全文获取类型
收费全文 | 8505篇 |
免费 | 743篇 |
国内免费 | 3篇 |
专业分类
9251篇 |
出版年
2023年 | 32篇 |
2022年 | 78篇 |
2021年 | 114篇 |
2020年 | 70篇 |
2019年 | 84篇 |
2018年 | 121篇 |
2017年 | 113篇 |
2016年 | 194篇 |
2015年 | 334篇 |
2014年 | 390篇 |
2013年 | 454篇 |
2012年 | 583篇 |
2011年 | 578篇 |
2010年 | 432篇 |
2009年 | 364篇 |
2008年 | 510篇 |
2007年 | 511篇 |
2006年 | 464篇 |
2005年 | 491篇 |
2004年 | 513篇 |
2003年 | 456篇 |
2002年 | 484篇 |
2001年 | 77篇 |
2000年 | 59篇 |
1999年 | 117篇 |
1998年 | 143篇 |
1997年 | 57篇 |
1996年 | 80篇 |
1995年 | 67篇 |
1994年 | 75篇 |
1993年 | 86篇 |
1992年 | 82篇 |
1991年 | 61篇 |
1990年 | 76篇 |
1989年 | 48篇 |
1988年 | 62篇 |
1987年 | 60篇 |
1986年 | 55篇 |
1985年 | 50篇 |
1984年 | 69篇 |
1983年 | 51篇 |
1982年 | 68篇 |
1981年 | 74篇 |
1980年 | 46篇 |
1979年 | 49篇 |
1978年 | 40篇 |
1977年 | 43篇 |
1976年 | 38篇 |
1975年 | 25篇 |
1974年 | 29篇 |
排序方式: 共有9251条查询结果,搜索用时 15 毫秒
11.
12.
13.
Informational interventions (e.g., awareness campaigns, carbon footprint calculators) are built on the assumption that informing the public about the environmental consequences of their actions should result in increased pro-environmental intentions and behavior. However, empirical support for this reasoning is mixed. In this paper, we argue that informational interventions may succeed in improving people’s knowledge about the negative environmental consequences of one’s actions, but this knowledge will not gain motivational force if people do not consider protecting the environment an important personal value. In an experiment, we measured individual differences in value priorities, and either presented participants a movie clip that portrayed the negative environmental consequences of using bottled water, or a control movie. As predicted, we found that the environmental movie improved recipients’ knowledge of the negative environmental impact of bottled water, but this knowledge only resulted in concomitant changes in intentions and acceptability of related policies among participants who strongly endorsed biospheric (i.e. environmental) values, while having no effect on those who care less about the environment. Interestingly, the results suggest that although informational interventions are perhaps not always successful in directly affecting less environmentally-conscious recipients, they could still have beneficial effects, because they make those who strongly care about the environment more inclined to act on their values. 相似文献
14.
Linda L. Chao Charles DeCarli Stephen Kriger Diana Truran Yu Zhang Joel Laxamana Sylvia Villeneuve William J. Jagust Nerses Sanossian Wendy J. Mack Helena C. Chui Michael W. Weiner 《PloS one》2013,8(6)
The goal of this study was to assess the relationship between Aβ deposition and white matter pathology (i.e., white matter hyperintensities, WMH) on microstructural integrity of the white matter. Fifty-seven participants (mean age: 78±7 years) from an ongoing multi-site research program who spanned the spectrum of normal to mild cognitive impairment (Clinical dementia rating 0–0.5) and low to high risk factors for arteriosclerosis and WMH pathology (defined as WMH volume >0.5% total intracranial volume) were assessed with positron emission tomography (PET) with Pittsburg compound B (PiB) and magnetic resonance and diffusion tensor imaging (DTI). Multivariate analysis of covariance were used to investigate the relationship between Aβ deposition and WMH pathology on fractional anisotropy (FA) from 9 tracts of interest (i.e., corona radiata, internal capsule, cingulum, parahippocampal white matter, corpus callosum, superior longitudinal, superior and inferior front-occipital fasciculi, and fornix). WMH pathology was associated with reduced FA in projection (i.e., internal capsule and corona radiate) and association (i.e., superior longitudinal, superior and inferior fronto-occipital fasciculi) fiber tracts. Aβ deposition (i.e., PiB positivity) was associated with reduced FA in the fornix and splenium of the corpus callosum. There were interactions between PiB and WMH pathology in the internal capsule and parahippocampal white matter, where Aβ deposition reduced FA more among subjects with WMH pathology than those without. However, accounting for apoE ε4 genotype rendered these interactions insignificant. Although this finding suggests that apoE4 may increase amyloid deposition, both in the parenchyma (resulting in PiB positivity) and in blood vessels (resulting in amyloid angiopathy and WMH pathology), and that these two factors together may be associated with compromised white matter microstructural integrity in multiple brain regions, additional studies with a longitudinal design will be necessary to resolve this issue. 相似文献
15.
