全文获取类型
收费全文 | 29689篇 |
免费 | 2169篇 |
国内免费 | 1619篇 |
专业分类
电工技术 | 2680篇 |
综合类 | 3987篇 |
化学工业 | 1617篇 |
金属工艺 | 875篇 |
机械仪表 | 2344篇 |
建筑科学 | 2243篇 |
矿业工程 | 976篇 |
能源动力 | 756篇 |
轻工业 | 729篇 |
水利工程 | 724篇 |
石油天然气 | 852篇 |
武器工业 | 232篇 |
无线电 | 1981篇 |
一般工业技术 | 2307篇 |
冶金工业 | 669篇 |
原子能技术 | 100篇 |
自动化技术 | 10405篇 |
出版年
2024年 | 52篇 |
2023年 | 216篇 |
2022年 | 349篇 |
2021年 | 486篇 |
2020年 | 590篇 |
2019年 | 597篇 |
2018年 | 506篇 |
2017年 | 749篇 |
2016年 | 814篇 |
2015年 | 895篇 |
2014年 | 1640篇 |
2013年 | 1888篇 |
2012年 | 1889篇 |
2011年 | 1988篇 |
2010年 | 1689篇 |
2009年 | 1861篇 |
2008年 | 1905篇 |
2007年 | 2146篇 |
2006年 | 1905篇 |
2005年 | 1608篇 |
2004年 | 1384篇 |
2003年 | 1268篇 |
2002年 | 1094篇 |
2001年 | 929篇 |
2000年 | 797篇 |
1999年 | 644篇 |
1998年 | 514篇 |
1997年 | 494篇 |
1996年 | 395篇 |
1995年 | 359篇 |
1994年 | 324篇 |
1993年 | 231篇 |
1992年 | 212篇 |
1991年 | 192篇 |
1990年 | 150篇 |
1989年 | 139篇 |
1988年 | 110篇 |
1987年 | 62篇 |
1986年 | 64篇 |
1985年 | 43篇 |
1984年 | 58篇 |
1983年 | 33篇 |
1982年 | 39篇 |
1981年 | 27篇 |
1980年 | 24篇 |
1979年 | 33篇 |
1978年 | 14篇 |
1977年 | 24篇 |
1976年 | 14篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 267 毫秒
91.
92.
93.
一种探测二维电磁目标的新方法 总被引:2,自引:0,他引:2
电磁目标的探测对通信而言有着十分重要的意义。本文描述一种收敛迅速、结果准确、抗强随机噪声的探测二维电磁目标的新方法。首先从体等效原理出发得到一个积分方程组,此方程组可求解散射问题。随后,对此方程组求变分,变形后得到散射场变化与介电参数变化之间关系的矩阵方程,即反演方程。文中列举了几个例子,通过数值实验结果证明本法收敛速度快、反演精度高、适应复杂目标的能力强,能抗强随机噪声干扰 相似文献
94.
We present our machine learning system, that uses inductive logic programming techniques to learn how to identify transmembrane
domains from amino acid sequences. Our system facilitates the use of operators such as ‘contains’, that act on entire sequences,
rather than on individual elements of a sequence. The prediction accuracy of our new system is around 93%, and this compares
favourably with earlier results.
This work was carried out with the support of a research grant from ISIS, Fujitsu Laboratories. 相似文献
95.
This paper demonstrates how the problem of tracking targets, which appear as either straight or curved lines in two-dimensional display images (or data images) can be formulated in terms of a directed weighted graph model and how dynamic programming techniques can be efficiently applied to reach an optimal or sub-optimal solution. In general, track detection algorithms providing optimal solutions have good detective ability, but most of them suffer from the inability to detect discontinuous lines or to resolve efficiently pairs of crossing lines. A sub-optimal solution is provided that efficiently overcomes these weaknesses. We focus on modeling the track detection problem in terms of a graph, formulating fast sequential/parallel sub-optimal track detection algorithms and testing them on simulated data in order to show their detective ability. Moreover, we specify the conditions under which sub-optimal algorithms can perform at least as well as their corresponding optimal algorithms. This is significant for the track detection problem where fast, accurate and real-time detection is considered a necessity. 相似文献
96.
新型迷宫式气锚及其应用 总被引:6,自引:1,他引:5
新型迷宫式气锚将重力分离原理和离心分离原理有机地结合在一起,其基本型气锚主要由上、下两级组成。上级为离心式螺旋气锚,下级为重力分离式和离心分离式综合气锚,可使油气流经同一长度锚筒时,达到双倍的分离效果。可根据油井气量的大小(气液比值)组成任意级数,实现油气的高效分离。还可对低产能井、沉没度易出现负值的油井进行油气分离,维持油井一定时间的生产。现场28口井的应用表明,新型迷宫式气锚油气分离效果理想,能有效地提高泵效,平均泵效由原来的28.9%提高到43.8%。 相似文献
97.
This paper formulates the pickup and delivery problem, also known as the dial-a-ride problem, as an integer program. Its polyhedral structure is explored and four classes of valid inequalities developed. The results of a branch-and-cut algorithm based on these constraints are presented. 相似文献
98.
99.
在基于单片机的智能化重力加速度测试仪中采用C语言编程简化了程序设计任务,对于汇编语言难于处理的浮点数运算及汉字打印输出可通过C语言编译器的内部库函数调用实现,介绍了一种专为8051系列单片机设计的C语言编译器Frankilin C51,它具有代码优化功能,能产生极高效率的机器码,并且提供了丰富的内部函数库。描述了C51函数库所支持的IEEE标准浮点数的内存格式以及采用sprintf()函数处理包括 相似文献
100.
J. Dingel 《Formal Aspects of Computing》2002,14(2):123-197
Parallel computers have not yet had the expected impact on mainstream computing. Parallelism adds a level of complexity to
the programming task that makes it very error-prone. Moreover, a large variety of very different parallel architectures exists.
Porting an implementation from one machine to another may require substantial changes. This paper addresses some of these
problems by developing a formal basis for the design of parallel programs in the form of a refinement calculus. The calculus
allows the stepwise formal derivation of an abstract, low-level implementation from a trusted, high-level specification. The
calculus thus helps structuring and documenting the development process. Portability is increased, because the introduction
of a machine-dependent feature can be located in the refinement tree. Development efforts above this point in the tree are
independent of that feature and are thus reusable. Moreover, the discovery of new, possibly more efficient solutions is facilitated.
Last but not least, programs are correct by construction, which obviates the need for difficult debugging. Our programming/specification
notation supports fair parallelism, shared-variable and message-passing concurrency, local variables and channels. The calculus
rests on a compositional trace semantics that treats shared-variable and message-passing concurrency uniformly. The refinement
relation combines a context-sensitive notion of trace inclusion and assumption-commitment reasoning to achieve compositionality.
The calculus straddles both concurrency paradigms, that is, a shared-variable program can be refined into a distributed, message-passing
program and vice versa.
Received July 2001 / Accepted in revised form May 2002 相似文献