全文获取类型
收费全文 | 412751篇 |
免费 | 5821篇 |
国内免费 | 1386篇 |
专业分类
电工技术 | 7704篇 |
综合类 | 349篇 |
化学工业 | 61998篇 |
金属工艺 | 14285篇 |
机械仪表 | 11871篇 |
建筑科学 | 11637篇 |
矿业工程 | 869篇 |
能源动力 | 11117篇 |
轻工业 | 43797篇 |
水利工程 | 3312篇 |
石油天然气 | 1835篇 |
武器工业 | 13篇 |
无线电 | 55390篇 |
一般工业技术 | 76630篇 |
冶金工业 | 74951篇 |
原子能技术 | 5568篇 |
自动化技术 | 38632篇 |
出版年
2021年 | 2669篇 |
2019年 | 2435篇 |
2018年 | 3839篇 |
2017年 | 3905篇 |
2016年 | 4146篇 |
2015年 | 3427篇 |
2014年 | 5714篇 |
2013年 | 19282篇 |
2012年 | 10204篇 |
2011年 | 14683篇 |
2010年 | 11284篇 |
2009年 | 12884篇 |
2008年 | 13915篇 |
2007年 | 14286篇 |
2006年 | 12778篇 |
2005年 | 11962篇 |
2004年 | 11574篇 |
2003年 | 11279篇 |
2002年 | 10914篇 |
2001年 | 11131篇 |
2000年 | 10271篇 |
1999年 | 10769篇 |
1998年 | 24010篇 |
1997年 | 17587篇 |
1996年 | 13903篇 |
1995年 | 10979篇 |
1994年 | 9772篇 |
1993年 | 9355篇 |
1992年 | 7121篇 |
1991年 | 6790篇 |
1990年 | 6397篇 |
1989年 | 6106篇 |
1988年 | 5860篇 |
1987年 | 4885篇 |
1986年 | 4834篇 |
1985年 | 5978篇 |
1984年 | 5599篇 |
1983年 | 4832篇 |
1982年 | 4496篇 |
1981年 | 4447篇 |
1980年 | 4208篇 |
1979年 | 4080篇 |
1978年 | 3771篇 |
1977年 | 4548篇 |
1976年 | 6097篇 |
1975年 | 3115篇 |
1974年 | 3011篇 |
1973年 | 2890篇 |
1972年 | 2318篇 |
1971年 | 2003篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
M.J. Seaton 《Computer Physics Communications》2002,146(2):225-249
The paper gives a review of the mathematical properties of the Coulomb radial wave functions, for attractive and repulsive potentials and for positive and negative energies, together with recommendations on best methods for their computation. It includes discussions of analytic continuations (complex energies, radial co-ordinates and angular momenta) and of relativistic Coulomb functions. 相似文献
992.
The conventional application of reduction factors to response spectrum analysis results is inappropriate for the abutment shear forces, which are based on elastic action. On the other hand, adopting the unreduced values from the elastic dynamic analysis does not achieve equilibrium among the abutment shear forces, deck inertia forces, and reduced pier forces. A simplified method is here proposed for the assessment of the shear on the abutments, documented by comparison with response spectrum and time history nonlinear analyses for several bridge configurations. For the analyzed configuration of the bridge with an internal movement joint, the response spectrum analysis underestimates the shear on the abutment for low values of the abutment flexibility and overestimates it when the stiffness of the abutments becomes higher than that of the piers. In all the case studies analyzed, the proposed method approximates the time history results better than the response spectrum. 相似文献
993.
994.
WS Ahn J Yoo SW Huh CK Kim JM Lee SE Namkoong SM Bae IP Lee 《Canadian Metallurgical Quarterly》2003,12(5):383-390
We investigated clinical efficacy of green tea extracts (polyphenon E; poly E and (-)-epigallocatechin-3-gallate [EGCG]) delivered in a form of ointment or capsule in patients with human papilloma virus (HPV) infected cervical lesions. Fifty-one patients with cervical lesions (chronic cervicitis, mild dysplasia, moderate dysplasia and severe dysplasia) were divided into four groups, as compared with 39 untreated patients as a control. Poly E ointment was applied locally to 27 patients twice a week. For oral delivery, a 200 mg of poly E or EGCG capsule was taken orally every day for eight to 12 weeks. In the study, 20 out of 27 patients (74%) under poly E ointment therapy showed a response. Six out of eight patients under poly E ointment plus poly E capsule therapy (75%) showed a response, and three out of six patients (50%) under poly E capsule therapy showed a response. Six out of 10 patients (60%) under EGCG capsule therapy showed a response. Overall, a 69% response rate (35/51) was noted for treatment with green tea extracts, as compared with a 10% response rate (4/39) in untreated controls (P<0.05). Thus, the data collected here demonstrated that green tea extracts in a form of ointment and capsule are effective for treating cervical lesions, suggesting that green tea extracts can be a potential therapy regimen for patients with HPV infected cervical lesions. 相似文献
995.
