全文获取类型
收费全文 | 1194篇 |
免费 | 131篇 |
国内免费 | 1篇 |
出版年
2023年 | 3篇 |
2021年 | 14篇 |
2020年 | 13篇 |
2019年 | 8篇 |
2018年 | 20篇 |
2017年 | 12篇 |
2016年 | 25篇 |
2015年 | 50篇 |
2014年 | 48篇 |
2013年 | 68篇 |
2012年 | 106篇 |
2011年 | 79篇 |
2010年 | 50篇 |
2009年 | 54篇 |
2008年 | 63篇 |
2007年 | 70篇 |
2006年 | 64篇 |
2005年 | 68篇 |
2004年 | 67篇 |
2003年 | 55篇 |
2002年 | 72篇 |
2001年 | 22篇 |
2000年 | 16篇 |
1999年 | 19篇 |
1998年 | 21篇 |
1997年 | 19篇 |
1996年 | 20篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 10篇 |
1991年 | 9篇 |
1990年 | 15篇 |
1989年 | 6篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 8篇 |
1973年 | 5篇 |
1971年 | 4篇 |
1969年 | 3篇 |
1930年 | 2篇 |
1910年 | 2篇 |
排序方式: 共有1326条查询结果,搜索用时 31 毫秒
41.
Katrin Spiesberger Florian Paulfranz Anton Egger Judith Reiser Claus Vogl Judith Rudolf-Scholik Corina Mayrhofer Ludger Grosse-Hovest Gottfried Brem 《PloS one》2015,10(10)
Background
30 years ago, the potential of bispecific antibodies to engage cytotoxic T cells for the lysis of cancer cells was discovered. Today a variety of bispecific antibodies against diverse cell surface structures have been developed, the majority of them produced in mammalian cell culture systems. Beside the r28M, described here, no such bispecific antibody is known to be expressed by transgenic livestock, although various biologicals for medical needs are already harvested—mostly from the milk—of these transgenics. In this study we investigated the large-scale purification and biological activity of the bispecific antibody r28M, expressed in the blood of transgenic cattle. This tandem single-chain variable fragment antibody is designed to target human CD28 and the melanoma/glioblastoma-associated cell surface chondroitin sulfate proteoglycan 4 (CSPG4).Results
With the described optimized purification protocol an average yield of 30 mg enriched r28M fraction out of 2 liters bovine plasma could be obtained. Separation of this enriched fraction by size exclusion chromatography into monomers, dimers and aggregates and further testing regarding the biological activity revealed the monomer fraction as being the most appropriate one to continue working with. The detailed characterization of the antibody’s activity confirmed its high specificity to induce the killing of CSPG4 positive cells. In addition, first insights into tumor cell death pathways mediated by r28M-activated peripheral blood mononuclear cells were gained. In consideration of possible applications in vivo we also tested the effect of the addition of different excipients to r28M.Conclusion
Summing up, we managed to purify monomeric r28M from bovine plasma in a large-scale preparation and could prove that its biological activity is unaffected and still highly specific and thus, might be applicable for the treatment of melanoma. 相似文献42.
We compare two broad types of empirically grounded random network models in terms of their abilities to capture both network features and simulated Susceptible-Infected-Recovered (SIR) epidemic dynamics. The types of network models are exponential random graph models (ERGMs) and extensions of the configuration model. We use three kinds of empirical contact networks, chosen to provide both variety and realistic patterns of human contact: a highly clustered network, a bipartite network and a snowball sampled network of a “hidden population”. In the case of the snowball sampled network we present a novel method for fitting an edge-triangle model. In our results, ERGMs consistently capture clustering as well or better than configuration-type models, but the latter models better capture the node degree distribution. Despite the additional computational requirements to fit ERGMs to empirical networks, the use of ERGMs provides only a slight improvement in the ability of the models to recreate epidemic features of the empirical network in simulated SIR epidemics. Generally, SIR epidemic results from using configuration-type models fall between those from a random network model (i.e., an Erdős-Rényi model) and an ERGM. The addition of subgraphs of size four to edge-triangle type models does improve agreement with the empirical network for smaller densities in clustered networks. Additional subgraphs do not make a noticeable difference in our example, although we would expect the ability to model cliques to be helpful for contact networks exhibiting household structure. 相似文献
43.
44.
