全文获取类型
收费全文 | 1159篇 |
免费 | 82篇 |
出版年
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 21篇 |
2020年 | 9篇 |
2019年 | 16篇 |
2018年 | 15篇 |
2017年 | 15篇 |
2016年 | 40篇 |
2015年 | 61篇 |
2014年 | 67篇 |
2013年 | 64篇 |
2012年 | 115篇 |
2011年 | 97篇 |
2010年 | 62篇 |
2009年 | 59篇 |
2008年 | 79篇 |
2007年 | 73篇 |
2006年 | 46篇 |
2005年 | 81篇 |
2004年 | 68篇 |
2003年 | 58篇 |
2002年 | 59篇 |
2001年 | 17篇 |
2000年 | 5篇 |
1999年 | 14篇 |
1998年 | 18篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1968年 | 2篇 |
1965年 | 1篇 |
1962年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有1241条查询结果,搜索用时 15 毫秒
91.
92.
93.
Giordanetto F Knerr L Selmi N Llinàs A Lindqvist A Wang QD Ståhlberg P Thorstensson F Ullah V Nilsson K O'Mahony G Högberg G Lindhardt E Strand A Duker G 《Bioorganic & medicinal chemistry letters》2011,21(18):5557-5561
Chemical evolution of a HTS-based fragment hit resulted in the identification of N-(1-adamantyl)-2-[4-(2-tetrahydropyran-4-ylethyl)piperazin-1-yl]acetamide, a novel, selective T-type calcium channel (Ca(v)3.2) inhibitor with in vivo antihypertensive effect in rats. 相似文献
94.
Westerlund F Elm J Lykkebo J Carlsson N Thyrhaug E Akerman B S?rensen TJ Mikkelsen KV Laursen BW 《Photochemical & photobiological sciences》2011,10(12):1963-1973
The 2,6,10-tris(dialkylamino)trioxatriangulenium dyes (ATOTA(+)) are highly stabilised cationic chromophores with D(3h) symmetry. The symmetry gives rise to a degeneracy of the main electronic transition. In low polarity solvents significant splitting of this degenerate transition is observed and assigned to ion pair formation. Ion pairing of the 2,6,10-tris(dioctylamino)trioxatriangulenium ion with Cl(-), BF(4)(-), PF(6)(-) and TRISPHAT anions was studied using absorption spectroscopy. A clear correlation is found between the size of the anion and the splitting of the ATOTA(+) transitions. In benzene the Cl(-) salt displays a splitting of 1955 cm(-1), while the salt of the much larger TRISPHAT ion has a splitting of 1543 cm(-1). TD-DFT calculations confirm the splitting of the states and provide a detailed insight into the electronic structure of the ion pairs. The different degree of splitting in different ion pairs is found to correlate with the magnitude of the electric field generated in each ion pair, thus leading to the conclusion that the effect seen is an internal Stark effect. By insertion of an amphiphilic derivative of the ATOTA(+) chromophore in an oriented lamellar liquid crystal, it was possible to resolve the two bands of the double peak spectrum and show their perpendicular orientation in the molecular framework, as predicted by the calculations. 相似文献
95.
96.
