全文获取类型
收费全文 | 17282篇 |
免费 | 519篇 |
国内免费 | 721篇 |
专业分类
系统科学 | 622篇 |
丛书文集 | 411篇 |
教育与普及 | 588篇 |
理论与方法论 | 106篇 |
现状及发展 | 202篇 |
研究方法 | 112篇 |
综合类 | 16476篇 |
自然研究 | 5篇 |
出版年
2024年 | 104篇 |
2023年 | 193篇 |
2022年 | 292篇 |
2021年 | 311篇 |
2020年 | 162篇 |
2019年 | 78篇 |
2018年 | 145篇 |
2017年 | 172篇 |
2016年 | 148篇 |
2015年 | 309篇 |
2014年 | 491篇 |
2013年 | 456篇 |
2012年 | 545篇 |
2011年 | 580篇 |
2010年 | 607篇 |
2009年 | 640篇 |
2008年 | 776篇 |
2007年 | 878篇 |
2006年 | 667篇 |
2005年 | 628篇 |
2004年 | 514篇 |
2003年 | 427篇 |
2002年 | 475篇 |
2001年 | 561篇 |
2000年 | 579篇 |
1999年 | 926篇 |
1998年 | 870篇 |
1997年 | 876篇 |
1996年 | 767篇 |
1995年 | 700篇 |
1994年 | 679篇 |
1993年 | 522篇 |
1992年 | 496篇 |
1991年 | 455篇 |
1990年 | 394篇 |
1989年 | 361篇 |
1988年 | 294篇 |
1987年 | 213篇 |
1986年 | 108篇 |
1985年 | 46篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1972年 | 5篇 |
1970年 | 5篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Remote sensing of spatial patterns of urban renewal using linear spectral mixture analysis: A case of central urban area of Shanghai (1997―2000) 总被引:2,自引:0,他引:2
YUE Wenze XU Jianhua WU Jiawei XU Lihua 《科学通报(英文版)》2006,51(8):977-986
It is very important to integrate remote sensing with urban geography that the spectral mixture analysis technique is applied to urban land cover evolvement and its eco-environmental effect. Urban land cover is mainly composed of complicated artificial materials, which is the key factor to limit the development of the spectral mixture analysis technique. There are two main aspects in which the technique of spectral mixture analysis is applied to urban geography: one is to calculate vegetation fraction; the other is to build quantitative model of the urban impervious surface obtained from the combination between high albedo fraction and low albedo fraction. The technique of spectral mixture analysis is firstly applied to study urban renewal pattern, scale and mode which happened in Shanghai City from 1997 to 2000, 相似文献
22.
WU Weiren HUANG Biguang 《科学通报(英文版)》2006,51(21):2619-2623
A qualitative trait is usually controlled by a single gene, but it may be sometimes controlled by two or even more genes. This phenomenon is called gene interaction. Rapidly searching for linked mo- lecular markers via bulked segregant analysis (BSA) and then constructing regional linkage map with Mapmaker/Exp has become a common approach to mapping single major genes. However, methods and computer programs developed for mapping single major genes cannot be simply applied to interactive genes because the genetic patterns of gene interac- tions are quite different from that of single-gene in- heritance. Up to now, experimental methods for quickly screening molecular markers linked to inter- active genes and statistical methods and corre- sponding computer softwares for simultaneously analyzing the linkage relationships of multiple mo- lecular markers to an interactive gene have not been available. To solve this problem, in this paper, we propose a strategy for mapping interactive genes using BSA and Mapmaker/Exp. We demonstrate that all interactive genes can be mapped by the 'BSA Mapmaker/Exp' strategy using F2 generation (in a few cases, F3 generation is also needed). As BSA and Mapmaker/Exp have been broadly used in gene mapping studies and are well known by many re- searchers, the strategies proposed in this paper will be useful for practical researches. 相似文献
23.
柳群英 《科技情报开发与经济》2004,14(6):197-198
计算机技术给人们的工作环境带来了质的变化,而这种高效便捷工作环境的获得是以人们丧失部分个人隐私权为代价的。从隐私权的概念出发,首先分析了计算机网络技术的发展给个人隐私权带来的一系列冲突问题,然后讨论了网络环境下对隐私权的保护措施和对策。 相似文献
24.
