全文获取类型
收费全文 | 8093篇 |
免费 | 606篇 |
国内免费 | 6篇 |
出版年
2023年 | 39篇 |
2022年 | 33篇 |
2021年 | 133篇 |
2020年 | 121篇 |
2019年 | 128篇 |
2018年 | 215篇 |
2017年 | 176篇 |
2016年 | 256篇 |
2015年 | 438篇 |
2014年 | 419篇 |
2013年 | 547篇 |
2012年 | 719篇 |
2011年 | 629篇 |
2010年 | 414篇 |
2009年 | 322篇 |
2008年 | 477篇 |
2007年 | 445篇 |
2006年 | 431篇 |
2005年 | 411篇 |
2004年 | 415篇 |
2003年 | 386篇 |
2002年 | 309篇 |
2001年 | 97篇 |
2000年 | 70篇 |
1999年 | 73篇 |
1998年 | 74篇 |
1997年 | 44篇 |
1996年 | 47篇 |
1995年 | 50篇 |
1994年 | 51篇 |
1993年 | 35篇 |
1992年 | 51篇 |
1991年 | 50篇 |
1990年 | 31篇 |
1989年 | 35篇 |
1988年 | 31篇 |
1987年 | 28篇 |
1986年 | 29篇 |
1985年 | 45篇 |
1984年 | 35篇 |
1983年 | 30篇 |
1982年 | 24篇 |
1981年 | 25篇 |
1980年 | 30篇 |
1979年 | 27篇 |
1978年 | 26篇 |
1977年 | 24篇 |
1976年 | 31篇 |
1975年 | 25篇 |
1974年 | 19篇 |
排序方式: 共有8705条查询结果,搜索用时 15 毫秒
1.
2.
Klára Grantz ?a?ková Milan Ko?í?ek Kirsten Stray Dorien de Jong Pavlína ?ezá?ová Ji?í Brynda Noortje M. van Maarseveen Monique Nijhuis Tomá? Cihlá? Jan Konvalinka 《Journal of virology》2014,88(6):3586-3590
Insertions in the protease (PR) region of human immunodeficiency virus (HIV) represent an interesting mechanism of antiviral resistance against HIV PR inhibitors (PIs). Here, we demonstrate the improved ability of a phosphonate-containing experimental HIV PI, GS-8374, relative to that of other PIs, to effectively inhibit patient-derived recombinant HIV strains bearing PR insertions and numerous other mutations. We correlate enzyme inhibition with the catalytic activities of corresponding recombinant PRs in vitro and provide a biochemical and structural analysis of the PR-inhibitor complex. 相似文献
3.
J. J. Soler C. Ruiz Castellano J. Martínez‐de la Puente G. Tomás M. Ruiz‐Rodríguez J. Figuerola 《Journal of evolutionary biology》2015,28(9):1610-1617
Although little is known on the impact of environment on telomere length dynamics, it has been suggested to be affected by stress, lifestyle and/or life‐history strategies of animals. We here compared telomere dynamics in erythrocytes of hatchlings and fledglings of the brood parasite great spotted cuckoos (Clamator glandarius) and of magpies (Pica pica), their main host in Europe. In magpie chicks, telomere length decreased from hatching to fledging, whereas no significant change in telomere length of great spotted cuckoo chicks was found. Moreover, we found interspecific differences in the association between laying date and telomere shortening. Interspecific differences in telomere shortening were interpreted as a consequence of differences in lifestyle and life‐history characteristics of magpies and great spotted cuckoos. In comparison with magpies, cuckoos experience reduced sibling competition and higher access to resources and, consequently, lower stressful environmental conditions during the nestling phase. These characteristics also explain the associations between telomere attrition and environmental conditions (i.e. laying date) for magpies and the absence of association for great spotted cuckoos. These results therefore fit expectations on telomere dynamics derived from interspecific differences in lifestyle and life history of brood parasites and their bird hosts. 相似文献
4.
Krista E. van Meijgaarden Mari?lle C. Haks Nadia Caccamo Francesco Dieli Tom H. M. Ottenhoff Simone A. Joosten 《PLoS pathogens》2015,11(3)
Mycobacterial antigens are not exclusively presented to T-cells by classical HLA-class Ia and HLA-class II molecules, but also through alternative antigen presentation molecules such as CD1a/b/c, MR1 and HLA-E. We recently described mycobacterial peptides that are presented in HLA-E and recognized by CD8+ T-cells. Using T-cell cloning, phenotyping, microbiological, functional and RNA-expression analyses, we report here that these T-cells can exert cytolytic or suppressive functions, inhibit mycobacterial growth, yet express GATA3, produce Th2 cytokines (IL-4,-5,-10,-13) and activate B-cells via IL-4. In TB patients, Mtb specific cells were detectable by peptide-HLA-E tetramers, and IL-4 and IL-13 were produced following peptide stimulation. These results identify a novel human T-cell subset with an unorthodox, multifunctional Th2 like phenotype and cytolytic or regulatory capacities, which is involved in the human immune response to mycobacteria and demonstrable in active TB patients’ blood. The results challenge the current dogma that only Th1 cells are able to inhibit Mtb growth and clearly show that Th2 like cells can strongly inhibit outgrowth of Mtb from human macrophages. These insights significantly expand our understanding of the immune response in infectious disease. 相似文献
5.