Heraty J Ronquist F Carpenter JM Hawks D Schulmeister S Dowling AP Murray D Munro J Wheeler WC Schiff N Sharkey M 《Molecular phylogenetics and evolution》2011,60(1):73-88
The Hymenoptera--ants, bees and wasps--represent one of the most successful but least understood insect radiations. We present the first comprehensive molecular study spanning the entire order Hymenoptera. It is based on approximately 7 kb of DNA sequence from 4 gene regions (18S, 28S, COI and EF-1α) for 116 species representing all superfamilies and 23 outgroup taxa from eight orders of Holometabola. Results are drawn from both parsimony and statistical (Bayesian and likelihood) analyses, and from both by-eye and secondary-structure alignments. Our analyses provide the first firm molecular evidence for monophyly of the Vespina (Orussoidea+Apocrita). Within Vespina, our results indicate a sister-group relationship between Ichneumonoidea and Proctotrupomorpha, while the stinging wasps (Aculeata) are monophyletic and nested inside Evaniomorpha. In Proctotrupomorpha, our results provide evidence for a novel core clade of proctotrupoids, and support for the recently proposed Diaprioidea. An unexpected result is the support for monophyly of a clade of wood-boring sawflies (Xiphydrioidea+Siricoidea). As in previous molecular studies, Orussidae remain difficult to place and are either sister group to a monophyletic Apocrita, or the sister group of Stephanidae within Apocrita. Both results support a single origin of parasitism, but the latter would propose a controversial reversal in the evolution of the wasp-waist. Generally our results support earlier hypotheses, primarily based on morphology, for a basal grade of phytophagous families giving rise to a single clade of parasitic Hymenoptera, the Vespina, from which predatory, pollen-feeding, gall-forming and eusocial forms evolved. 相似文献
97.
The HIV-1 epidemic in West Africa has been dominated by subtype A and the recombinant form CRF02_AG. Little is known about the origins and the evolutionary history of HIV-1 in this region. We employed Maximum likelihood and Bayesian methods in combination with temporal and spatial information to reconstruct the HIV-1 subtype distribution, demographic history and migration patterns over time in Guinea-Bissau, West Africa. We found that CRF02_AG and subsubtype A3 were the dominant forms of HIV-1 in Guinea-Bissau and that they were introduced into the country on at least six different occasions between 1976 and 1981. These estimates also corresponded well with the first reported HIV-1 cases in Guinea-Bissau. Migration analyses suggested that (1) the HIV-1 epidemic started in the capital Bissau and then dispersed into more rural areas, and (2) the epidemic in Guinea-Bissau was connected to both Cameroon and Mali. This is the first study that describes the HIV-1 molecular epidemiology in a West African country by combining the results of subtype distribution with analyses of epidemic origin and epidemiological linkage between locations. The multiple introductions of HIV-1 into Guinea-Bissau, during a short time-period of five years, coincided with and were likely influenced by the major immigration wave into the country that followed the end of the independence war (1963-1974). 相似文献
98.
Background
Variation in the serotonin transporter (5-HTT) gene (SLC6A4) has been shown to influence a wide range of affective processes. Low 5-HTT gene-expression has also been suggested to increase the risk of chronic pain. Conditioned pain modulation (CPM) - i.e. ‘pain inhibits pain’ - is impaired in chronic pain states and, reciprocally, aberrations of CPM may predict the development of chronic pain. Therefore we hypothesized that a common variation in the SLC6A4 is associated with inter-individual variation in CPM. Forty-five healthy subjects recruited on the basis of tri-allelic 5-HTTLPR genotype, with inferred high or low 5-HTT-expression, were included in a double-blind study. A submaximal-effort tourniquet test was used to provide a standardized degree of conditioning ischemic pain. Individualized noxious heat and pressure pain thresholds (PPTs) were used as subjective test-modalities and the nociceptive flexion reflex (NFR) was used to provide an objective neurophysiological window into spinal processing.Results
The low, as compared to the high, 5-HTT-expressing group exhibited significantly reduced CPM-mediated pain inhibition for PPTs (p = 0.02) and heat-pain (p = 0.02). The CPM-mediated inhibition of the NFR, gauged by increases in NFR-threshold, did not differ significantly between groups (p = 0.75). Inhibition of PPTs and heat-pain were correlated (Spearman’s rho = 0.35, p = 0.02), whereas the NFR-threshold increase was not significantly correlated with degree of inhibition of these subjectively reported modalities.Conclusions
Our results demonstrate the involvement of the tri-allelic 5-HTTLPR genotype in explaining clinically relevant inter-individual differences in pain perception and regulation. Our results also illustrate that shifts in NFR-thresholds do not necessarily correlate to the modulation of experienced pain. We discuss various possible mechanisms underlying these findings and suggest a role of regulation of 5-HT receptors along the neuraxis as a function of differential 5-HTT-expression. 相似文献99.
100.