全文获取类型
收费全文 | 1650篇 |
免费 | 91篇 |
国内免费 | 36篇 |
专业分类
1777篇 |
出版年
2023年 | 25篇 |
2022年 | 33篇 |
2021年 | 46篇 |
2020年 | 37篇 |
2019年 | 44篇 |
2018年 | 43篇 |
2017年 | 28篇 |
2016年 | 31篇 |
2015年 | 42篇 |
2014年 | 36篇 |
2013年 | 84篇 |
2012年 | 43篇 |
2011年 | 64篇 |
2010年 | 50篇 |
2009年 | 55篇 |
2008年 | 92篇 |
2007年 | 83篇 |
2006年 | 61篇 |
2005年 | 39篇 |
2004年 | 62篇 |
2003年 | 57篇 |
2002年 | 53篇 |
2001年 | 34篇 |
2000年 | 36篇 |
1999年 | 26篇 |
1998年 | 41篇 |
1997年 | 39篇 |
1996年 | 34篇 |
1995年 | 29篇 |
1994年 | 23篇 |
1993年 | 27篇 |
1992年 | 36篇 |
1991年 | 31篇 |
1990年 | 14篇 |
1989年 | 33篇 |
1988年 | 25篇 |
1987年 | 13篇 |
1986年 | 18篇 |
1985年 | 21篇 |
1984年 | 32篇 |
1983年 | 16篇 |
1982年 | 36篇 |
1981年 | 21篇 |
1980年 | 13篇 |
1979年 | 10篇 |
1978年 | 18篇 |
1977年 | 8篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1971年 | 6篇 |
排序方式: 共有1777条查询结果,搜索用时 0 毫秒
51.
Luis A. Herrera Regina Montero Jesús M. Len-Czares Emilio Rojas María E. Gonsebatt Patricia Ostrosky-Wegman 《Mutation research》1992,270(2):211-218
In this paper we report on a study to elucidate whether the response of human lymphocytes to mitogenic stimulation was modified by physiological changes which occur during the menstrual cycle. Experiments with untreated cultures showed intra-individual variation to mitogen stimulation in female lymphocyte cultures, but a significant correlation between the menstrual cycle and the proliferation kinetics of lymphocytes was not found. Consequently, we performed experiments in which two of the hormones that regulate the menstrual cycle in women, estradiol and progesterone, were added to cultured human lymphocytes obtained from both men and women. The results indicate that both hormones at physiological concentrations have the capacity to modify the proliferation of PHA-stimulated human lymphocytes. Therefore, both hormones could play a role in the induction of the intra-individual variation observed in the untreated female cultures. However, in vivo other factors could also modify the proliferation kinetics of human lymphocytes preventing the demonstration of the effects of a single factor, such as the hormonal changes occurring during the menstrual cycle. 相似文献
52.
The concentrations of LH, total estrogens, and pregnanediol 3 alpha-glucuronide (PdG) were determined by specific radioimmunoassays on daily overnight urine samples obtained in 13 menstrual cycles of six adult female chimpanzees during the periods of increasing, maximal, and decreasing tumescence of the perineal sex skin. The peaks of estrogens and LH and the rise in PdG in urine accurately reflected the peaks of estradiol-17 beta and LH and the subsequent rise in progesterone in the serum of the same animals during the same menstrual cycles, and can be used to predict and verify the occurrence of ovulation, thus avoiding the repeated tranquilizations necessary to obtain daily blood samples. 相似文献
53.
