全文获取类型
收费全文 | 67682篇 |
免费 | 5798篇 |
国内免费 | 31篇 |
出版年
2022年 | 409篇 |
2021年 | 939篇 |
2020年 | 596篇 |
2019年 | 704篇 |
2018年 | 913篇 |
2017年 | 856篇 |
2016年 | 1503篇 |
2015年 | 2629篇 |
2014年 | 2777篇 |
2013年 | 3644篇 |
2012年 | 4629篇 |
2011年 | 4613篇 |
2010年 | 3007篇 |
2009年 | 2656篇 |
2008年 | 3854篇 |
2007年 | 3910篇 |
2006年 | 3656篇 |
2005年 | 3658篇 |
2004年 | 3611篇 |
2003年 | 3380篇 |
2002年 | 3361篇 |
2001年 | 954篇 |
2000年 | 743篇 |
1999年 | 955篇 |
1998年 | 969篇 |
1997年 | 678篇 |
1996年 | 692篇 |
1995年 | 657篇 |
1994年 | 640篇 |
1993年 | 677篇 |
1992年 | 686篇 |
1991年 | 610篇 |
1990年 | 520篇 |
1989年 | 549篇 |
1988年 | 528篇 |
1987年 | 440篇 |
1986年 | 436篇 |
1985年 | 519篇 |
1984年 | 533篇 |
1983年 | 456篇 |
1982年 | 532篇 |
1981年 | 479篇 |
1980年 | 421篇 |
1979年 | 323篇 |
1978年 | 365篇 |
1977年 | 350篇 |
1976年 | 277篇 |
1975年 | 269篇 |
1974年 | 304篇 |
1973年 | 290篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
12.
Peter J Stephens 《BMJ (Clinical research ed.)》2005,330(7506):1508-1509
13.
Are we able to infer what happened to a person from a brief sample of his/her behaviour? It has been proposed that mentalising skills can be used to retrodict as well as predict behaviour, that is, to determine what mental states of a target have already occurred. The current study aimed to develop a paradigm to explore these processes, which takes into account the intricacies of real-life situations in which reasoning about mental states, as embodied in behaviour, may be utilised. A novel task was devised which involved observing subtle and naturalistic reactions of others in order to determine the event that had previously taken place. Thirty-five participants viewed videos of real individuals reacting to the researcher behaving in one of four possible ways, and were asked to judge which of the four ‘scenarios’ they thought the individual was responding to. Their eye movements were recorded to establish the visual strategies used. Participants were able to deduce successfully from a small sample of behaviour which scenario had previously occurred. Surprisingly, looking at the eye region was associated with poorer identification of the scenarios, and eye movement strategy varied depending on the event experienced by the person in the video. This suggests people flexibly deploy their attention using a retrodictive mindreading process to infer events. 相似文献
14.
15.
The aquatic larvae of the genus Chironomus (Diptera, Insecta) contain at least 12 different hemoglobin (Hb) variants in their hemolymph. In the present study we have analysed the structure and part of the nucleotide sequence of a Hb gene cluster cloned from the genomic DNA of Chironomus thummi piger. The cluster contains probably 6 different genes, separated by intergenic regions of various lengths. The nucleotide sequence of three putative Hb genes including the intergenic regions is presented. The inferred amino-acid sequences show clearly that two of these putative genes code for subvariants of the Hb variant VIIB. The third gene codes for a so far unknown Hb protein. As known already for other chironomid Hb genes, there are no intron sequences present in the coding regions. 相似文献
16.
E Ortega Rincón J M Marchena J J García A Schmidt T Schulz I Malpica A B Rodríguez C Barriga H Michna H L?tzerich 《Journal of applied physiology》2001,91(3):1067-1072
Flow cytometer measurements were made of the basal variations in peripheral blood functional monocytes and granulocytes over the course of a training season (January to November) of a cycling team. Parallel determinations were made of plasma concentration of catecholamines (chromatography) and cortisol (RIA) in a search for neuroendocrine markers. The results showed the greatest phagocytic capacity to occur in the central months (March, May, and July), coinciding with the greatest number and highest level of competitive events with good correlation with a peak in epinephrine during these months (r(2) = 0.998 for monocytes and r(2) = 0.674 for granulocytes). No good correlations were found between phagocytosis and norepinephrine or cortisol. The highest values for phagocytosis and epinephrine concentration were found in May. These results suggest that blood epinephrine concentration could be a good neuroendocrine marker of sportspeople's phagocytic response. 相似文献
17.
