全文获取类型
收费全文 | 41969篇 |
免费 | 88篇 |
国内免费 | 116篇 |
专业分类
系统科学 | 392篇 |
丛书文集 | 1022篇 |
教育与普及 | 107篇 |
理论与方法论 | 236篇 |
现状及发展 | 18788篇 |
研究方法 | 1598篇 |
综合类 | 19545篇 |
自然研究 | 485篇 |
出版年
2013年 | 213篇 |
2012年 | 527篇 |
2011年 | 1081篇 |
2010年 | 240篇 |
2008年 | 703篇 |
2007年 | 753篇 |
2006年 | 748篇 |
2005年 | 766篇 |
2004年 | 687篇 |
2003年 | 778篇 |
2002年 | 715篇 |
2001年 | 1286篇 |
2000年 | 1220篇 |
1999年 | 768篇 |
1992年 | 739篇 |
1991年 | 606篇 |
1990年 | 645篇 |
1989年 | 643篇 |
1988年 | 643篇 |
1987年 | 637篇 |
1986年 | 650篇 |
1985年 | 792篇 |
1984年 | 622篇 |
1983年 | 539篇 |
1982年 | 470篇 |
1981年 | 496篇 |
1980年 | 598篇 |
1979年 | 1302篇 |
1978年 | 1116篇 |
1977年 | 1114篇 |
1976年 | 825篇 |
1975年 | 872篇 |
1974年 | 1302篇 |
1973年 | 1052篇 |
1972年 | 1072篇 |
1971年 | 1326篇 |
1970年 | 1764篇 |
1969年 | 1385篇 |
1968年 | 1269篇 |
1967年 | 1329篇 |
1966年 | 1127篇 |
1965年 | 827篇 |
1964年 | 220篇 |
1959年 | 503篇 |
1958年 | 731篇 |
1957年 | 577篇 |
1956年 | 486篇 |
1955年 | 442篇 |
1954年 | 483篇 |
1948年 | 265篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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
82.
83.
A New Discipline of Science-The Study of Open Complex Giant System and Its Methodology 总被引:2,自引:0,他引:2
Qian XuesenChina Association for Science Technology Beijing ChinaYu JingyuanBeijing Institute of Information Control P.O.Box Beijing ChinaDai RuweiInstitute of Automation Chinese Academy of Sciences Beijing China 《系统工程与电子技术(英文版)》1993,(2)
This paper introduces the conception of open complex giant system and the methodology for dealing with the system, with stress on its profound significance in development of science and technology. The authors conclude that the reductionism underlying the exact science is not suitable to open complex giant system, and the only feasible alternative is the meta-synthetic engineering from the qualitative to the quantitative. 相似文献
84.
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
85.
86.
J E Landegent N Jansen in de Wal G J van Ommen F Baas J J de Vijlder P van Duijn M Van der Ploeg 《Nature》1985,317(6033):175-177
During the past few years, several methods have been developed for the detection of specific nucleic acid sequences by in situ hybridization using non-radioactive labels such as fluorochromes, cytochemically detectable enzymes and electron-dense markers. These methods are preferable to autoradiography in terms of speed of performance and topological resolution. Their limited sensitivity, however, has so far restricted their use to the detection of repeated sequences. Here we report single gene detection with a procedure using 2-acetylaminofluorene (AAF)-modified probes, immunoperoxidase cytochemistry and reflection-contrast microscopy. We confirmed the autoradiographic data on the localization of the human thyroglobulin (Tg) gene to the distal end of the long arm of chromosome 8. A mixture of cosmid cHT2-derived subclones of the 3' part of the Tg gene, 22.3 kilobase pairs (kbp) in total, was used as a hybridization probe. This procedure can be used to map other unique sequences, if genomic clones are available from which clones with an appropriate amount of inserts can be isolated. 相似文献
87.
88.
Acquired immunity and epidemiology of Schistosoma haematobium 总被引:1,自引:0,他引:1
Human immune responses to schistosome infection have been characterized in detail. But there has been controversy over the relative importance of ecological factors (variation in exposure to infection) and immunological factors (acquired immunity) in determining the relationships between levels of infection and age typically found in areas where infection is endemic. Independent effects of exposure and age on the rates of reinfection with Schistosoma haematobium after chemotherapy have been demonstrated in the Gambia and Zimbabwe. This age effect could be the result of acquired immunity to infection. Indeed, allowing for variation in exposure and age, low rates of reinfection in the Gambia are correlated with high amounts of specific IgE antibodies--human IgE can kill S. mansoni schistosomulae in vitro. Further, animals can acquire immunologically mediated resistance to S. mansoni infection, although nonimmunological factors could also be involved. Acquisition of this immunity seems to be related to the cumulative effects of repeated infection and provides only partial protection. These characteristics are consistent with immuno-epidemiological data for both S. mansoni and S. haematobium infections of humans. We have now analysed age-prevalence data for human infection with S. haematobium, and find patterns of variation that are indeed consistent with the epidemiological effects of acquired immunity predicted by mathematical models. 相似文献
89.
90.
Descartes is always concerned about knowledge. However, the Galileo affair in 1633, the reactions to his Discourse on method, and later his need to reply to objections to his Meditations provoked crises in Descartes’s intellectual development the import of which has not been sufficiently recognized. These events are the major reasons why Descartes’s philosophical position concerning how we know and what we may know is radically different at the end of his life from what it was when he began. We call this later position Descartes’s epistemic stance and contrast it with his earlier methodological, metaphysical realism. Yet Descartes’s epistemic views cannot be separated from other aspects of his work, for example, his views concerning God, causality, metaphysics, and the nature of science. A further meta-implication is that serious errors await any scholar who cites early Cartesian texts in support of late Cartesian positions, or who uses later texts in conjunction with early ones to support a reading of Descartes’s philosophy. 相似文献