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61.
Baret Stéphane Maurice Sandrine Le Bourgeois Thomas Strasberg Dominique 《Plant Ecology》2004,172(2):265-273
Rubus alceifolius Poiret (Rosaceae) was introduced to the island of Réunion in the southeastern Indian Ocean about 1850 and is now highly invasive. This bramble, native from southeastern Asia and Malaysia, has invaded a wide variety of habitats (lowland rainforest, mountain and submountain rainforest, Acacia heterophylla rainforest) from sea level to 1700 m. It is suspected to be monoclonal so, its remarkable success may be due in part to great phenotypic plasticity. On Réunion, bud, flower, fruit and seed production, the duration of the flowering period and the importance of the seed bank were found to be negatively correlated with elevation (50-1500 m a.s.l.). At a lowland site, fruit production in mature stands averaged between 30 and 80 fruits/m2 during 1999 and 2000. No fruit set occurred above 1100 m. This fruit production pattern was similar over two years. Although the number of leaves per unit area is similar along the whole gradient studied, decrease of fruit set in upland areas might be compensated for by an increase in vegetative growth. Temperature variation is very sharp along the elevation gradient and may control the fruit and the seed production. Fruit production allows establishment of new populations all around the island via bird dissemination. Once established, R. alceifolius maintains dense patches that can grow vegetatively. Our results may be relevant for eradication programs that should take into account variation in reproductive strategy in lowland vs. highland habitats. 相似文献
62.
This paper aims to study the fertility rate of the migrant Tibetans residing in Northern India and finding out the factors
which are affecting the fertility level among them. Data are reported on age at menarche, age at marriage, first childbirth,
use of contraception, widowhood, migration and on various fertility measures in the Tibetan of Northern India living at low
and moderate altitude (600–2000 m), who have migrated from high altitude (4000 m above sea level) in Tibet. The migrant Tibetans
reported a relatively lower fertility as compared to the high and moderate altitude populations. This lower fertility is mostly
attributable to the use of contraception, the later mean age at marriage and first childbirth, and relatively high proportion
of widows in the migrant Tibetans. However, the social as well as biological changes in population during migration should
not be overlooked, which have a sufficient impact on fertility. 相似文献
63.
Braxton M. Alfred 《American journal of physical anthropology》1980,52(3):341-349
Frequencies of HbS obtained by several screening clinics are analyzed for age, sex, and location effects. All seem to be present in some form, though age and sex effects may be conditional on location. An attempt is made to elaborate the common observation of increasing frequency with age. This is shown to be the result of differences in fertility favoring the normal. A simulation which íncludes 25% admixture was done. The results indicate a genetically relevant New World experience for the population to be about 9–12 generations with the heterozygote having fitness of 0.96–0.99. 相似文献
64.
65.
Mating is an energy demanding process, imposing risks to physical injuries, pathogen infection and predation. Nevertheless, repeated and multiple mating are widespread even in insect species where nuptial gifts are not involved. The effects of repeated mating, by the same male, are examined on the reproductive performance of female Southern green stink bug Nezara viridula (L.). Fecundity is reduced in females mated three or four times, although there is increased longevity. Females mated once or twice produce more egg clusters and concentrate egg‐laying activity in the early part of adult life, whereas those mating more often lay eggs throughout the life span, with fewer egg clusters. Although fecundity is negatively affected by the number of matings, egg fertility remains unaffected. 相似文献
66.
Establishing life is a calcium-dependent TRiP: Transient receptor potential channels in reproduction
Katrien De Clercq Joris Vriens 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》2018,1865(11):1815-1829
Calcium plays a key role in many different steps of the reproduction process, from germ cell maturation to placental development. However, the exact function and regulation of calcium throughout subsequent reproductive events remains rather enigmatic. Successful pregnancy requires the establishment of a complex dialogue between the implanting embryo and the endometrium. On the one hand, endometrial cell will undergo massive changes to support an implanting embryo, including stromal cell decidualization. On the other hand, trophoblast cells from the trophectoderm surrounding the inner cell mass will differentiate and acquire new functions such as hormone secretion, invasion and migration. The need for calcium in the different gestational processes implicates the presence of specialized ion channels to regulate calcium homeostasis. The superfamily of transient receptor potential (TRP) channels is a class of calcium permeable ion channels that is involved in the transformation of extracellular stimuli into the influx of calcium, inducing and coordinating underlying signaling pathways. Although the necessity of calcium throughout reproduction cannot be negated, the expression and functionality of TRP channels throughout gestation remains elusive. This review provides an overview of the current evidence regarding the expression and function of TRP channels in reproduction. 相似文献
67.