Ivonne J. Garzn‐Ordua Shaun L. Winterton Yunlan Jiang Laura C.V. Breitkreuz Peter Duelli Michael S. Engel Norman D. Penny Catherine A. Tauber Atsushi Mochizuki Xingyue Liu 《Systematic Entomology》2019,44(3):499-513
We present a time‐calibrated phylogeny of the charismatic green lacewings (Neuroptera: Chrysopidae). Previous phylogenetic studies on the family using DNA sequences have suffered from sparse taxon sampling and/or limited amounts of data. Here we combine all available previously published DNA sequence data and add to it new DNA sequences generated for this study. We analysed these data in a supermatrix using Bayesian and maximum likelihood methods and provide a phylogenetic hypothesis for the family that recovers strong support for the monophyly of all subfamilies and resolves relationships among a large proportion of chrysopine genera. Chrysopinae tribes Leucochrysini and Belonopterygini were recovered as monophyletic sister clades, while the species‐rich tribe Chrysopini was rendered paraphyletic by Ankylopterygini. Relationships among the subfamilies were resolved, although with relatively low statistical support, and the topology varied based on the method of analysis. Greatest support was found for Apochrysinae as sister to Nothochrysinae and Chrysopinae, which is in contrast to traditional concepts that place Nothochrysinae as sister to the rest of the family. Divergence estimates suggest that the stem groups to the various subfamilies diverged during the Triassic‐Jurassic, and that stem groups of the chrysopine tribes diverged during the Cretaceous. 相似文献
18.
19.
Jin Wei Mia Madel Alfajaro Peter C. DeWeirdt Ruth E. Hanna William J. Lu-Culligan Wesley L. Cai Madison S. Strine Shang-Min Zhang Vincent R. Graziano Cameron O. Schmitz Jennifer S. Chen Madeleine C. Mankowski Renata B. Filler Neal G. Ravindra Victor Gasque Fernando J. de Miguel Ajinkya Patil Huacui Chen Craig B. Wilen 《Cell》2021,184(1):76-91.e13
20.
Charles L. Nunn Peter H. Thrall Kelly Stewart Alexander H. Harcourt 《Evolutionary ecology》2008,22(4):519-543
Emerging infectious diseases threaten a wide diversity of animals, and important questions remain concerning disease emergence
in socially structured populations. We developed a spatially explicit simulation model to investigate whether—and under what
conditions—disease-related mortality can impact rates of pathogen spread in populations of polygynous groups. Specifically,
we investigated whether pathogen-mediated dispersal (PMD) can occur when females disperse after the resident male dies from
disease, thus carrying infections to new groups. We also examined the effects of incubation period and virulence, host mortality
and rates of background dispersal, and we used the model to investigate the spread of the virus responsible for Ebola hemorrhagic
fever, which currently is devastating African ape populations. Output was analyzed using regression trees, which enable exploration
of hierarchical and non-linear relationships. Analyses revealed that the incidence of disease in single-male (polygynous)
groups was significantly greater for those groups containing an average of more than six females, while the total number of
infected hosts in the population was most sensitive to the number of females per group. Thus, as expected, PMD occurs in polygynous
groups and its effects increase as harem size (the number of females) increases. Simulation output further indicated that
population-level effects of Ebola are likely to differ among multi-male–multi-female chimpanzees and polygynous gorillas,
with larger overall numbers of chimpanzees infected, but more gorilla groups becoming infected due to increased dispersal
when the resident male dies. Collectively, our results highlight the importance of social system on the spread of disease
in wild mammals. 相似文献