全文获取类型
收费全文 | 1678篇 |
免费 | 165篇 |
国内免费 | 123篇 |
出版年
2024年 | 5篇 |
2023年 | 54篇 |
2022年 | 22篇 |
2021年 | 71篇 |
2020年 | 88篇 |
2019年 | 100篇 |
2018年 | 82篇 |
2017年 | 82篇 |
2016年 | 64篇 |
2015年 | 71篇 |
2014年 | 93篇 |
2013年 | 123篇 |
2012年 | 83篇 |
2011年 | 94篇 |
2010年 | 60篇 |
2009年 | 67篇 |
2008年 | 65篇 |
2007年 | 80篇 |
2006年 | 73篇 |
2005年 | 68篇 |
2004年 | 55篇 |
2003年 | 48篇 |
2002年 | 60篇 |
2001年 | 45篇 |
2000年 | 35篇 |
1999年 | 47篇 |
1998年 | 27篇 |
1997年 | 23篇 |
1996年 | 13篇 |
1995年 | 26篇 |
1994年 | 18篇 |
1993年 | 12篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 1篇 |
排序方式: 共有1966条查询结果,搜索用时 15 毫秒
41.
Incidence of early maturation of female amago salmon was reduced by >32% by feed restriction beginning in May, 5 months prior to spawning. Male early maturation was unaffected by this feed restriction regime. 相似文献
42.
Bacillus thuringiensis crystal toxin: Ultrastructural studies of its effect on silkworm midgut cells
Bacillus thuringiensis crystal toxin induced a cytoplasmic response in columnar cells within 1 min after ingestion although external symptoms were not exhibited by larvae until 15 min after ingestion. Microvilli became less consistently uniform in diameter; their organized internal microfilaments were disrupted and disappeared. The cisternae of rough endoplasmic reticulum were enlarged and denuded of ribosomes. By 5 min after ingestion, microvilli of some columnar cells disappeared entirely and gross ultrastructural changes were observed in other regions of the cells. Up to 5 min after ingestion there were few, if any, ultrastructural changes observed within goblet cells. Mitochondria in columnar cells were swollen but did not exhibit the condensed configuration reported by other workers. Both the buffer system used in the fixation medium and its osmolarity influenced the changes in the ultrastructure of midgut cells exposed to B. thuringiensis crystal toxin. 相似文献
43.
《Epigenetics》2013,8(1):23-27
Epigenetic modifications may be one mechanism linking early life factors, including parental socioeconomic status (SES), to adult onset disease risk. However, SES influences on DNA methylation patterns remain largely unknown. In a US birth cohort of women, we examined whether indicators of early life and adult SES were associated with white blood cell methylation of repetitive elements (Sat2, Alu and LINE-1) in adulthood. Low family income at birth was associated with higher Sat2 methylation (β = 19.7, 95% CI: 0.4, 39.0 for lowest vs. highest income quartile) and single parent family was associated with higher Alu methylation (β = 23.5, 95% CI: 2.6, 44.4), after adjusting for other early life factors. Lower adult education was associated with lower Sat2 methylation (β = -16.7, 95% CI: -29.0, -4.5). There were no associations between early life SES and LINE-1 methylation. Overall, our preliminary results suggest possible influences of SES across the life-course on genomic DNA methylation in adult women. However, these preliminary associations need to be replicated in larger prospective studies. 相似文献
44.
《Current biology : CB》2020,30(20):4078-4084.e3
45.
《Animal : an international journal of animal bioscience》2020,14(4):807-813
The research has shown the interesting contributions of shearing in mid-gestation on the performance of lambs from birth to weaning. Other studies have reported that shearing at early pregnancy influences the development of the placenta and lamb live weight at birth. However, there was a lack of information on the effect of early-prepartum shearing on the behavior of the offspring from weaning onward. This study evaluated the effect of shearing ewes at 50 days of gestation on the growth, reproductive behavior and response to a gastrointestinal parasite challenge in the female offspring from weaning to 18 months old. Fifty-seven Polwarth female lambs were used, 22 being singles and 35 twins born to ewes either shorn at 50 days of pregnancy (PS, n = 23) or shorn at 62 days postpartum (U, control, n = 34) resulting in four subgroups: single lambs born to PS ewes (n = 8), born to U ewes (n = 14), twin lambs born to PS ewes (n = 15) or born to U ewes (n = 20). All progeny were managed together under improved pasture with a minimum forage allowance of 6% live weight on dry basis. Body weight, body condition score and fecal eggs count were recorded every 14 days from weaning to 18 months of age. Concentrations of progesterone were measured weekly (from 4 to 10 months of age and from 14 to 18 months of age) to establish the onset of puberty. Ovulation rate at an induced and a natural heat (545 ± 1.0 and 562 ± 1.0 day old) was recorded. Prepartum shearing did not affect the age at puberty or the ovulation rate of female offspring, but those born as singles were more precocious ( P = 0.03) and heavier ( P = 0.02) at puberty than twin born lambs. Both the average value of parasite egg count ( P = 0.0 7) and the Famacha index ( P = 0.02) for the entire study period were lower in lambs born to prepartum shorn ewes than those born to postpartum shorn ewes. In conclusion, shearing at 50 days of gestation did not affect the growth or the reproductive behavior of female offspring. However, female lambs born from ewe shorn during gestation showed a better response to the parasitic challenge, and further research is required to confirm this. 相似文献
46.
