全文获取类型
收费全文 | 180460篇 |
免费 | 2332篇 |
国内免费 | 726篇 |
专业分类
电工技术 | 3351篇 |
综合类 | 108篇 |
化学工业 | 28865篇 |
金属工艺 | 7851篇 |
机械仪表 | 5225篇 |
建筑科学 | 4501篇 |
矿业工程 | 883篇 |
能源动力 | 4935篇 |
轻工业 | 16659篇 |
水利工程 | 1743篇 |
石油天然气 | 3177篇 |
武器工业 | 2篇 |
无线电 | 20235篇 |
一般工业技术 | 33942篇 |
冶金工业 | 33281篇 |
原子能技术 | 4330篇 |
自动化技术 | 14430篇 |
出版年
2021年 | 1513篇 |
2019年 | 1424篇 |
2018年 | 2332篇 |
2017年 | 2255篇 |
2016年 | 2392篇 |
2015年 | 1699篇 |
2014年 | 2894篇 |
2013年 | 8139篇 |
2012年 | 4756篇 |
2011年 | 6597篇 |
2010年 | 5206篇 |
2009年 | 6027篇 |
2008年 | 5982篇 |
2007年 | 5916篇 |
2006年 | 5111篇 |
2005年 | 4735篇 |
2004年 | 4525篇 |
2003年 | 4189篇 |
2002年 | 4150篇 |
2001年 | 4148篇 |
2000年 | 3947篇 |
1999年 | 4067篇 |
1998年 | 10439篇 |
1997年 | 7428篇 |
1996年 | 5691篇 |
1995年 | 4303篇 |
1994年 | 3643篇 |
1993年 | 3587篇 |
1992年 | 2628篇 |
1991年 | 2554篇 |
1990年 | 2429篇 |
1989年 | 2453篇 |
1988年 | 2389篇 |
1987年 | 2139篇 |
1986年 | 2072篇 |
1985年 | 2380篇 |
1984年 | 2193篇 |
1983年 | 2020篇 |
1982年 | 1887篇 |
1981年 | 1953篇 |
1980年 | 1806篇 |
1979年 | 1823篇 |
1978年 | 1783篇 |
1977年 | 2114篇 |
1976年 | 2700篇 |
1975年 | 1559篇 |
1974年 | 1551篇 |
1973年 | 1610篇 |
1972年 | 1353篇 |
1971年 | 1265篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Built-in test factors in a life cycle cost model 总被引:1,自引:0,他引:1
A method is given for incorporating the effects of built-in test (BIT) into the life cycle cost of a given electronic system. A cost model is derived that captures the savings achieved by BIT through reducing the maintenance times, complexity of external test equipment, personnel skill levels, amount of spare parts, and the need for preventive maintenance. The model also includes such design considerations as false alarms, diagnostic errors, undetected faults, BIT hardware failures, and diagnostic ambiguity. 相似文献
992.
A general finite element approach to computing the modes of open-boundary waveguides is presented. This efficient and robust scheme applies equally to situations with real and complex propagation constants. By using a localised boundary impedance condition, the approach preserves the sparsity of the global matrices. A comparison with the well established infinite element technique and the analysis of a 2-D leaky optical structure are given as examples 相似文献
993.
D. Li A. F. Yee I. -W. Chen S. -C. Chang K. Takahashi 《Journal of Materials Science》1994,29(8):2205-2215
The fracture toughness and uniaxial tensile yield strengths of unmodified and CTBN-rubber-modified epoxies were measured under hydrostatic pressure. The purpose of these experiments was to learn how suppressing cavitation in rubber particles affects the deformation mechanisms and the fracture toughness of rubber-modified epoxy. It was found that the cavitation of CTBN-rubber could be suppressed at a relatively low pressure (between 30 and 38 M Pa). With cavitation suppressed, the rubber particles are unable to induce massive shearyielding in the epoxy matrix, and the fracture toughness of the rubber-modified epoxy is no higher than that of the unmodified epoxy in the pressure range studied. Unmodified epoxy shows a brittle-to-ductile transition in fracture toughness test. The reason for this transition is the postponement of the cracking process by applied pressure.Work performed while on a sabbatical leave at the University of Michigan. 相似文献
994.
