全文获取类型
收费全文 | 407772篇 |
免费 | 4826篇 |
国内免费 | 1369篇 |
专业分类
电工技术 | 7584篇 |
综合类 | 324篇 |
化学工业 | 60944篇 |
金属工艺 | 16464篇 |
机械仪表 | 13531篇 |
建筑科学 | 8529篇 |
矿业工程 | 2167篇 |
能源动力 | 11588篇 |
轻工业 | 29138篇 |
水利工程 | 4290篇 |
石油天然气 | 7922篇 |
武器工业 | 17篇 |
无线电 | 49342篇 |
一般工业技术 | 83414篇 |
冶金工业 | 75923篇 |
原子能技术 | 9204篇 |
自动化技术 | 33586篇 |
出版年
2022年 | 2732篇 |
2021年 | 4083篇 |
2020年 | 3019篇 |
2019年 | 3890篇 |
2018年 | 6581篇 |
2017年 | 6549篇 |
2016年 | 7011篇 |
2015年 | 4406篇 |
2014年 | 7258篇 |
2013年 | 20266篇 |
2012年 | 11569篇 |
2011年 | 15472篇 |
2010年 | 12316篇 |
2009年 | 13857篇 |
2008年 | 14247篇 |
2007年 | 13990篇 |
2006年 | 12555篇 |
2005年 | 11234篇 |
2004年 | 10615篇 |
2003年 | 10506篇 |
2002年 | 9939篇 |
2001年 | 9800篇 |
2000年 | 9194篇 |
1999年 | 9599篇 |
1998年 | 24399篇 |
1997年 | 16751篇 |
1996年 | 12866篇 |
1995年 | 9559篇 |
1994年 | 8413篇 |
1993年 | 8429篇 |
1992年 | 6109篇 |
1991年 | 5710篇 |
1990年 | 5724篇 |
1989年 | 5380篇 |
1988年 | 5081篇 |
1987年 | 4464篇 |
1986年 | 4348篇 |
1985年 | 4856篇 |
1984年 | 4471篇 |
1983年 | 4033篇 |
1982年 | 3679篇 |
1981年 | 3773篇 |
1980年 | 3454篇 |
1979年 | 3348篇 |
1978年 | 3354篇 |
1977年 | 3772篇 |
1976年 | 4875篇 |
1975年 | 2875篇 |
1974年 | 2679篇 |
1973年 | 2745篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
S. Hashemi 《Journal of Materials Science》2003,38(14):3055-3062
Essential work of fracture methodology was used to determine plane-stress ductile fracture toughness of high impact polystyrene film of thickness 0.26 mm. Results obtained indicated that specific essential work of fracture, w
e, is independent of loading rate, and for certain specimen sizes, independent of both gauge length and width of the specimen. On the other hand, w
e was found to be affected by the temperature, molecular anisotropy and the geometry of the test specimens. Reasonable estimate of w
e was obtained via crack opening displacement value. 相似文献
22.
Hasegawa M. Furutani S. Doki S. Okuma S. 《Industrial Electronics, IEEE Transactions on》2003,50(5):912-919
This paper proposes a method for designing a robust full-order observer for vector-controlled induction motors taking core loss into account. Although conventional research focuses on parameter identification, global stability of the identification remains questionable. Therefore, robustness against some parameters is required. This paper describes the design of a robust full-order observer which takes core loss into account, using both the gain-scheduled H/sub /spl infin// control and the linear matrix inequality technique. This design always results in a stable controller. The robustness of the proposed method against variations of resistances is evaluated by experiments. 相似文献
23.
Honour Index (HoI), a method to evaluate research performance within different research fields, was derived from the impact
factor (IF). It can be used to rate and compare different categories of journals. HoI was used in this study to determine
the scientific productivity of stem cell research in the Asian Four Dragons (Hong Kong, Singapore, South Korea and Taiwan)
from 1981 to 2001. The methodology applied in this study represents a synthesis of universal indicator studies and bibliometric
analyses of subfields at the micro-level. We discuss several comparisons, and conclude the developmental trend in stem cell
research for two decades.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
24.
