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991.
On the relevance of using laboratory selection to study the adaptive value of circadian clocks
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The phrase ‘as sure as night comes after day’ highlights the most conspicuous phenomenon on earth (i.e. the daily cycling of geophysical factors). It is hypothesized that life‐forms on earth have evolved timekeeping mechanisms (circadian clocks) as adaptations to cope with such cyclic variations in their environment and, to test this hypothesis, diverse strategies have been employed. In this review, these different approaches, including comparative, clinal, ecology and/or trait manipulation and laboratory selection strategies are discussed, aiming to evaluate the adaptive value of circadian clocks. The limitations of each of these methods are assessed, and it is suggested that laboratory selection is an ideal, potent and suitable strategy for examining whether circadian clocks are indeed adaptations. In support of this, laboratory selection strategies are highlighted and critically reviewed in a discussion of studies that demonstrate the evolution of circadian clocks and life‐history traits in response to selection for the timing of rhythmic behaviours, as well as those studies that demonstrate the evolution of circadian clocks in response to selection for life‐history traits. Finally, newer approaches are proposed that involve the use of mutants, simultaneous manipulation of multiple environmental factors and genomic technologies in conjunction with laboratory selection to further explore the adaptive significance of circadian clocks. 相似文献
992.
The homeodomain protein Fushi tarazu (Ftz) is required for several embryonic patterning processes including segmentation
and neurogenesis. During the stages that these processes are regulated the protein is differentially phosphorylated, suggesting
that phosphorylation plays a role in helping the protein to regulate different functions in different tissues. We showed in
a recent study that one of the Ftz phosphorylation sites, a protein kinase A-type site in the N-terminal arm of the homeodomain,
is required for normal Ftz-dependent segmentation. Here we test whether phosphorylation of this site (Thr-263) is also required
in the developing central nervous system (CNS). A well-established role for Ftz in the CNS is for the differentiation of neurons
referred to as RP2 neurons. Absence of Ftz expression in these cells causes a failure of certain target genes to be expressed
and subsequent defects in RP2 differentiation. In contrast to its effect on segmentation, we find that mutation of Thr-263
to Ala (or Asp) has no effect on these CNS functions. This suggests that the phosphorylation state of this site is irrelevant
for Ftz function in the CNS, and that there are tissue-specific differences in the requirements for Ftz phosphorylation.
Received: 28 February 1999 / Accepted: 10 March 1999 相似文献
993.
木耳属真菌rDNA特异性扩增片段的RFLP研究 总被引:3,自引:0,他引:3
对木耳属8个种25个菌株的ITS和28SrDNA5’端两个区域分别进行了PCR扩增和限制酶切片段长度多态性(RFLP)研究。ITS-RFMP研究结果表明,HaeⅢ可将黑木耳与其它种区分开,MspⅠ可将盾形木耳、角质木耳、琥珀木耳和黑木耳4个种区分开,而供试的HaeⅢ、TaqⅠ、HinfⅠ和MaPⅠ这四种限制酶均不能将皱木耳、大木耳、网脉木耳及毛木耳4个种区分开,表明它们之间的亲缘关系较近;结果还表明,ITS—rDNA拷贝在毛木耳和琥珀木耳种内是异质性的,而在黑木耳种内是同质性的。285rDNA-RFLP研究结果表明,供试的4种限制酶中,仅MspⅠ可将盾形木耳和角质木耳区分开,而不能将其它种区分开,这显示了28SrDNA序列在木耳属不同种间的保守性。 相似文献
994.
