全文获取类型
收费全文 | 6558篇 |
免费 | 422篇 |
出版年
2024年 | 6篇 |
2023年 | 52篇 |
2022年 | 67篇 |
2021年 | 220篇 |
2020年 | 164篇 |
2019年 | 210篇 |
2018年 | 248篇 |
2017年 | 198篇 |
2016年 | 313篇 |
2015年 | 430篇 |
2014年 | 421篇 |
2013年 | 484篇 |
2012年 | 581篇 |
2011年 | 542篇 |
2010年 | 343篇 |
2009年 | 286篇 |
2008年 | 352篇 |
2007年 | 331篇 |
2006年 | 292篇 |
2005年 | 231篇 |
2004年 | 218篇 |
2003年 | 164篇 |
2002年 | 150篇 |
2001年 | 91篇 |
2000年 | 90篇 |
1999年 | 60篇 |
1998年 | 45篇 |
1997年 | 25篇 |
1996年 | 27篇 |
1995年 | 22篇 |
1994年 | 19篇 |
1993年 | 18篇 |
1992年 | 29篇 |
1991年 | 30篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 11篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1976年 | 5篇 |
1975年 | 10篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1972年 | 9篇 |
排序方式: 共有6980条查询结果,搜索用时 24 毫秒
11.
12.
13.
14.
Rodrigo Trigosso-Venario Antonieta Labra & Hermann M. Niemeyer 《Ethology : formerly Zeitschrift fur Tierpsychologie》2002,108(12):1057-1064
For territorial organisms, recognition of familiar individuals can reduce the frequency and intensity of aggressive encounters (‘dear enemy’ phenomenon), stabilize social systems, and reduce the cost of territory maintenance. Here, we investigated the behavioural events displayed during contests between familiar and unfamiliar individuals in the lizard Liolaemus tenuis (Liolaemidae), a species in which males are territorial. The behaviours recorded were attack, warning, evasion, and submission, and the latencies to the first aggressive (attack or warning) behaviour. Additionally, we assessed the ability of individuals to remember a familiar conspecific after a period without social interaction. Individual males reduced and delayed aggressive behaviour directed towards socially familiar individuals compared with unfamiliar ones. These results suggest that males distinguished between familiar and unfamiliar conspecific males and are in agreement with the ‘dear enemy’ phenomenon. Other behaviours were similar in the contests between familiar and unfamiliar individuals. Recognition of familiar conspecifics was lost after 20 d without social interactions. This may be relevant for interactions with floater males or with neighbours that lose their territory and subsequently attempt to fight for their ex‐neighbour's territory. 相似文献
15.
Almeida AP 《Theriogenology》1987,27(2):329-335
A comparison between different superovulatory treatments in dairy cattle was carried out at a commercial embryo transfer unit in Israel. Both pregnant mare serum gonadotrophin (PMSG) and follicle stimulating hormone (FSH) were used, either alone or combined with Syncromate B (SMB). The use of PMSG + SMB significantly decreased the number of corpora lutea present at the time of embryo collection 7 d after insemination, as compared with other treatment regimens. Consequently, a significantly lower number of ova was found in those animals treated with PMSG + SMB. Better superovulatory responses were obtained when FSH, rather than PMSG, was used, regardless of whether they were administered alone or combined with SMB. It was clear that the use of SMB combined either with PMSG or FSH resulted in poorer responses than when either gonadotrophin was used alone. 相似文献
16.
Stimulation of quiescent 3T3 cells by serum dramatically induces the synthesis of a group of secreted polypeptides with a molecular weight (MW) of 45 K (p45 A, B, C, D). The synthesis of these polypeptides increases 10-fold during the first 2 h. Cycloheximide superinduces the 45 K polypeptides and actinomycin D (actD) blocks completely their induction by serum. Peptide mapping analysis and pulse-chase experiments revealed that p45 A is a precursor of polypeptides p45 B, C, D. Tunicamycin treatment inhibits the synthesis of all four polypeptides but a new related protein appears, p-p45, the unglycosylated precursor. In the presence of tunicamycin, p-p45 is also found in the medium, demonstrating that glycosylation is not essential for the secretion. In vitro translation experiments show that the levels of p45 mRNA present in stimulated cells are severalfold higher than that of non-stimulated cells. Purified growth factors, such as platelet-derived growth factor (PDGF), fibroblast growth factor (FGF) and epidermal growth factor (EGF) induce the synthesis of p45 in quiescent cells. 相似文献
17.
