全文获取类型
收费全文 | 18830篇 |
免费 | 1693篇 |
国内免费 | 1427篇 |
专业分类
21950篇 |
出版年
2023年 | 242篇 |
2022年 | 531篇 |
2021年 | 893篇 |
2020年 | 604篇 |
2019年 | 687篇 |
2018年 | 726篇 |
2017年 | 538篇 |
2016年 | 699篇 |
2015年 | 1147篇 |
2014年 | 1265篇 |
2013年 | 1364篇 |
2012年 | 1561篇 |
2011年 | 1498篇 |
2010年 | 980篇 |
2009年 | 833篇 |
2008年 | 905篇 |
2007年 | 875篇 |
2006年 | 770篇 |
2005年 | 656篇 |
2004年 | 617篇 |
2003年 | 543篇 |
2002年 | 515篇 |
2001年 | 392篇 |
2000年 | 390篇 |
1999年 | 359篇 |
1998年 | 169篇 |
1997年 | 161篇 |
1996年 | 158篇 |
1995年 | 119篇 |
1994年 | 146篇 |
1993年 | 90篇 |
1992年 | 155篇 |
1991年 | 147篇 |
1990年 | 122篇 |
1989年 | 98篇 |
1988年 | 82篇 |
1987年 | 96篇 |
1986年 | 83篇 |
1985年 | 92篇 |
1984年 | 48篇 |
1983年 | 48篇 |
1982年 | 48篇 |
1981年 | 36篇 |
1980年 | 37篇 |
1979年 | 52篇 |
1978年 | 41篇 |
1977年 | 45篇 |
1976年 | 33篇 |
1975年 | 35篇 |
1974年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
10个园林绿化树苗对SO2的反应特性 总被引:4,自引:0,他引:4
用开顶式熏气装置对10种2年生园林绿化树苗进行不同浓度的SO2胁迫,并对其叶片气体交换特征参数进行了测定,研究了参试树种对SO2的生理反应及其在绿化中的应用.结果表明:在SO2胁迫条件下,大多数树种的净光合速率(P n)、蒸腾速率(T r)和气孔导度(G s)均出现下降趋势,下降幅度因树种和SO2浓度不同而有较大差异.树种P n与G s、T r与G s之间存在显著线性正相关关系,但是随SO2浓度增加,P n与G s以及T r与G s线性相关的显著程度被削弱,表现出SO2胁迫下不同树种P n变化与G s变化、T r变化与G s变化的复杂性.根据P n下降幅度将树种分为3种类型:轻度敏感(3种)、中度敏感(4种)和高度敏感树种(3种). 相似文献
43.
44.
45.
Brome mosaic virus, good for an RNA virologist's basic needs 总被引:3,自引:0,他引:3
46.
利用外源性碱性成纤维细胞生长因子(Basic Fibroblast Growth Factor,bFGF)刺激体外培养的人正常牙周膜细胞.采用逆转录-聚合酶链式反应(RT-PCR)检测细胞内decorin的基因表达的变化,研究bFGF对体外培养的人牙周膜细胞内核心蛋白多糖(decorin)的作用,进一步探讨bFGF抑制Ⅰ型胶原的作用机制.发现bFGF刺激牙周膜细胞后能促进牙周膜细胞的增殖,bFGF抑制decorin的合成是bFGF促进牙周膜细胞增殖的重要调节因素之一. 相似文献
47.
48.
Insulin-like growth factor 1 (IGF-1) mediates many of the actions of growth hormone. Overexpression of IGF-1 was reported to have endocrine and paracrine/autocrine effects on somatic growth in transgenic mice. To study the paracrine/autocrine effects of IGF-1 in mammary gland, transgenic mice were produced by pronuclear microinjection of a construct containing a bovine alpha-lactalbumin (alpha-LA) promoter linked to an ovine IGF-1 cNDA. This alpha-LA promoter has previously been shown to direct expression of a human factor VIII gene specifically to the mammary gland of transgenic mice. Three transgenic mouse lines were established as a result of microinjection of 398 embryos. Transgene expression was found in mammary gland at day 1 of lactation from these three lines. Progeny test were carried out by mating two transgenic males/one transgenic female to two nontransgenic females/one nontransgenic male. Mice from one line (line 1225) were all nonexpressors and the other (line 1372) failed to produce offspring. Milk yield was analyzed in the line 1137 that produced 10 mice, of which three were transgenic females and three nontransgenic females. All of the three transgenic females showed integration of the transgene and expressed transgene IGF-1 mRNA in the mammary gland. Milk yields from days 5, 10, and 15 of lactation were significant greater in transgenic expressors than in their nontransgenic littermates. Specifically, there is 17.9% increase in total milk yield from these three days for transgenics compared with nontransgenics. These results demonstrate that local overexpression of IGF-1 in transgenic mice is capable to stimulating milk yield during the first lactation. 相似文献
49.
Xiong XH Han S Wang JH Jiang ZH Chen W Jia N Wei HL Cheng H Yang YX Zhu B You S He JY Hou W Chen MX Yu CJ Jiao YH Zhang WC 《Journal of bacteriology》2011,193(1):315-316
Ketogulonicigenium vulgare is characterized by the efficient production of 2KGA from L-sorbose. Ketogulonicigenium vulgare Y25 is known as a 2-keto-L-gulonic acid-producing strain in the vitamin C industry. Here we report the finished, annotated genome sequence of Ketogulonicigenium vulgare Y25. 相似文献
50.
Li-bo Cheng Lei Cheng Hui-e Bi Zhi-qing Zhang Jin Yao Xiao-zhong Zhou Qin Jiang 《Biochemical and biophysical research communications》2014
Patients with age related macular degeneration (AMD) will develop vision loss in the center of the visual field. Reactive oxygen species (ROS)-mediated retinal pigment epithelium (RPE) cell apoptosis is an important contributor of AMD. In this study, we explored the pro-survival effect of α-melanocyte stimulating hormone (α-MSH) on oxidative stressed RPE cells. We found that α-MSH receptor melanocortin 1 receptor (MC1R) was functionally expressed in primary and transformed RPE cells. RPE cells were response to α-MSH stimulation. α-MSH activated Akt/mammalian target of rapamycin (mTOR) and Erk1/2 signalings in RPE cells, which were inhibited by MC1R siRNA knockdown. α-MSH protected RPE cells from hydrogen peroxide (H2O2)-induced apoptosis, an effect that was almost abolished when MC1R was depleted by siRNA. α-MSH-mediated S6K1 activation and pro-survival effect against H2O2 was inhibited by Akt inhibitors (perifosine, MK-2206 and LY294002). Further, mTOR inhibition by rapamycin, or by mTOR siRNA knockdown, diminished α-MSH’s pro-survival effect in RPE cells. Thus, Akt and its downstream mTOR signaling mediates α-MSH-induced survival in RPE cells. In summary, we have identified a new α-MSH–MC1R physiologic pathway that reduces H2O2-induced RPE cell damage, and might minimize the risk of developing AMD. 相似文献