全文获取类型
收费全文 | 5846篇 |
免费 | 248篇 |
国内免费 | 340篇 |
专业分类
系统科学 | 264篇 |
丛书文集 | 158篇 |
教育与普及 | 96篇 |
理论与方法论 | 21篇 |
现状及发展 | 33篇 |
研究方法 | 23篇 |
综合类 | 5839篇 |
出版年
2024年 | 39篇 |
2023年 | 81篇 |
2022年 | 131篇 |
2021年 | 131篇 |
2020年 | 116篇 |
2019年 | 69篇 |
2018年 | 71篇 |
2017年 | 80篇 |
2016年 | 104篇 |
2015年 | 173篇 |
2014年 | 297篇 |
2013年 | 259篇 |
2012年 | 280篇 |
2011年 | 253篇 |
2010年 | 285篇 |
2009年 | 300篇 |
2008年 | 359篇 |
2007年 | 346篇 |
2006年 | 247篇 |
2005年 | 222篇 |
2004年 | 183篇 |
2003年 | 164篇 |
2002年 | 164篇 |
2001年 | 166篇 |
2000年 | 159篇 |
1999年 | 214篇 |
1998年 | 201篇 |
1997年 | 215篇 |
1996年 | 183篇 |
1995年 | 166篇 |
1994年 | 146篇 |
1993年 | 112篇 |
1992年 | 102篇 |
1991年 | 125篇 |
1990年 | 80篇 |
1989年 | 77篇 |
1988年 | 54篇 |
1987年 | 42篇 |
1986年 | 21篇 |
1985年 | 12篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 1篇 |
排序方式: 共有6434条查询结果,搜索用时 31 毫秒
961.
An ant colony algorithm for solving Max-cut problem 总被引:1,自引:0,他引:1
Max-cut problem is an NP-complete and classical combinatorial optimization problem that has a wide range of applications in different domains, such as bioinformatics, network optimization, statistical physics, and very large scale integration design. In this paper we investigate the capabilities of the ant colony optimization (ACO) heuristic for solving the Max-cut problem and present an AntCut algorithm. A large number of simulation experiments show that the algorithm can solve the Max-cut problem more efficiently and effectively. 相似文献
962.
Based on analysis of the structure characteristics and implementation methods of some representative word oriented linear feedback shift registers (LFSRs) in several modem software oriented stream ciphers, this paper firstly classifies the word oriented LFSRs into two classes: the machine instruction type and the arithmetic type. The similarities and differences between each type are illustrated by concrete examples. Then we give a detailed analysis about the word oriented LFSRs in each category from design structure, cryptographic properties and implementation issue aspects. Finally, some basic design criteria for modem word oriented LFSRs and suitable for software implementation are summarized. 相似文献
963.
Three suborder soils in southwest China were adopted, namely Ustic Vertisol, Stagnic Anthrosol and Ustic Ferrosol, so as to carry out the basic physical and chemical analysis respectively, to design a dynamic measuring method for water stability of soil structure and conduct the comparative study on the quality of the soil structure. The results indicated that (1) The water stability dynamic characteristic of the soil structure could well reflect the maintaining capability of the soil structure as time goes on. (2) The quality of several soil structures in southwest China was sequenced as follows: Stagnic Anthrosols 〉 Ustic Vertisols 〉 Ustic Ferrosols. (3) The water stability of soil structure is very positively correlated with the capillary porosity and the clay particle (D 〈 0.002 mm) content (Co), but is very negatively correlated with the silt (D is 0.05-0.002 ram) content (Csc), and (4) The dynamic functional equation of the water stability of soil structure in southwest China was established, so that the water stability characteristics of various soil structures could be quantitatively expressed and the quality of different soil structures can be quantitatively compared from each other. 相似文献
964.
965.
陈楠 《长春师范学院学报》2008,27(2):157-160
新世纪的到来给图书馆馆员队伍建设提出了新的要求。本文在分析这些新要求的基础上,对如何建立面向21世纪的公共图书馆馆员队伍提出了几点看法。 相似文献
966.
urse plants are those that facilitate the growth and development of other plant species (target species) beneath their canopy because they offer benign microhabitats that are more favorable for seed germination and/or seedling recruitment than their surrounding environment. Nurse plants have been mainly used to restore vegetation in arid and sub-arid zones in recent years. Based on summarizing the definition of nurse plant and target plant, we review the nursing effect mechanisms, ecological factors that influence nursing effect, relationships between nurse plant and ecological restoration. This review also brings forward possible pairs of nurse and target species at lower subtropical areas. Furthermore, we provide the potential tendency in nurse plant research and application. 相似文献
967.
968.
通过对日本、韩国基础研究投入的历史演变分析,总结并比较其变化特征,同时,从宏观层面和中观层面探讨两国基础研究投入的协调机制,得到三点主要的结论和启示。 相似文献
969.
中国古建筑虚拟现实系统的数据采集和处理 总被引:4,自引:0,他引:4
利用虚拟现实技术实现对古建筑的浏览漫游已经成为当前计算机三维制作技术在文物古迹方面的主要应用之一.Virtual Reality-Platform是近年来应用较广的三维虚拟现实平台软件,在介绍基于VRP实现古建筑三维模型虚拟现实步骤的同时,结合大觉寺的虚拟现实系统,重点探讨了中国古建筑虚拟现实系统实现过程的数据采集和处理,针对古建筑的特点和虚拟现实实现的需求对这两个过程提出了较为实用的建议. 相似文献
970.
Characterization of high-yield performance as affected by genotype and environment in rice
下载免费PDF全文
![点击此处可从《浙江大学学报(自然科学英文版)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We characterized yield-relevant characters and their variations over genotypes and environments (locations and years) by examining two rice varieties (9746 and Jinfeng) with high yield potential. 9746 and Jinfeng were planted in two locations of Shanghai, China, during 2005 and 2006. The results show that there was a large variation in grain yield between locations and years. The realization of high yield potential for the two types of rice was closely related to the improved sink size, such as more panicles per square meter or grains per panicle. Stem and leaf biomasses were mainly accumulated from tillering stage to heading stage, and showed slow decline during grain filling. Meanwhile, some photosynthetic characters including net photosynthesis rate (Pn), leaf area index (LAI), specific leaf area (SLA), fluorescence parameter (maximum quantum yield ofPSll, Fv/Fm), chlorophyll content (expressed as SPAD value), as well as nutrient (N, P, K) uptake were also measured to determine their variations over genotypes and environments and their relationships with grain yield. Although there were significant differences between years or locations for most measurements, SLA at tillering and heading stages, Fv/Fm and LAI at heading stage, stem biomass at heading and maturity stages, and leaf nitrogen concentration at tillering and heading stages remained little changed, indicating their pos- sible applications as selectable characters in breeding programs. It was also found that stem nitrogen accumulation at tillering stage is one of the most important and stable traits for high yield formation. 相似文献