全文获取类型
收费全文 | 10712篇 |
免费 | 881篇 |
国内免费 | 291篇 |
出版年
2023年 | 90篇 |
2022年 | 77篇 |
2021年 | 337篇 |
2020年 | 263篇 |
2019年 | 344篇 |
2018年 | 357篇 |
2017年 | 331篇 |
2016年 | 484篇 |
2015年 | 644篇 |
2014年 | 711篇 |
2013年 | 826篇 |
2012年 | 963篇 |
2011年 | 881篇 |
2010年 | 602篇 |
2009年 | 463篇 |
2008年 | 629篇 |
2007年 | 560篇 |
2006年 | 481篇 |
2005年 | 421篇 |
2004年 | 426篇 |
2003年 | 340篇 |
2002年 | 363篇 |
2001年 | 137篇 |
2000年 | 135篇 |
1999年 | 138篇 |
1998年 | 86篇 |
1997年 | 95篇 |
1996年 | 69篇 |
1995年 | 54篇 |
1994年 | 55篇 |
1993年 | 39篇 |
1992年 | 56篇 |
1991年 | 43篇 |
1990年 | 24篇 |
1989年 | 30篇 |
1988年 | 32篇 |
1987年 | 33篇 |
1986年 | 26篇 |
1985年 | 29篇 |
1984年 | 26篇 |
1983年 | 30篇 |
1982年 | 10篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Zhou J Chen F Xiao J Li C Liu Y Ding Y Wan P Wang X Huang J Wang Z 《The international journal of biochemistry & cell biology》2011,43(8):1168-1177
Adult stem cells are important cell sources in regenerative medicine, but isolating them is technically challenging. This study employed a novel strategy to generate stem-like corneal epithelial cells and promote the functional properties of these cells by coculture with embryonic stem cells. The primary corneal epithelial cells were labelled with GFP and cocultured with embryonic stem cells in a transwell or by direct cell-cell contact. The embryonic stem cells were pre-transfected with HSV-tk-puro plasmids and became sensitive to ganciclovir. After 10 days of coculture, the corneal epithelial cells were isolated by treating the cultures with ganciclovir to kill the embryonic stem cells. The expression of stem cell-associated markers (ABCG2, p63) increased whereas the differentiation mark (Keratin 3) decreased in corneal epithelial cells isolated from the cocultures as evaluated by RT-PCR and flow cytometry. Their functional properties of corneal epithelial cells, including cell adhesion, migration and proliferation, were also enhanced. These cells could regenerate a functional stratified corneal epithelial equivalent but did not form tumors. Integrin β1, phosphorylated focal adhesion kinase and Akt were significantly upregulated in corneal epithelial cells. FAK Inhibitor 14 that suppressed the expression of phosphorylated focal adhesion kinase and Akt inhibited cell adhesion, migration and proliferation. LY294002 that suppressed phosphorylated Akt but not phosphorylated focal adhesion kinase inhibited cell proliferation but had no effect on cell adhesion or migration. These findings demonstrated that the functional properties of stem-like corneal epithelial cells were enhanced by cocultured embryonic stem cells via activation of the integrin β1-FAK-PI3K/Akt signalling pathway. 相似文献
992.
Kim SY Ryu SJ Kang HT Choi HR Park SC 《Apoptosis : an international journal on programmed cell death》2011,16(8):795-807
In order to study the nature of aging-dependent apoptosis resistance, we compared the activation pattern of mitogen-activated
protein kinases (MAPK) in response to three different stress modalities: hydrogen peroxide (H2O2), staurosporine, and thapsigargin. We observed the agonist-specific activation pattern of MAP kinases in human diploid fibroblasts
(HDFs). When young HDFs were treated with PD98059, a specific inhibitor of extracellular signal-regulated kinase (ERK), H2O2-induced apoptosis was blocked, whereas staurosporine-induced apoptosis was inhibited by treatment with SB203580, a specific
inhibitor of p38. In addition, the levels of anti-apoptotic protein Bcl-2 (B-cell lymphoma protein-2) were restored by PD98059
or SB239063 in cells treated with H2O2 or staurosporine, respectively. We also found that inhibition of the nuclear import of p-Erk and p-p38 using wheat germ agglutinin
induced apoptosis resistance in young HDF cells in response to H2O2 or staurosporine. These data indicate a potential role of the nuclear translocation of apoptotic signals in the induction
of apoptosis. Moreover, the nuclear translocation of activated ERK1/2 and p38 in response to H2O2 or staurosporine was significantly compromised in senescent HDFs, compared with young cells. Taken together, we propose that
the apoptosis resistance of senescent HDFs might be related to the defective nuclear translocation of stress-activated signals
in an agonist-specific manner, which would imply the operation of an aging-dependent functional nucleo-cytoplasmic trafficking
barrier. 相似文献
993.
