全文获取类型
收费全文 | 2259篇 |
免费 | 210篇 |
国内免费 | 1篇 |
出版年
2022年 | 20篇 |
2021年 | 37篇 |
2020年 | 24篇 |
2019年 | 28篇 |
2018年 | 32篇 |
2017年 | 21篇 |
2016年 | 33篇 |
2015年 | 79篇 |
2014年 | 105篇 |
2013年 | 123篇 |
2012年 | 151篇 |
2011年 | 143篇 |
2010年 | 92篇 |
2009年 | 67篇 |
2008年 | 121篇 |
2007年 | 122篇 |
2006年 | 129篇 |
2005年 | 120篇 |
2004年 | 105篇 |
2003年 | 120篇 |
2002年 | 103篇 |
2001年 | 27篇 |
2000年 | 23篇 |
1999年 | 30篇 |
1998年 | 34篇 |
1997年 | 16篇 |
1996年 | 15篇 |
1995年 | 20篇 |
1994年 | 22篇 |
1993年 | 19篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 16篇 |
1988年 | 19篇 |
1987年 | 15篇 |
1985年 | 18篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1980年 | 21篇 |
1979年 | 14篇 |
1978年 | 11篇 |
1977年 | 16篇 |
1976年 | 22篇 |
1975年 | 17篇 |
1974年 | 12篇 |
1973年 | 19篇 |
1971年 | 16篇 |
排序方式: 共有2470条查询结果,搜索用时 31 毫秒
1.
2.
Keith G. Danielson Janice E. Knepper Frances S. Kittrell Janet S. Butel Daniel Medina Elisa M. Durban 《In vitro cellular & developmental biology. Plant》1989,25(6):535-543
Summary Clonal populations were isolated from the mouse mammary cell line, COMMA-D, by transfection with a dominant-selectable gene,
pSV2Neo, which confers resistance to the antibiotic, G418. Seven of twenty-four clones isolated retained the ability of the
parental line to repopulate cleared mammary fat pads in vivo as ductal-alveolar hyperplasias. Two sublines designated CDNR2
and CDNR4 retained hyperplastic growth potential after multiple passages in vitro with low incidence of tumor formation. A
third subpopulation, CDNR1, contained a single integration site for the pSV2Neo plasmid indicating a bonafide clonal origin
for this subline. CDNR1 cells displayed heterogeneous growth phenotypes in vivo including hyperplasia, adenocarcinoma, and
bone formation. Functional differentiation of CDNR1 cells organized as alveolarlike structures in vivo or on floating collagen
gels in vitro was observed as determined by immunoperoxidase staining for the milk-specific protein, casein. Overall, the
results indicate that a subset of cells from the COMMA-D cell line may be functionally analogous to stem cells existing in
the mammary gland.
Supported by NCI research grants CA-38650, CA-33369, CA-39017, and CA-25215. 相似文献
3.
4.
5.
6.
Abstract The effects of an unusual high frequency mowing regime, which involved the removal of slash, were compared to moderate grazing through the method of paired quadrats across a fenceline, which was orthogonal to a weak environmental gradient. The mown plots proved superior in their conservation characteristics to the moderately grazed plots. The mowing regime produced greater cover of rare or threatened species, greater native cover and lesser exotic grass cover. It thus presents an opportunity for maintaining or improving the condition of previously grazed remnants in reserves without resorting to the use of stock or fire for biomass reduction. 相似文献
7.
8.
The local chromatin structure of the Shrunken-1 (Sh) gene of maize was probed by analyzing DNase I hypersensitivity. Sh encodes the gene for sucrose synthetase, a major starch biosynthetic enzyme, which is maximally expressed in the endosperm during seed maturation. In addition to general DNase I sensitivity, specific DNase I hypersensitive sites were identified in endosperm chromatin that mapped near the 5 end of the Sh gene. The pattern of hypersensitive sites and their relative sensitivity were altered in other non-dormant tissues that produce little or no enzyme. However, some changes in chromatin structure appear to be independent of Sh gene expression and may reflect general alterations associated with plant development. The chromatin structure of several sh mutations, induced by Ds controlling element insertions, was also analyzed. Although the insertions perturbed expression of the gene, there were no notable effects on local chromatin structure. 相似文献
9.
The avidin-biotin immunoperoxidase method and antisera to purified porcine relaxin were used to localize relaxin in sections of follicles from pregnant mare's serum gonadotropin (PMSG)/human chorionic gonadotropin (hCG)-primed pigs during preovulatory development. Prepubertal pigs were treated i.m. with PMSG (750 IU) and 72 h later with hCG (500 IU) to induce follicular development and ovulation. Follicles were collected from untreated gilts or from gilts 24, 48, 60, 72, 84, 96, or 108 h after PMSG treatment. Light immunostaining in the theca interna was observed early in follicular development, at 48 and 60 h post-PMSG. At 72 h post-PMSG, relaxin immunostaining in the theca interna of the preovulatory follicle was more intense. After hCG treatment, the intense thecal immunostaining persisted and was apparent 84 and 96 h after PMSG. At about 6 h prior to expected ovulation (108 h post-PMSG), there was thinning of the follicle wall and a reduction in relaxin immunostaining in the theca interna. Immunoactive relaxin was not detected in follicles from untreated gilts, follicles 24 h post-PMSG, small healthy or atretic follicles, or in granulosa cells, theca externa or ovarian stroma, at any of the time points studied. These studies support the hypothesis that the theca interna is the primary source of follicular relaxin and provide further evidence for a paracrine role for relaxin in the ovulatory process. 相似文献
10.
Prepuberal gilts were treated with 750 IU pregnant mare serum gonadotropin (PMSG) followed 72 h later by 500 IU human chorionic gonadotropin (hCG) to induce follicular growth and ovulation. In this model, ovulation occurred at 42 +/- 2 h post hCG treatment. When 500 mug of cloprostenol was injected at 34 and of 36 h after hCG injection, 78% of the preovulatory follicles ovulated by 38 h compared with 0% in the control gilts. In addition, plasma progesterone concentrations were significantly higher in the cloprostenol-treated group than in the control group (P<0.01) at 38 h, indicating luteinization along with premature ovulation. These results suggest that prostaglandin F(2)alpha (PGF(2)alpha) or an analog can be used to advance, synchronize or induce ovulation in gilts. 相似文献