全文获取类型
收费全文 | 1009978篇 |
免费 | 99549篇 |
国内免费 | 634篇 |
出版年
2018年 | 10369篇 |
2017年 | 9898篇 |
2016年 | 14861篇 |
2015年 | 20991篇 |
2014年 | 23760篇 |
2013年 | 31881篇 |
2012年 | 34944篇 |
2011年 | 33568篇 |
2010年 | 23557篇 |
2009年 | 21492篇 |
2008年 | 28749篇 |
2007年 | 29603篇 |
2006年 | 28007篇 |
2005年 | 32057篇 |
2004年 | 30922篇 |
2003年 | 28280篇 |
2002年 | 25575篇 |
2001年 | 44080篇 |
2000年 | 43785篇 |
1999年 | 35180篇 |
1998年 | 12242篇 |
1997年 | 12456篇 |
1996年 | 11668篇 |
1995年 | 10939篇 |
1994年 | 10646篇 |
1993年 | 10380篇 |
1992年 | 28938篇 |
1991年 | 28435篇 |
1990年 | 27880篇 |
1989年 | 27210篇 |
1988年 | 25381篇 |
1987年 | 23716篇 |
1986年 | 21967篇 |
1985年 | 22032篇 |
1984年 | 18062篇 |
1983年 | 15012篇 |
1982年 | 11158篇 |
1981年 | 9879篇 |
1980年 | 9335篇 |
1979年 | 16383篇 |
1978年 | 12719篇 |
1977年 | 11475篇 |
1976年 | 10589篇 |
1975年 | 12008篇 |
1974年 | 12940篇 |
1973年 | 12823篇 |
1972年 | 11486篇 |
1971年 | 10613篇 |
1970年 | 9049篇 |
1969年 | 8833篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
The succinate dehydrogenase consists of only four subunits, all nuclearly encoded, and is part of both the respiratory chain and the Krebs cycle. Mutations in the four genes encoding the subunits of the mitochondrial respiratory chain succinate dehydrogenase have been recently reported in human and shown to be associated with a wide spectrum of clinical presentations. Although a comparatively rare deficiency in human, molecularly defined succinate dehydrogenase deficiency has already been found to cause encephalomyopathy in childhood, optic atrophy or tumor in adulthood. Because none of the typical housekeeping genes encoding this respiratory chain complex is known to present tissue-specific isoforms, the tissue-specific involvement represents a quite intriguing question, which is mostly addressed in this review. A differential impairment of electron flow through the respiratory chain, handling of oxygen, and/or metabolic blockade possibly associated with defects in the different subunits that can be advocated to account for tissue-specific involvement is discussed. 相似文献
992.
L. M. Saunders D. M. Tompkins P. J. Hudson 《International journal for parasitology》2000,30(14):1481-1485
The importance of oxygen availability in the embryonation of the infective egg stages of the gastrointestinal nematode parasite Heterakis gallinarum was studied in the laboratory. Unembryonated H. gallinarum eggs were kept under either aerobic conditions by gassing with oxygen, or anaerobic conditions by gassing with the inert gas nitrogen, under a range of constant temperatures. Oxygenated eggs embryonated at a rate influenced by temperature. Conversely, eggs treated with nitrogen showed no embryonation although when these eggs were transferred from nitrogen to oxygen gas after 60 days of treatment, embryonation occurred. This demonstrated that oxygen is an essential requirement for H. gallinarum egg development, although undeveloped eggs remain viable, even after 60 days in low oxygen conditions. The effects of climate on the biology of free-living stages studied under constant laboratory conditions cannot be applied directly to the field where climatic factors exhibit daily cycles. The effect of fluctuating temperature on development was investigated by including an additional temperature group in which H. gallinarum eggs were kept under daily temperature cycles between 12 and 22°C. Cycles caused eggs to develop significantly earlier than those in the constant mean cycle temperature, 17°C, but significantly slower than those in constant 22°C suggesting that daily temperature cycles had an accelerating effect on H. gallinarum egg embryonation but did not accelerate to the higher temperature. These results suggest that daily fluctuations in temperature influence development of the free-living stages and so development cannot be accurately predicted on the basis of constant temperature culture. 相似文献
993.
994.
Emerging buds of rhizome of Alpinia galanga Willd produced shoots and roots simultaneously when cultured in MS medium supplemented
with kinetin 3.0 mg l-1. Each explanted shoot bud produced 8 shoots in average and roots simultaneously within 8 weeks. Shoot proliferation could
be continued even after a year by transferring each divided shoot explant to the same medium. Regenerated plantlets could
be sucessfully transferred to soil where they grew well within 10–12 weeks with 80% survivality.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
995.
996.
997.
998.
999.
1000.
Scots pine (Pinus sylvestris L.) seedlings were grown for 3years in the ground in open top chambers and exposed to twoconcentrations of atmospheric CO2(ambient or ambient + 400 µmol mol-1) without addition of nutrients and water. Biomassproduction (above-ground and below-ground) and allocation, aswell as canopy structure and tissue nitrogen concentrationsand contents, were examined by destructive harvest after 3 years.Elevated CO2increased total biomass production by 55%, reducedneedle area and needle mass as indicated, respectively, by lowerleaf area ratio and leaf mass ratio. A relatively smaller totalneedle area was produced in relation to fine roots under elevatedCO2. The proportion of dry matter in roots was increased byelevated CO2, as indicated by increased root-to-shoot ratioand root mass ratio. Within the root system, there was a significantshift in the allocation towards fine roots. Root litter constituteda much higher fraction of fine roots in trees grown in the elevatedCO2than in those grown in ambient CO2. Growth at elevated CO2causeda significant decline in nitrogen concentration only in theneedles, while nitrogen content significantly increased in branchesand fine roots (with diameter less than 1 mm). There were nochanges in crown structure (branch number and needle area distribution).Based upon measurements of growth made throughout the 3 years,the greatest increase in biomass under elevated CO2took placemainly at the beginning of the experiment, when trees grownin elevated CO2had higher relative growth rates than those grownunder ambient CO2; these differences disappeared with time.Symptoms of acclimation of trees to growth in the elevated CO2treatmentwere observed and are discussed. Copyright 2000 Annals of BotanyCompany Elevated CO2, Pinus sylvestris, biomass production, allocation, fine roots, root litter, crown structure, nitrogen, C/N ratio 相似文献