全文获取类型
收费全文 | 8696篇 |
免费 | 449篇 |
国内免费 | 104篇 |
专业分类
化学 | 1312篇 |
晶体学 | 5篇 |
力学 | 143篇 |
综合类 | 37篇 |
数学 | 1538篇 |
物理学 | 1086篇 |
无线电 | 5128篇 |
出版年
2024年 | 31篇 |
2023年 | 174篇 |
2022年 | 142篇 |
2021年 | 188篇 |
2020年 | 175篇 |
2019年 | 122篇 |
2018年 | 154篇 |
2017年 | 249篇 |
2016年 | 296篇 |
2015年 | 297篇 |
2014年 | 569篇 |
2013年 | 624篇 |
2012年 | 502篇 |
2011年 | 470篇 |
2010年 | 384篇 |
2009年 | 497篇 |
2008年 | 390篇 |
2007年 | 477篇 |
2006年 | 387篇 |
2005年 | 377篇 |
2004年 | 372篇 |
2003年 | 276篇 |
2002年 | 271篇 |
2001年 | 195篇 |
2000年 | 160篇 |
1999年 | 196篇 |
1998年 | 185篇 |
1997年 | 173篇 |
1996年 | 169篇 |
1995年 | 112篇 |
1994年 | 88篇 |
1993年 | 93篇 |
1992年 | 73篇 |
1991年 | 55篇 |
1990年 | 45篇 |
1989年 | 44篇 |
1988年 | 36篇 |
1987年 | 28篇 |
1986年 | 19篇 |
1985年 | 16篇 |
1984年 | 23篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1974年 | 10篇 |
1967年 | 8篇 |
排序方式: 共有9249条查询结果,搜索用时 15 毫秒
51.
长江中下游的主要防洪工程是长江干堤 ,长江堤防线路长、工程浩大、堤基工程地质水文地质条件复杂 ,涉及大量的已有地质数据和资料。今后在整治加固堤防的工程地质勘察工作中 ,还需随时进行数据的收集、存储、检索、分析、统计和维护 ,随时调用这些数据进行综合处理、编制报告和图件 ;在防汛期间可以针对堤防险工险段的险情 ,随时查询和调用有关的资料、数据或者图件 ,提供采取抢险措施决策的地质依据。这既提高了地质数据的利用价值和利用率 ,又保证了信息的准确性、完整性和共享性。因此 ,建立合理的长江堤防工程地质信息处理模型及其成熟的技术方法具有重要的意义。 相似文献
52.
Bing Yong HSIE 《数学学报(英文版)》2006,22(2):507-514
This paper gives a p-adic analogue of the Mackey theory, which relates representations of a group of type G - H × t A to systems of imprimitivity. 相似文献
53.
54.
Maria Conceição A. Silva Portela Emmanuel Thanassoulis 《Annals of Operations Research》2006,145(1):129-147
This paper re-assesses three independently developed approaches that are aimed at solving the problem of zero-weights or non-zero
slacks in Data Envelopment Analysis (DEA). The methods are weights restricted, non-radial and extended facet DEA models. Weights
restricted DEA models are dual to envelopment DEA models with restrictions on the dual variables (DEA weights) aimed at avoiding
zero values for those weights; non-radial DEA models are envelopment models which avoid non-zero slacks in the input-output
constraints. Finally, extended facet DEA models recognize that only projections on facets of full dimension correspond to
well defined rates of substitution/transformation between all inputs/outputs which in turn correspond to non-zero weights
in the multiplier version of the DEA model. We demonstrate how these methods are equivalent, not only in their aim but also
in the solutions they yield. In addition, we show that the aforementioned methods modify the production frontier by extending
existing facets or creating unobserved facets. Further we propose a new approach that uses weight restrictions to extend existing
facets. This approach has some advantages in computational terms, because extended facet models normally make use of mixed
integer programming models, which are computationally demanding. 相似文献
55.
In this paper, an adaptive FE analysis is presented based on error estimation, adaptive mesh refinement and data transfer for enriched plasticity continua in the modelling of strain localization. As the classical continuum models suffer from pathological mesh-dependence in the strain softening models, the governing equations are regularized by adding rotational degrees-of-freedom to the conventional degrees-of-freedom. Adaptive strategy using element elongation is applied to compute the distribution of required element size using the estimated error distribution. Once a new mesh is generated, state variables and history-dependent variables are mapped from the old finite element mesh to the new one. In order to transfer the history-dependent variables from the old to new mesh, the values of internal variables available at Gauss point are first projected at nodes of old mesh, then the values of the old nodes are transferred to the nodes of new mesh and finally, the values at Gauss points of new elements are determined with respect to nodal values of the new mesh. Finally, the efficiency of the proposed model and computational algorithms is demonstrated by several numerical examples. 相似文献
56.
George Lagogiannis Christos Makris Athanasios Tsakalidis 《Journal of Discrete Algorithms》2006,4(1):106-141
We consider the problem of maintaining a dynamic ordered set of n integers in a universe U under the operations of insertion, deletion and predecessor queries. The computation model used is a unit-cost RAM, with a word length of w bits, and the universe size is |U|=2w. We present a data structure that uses O(|U|/log|U|+n) space, performs all the operations in O(loglog|U|) time and needs O(loglog|U|/logloglog|U|) structural changes per update operation. The data structure is a simplified version of the van Emde Boas' tree introducing, in its construction and functioning, new concepts, which help to keep the important information for searching along the path of the tree, in a more compact and organized way. 相似文献
57.
58.
59.
一种数字电视条件接收系统的设计与实现 总被引:2,自引:2,他引:0
为支撑业务的安全开展,有线数字电视系统需提供一个安全可靠的加密系统,即条件接收系统。条件接收系统是对数字电视节目进行加密,以实现有线电视运营商对用户进行管理和收费。本文介绍了一种数字电视系统中的条件接收系统实现方案。 相似文献
60.
介绍了视频编码新标准———H .2 6 4中采用的几种抗误码技术 ,基于这些技术 ,新标准确保了压缩视频流在接收端的恢复质量。 相似文献