全文获取类型
收费全文 | 11471篇 |
免费 | 358篇 |
国内免费 | 462篇 |
专业分类
系统科学 | 420篇 |
丛书文集 | 346篇 |
教育与普及 | 231篇 |
理论与方法论 | 66篇 |
现状及发展 | 74篇 |
研究方法 | 47篇 |
综合类 | 11105篇 |
自然研究 | 2篇 |
出版年
2024年 | 63篇 |
2023年 | 131篇 |
2022年 | 197篇 |
2021年 | 213篇 |
2020年 | 145篇 |
2019年 | 40篇 |
2018年 | 84篇 |
2017年 | 86篇 |
2016年 | 90篇 |
2015年 | 239篇 |
2014年 | 309篇 |
2013年 | 287篇 |
2012年 | 369篇 |
2011年 | 403篇 |
2010年 | 349篇 |
2009年 | 474篇 |
2008年 | 512篇 |
2007年 | 578篇 |
2006年 | 414篇 |
2005年 | 434篇 |
2004年 | 332篇 |
2003年 | 298篇 |
2002年 | 320篇 |
2001年 | 355篇 |
2000年 | 409篇 |
1999年 | 668篇 |
1998年 | 539篇 |
1997年 | 626篇 |
1996年 | 515篇 |
1995年 | 448篇 |
1994年 | 423篇 |
1993年 | 344篇 |
1992年 | 334篇 |
1991年 | 317篇 |
1990年 | 263篇 |
1989年 | 229篇 |
1988年 | 207篇 |
1987年 | 129篇 |
1986年 | 81篇 |
1985年 | 30篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1980年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
证明了Banach空间值独立随机变量序列的Hàjek-Rènyi型不等式,并利用该不等式证明了Banach空间值独立随机变量序列的强大数定律,所得结果刻画了Banach空间的p型性质. 相似文献
962.
在分析比较各种更新页面技术的基础上,利用Ajax的核心技术XMLHTTP组件,设计并实现了多媒体会议系统中无刷新页面的功能,它具有Web页面与后台数据库信息同步更新、响应速度快的特点.系统测试表明:此无刷新技术比其他技术具有更多的优越性. 相似文献
963.
Field trial of an HTS filter system on a CDMA base station 总被引:3,自引:0,他引:3
YIN ZheSheng WEI Bin CAO BiSong WANG Xin GUO XuBo ZHANG XiaoPing GAO LongMa PIAO YunLong ZHU MaFeng LIANG Yong WANG Fan H. PIEL B. AMINOV F. AMINOVA M. GETTA S. KOLESOV A. KNACK N. PUPETER D. WEHLER 《科学通报(英文版)》2007,52(2):171-174
This paper presents the field trial results of a high temperature superconductor filter system (HTSFS) in a code division multiple access (CDMA) mobile communication base station (BTS) in Tangshan, China. The center frequency of the HTSFS is 830 MHz with 1.4% fractional bandwidth. The noise figure (NF) of the HTSFS, including connectors and cables, is 0.8 dB. The field trial results show that after the HTSFS was installed in the receiver front-end of a CDMA base station, the transmitting power of handset was decreased by 3.1 dB on average. Up to now, the HTSFS has been running steadily in the base station for more than 22 months, demonstrating the reliability and stability of the system. 相似文献
964.
YANG MeiYing MA PengDa LI WenMing LIU JinYing LI Liang ZHU XiaoJuan WANG XingZhi 《科学通报(英文版)》2007,52(9):1205-1211
Bacterium strain PJ3,isolated from wastewater and identified as Arthrobacter sp. bacterium based on its 16S rDNA gene,could use carbazole as the sole carbon,nitrogen and energy source. The genomic library of strain PJ3 was constructed and a positive clone JM109(pUCW402) was screened out for the expression of dioxygenase by the ability to form yellow ring-fission product. A 2,3-dihydroxybiphenyl dioxygenase(23DHBD) gene of 933 bp was found in the 3360 bp exogenous fragment of pUCW402 by GenSCAN software and BLAST analysis. The phylogenetic analysis showed that 23DHBD from strain PJ3 formed a deep branch separate from a cluster containing most known 23DHBD in GenBank. Southern hybridization confirmed for the first time that the 23DHBD gene was from the genomic DNA of Arthrobacter sp. PJ3. In order to test the gene function,recombinant bacterium BL21(pETW-8) was constructed to express 23DHBD. The expression level in BL21(pETW-8) was highest compared with the recombinant bacteria JM109(pUCW402) and strain PJ3. We observed that 23DHBD was not absolute specific. The enzyme activity was higher with 2,3-dihydroxybiphenyl as a substrate than with catechol. The substrate specificity assay suggested that 23DHBD was essential for cleavage of bi-cyclic aromatic compounds during the course of aromatic compound biodegradation in Arthrobacter sp. strain PJ3. 相似文献
965.
