全文获取类型
收费全文 | 3164篇 |
免费 | 318篇 |
国内免费 | 2篇 |
出版年
2023年 | 24篇 |
2022年 | 30篇 |
2021年 | 85篇 |
2020年 | 66篇 |
2019年 | 91篇 |
2018年 | 87篇 |
2017年 | 95篇 |
2016年 | 116篇 |
2015年 | 179篇 |
2014年 | 169篇 |
2013年 | 235篇 |
2012年 | 247篇 |
2011年 | 249篇 |
2010年 | 122篇 |
2009年 | 124篇 |
2008年 | 185篇 |
2007年 | 150篇 |
2006年 | 147篇 |
2005年 | 141篇 |
2004年 | 125篇 |
2003年 | 129篇 |
2002年 | 110篇 |
2001年 | 63篇 |
2000年 | 47篇 |
1999年 | 66篇 |
1998年 | 42篇 |
1997年 | 33篇 |
1996年 | 24篇 |
1995年 | 14篇 |
1994年 | 20篇 |
1993年 | 17篇 |
1992年 | 21篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 12篇 |
1988年 | 18篇 |
1987年 | 9篇 |
1986年 | 17篇 |
1985年 | 7篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1977年 | 9篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1974年 | 16篇 |
1973年 | 6篇 |
1972年 | 7篇 |
1968年 | 4篇 |
排序方式: 共有3484条查询结果,搜索用时 203 毫秒
51.
We studied the effects of methanol, ethanol, iso-propanol, and n-propanol on the reaction of hemoglobin with oxygen at various temperatures. The analysis of the results in terms of the Monod-Wyman-Changeux model allowed determination of the overall contribution of the alcohols to the standard enthalpy and entropy differences between the T and R states of hemoglobin. A phenomenological approach allowed us to obtain separately the contributions related to the variations of the bulk dielectric constant of the solvent (bulk electrostatic contributions) and the contributions related to other effects (non-bulk-electrostatic contributions). The values of non-bulk-electrostatic contributions to ΔΔH and ΔΔS supported the suggestion that these contributions are mainly related to protein-solvent hydrophobic interactions. 相似文献
52.
53.
J Garcia-Martinez J L Segovia M D Suarez E Garcia-Peregrin 《Biochemical and biophysical research communications》1976,72(1):202-208
The phosphorylation of mevalonic acid by cell-free extracts from chick liver in the early steps of development was studied. A clear difference in the pH-activity profiles for phosphomevalonate and pyrophosphomevalonate formation has been observed. the amount of phosphomevalonate formed is quite similar at pH 7.5–9.5 whereas the pyrophosphomevalonate shows a clear maximum at pH 9.5. The pattern of mevalonate phosphorylation during the neonatal development shows no significant difference between 1–6 days after hatching, but a significant increase in the amount of phosphomevalonate formed at day 7 after hatching. 相似文献
54.
55.
Jacopo Burrello Sara Bolis Carolina Balbi Alessio Burrello Elena Provasi Elena Caporali Lorenzo Grazioli Gauthier Andrea Peirone Fabrizio D'Ascenzo Silvia Monticone Lucio Barile Giuseppe Vassalli 《Journal of cellular and molecular medicine》2020,24(17):9945-9957
The current standard biomarker for myocardial infarction (MI) is high‐sensitive troponin. Although powerful in clinical setting, search for new markers is warranted as early diagnosis of MI is associated with improved outcomes. Extracellular vesicles (EVs) attracted considerable interest as new blood biomarkers. A training cohort used for diagnostic modelling included 30 patients with STEMI, 38 with stable angina (SA) and 30 matched‐controls. Extracellular vesicle concentration was assessed by nanoparticle tracking analysis. Extracellular vesicle surface‐epitopes were measured by flow cytometry. Diagnostic models were developed using machine learning algorithms and validated on an independent cohort of 80 patients. Serum EV concentration from STEMI patients was increased as compared to controls and SA. EV levels of CD62P, CD42a, CD41b, CD31 and CD40 increased in STEMI, and to a lesser extent in SA patients. An aggregate marker including EV concentration and CD62P/CD42a levels achieved non‐inferiority to troponin, discriminating STEMI from controls (AUC = 0.969). A random forest model based on EV biomarkers discriminated the two groups with 100% accuracy. EV markers and RF model confirmed high diagnostic performance at validation. In conclusion, patients with acute MI or SA exhibit characteristic EV biomarker profiles. EV biomarkers hold great potential as early markers for the management of patients with MI. 相似文献
56.