Eduard Kühn Rudi Van Cauwenbergh Leo Huybrechts Hendrik Deelstra 《Biological trace element research》1992,32(1-3):289-292
Plasma concentrations of cGH, T3, and T4 were not different between dwarf and normal broiler breeders. Normal hens had a liver selenium content of 710±35 ng/g, and
dwarf hens 656 ±nine ng/g (n=8). Following injections into a wing vein of different doses (1.5, 3, 6, 12, and 24 μg/kg) of the hypothalamic hormone TRH,
GH was increased after 15 min. This effect seemed to last longer in dwarf chickens. Plasma concentrations of T3 increased significantly 1 h after TRH in normal hens, but TRH was ineffective in raising T3 levels in dwarf animals. The selenium content of livers obtained following decapitation after 2 h was also increased in normal
hens up to 902±42 ng/g using the highest dose of TRH (24 μg/kg). This seemed not to be the case for dwarf animals. A much
smaller. number of hepatic cGH receptors was also found in dwarf hens, whereas the affinity of the hepatic GH receptor was
not influenced by the genotype. It is concluded that the sex-linked dwarf hens are unable to increase their hepatic T4 into T3 conversion following a TRH challenge probably because of a deficiency in hepatic GH receptors. The lower content of selenium
in dwarfs and their inability to increase its uptake after TRH seem therefore to support the hypothesis that selenium has
a direct role in the activity of the 5′-deiodinase complex. 相似文献
54.
Inclusion of IAA in the vase water had little effect on leaf yellowing in cut flowering branches of Alstroemeria pelegrina L. while kinetin delayed leaf yellowing at 10-4M (continuous treatment). Chlorophyll was effectively retained by 10-7M gibberellic acid (GA) in the vase water or by a 20h pulse at 5°C with 10-5/10-4M GA. After 16h of 14C-GA, uptake at 20°C relatively high levels of 14C were found in leaves and low levels in stems and flowers. After this treatment about half of the 14C-GA, in leaves was metabolized into unknown compounds.
Corrigendum. Owing to an error in the proofreading process, the article was published incorrectly. The article as it should have been published is presented here. 相似文献
55.
Proliferating axillary shoots of the difficult-to-root apple cultivar Jonathan acquired an enhanced ability to form adventitious roots with increasing number of subcultures in vitro. The transition between the difficult-to-root and the easy-to-root condition occurred at the fourth subculture.Endogenous levels of free IAA and ABA in shoot tissues were analysed by gas chromatography/mass spectrometry/single ion monitoring (GC/MS/SIM) using negative ion chemical ionisation. Tissues from the mother plants grown in the glasshouse contained more IAA and ABA than those from tissue-culture material. After establishment in vitro there was no variation in the IAA content throughout the subcultures but a decrease in ABA content was observed after the fourth transfer. The IAA/ABA ratio increased from 0.2 in difficult-to-root shoots from the initial culture up to 0.7 in easy-to-root shoots from the long-term subculture. 相似文献
56.
Summary From studies conducted with the pineal organ of the mouse, it was ascertained that for the in vitro investigation of secretory processes (synthesis and release) of proteic/peptidic compound(s), a culture time of 5 to 14 days is optimal. A 5-day organ culture was therefore chosen to study the effects of noradrenaline on these secretory processes.Addition of noradrenaline to the culture medium provokes, in pineal explants of the normal mouse and the eyeless mouse, an inhibition of the secretory process, characterized by the formation of granular vesicles. In the hamster and rat, however, opposite results were obtained. Moreover, it appears that noradrenaline, at least in the rat, may also be involved in the regulation of the ependymal-like secretory process.The present results indicate clearly that noradrenaline (thus, the sympathetic innervation) is implicated in the regulation of the production of proteic/peptidic hormonal agents, but that the effect of this neurotransmitter is species-specific. This could explain the numerous contradictory results reported in the literature.IBRO/UNESCO fellow 相似文献
57.
Morphology and lactose synthesis in tissue culture of mammary alveoli isolated from lactating mice 总被引:1,自引:0,他引:1
Polly R. Cline Paul O. Zamora Howard L. Hosick 《In vitro cellular & developmental biology. Plant》1982,18(8):694-702
Summary Mammary epithelial cells from lactating mice synthesize and secrete lactose in culture and retain many features of their in
vivo morphology if mammary glands are only partially dissociated to alveoli, rather than completely dissociated to single
cells. After 5 d in culture lactose synthesis by alveoli cultured on floating collagen gels is 10 to 20 times higher than
in cultures of single cells on floating collagen gels. Moreover, mammary alveoli in culture retain sensitivity to lactogenic
hormones; the synthesis of lactose by alveoli depends on the continued presence of insulin and either hydrocortisone or prolactin.