Reconstruction of linkage maps in the distorted segregation populations of backcross, doubled haploid and recombinant inbred lines 总被引:1,自引:0,他引:1
ZHU ChengSong WANG FuHua WANG JianFei LI GuangJun ZHANG HongSheng ZHANG YuanMing 《科学通报(英文版)》2007,52(12):1648-1653
Non-Mendelian segregation of markers, known as distorted segregation, is a common biological phenomenon. Although segregation distortion affects the estimation of map distances and the results of quantitative trait loci (QTL) mapping, the effects of distorted markers are often ignored in the construction of linkage maps and in QTL mapping. Recently, we have developed a multipoint method via a Hidden Markov chain method to reconstruct linkage maps in an F2 population that corrects for bias of map distances between distorted markers. In this article, the method is extended to cover backcross, doubled haploid and recombinant inbred line (RIL) populations. The results from simulated experiments show that: (1) the degree that two linked segregation distortion loci (SDL) affect the estimation of map distances increases as SDL heritability and interval length between adjacent markers increase, whereas sample size has little effect on the bias; (2) two linked SDL result in the underesti- mation of linkage distances for most cases, overestimation for an additive model with opposite additive effects, and unbiased estimation for an epistatic model with negative additive-by-additive effects; (3) the proposed method can obtain the unbiased estimation of linkage distance. This new method was applied to a rice RIL population with severely distorted segregation to reconstruct the linkage maps, and a bootstrap method was used to obtain 95% confidence intervals of map distances. The results from real data analysis further demonstrate the utility of our method, which provides a foundation for the inheritance analysis of quantitative and viability traits. 相似文献
966.
Coupling and propagating of mesoscale sea level variability between the western Pacific and the South China Sea 总被引:4,自引:0,他引:4
LI Li JING ChunSheng ZHU DaYong 《科学通报(英文版)》2007,52(12):1699-1707
The coupling and propagating features of mesoscale sea level variability between the western Pacific (WP) and the South China Sea (SCS) were studied based on time series analyses of satellite altimeter measured, along-track sea surface height anomalies (SSHA) along 21°N and the slope of the northern SCS. The analyses show that mesoscale sea level fluctuations in the WP have rather limited coherent effects on the SCS, and no statistically significant propagation of mesoscale variability through the Luzon Strait was observed except in the 45-day band. Evidence suggests that the 45-day fluctuation is very much likely a character of the Kuroshio originating from its low-latitude beginning. It is also sug- gested that the westward propagating Rossby waves will deform when they encounter the dynamical barrier of the Kuroshio. The Kuroshio will then acts on the SCS in its own way. The SCS is a relatively isolated system in the sense of coupling and propagating of oceanic mesoscale waves. 相似文献
967.
TBM工作原理及设备选型 总被引:1,自引:0,他引:1
张铸 《科技情报开发与经济》2007,17(9):264-265
结合山西省万家寨引黄工程中隧洞工程的实践,介绍了全断面掘进机(TBM)的工作原理及设备选型等问题。 相似文献
968.
应用多源理想气体模型(MSIG)的蒙特卡罗方法,计算25AMeV能量下,碰撞参数较大时(b=7—10fm),^86Kr-^124Sn碰撞产生的轻碎片的几种分布.将MSIG模型的计算结果与同位旋依赖的量子分子动力学模型(IDQMD)的计算结果进行比较,发现二者得到的模动量分布定性地符合,动量分量分布和方位角分布符合得很好,椭圆流和4阶动量各向异性流对模动量的依赖关系基本符合. 相似文献
969.
中国东部地区一个中尺度对流涡旋的涡度收支分析 总被引:5,自引:0,他引:5
中尺度对流涡旋(MCV),与其他中尺度涡旋不同,有着其独特的动力机制与发展途径.一旦MCV形成,极易产生灾害性天气过程.为了解我国的MCV,使用非静力中尺度模式天气预报和研究模式对中国东部2003年7月4至5日降水过程进行了高分辨率的双向三重嵌套的数值模拟.与观测资料比较,模拟结果较为准确地再现了当时的大气状况.采用了空间滤波的方法对模式结果进行了大尺度背景场与中尺度扰动场的尺度分离,对MCV的结构与移动进行分析,并追随MCV的活动对其的涡度收支情况进行诊断分析.分析表明,大尺度背景场与中尺度扰动场对MCV的作用有着明显的差异.MCV的移动由大尺度背景风场引导;其中辐合作用直接决定了MCV的形成与发展,大尺度水平运动对中尺度涡度的水平输送为水平平流项的主要部分.而由垂直风速的水平变化所导致的水平涡度的倾斜作用在此MCV形成与发展阶段作用并不明显.成熟时的MCV与成熟时的中尺度对流复合体类似有着3个明显的环流,在对流层高层与低层均为辐散反气旋性环流,对流层中层则为较为深厚的气旋性环流. 相似文献
970.