全文获取类型
收费全文 | 612228篇 |
免费 | 64316篇 |
国内免费 | 311篇 |
出版年
2018年 | 10067篇 |
2017年 | 9834篇 |
2016年 | 9768篇 |
2015年 | 8568篇 |
2014年 | 10045篇 |
2013年 | 14527篇 |
2012年 | 18018篇 |
2011年 | 22704篇 |
2010年 | 16321篇 |
2009年 | 15249篇 |
2008年 | 19872篇 |
2007年 | 21810篇 |
2006年 | 14765篇 |
2005年 | 14893篇 |
2004年 | 14431篇 |
2003年 | 14483篇 |
2002年 | 14160篇 |
2001年 | 26278篇 |
2000年 | 26680篇 |
1999年 | 20630篇 |
1998年 | 7088篇 |
1997年 | 7670篇 |
1996年 | 7163篇 |
1995年 | 6680篇 |
1994年 | 6475篇 |
1993年 | 6738篇 |
1992年 | 17502篇 |
1991年 | 17485篇 |
1990年 | 16734篇 |
1989年 | 16593篇 |
1988年 | 15199篇 |
1987年 | 14648篇 |
1986年 | 13556篇 |
1985年 | 13665篇 |
1984年 | 11353篇 |
1983年 | 9766篇 |
1982年 | 7276篇 |
1981年 | 6472篇 |
1980年 | 6257篇 |
1979年 | 10694篇 |
1978年 | 8520篇 |
1977年 | 7755篇 |
1976年 | 7235篇 |
1975年 | 8187篇 |
1974年 | 8697篇 |
1973年 | 8583篇 |
1972年 | 8327篇 |
1971年 | 7621篇 |
1970年 | 6133篇 |
1969年 | 5859篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
91.
V K Khugaeva E D Klimenko P N Aleksandrov G F Leskova M I Reutov 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(7):15-19
Experiments were made on rabbit fed an atherogenic diet (0.5 g/kg cholesterol) singly for 15 and 24 h and repeatedly for 3, 9 and 30 days. At early stages of lipid metabolism distress the interrelationship was established between blood rheological disorders and microcirculatory abnormalities. The dependence of the initial reaction of some rheological characteristics on their initial level was marked. 相似文献
92.
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
93.
Lincoln D Stein 《Genome biology》2010,11(5):207
With DNA sequencing now getting cheaper more quickly than data storage or computation, the time may have come for genome informatics
to migrate to the cloud. 相似文献
94.
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
95.
Synthesis of prenylquinones in chloroplasts 总被引:3,自引:0,他引:3
96.
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
97.
98.
An earlier report (1) of an adverse effect of high doses of oxytocin on human memory included results of studies on women receiving oxytocin as part of the treatment to induce 2nd trimester therapeutic abortion. These women served as their own controls. We have now been able to study a group of women who have been treated in all ways like the original group, with the exception that they did not receive oxytocin. The results from this external control corroborate the finding that oxytocin affected memory. 相似文献
99.
The absence of centromeric bands in the karyotype of Felis catus is confirmed. It is also confirmed that no satellite band is visible in CsCl density gradients. However, a satellite is observed both by recentrifuging the fraction of the DNA that bands at high density in CsCl and by using netropsin to enhance the resolution of a CsCl gradient containing total F. catus DNA. The satellite, about 0.5% of total DNA, was isolated by repeated centrifugation in CsCl alone and in CsCl with netropsin. Netropsin was removed and a pure satellite DNA obtained. The reassociation kinetics (C0t1/2 less than 10(-3) M . s) show that the satellite is of the simple sequence type and hence a candidate for centromeric heterochromatin. Its cytological localisation awaits in situ hybridisation experiments. 相似文献
100.
Several synthetic 7-hydroxyflavylium salts related to apigeninidin, a natural 3-deoxyanthocyanidin, have been studied in the Ames mutagenicity test using strain TA1537 of Salmonella typhimurium. Under the neutral pH conditions of the test, these flavylium salts are deprotonated through ionization of the C7-OH (pKa′ = 4.2–4.4) to form quinone methides. Only the quinone methides of 4-methyl-7-hydroxyflavylium chloride and 4′-methoxy-4-methyl-7-hydroxy-flavylium chloride showed mutagenicity. Responses of 4–8 times the background were observed at the higher doses (1000 μg/plate), both with and without metabolic activation. It was concluded that the induction of frameshift mutagenicity by this group of compounds is caused by those quinone methides that have non-ionic, stable polycyclic structures at neutral pH. 相似文献