》2007,42(14):5875-5879
Capacitance and dielectric loss measurements were carried out using an Al/Cu–GeO2/Al sandwich structure for 0 to 10 vol% Cu films, 120–400 nm thick, deposited at 0.4–1.5 nm/s in the frequency and temperature
range 1–106 Hz and 90–573 K, respectively. The variation of capacitance and dielectric loss with frequency and temperature follows the
Goswami and Goswami model. Capacitance decreases slowly with increasing thickness and also varies with the change in deposition
rate of the cermet film. 相似文献
80.
The field emission characteristics of an oxidized porous polysilicon (OPPS) were investigated with a Pt/Ti multilayer electrode,
which showed highly efficient and stable electron emission characteristics compared with those of conventional Au/NiCr electrodes.
The thin Ti layer played an important role in promoting the adhesion of Pt to SiO2 surface and the distribution of the electric field on the OPPS surface. Additionally, the Ti layer efficiently blocked the
diffusion of emitter metal, which resulted in more reliable emission characteristics. 相似文献