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991.
Leaf structure and anatomy as related to leaf mass per area variation in seedlings of a wide range of woody plant species and types 总被引:3,自引:0,他引:3
The structural causes of variation in leaf mass per area, and of variations in leaf structure accounted for by leaf habit
and life form, were explored in a set of laboratory-grown seedlings of 52 European woody species. The leaf traits analysed
included density, thickness, saturated mass/dry mass, and leaf nitrogen per mass and per area. Other traits described the
anatomy of leaves, most of them relating to the lamina (proportions of palisade and spongy parenchymata, epidermis, air space
and sclerified tissues, expressed as volume per leaf area, and per-cell transversal areas of epidermis and parenchymata),
and another referring to the mid rib (transversal section of sclerified tissues). Across the whole set of species leaf mass
per area was correlated with leaf density but not with thickness, and this was confirmed by taxonomic relatedness tests. Denser
leaves corresponded with greater proportion of sclerified tissues in the lamina, smaller cells and lower water and N contents,
but no relation was found with the proportion of air space in the lamina. Taxonomic relatedness analysis statistically supported
the negative association of leaf density with saturated to dry leaf mass ratio. Thicker leaves also exhibited greater volume
per leaf area and greater individual cell area in each of the tissues, particularly parenchyma. Mean leaf mass per area and
leaf thickness were lower in deciduous than in evergreen species, but no significant differences in leaf density, proportion
of sclerified tissues in the lamina or cell area were found between the two groups. Leaf mass per area was higher in trees
and subshrubs than in shrubs and climbers-plus-scramblers, this rank being equal for leaf density and proportion of sclerified
tissues in the lamina, and reversed for cell area. Given the standardised environment and ontogenetic phase of the seedlings,
we conclude that variation in leaf structure and anatomy among species and species groups has a strong genetic basis, and
is already expressed early in the development of woody plants. From an ecological viewpoint, we can interpret greater leaf
mass per area across this species set as greater allocation to support and defence functions, as shown predominantly by species
from resource-poor environments.
Received: 16 August 1999 / Accepted: 29 March 2000 相似文献
992.
人类M6b基因一种剪接型cDNA的分子克隆 总被引:3,自引:1,他引:2
蛋白脂蛋白基因突变导致Pelizaeus-Merzbacher病(PMD)和部分-X连锁的痉挛性截瘫。Olinsky等克隆了M6b的部分序列(U45955),该基因认为是PLP基因家族成员之一。我们以巢式PCR得到一约300bp的片段,测序为与U45955的5‘端局部重叠的新序列,拼接后得到1.642kb的序列,其中含有可编程265个氨基酸的开放阅读框。 相似文献
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997.
氮素形态对不同专用型小麦根系及氮素利用率影响的研究 总被引:22,自引:4,他引:22
采用盆栽方法研究了3种氮素形态对不同专用型小麦根系及氮素利用率的影响.结果表明,拔节期以后,强筋型小麦豫麦34在酰胺态氮处理下,根系生物量、根系活力、氮素利用率、氮收获指数和籽粒蛋白质含量最高,铵态氮处理次之,硝态氮处理最低.中筋型小麦豫麦49的各测定指标以铵态氮处理最高,其它指标在酰胺态氮和铵态氮间的趋势不同;弱筋型小麦豫麦50在酰胺态氮处理下各项指标最高,而铵态氮处理下蛋白质含量最低,符合品种优质和专用,氮收获指数与籽粒蛋白质含量之间呈现极显著正相关。 相似文献
998.
Sunghark Kwon Hyun H. Park 《Protein science : a publication of the Protein Society》2019,28(5):964-970
Pyridoxal 5′‐phosphate (PLP)‐dependent β‐transaminases (βTAs) reversibly catalyze transamination reactions by recognizing amino groups linked to the β‐carbon atoms of their substrates. Although several βTA structures have been determined as holo forms containing PLP, little is known about the effect of PLP on the conversion of the apo structure to the holo structure. We determined the crystal structure of the apo form of a βTA from Mesorhizobium sp. strain LUK at 2.2 Å resolution to elucidate how PLP affects the βTA structure. The structure revealed three major disordered regions near the active site. Structural comparison with the holo form also showed that the disordered regions in the apo form are ordered and partially adopt secondary structures in the holo form. These findings suggest that PLP incorporation into the active site contributes to the structural stability of the active site architecture, thereby forming the complete active site. Our results provide novel structural insights into the role of PLP in terms of active site formation. 相似文献
999.
Cd^2+或Hg^2+水污染对菱体细胞的细胞核及叶绿体超微结构的影响 总被引:16,自引:0,他引:16
用Cd2+、Hg2+两种重金属离子溶液培育菱(TrapabicornisOsbeck.)植物体后,观察体细胞的细胞核及叶绿体超微结构的变化。处理后第8天,菱浮水叶叶片和不定根细胞中细胞核的染色质与核质遭到破坏,不定根中细胞核的核仁消失。但在各处理浓度(10μmol/L~50μmol/LCd2+或Hg2+)下,核膜均保持完整。叶片细胞的叶绿体基粒数目减少,基粒片层解体,叶绿体双层膜断裂,叶绿体中的质体球流入细胞基质中。两种结构的破坏程度随处理的离子浓度提高而增大。说明菱体细胞超微结构的变化观测可作为监测重金属污染的一种方法。 相似文献
1000.
Natural occurrence of C4 species, life forms, and their longitudinal distribution patterns along the Northeast China Transect (NECT) were studied. Six vegetation regions experiencing similar irradiation regimes, but differing in longitude, precipitation, and altitude were selected along the NECT from 108 to 131 °E, around altitude of 43.5 °N. Seventy C4 species were identified in 41 genera and 13 families. 84 % of the total C4 species were found in four families: Gramineae (38 species), Chenopodiaceae (11 species), Cyperaceae (5 species), and Amaranthaceae (5 species). C4 grasses make up 54 % of the total identified C4 species along the NECT and form the leading C4 family in meadow, steppe, and desert along the NECT. C4
Chenopodiaceae species make up about 16 % of the C4 species and become less important, particularly in the meadow and the eastern end of the NECT. 57 % of the total C4 species are therophytes and 37 % are hemicryptophytes, which is consistent with floristic composition and land utilization. In general, the number of C4 species decreased significantly from the west to the east or from dry to moist areas along the NECT, and was remarkably correlated with annual precipitation (r
2= 0.677) and aridity (r
2= 0.912), except for salinized meadow region. The proportion of C4 species from all the six vegetation regions was considerably correlated with these two climatic parameters (r
2= 0.626 or 0.706, respectively). These findings suggest that the natural occurrence of C4 species varies significantly along the large-scale longitudinal gradient of the NECT. The notable relationship of C4 species number and proportion in the flora with variations in annual precipitation and aridity suggest that these two climatic parameters are the main factors controlling the longitudinal distribution patterns of C4 species along the NECT. 相似文献