本文运用文献资料,比较分析法对奥运会影响下的中国经济进行分析研究,阐述了奥运经济对中国体育产业、房地产、证券、就业、旅游等方面的积极影响,以抓住奥运契机,充分发挥奥运经济带动效应,推动中国经济的发展。 相似文献
25.
用于多指数拟合的一种混沌免疫粒子群优化 总被引:3,自引:0,他引:3
为了更好地逼近真实物理场景,对传统的多指数模型作了一些改进,将权因子设置为噪声方差平方的倒数,提出一种基于循环矩阵(CM)的算法用于估计衰减项数.为了求解上述改进模型,提出一种混沌免疫粒子群优化(CIPSO)算法.该算法将人工免疫系统中的克隆、交叉、变异和接收器修正算法嵌入粒子群算法中,并采用混沌算子实现变异,然后将惯性因子改为自适应变化.实验表明:提出的权因子设置更符合实际;用于估计项数的CM算法在估计精度与运行时间上均优于传统的ILS算法;CIPSO算法在收敛精度与运行时间上也优于传统的优化算法,如可信域法、LM法、高斯-牛顿法、差分进化算法和粒子群算法等. 相似文献
26.
在全球气候变暖的背景下,树木年轮宽度与气候变化间的响应关系逐渐进入研究者的视野.大兴安岭地区位于欧亚大陆的气候敏感区和气候脆弱区,是中国纬度最高和增温最快的地区.同时地处寒温带明亮针叶林的南缘,地下存在多年冻土层.所以大兴安岭地区对气候具有独特的区域变化,在树木年轮宽度与气候变化的响应研究中以该地区作为研究区更具有研究意义.主要综述了树轮气候学的研究背景、树木径向生长的研究方法、气候变化对树木径向生长影响的研究进展,重点分析大兴安岭地区树木径向生长的研究情况.为未来树轮气候学的研究发展方向上提供依据,在气候变化对森林植被的影响和预测未来全球变化对陆地生态系统的影响等方面有重要的理论意义. 相似文献
27.
提出了利用微扰正向扩散计算方法的思想,建立了全堆芯格林函数方法(CGFM)中的格林函数库。利用格林函数库取消了内迭代,从而大大提高了中子扩散方程的求解速度。针对我国秦山核电厂的外-内和低泄漏两种布料方案进行了校核计算。结果表明,计算精度与格林函数节块方法(NGFM)相当,计算速度提高近9倍。 相似文献
28.
This study addresses the issue of dynamic event-triggered-based filtering for fuzzy affine systems. To alleviate the utilization of constraint bandwidth resources and improve the efficiency of the signals exchange, a dynamic event-triggered protocol is forwarded to regulate the trigger instants with objective system states. Meanwhile, the nonhomogeneous Markov process is proposed to characterize the dynamic behaviors of sensor faults, where the time-varying transition probabilities belong to a c... 相似文献
29.
In this study, an adaptive asymptotic tracking control problem is considered for stochastic nonlinear systems with unknown backlash-like hysteresis. By utilizing backstepping technology and bound estimation approach, an adaptive asymptotic tracking control scheme is designed, where fuzzy systems are applied to approximate unknown function terms, the effect of hysteresis and stochastic disturbances is compensated appropriately. The proposed scheme ensures that the tracking error can asymptoticall... 相似文献
30.
The Kinetic Monte Carlo(KMC) is one of the commonly used methods for simulating radiation damage of materials. Our team develops a parallel KMC software named Crystal-KMC, which supports the Embedded Atom Method(EAM) potential energy and utilizes the Message Passing Interface(MPI) technology to simulate the vacancy transition of the Copper(Cu) element under neutron radiation. To make better use of the computing power of modern supercomputers, we develop the parallel efficiency optimization model for the Crystal-KMC on Tianhe-2, to achieve a larger simulation of the damage process of materials under irradiation environment. Firstly, we analyze the performance bottleneck of the Crystal-KMC software and use the MIC offload statement to implement the operation of key modules of the software on the MIC coprocessor. We use Open MP to develop parallel optimization for the Crystal-KMC, combined with existing MPI inter-process communication optimization, finally achieving hybrid parallel optimization. The experimental results show that in the single-node CPU and MIC collaborative parallel mode, the speedup of the calculation hotspot reaches 30.1, and the speedup of the overall software reaches 7.43. 相似文献