全文获取类型
收费全文 | 121066篇 |
免费 | 7460篇 |
国内免费 | 526篇 |
出版年
2023年 | 731篇 |
2022年 | 663篇 |
2021年 | 1776篇 |
2020年 | 1517篇 |
2019年 | 1662篇 |
2018年 | 3383篇 |
2017年 | 2959篇 |
2016年 | 4015篇 |
2015年 | 5458篇 |
2014年 | 5607篇 |
2013年 | 7405篇 |
2012年 | 8625篇 |
2011年 | 7599篇 |
2010年 | 4933篇 |
2009年 | 3808篇 |
2008年 | 5878篇 |
2007年 | 5611篇 |
2006年 | 5486篇 |
2005年 | 4593篇 |
2004年 | 4547篇 |
2003年 | 4062篇 |
2002年 | 3741篇 |
2001年 | 2925篇 |
2000年 | 2769篇 |
1999年 | 2174篇 |
1998年 | 986篇 |
1997年 | 733篇 |
1996年 | 784篇 |
1995年 | 711篇 |
1994年 | 648篇 |
1992年 | 1343篇 |
1991年 | 1221篇 |
1990年 | 1168篇 |
1989年 | 1183篇 |
1988年 | 1021篇 |
1987年 | 1029篇 |
1986年 | 934篇 |
1985年 | 1004篇 |
1984年 | 825篇 |
1983年 | 723篇 |
1979年 | 871篇 |
1978年 | 620篇 |
1975年 | 704篇 |
1974年 | 769篇 |
1973年 | 727篇 |
1972年 | 680篇 |
1971年 | 610篇 |
1970年 | 658篇 |
1969年 | 726篇 |
1968年 | 682篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
51.
52.
Luis Santamaría Jesús Balsa Beatriz Bidondo Angel Baltanás Carlos Montes 《Hydrobiologia》1992,246(2):89-98
Laboratory experiments and field data were used to determine salinity tolerance limits of three ostracode species (Prionocypris aragonica, Eucypris mareotica and Heterocypris barbara) from Iberian saline lakes. Salinity tolerance appeared related to ionic composition and temperature. Implications for ostracode ecology and geographical distribution are evaluated. 相似文献
53.
A dominant mutation, responsible for the resistance to oxythiamin inSaccharomyces cerevisiae was mapped on the right arm of chromosome IV, 4.6 cM centromere-distally totrp1. The corresponding gene is not involved in the control of intracellular content of total thiamin during growth on a minimal
medium without thiamin. 相似文献
54.
Miguel Angel Pujana Monica Gratacós Jordi Corral Isabel Banchs Aurora Sánchez David Genís Carlos Cervera Víctor Volpini X. Estivill 《Human genetics》1997,101(1):18-21
Genetic anticipation – increasing severity and a decrease in the age of onset with successive generations of a pedigree –
is clearly present in autosomal dominant cerebellar ataxia (ADCA). Anticipation is correlated with expansion of the CAG/CTG
repeat sequence to sizes above those in the normal range through the generations of a pedigree. Genetic heterogeneity has
been demonstrated for ADCA, with four cloned genes (SCA1, SCA2, SCA3/MJD, and SCA6) and three mapped loci (SCA4, SCA5 and
SCA7). Another related dominant ataxia, dentatorubral-pallidoluysian atrophy (DRPLA), presents anticipation with CAG/CTG repeat
expansions. We had previously analysed ADCA patients who had not shown repeat expansions in cloned genes for CAG/CTG repeat
expansions by the repeat expansion detection method (RED) and had detected expansions of between 48 and 88 units in 17 unrelated
familial cases. We present here an analysis of 13 genes and expressed sequence tags (ESTs) containing 10 or more CAG/ CTG
repeat sequences selected from public databases in the 17 unrelated ADCA patients. Of the 13 selected genes and ESTs, 9 were
found to be polymorphic with heterozygosities ranging between 0.09 and 0.80 and 2 to 17 alleles. In ADCA patients none of
the loci showed expansions above the normal range of the CAG/CTG repeat sequences, excluding them as the mutation causing
ADCA.
Received: 28 May 1997 / Accepted: 30 June 1997 相似文献
55.
Autonomic Adaption to Clinical Simulation in Psychology Students: Teaching Applications 总被引:1,自引:0,他引:1
Vicente Javier Clemente-Suárez Ana Isabel Beltrán-Velasco Alberto Bellido-Esteban Pablo Ruisoto-Palomera 《Applied psychophysiology and biofeedback》2018,43(3):239-245
Simulation is used to facilitate new learning in a variety of situations. One application of simulation could be to help therapists gain therapeutic skills prior to seeing clients. This particular study was interested in measuring changes in stress response by looking at subjective and objective measures of distress (as measured by SUDS, HR, and HRV) over three sessions of simulated therapy. 16 second year psychology students participated in three sessions, and had their HR and HRV measured by Polar watches. Over the three sessions, there was a decrease in perceived distress, as measured by SUDS ratings. During and between sessions, there was inconclusive change in physiological parameters. 相似文献
56.
Barbora Straková Michail Rovatsos Lukáš Kubička Lukáš Kratochvíl 《BioEssays : news and reviews in molecular, cellular and developmental biology》2020,42(10):2000050
Frequent independent origins of environmental sex determination (ESD) are assumed within amniotes. However, the phylogenetic distribution of sex-determining modes suggests that ESD is likely very ancient and may be homologous across ESD groups. Sex chromosomes are demonstrated to be old and stable in endothermic (mammals and birds) and many ectothermic (non-avian reptiles) lineages, but they are mostly non-homologous between individual amniote lineages. The phylogenetic pattern may be explained by ancestral ESD with multiple transitions to later evolutionary stable genotypic sex determination. It is pointed out here that amniote ESD shares several key aspects with sequential hermaphroditism of fishes such as a lack of sex differences in genomes, biased population sex ratios, and potentially also molecular mechanism related to general stress responses. Here, it is speculated that ESD evolves via a heterochronic shift of the sensitive period of sex change from the adult to the embryonic stage in a hermaphroditic amniote ancestor. Also see the video abstract here https://youtu.be/q2mjtlCefu4 . 相似文献
57.
58.
59.
60.
Background The cost–benefit model for the evolution of botanical carnivory provides a conceptual framework for interpreting a wide range of comparative and experimental studies on carnivorous plants. This model assumes that the modified leaves called traps represent a significant cost for the plant, and this cost is outweighed by the benefits from increased nutrient uptake from prey, in terms of enhancing the rate of photosynthesis per unit leaf mass or area (AN) in the microsites inhabited by carnivorous plants.Scope This review summarizes results from the classical interpretation of the cost–benefit model for evolution of botanical carnivory and highlights the costs and benefits of active trapping mechanisms, including water pumping, electrical signalling and accumulation of jasmonates. Novel alternative sequestration strategies (utilization of leaf litter and faeces) in carnivorous plants are also discussed in the context of the cost–benefit model.Conclusions Traps of carnivorous plants have lower AN than leaves, and the leaves have higher AN after feeding. Prey digestion, water pumping and electrical signalling represent a significant carbon cost (as an increased rate of respiration, RD) for carnivorous plants. On the other hand, jasmonate accumulation during the digestive period and reprogramming of gene expression from growth and photosynthesis to prey digestion optimizes enzyme production in comparison with constitutive secretion. This inducibility may have evolved as a cost-saving strategy beneficial for carnivorous plants. The similarities between plant defence mechanisms and botanical carnivory are highlighted. 相似文献