Mariia Nesterkina Svitlana Bilokon Tetiana Alieksieieva Inna Chubyk Iryna Kravchenko 《Journal of Asia》2018,21(3):793-796
The present study investigated the effect of mono/bicyclic terpenoids and phenol derivatives on the viability of Drosophila melanogaster and their influence on the multiplication of the nuclear genome. The fertility and viability of fruit flies were assessed after oral administration and inhalation exposure of compounds 1–5: guaiacol, eugenol, borneol, menthol and carvacrol. The influence of terpenoids and phenols on the degree of chromosomes polyteny in salivary gland cells of D. melanogaster larvae was determined. Among all tested compounds, carvacrol demonstrated the most significant impact on fecundity and insect survival when inhaled or adding to the culture medium. Oral administration of carvacrol had an impact on giant chromosomes increasing their average level of chromosome polyteny degree while eugenol adding to culture medium had the opposite effect. The possible mechanism of terpenoids and phenols action is discussed. 相似文献
68.
The mechanism of fertility inhibition of conjugation by the F plasmid depends on the presence of both the FinO protein and
an antisense RNA, FinP, which together control the expression of the positive regulator of the transfer operon TraJ. FinO
both prevents the degradation of FinP, allowing its intracellular concentration to rise, and promotes duplex formation with
its target, the traJ mRNA. In this study, deletions in finO were constructed and fused to gst, encoded by the pGEX-2T expression vector, to give GST-FinO fusions of varying lengths. These fusions were then tested for
their ability to bind FinP and traJ mRNA, and to promote duplex formation. Our results suggest that the predicted basic N-terminal α-helix is involved in RNA
binding, while the central domain is involved in duplex formation. The presence of the acidic C-terminal domain protects FinP
from ribonucleolase degradation and might enhance binding of the N-terminal α-helical domain in a manner reminiscent of the
Rom protein of ColE1.
Received: 4 May 1998 / Accepted: 15 June 1998 相似文献
69.
玉米是杂种优势利用最成功的作物之一,采用细胞质雄性不育(CMS)进行玉米杂交种生产已成为杂种优势利用的有力工具。CMS是由于细胞质和细胞核的基因表达产物的不协调而产生的不育性,可被核基因组中的恢复基因恢复。根据育性恢复专效性,玉米CMS材料主要分为T、C和S三种类型。综述了这三种类型不育及其恢复基因的研究进展,分析了在不育化制种中的应用情况。 相似文献
70.
Rice with LD-type cytoplasmic male sterility (CMS) possesses the cytoplasm of ‘Lead Rice’ and its fertility is recovered by
a nuclear fertility restorer gene Rf1. Rf1 promotes processing of a CMS-associated mitochondrial RNA of atp6–orf79, which consists of atp6 and orf79, in BT-CMS with the cytoplasm of ‘Chinsurah Boro II’. In this study, we found that LD-cytoplasm contained a sequence variant
of orf79 downstream of atp6. Northern blot analysis showed that atp6–orf79 RNA of LD-cytoplasm was co-transcribed and was processed in the presence of Rf1 in the same manner as in BT-cytoplasm. Western blot analysis showed that the ORF79 peptide did not accumulate in an LD-CMS
line, while ORF79 accumulated in a BT-CMS line and was diminished by Rf1. These results suggest that accumulation of ORF79 is not the cause of CMS in LD-cytoplasm and the mechanism of male-sterility
induction/fertility restoration in LD-CMS is different from that in BT-CMS. 相似文献