Fitness of wild‐caught Drosophila melanogaster females: allozyme variants of GPDH, ADH, PGM, and EST
We have collected several hundred Drosophila melanogaster flies (near Davis, California), isolated them individually, without anesthesia, at the collecting site, and estimated the
fitness components of the wild‐caught females under different environmental conditions. The fitness parameters measured are
fecundity, oviposition rate, and productivity (egg‐to‐adult viability, development rate, and number of progeny). The environmental
variables are two temperatures (22°C and 28°C) and two densities (‘scant’ and ‘crowded’). After the fitness measurements are
completed for each individual female, its genotype is determined at four loci encoding enzymes: GPDH and ADH, located on chromosome
II and PGM and EST‐C, located on chromosome III. Density has a large significant effect on productivity; temperature has significant
effects on fecundity, oviposition rate, and development rate. The experiments show that allozyme polymorphisms are associated
with selection effects. Fitness differences between allozyme genotypes occur for all fitness components, except oviposition
rate. But which genotype is superior depends on the environmental conditions; heterozygotes exhibit higher fitness than homozygotes
in a number of cases, but inferior in others. A unique feature of the present experiments is that the experimental flies are
wild‐caught females rather than laboratory‐bred individuals.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
995.
Chrysosporium undulatum sp. nov., showing intermediate characteristics between Chrysosporium and Malbranchea, is described and illustrated. This taxon is characterised by long and curved to loosely coiled hyphal appendages, deflected to wavy fertile hyphae forming dense tufts and small, subglobose, frequently intercalary, verrucose conidia. Restriction enzyme analysis and comparison of sequences of the ITS1-5.8S-ITS2 ribosomal DNA region of the most similar species strongly support this proposal. 相似文献
996.
胡枝子属根瘤菌的多相分类研究 总被引:5,自引:0,他引:5
采用了数值分类、全细胞可溶性蛋白电泳分析、DNAG+Cmol%和DNA相关性的测定以及16SrDNAPCRRFLP分析等多相分类技术对来源于不同地区的16种寄主的胡枝子根瘤菌进行了系统的分类研究。数值分类的结果表明,在67%的相似性水平上,全部供试菌可以分为快生型根瘤菌和慢性型根瘤菌两大群,在80%的相似性水平上又可分为四个亚群。在此基础上,对各亚群的胡枝子根瘤菌进行了DNA相关性的测定,以进一步证实和确定它们的分类地位,并通过16SrDNAPCRRFLP分析对各亚群的系统发育关系进行了初步研究。 相似文献
997.
998.
浙江无核柿炭疽病菌鉴定及附着胞形成过程中的核相变化 总被引:8,自引:1,他引:7
浙江无核柿炭疽病近年来在浙江淳安地区严重发生,根据形态学特征病原菌鉴定为胶孢炭疽菌ColletotrichumgloeosporioidesPenz.,在枝条病斑上的分生孢子盘通常不产生刚毛,分生孢子顶端顶部钝圆,基部平截,分生孢子盘中的孢子包埋在基质中,紧密结合在一起。分生孢子在自然寄主和人工培养条件下形态特征相似。6个柿树炭疽菌菌株的rDNAITS序列联配显示,其序列是相同的。用UPGMA方法分析ITS1-ITS2序列构建的炭疽菌系统发育树把6个柿树炭疽菌菌株和其它寄主上的胶孢炭疽菌或其有性型围小丛壳菌菌系分入同一个组,与根据形态学的鉴定结果一致。在附着胞形成过程中,用DAPI荧光染色观察到核相发生两次有丝分裂变化。第一次有丝分裂发生在分生孢子固着聚苯乙烯塑料培养皿3-4h后,随后,分生孢子中部形成一个隔膜,把它分成两个细胞;6~7h后,分生孢子发生第二次有丝分裂。分裂后,一个核通过芽管移入附着胞中。 相似文献
999.
Drosophila ananassae, a cosmopolitan and domestic species, belongs to theananassae subgroup of themelanogaster species group. Female remating was observed in ten mass culture stocks of this species, which were initiated from flies collected
from different geographic localities. The frequency of female remating ranges from 24% to 56% in different strains. Strains
show significant variation in remating latency (days). Significant variation has also been found in all the stocks for duration
of copulation between first and second matings. The duration of copulation is shorter in second mating as compared to first
mating inD. ananassae. 相似文献
1000.