全文获取类型
收费全文 | 3297篇 |
免费 | 174篇 |
国内免费 | 1篇 |
出版年
2021年 | 39篇 |
2019年 | 18篇 |
2018年 | 38篇 |
2017年 | 29篇 |
2016年 | 37篇 |
2015年 | 81篇 |
2014年 | 98篇 |
2013年 | 252篇 |
2012年 | 146篇 |
2011年 | 161篇 |
2010年 | 120篇 |
2009年 | 109篇 |
2008年 | 147篇 |
2007年 | 125篇 |
2006年 | 120篇 |
2005年 | 126篇 |
2004年 | 135篇 |
2003年 | 129篇 |
2002年 | 156篇 |
2001年 | 134篇 |
2000年 | 133篇 |
1999年 | 114篇 |
1998年 | 52篇 |
1997年 | 26篇 |
1996年 | 34篇 |
1995年 | 28篇 |
1994年 | 19篇 |
1993年 | 26篇 |
1992年 | 79篇 |
1991年 | 75篇 |
1990年 | 70篇 |
1989年 | 62篇 |
1988年 | 59篇 |
1987年 | 57篇 |
1986年 | 49篇 |
1985年 | 49篇 |
1984年 | 28篇 |
1983年 | 31篇 |
1982年 | 24篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 28篇 |
1978年 | 19篇 |
1977年 | 18篇 |
1976年 | 23篇 |
1975年 | 20篇 |
1974年 | 27篇 |
1973年 | 13篇 |
1969年 | 13篇 |
1968年 | 13篇 |
排序方式: 共有3472条查询结果,搜索用时 15 毫秒
81.
Hormonal induction of all stages of spermatogenesis in germ-somatic cell coculture from immature Japanese eel testis 总被引:2,自引:1,他引:1
Chiemi Miura Takeshi Miura Masakane Yamashita Kohei Yamauchi Yoshitaka Nagahama 《Development, growth & differentiation》1996,38(3):257-262
In cultivated male eel, spermatogonia are the only germ cells present in testis. Our previous studies using an organ culture system have shown that gonadotropin and 11-ketotestosterone (11-KT, a potent androgen in teleost fishes) can induce all stages of spermatogenesis in vitro. for detailed investigation of the control mechanisms of spermatogenesis, especially of the interaction between germ cells and testicular somatic cells during 11-KT-induced spermatogenesis in vitro, we have established a new culture system in which germ cells and somatic cells are cocultured after they are aggregated into pellets by centrifugation. Germ cells (spermatogonia) and somatic cells (mainly Sertoli cells) were isolated from immature eel testis. Coculture of the isolated germ cells and somatic cells without forming aggregation did not induce spermatogenesis, even in the presence of 11-KT. In contrast, when isolated germ cells and somatic cells were formed into pellets by centrifugation and were then cultured with 11-KT for 30 days, the entire process of spermatogenesis from premitotic spermatogonia to spermatozoa was induced. However, in the absence of 11-KT in the culture medium spermatogenesis was not induced, even when germ cell and somatic cells were aggregated. These results demonstrate that physical contact of germ cells to Sertoli cells is required for inducing spermatogenesis in response to 11-KT. 相似文献
82.
Caffeine-induced chloride current in dissociated rat hepatocytes 总被引:1,自引:0,他引:1
83.
84.
Mode of photosynthesis in Mesembryanthemum crystallinum changesfrom C3 to Crassulacean acid metabolism (CAM) when the plantswere stressed with high salinity. [14C]Pyruvate uptake for 30s into intact chloroplasts isolated from leaves of the CAM modeof M. crystallinum was enhanced more than 5-fold in the lightcompared with that in the dark. The stromal concentration ofpyruvate in the light reached to more than 2.5 times of themedium. In contrast, little or no pyruvate uptake occurred inchloroplasts from C3 leaves in either light or dark condition.The initial uptake rate (10 s incubation at 4°C) into theCAM chloroplasts in the light was about 3-fold higher than therate in the dark. Km and Vmax of the initial uptake in the lightwere 0.54 mM and 8.5 µmol (mg Chl)1 h1 respectively.These suggest that pyruvate was actively incorporated into theCAM chloroplasts against its concentration gradient across theenvelope in the light. When hydroponically grown M. crystallinumwere stressed by 350 mM NaCl, the capacity of chloroplasts forpyruvate uptake was induced in 6 d corresponding to the inductionof the activities of PEP-carboxylase and NAD(P)+-malic enzymesin response to salt stress. (Received October 12, 1995; Accepted January 19, 1996) 相似文献
85.
