全文获取类型
收费全文 | 1100966篇 |
免费 | 88358篇 |
国内免费 | 1330篇 |
出版年
2021年 | 17511篇 |
2020年 | 12507篇 |
2019年 | 16056篇 |
2018年 | 16523篇 |
2017年 | 15272篇 |
2016年 | 27131篇 |
2015年 | 41685篇 |
2014年 | 49607篇 |
2013年 | 75962篇 |
2012年 | 28573篇 |
2011年 | 14986篇 |
2010年 | 40648篇 |
2009年 | 42931篇 |
2008年 | 15384篇 |
2007年 | 12558篇 |
2006年 | 19519篇 |
2005年 | 20689篇 |
2004年 | 20036篇 |
2003年 | 17788篇 |
2002年 | 16045篇 |
2001年 | 19037篇 |
2000年 | 15904篇 |
1999年 | 20040篇 |
1998年 | 23672篇 |
1997年 | 23424篇 |
1996年 | 23294篇 |
1995年 | 21409篇 |
1994年 | 21295篇 |
1993年 | 20286篇 |
1992年 | 18212篇 |
1991年 | 16652篇 |
1990年 | 15419篇 |
1989年 | 16684篇 |
1988年 | 15195篇 |
1987年 | 14344篇 |
1986年 | 13853篇 |
1985年 | 15987篇 |
1984年 | 17473篇 |
1983年 | 15599篇 |
1982年 | 17884篇 |
1981年 | 17514篇 |
1980年 | 16271篇 |
1979年 | 13371篇 |
1978年 | 13890篇 |
1977年 | 13615篇 |
1976年 | 13042篇 |
1975年 | 11894篇 |
1974年 | 11914篇 |
1973年 | 12426篇 |
1972年 | 10178篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
E. Rachor 《Helgoland Marine Research》1980,33(1-4):522-530
The muddy sediments of the sublittoral area of the inner German Bight are inhabited by a specialized macrofauna with few species.
Long-term investigations on community and population dynamics have shown that the majority of this fauna are very susceptible
to environmental stress (e. g. oxygen deficiency), and that the impoverishment trend recorded in 1977 has continued. The special
hydrographic conditions of the inner German Bight, especially a long flushing time and the possibility of thermohaline stratifications,
together with its function as a sediment trap are discussed. It is proposed that such areas should be considered as sensitive,
and hence be protected from avoidable additional stress, e. g. introduction of wastes. This proposal is discussed with regard
to the dangers arising from the view that muddy areas enriched with organic matter are inhabited by organisms preadapted to
the decomposition of additional waste matter. 相似文献
992.
Summary Between 3 Nov. 1983 and 9 Apr. 1984, six applications of fertiliser N (ammonium, nitrate or urea) were given to four autumn
sown (26 Oct. 1983)Vicia faba L cultivars, Banner Winter (BW) and Maris Beagle (MBg), cold tolerant cultivars normally sown in the autumn, and Herz Freya
(HF) and Maris Bead (MBd), cold sensitive cultivars more commonly sown in the spring. The effects of additional N were determined
by comparison with plants given zero-N (controls).
Application of N, regardless of form, had no effect on % emergence at the first sampling (15 Dec. 1983); >90% for BW, MBg
and HF, but only 40–60% for MBd. At this time the dry weight, carbon content and nitrogen content of all cultivars was approximately
20% less than that of the seed on planting. No more plants emerged after 15 Dec. 1983. Between 15 Dec. 1983 and 20 Feb. 1984,
all cultivars, regardless of N treatment, showed little change in dry weight, carbon content and nitrogen content but the
proportion of total plant dry weight, carbon content and nitrogen content in the cotyledons decreased while the proportions
in root, stem and leaf tissue increased. On 20 Feb. 1984 there were no N effects. All cultivars but especially BW and MBg,
showed progressive increases in dry weight, carbon content and nitrogen content during the period 20 Feb. 1984 to 8 May 1984.
Pooled results for all four cultivars indicated that on 8 May 1984, plants given ammonium and urea had a greater dry weight,
carbon content and nitrogen content than controls.
At harvest (1–3 Sep. 1984), BW and MBg outyielded (g dw seed m−2) HF and MBd. Pooled results for all cultivars indicated that application of N regardless of form gave increased yield and
an increased N concentration (mg N g−1 dw) in the seed. 相似文献
993.
994.
995.
996.
Inge N. Bojesen 《Prostaglandins & other lipid mediators》1985,30(3):479-489
The glycerolipid production by rat renal papillary slices varied inversely with the urea concentration (0a–1660 mM) whether the production was measured as labelling of the glycerol backbone from glucose or as incorporation of labelled arachidonic acid and palmitic acid. The rate of phospholipid formation was most dependent on medium urea concentrations in the range between 0 and 1100 mM. The production of prostaglandins PGE2 and PGF2α, measured radioimmunologically or by an isotope derivative method was in the same range inversely related to the production of glycerolipids and chain elongations. The effect of urea on prostaglandin formation is probably indirectly caused by the inhibition of the phospholipid formation and chain elongation, since the effect was abolished by 1% defatted albumin in the medium. The data suggest that the level of free arachidonic acid within the cells is controlled to an important extent by glycerolipid formation and chain elongation. 相似文献
997.
Dan B. Lindholm 《Biochemical and biophysical research communications》1982,109(3):805-812
Neuronal perikarya isolated from developing rat brain cortex were employed for studying the effect of hypothyroidism on RNA and protein synthesis in vitro. Neuronal protein synthesis was inhibited by hypothyroidism during the second week of brain development. Thyroxine treatment in vivo stimulated neuronal protein synthesis in hypothyroid rats. The synthesis of neuronal RNA was depressed by hypothyroidism in 7-day old rats. The inhibition of neuronal protein synthesis due to the lack of thyroid hormaones was restricted to membrane-bound ribosomes. The results suggest that the maturation of the neurone is very sensitive to hormonal imbalance during the critical period of brain development. 相似文献
998.
999.
1000.
The effect of insulin on phosphatidylcholine biosynthesis in cultured rat liver cells was assessed by measuring changes in the activity of the first enzyme in the choline pathway of phosphatidylcholine biosynthesis, choline kinase (ATP: cholinephosphortransferase, EC 2.7.1.32), in the presence or absence of the hormone. Choline kinase specific activity in liver cells incubated for 18 hours in the presence of 10?7M insulin increased two-fold from 3.4 ± 0.3 nmoles phosphorylcholine formed/min/mg protein to 7.5 ± 0.6 nmoles/min/mg protein. This effect was dose dependent and reversed by the addition of actinomycin D and cycloheximide. It is concluded that the increase in specific activity is due to synthesis of new enzyme rather than activation of existing enzyme. 相似文献