全文获取类型
收费全文 | 5342篇 |
免费 | 497篇 |
国内免费 | 1篇 |
出版年
2023年 | 24篇 |
2022年 | 26篇 |
2021年 | 128篇 |
2020年 | 72篇 |
2019年 | 106篇 |
2018年 | 103篇 |
2017年 | 92篇 |
2016年 | 175篇 |
2015年 | 253篇 |
2014年 | 294篇 |
2013年 | 379篇 |
2012年 | 413篇 |
2011年 | 392篇 |
2010年 | 261篇 |
2009年 | 193篇 |
2008年 | 312篇 |
2007年 | 308篇 |
2006年 | 311篇 |
2005年 | 255篇 |
2004年 | 232篇 |
2003年 | 195篇 |
2002年 | 170篇 |
2001年 | 91篇 |
2000年 | 104篇 |
1999年 | 67篇 |
1998年 | 61篇 |
1997年 | 45篇 |
1996年 | 47篇 |
1995年 | 46篇 |
1994年 | 45篇 |
1993年 | 53篇 |
1992年 | 50篇 |
1991年 | 56篇 |
1990年 | 47篇 |
1989年 | 37篇 |
1988年 | 46篇 |
1987年 | 22篇 |
1986年 | 30篇 |
1985年 | 29篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1979年 | 12篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1974年 | 13篇 |
1973年 | 15篇 |
1972年 | 17篇 |
1968年 | 12篇 |
1967年 | 12篇 |
1966年 | 11篇 |
排序方式: 共有5840条查询结果,搜索用时 703 毫秒
1.
Stanislav Lhota Veronika Roubov Vendula Gregorov Martina Kone
n 《American journal of primatology》2019,81(9)
Grooming in primates is often considered a “currency” that can be exchanged for other “services” or “commodities” such as reciprocal grooming, coalitionary support, infant handling, tolerance around food sources, active food sharing, or mating opportunities. Previous studies on primate grooming‐for‐sex exchange viewed the males as the demanding class, with the females as suppliers of mating opportunities. In this study, we examine the broader context of grooming‐for‐mating exchange in Barbary macaques in Gibraltar. Our data show that Barbary macaque males groom females with whom they are mating more frequently and for longer periods than other females, and the relationship between grooming and mating remains significant in both sexual and nonsexual contexts. In addition, females groomed males with whom they were mating more frequently and for longer periods than other males. In both sexes, grooming was observed to be far more frequent and to occur for longer durations in sexual compared to nonsexual contexts. We did not find any difference in grooming behavior between presexual and postsexual contexts. Our data suggest that there is no simple model to describe Barbary macaque grooming patterns in sexual contexts. Although our results are partly consistent with male use of grooming as payment for mating, broadly assessed grooming‐mating patterns cannot be solely explained by a male‐driven grooming‐for‐mating exchange. 相似文献
2.
Nevenka Me?trovi? Martina Pavlek Ana Car Philippe Castagnone-Sereno Pierre Abad Miroslav Plohl 《PloS one》2013,8(6)
Tandemly arrayed non-coding sequences or satellite DNAs (satDNAs) are rapidly evolving segments of eukaryotic genomes, including the centromere, and may raise a genetic barrier that leads to speciation. However, determinants and mechanisms of satDNA sequence dynamics are only partially understood. Sequence analyses of a library of five satDNAs common to the root-knot nematodes Meloidogyne chitwoodi and M. fallax together with a satDNA, which is specific for M. chitwoodi only revealed low sequence identity (32–64%) among them. However, despite sequence differences, two conserved motifs were recovered. One of them turned out to be highly similar to the CENP-B box of human alpha satDNA, identical in 10–12 out of 17 nucleotides. In addition, organization of nematode satDNAs was comparable to that found in alpha satDNA of human and primates, characterized by monomers concurrently arranged in simple and higher-order repeat (HOR) arrays. In contrast to alpha satDNA, phylogenetic clustering of nematode satDNA monomers extracted either from simple or from HOR array indicated frequent shuffling between these two organizational forms. Comparison of homogeneous simple arrays and complex HORs composed of different satDNAs, enabled, for the first time, the identification of conserved motifs as obligatory components of monomer junctions. This observation highlights the role of short motifs in rearrangements, even among highly divergent sequences. Two mechanisms are proposed to be involved in this process, i.e., putative transposition-related cut-and-paste insertions and/or illegitimate recombination. Possibility for involvement of the nematode CENP-B box-like sequence in the transposition-related mechanism and together with previously established similarity of the human CENP-B protein and pogo-like transposases implicate a novel role of the CENP-B box and related sequence motifs in addition to the known function in centromere protein binding. 相似文献
3.
