全文获取类型
收费全文 | 44717篇 |
免费 | 713篇 |
国内免费 | 107篇 |
专业分类
系统科学 | 1241篇 |
丛书文集 | 779篇 |
教育与普及 | 99篇 |
理论与方法论 | 496篇 |
现状及发展 | 18314篇 |
研究方法 | 1588篇 |
综合类 | 22517篇 |
自然研究 | 503篇 |
出版年
2018年 | 763篇 |
2017年 | 781篇 |
2016年 | 548篇 |
2012年 | 804篇 |
2011年 | 2002篇 |
2010年 | 1053篇 |
2009年 | 628篇 |
2008年 | 1165篇 |
2007年 | 1565篇 |
2006年 | 734篇 |
2005年 | 782篇 |
2004年 | 774篇 |
2003年 | 896篇 |
2002年 | 774篇 |
2001年 | 1154篇 |
2000年 | 1072篇 |
1999年 | 740篇 |
1992年 | 704篇 |
1991年 | 563篇 |
1990年 | 603篇 |
1989年 | 598篇 |
1988年 | 602篇 |
1987年 | 614篇 |
1986年 | 582篇 |
1985年 | 745篇 |
1984年 | 589篇 |
1983年 | 496篇 |
1982年 | 446篇 |
1981年 | 437篇 |
1980年 | 573篇 |
1979年 | 1220篇 |
1978年 | 1038篇 |
1977年 | 1026篇 |
1976年 | 761篇 |
1975年 | 827篇 |
1974年 | 1132篇 |
1973年 | 1014篇 |
1972年 | 1077篇 |
1971年 | 1261篇 |
1970年 | 1636篇 |
1969年 | 1263篇 |
1968年 | 1214篇 |
1967年 | 1245篇 |
1966年 | 1061篇 |
1965年 | 756篇 |
1959年 | 446篇 |
1958年 | 682篇 |
1957年 | 542篇 |
1956年 | 458篇 |
1954年 | 424篇 |
排序方式: 共有10000条查询结果,搜索用时 765 毫秒
101.
102.
The rough endoplasmic reticulum membranes of mammalian cells contain specific ribosome-binding sites. A purification to apparent homogeneity of a negatively charged protein (ERp180) of relative molecular mass 180,000 (180 K) was reported which was proposed to function as a rough endoplasmic reticulum ribosome receptor. We report here that ribosome-binding site activity quantitatively solubilized from rough endoplasmic reticulum membranes does not cofractionate with ERp180. By contrast, ribosome-binding site activity fractionates as a much smaller, positively charged protein. 相似文献
103.
Shape skeletonization (i.e., medial axis extraction) is powerful in many visual computing applications, such as pattern recognition, object segmentation, registration, and animation. In this paper, the authors expand the use of diffusion equations combined with distance field information to approximate medial axes of arbitrary 3D differential properties. It offers an alternative solids represented by polygonal meshes based on their but natural way for medial axis extraction for commonly used 3D polygonal models. By solving the PDE along time axis, this system can not only quickly extract diffusion-based medial axes of input meshes, but also allow users to visualize the extraction process at each time step. In addition, the proposed model provides users a set of manipulation toolkits to sculpt extracted medial axes, then use diffusion-based techniques to recover corresponding deformed shapes according to the original input datasets. This skeleton-based shape manipulation offers a fast and easy way for animation and deformation of complicated mesh objects. 相似文献
104.
105.
Systemic Intervention in a University Department: Reflections on Arrested Action Research 总被引:1,自引:1,他引:0
Don Houston 《Systemic Practice and Action Research》2008,21(2):133-152
This paper reflects on my experience as an insider researcher attempting to use critical systems ideas and practices to promote
quality improvement in a university engineering department. Reflection is a key part of learning. This paper is intended to
contribute to critically, self-reflective learning for the community of systems practitioners. These reflections on my questions
about participation, ethics, politics of process, and the choices and actions resulting from them may help others to formulate
their own. The complexity of systems practice places substantial demands on the researcher, particularly in the case of insider,
practitioner research. Nevertheless, the exploration of critical systems approaches to critique boundaries and structure ‘problems’
in the core aspects of higher education in locally meaningful ways should continue. While demanding, it still can work to
promote learning about authentic quality. 相似文献
106.
107.
108.
Edwin Y.B.Pun 《复旦学报(自然科学版)》2007,(5)
1 Results Rare earth doped waveguide amplifiers and devices have been demonstrated in silica, crystal and other glass hosts. These rare earth doped optical waveguide devices are based on inorganic materials. Many processing steps are required and can lead to long fabrication time and low yield.Polymer materials offer many distinct properties compared to inorganic materials, such as ease of fabrication, low production costs, simple processing steps, and compatibility with micro-fabrication technologies. ... 相似文献
109.
J. Brachet 《Cellular and molecular life sciences : CMLS》1948,4(9):353
Summary If amphibian gastrulæ are heated at 36 to 37°C for one hour, their development is blocked irreversibly; if, however, the dorsal lip is removed from these blocked gastrulæ and implanted in a normal gastrula, its development is resumed and the host is the site of a neural induction. 相似文献
110.