S. M. Arnold A. F. Saleeb H. Q. Tan Y. Zang 《International journal for numerical methods in engineering》1994,37(11):1931-1944
The issue of developing effective and robust schemes to implement a class of the Ogden-type hyperelastic constitutive models is addressed. To this end, special purpose functions (running under MACSYMA) are developed for the symbolic derivation, evaluation, and automatic FORTRAN code generation of explicit expressions for the corresponding stress function and material tangent stiffness tensors. These explicit forms are valid over the entire deformation range, since the singularities resulting from repeated principal-stretch values have been theorectically removed. The required computational algorithms are outlined, and the resulting FORTRAN computer code is presented. 相似文献
995.
We derive an effective single-band Hubbard type Hamiltonian for CuO2 planes. The Hamiltonian includes both electron-electron repulsion and electron-phonon coupling to oxygen vibrational modes. We start with first-principles density functional theory parameters and then map onto a single-band model. Unlike previous mappings to a single-band Hamiltonian, ours explicitly preserves the Fermi surface shape and matrix elements of the many-band Hamiltonian. We consider both in-plane oxygen breathing modes as well as out-of-plane tilting modes. The latter modes have a quadratic electron-phonon coupling, and are also highly anharmonic in La2CuO4 based superconductors. The coupling to breathing modes is too small to account for highT
c, while the coupling to quadratic modes is much stronger even though they would be neglected in a standard Migdal-Eliashberg approach to superconductivity. 相似文献
996.
Highlights key considerations that should be addressed by consulting psychologists to demonstrate the value of assessment services that they provide to clients. Executive and managerial assessment (EMA) is done in a variety of contexts, at multiple levels, and for multiple purposes. In order to demonstrate the value of EMA, it is suggested that consultants present a 2-part framework of evidence to decision makers. First, they should present the results of utility analysis, using the very best parameter estimates available. Second, they should present a detailed linkage of essential job tasks to required knowledge, skills, abilities, and other characteristics (KSAOs). Then, KSAOs should be linked to instruments of prediction back to essential job tasks. Value is therefore demonstrated in 2 ways: in financial terms as well as by presenting construct-oriented evidence of validity. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
997.
998.
Centralized and distributed automated guided vehicle system (AGVS) models for materials handling, and the model for part processing are integrated into a single coherent model. This formulation can be used to collectively schedule and control the entire flexible manufacturing system (FMS) as opposed to the traditional separate scheduling of part processing and material handling. The two AGVS models are based on Petri nets and can be directly used in the scheduling method that uses Petri nets for formulation and heuristic search for solution. This method employs a global search to seek the optimal operation of an entire FMS. Scheduling examples are presented and the method compares favorably with the results simulated using heuristic dispatch rules 相似文献
999.
Wang F.-Y. Gildea K. Jungnitz H. Chen D.D. 《Industrial Electronics, IEEE Transactions on》1994,41(6):641-653
The manufacturing message specification (MMS) is the ISO standard communication protocol specific to manufacturing. To analyze MMS design and performance, service unit automats are introduced to represent individual MMS services, while service connection Petri Nets (PNs) are constructed from these automats to describe MMS service connections and processes. This approach makes MMS protocol specification and analysis possible in terms of well-developed concepts and methods in PN theory. It leads to a distributed and hierarchical model of MMS software system by integrating service connection PNs. A generalized stochastic PN for MMS performance evaluation is obtained by incorporating service parameters and time factors into the model. A technique based on T-invariants is used to simplify the performance analysis 相似文献
1000.
Enhanced performance is demonstrated in n-type metal-oxide-semiconductor field-effect transistors with channel regions formed by pseudomorphic growth of strained Si on relaxed Si1-xGex. Standard MOS fabrication techniques were utilized, including thermal oxidation of the strained Si. Surface channel devices show low-field mobility enhancements of 80% at room temperature and 12% at 10 K, when compared to control devices fabricated in Czochralski Si. Similar enhancements are observed in the device transconductance. In addition, buried channel devices show peak room temperature mobilities about three times that of control devices 相似文献