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991.
1. We describe a generalized mainland-island metapopulation model which includes migration among the island populations. We test model predictions with quantitative data on more than 200 species of moths in two contrasting networks of small islands. The data include a direct measure of migration rate, based on trapping of moths on rocky skerries with no local populations of the vast majority of species.
2. We predicted that moths which are strong fliers but uncommon on the islands have a higher incidence on scattered islands than on islands in a group, because the latter 'compete' for immigrants from the mainland. In contrast, we predicted that weakly flying species with potentially large local populations on the islands occur more frequently on islands in a group due to enhanced colonization rate.
3. Both predicted patterns were observed. Island occupancy increased significantly with the number of individuals caught on the rocky skerries, which is our measure of migration rate from the mainland, supporting the basic assumption that the species occur on the islands in a balance between colonizations and extinctions.
4. These results demonstrate that the moth metapopulations on islands represent a mixture of Levins's and mainland-island metapopulations, and that the mixture is different for different species in the same landscape. 相似文献
2. We predicted that moths which are strong fliers but uncommon on the islands have a higher incidence on scattered islands than on islands in a group, because the latter 'compete' for immigrants from the mainland. In contrast, we predicted that weakly flying species with potentially large local populations on the islands occur more frequently on islands in a group due to enhanced colonization rate.
3. Both predicted patterns were observed. Island occupancy increased significantly with the number of individuals caught on the rocky skerries, which is our measure of migration rate from the mainland, supporting the basic assumption that the species occur on the islands in a balance between colonizations and extinctions.
4. These results demonstrate that the moth metapopulations on islands represent a mixture of Levins's and mainland-island metapopulations, and that the mixture is different for different species in the same landscape. 相似文献
992.
Rajesh M.K. Radha E. Karun Anitha Parthasarathy V.A. 《Plant Cell, Tissue and Organ Culture》2003,75(1):41-47
Regeneration in oil palm was achieved through somatic embryogenesis/organogenesis from embryo-derived callus. Callus was induced from mature embryos of the cross 281 (D)×18 (P) on modified MS medium supplemented with 2,4-D (113.12 M) and 2-iP (14.76 M). The embryogenic calluses obtained were transferred to Blaydes medium supplemented with 2,4-D (0.045 M) and one of the following growth regulators: TDZ (4.54 M), zeatin riboside (2.85 M), putrescine (1 mM) and spermine (100 M). Secondary somatic embryogenesis was found to occur in media supplemented with polyamines. The efficiency of formation of somatic embryos, secondary somatic embryos and shoot meristemoids were significantly higher in putrescine containing medium. Histological studies were also undertaken. 相似文献
993.
The evolutionary relationships between three major components of Darwinian fitness, development rate, growth rate and preadult
survival, were estimated using a comparison of 55 distinct populations ofDrosophila melanogaster variously selected for age-specific fertility, environmental-stress tolerance and accelerated development. Development rate
displayed a strong net negative evolutionary correlation with weight at eclosion across all selection treatments, consistent
with the existence of a size-versus-time tradeoff between these characters. However, within the data set, the magnitude of
the evolutionary correlation depended upon the particular selection treatments contrasted. A previously proposed tradeoff
between preadult viability and growth rate was apparent only under weak selection for juvenile fitness components. Direct
selection for rapid development led to sharp reductions in both growth rates and viability. These data add to the mounting
results from experimental evolution that illustrate the sensitivity of evolutionary correlations to (i) genotype-by-environment
(G X E) interaction, (ii) complex functional-trait interactions, and (iii) character definition. Instability, disappearance
and reversal of patterns of genetic covariation often occur over short evolutionary time frames and as the direct product
of selection, rather than some stochastic process. We suggest that the functional architecture of fitness is a rapidly evolving
matrix with reticulate properties, a matrix that we understand only poorly. 相似文献
994.
Many reports have shown that tongue striated muscles have several unique characteristics not found in other skeletal muscles such as limb and trunk. Several peptide growth factors are reported to play important roles in skeletal myogenesis. In this article, the roles of insulin-like growth factors (IGF), hepatocyte growth factor (HGF) and transforming growth factor (TGF)-alpha in mouse tongue myogenesis were studied using an organ culture system of the mandible or tongue obtained from mouse embryos. It was found that IGF-I promotes the differentiation of tongue myoblasts. HGF plays an essential role in the migration and proliferation of tongue myogenic cells, and inhibits the differentiation of tongue myoblasts. TGF-alpha does not play an essential role in the proliferation of tongue myogenic cells, but does promote the early differentiation of tongue myoblasts. The role of IGF-I in the differentiation of tongue myoblasts, and that of HGF in the migration, proliferation and differentiation of tongue myogenic cells appear to be almost identical to their roles in the myogenesis of limb and cultured myogenic cell lines. However, the role of TGF-alpha in the proliferation and differentiation of tongue myogenic cells appears to be different from its role in the myogenesis of limb and cultured myogenic cell lines such as C2 and L6. 相似文献
995.
