全文获取类型
收费全文 | 62701篇 |
免费 | 646篇 |
国内免费 | 1134篇 |
专业分类
系统科学 | 1638篇 |
丛书文集 | 606篇 |
教育与普及 | 566篇 |
理论与方法论 | 582篇 |
现状及发展 | 31333篇 |
研究方法 | 538篇 |
综合类 | 27023篇 |
自然研究 | 2195篇 |
出版年
2014年 | 773篇 |
2013年 | 1208篇 |
2012年 | 939篇 |
2011年 | 3000篇 |
2010年 | 813篇 |
2009年 | 1082篇 |
2008年 | 1255篇 |
2007年 | 1315篇 |
2006年 | 1317篇 |
2005年 | 1468篇 |
2004年 | 2438篇 |
2003年 | 2059篇 |
2002年 | 1755篇 |
2001年 | 1459篇 |
2000年 | 995篇 |
1999年 | 1405篇 |
1998年 | 1144篇 |
1997年 | 1259篇 |
1996年 | 1064篇 |
1995年 | 866篇 |
1994年 | 1120篇 |
1993年 | 990篇 |
1992年 | 1081篇 |
1991年 | 979篇 |
1990年 | 972篇 |
1989年 | 808篇 |
1988年 | 763篇 |
1987年 | 682篇 |
1986年 | 715篇 |
1985年 | 803篇 |
1984年 | 708篇 |
1983年 | 624篇 |
1982年 | 752篇 |
1981年 | 803篇 |
1980年 | 883篇 |
1979年 | 1303篇 |
1978年 | 1180篇 |
1977年 | 1197篇 |
1976年 | 1035篇 |
1975年 | 1008篇 |
1974年 | 874篇 |
1973年 | 1117篇 |
1972年 | 1207篇 |
1971年 | 1171篇 |
1970年 | 1252篇 |
1969年 | 1168篇 |
1968年 | 1132篇 |
1967年 | 979篇 |
1966年 | 816篇 |
1965年 | 661篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
M. Lazzari V. Franceschini G. Minelli F. Ciani 《Cellular and molecular life sciences : CMLS》1993,49(4):277-281
The corrosion cast technique provided for the first time an excellent three-dimensional visualization of the vascular pattern of the choroid and iris in the newt eye. The results show the presence of a single arterial afference to the choroidal and iris capillaries: the ophthalmic artery is the origin fo both ciliary arteries and the long posterior ciliary artery. Slightly behind the equatorial circumference of the eyeball the venous drainage consists of a single vessel on the dorsal side and two distinct vessels on the ventral one. It receives blood from both iris and choroid. The surface of the plastic endocasts shows some details of fine luminal structures of the endothelial cells. Shallow depressions may be regarded as imprints of endothelial cell nuclei, and they are distinctly different for arteries and capillaries. The angioarchitecture of the newt eye differs from that of brain in that hairpin-shaped capillary loops are not observed at all. 相似文献
82.
中药材中孳生粉螨的初步调查 总被引:1,自引:0,他引:1
本文采用清水漂浮法和塔氏电热集螨器分离法,共分离中药材样本124种,1240份,从中分离出粉螨45种,隶属7科23属.得出结论:中药材粉螨的污染严重,应加强对中药螨类的防治,以保护中药材及预防人体螨病. 相似文献
83.
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
84.
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
85.
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
86.
Studies of intracellular traffic in yeast and mammalian systems have implicated members of the Rab family of small GTP-binding proteins as regulators of membrane fusion. We have used the patch clamp technique to measure exocytotic fusion events directly and investigate the role of GTP-binding proteins in regulating exocytosis in mast cells. Intracellular perfusion of mast cells with GTP-gamma S is sufficient to trigger complete exocytotic degranulation in the absence of other intracellular messengers. Here we show that GTP is a potent inhibitor of GTP-gamma S-induced degranulation, indicating that sustained activation of a GTP-binding protein is sufficient for membrane fusion. We have found that synthetic oligopeptides, corresponding to part of the effector domain of Rab3a, stimulate complete exocytotic degranulation, similar to that induced by GTP-gamma S. The response is selective for Rab3a sequence and is strictly dependent on Mg2+ and ATP. This suggests that sustained activation of a Rab3 protein causes exocytotic fusion. The peptide response can be accelerated by GDP-beta S, suggesting that Rab3a peptides compete with endogenous Rab3 proteins for a binding site on a target effector protein, which causes fusion on activation. 相似文献
87.
88.
89.
从嗜热蓝藻鞭枝藻(Mastigocladuslaminosus)中分离出藻胆体,并对其光谱特性进行了研究.完整藻胆体的室温荧光峰位于673um,77K荧光发射光谱中只有一个峰,位于685um,解离的藻胆体的77K荧光峰位于683nm,并在666nm和650nm处形成小的荧光发射峰.严重解离的藻胆体室温荧光峰位于645um,77K荧光峰位于644um,683um荧光显著下降,成为小峰.完整藻胆体与解离的及严重解离的藻胆体的吸收光谱没有显著差别,吸收峰位于622um,在580um处有一吸收肩. 相似文献
90.
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