全文获取类型
收费全文 | 43401篇 |
免费 | 94篇 |
国内免费 | 146篇 |
专业分类
系统科学 | 212篇 |
丛书文集 | 826篇 |
教育与普及 | 115篇 |
理论与方法论 | 231篇 |
现状及发展 | 19302篇 |
研究方法 | 1681篇 |
综合类 | 20747篇 |
自然研究 | 527篇 |
出版年
2013年 | 301篇 |
2012年 | 576篇 |
2011年 | 1117篇 |
2010年 | 259篇 |
2008年 | 754篇 |
2007年 | 782篇 |
2006年 | 821篇 |
2005年 | 830篇 |
2004年 | 734篇 |
2003年 | 792篇 |
2002年 | 768篇 |
2001年 | 1334篇 |
2000年 | 1217篇 |
1999年 | 805篇 |
1994年 | 373篇 |
1992年 | 786篇 |
1991年 | 619篇 |
1990年 | 681篇 |
1989年 | 673篇 |
1988年 | 642篇 |
1987年 | 686篇 |
1986年 | 682篇 |
1985年 | 857篇 |
1984年 | 670篇 |
1983年 | 570篇 |
1982年 | 523篇 |
1981年 | 499篇 |
1980年 | 603篇 |
1979年 | 1398篇 |
1978年 | 1180篇 |
1977年 | 1115篇 |
1976年 | 835篇 |
1975年 | 909篇 |
1974年 | 1245篇 |
1973年 | 1074篇 |
1972年 | 1072篇 |
1971年 | 1332篇 |
1970年 | 1754篇 |
1969年 | 1330篇 |
1968年 | 1284篇 |
1967年 | 1276篇 |
1966年 | 1126篇 |
1965年 | 820篇 |
1959年 | 483篇 |
1958年 | 729篇 |
1957年 | 565篇 |
1956年 | 496篇 |
1955年 | 433篇 |
1954年 | 470篇 |
1948年 | 298篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
51.
52.
53.
Enzymatic control of cell division in micro-organisms 总被引:1,自引:0,他引:1
NICKERSON WJ 《Nature》1948,162(4111):241-245
54.
Hong Zhang Kui Zhang Ying Mu Ning Yao Robert J. Sclabassi Mingui Sun 《自然科学进展(英文版)》2008,18(12):1507-1512
Image-based gait analysis as a means of biometric identification has attracted much research attention. Most of the existing methods focus on human identification, posture analysis and movement tracking. There have been few investigations on measuring the carried load based on the carrier's gait characteristics by automatic image processing. Nevertheless, this measurement is very useful in a number of applications, such as the study of the carried load on the postural development of children and adolescence. In this paper, we investigate how to automatically estimate the carried weight from a sequence of images. We present a method to extract human gait silhouette based on an observation that humans tend to minimize the energy during motion. We compute several angles of body leaning and determine the relationship of the carried weight, the leaning angles and the centroid location according to a human kinetic study. Our weight determination method has been verified successfully by experiments. 相似文献
55.
56.
The effects of alcohol consumption, cigarette smoking and age on sister chromatid exchange (SCE) frequency in human lymphocytes were assessed by means of multiple linear regression. An increase in SCE rates was associated with alcohol consumption (p = 0.0001), smoking (p = 0.0231), and, to a small extent (p = 0.057), age. These three confounding factors explain 48% of the inter-personal variation in SCE rates among subjects studied. 相似文献
57.
A. Farina A. ProtopapaRadar Dpt Selenia S. p. A. Via Tiburtina Km. - Rome Italy 《系统工程与电子技术(英文版)》1992,(3)
After a brief recall of the Sidelobe Canceler (SLC) working principle, including the derivation of a general formula for the Cancellation Ratio (CR), the effects of channel mismatching are investigated. In particular, curves providing CRvalues as a function of amplitude and phase channel mismatching, radar bandwidth, and jammer direction of arrival (JDOA) are provided for the cases of one and two auxiliary antennas. Subsequently, a time -space processor for performance restoration is analyzed in detail. In addition to the above mentioned quantities, the attainable CR value is expressed as a function of the space-time processor parameters. The contribution of the paper is related to the derivation of a number of mathematical equations of CR for several cases of practical interest for the radar engineer. In addition, several curves are presented to assist design of SLC systems. 相似文献
58.
59.
M. Harada S. Yenbutra K. Tsuchiya S. Takada 《Cellular and molecular life sciences : CMLS》1985,41(12):1610-1611
Summary Karyotypes ofMyotis siligorensis, Myotis mystacinus, Pipistrellus pulveratus, Tylonycteris robustula, Miniopterus schreibersi fuliginosus, Hipposideros fulvus andAselliscus stoliczkanus from Thailand are investigated.Acknowledgment. The authors are very grateful to Dr N. Ratanawarabhan, Mrs S. Sittilert, P. Noonpakdee and S. Kuanchalern of Thailand Institute of Scientific and Technological Research for their valuable advice and assistance during our field survey in Thailand. 相似文献
60.