The unicellular cyanobacterium Synechocystis sp. PCC6803 can grow heterotrophically in complete darkness, given that a brief period of illumination is supplemented every day (light-activated heterotrophic growth, LAHG), or under very weak (<0.5 micromol m(-2) s(-1)) but continuous light. By random insertion of the genome with an antibiotic resistance cassette, mutants defective in LAHG were generated. In two identical mutants, sll0886, a tetratricopeptide repeat (TPR)-family membrane protein gene, was disrupted. Targeted insertion of sll0886 and three downstream genes showed that the phenotype was not due to a polar effect. The sll0886 mutant shows normal photoheterotrophic growth when the light intensity is at 2.5 micromol m(-2) s(-1) or above, but no growth at 0.5 micromol m(-2) s(-1). Homologs to sll0886 are also present in cyanobacteria that are not known of LAHG. sll0886 and homologs may be involved in controlling different physiological processes that respond to light of low fluence. 相似文献
996.
A simple protocol for mass multiplication of Crataeva nurvala, a medicinal tree, from seedling-derived explants is described. Six different types of explants (cotyledonary nodes, epicotyl
nodes, hypocotyl segments, first pair of leaves, cotyledons, and root segments) developed shoots on Murashige and Skoog's
(MS) basal medium or the same supplemented with different concentrations of 6-benzylaminopurine (BAP). Among the explants
tested for caulogenic potential, only the epicotyl and cotyledonary nodal explants developed shoots on MS basal medium, while
on BAP (0 – 2.0 mg dm−3) adjuvated media all the explants exhibited caulogenesis. The optimum concentration of BAP varied for these explants. The
shoots could be rooted on half strength MS with 0.02 mg dm−3 α-naphthalene acetic acid to get plants, which have been transferred to soil. The explants from in vitro regenerated shoots also possessed a similar caulogenic potential.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
997.
Adventitious roots of Primula acaulis Jacq. are characterized by broad cortex and narrow stele during the primary development. Secondary thickening of roots occurs
through limited cambial growth together with secondary dilatation growth of the persisting cortex. Close to the root tip,
at a distance of ca. 4 mm from the apex, Casparian bands (state I of endodermal development) within endodermal cells develop synchronously. During
late, asynchronous deposition of suberin lamellae (state II of endodermal development), a positional effect is clearly expressed
- suberization starts in the cells opposite to the phloem sectors of the vascular cylinder at a distance of 30 – 40 mm from
the root tip. The formation of secondary walls in endodermis (state III of endodermal development) correlates with the beginning
of secondary growth of the root at a distance of ca. 60 mm. Endodermis is the only cortical layer of primrose, where not only cell enlargement but also renewed cell division
participate in the secondary dilatation growth. The original endodermal cells additionally divide anticlinally only once.
Newly-formed radial walls acquire a typical endodermal character by forming Casparian bands and deposition of suberin lamellae.
A network of endodermal Casparian bands of equal density develops during the root thickening by the tangential expansion of
cells and by the formation of new radial walls with characteristic wall modifications. These data are important since little
attention has been paid up till now to the density of endodermal network as a generally significant structural and functional
trait of the root.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
998.
幽门螺旋杆菌感染的慢性胃炎胃窦粘膜内NF-κB和TGF-α表达及其意义 总被引:2,自引:0,他引:2
目的 探讨幽门螺旋杆菌 (Hp)与慢性胃炎患者胃窦粘膜内NF κB和TGF α表达之间的关系。方法 用免疫细胞化学方法 ,检测Hp+ 和Hp-胃炎患者及正常人的胃窦部活检标本。结果 NF κB和TGF α在正常组胃粘膜内弱表达。在胃炎病人 ,NF κB和TGF α表达增强。特别是在Hp+ 组 ,NF κB和TGF α呈高表达 ,与Hp-组和正常组比较均有显著性差异 (P <0 0 5和P <0 0 1)。此外在G细胞和部分腺上皮的细胞核内也呈高表达。TGF α常以颗粒状的特征位于腺上皮细胞核上区而且高表达。结论 NF κB和TGF α的表达在胃炎组增强 ,而且Hp+ 组远高于其他两组。NF κB和TGF α二者的表达平行且成呈正相关。 相似文献
999.
1000.