Response of wheat growth,grain yield and water use to elevated CO2 under a Free‐Air CO2 Enrichment (FACE) experiment and modelling in a semi‐arid environment 下载免费PDF全文
Garry J. O'Leary Brendan Christy James Nuttall Neil Huth Davide Cammarano Claudio Stöckle Bruno Basso Iurii Shcherbak Glenn Fitzgerald Qunying Luo Immaculada Farre‐Codina Jairo Palta Senthold Asseng 《Global Change Biology》2015,21(7):2670-2686
The response of wheat crops to elevated CO2 (eCO2) was measured and modelled with the Australian Grains Free‐Air CO2 Enrichment experiment, located at Horsham, Australia. Treatments included CO2 by water, N and temperature. The location represents a semi‐arid environment with a seasonal VPD of around 0.5 kPa. Over 3 years, the observed mean biomass at anthesis and grain yield ranged from 4200 to 10 200 kg ha?1 and 1600 to 3900 kg ha?1, respectively, over various sowing times and irrigation regimes. The mean observed response to daytime eCO2 (from 365 to 550 μmol mol?1 CO2) was relatively consistent for biomass at stem elongation and at anthesis and LAI at anthesis and grain yield with 21%, 23%, 21% and 26%, respectively. Seasonal water use was decreased from 320 to 301 mm (P = 0.10) by eCO2, increasing water use efficiency for biomass and yield, 36% and 31%, respectively. The performance of six models (APSIM‐Wheat, APSIM‐Nwheat, CAT‐Wheat, CROPSYST, OLEARY‐CONNOR and SALUS) in simulating crop responses to eCO2 was similar and within or close to the experimental error for accumulated biomass, yield and water use response, despite some variations in early growth and LAI. The primary mechanism of biomass accumulation via radiation use efficiency (RUE) or transpiration efficiency (TE) was not critical to define the overall response to eCO2. However, under irrigation, the effect of late sowing on response to eCO2 to biomass accumulation at DC65 was substantial in the observed data (~40%), but the simulated response was smaller, ranging from 17% to 28%. Simulated response from all six models under no water or nitrogen stress showed similar response to eCO2 under irrigation, but the differences compared to the dryland treatment were small. Further experimental work on the interactive effects of eCO2, water and temperature is required to resolve these model discrepancies. 相似文献
45.
DNA barcoding largely supports 250 years of classical taxonomy: identifications for Central European bees (Hymenoptera,Apoidea partim) 下载免费PDF全文
Stefan Schmidt Christian Schmid‐Egger Jérôme Morinière Gerhard Haszprunar Paul D. N. Hebert 《Molecular ecology resources》2015,15(4):985-1000
This study presents DNA barcode records for 4118 specimens representing 561 species of bees belonging to the six families of Apoidea (Andrenidae, Apidae, Colletidae, Halictidae, Megachilidae and Melittidae) found in Central Europe. These records provide fully compliant barcode sequences for 503 of the 571 bee species in the German fauna and partial sequences for 43 more. The barcode results are largely congruent with traditional taxonomy as only five closely allied pairs of species could not be discriminated by barcodes. As well, 90% of the species possessed sufficiently deep sequence divergence to be assigned to a different Barcode Index Number (BIN). In fact, 56 species (11%) were assigned to two or more BINs reflecting the high levels of intraspecific divergence among their component specimens. Fifty other species (9.7%) shared the same Barcode Index Number with one or more species, but most of these species belonged to a distinct barcode cluster within a particular BIN. The barcode data contributed to clarifying the status of nearly half the examined taxonomically problematic species of bees in the German fauna. Based on these results, the role of DNA barcoding as a tool for current and future taxonomic work is discussed. 相似文献
46.
Kimberly L. H. Carpenter Adrian Angold Nan-Kuei Chen William E. Copeland Pooja Gaur Kevin Pelphrey Allen W. Song Helen L. Egger 《PloS one》2015,10(1)
Objective
In this prospective, longitudinal study of young children, we examined whether a history of preschool generalized anxiety, separation anxiety, and/or social phobia is associated with amygdala-prefrontal dysregulation at school-age. As an exploratory analysis, we investigated whether distinct anxiety disorders differ in the patterns of this amygdala-prefrontal dysregulation.Methods
Participants were children taking part in a 5-year study of early childhood brain development and anxiety disorders. Preschool symptoms of generalized anxiety, separation anxiety, and social phobia were assessed with the Preschool Age Psychiatric Assessment (PAPA) in the first wave of the study when the children were between 2 and 5 years old. The PAPA was repeated at age 6. We conducted functional MRIs when the children were 5.5 to 9.5 year old to assess neural responses to viewing of angry and fearful faces.Results
A history of preschool social phobia predicted less school-age functional connectivity between the amygdala and the ventral prefrontal cortices to angry faces. Preschool generalized anxiety predicted less functional connectivity between the amygdala and dorsal prefrontal cortices in response to fearful faces. Finally, a history of preschool separation anxiety predicted less school-age functional connectivity between the amygdala and the ventral prefrontal cortices to angry faces and greater school-age functional connectivity between the amygdala and dorsal prefrontal cortices to angry faces.Conclusions
Our results suggest that there are enduring neurobiological effects associated with a history of preschool anxiety, which occur over-and-above the effect of subsequent emotional symptoms. Our results also provide preliminary evidence for the neurobiological differentiation of specific preschool anxiety disorders. 相似文献47.
