全文获取类型
收费全文 | 1438041篇 |
免费 | 137661篇 |
国内免费 | 1442篇 |
专业分类
1577144篇 |
出版年
2021年 | 17936篇 |
2019年 | 16146篇 |
2018年 | 17788篇 |
2017年 | 16489篇 |
2016年 | 28204篇 |
2015年 | 42546篇 |
2014年 | 50580篇 |
2013年 | 76810篇 |
2012年 | 38776篇 |
2011年 | 27481篇 |
2010年 | 43835篇 |
2009年 | 45198篇 |
2008年 | 26103篇 |
2007年 | 24390篇 |
2006年 | 29314篇 |
2005年 | 30348篇 |
2004年 | 29590篇 |
2003年 | 27097篇 |
2002年 | 25088篇 |
2001年 | 38433篇 |
2000年 | 36207篇 |
1999年 | 35058篇 |
1998年 | 25985篇 |
1997年 | 25988篇 |
1996年 | 25469篇 |
1995年 | 23640篇 |
1994年 | 23452篇 |
1993年 | 22662篇 |
1992年 | 30846篇 |
1991年 | 29495篇 |
1990年 | 28165篇 |
1989年 | 28585篇 |
1988年 | 26470篇 |
1987年 | 25213篇 |
1986年 | 24064篇 |
1985年 | 25912篇 |
1984年 | 25036篇 |
1983年 | 22163篇 |
1982年 | 21922篇 |
1981年 | 21208篇 |
1980年 | 19752篇 |
1979年 | 21725篇 |
1978年 | 19808篇 |
1977年 | 18867篇 |
1976年 | 17974篇 |
1975年 | 17822篇 |
1974年 | 18264篇 |
1973年 | 18553篇 |
1972年 | 16125篇 |
1971年 | 14508篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
141.
Scott M. Montgomery 《CMAJ》2010,182(11):1157-1158
142.
143.
144.
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
145.
146.
147.
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
148.
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
149.
Synthesis of prenylquinones in chloroplasts 总被引:3,自引:0,他引:3
150.
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