全文获取类型
收费全文 | 1594510篇 |
免费 | 157895篇 |
国内免费 | 1597篇 |
专业分类
1754002篇 |
出版年
2021年 | 18188篇 |
2019年 | 16253篇 |
2018年 | 18218篇 |
2017年 | 16943篇 |
2016年 | 28642篇 |
2015年 | 43188篇 |
2014年 | 51341篇 |
2013年 | 77639篇 |
2012年 | 45455篇 |
2011年 | 35323篇 |
2010年 | 45890篇 |
2009年 | 46611篇 |
2008年 | 33459篇 |
2007年 | 31917篇 |
2006年 | 35832篇 |
2005年 | 36301篇 |
2004年 | 35680篇 |
2003年 | 33158篇 |
2002年 | 31094篇 |
2001年 | 48339篇 |
2000年 | 46173篇 |
1999年 | 42015篇 |
1998年 | 27374篇 |
1997年 | 27389篇 |
1996年 | 26638篇 |
1995年 | 24805篇 |
1994年 | 24489篇 |
1993年 | 23876篇 |
1992年 | 36099篇 |
1991年 | 34365篇 |
1990年 | 33108篇 |
1989年 | 33398篇 |
1988年 | 30611篇 |
1987年 | 29721篇 |
1986年 | 27809篇 |
1985年 | 29426篇 |
1984年 | 27668篇 |
1983年 | 24350篇 |
1982年 | 23405篇 |
1981年 | 22200篇 |
1980年 | 20769篇 |
1979年 | 24264篇 |
1978年 | 21740篇 |
1977年 | 20481篇 |
1976年 | 19471篇 |
1975年 | 19454篇 |
1974年 | 20362篇 |
1973年 | 20560篇 |
1972年 | 17700篇 |
1971年 | 16385篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
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
152.
153.
154.
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
155.
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
156.
157.
Synthesis of prenylquinones in chloroplasts 总被引:3,自引:0,他引:3
158.
CONSENSUS CLADOGRAMS AND GENERAL CLASSIFICATIONS 总被引:2,自引:0,他引:2
159.
160.