Jonas G. Barlind Linda K. Buckett Sharon G. Crosby Öjvind Davidsson Hans Emtenäs Anne Ertan Ulrik Jurva Malin Lemurell Pablo Morentin Gutierrez Karolina Nilsson Gavin O’Mahony Annika U. Petersson Alma Redzic Fredrik Wågberg Zhong-Qing Yuan 《Bioorganic & medicinal chemistry letters》2013,23(9):2721-2726
[Acyl CoA]monoacylglycerol acyltransferase 2 (MGAT2) is of interest as a target for therapeutic treatment of diabetes, obesity and other diseases which together constitute the metabolic syndrome. In this Letter we report our discovery and optimisation of a novel series of MGAT2 inhibitors. The development of the SAR of the series and a detailed discussion around some key parameters monitored and addressed during the lead generation phase will be given. The in vivo results from an oral lipid tolerance test (OLTT) using the MGAT2 inhibitor (S)-10, shows a significant reduction (68% inhibition relative to na?ve, p <0.01) in plasma triacylglycerol (TAG) concentration. 相似文献
16.
Childhood obesity is becoming a topic of great concern due to the rising prevalence of this condition in North America. Studies conducted in the United States have indicated that the prevalence of obesity has increased dramatically over the past few decades. The purpose of this study was to estimate the prevalence of obesity in Canadian children between the ages of 5 and 12 years by examining data from two national and two regional surveys. The 85th percentiles of each of four anthropometric indices derived from large normative populations were used as diagnostic criteria for obesity. As expected, the resulting prevalences varied according to the criteria used. A significant increase in childhood obesity between the 1981 to 1988 national surveys was observed when the three indices which used skinfolds were applied. Weight-for-height percentiles did not indicate an increase in obesity in these samples. Regional samples showed a less than expected prevalence of obesity among the middle-class children and a higher than expected rate among the inner city boys. It can be concluded that there is a need for a defined criteria for identifying obesity in children in order to avoid confusion resulting from the wide variation in estimates of prevalence resulting from different standards and measurements. Using adiposity-based criteria for obesity it was clearly evident that the prevalence of obesity has increased in Canadian children. 相似文献
17.
Linda F. Hogle 《Medical anthropology quarterly》2001,15(2):275-276
Body Talk: Rhetoric, Technology, Reproduction. Mary M. Lay. Laura J. Gurak. Clare Gravon. and Cynthia Myntii. eds. Madison: University of Wisconsin Press, 2000. xiii. 307 pp. 相似文献
18.
Effect of incubation temperature on the hatching of rotifer resting eggs collected from sediments 总被引:6,自引:4,他引:2
Linda May 《Hydrobiologia》1987,147(1):335-338
Sediment samples from Loch Leven, Scotland, were incubated at 5°C, 10°C and 15°C to induce hatching of rotifer resting eggs. The emergent animals were identified and counted. The temperature which induced hatching varied among the nine species studied. These results are discussed in relation to seasonality and temperature preferences previously recorded for the most abundant species. Resting egg densities of 2.2–13.9 eggs cm–3 were recorded in the upper 5 cm of sediment. 相似文献
19.
Summary The uptake of deoxyguanosine by rat liver mitochondria was characterized. The process required an intact mitochondrial membrane and exhibited a dependence on added phosphate. Deoxyguanosine uptake was minimally influenced by Mg2+ or Mn2+, but Ca2+ at concentrations above 0.5 mM were detrimental. Of the deoxynucleosides tested, only deoxyinosine inhibited the uptake of deoxyguanosine. The ribonucleoside guanosine was not observed to compete with its deoxynucleoside analog. Known inhibitors of nucleoside transport, cytochalasin B and NBMPR, did not block deoxyguanosine uptake, but the sulfhydryl reagents NEM and pCMB were both inhibitory. The uptake of deoxyguanosine was shown to be a saturable process and an apparent Km of 0.64 M was calculated from a Hanes plot. 相似文献
20.
Control of a teleost social signal 总被引:1,自引:0,他引:1
Linda E. Muske Russell D. Fernald 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1987,160(1):89-97
Territorial male Haplochromis burtoni (Teleostei; Cichlidae) have a dark facial stripe, the 'eyebar', which can appear and disappear within seconds, independently of other coloration patterns. It is used to signal territory ownership and aggressive intent. Some males, called 'barless', have functional melanophores in the eyebar region but never display this pattern, because melanin in eyebar pigment cells is never dispersed. The eyebar melanophores are controlled by a specialized branch of the maxillary nerve. Lesioning the 'eyebar nerve' resulted in immediate melanin dispersion and consequent darkening of the eyebar pattern, and it abolished the normal paling response in all behavioral situations. Nerve lesion produced similar results in both barred and barless males, except that the coloration of the denervated eyebar in barless males was more similar to camouflage markings than to the conspicuous black eyebar used as a social signal. Electrical stimulation of the maxillary nerve produced melanin aggregation. Photoelectric recordings of this paling response revealed no differences between barred and barless males, or between the eyebar and other facial chromatophores that do not function as visual displays. Thus, the difference in the physiological state of eyebar melanophores in intact barred and barless males cannot be explained by differences in peripheral nerve anatomy or physiology. 相似文献