全文获取类型
收费全文 | 1355099篇 |
免费 | 121944篇 |
国内免费 | 1518篇 |
专业分类
1478561篇 |
出版年
2021年 | 17753篇 |
2019年 | 16139篇 |
2018年 | 17335篇 |
2017年 | 16123篇 |
2016年 | 27834篇 |
2015年 | 42333篇 |
2014年 | 50501篇 |
2013年 | 76716篇 |
2012年 | 35537篇 |
2011年 | 23423篇 |
2010年 | 42830篇 |
2009年 | 44426篇 |
2008年 | 22532篇 |
2007年 | 20511篇 |
2006年 | 26231篇 |
2005年 | 27188篇 |
2004年 | 26564篇 |
2003年 | 24183篇 |
2002年 | 22518篇 |
2001年 | 35077篇 |
2000年 | 32684篇 |
1999年 | 32366篇 |
1998年 | 25510篇 |
1997年 | 25307篇 |
1996年 | 24794篇 |
1995年 | 23002篇 |
1994年 | 22814篇 |
1993年 | 21899篇 |
1992年 | 27825篇 |
1991年 | 25950篇 |
1990年 | 24572篇 |
1989年 | 25364篇 |
1988年 | 23326篇 |
1987年 | 22074篇 |
1986年 | 21218篇 |
1985年 | 23129篇 |
1984年 | 22784篇 |
1983年 | 20022篇 |
1982年 | 20750篇 |
1981年 | 19968篇 |
1980年 | 18567篇 |
1979年 | 19010篇 |
1978年 | 18016篇 |
1977年 | 17275篇 |
1976年 | 16448篇 |
1975年 | 16077篇 |
1974年 | 16772篇 |
1973年 | 17097篇 |
1972年 | 14660篇 |
1971年 | 13402篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
Auxotrophic mutants of Candida albicans FC18 were induced by a combination of treatments with nitrous acid and UV irradiation. Arginine (Arg-), histidine (His-) and methionine/cysteine (MetA-) auxotrophs were recovered by this means. The Arg- auxotrophs lacked active argininosuccinate lyase (EC 4.3.2.1), the enzyme catalysing the final step in arginine biosynthesis. Thus the locus may be designated arg-4. The mutant strains bearing this mutation did not form germ tubes unless the germination medium contained arginine. 相似文献
152.
S-adenosyl-L-homocysteine (S-AH), a potent inhibitor of biological transmethylation, decreased the response of rat retina adenylate cyclase to dopamine and to 2-amino-6, 7-dihydroxytetrahydronaphtalene (ADTN). This effect appeared for 10?7M of S-adenosyl-L-homocysteine and was linear for concentration ranging to 10?4M. S-adenosyl-L-homocysteine did not decrease the cyclic AMP accumulation with sodium fluoride, a non specific adenylate cyclase activator. On the other hand, the incorporation of methyl group was reduced in rat retina homogenates by S-adenosyl-L-homocysteine. These findings suggest that the activity of the dopamine dependent adenylate cyclase is linked to a methylation process. 相似文献
153.
Scott M. Montgomery 《CMAJ》2010,182(11):1157-1158
154.
155.
156.
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
157.
158.
159.
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
160.
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