Alberto Barros M. Carmo Tavares Sérgio Castedo M. Salomé Pereira M. Purificação Tavares M. Almeida e Costa 《Human genetics》1987,75(4):388-390
Summary A double balanced reciprocal translocation involving four chromosomes, t(1;19;6;14) (1p11; 19p11; 6q25; 14q21), was found in the phenotypically normal husband in a couple referred because of repeated abortions. Reciprocal translocations, t(6;14), had been transmitted by his mother, his father being apparently homozygous for a translocation comprising pairs 1 and 19-t(1;19)(1;19). The genetic consequences of this complex chromosomal rearrangement are analyzed. 相似文献
18.
Prenatal diagnosis of familial amyloidotic polyneuropathy: evidence for an early expression of the associated transthyretin methionine 30 总被引:3,自引:0,他引:3
Maria Rosário Almeida Isabel Longo Alves Yoshiuki Sakaki Pedro Pinho Costa Maria João M. Saraiva 《Human genetics》1990,85(6):623-626
Summary Transthyretin methionine 30 (TTR Met 30), which is associated with familial amyloidotic polyneuropathy, originates in a single base substitution (A for G) in the second exon of the TTR gene. This autosomal dominant disease can be diagnosed by RFLP analysis of NsiI-digested DNA. The amplification of DNA by PCR improves the diagnosis method, making it suitable for prenatal diagnosis. Using PCR-amplified DNA, prenatal diagnosis of two at-risk fetuses was performed. Control Met 30 and normal DNA (either genomic or produced by site directed mutagenesis) were processed in parallel. The diagnosis was made by hybridization with allele-specific oligonucleotide probes, and later confirmed by screening of the mutant protein in the amniotic fluid and, when possible, in the sera from the newborns. TTR Met 30 was detected in the amniotic fluid of a positive fetus whose father was the carrier of the mutation. This indicates that the mutant protein is expressed very early in development. 相似文献
19.
Synthesis of the nuclear protein cyclin (PCNA) and its relationship with DNA replication 总被引:38,自引:0,他引:38
Rodrigo Bravo 《Experimental cell research》1986,163(2):287-293
Synthesis of the nuclear protein cyclin (MW 36 000) and DNA in quiescent mouse fibroblasts is coordinately induced by serum and purified growth factors. Inhibition of DNA synthesis by hydroxyurea or aphidicolin in serum-stimulated quiescent cells does not affect the induction of cyclin. The levels of cyclin synthesis decrease rapidly at the end of the S phase. Immunofluorescence studies reveal that there are dramatic changes in the nuclear distribution of cyclin during S phase and that these depend on DNA synthesis or events during S phase. These observations strengthen the notion that cyclin is an important component of the events leading to DNA replication. 相似文献
20.
Comparative Growth of Natural Bacterial Isolates on Various Lignin-Related Compounds 总被引:5,自引:2,他引:3 下载免费PDF全文
Bacterial strains were isolated on the basis of their ability to proliferate in a minimal medium containing one of a series of lignin-related compounds as the sole carbon and energy source. These included the aromatic monomers guaiacol, vanillic and coumaric acids, a dimer and a trimer possessing the arylglycerol-β-aryl ether linkage, anisoin, and both the ether-soluble and -insoluble fractions of kraft lignin. The growth of the strains on each of these compounds was measured. The results showed that the metabolic properties of the strains varied according to the structure of the carbon sources used for their selection. Spectrophotometric tracings of the culture medium during the log phase of growth of one of the strains on the β-O-4 dimer revealed decomposition with the release of guaiacol. 相似文献