During photoreactivation of the O2-evolving center in Tris-inactivated/Mn-depletedthylakoids, a slow O2-consumption occurred. This O2-consumptionbecame detectable when the O2-evolving activity of thylakoidswas inactivated by Tris-treatment and decreased as photoreactivationproceeded. The O2-consumption and photoreactivation similarlyrequired Mn2+ at µM levels in addition to PSII electrondonors and shared severa common characteristics. Stimulationof O2-consumption and photoreactivation by these cofactors werealways accompanied by enhancement in chlorophyll fluorescenceinduction, suggesting the involvement of a Mehler-type reactionin photoreactivation. Although the electron transport due tothis O2-consumption was rapid enough to oxidize 4 Mn2+ ionsto reconstitute the tetranuclear Mn-cluster in each O2-evolvingcenter in a few seconds, actual recovery of O2-evolving activityoccurred more slowly in a few minutes. It was inferred thatphotoreactivation in Tris-inactivated thylakoids is not a simplephotooxidation of Mn22+ but involves more complicated processeswhich are coupled to the Mehlertype electron transport fromPSII to oxygen via PSI. (Received July 11, 1994; Accepted August 23, 1996) 相似文献
86.
Fission yeast cut3 and cut14, members of a ubiquitous protein family, are required for chromosome condensation and segregation in mitosis. 总被引:22,自引:1,他引:21 下载免费PDF全文
Y Saka T Sutani Y Yamashita S Saitoh M Takeuchi Y Nakaseko M Yanagida 《The EMBO journal》1994,13(20):4938-4952
Fission yeast temperature-sensitive mutants cut3-477 and cut14-208 fail to condense chromosomes but small portions of the chromosomes can separate along the spindle during mitosis, producing phi-shaped chromosomes. Septation and cell division occur in the absence of normal nuclear division, causing the cut phenotype. Fluorescence in situ hybridization demonstrated that the contraction of the chromosome arm during mitosis was defective. Mutant chromosomes are apparently not rigid enough to be transported poleward by the spindle. Loss of the cut3 protein by gene disruption fails to maintain the nuclear chromatin architecture even in interphase. Both cut3 and cut14 proteins contain a putative nucleoside triphosphate (NTP)-binding domain and belong to the same ubiquitous protein family which includes the budding yeast Smc1 protein. The cut3 mutant was suppressed by an increase in the cut14+ gene dosage. The cut3 protein, having the highest similarity to the mouse protein, is localized in the nucleus throughout the cell cycle. Plasmids carrying the DNA topoisomerase I gene partly suppressed the temperature sensitive phenotype of cut3-477, suggesting that the cut3 protein might be involved in chromosome DNA topology. 相似文献
87.
88.
89.
Masakane Yamashita Jianqiao Jiang Hiroshi Onozato Teruyuki Nakanishi Yoshitaka Nagahama 《Development, growth & differentiation》1993,35(6):631-636
A triploid crucian carp, ginbuna ( Carassius auratus langsdorfii ), reproduces by gynogenesis, in which sperm of diploid ginbuna or of other species triggers the development of the triploid eggs, but a male genome makes no contribution to the zygotic genome. Gynogenesis is maintained by two mechanisms: exclusion of male genome during fertilization and retention of somatic ploidy levels during oogenesis. We examined the mechanisms responsible for producing unreduced eggs. Microfluorometry with a DNA staining dye showed that DNA content in the ginbuna oocytes was not reduced in half during meiosis I. Cytological observations revealed that a tripolar spindle was formed at meiosis I and the first polar body was not extruded, whereas an ordinary bipolar spindle was formed and the second polar body was extruded at meiosis II. Activity of histone H1 kinase (as an indicator of maturation-promoting factor) decreased transiently between meiosis I and II, strongly suggesting a "normal" meiotic cycle progression in the ginbuna oocytes. These results have indicated that in the gynogenetic ginbuna the somatic ploidy levels are maintained by inhibiting the first polar body extrusion via the formation of the tripolar spindle at meiosis I. 相似文献
90.