全文获取类型
收费全文 | 3954篇 |
免费 | 397篇 |
出版年
2022年 | 31篇 |
2021年 | 55篇 |
2020年 | 44篇 |
2019年 | 51篇 |
2018年 | 60篇 |
2017年 | 64篇 |
2016年 | 97篇 |
2015年 | 139篇 |
2014年 | 152篇 |
2013年 | 206篇 |
2012年 | 258篇 |
2011年 | 232篇 |
2010年 | 127篇 |
2009年 | 125篇 |
2008年 | 211篇 |
2007年 | 187篇 |
2006年 | 145篇 |
2005年 | 166篇 |
2004年 | 172篇 |
2003年 | 151篇 |
2002年 | 152篇 |
2001年 | 80篇 |
2000年 | 52篇 |
1999年 | 65篇 |
1998年 | 49篇 |
1997年 | 43篇 |
1996年 | 24篇 |
1995年 | 36篇 |
1994年 | 32篇 |
1993年 | 44篇 |
1992年 | 76篇 |
1991年 | 51篇 |
1990年 | 52篇 |
1989年 | 67篇 |
1988年 | 46篇 |
1987年 | 55篇 |
1986年 | 38篇 |
1985年 | 42篇 |
1984年 | 42篇 |
1983年 | 44篇 |
1982年 | 38篇 |
1981年 | 27篇 |
1980年 | 30篇 |
1979年 | 42篇 |
1978年 | 31篇 |
1977年 | 25篇 |
1973年 | 29篇 |
1972年 | 22篇 |
1971年 | 29篇 |
1969年 | 26篇 |
排序方式: 共有4351条查询结果,搜索用时 31 毫秒
91.
Dr. Sally Hughes-Schrader 《Chromosoma》1959,10(1-6):268-277
Summary A wide diversity in chromosome complement is found in two species of phasmids of the primitive group Prisopini—Prisopus ariadne
Hebard and Prisopus berosus
Westwood.
P. ariadne has a diploid male complement of 28, comprising 13 pairs of relatively large mediokinetic autosomes and Neo XY sex chromosomes.
P. berosus, 2n =49, has relatively small autosomes most of which are mediokinetic, and retains the XO—XX sex mechanism. Chromosomal polymorphism in this species is suggested by the presence of an unequal pair of autosomes and a structural differentiation in the X in one of two males studied.The relative amount of DNA per nucleus in male germ cells (Peulgen cytophotometry) shows a significant difference in total chromosomal content between the complements of the two species.These data are discussed with reference to the cytotaxonomy of phasmids.Supported in part by research grant G-4370 from the National Institutes of Health, Public Health Service. 相似文献
92.
Synchronously dividing cultures of the unicellular green alga Scenedesmus obtusiusculus were cultivated for 24 or 70 h in medium high (1000 μM) or low (60 μM) in phosphorus. Aliquots of AlCl3 (0, 37, 74, 111, 148, 185, or 222 μmol) were added daily to 1 l cell suspension at the end of the cell division phase. Algae were also grown in media with different pH, adjusted with HCl, in the absence of AlCl3 .
Effects of Al on cell metabolism vary with the intracellular Al concentration and with the concentration of Al available per cell. When the concentration of phosphorus is low, internal concentrations of Al are high and the chlorophyll content and the net dry matter production per cell increase, whereas the photosynthesis and the cell division are increased. Presence of Al in a low P medium decreases the pH of the medium down to 4.5. There are only small effects of Al in the presence of P, due to precipitation of most of the Al with P in the medium.
Despite the Al-induced decrease of the pH of the culture medium, effects caused by Al cannot be explained as a pH effect. Instead, the Al effect may, at least to some extent, be related to a decrease in availability of P in the metabolism, due to formation of aluminium phosphate inside the cell. 相似文献
Effects of Al on cell metabolism vary with the intracellular Al concentration and with the concentration of Al available per cell. When the concentration of phosphorus is low, internal concentrations of Al are high and the chlorophyll content and the net dry matter production per cell increase, whereas the photosynthesis and the cell division are increased. Presence of Al in a low P medium decreases the pH of the medium down to 4.5. There are only small effects of Al in the presence of P, due to precipitation of most of the Al with P in the medium.
Despite the Al-induced decrease of the pH of the culture medium, effects caused by Al cannot be explained as a pH effect. Instead, the Al effect may, at least to some extent, be related to a decrease in availability of P in the metabolism, due to formation of aluminium phosphate inside the cell. 相似文献
93.
94.
Sally Cole 《American anthropologist》2003,105(2):414-416
Feminine Matters: Women's Religious Practices in. Portuguese Town. Lena Gemzöe. Berlin: Walter de Gruyter, 2000. 273 pp. 相似文献
95.
96.
Sally Gregory Kohlstedt 《Journal of the history of biology》1995,28(1):151-166
Mary P. Winsor,Reading the shape of Nature: Comparative zoology at the Agassiz Museum (Chacago: University of Chicago Press, 1991); Ronald Rainger,An Agenda for Antiquty: Henry Fairfield Osborn and Vertedrate Paleontology at the American Meseum of Natural History, 1890–1935 (Tuscaloosa: University of Aladama Press, 1991). 相似文献
97.
Volume 61, no. 9, p. 3323: the title of the article should read as shown above. [This corrects the article on p. 3323 in vol. 61.]. 相似文献
98.
Zfy1 is a mouse Y chromosomal gene encoding a zincfinger protein which is thought to have some function during spermatogenesis. Here we show that, when introduced into tissue culture cells, Zfy1 is targeted to the nucleus. Two independent signals are present within the protein for nuclear localization. This nuclear Zfy1 protein is able to bind strongly to DNA-cellulose and, using site-selection assays, we have identified specific Zfy1 DNA binding sites. Taken together these results suggest that Zfy1 is a nuclear-located sequence-specific DNA binding protein which functions during spermatogenesis. 相似文献
99.
Initiation of latent DNA replication in the Epstein-Barr virus genome can occur at sites other than the genetically defined origin. 总被引:7,自引:2,他引:5
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Our laboratory has previously shown that replication of a small plasmid, p174, containing the genetically defined Epstein-Barr virus (EBV) latent origin of replication, oriP, initiates within oriP at or near a dyad symmetry (DS) element and terminates specifically at a family of repeated sequences (FR), also located within oriP. We describe here an analysis of the replication of intact approximately 170-kb EBV genomes in four latently infected cell lines that uses two-dimensional gel replicon mapping. Initiation was detected at oriP in all EBV genomes examined; however, some replication forks appear to originate from alternative initiation sites. In addition, pausing of replication forks was observed at the two clusters of EBV nuclear antigen 1 binding sites within oriP and at or near two highly expressed viral genes 0.5 to 1 kb upstream of oriP, the EBV-encoded RNA (EBER) genes. In the Raji EBV genome, the relative abundance of these stalled forks and the direction in which they are stalled indicate that most replication forks originate upstream of oriP. We thus searched for additional initiation sites in the Raji EBV and found that the majority of initiation events were distributed over a broad region to the left of oriP. This delocalized pattern of initiation resembles initiation of replication in several well-characterized mammalian chromosomal loci and is the first described for any viral genome. EBV thus provides a unique model system with which to investigate factors influencing the selection of replication initiation and termination sites in mammalian cells. 相似文献
100.