全文获取类型
收费全文 | 15178篇 |
免费 | 1303篇 |
国内免费 | 18篇 |
出版年
2023年 | 56篇 |
2022年 | 42篇 |
2021年 | 280篇 |
2020年 | 211篇 |
2019年 | 261篇 |
2018年 | 394篇 |
2017年 | 354篇 |
2016年 | 515篇 |
2015年 | 834篇 |
2014年 | 877篇 |
2013年 | 1032篇 |
2012年 | 1293篇 |
2011年 | 1232篇 |
2010年 | 778篇 |
2009年 | 699篇 |
2008年 | 973篇 |
2007年 | 884篇 |
2006年 | 779篇 |
2005年 | 701篇 |
2004年 | 713篇 |
2003年 | 576篇 |
2002年 | 522篇 |
2001年 | 271篇 |
2000年 | 257篇 |
1999年 | 188篇 |
1998年 | 128篇 |
1997年 | 93篇 |
1996年 | 73篇 |
1995年 | 99篇 |
1994年 | 61篇 |
1993年 | 60篇 |
1992年 | 107篇 |
1991年 | 88篇 |
1990年 | 88篇 |
1989年 | 91篇 |
1988年 | 85篇 |
1987年 | 81篇 |
1986年 | 69篇 |
1985年 | 74篇 |
1984年 | 55篇 |
1983年 | 48篇 |
1982年 | 35篇 |
1980年 | 31篇 |
1979年 | 48篇 |
1978年 | 43篇 |
1977年 | 30篇 |
1976年 | 42篇 |
1975年 | 33篇 |
1974年 | 33篇 |
1973年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Hee-Jung Choi Tae-Wook Chung Mi-Ju Park Kyu Sup Lee Youngjin Yoon Hyung Sik Kim Jun Hee Lee Sang-Mo Kwon Syng-Ook Lee Keuk-Jun Kim Jin-Ho Baek Ki-Tae Ha 《PloS one》2016,11(2)
In the present study, we investigated the role of Paeonia lactiflora Pall. extract on embryo implantation in vitro and in vivo. A polysaccharides depleted-water extract of P. lactiflora (PL-PP) increased LIF expression in human endometrial Ishikawa cells at non-cytotoxic doses. PL-PP significantly increased the adhesion of the human trophectoderm-derived JAr spheroids to endometrial Ishikawa cells. PL-PP-induced LIF expression was decreased in the presence of a p38 kinase inhibitor SB203580 and an MEK/ERK inhibitor U0126. Furthermore, endometrial LIF knockdown by shRNA reduced the expression of integrins β3 and β5 and adhesion of JAr spheroids to Ishikawa cells. In vivo administration of PL-PP restored the implantation of mouse blastocysts in a mifepristone-induced implantation failure mice model. Our results demonstrate that PL-PP increases LIF expression via the p38 and MEK/ERK pathways and favors trophoblast adhesion to endometrial cells. 相似文献
22.
23.
Ho WW Fernandes CC Alves-Gomes JA Smith GT 《Ethology : formerly Zeitschrift fur Tierpsychologie》2010,116(11):1050-1064
The South American weakly-electric knifefish (Apteronotidae) produce highly diverse and readily quantifiable electrocommunication signals. The electric organ discharge frequency (EODf), and EOD modulations (chirps and gradual frequency rises (GFRs)), vary dramatically across sexes and species, presenting an ideal opportunity to examine the proximate and ultimate bases of sexually dimorphic behavior. We complemented previous studies on the sexual dimorphism of apteronotid communication signals by investigating electric signal features and their hormonal correlates in Apteronotus bonapartii, a species which exhibits strong sexual dimorphism in snout morphology. Electrocommunication signals were evoked and recorded using a playback paradigm, and were analyzed for signal features including EOD frequency and the structure of EOD modulations. To investigate the androgenic correlates of sexually dimorphic EOD signals, we measured plasma concentrations of testosterone and 11-ketotestosterone. A. bonapartii responded robustly to stimulus playbacks. EODf was sexually monomorphic, and males and females produced chirps with similar durations and amounts of frequency modulation. However, males were more likely than females to produce chirps with multiple frequency peaks. Sexual dimorphism in apteronotid electrocommunication signals appears to be highly evolutionarily labile. Extensive interspecific variation in the magnitude and direction of sex differences in EODf and in different aspects of chirp structure suggest that chirp signals may be an important locus of evolutionary change within the clade. The weakly-electric fish represent a rich source of data for understanding the selective pressures that shape, and the neuroendocrine mechanisms that underlie, diversity in the sexual dimorphism of behavior. 相似文献
24.
