全文获取类型
收费全文 | 49270篇 |
免费 | 395篇 |
国内免费 | 737篇 |
专业分类
系统科学 | 1409篇 |
丛书文集 | 203篇 |
教育与普及 | 409篇 |
理论与方法论 | 528篇 |
现状及发展 | 29128篇 |
研究方法 | 100篇 |
综合类 | 16437篇 |
自然研究 | 2188篇 |
出版年
2014年 | 519篇 |
2013年 | 927篇 |
2012年 | 542篇 |
2011年 | 2558篇 |
2010年 | 511篇 |
2009年 | 780篇 |
2008年 | 819篇 |
2007年 | 851篇 |
2006年 | 919篇 |
2005年 | 1103篇 |
2004年 | 2219篇 |
2003年 | 1774篇 |
2002年 | 1452篇 |
2001年 | 1109篇 |
2000年 | 625篇 |
1999年 | 996篇 |
1998年 | 878篇 |
1997年 | 1040篇 |
1996年 | 790篇 |
1995年 | 627篇 |
1994年 | 902篇 |
1993年 | 848篇 |
1992年 | 796篇 |
1991年 | 717篇 |
1990年 | 791篇 |
1989年 | 593篇 |
1988年 | 551篇 |
1987年 | 508篇 |
1986年 | 581篇 |
1985年 | 650篇 |
1984年 | 614篇 |
1983年 | 530篇 |
1982年 | 704篇 |
1981年 | 752篇 |
1980年 | 814篇 |
1979年 | 1045篇 |
1978年 | 1000篇 |
1977年 | 1009篇 |
1976年 | 910篇 |
1975年 | 871篇 |
1974年 | 598篇 |
1973年 | 937篇 |
1972年 | 1013篇 |
1971年 | 947篇 |
1970年 | 914篇 |
1969年 | 905篇 |
1968年 | 866篇 |
1967年 | 725篇 |
1966年 | 580篇 |
1965年 | 503篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
It was established that there is little diversity of bryophytes in the derived savanna. Mosses were found in the sampling sites, whereas liverworts were rarely observed. The reproductive methods of four dominant sexually reproducing savanna mosses —Archidium ohioense, Bryum coronatum, Fissidens minutifolius andTrachycarpidium tisserantii were monitored over two consecutive rainy seasons. Protonemal and gametophyte production were noticed in the field in March/April, and capsule dehiscence and spore dispersal occurred in September/October. The sequential stages of development, starting with gametangial production and ending with the falling of the dehisced capsules, occurred within the rainy season. However,A. ohioense andT. tisserantii did not discharge their spores easily (cleistocarpous), unlike the stegocarpous speciesB. coronatum andF. minutifolius. Water availability and possibly high humidity may have contributed to growth. The short period between sex organ formation and dehiscence of capsule seen in these studies, compared with the longer period in some temperate mosses, may be an advantage for bryophytes in a savanna environment. 相似文献
42.
James T. Ziegenfuss Jr. 《Systemic Practice and Action Research》1992,5(5):509-527
This paper discusses the use of the Kast and Rosenzweig systems and contingency model for teaching and practice in organizational analysis and planning, management policy, and organizational development. The need for an organizational model for graduate students and field-based managers and executives is identified. The model is presented beginning with the Kast and Rosenzweig work, with integration of research by Daft, Schein, Trist, Deal and Kennedy, Ackoff, Delbecq, and Mintzberg. The teaching and practice uses of the model in four areas are presented, including organizational analysis and planning, management policy making, and organizational development. In each area case examples of the use of the model in teaching and practice are presented. Needs for future research and implications for the use of the model are discussed. 相似文献
43.
In this paper two alternative loss criteria for the least squares Procrustes problem are studied. These alternative criteria
are based on the Huber function and on the more radical biweight function, which are designed to be resistant to outliers.
Using iterative majorization it is shown how a convergent reweighted least squares algorithm can be developed. In asimulation
study it turns out that the proposed methods perform well over a specific range of contamination. When a uniform dilation
factor is included, mixed results are obtained. The methods also yield a set of weights that can be used for diagnostic purposes. 相似文献
44.
45.
通过对“洋务运动博物馆”东立面形象的反思 ,讨论了建筑形态设计中隐喻手法的运用 ;就此引申 ,探讨传统问题 ,指出正确理解传统与创新的四个方面。 相似文献
46.
诉讼证据的基本属性在传统上被认为是客观性、相关性和合法性,这是在我国长期流传的正统观点。但笔者认为并不能准确反映诉讼法学和证据学上的特点,应该用真实性、相关性和合法性来概括其基本属性,才有利于对诉讼证据的正确认识和把握。通过对诉讼证据基本属性的分析批判,可以深入了解诉讼法学和证据学意义上的关于证据属性的理论和司法实践有关问题,以期有利于我国的法制进程。 相似文献
47.
R. Poggioli A. V. Vergoni A. Bertolini 《Cellular and molecular life sciences : CMLS》1985,41(2):265-266
Summary Hydrochlorothiazide, acutely injected in rats, has a weak analgesic activity per se and potentiates and prolongs the antinociceptive effect of morphine.This work was supported in part by grants from Consiglio Nazionale delle Ricerche, and by Ministero della Pubblica Istruzione, Roma. 相似文献
48.
David H. Hubel 《自然科学进展(英文版)》2007,17(13):1-3
The visual field is topographically mapped onto the primary visual cortex (V1), forming a retinotopic map which is far more detailed for the foveal regions than for the periphery. We found that receptive field (RF) size in monkey V1 increases with eccentricity, and that a 1—2 m2 V1 region contains roughly a complete set of machinery necessary to analyze a visual-field area whose size is about that of the RFs of the cells. This allows V1 to be anatomically uniform, and is in sharp contrast with the retina. 相似文献
49.
1 Results This paper presents the development of platinum nanocomposites structures based on organically modified c.a.2 nm core platinum nanoparticles.The chemical modification of the 4-mercaptoaniline functionalized particles by various in coming molecules is evidenced and precisely quantified.The particles can be dissolved like molecules in various solvents depending on the features of the new crown and X-rays shows that the interparticle distance is affected by the crown modification.These platinum n... 相似文献