994.
995.
996.
997.
Liangming Chen Zhigang Zhao Xi Liu Linglong Liu Ling Jiang Shijia Liu Wenwei Zhang Yihua Wang Yuqiang Liu Jianmin Wan 《Molecular breeding : new strategies in plant improvement》2011,27(2):247-258
The incomplete fertility of japonica × indica rice hybrids has inhibited breeders’ access to the substantial heterotic potential of these hybrids. As hybrid sterility
is caused by an allelic interaction at a small number of loci, it is possible to overcome it by simple introgression at the
major sterility loci. Here we report the use of marker-assisted backcrossing to transfer into the elite japonica cv. Zhendao88 a photoperiod-sensitive male sterility gene from cv. Lunhui422S (indica) and the yellow leaf gene from line Yellow249 (indica). The microsatellite markers RM276, RM455, RM141 and RM185 were used to tag the fertility genes S5, S8, S7 and S9, respectively. Line 509S is a true-breeding photoperiod-sensitive male sterile plant, which morphologically closely resembles
the japonica type. Genotypic analysis showed that the genome of line 509S comprises about 92% japonica DNA. Nevertheless, hybrids between line 509S and japonica varieties suffer from a level of hybrid sterility, although the line is highly cross-compatible with indica types, with the resulting hybrids expressing a significant degree of heterosis. Together, these results suggest that segment
substitution on fertility loci based on known information and marker-assisted selection are an effective approach for utilizing
the heterosis of rice inter-subspecies. 相似文献
998.
Microbial infections in the mosquito Aedes aegypti activate the newly identified CLSP1 and CLSP2 genes, which encode modular proteins composed of elastase-like serine protease and C-type lectin domains. These genes are predominantly regulated by the immune deficiency pathway, but also by the Toll pathway. Silencing of CLSP2, but not CLSP1, results in the activation of prophenoloxidase (PPO), the terminal enzyme in the melanization cascade, suggesting that CLSP2 is a negative modulator of this reaction. Haemolymph PPO activation is normally inhibited in the presence of Plasmodium parasites, but in CLSP2-depleted mosquitoes, the Plasmodium-induced block of melanization is reverted, and these mosquitoes are refractory to the parasite. Thus, CLSP2 is a new component of the mosquito immune response. 相似文献
999.
An HJ Lee HJ Jun SH Hwang SY Kim BC Kim K Lee KM Oh MK Kim J 《Bioprocess and biosystems engineering》2011,34(7):841-847
Lipase (LP) was immobilized on electrospun and ethanol-dispersed polystyrene–poly(styrene-co-maleic anhydride) (PS–PSMA) nanofibers
(EtOH-NF) in the form of enzyme precipitate coatings (EPCs). LP precipitate coatings (EPCs-LP) were prepared in a three-step
process, consisting of covalent attachment, LP precipitation, and crosslinking of precipitated LPs onto the covalently attached
LPs via glutaraldehyde treatment. The LP precipitation was performed by adding various concentrations of ammonium sulfate
(20–50%, w/v). EPCs-LP improved the LP activity and stability when compared to covalently attached LPs (CA-LP) and the enzyme
coatings of LPs (EC-LP) without the LP precipitation. For example, the use of 40% (w/v) ammonium sulfate resulted in EPC40-LP
with the highest activity, which was 4.0 and 3.6 times higher than those of CA-LP and EC-LP, respectively. After 165-day incubation
under rigorous shaking at 200 rpm, the residual activities of EPC50-LP were 0.5 μM/min mg of EtOH-NF, representing 113 and
75 times higher than those of CA-LP and EC-LP, respectively. When LP was partially purified via a simple ammonium sulfate
precipitation and dialysis, both activities and stabilities of EC-LP and EPC-LP could be marginally improved. It is anticipated
that the improved LP activity and stability in the form of EPCs would allow for their potential applications in various bioconversion
processes such as biodiesel production and ibuprofen resolution. 相似文献
1000.