全文获取类型
收费全文 | 6452篇 |
免费 | 656篇 |
国内免费 | 4篇 |
出版年
2022年 | 42篇 |
2021年 | 69篇 |
2020年 | 57篇 |
2019年 | 44篇 |
2018年 | 63篇 |
2017年 | 67篇 |
2016年 | 103篇 |
2015年 | 155篇 |
2014年 | 204篇 |
2013年 | 248篇 |
2012年 | 360篇 |
2011年 | 362篇 |
2010年 | 226篇 |
2009年 | 199篇 |
2008年 | 292篇 |
2007年 | 380篇 |
2006年 | 276篇 |
2005年 | 319篇 |
2004年 | 311篇 |
2003年 | 268篇 |
2002年 | 289篇 |
2001年 | 134篇 |
2000年 | 110篇 |
1999年 | 128篇 |
1998年 | 100篇 |
1997年 | 78篇 |
1996年 | 73篇 |
1995年 | 68篇 |
1994年 | 77篇 |
1993年 | 74篇 |
1992年 | 101篇 |
1991年 | 92篇 |
1990年 | 109篇 |
1989年 | 99篇 |
1988年 | 72篇 |
1987年 | 88篇 |
1986年 | 57篇 |
1985年 | 89篇 |
1984年 | 64篇 |
1983年 | 86篇 |
1982年 | 73篇 |
1981年 | 66篇 |
1980年 | 59篇 |
1979年 | 82篇 |
1978年 | 66篇 |
1977年 | 60篇 |
1976年 | 50篇 |
1974年 | 62篇 |
1973年 | 61篇 |
1972年 | 60篇 |
排序方式: 共有7112条查询结果,搜索用时 109 毫秒
1.
Ernst Wm. Spannhake Terry L. Adams Steven R. Kleeberger 《Prostaglandins & other lipid mediators》1985,30(6):1041-1055
The effects of repeated antigen exposure on the synthesis of mediators by lung tissues are not well understood. To investigate the influence of antigen challenge on the synthesis of prostaglandins by central airway and peripheral lung tissues, fourteen sensitive sheep underwent biweekly exposure to aerosolized antigen (7) or saline (7). Following the fifth exposure, microsomal and high speed supernatant fractions were prepared from trachealis muscle and lung parenchyma. Synthesis of thromboxane (TX) A2, prostaglandin (PG) D2 and PGI2 from the PG endoperoxide intermediate, PGH2, was assayed over a range of substrate concentrations from 3–200 uM. Synthesis of PGI2 by trachealis microsomes was approximately 5-fold greater than that of TXA2. PGI2 and TXA2 production was identical in tracheal preparations from Ascaris- and saline-exposed animals. In parenchymal tissues, where TXA2 production predominated over PGI2 by 9-fold, preparations from Ascaris- exposed animals synthesized 50% more TXA2 than controls at PGH2 concentrations of 25 uM and above, whereas synthesis of PGI2 and PGD2 were similar in preparations from both groups of animals. The density of pulmonary mast cells was decreased by 21% in the Ascaris group, whereas polymorphonuclear leukocyte density was unchanged. These results demonstrate the differential synthesis of TXA2 and PGI2 in central airways and peripheral lung regions of the sheep. They further indicate that repeated exposure of the airways to antigen selectively enhances TXA2 synthesis in the lung periphery of sensitized animals. The site of this increased enzymatic activity, whether in resident cells or newly-infiltrated cells, has not been determined. 相似文献
2.
3.
4.
5.
In Exp. 1, PMSG was injected to 26-day-old prepubertal rats to induce ovulations. On Day 2 (2 days later, the equivalent of the day of pro-oestrus) they received at 08:00 h 5 mg hydroxyflutamide or vehicle and at 12:00 h 2 mg progesterone or testosterone or vehicle. Animals were killed at 18:00 h on Day 2 or at 09:00 h on Day 3. Progesterone but not testosterone restored the preovulatory LH surge and ovulation in hydroxyflutamide-treated rats. In Exp. 2, 2 mg progesterone or testosterone were injected between 10:30 and 11:00 h on Day 2, to advance the pro-oestrous LH surge and ovulation in PMSG-primed prepubertal rats. Injection of hydroxyflutamide abolished the ability of progesterone to advance the LH surge or ovulation. Testosterone did not induce the advancement of LH surge or ovulation. In Exp. 3, ovariectomized prepubertal rats implanted with oestradiol-17 beta showed significantly (P less than 0.01) elevated serum LH concentrations at 18:00 h over those observed at 10:00 h. Progesterone injection to these animals further elevated the serum LH concentrations at 18:00 h, in a dose-dependent manner, with maximal values resulting from 1 mg progesterone. Hydroxyflutamide treatment significantly (P less than 0.003) reduced the serum LH values in rats receiving 0-1 mg progesterone but 2 mg progesterone were able to overcome this inhibition. It is concluded that progesterone but not testosterone can reverse the effects of hydroxyflutamide on the preovulatory LH surge and ovulation. It appears that hydroxyflutamide may interfere with progesterone action in induction of the LH surge, suggesting a hitherto undescribed anti-progestagenic action of hydroxyflutamide. 相似文献
6.
7.
8.
G Terry Molinert A A Demina M Valcarcel Novo 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1986,(2):54-59
The results of the epidemiological analysis of the morbidity rate in meningococcal infection for 1976-1984 are presented. The maximum rise of morbidity rate, equal to 14.4 per 100000 of population, was observed in 1983. Primarily, the rise of morbidity rate in 1979 was induced by meningococci of two serogroups: C (44.6%) and B (36.4%). The vaccinal prophylaxis of the population, carried out in 1979 with the use of polysaccharide vaccine A + C, did not affect morbidity caused by group B meningococci. The isolation rate of these organisms reached 98.7% from patients and 81.0% from carriers. The characteristic feature of the epidemic process of meningococcal infection in Cuba was a considerable increase in the number of patients under 1 year of age and the absence of seasonal fluctuations in morbidity rate. 相似文献
9.
10.
Structures of Gram-Negative Cell Walls and Their Derived Membrane Vesicles 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Terry J. Beveridge 《Journal of bacteriology》1999,181(16):4725-4733