全文获取类型
收费全文 | 1640069篇 |
免费 | 154164篇 |
国内免费 | 1734篇 |
专业分类
1795967篇 |
出版年
2021年 | 18380篇 |
2019年 | 16340篇 |
2018年 | 19276篇 |
2017年 | 18134篇 |
2016年 | 29437篇 |
2015年 | 43518篇 |
2014年 | 51604篇 |
2013年 | 77898篇 |
2012年 | 48232篇 |
2011年 | 39494篇 |
2010年 | 47583篇 |
2009年 | 47710篇 |
2008年 | 36293篇 |
2007年 | 35042篇 |
2006年 | 38184篇 |
2005年 | 39193篇 |
2004年 | 38304篇 |
2003年 | 35552篇 |
2002年 | 33478篇 |
2001年 | 51894篇 |
2000年 | 49702篇 |
1999年 | 44985篇 |
1998年 | 27675篇 |
1997年 | 27453篇 |
1996年 | 26607篇 |
1995年 | 24771篇 |
1994年 | 24385篇 |
1993年 | 23615篇 |
1992年 | 37858篇 |
1991年 | 35915篇 |
1990年 | 34547篇 |
1989年 | 34947篇 |
1988年 | 32240篇 |
1987年 | 30249篇 |
1986年 | 28621篇 |
1985年 | 30035篇 |
1984年 | 28175篇 |
1983年 | 24392篇 |
1982年 | 23148篇 |
1981年 | 22026篇 |
1980年 | 20517篇 |
1979年 | 23800篇 |
1978年 | 21305篇 |
1977年 | 20143篇 |
1976年 | 18875篇 |
1975年 | 18932篇 |
1974年 | 19708篇 |
1973年 | 19987篇 |
1972年 | 17140篇 |
1971年 | 15636篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Vernon Shattuck Frank R. Katterman 《Biochemical and biophysical research communications》1982,109(3):1017-1025
When cotyledonary tissue of cotton are treated with the mutagen ethyl methanesulfonate and then germinated, an enhanced, unscheduled DNA synthesis response is observed, along with a concomitant increase in the thymidine triphosphate precursor pool size. The implications of these results are discussed in this paper. 相似文献
192.
193.
194.
Nitrogen fertigation of greenhouse-grown cucumber 总被引:2,自引:0,他引:2
I. Papadopoulos 《Plant and Soil》1986,93(1):87-93
Summary This greenhouse study investigated the response of trickle-irrigated cucumber (Cucumis sativa cv. ‘Petita’) to three N levels applied with every irrigation via the irrigation stream. The plants were grown in pots filled
with 12 kg of soil. Water containing 5.8, 11.8, or 17.8 mmol N/l, and uniformly supplied with 2.0 and 3.9 mmol/l of P and
K, respectively, was applied two to three times daily. In all treatments of 0.3 leaching fraction was allowed.
The resulting total N applications were 15.7, 31., and 47.2 g N/plant. The total amount of water applied was 1851/plant. Total
N and NO3-N, in lajinae and petioles, increased with increasing N level whereas P and K in generated decreased. Although different
NO3/NH4 ratios in the treatments may have influeced the response to N, it could be concluded that the highest yield was obtained
with 11.8 mmol N/1 due to increased number of fruit. In the root volume of this treatment the NO3-N concentration in the soil solution was aroun 7 mmol/1 for most of the growing season. The dry matter concentration of fruits
was not affected by the N levels.
It was concluded that 11.8 mmol N/1 applied with every irrigation via the irrigation stream is adequate to cover the needs
of greenhous-grown cucumber for higher yield (9.42 kg/plant over a harvesting period of 93 days). 相似文献
195.
OBJECTIVE--To test the hypothesis that farmers are at high risk of hip osteoarthritis and to investigate possible causes for such a hazard. DESIGN--Cross sectional survey. SETTING--Five rural general practices. SUBJECTS--167 male farmers aged 60-76 and 83 controls from mainly sedentary jobs. All those without previous hip replacement underwent radiography of the hip. MAIN OUTCOME MEASURES--Hip replacement for osteoarthritis or radiological evidence of hip osteoarthritis. RESULTS--Prevalence of hip osteoarthritis was higher in farmers than controls and especially in those who had farmed for over 10 years (odds ratio 9.3, 95% confidence interval 1.9 to 44.5). The excess could not be attributed to any one type of farming, and heavy lifting seems the likely explanation. CONCLUSIONS--Manual handling in agriculture should be limited where possible. Consideration should be given to making hip osteoarthritis a prescribed industrial disease in farmers. There may be wider implications for the prevention of hip osteoarthritis in the general population. 相似文献
196.
Synthesis of prenylquinones in chloroplasts 总被引:3,自引:0,他引:3
197.
M A Pass M W Goosem S Pollitt 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1985,82(2):457-461
The metabolism of the cholestatic triterpene acid reduced lantadene A has been studied in susceptible and resistant rats and in sheep which are susceptible to intoxication. Sheep and susceptible female rats produced a similar major metabolite and rats produced a second metabolite which was a glucuronide. These metabolites were also observed in extracts of bile canalicular membranes prepared from intoxicated rats. Resistant male and female rats produced a similar major metabolite which was different to those synthesized by susceptible animals. It is concluded that in rats and sheep there is a correlation between the type of metabolites produced in the liver and the susceptibility to intoxication by reduced lantadene A. 相似文献
198.
Growth of fathead minnow yolk sac larvae was characterized from changes in dry weight and total content and concentrations of RNA, DNA and protein in fish exposed to a sublethal level of HCN (58 micrograms/l) and in age matched controls. Cyanide toxicosis occurred within 24 hr of exposure as evidenced by significant reductions in protein and RNA content and RNA/DNA ratio of larvae. After 96 hr exposure to HCN, larvae exhibited the same growth rate and protein synthetic rate (RNA/DNA) as control fish. HCN toxicosis and recovery is rapid and at least partial tolerance to HCN develops within 96 hr of exposure in larval fathead minnows. 相似文献
199.
CONSENSUS CLADOGRAMS AND GENERAL CLASSIFICATIONS 总被引:2,自引:0,他引:2
200.