Probabilistic reliable dissemination in large-scale systems 总被引:2,自引:0,他引:2
Kermarrec A.-M. Massoulie L. Ganesh A.J. 《Parallel and Distributed Systems, IEEE Transactions on》2003,14(3):248-258
The growth of the Internet raises new challenges for the design of distributed systems and applications. In the context of group communication protocols, gossip-based schemes have attracted interest as they are scalable, easy to deploy, and resilient to network and process failures. However, traditional gossip-based protocols have two major drawbacks: 1) they rely on each peer having knowledge of the global membership; and 2) being oblivious to the network topology, they can impose a high load on network links when applied to wide-area settings. In this paper, we provide a theoretical analysis of gossip-based protocols which relates their reliability to key system parameters (the system size, failure rates, and number of gossip targets). The results provide guidelines for the design of practical protocols. In particular, they show how reliability can be maintained while alleviating drawback by: 1) providing each peer with only a small subset of the total membership information and drawback; and 2) organizing members into a hierarchical structure that reflects their proximity according to some network-related metric. We validate the analytical results by simulations and verify that the hierarchical gossip protocol considerably reduces the load on the network compared to the original, non-hierarchical protocol. 相似文献
996.
This paper presents two independent dynamic models of a nuclear gas turbine power plant. Both the high temperature nuclear reactor (HTR) and its energy conversion system (ECS) based on a direct Brayton cycle have been modelled. One model utilises RELAP5 for the ECS, the other Aspen Custom Modeler (ACM). The reactor model used in both models is a point kinetic model derived from a detailed reactor model. The ECS model is described and compared componentwise, with an emphasis on the turbomachinery. The total plant models are compared with each other by calculating two representative transients: one load rejection transient and one transient with the system at part load. 相似文献
997.
J Valla A Leguerrier H Corbineau B Sevray T Langanay H Le Couls M Sellin C Rioux Y Logeais 《Canadian Metallurgical Quarterly》1995,49(9):816-823
From 1978 to 1992, 121 cases of postinfarction left ventricular aneurysm (99 males, 22 females, mean age 60 years) were operated on. The authors insist on a high rate of clinical arhythmogenicity (31.4%) and associated mechanical complications (21%). 76% of patients were in functional NYHA class III or IV. Resection was performed in 90% of patients, plication in 10%. 58% underwent coronary artery bypass grafting (1.7 graft/patient), 16% encircling ventriculotomy, 8% mitral valve replacement and 13% closure of ventricular septal defect. Operative mortality was 14.9% (10% when other mechanical complications where excluded). 5-year survival is 67.9%. Late cardiac deaths are as follow: left ventricular failure (1.8% A/P), Sudden death (1.4% A/P), Myocardial infarction (0.6% A/P). 82% of survivals are in functional NYHA class I or II. Only functional class NYHA III or IV is predictive of late death. We conclude that postinfarction left ventricular aneurysm remains a high risk complication especially when associated with other mechanical complications. When arhythmogenicity is present we suggest rhythmologic surgery and in all cases, complete revascularization. 相似文献
998.
We explain why the methods in Langridge, Hart and Crampin [Comput. Phys. Commun. 134 (2001) 78] suffice for the evaluation of the lattice sums entering the Madelung matrix describing multipole interactions in systems with one-dimensional translational periodicity. 相似文献
999.
Computational and laboratory experiments generate masses of data that must be stored reliably, with minimal effort on each researcher's part, and must be retrievable for decades. The storage environment must also work seamlessly across scientific disciplines and capture all of a file system's features in a semantically-based catalog that provides Boolean, keyword, and tree-based data access. The authors describe a metadata-based archive for scientific data that provides flexible archive storage for very large data sets. The system uses metadata to organize and manage the data without imposing predefined metadata formats on scientists. 相似文献
1000.
Shape memory properties of Ni-Ti based melt-spun ribbons 总被引:1,自引:0,他引:1
R. Santamarta E. Cesari J. Pons T. Goryczka 《Metallurgical and Materials Transactions A》2004,35(3):761-770
Shape-memory properties of equiatomic NiTi, Ni45Ti50Cu5, and Ni25Ti50Cu25 ribbons made by melt spinning have been studied by temperature inducing the martensitic transformation under constant tensile
loads. Recoverable strains above 4 pct can be obtained under ∼100 MPa loads for the NiTi and Ni45Ti50Cu5 ribbons, transforming to B19’ martensite. The B19 martensite is formed in the Ni25Ti50Cu25 ribbon after crystallization, and according to the lowering in transformation strain as Cu content increases, the recoverable
strain is close to 2.5 pct for ∼150 MPa load. The transformation temperatures exhibit a linear dependence on the applied stress,
which can be quantitatively described by means of a Clausius-Clapeyron type equation. The NiTi and Ni45Ti50Cu5 ribbons exhibited some degree of two-way shape-memory effect (TWSME) after thermomechanical cycling. Texture analyses performed
on the different ribbons allow us to better understand the transformation strains obtained in each ribbon. The amounts of
shape-memory effect (SME) and nonrecoverable strain shown by the studied ribbons are of the same order as those already observed
in bulk materials, which makes melt spinning an ideal substitute to complicated manufacturing processes if really thin samples
are needed. However, applicable stresses in melt-spun ribbons are limited by a relatively “premature” brittle fracture caused
by irregularities in ribbon thickness. 相似文献