6.
Koldo Garcia-Etxebarria María Alma Bracho Juan Carlos Galán Tomàs Pumarola Jesús Castilla Raúl Ortiz de Lejarazu Mario Rodríguez-Dominguez Inés Quintela Núria Bonet Marc Garcia-Garcerà Angela Domínguez Fernando González-Candelas Francesc Calafell CIBERESP Cases Controls in Pandemic Influenza Working Group 《PloS one》2015,10(10)
7.
Greg O'Corry‐Crowe Tom Gelatt Lorrie Rea Carolina Bonin Michael Rehberg 《Molecular ecology》2014,23(22):5415-5434
Population growth typically involves range expansion and establishment of new breeding sites, while the opposite occurs during declines. Although density dependence is widely invoked in theoretical studies of emigration and colonization in expanding populations, few empirical studies have documented the mechanisms. Still fewer have documented the direction and mechanisms of individual transfer in declining populations. Here, we screen large numbers of pups sampled on their natal rookeries for variation in mtDNA (n = 1106) and 16 microsatellite loci (n = 588) and show that new Steller sea lion breeding sites did not follow the typical paradigm and were instead colonized by sea lions from both a declining (Endangered) population and an increasing population. Dispersing individuals colonized rookeries in the distributional hiatus between two evolutionarily distinct ( = 0.222, = 0.053, K = 2) metapopulations recently described as separate subspecies. Hardy–Weinberg, mixed‐stock and relatedness analysis revealed levels of interbreeding on the new rookeries that exclude (i) assortative mating among eastern and western forms, and (ii) inbreeding avoidance as primary motivations for dispersal. Positive and negative density dependence is implicated in both cases of individual transfer. Migration distance limits, and conspecific attraction and performance likely influenced the sequence of rookery colonizations. This study demonstrates that resource limitation may trigger an exodus of breeding animals from declining populations, with substantial impacts on distribution and patterns of genetic variation. It also revealed that this event is rare because colonists dispersed across an evolutionary boundary, suggesting that the causative factors behind recent declines are unusual or of larger magnitude than normally occur. 相似文献
8.
Induction of c-fos mRNA Expression by Afterdischarge in the Hippocampus of Naive and Kindled Rats 总被引:5,自引:3,他引:2
Cheolsu Shin‡ James O. McNamara†‡ James I. Morgan§ Tom Curran Donna R. Cohen 《Journal of neurochemistry》1990,55(3):1050-1055
Periodic induction of focal electrical seizure [afterdischarge (AD)] is an absolute prerequisite for the development of kindling, an animal model of complex partial epilepsy. Once established, it is a permanent condition. The mechanism(s) that translate ADs, which last tens of seconds, into life-long alterations in the CNS is unclear. Cellular immediate-early genes have been implicated in the conversion of short-term stimuli to long-term alterations in cellular phenotypes by regulating target gene expression. We have investigated the contribution of one such early gene, c-fos, to this process. The relationship between ADs and expression of c-fos gene in the rat hippocampus, a key structure in kindling development, was studied by analysis of mRNA levels. The low constitutive expression of c-fos mRNA in the hippocampus was not altered by kindling. There was an "all-or-none" relationship between induction of c-fos and the duration of AD. The threshold for induction was approximately 30 s of AD. Above-threshold ADs induced c-fos in both naive and kindled animals to the same extent and with identical temporal profiles. Although the expression of c-fos is unchanged with kindling, c-fos may nonetheless contribute to many long-term changes of kindling, both adaptive and epileptogenic. 相似文献
9.
Niklas Bosaeus Afaf H. El-Sagheer Tom Brown Bj?rn ?kerman Bengt Nordén 《Nucleic acids research》2014,42(12):8083-8091
Overstretching of DNA occurs at about 60–70 pN when a torsionally unconstrained double-stranded DNA molecule is stretched by its ends. During the transition, the contour length increases by up to 70% without complete strand dissociation. Three mechanisms are thought to be involved: force-induced melting into single-stranded DNA where either one or both strands carry the tension, or a B-to-S transition into a longer, still base-paired conformation. We stretch sequence-designed oligonucleotides in an effort to isolate the three processes, focusing on force-induced melting. By introducing site-specific inter-strand cross-links in one or both ends of a 64 bp AT-rich duplex we could repeatedly follow the two melting processes at 5 mM and 1 M monovalent salt. We find that when one end is sealed the AT-rich sequence undergoes peeling exhibiting hysteresis at low and high salt. When both ends are sealed the AT sequence instead undergoes internal melting. Thirdly, the peeling melting is studied in a composite oligonucleotide where the same AT-rich sequence is concatenated to a GC-rich sequence known to undergo a B-to-S transition rather than melting. The construct then first melts in the AT-rich part followed at higher forces by a B-to-S transition in the GC-part, indicating that DNA overstretching modes are additive. 相似文献
10.