Olivia Sackett Katherina Petrou Brian Reedy Ross Hill Martina Doblin John Beardall Peter Ralph Philip Heraud 《The ISME journal》2016,10(2):416-426
Diatoms, an important group of phytoplankton, bloom annually in the Southern Ocean, covering thousands of square kilometers and dominating the region''s phytoplankton communities. In their role as the major food source to marine grazers, diatoms supply carbon, nutrients and energy to the Southern Ocean food web. Prevailing environmental conditions influence diatom phenotypic traits (for example, photophysiology, macromolecular composition and morphology), which in turn affect the transfer of energy, carbon and nutrients to grazers and higher trophic levels, as well as oceanic biogeochemical cycles. The paucity of phenotypic data on Southern Ocean phytoplankton limits our understanding of the ecosystem and how it may respond to future environmental change. Here we used a novel approach to create a ‘snapshot'' of cell phenotype. Using mass spectrometry, we measured nitrogen (a proxy for protein), total carbon and carbon-13 enrichment (carbon productivity), then used this data to build spectroscopy-based predictive models. The models were used to provide phenotypic data for samples from a third sample set. Importantly, this approach enabled the first ever rate determination of carbon productivity from a single time point, circumventing the need for time-series measurements. This study showed that Chaetoceros simplex was less productive and had lower protein and carbon content during short-term periods of high salinity. Applying this new phenomics approach to natural phytoplankton samples could provide valuable insight into understanding phytoplankton productivity and function in the marine system. 相似文献
4.
D Matthias E Engler L Will-Shahab H J Herrmann C H Becker 《Acta biologica et medica Germanica》1977,36(9):1279-1284
A 14-days' training of rats designed to adapt the animals to the procedure of blood-pressure measurement caused in the myocardium a decrease, in serum an increase in noradrenaline ( NA) content. The latter remained unchanged following 3 days of treatment with 2.5 mg depot angiotensin II (AII) but decreased by more than one-half in the myocardium of untreated animals, and increased in serum. Despite the considerable difference in myocardial NA content and blood-pressure behaviour, both trained and untrained rats showed the same morphological reactions following administration of A II. These myocardial alterations which largely correspond to the so-called epinephrine myocarditis should not therefore be due solely to NA action; rather, the involvement of A II should be considered also. 相似文献
5.
6.
How often will elections end in landslides? What is the probability for a head-to-head race? Analyzing ballot results from several large countries rather anomalous and yet unexplained distributions have been observed. We identify tactical voting as the driving ingredient for the anomalies and introduce a model to study its effect on plurality elections, characterized by the relative strength of the feedback from polls and the pairwise interaction between individuals in the society. With this model it becomes possible to explain the polarization of votes between two candidates, understand the small margin of victories frequently observed for different elections, and analyze the polls'' impact in American, Canadian, and Brazilian ballots. Moreover, the model reproduces, quantitatively, the distribution of votes obtained in the Brazilian mayor elections with two, three, and four candidates. 相似文献
7.
M Plat J Fleischer T Herrmann U Plat A Lesche E M Grafe H Wolf U Reinhardt 《Folia haematologica (Leipzig, Germany : 1928)》1987,114(6):797-809
The total population affected with non-Hodgkin's lymphoma and treated by means of radiotherapy or combined radio-chemotherapy between 1960 and 1985 at the Medical Academy Dresden was analysed as to prognosis. 247 patients were classified according to the previous German scheme, 79 were subdivided on the basis of the recommendations laid down in the Kiel classification. The remission rates and survival curves achieved will stand out the comparison with international literature (remission rates of the low malignancy group amounted to 85.3 p.c. and those of the high malignancy group to 80.0 p.c.; the 5-years survival rates of the low malignancy group amounted to 61.9 p.c. and those of the high malignancy group to 41.7 p.c.). The influence of histology, clinical stage and involvement of organs is discussed on the basis of our results and informations obtained in literature. Our analysis confirms the high importance which must be attached to a common radiologic-internal outpatient-department for co-ordinating the diagnostic and therapeutical programme. 相似文献
8.
9.
Seed dispersal influences a wide range of ecological processes. However, measuring dispersal patterns, particularly long‐distance dispersal, has been a difficult task. Marking bird‐dispersed seeds with stable 15N isotopes has been shown to be a user‐friendly method to trace seed dispersal. In this study, we determined whether 15N urea solution could be used to enrich seeds of two common wind‐dispersed plants, Eupatorium glaucescens (Asteraceae) and Sericocarpus tortifolius (Asteraceae). We further tested if the water type (distilled versus tap) in 15N urea solutions influences the level and variability of enrichment of plant seeds, and if increasing spraying frequency per se increases enrichment. Because droughts may lower seed set or kill plants, we wanted to investigate if the additional use of an externally applied anti‐transpirant affects the intake of externally applied 15N into seeds. The results demonstrate that 15N enrichment of seeds can facilitate dispersal experiments with wind‐dispersed plants. The use of distilled water in 15N urea solutions did not increase 15N enrichment compared to tap water. Further, enrichment was more efficient at lower spray frequencies. Both the use of tap water and low frequencies could lower time, effort and project costs. The results suggest that species can be protected from drought using an anti‐transpirant without decreasing the incorporation of 15N into seeds. 相似文献
10.