全文获取类型
收费全文 | 11647篇 |
免费 | 723篇 |
国内免费 | 12篇 |
出版年
2022年 | 87篇 |
2021年 | 157篇 |
2020年 | 149篇 |
2019年 | 126篇 |
2018年 | 298篇 |
2017年 | 246篇 |
2016年 | 302篇 |
2015年 | 401篇 |
2014年 | 455篇 |
2013年 | 705篇 |
2012年 | 701篇 |
2011年 | 748篇 |
2010年 | 478篇 |
2009年 | 374篇 |
2008年 | 520篇 |
2007年 | 570篇 |
2006年 | 494篇 |
2005年 | 468篇 |
2004年 | 440篇 |
2003年 | 427篇 |
2002年 | 356篇 |
2001年 | 250篇 |
2000年 | 258篇 |
1999年 | 200篇 |
1998年 | 119篇 |
1997年 | 100篇 |
1996年 | 103篇 |
1995年 | 93篇 |
1994年 | 97篇 |
1993年 | 79篇 |
1992年 | 142篇 |
1991年 | 163篇 |
1990年 | 158篇 |
1989年 | 151篇 |
1988年 | 115篇 |
1987年 | 123篇 |
1986年 | 143篇 |
1985年 | 135篇 |
1984年 | 144篇 |
1983年 | 91篇 |
1982年 | 92篇 |
1981年 | 92篇 |
1980年 | 58篇 |
1979年 | 81篇 |
1978年 | 75篇 |
1977年 | 80篇 |
1976年 | 66篇 |
1975年 | 65篇 |
1974年 | 63篇 |
1972年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Bacopa monniera Wettst. (BM, syn. Herpestis monniera L; Scrophulariaceae), is an Ayurvedic drug used as a rasayana. Its fresh juice was earlier reported to have significant antiulcerogenic activity. In continuation, methanolic extract of BM (BME) standardized to bacoside-A content (percentage-38.0 ± 0.9), when given in the dose of 10–50 mg/kg, twice daily for 5 days, showed dose-dependent anti-ulcerogenic on various gastric ulcer models induced by ethanol, aspirin, 2 h cold restraint stress and 4 h pylorus ligation. BME in the dose of 20 mg/kg, given for 10 days, twice daily showed healing effects against 50% acetic acid-induced gastric ulcers. Further work was done to investigate the possible mechanisms of its action by studying its effect on various mucosal offensive acid-pepsin secretion and defensive factors like mucin secretion, mucosal cell shedding, cell proliferation and antioxidant activity in rats. BME 20 mg/kg showed no effect on acid-pepsin secretion, increased mucin secretion, while it decreased cell shedding with no effect on cell proliferation. BME showed significant antioxidant effect per se and in stressed animals. Thus, the gastric prophylactic and curative effects of BME may be due to its predominant effect on mucosal defensive factors. 相似文献
3.
4.
K. Sasikala Ch.V. Ramana P. Raghuveer Rao M. Subrahmanyam 《FEMS microbiology letters》1990,72(1-2):23-28
Abstract Photoproduction of hydrogen, nitrogenase activity (acetylene reduction) and hydrogenase activity (methylene blue dye reduction) were studied in free and alginate immobilized whole cells of a purple non-sulfur photosynthetic bacterium Rhodobacter sphaeroides O.U. 001. Four-fold increase in hydrogen production, two-fold increase in nitrogenase activity and 1.2-fold increase in the hydrogenase activity were observed in immobilized cells compared to free cells. Effect of various inhibitors (CO and C2 H2 ) and electron donor (H2 ) on the above three functions by free and immobilized cells has also been studied. 相似文献
5.
6.
Mesophyll derived protoplasts ofCatharanthus roseus cv. Little pinkie were fused with protoplasts derived from an habituated cell line ofC. roseus. Polyethylene glycol was used as agglutinating agent while fusions were induced by square pulses. Best results were obtained
by fusing protoplasts from primary leaves with those from three-day-old cell cultures. Adding calcium ions considerably enhanced
heterofusion rate. Good cell viabilities indicated that this fusion process was not cytotoxic. The heterofusion frequency
was up to 10% or more. Most of the heterokaryons were able to regenerate their cell walls and underwent division.
Communicated by J. TUPY 相似文献
7.
Starch supported production of maximum α-amylases (dextrinizing and saccharifying) byFusarium oxysporum andF. scirpi. Addition of gibberellic acid resulted in an increased production of α-amylase. Presence of glucose depressed the enzyme production. pH 4.5 and 4.0 was found to be optimum for the dextrinizing enzyme secreted by both species. The temperature of 25 and 40 °C was optimum for the dextrinizing enzyme secreted byF. oxysporum andF. scirpi, respectively. Saccharifying enzymes of both species showed their optimum at pH 6.9. The optimum temperature for the activity of the saccharifying enzyme was 30 and 40 °C, respectively. 相似文献
8.
Uranium (U) tolerant aerobic heterotrophs were isolated from the subsurface soils of one of the pre-mined U-rich deposits at Domiasiat located in the north-eastern part of India. On screening of genomic DNA from 62 isolates exhibiting superior U and heavy metal tolerance, 32 isolates were found to be positive for PIB-type ATPase genes. Phylogenetic incongruence and anomalous DNA base compositions revealed the acquisition of PIB-type ATPase genes by six isolates through horizontal gene transfer (HGT). Three of these instances of HGT appeared to have occurred at inter-phylum level and the other three instances indicated to have taken place at intra-phylum level. This study provides an insight into one of the possible survival strategies that bacteria might employ to adapt to environments rich in uranium and heavy metals. 相似文献
9.
10.