Michaela A. Mausz María Segovia Aud Larsen Stella A. Berger Jorun K. Egge Georg Pohnert 《Environmental microbiology》2020,22(9):3863-3882
Ocean acidification (OA), a consequence of anthropogenic carbon dioxide (CO2) emissions, strongly impacts marine ecosystems. OA also influences iron (Fe) solubility, affecting biogeochemical and ecological processes. We investigated the interactive effects of CO2 and Fe availability on the metabolome response of a natural phytoplankton community. Using mesocosms we exposed phytoplankton to ambient (390 μatm) or future CO2 levels predicted for the year 2100 (900 μatm), combined with ambient (4.5 nM) or high (12 nM) dissolved iron (dFe). By integrating over the whole phytoplankton community, we assigned functional changes based on altered metabolite concentrations. Our study revealed the complexity of phytoplankton metabolism. Metabolic profiles showed three stages in response to treatments and phytoplankton dynamics. Metabolome changes were related to the plankton group contributing respective metabolites, explaining bloom decline and community succession. CO2 and Fe affected metabolic profiles. Most saccharides, fatty acids, amino acids and many sterols significantly correlated with the high dFe treatment at ambient pCO2. High CO2 lowered the abundance of many metabolites irrespective of Fe. However, sugar alcohols accumulated, indicating potential stress. We demonstrate that not only altered species composition but also changes in the metabolic landscape affecting the plankton community may change as a consequence of future high-CO2 oceans. 相似文献
57.
Matthias Albrecht David Kleijn Neal M. Williams Matthias Tschumi Brett R. Blaauw Riccardo Bommarco Alistair J. Campbell Matteo Dainese Francis A. Drummond Martin H. Entling Dominik Ganser G. Arjen de Groot Dave Goulson Heather Grab Hannah Hamilton Felix Herzog Rufus Isaacs Katja Jacot Philippe Jeanneret Mattias Jonsson Eva Knop Claire Kremen Douglas A. Landis Gregory M. Loeb Lorenzo Marini Megan McKerchar Lora Morandin Sonja C. Pfister Simon G. Potts Maj Rundlf Hillary Sardias Amber Sciligo Carsten Thies Teja Tscharntke Eric Venturini Eve Veromann Ines M.G. Vollhardt Felix Wckers Kimiora Ward Andrew Wilby Megan Woltz Steve Wratten Louis Sutter 《Ecology letters》2020,23(10):1488-1498
Floral plantings are promoted to foster ecological intensification of agriculture through provisioning of ecosystem services. However, a comprehensive assessment of the effectiveness of different floral plantings, their characteristics and consequences for crop yield is lacking. Here we quantified the impacts of flower strips and hedgerows on pest control (18 studies) and pollination services (17 studies) in adjacent crops in North America, Europe and New Zealand. Flower strips, but not hedgerows, enhanced pest control services in adjacent fields by 16% on average. However, effects on crop pollination and yield were more variable. Our synthesis identifies several important drivers of variability in effectiveness of plantings: pollination services declined exponentially with distance from plantings, and perennial and older flower strips with higher flowering plant diversity enhanced pollination more effectively. These findings provide promising pathways to optimise floral plantings to more effectively contribute to ecosystem service delivery and ecological intensification of agriculture in the future. 相似文献
58.
Giovanni Astuti Sandro Pratesi Angelino Carta Lorenzo Peruzzi 《Plant Species Biology》2020,35(2):130-137
We found functionally male individuals in an otherwise hermaphroditic population of Tulipa pumila (Liliaceae) located in Tuscany (central Italy). We investigated the sex ratio of this population, followed by morphometric analyses of the scape, leaves and flowers, and tests on pollen germinability and seed number and mass, in order to infer which sexual strategy produced the observed co-occurrence of male and hermaphrodite individuals. We found that sex ratio deviated from 1:1, and functionally male individuals showed a smaller plant size and a reduced pollen fitness (germinability and siring ability) compared to hermaphrodites. These findings point to a resource-dependent sexual allocation strategy, probably associated with gender diphasy. 相似文献
59.
Davide Marzi Patrizia Brunetti Giovanni Mele Nadia Napoli Lorenzo Cal Erica Spaziani Minami Matsui Simone De Panfilis Paolo Costantino Giovanna Serino Maura Cardarelli 《The Plant journal : for cell and molecular biology》2020,103(1):379-394
In Arabidopsis, stamen elongation, which ensures male fertility, is controlled by the auxin response factor ARF8, which regulates the expression of the auxin repressor IAA19. Here, we uncover a role for light in controlling stamen elongation. By an extensive genetic and molecular analysis we show that the repressor of light signaling COP1, through its targets HY5 and HYH, controls stamen elongation, and that HY5 – oppositely to ARF8 – directly represses the expression of IAA19 in stamens. In addition, we show that in closed flower buds, when light is shielded by sepals and petals, the blue light receptors CRY1/CRY2 repress stamen elongation. Coherently, at flower disclosure and in subsequent stages, stamen elongation is repressed by the red and far‐red light receptors PHYA/PHYB. In conclusion, different light qualities – sequentially perceived by specific photoreceptors – and the downstream COP1–HY5/HYH module finely tune auxin‐induced stamen elongation and thus male fertility. 相似文献
60.