全文获取类型
收费全文 | 1608篇 |
免费 | 122篇 |
国内免费 | 90篇 |
专业分类
1820篇 |
出版年
2024年 | 9篇 |
2023年 | 31篇 |
2022年 | 39篇 |
2021年 | 44篇 |
2020年 | 51篇 |
2019年 | 49篇 |
2018年 | 87篇 |
2017年 | 62篇 |
2016年 | 61篇 |
2015年 | 47篇 |
2014年 | 89篇 |
2013年 | 174篇 |
2012年 | 75篇 |
2011年 | 67篇 |
2010年 | 57篇 |
2009年 | 53篇 |
2008年 | 55篇 |
2007年 | 78篇 |
2006年 | 77篇 |
2005年 | 54篇 |
2004年 | 56篇 |
2003年 | 50篇 |
2002年 | 40篇 |
2001年 | 32篇 |
2000年 | 35篇 |
1999年 | 20篇 |
1998年 | 31篇 |
1997年 | 31篇 |
1996年 | 24篇 |
1995年 | 29篇 |
1994年 | 22篇 |
1993年 | 26篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 17篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有1820条查询结果,搜索用时 15 毫秒
71.
本研究通过对123只陕北白绒山羊DRB1基因外显子2的遗传变异分析,旨在获得陕北白绒山羊DRB1基因的多态性及变异信息,为山羊抗病基因的挖掘研究提供基础资料。本研究共获得6条陕北白绒山羊DRB1基因外显子2序列,其中4条为首次发现。生物信息学分析表明DRB1位点具有较高的多态性,6条等位基因可能起源于2个祖先基因。在长期的进化过程中,DRB1位点受到了明显的选择压力作用,这种选择作用有助于陕北白绒山羊对当地气候的适应。蛋白质结构的预测证实了DRB1*1与其它等位基因间的差异性,说明核苷酸变异可能会引起蛋白质结构的改变,最终可能影响宿主对病原体的免疫应答。本次对陕北白绒山羊DRB1基因多态性的调查与分析有助于筛选疾病抗性和易感性MHC (Major histocompatibility complex)候选基因,进而可加速绒山羊抗病品系的改良与培育进程。 相似文献
72.
Emmanuelle Frchette Christine Yao‐Yun Chang Ingo Ensminger 《Global Change Biology》2020,26(9):5217-5234
In higher‐latitude trees, temperature and photoperiod control the beginning and end of the photosynthetically active season. Elevated temperature (ET) has advanced spring warming and delayed autumn cooling while photoperiod remains unchanged. We assessed the effects of warming on the length of the photosynthetically active season of three provenances of Pinus strobus L. seedlings from different latitudes, and evaluated the accuracy of the photochemical reflectance index (PRI) and the chlorophyll/carotenoid index (CCI) for tracking the predicted variation in spring and autumn phenology of photosynthesis among provenances. Seedlings from northern, local and southern P. strobus provenances were planted in a temperature‐free‐air‐controlled enhancement (T‐FACE) experiment and exposed to ET (+1.5/3°C; day/night). Over 18 months, we assessed photosynthetic phenology by measuring chlorophyll fluorescence, gas exchange, leaf spectral reflectance and pigment content. During autumn, all seedlings regardless of provenance followed the same sequence of phenological events with the initial downregulation of photosynthesis, followed by the modulation of non‐photochemical quenching and associated adjustments of zeaxanthin pool sizes. However, the timing of autumn downregulation differed between provenances, with delayed onset in the southern provenance (SP) and earlier onset in the northern relative to the local provenance, indicating that photoperiod at the provenance origin is a dominant factor controlling autumn phenology. Experimental warming further delayed the downregulation of photosynthesis during autumn in the SP. A provenance effect during spring was also observed but was generally not significant. The vegetation indices PRI and CCI were both effective at tracking the seasonal variations of energy partitioning in needles and the differences of carotenoid pigments indicative of the stress status of needles. These results demonstrate that PRI and CCI can be useful tools for monitoring conifer phenology and for the remote monitoring of the length of the photosynthetically active season of conifers in a changing climate. 相似文献
73.
Yu‐Guo Yang Xu‐Ping Wang Bing Liu Yuan‐Yuan Zhang Xian‐Shun Lv Jing Li Lei Wei Hua‐Jian Yu Yanyan Hu Hua‐Di Zhang 《Luminescence》2020,35(4):580-585
Dy3+‐doped Y3Al5O12 phosphors were prepared at a relatively low temperature using molten salt synthesis. The phase of the prepared Dy3+‐doped Y3Al5O12 phosphors was confirmed using X‐ray powder diffraction. Results indicated that Dy3+ doping did not change the Y3Al5O12 phase. Following excitation at 352 nm, emission spectra of the Dy3+‐doped Y3Al5O12 phosphors consisted of blue, yellow, and red emission bands. The influence of Dy3+ concentration and excitation wavelength on emission was investigated. The ratio of yellow light to blue light varied with change in Dy3+ doping concentration, due to changes in the structure around Dy3+. Emission intensities also changed when the excitation wavelength was changed. This variation is luminescence generated a system for tunable white light for Dy3+‐doped Y3Al5O12 phosphors. 相似文献
74.