Barbara M. Johnston Peter R. Johnston 《International journal for numerical methods in engineering》2003,56(4):589-607
Accurate numerical evaluation of integrals arising in the boundary element method is fundamental to achieving useful results via this solution technique. In this paper, a number of techniques are considered to evaluate the weakly singular integrals which arise in the solution of Laplace's equation in three dimensions and Poisson's equation in two dimensions. Both are two‐dimensional weakly singular integrals and are evaluated using (in a product fashion) methods which have recently been used for evaluating one‐dimensional weakly singular integrals arising in the boundary element method. The methods used are based on various polynomial transformations of conventional Gaussian quadrature points where the transformation polynomial has zero Jacobian at the singular point. Methods which split the region of integration into sub‐regions are considered as well as non‐splitting methods. In particular, the newly introduced and highly accurate generalized composite subtraction of singularity and non‐linear transformation approach (GSSNT) is applied to various two‐dimensional weakly singular integrals. A study of the different methods reveals complex relationships between transformation orders, position of the singular point, integration kernel and basis function. It is concluded that the GSSNT method gives the best overall results for the two‐dimensional weakly singular integrals studied. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
25.
Because biological wastewater treatment plants (WWTPs) involve a long time-delay and various disturbances, in general, skilled operators manually control the plant based on empirical knowledge. And operators usually diagnose the plant using similar cases experienced in the past. For the effective management of the plant, system automation has to be accomplished based upon operating recipes. This paper introduces automatic control and diagnosis based upon the operator's knowledge. Fuzzy logic was employed to design this knowledge-based controller because fuzzy logic can convert the linguistic information to rules. The controller can manage the influent and external carbon in considering the loading rate. The input of the controller is not the loading rate but the dissolved oxygen (DO) lag-time, which has a strong relation to the loading rate. This approach can replace an expensive sensor, which measures the loading rate and ammonia concentration in the reactor, with a cheaper DO sensor. The proposed controller can assure optimal operation and prevent the over-feeding problem. Case-based diagnosis was achieved by the analysis of profile patterns collected from the past. A new test profile was diagnosed by comparing it with template patterns containing normal and abnormal cases. The proposed control and diagnostic system will guarantee the effective and stable operation of WWTPs. 相似文献
26.
Y Terashima H Ozaki R R Giri T Tano S Nakatsuji R Takanami S Taniguchi 《Water science and technology》2006,54(8):55-63
Environmental pollution by low concentrations of 2,4-Dichlorophenoxyacetic acid (2,4-D) is a concern these days due to ever increasingly stringent regulations. Photocatalysis with immobilized TiO2 fiber is a promising oxidation method. Laboratory experiments on photocatalytic degradation of 0.045 mmol l(-1) 2,4-D with the world's first high-strength TiO2 fiber catalyst were carried out in a continuous flow reactor in which the degradations were, in general, similar to those with high 2,4-D concentrations investigated elsewhere. Degradation and mineralization of 2,4-D were significantly enhanced with no initial pH adjustments. The rate constants for total organic carbon (TOC) without pH adjustment were about two-fold bigger than the pH adjustment cases. CO2 gas measurement and carbon mass-balance were carried out for the first time, where about 34% organic carbon converted into CO2 gas during four-hour oxidation. 2,4-Dichlorophenol (2,4-DCP), phenol, benzyl alcohol and two unknowns (RT = 2.65 and 3.78 min.) were detected as aromatic intermediates while Phenol was the new aromatic in HPLC analysis. Dechlorination efficiencies were high (> 70%) in all the cases, and more than 90% efficiencies were observed in chloride mass balance. Bigger flow rates and solution temperature fixed at 20 degrees C without pH adjustment greatly enhanced 2,4-D mineralization. These results can be an important basis in applying the treatment method for dioxin-contaminated water and wastewater. 相似文献
27.
28.
29.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
30.