全文获取类型
收费全文 | 157566篇 |
免费 | 20775篇 |
国内免费 | 15013篇 |
学科分类
工业技术 | 193354篇 |
出版年
2024年 | 543篇 |
2023年 | 2445篇 |
2022年 | 4401篇 |
2021年 | 5590篇 |
2020年 | 5857篇 |
2019年 | 5328篇 |
2018年 | 4985篇 |
2017年 | 6026篇 |
2016年 | 6926篇 |
2015年 | 7120篇 |
2014年 | 9620篇 |
2013年 | 10442篇 |
2012年 | 11627篇 |
2011年 | 12354篇 |
2010年 | 9551篇 |
2009年 | 9911篇 |
2008年 | 9751篇 |
2007年 | 11182篇 |
2006年 | 9737篇 |
2005年 | 8537篇 |
2004年 | 6876篇 |
2003年 | 6065篇 |
2002年 | 4860篇 |
2001年 | 4077篇 |
2000年 | 3550篇 |
1999年 | 2792篇 |
1998年 | 2351篇 |
1997年 | 1953篇 |
1996年 | 1736篇 |
1995年 | 1550篇 |
1994年 | 1218篇 |
1993年 | 932篇 |
1992年 | 767篇 |
1991年 | 564篇 |
1990年 | 456篇 |
1989年 | 382篇 |
1988年 | 254篇 |
1987年 | 156篇 |
1986年 | 129篇 |
1985年 | 143篇 |
1984年 | 146篇 |
1983年 | 77篇 |
1982年 | 87篇 |
1981年 | 56篇 |
1980年 | 68篇 |
1979年 | 50篇 |
1978年 | 21篇 |
1974年 | 12篇 |
1959年 | 19篇 |
1951年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
992.
993.
欧阳子劲 《石油化工设备技术》2007,28(3):27-29,32
K202A压缩机的电机轴瓦采用的是动压轴承,经常持续升温。其主要原因是由于滑动轴承和轴之间是半液体摩擦,润滑油在轴颈及轴瓦之间没有形成具有足够压力的油膜,造成滑动轴承和轴局部形成半液体摩擦而产生大量的热量,又无法被带走引起的。文章通过验算K202压缩机电机滑动轴承温度,分析影响滑动轴承运行温度的因素,提出在原滑动轴承上开油楔及加装一台齿轮油泵为滑动轴承强制润滑,并且通过联轴器把电机和压缩机连接起来,用压缩机轴瓦托起电机轴,使电机轴颈和轴瓦之间处于液体摩擦状态,可有效地降低滑动轴承的运行温度。 相似文献
994.
A pseudohyperbolic problem of optimal control of intratumoral drug distribution is formulated. It takes into account the heterogeneity
of tumor tissues and effects of convection diffusion in a fissured porous medium. A mathematical model constructed and the
corresponding optimal control problem are shown to be correct.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 6, pp. 147–154, November–December 2007. 相似文献
995.
在冶金热力学和动力学及反应工程学原理的基础上,建立了模拟复吹转炉冶炼过程的数学模型.在用梅钢150t复吹转炉工业试验的结果对模型加以验证之后,利用模型对具有中高磷铁水特点的梅钢转炉吹炼工艺进行了分析讨论. 相似文献
996.
简介了关系模型、键、完整性规则、E-R模型、函数依赖、模式分解和关系模式的范式等数据库技术基础和规范化设计理论,从键和完整性规则的实现、数据冗余的特殊情况和字典设计等方面论述了在实际设计工作中如何灵活运用关系数据库设计理论。 相似文献
997.
András Faragó 《Algorithmica》2007,49(4):337-356
We prove two results that provide new fundamental limits for topology control in large ad hoc and sensor networks. First,
we show that it remains true under very general conditions that the maximum expected node degree must grow to infinity at
least logarithmically if we want to maintain asymptotic connectivity. This has been known so far only for much more special
models than ours. Building on this result, we prove a new fundamental limit regarding link dynamics, which means the worst case length ratio of the longest and shortest link adjacent to the same node. We prove that if link
dynamics remains bounded, then no topology control algorithm can keep a large network connected with high probability. Moreover,
bounded link dynamics prevents connectivity in the limit without any a priori assumption on node degrees or transmission ranges.
Our results hold in a model that is much more general than the frequently used assumption of uniformly distributed nodes in
a regularly shaped planar domain. Our more abstract setting also aims at finding (hopefully) more robust and elegant proofs
that have less dependence on the special geometry. Since link dynamics is expected to be bounded in practice, the results
strenghten the theoretical basis for the argument that a very large ad hoc or sensor network is unable to maintain connectivity
if it has a flat, random organization without additional structure.
Supported in part by NSF Grants ANI-0220001 and CCF-0634848. 相似文献
998.
Chen-Tsung Kuo Author Vitae 《Pattern recognition》2007,40(2):742-755
Three dimensional models play an important role in many applications; the problem is how to select the appropriate models from a 3D database rapidly and accurately. In recent years, a variety of shape representations, statistical methods, and geometric algorithms have been proposed for matching 3D shapes or models. In this paper, we propose a 3D shape representation scheme based on a combination of principal plane analysis and dynamic programming. The proposed 3D shape representation scheme consists of three steps. First, a 3D model is transformed into a 2D image by projecting the vertices of the model onto its principal plane. Second, the convex hall of the 2D shape of the model is further segmented into multiple disjoint triangles using dynamic programming. Finally, for each triangle, a projection score histogram and moments are extracted as the feature vectors for similarity searching. Experimental results showed the robustness of the proposed scheme, which resists translation, rotation, scaling, noise, and destructive attacks. The proposed 3D model retrieval method performs fairly well in retrieving models having similar characteristics from a database of 3D models. 相似文献
999.
A theoretical framework is presented to study the consistency of robust estimators used in vision problems involving extraction of fine details. A strong correlation between asymptotic performance of a robust estimator and the asymptotic bias of its scale estimate is mathematically demonstrated where the structures are assumed to be linear corrupted by Gaussian noise. A new measure for the inconsistency of scale estimators is defined and formulated by deriving the functional forms of four recent high-breakdown robust estimators. For each estimator, the inconsistency measures are numerically evaluated for a range of mutual distances between structures and inlier ratios, and the minimum mutual distance between the structures, for which each estimator returns a non-bridging fit, is calculated. 相似文献
1000.
C.Y. Tang C.P. Tsui B. Stojanovic M. Kojic 《International Journal of Mechanical Sciences》2007,49(10):1179-1191
In this study, Hill's muscle theory coupled with fatigue was proposed to describe mechanical behaviours of skeletal muscles. The force developed by a fatigued muscle was described by a muscle fatigue formula which was a time function of the activation αa and the stretch λ. The modified Hill's muscle theory was hence incorporated into a three-dimensional (3D) finite element model using the PAK finite element code. In this paper, the theoretical derivation of the 3D muscle model was firstly described. After presenting the method of establishing the finite element programme, a case example of studying the mechanical response of a frog gastrocnemius muscle was used to illustrate the applicability of the proposed methodology. The effects of the muscle fatigue on the deformation as well as the stress and strain distribution of the frog muscle subject to a cyclic activation function have been determined. An experiment capturing the real-time shape change of a frog muscle was also conducted to assess the applicability of the proposed method. A comparison between the deformed shapes of the predictive model and the frog muscles was also made. It was shown that the method is capable of providing a reasonable model for describing the mechanical behaviour of skeletal muscles. 相似文献