J. S. Cho B. K. Jang S. M. Lee I. J. Lee C. H. Lee 《Plant biology (Stuttgart, Germany)》2020,22(3):514-521
- Information on the optimal conditions to promote the germination of Lamprocapnos spectabilis (L.) Fukuhara seeds is limited; consequently, this study was conducted to establish the requirements to break seed dormancy and promote germination.
- The selected seeds had morphophysiological dormancy and had not begun embryo development. To study the dormancy breaking and embryo development processes, seeds were subjected to constant or changing temperature treatments during moist stratification.
- High temperature and humidity resulted in vigorous embryo growth, with the longest embryos occurring after 1 month of incubation at 20 °C. At 4 °C, the seeds required incubation period of at least 3 months to germinate. Embryo growth and germination were higher with changing high and low temperatures than under a constant temperature, and changing temperatures also considerably changed the endogenous hormone levels, embryo development and germination. Bioactive gibberellin (GA) content was higher in seeds incubated at 20 °C for 1 month, then at 4 °C for 2 months. The content of endogenous abscisic acid in seeds subjected to the same treatment decreased by 97.6% compared with that of the untreated seeds.
- Embryo growth and seed germination require changing high and low temperatures; however, exogenous GA3 could substitute for high temperatures, as it also causes accelerated germination. In this study, the seeds of L. spectabilis were identified as an intermediate simple type, a sub‐level of morphophysiologically dormant seeds.
25.
It is argued that complexity, rather than fitness or organization, is the quantity whose increase gives a direction to evolution.The increase in complexity is shown to be a consequence of the process by which a self-organizing system optimizes its organization with respect to a locally defined fitness potential. 相似文献
26.
Extraction of bovine pituitaries at pH 7.0, in the presence or absence of protease inhibitors (PMSF, leupeptin, pepstatin A and EDTA) yielded both basic and acidic FGF components that were characterized by Western blotting and sequence analysis. Basic FGF comprised several components: an 18 KDa form that is similar, if not identical, to the basic FGF (1-146) already described; a 17 KDa form that is likely to be a new truncated molecular species (11-146) and a group of immunoreactive components of about 29 KDa. Acidic FGF showed several active components of pI 4.5-6.5. The most active component has a pI of approximately 5.0; molecular weight of 17 KDa and is shown, by Western blotting, to be similar to a truncated form of bovine brain acidic FGF. The biological activity of the latter component is shown to be neutralized by anti-brain acidic FGF antiserum. 相似文献
27.
The amounts of cAMP and cGMP in the rat pinealocyte are regulated by norepinephrine acting through synergistic dual receptor mechanisms involving alpha 1- and beta-adrenoceptors (Vanecek, J., Sugden, D., Weller, J.L., and Klein, D.C. (1985) Endocrinology 116, 2167-2173; Sugden, L., Sugden, D., and Klein, D.C. (1986) J. Biol. Chem. 261, 11608-11612). Based on the available evidence, it appears that Ca2+-phospholipid-dependent protein kinase is involved in the alpha 1-adrenergic potentiation of beta-adrenergic stimulation of cAMP, but not in the stimulation of cGMP (Sugden, D., Vanecek, J., Klein, D.C., Thomas, T.P., and Anderson, W.B. (1985) Nature 314, 359-361). In the present study the role of protein kinase C in the adrenergic stimulation of cGMP was reinvestigated, with the purpose of determining whether protein kinase C activators would potentiate the effects of beta-adrenergic agonists on cGMP if cells were also treated with agents known to elevate intracellular free Ca2+. The protein kinase C activator 4 beta-phorbol 12-myristate 13-acetate (PMA) markedly elevated the cGMP content of beta-adrenergically stimulated pinealocytes which had also been treated with 1 microM A23187, 15 mM K+, or 1 microM ouabain. The effects of A23187 were blocked by EGTA and those of K+ were blocked by nifedipine, establishing the involvement of Ca2+. The stimulatory effects of PMA on cGMP accumulation were mimicked by other protein kinase C activators. PMA also stimulated cGMP accumulation in cells treated with cholera toxin (1 microgram/ml) and A23187 (1 microM), but not in cells treated only with cholera toxin. These results suggest that protein kinase C, which is activated in the pinealocyte by the alpha-adrenergic agonist phenylephrine, is probably involved in the adrenergic regulation of cGMP accumulation at a step distal to receptor activation. 相似文献
28.
29.
30.