Michael J. D'Occhio Giuseppe Campanile Luigi Zicarelli Jos A. Visintin Pietro S. Baruselli 《Molecular reproduction and development》2020,87(2):206-222
Cell–cell adhesion molecules have critically important roles in the early events of reproduction including gamete transport, sperm–oocyte interaction, embryonic development, and implantation. Major adhesion molecules involved in reproduction include cadherins, integrins, and disintegrin and metalloprotease domain‐containing (ADAM) proteins. ADAMs on the surface of sperm adhere to integrins on the oocyte in the initial stages of sperm–oocyte interaction and fusion. Cadherins act in early embryos to organize the inner cell mass and trophectoderm. The trophoblast and uterine endometrial epithelium variously express cadherins, integrins, trophinin, and selectin, which achieve apposition and attachment between the elongating conceptus and uterine epithelium before implantation. An overview of the major cell–cell adhesion molecules is presented and this is followed by examples of how adhesion molecules help shape early reproductive events. The argument is made that a deeper understanding of adhesion molecules and reproduction will inform new strategies that improve embryo survival and increase the efficiency of natural mating and assisted breeding in cattle. 相似文献
47.
胃癌是全球第四大最常见的癌症,也是全球癌症中引起死亡的第二大原因。为了降低胃癌的死亡率,目前亟需解决的问题是发现新的早期胃癌特异性的标志物,提高早期胃癌的检出率,从而从根本上解决胃癌死亡率高的问题。实验室前期研究发现过氧化物酶4 (Peroxiredoxin 4,PRDX4)具有早期胃癌标志物的潜能,文中通过建立恶性转化模型及转化细胞过表达等方法,研究PRDX4在转化细胞中的作用。结果显示PRDX4通过减少转化细胞中活性氧(Reactive oxygen species,ROS)含量,使细胞处在利于生长增殖的微环境中,从而促进细胞发生恶性转化,即PRDX4通过清除ROS促进胃癌的发生发展。 相似文献
48.
49.
50.
Vincent A. Viblanc Quentin Schull Antoine Stier Laureline Durand Emilie Lefol Jean‐Patrice Robin Sandrine Zahn Pierre Bize Franois Criscuolo 《Molecular ecology》2020,29(16):3154-3166
Because telomere length and dynamics relate to individual growth, reproductive investment and survival, telomeres have emerged as possible markers of individual quality. Here, we tested the hypothesis that, in species with parental care, parental telomere length can be a marker of parental quality that predicts offspring phenotype and survival. In king penguins (Aptenodytes patagonicus), we experimentally swapped the single egg of 66 breeding pairs just after egg laying to disentangle the contribution of prelaying parental quality (e.g., genetics, investment in the egg) and/or postlaying parental quality (e.g., incubation, postnatal feeding rate) on offspring growth, telomere length and survival. Parental quality was estimated through the joint effects of biological and foster parent telomere length on offspring traits, both soon after hatching (day 10) and at the end of the prewinter growth period (day 105). We expected that offspring traits would be mostly related to the telomere lengths (i.e., quality) of biological parents at day 10 and to the telomere lengths of foster parents at day 105. Results show that chick survival up to 10 days was negatively related to biological fathers’ telomere length, whereas survival up to 105 days was positively related to foster fathers’ telomere lengths. Chick growth was not related to either biological or foster parents’ telomere length. Chick telomere length was positively related to foster mothers’ telomere length at both 10 and 105 days. Overall, our study shows that, in a species with biparental care, parents’ telomere length is foremost a proxy of postlaying parental care quality, supporting the “telomere – parental quality hypothesis.” 相似文献