In addition, within alveoli the original juxtaposition of constituent epithelial cells is retained, and cells are cuboidal
and have many microvilli and fat droplets. In contrast, alveoli on attached gels flatten and lose their secretory morphology.
These results indicate that the shape of the cells, presence of lactogenic hormones, and maintenance of epithelial:epithelial
cell contacts are required for maintenance of mammary epithelial cell differentiation in culture.
This research was supported by Grants CA-16392 and AG-02909 from the National Institutes of Health and Institutional Grant
IN 119 from the American Cancer Society. 相似文献
58.
Stephen R. Sizemore R. David Cole 《In vitro cellular & developmental biology. Plant》1982,18(8):668-674
Summary The NMuMG cell line derived from normal mouse mammary epithelial cells was tested for responsiveness to hormones. The hormones
studied included insulin, glucocorticoids (cortisol and dexamethasone), and prolactin. In addition to membrane bound insulin
receptors and prolactin receptors, the cells had 2 × 104 cytoplasmic glucocorticoid receptors per cell. Morphological changes were observed in response to hormones. Clusters of cells
appeared with greatly increased diameter, and the number of cells per plate was reduced. The rate of DNA synthesis, corrected
by cell number, indicates that cell division, and hence cell turnover, was increased by the combination of all three hormones.
Insulin greatly enhanced protein synthesis, but glucocorticoid and prolactin did not further increase the rate. The combination
of the three hormones produced a change in the synthesis of histones, consistent with the increase in cell turnover.
There were substantial responses of enzyme activities to hormonal treatment of the cells. Insulin by itself induced a doubling
of the activity of glyceraldehyde phosphate dehydrogenase and perhaps a modest increase in NADH-cytochromec reductase. Lactose synthetase activity showed a three- to fourfold induction of both A and B subunits of the enzyme when
the cells were treated with insulin, glucocorticoid, and prolactin, and the effect of the latter two hormones was shown to
be additional to that of insulin.
This work was supported by Contract N01-CB-43866 from the National Cancer Institute, by Grants GB-38658 from the National
Science Foundation and GMS-20338 from the National Institutes of Health, and by the Agricultural Experimental Station at the
University of California. 相似文献
59.
External application of estradiol-17β increased shoot growth but decreased root growth of sunflower seedlings. It completely inhibited cotyledonary axillary bud development in decapitated plants at the concentration of 1 μg/plant. Concentrations lower than this promoted cotyledonary axillary bud formation. Testosterone on the other hand inhibited both shoot and root growth and promoted cotyledonary axillary bud formation at all the concentrations used. Progesterone at high (0.25,μg/plant) concentration promoted shoot growth but inhibited root growth. A low concentration (0.1 μg/plant) of progesterone produced the opposite effect. 相似文献
60.
Paula Klevjer-Anderson Gertrude Case Buehring 《In vitro cellular & developmental biology. Plant》1980,16(6):491-501
Summary The individual effects of seven hormones on the in vitro growth rate of different classifications of human mammary epithelium
were compared. Hormones used were: 17β-estradiol, estriol, progesterone, hydrocortisone, testosterone, prolactin, and growth
hormone. Cell cultures included three established breast cell lines and primary monolayer cultures established form breast
fluids and excised mammary tissue from 40 women and 4 men. Specimens comprised three classifications: normal, nonmalignant
atypical, and malignant. Growth was quantitated in situ and expressed as population doubling time. Principal findings were:
(a) estrogens, prolactin, and growth hormone stimulated growth of normal cells more frequently than growth of malignant cells,
whereas testosterone and hydrocortisone stimulated growth of malignant cells more frequently than growth of normal cells;
(b) cells cultured from nonmalignant atypias generally showed hormone response profiles intermediate between those of normal
and malignant cells; (c) progesterone stimulated the growth of cells from malignant specimens but not the growth of cells
from normal and nonmalignant atypical samples.
This research was supported by NIAID Research Training Grant 5-TO1-A1-00332-06. 相似文献