全文获取类型
收费全文 | 29834篇 |
免费 | 1806篇 |
国内免费 | 2106篇 |
专业分类
33746篇 |
出版年
2023年 | 290篇 |
2022年 | 461篇 |
2021年 | 556篇 |
2020年 | 567篇 |
2019年 | 804篇 |
2018年 | 846篇 |
2017年 | 678篇 |
2016年 | 690篇 |
2015年 | 794篇 |
2014年 | 1553篇 |
2013年 | 1936篇 |
2012年 | 1358篇 |
2011年 | 1703篇 |
2010年 | 1278篇 |
2009年 | 1447篇 |
2008年 | 1572篇 |
2007年 | 1682篇 |
2006年 | 1386篇 |
2005年 | 1323篇 |
2004年 | 1156篇 |
2003年 | 1136篇 |
2002年 | 959篇 |
2001年 | 664篇 |
2000年 | 597篇 |
1999年 | 659篇 |
1998年 | 625篇 |
1997年 | 547篇 |
1996年 | 477篇 |
1995年 | 475篇 |
1994年 | 463篇 |
1993年 | 446篇 |
1992年 | 397篇 |
1991年 | 335篇 |
1990年 | 278篇 |
1989年 | 273篇 |
1988年 | 233篇 |
1987年 | 217篇 |
1986年 | 198篇 |
1985年 | 306篇 |
1984年 | 417篇 |
1983年 | 290篇 |
1982年 | 328篇 |
1981年 | 270篇 |
1980年 | 228篇 |
1979年 | 202篇 |
1978年 | 130篇 |
1977年 | 119篇 |
1976年 | 108篇 |
1975年 | 93篇 |
1974年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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
2.
3.
4.
5.
David R. Nelson 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2013,368(1612)
The world we live in is a biosphere influenced by all organisms who inhabit it. It is also an ecology of genes, with some having rather startling effects. The premise put forth in this issue is cytochrome P450 is a significant player in the world around us. Life and the Earth itself would be visibly different and diminished without cytochrome P450s. The contributions to this issue range from evolution on the billion year scale to the colour of roses, from Darwin to Rachel Carson; all as seen through the lens of cytochrome P450. 相似文献
6.
Summary A field experiment was conducted using15N-labelled urea on a Reddish Brown Lateritic (Peleustult) soil. Growing two crops on flat land and on soil ridges of 15 cm
height produced similar comparative effects from fertilizer on maize. However, fertilizer applied by broadcasting on maize
with a 50 cm effective band followed by incorporating was more useful to mungbean than that applied by banding below the cereal
seed rows when crops were grown on flat land. The reverse was observed when crops were grown on ridges. It was deduced that
the maize cultivar was not likely to affect comparative efficiencies of fertilizer.
For fertilizer application at sowing, broadcasting in 50 cm maize effective band followed by incorporating was slightly superior
to banding below maize seed rows. Side-dressing of fertilizer to maize at 4 weeks after sowing was superior to application
at sowing. Evenly-split application, at sowing and at 4 weeks after sowing, was either only slightly superior or comparable
to non-split application by banding below maize seed rows at sowing, depending on placement method of the first application.
Soil moisture status as a possible factor rendering discrepancy in the comparative efficiencies obtained by different authors
is discussed. 相似文献
7.
8.
Feral and laboratory flocks of rock doves () show a pattern of grouped sequential exploitation when simultaneously presented with two dispersed, depleting patches of seed. This behavior contrasts with the ideal free distribution pattern shown when patches are small and concentrated. Grouped sequential exploitation consists of two phases: all pigeons first land together and feed at one patch, then leave one by one for the other patch. Departure times of individuals for the second patch are correlated with feeding rate at patch 1, which is in turn correlated with position in the dominance hierarchy. The decision to switch from patch 1 to patch 2 improves individual feeding rates in all cases, but is done slightly later than it should according to optimal foraging theory. 相似文献
9.
Gaelle Jan Violaine Delorme Nehm Saksouk Marie Abrivard Virginie Gonzalez Xavier Cayla Mohamed-Ali Hakimi Isabelle Tardieux 《Microbes and infection / Institut Pasteur》2009,11(12):935-945
Toxoplasma gondii is a human protozoan parasite that belongs to the phylum of Apicomplexa and causes toxoplasmosis. As the other members of this phylum, T. gondii obligatory multiplies within a host cell by a peculiar type of mitosis that leads to daughter cell assembly within a mother cell. Although parasite growth and virulence have been linked for years, few molecules controlling mitosis have been yet identified and they include a couple of kinases but not the counteracting phosphatases. Here, we report that in contrast to other animal cells, type 2C is by far the major type of serine threonine phosphatase activity both in extracellular and in intracellular dividing parasites. Using wild type and transgenic parasites, we characterized the 37 kDa TgPP2C molecule as an abundant cytoplasmic and nuclear enzyme with activity being under tight regulation. In addition, we showed that the increase in TgPP2C activity significantly affected parasite growth by impairing cytokinesis while nuclear division still occurred. This study supports for the first time that type 2C protein phosphatase is an important regulator of cell growth in T. gondii. 相似文献
10.
新的抑癌基因家族--ASPP 总被引:2,自引:0,他引:2
P53是重要的抑癌基因之一的产物,其在抑制肿瘤功能的重要方面是诱导凋亡的能力。但多年来P53诱导凋亡的机制还不清楚,最近发现的ASPP蛋白较好的解释了这个问题,ASPP蛋白能和P53结合形成复合物,再作用于原凋亡基因的启动子区域,从而诱导细胞凋亡的发生,ASPP表达水平的改变能影响P53与DNA结合的能力,进而控制细胞是进入凋亡还是进入停滞的途径,影响P53诱导肿瘤抑制的效应。 相似文献