全文获取类型
收费全文 | 5454篇 |
免费 | 595篇 |
国内免费 | 6篇 |
出版年
2023年 | 31篇 |
2022年 | 41篇 |
2021年 | 137篇 |
2020年 | 72篇 |
2019年 | 82篇 |
2018年 | 99篇 |
2017年 | 99篇 |
2016年 | 169篇 |
2015年 | 230篇 |
2014年 | 242篇 |
2013年 | 298篇 |
2012年 | 381篇 |
2011年 | 366篇 |
2010年 | 256篇 |
2009年 | 198篇 |
2008年 | 320篇 |
2007年 | 305篇 |
2006年 | 320篇 |
2005年 | 271篇 |
2004年 | 222篇 |
2003年 | 231篇 |
2002年 | 207篇 |
2001年 | 102篇 |
2000年 | 75篇 |
1999年 | 80篇 |
1998年 | 51篇 |
1997年 | 43篇 |
1996年 | 47篇 |
1995年 | 47篇 |
1994年 | 38篇 |
1993年 | 37篇 |
1992年 | 54篇 |
1991年 | 54篇 |
1990年 | 42篇 |
1989年 | 40篇 |
1988年 | 47篇 |
1987年 | 31篇 |
1986年 | 34篇 |
1985年 | 35篇 |
1984年 | 47篇 |
1982年 | 44篇 |
1980年 | 40篇 |
1979年 | 25篇 |
1978年 | 32篇 |
1977年 | 37篇 |
1976年 | 25篇 |
1974年 | 34篇 |
1973年 | 31篇 |
1972年 | 23篇 |
1970年 | 25篇 |
排序方式: 共有6055条查询结果,搜索用时 15 毫秒
151.
Thomas E. Schroeder 《Experimental cell research》1980,128(2)
The jelly coat of a sea urchin egg possesses a narrow conical channel which identifies the animal pole. This rarely seen structure was first reported by Boveri in 1901 and is easily demonstrated by immersing freshly ovulated eggs into an ink suspension. The jelly canal, as this feature is called, fills with ink particles as the jelly swells. The jelly canal occurs on full-sized primary oocytes and unfertilized eggs. When filled with ink it serves as a useful marker of the animal pole during fertilization and early development when it is not otherwise visible. A common synonym for the jelly canal is ‘micropyle’, but this is a misnomer because sperm do not selectively pass through it for fertilization. The presence of the jelly canal on oocytes suggests how it might form and does not prove that the animal-vegetal polar axis in sea urchin eggs is defined before meiotic maturation. 相似文献
152.
Oocyte-follicle cell relationships in a starfish 总被引:2,自引:0,他引:2
Summary The follicle cells which surround the oocytes of starfish are known to both release the hormone 1-methyladenine and to respond to it by an active movement which forms a component of the spawning response to the hormone. In Patiria miniata these flagellated cells are located peripheral to the oocyte and have long cytoplasmic processes which penetrate the vitelline layer to the egg surface to form an adhering zonule-like junction. Within the follicle cell cytoplasm are located elongate filamentous bands which appear to represent a component of the contractile mechanism that mediates follicle cell response to 1-methyladenine. These bands do not resemble the filaments of vertebrate smooth muscle cells (quantity, distribution and size of filaments; lack of dense bodies in the filament mass), nor the contractile units of the superficial epithelium of lower vertebrate follicles.This investigation was supported by grants HD-07194 and HD-12499 from the National Institutes of Health. We are indebted to Mr. James D. Huber for able technical assistance 相似文献
153.
A combination of light, transmission and scanning electron microscopy was employed to demonstrate the occurrence, arrangement and structure of taste buds in the oral mucosa of the soft palate of monkeys (Macaca irus). Taste buds are found in aggregates confined to 0.15 to 0.3 mm wide, round islands of keratinizing epithelium embedded in the normally non-keratinizing integument. Topography, configuration and structure of these epithelial islands and their taste buds are described, and the question of a developmental and functional interrelationship between epithelial differentiation and properties, and taste bud function is discussed. 相似文献
154.
Julian A. Steyermark 《Brittonia》1978,30(1):39-49
Ten new species (Billbergia manarae, Croizatia naiguatensis, Croton huberi, Rinorea oraria, Anaectocalyx manarae, Linociera avilensis, Cynanchum beatricis, C. manarae, Matelea costanensis, and M. manarae) are described in preparation for the forthcoming Flora of Avila and Naiguatá. 相似文献
155.
The enzyme tyrosinase (E.G. 1.14.18.1) has been immobilized in a polyacrylamide gel and intermittently assayed for enzyme activity over a period of 19 days using phenol as the substrate. The results of these studies indicate that the immobilized enzyme could be incorporated into a system to detect phenol and related compounds that are found in industrial effluents and as surface water contaminants. 相似文献
156.
157.
158.
Maintaining up-to-date annotation on reference genomes is becoming more important, not less, as the ability to rapidly and
cheaply resequence genomes expands. 相似文献
159.
160.