48.
49.
Yusuke Fukuda Grahame Webb Charlie Manolis Robyn Delaney Mike Letnic Garry Lindner Peter Whitehead 《The Journal of wildlife management》2011,75(6):1253-1266
Saltwater crocodiles (Crocodylus porosus) in the Northern Territory of Australia were protected in 1971, after a severe population decline resulting from 26 yr of intense commercial hunting. By that time wild saltwater crocodiles were rarely sighted anywhere and they were commercially extinct in areas where they had once been abundant. Standardized monitoring by spotlight surveys started in 1975 and provided relative density indices over time (1975–2009) as a unique record of the post-protection recovery of a wild crocodilian population. We examined the survey data for populations at 12 major tidal rivers, individually and as a single subpopulation. The pattern of recovery in the subpopulation in both abundance and biomass was approximated by logistic curves, predicting 5.26 non-hatchling crocodiles weighing 387.64 kg sighted per kilometer of river in 2010. We predicted potential carrying capacity as 5.58 non-hatchling crocodiles (5.73% higher than 2010) weighing 519.0 kg (25.31% higher than 2010). Individual rivers showed largely different abundance and biomass among rivers. The statistical model that best described the recovery in individual rivers was not always logistic. However, where it was logistic, expected carrying capacity of different rivers showed considerable variation in abundance and biomass. The variation indicates different habitat quality among the rivers. Recovery occurred despite various consumptive uses, particularly a widespread egg-harvest program, which has been an integral part of the incentive-driven conservation program for saltwater crocodiles in the Northern Territory since 1983. We suggest that the saltwater crocodile population of the Northern Territory is achieving full recovery from uncontrolled hunting in 1945–1971. Although saltwater crocodiles are considered an important natural resource, their increase in number, size, and distribution is posing management issues for public safety. Continuation of human–crocodile conflict management through public education and strategic removal of problem crocodiles will be essential. © 2011 The Wildlife Society. 相似文献
50.
Assortative mating preferences between colour morphs of the endemic Lake Tanganyika cichlid genus Tropheus 总被引:1,自引:1,他引:0
Bernd Egger Beate Obermüller Eva Eigner Christian Sturmbauer Kristina M. Sefc 《Hydrobiologia》2008,615(1):37-48
Female mate preferences effectuate reproductive isolation among and sexual selection within species. Both mechanisms have
been associated with the diversification and speciation of cichlid species flocks of the East African Great Lakes. In Lake
Tanganyika, the endemic genus Tropheus has diversified into >100 geographic colour morphs. Although distributed allopatrically at present, water level fluctuations
have repeatedly displaced and merged the benthic, rock-dwelling populations. Tests for assortative mating were performed to
explore the potential for reproductive isolation between morphs in secondary contact, and to assess the importance of sexual
selection for the diversification of this group. In contrast to other haplochromine cichlids, Tropheus is a sexually monochromatic, territorial and maternally mouthbrooding fish, which establishes temporary pair bonds prior
to spawning. Female mate preference trials involved two-way choices between a homotypic and a heterotypic male and were conducted
on allopatric populations of red and blue morphs from the southern part of Lake Tanganyika. Female affiliation time near each
male’s compartment did not predict the mate preferences subsequently expressed in unrestrained interactions after removal
of the compartment separators (spawning, pseudospawning and courtship). Consequently, mate preferences were inferred from
unrestrained interactions with one test male at a time in replicate observation sessions. Of the 23 females tested, 13 courted,
pseudospawned or spawned with the homotypic male, one blue female courted a red male, and nine females expressed no sexual
motivation. The assortative mate preferences in the experiments (P < 0.01) suggest that colour differentiation between Tropheus populations can effectuate reproductive isolation, and is consistent with the notion that sexual selection contributed to
the diversification of the genus.
Guest editors: T. Wilke, R. V?in?l? & F. Riedel
Patterns and Processes of Speciation in Ancient Lakes: Proceedings of the Fourth Symposium on Speciation in Ancient Lakes,
Berlin, Germany, September 4–8, 2006 相似文献