Patrícia Barros Pinheiro Igor Da Mata-Oliveira Mariana Gomes do Rêgo Bruno Mourato Fábio Hissa Vieira Hazin 《Zeitschrift fur angewandte Ichthyologie》2021,37(4):523-533
The present work describes the reproductive biology of the white marlin (Kajikia albida) caught in the southwestern and equatorial Atlantic Ocean. The gonads of 924 fish were collected by observers on board Brazilian tuna longliners, between November 2004 and December 2006. The spawning season was assessed by the monthly frequency distribution of distinct stages of maturity and monthly mean female gonadosomatic index GSI. Sixty-one percent (n = 656) of the fish examined were female, with a Lower Jaw Fork Length (LJFL) between 83 and 236 cm (mean = 155.5 ± 16.63). The 268 males had a LJFL between 90 and 220 cm (mean = 152.3 ± 34.62). Although the northeastern region of Brazil does not appear to be a significant spawning area for the species, the results suggest a higher reproductive activity in the third quarter of the year. Using a Bayesian logistic model approach, length at 50% maturity was estimated at 145.04 cm (credibility interval of 95%, 143.94–146.09 cm), for females, and at 140.03 cm (credibility interval of 95%, 137.28–142.52 cm), for males. 相似文献
75.
基于代谢组学技术,比较室内自然萎凋和空气能萎凋两种萎凋工艺对白茶萎凋过程代谢物与品质的影响。结果表明,不同代谢物对2种萎凋工艺的响应存在差异,体现三种变化规律:第一类代谢物受萎凋工艺影响小,如咖啡碱、表没食子儿茶素和2'-羟基二氢大豆素等;第二类代谢物含量变化速率在空气能萎凋时加快,但其最终含量受影响小,如表没食子儿茶素没食子酸酯、聚酯型儿茶素A和木麻黄素等;第三类代谢物则受萎凋时间影响大,如茶没食子素与奎宁酸等。两种萎凋工艺对白茶品质影响存在差异,自然萎凋下黄酮(醇)糖苷类、儿茶素聚合体等含量更高,这些物质多在萎凋中后期含量提升;空气能萎凋下酚酸、茶氨酸含量更高,这些物质在自然萎凋后期含量大幅下降。萎凋时长是两种萎凋工艺导致代谢物含量差异的重要因素。 相似文献
76.
《Biomarkers》2013,18(5):378-384
AbstractContext: Leukocytes have been found to be the predictor of outcome following acute coronary syndrome (ACS).Objective: We sought to determine the relationship between leukocyte differentials and developing major adverse cardiac events (MACE) in patients with non-ST elevation ACS (NSTE-ACS).Materials and methods: A total of 490 consecutive patients were enrolled, and MACE incidence was evaluated at long-term follow-up period.Results: Total white blood cell (WBC) was higher in subjects occurring MACE. Moreover, elevated total WBC, ≥7.5?×?103/µL, independently predicted MACE.Discussion and conclusion: Elevated admission total WBC can predict long-term MACE in NSTE-ACS patients better than other differentials. 相似文献
77.
D. Lasar A. Julius T. Fromme M. Klingenspor 《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》2013,1831(5):960-968
During postnatal development of mice distinct white adipose tissue depots display a transient appearance of brown-like adipocytes. These brite (brown in white) adipocytes share characteristics with classical brown adipocytes including a multilocular appearance and the expression of the thermogenic protein uncoupling protein 1. In this study, we compared two inbred mouse strains 129S6sv/ev and C57BL6/N known for their different propensity to diet-induced obesity. We observed transient browning in retroperitoneal and inguinal adipose tissue depots of these two strains. From postnatal day 10 to 20 the increase in the abundance of multilocular adipocytes and uncoupling protein 1 expression was higher in 129S6sv/ev than in C57BL6/N pups. The parallel increase in the mass of the two fat depots was attenuated during this browning period. Conversely, epididymal white and interscapular brown adipose tissue displayed a steady increase in mass during the first 30 days of life. In this period, 129S6sv/ev mice developed a significantly higher total body fat mass than C57BL6/N. Thus, while on a local depot level a high number of brite cells is associated with the attenuation of adipose tissue expansion the strain comparison reveals no support for a systemic impact on energy balance. This article is part of a Special Issue entitled Brown and White Fat: From Signaling to Disease. 相似文献
78.
《Cell cycle (Georgetown, Tex.)》2013,12(15):2765-2766
Comment on: Tran KV, et al. Cell Metab 2012; 15:222-9. 相似文献
79.
80.
Petr Martinek Josef Hedbávný Tomáš Kudláček Michal Šťasta Emanuel Kula 《Entomologia Experimentalis et Applicata》2020,168(8):635-643
The adaptation of insects to environmental changes can constitute a crucial factor in their development and activity. The response of Cabera pusaria L. (Lepidoptera: Geometridae) caterpillars to high manganese (Mn) concentrations in the diet was studied. Birch leaves were treated by dipping in MnCl2·4H2O solutions, thereby achieving Mn contents of 370 (T0), 695 (T1), 3 198 (T2), and 6 302 mg kg−1 (T3). The reactions were determined by observing caterpillar mortality, development time, food consumption, and pupal weight. Manganese concentrations in larval excrement, pupae, and food were determined. Manganese in the diet at unnaturally increased concentrations caused great stress for caterpillars. All individuals in the treatment with the highest Mn concentration (T3) died during rearing and successful pupation occurred in only four individuals in T2. Even in the case of caterpillars from T1 (twofold higher than T0) a negative reaction (increased food consumption and prolonged development) was recorded. We also determined significantly increased Mn concentration in pupae from T1 (T2 and T3 were not included in this evaluation due to mortality) and excrement (T1‒T3) compared with T0 having a natural Mn concentration. Caterpillars were seen to eliminate negatively acting dietary Mn by its translocation to excrement. However, the highest mortality rate in T2 and T3 and negative reactions of individuals in T1 very likely demonstrate energy insufficiency and the high energy requirements of Mn elimination mechanisms. 相似文献