全文获取类型
收费全文 | 5839篇 |
免费 | 497篇 |
国内免费 | 1篇 |
出版年
2023年 | 22篇 |
2021年 | 120篇 |
2020年 | 74篇 |
2019年 | 93篇 |
2018年 | 89篇 |
2017年 | 89篇 |
2016年 | 155篇 |
2015年 | 292篇 |
2014年 | 304篇 |
2013年 | 378篇 |
2012年 | 498篇 |
2011年 | 461篇 |
2010年 | 324篇 |
2009年 | 223篇 |
2008年 | 384篇 |
2007年 | 365篇 |
2006年 | 344篇 |
2005年 | 322篇 |
2004年 | 315篇 |
2003年 | 300篇 |
2002年 | 246篇 |
2001年 | 85篇 |
2000年 | 71篇 |
1999年 | 63篇 |
1998年 | 57篇 |
1997年 | 53篇 |
1996年 | 45篇 |
1995年 | 39篇 |
1994年 | 31篇 |
1993年 | 35篇 |
1992年 | 44篇 |
1991年 | 39篇 |
1990年 | 21篇 |
1989年 | 18篇 |
1988年 | 20篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 21篇 |
1984年 | 27篇 |
1983年 | 19篇 |
1982年 | 16篇 |
1981年 | 20篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1973年 | 10篇 |
1972年 | 8篇 |
1968年 | 8篇 |
1880年 | 8篇 |
排序方式: 共有6337条查询结果,搜索用时 258 毫秒
991.
Lithium‐Ion Batteries: Experimental Studies on Work Functions of Li+ Ions and Electrons in the Battery Electrode Material LiCoO2: A Thermodynamic Cycle Combining Ionic and Electronic Structure (Adv. Energy Mater. 18/2018) 下载免费PDF全文
992.
993.
Stephan Scholz Stefan Richter Christian S. Wirkner 《Arthropod Structure & Development》2018,47(3):248-267
We present a study of the hemolymph vascular system of the marbled crayfish, Procambarus fallax f. virginalis, the only crayfish species known to be parthenogenetic. To identify potential evolutionary patterns, we compared data from a total of 48 specimens of P. fallax with 22 specimens of Orconectes limosus. Visualizations (2D and 3D) were carried out using a combination of classical and modern morphological techniques. Our data were compared to the existing literature.Like all Decapoda, both P. fallax and O. limosus have a hemolymph vascular system, consisting of a globular heart with seven off-branching arteries. We were able to visualize in detail the heart of crayfish for the first time, i.e., the myocard with its clusters of muscles running through the lumen of the heart, the valves and flaps of ostia and arteries. Furthermore, the branching patterns of the seven artery systems were analyzed. Anatomical structures identified to be consistent in all specimens of both species were combined as ground pattern of hemolymph vascular system features for Astacida. 相似文献
994.
Induction and recovery of copy number variation in banana through gamma irradiation and low‐coverage whole‐genome sequencing 下载免费PDF全文
Traditional breeding methods are hindered in bananas due to the fact that major cultivars are sterile, parthenocarpic, triploid and thus clonally propagated. This has resulted in a narrow genetic base and limited resilience to biotic and abiotic stresses. Mutagenesis of in vitro propagated bananas is one method to introduce novel alleles and broaden genetic diversity. We previously established a method for the induction and recovery of single nucleotide mutations generated with the chemical mutagen EMS. However, officially released mutant banana varieties have been created using gamma rays, a mutagen that can produce large genomic insertions and deletions (indels). Such dosage mutations may be important for generating observable phenotypes in polyploids. In this study, we establish a low‐coverage whole‐genome sequencing approach in triploid bananas to recover large genomic indels caused by treatment with gamma irradiation. We first evaluated the commercially released mutant cultivar ‘Novaria’ and found that it harbours multiple predicted deletions, ranging from 0.3 to 3.8 million base pairs (Mbp). In total, predicted deletions span 189 coding regions. To evaluate the feasibility of generating and maintaining new mutations, we developed a pipeline for mutagenesis and screening for copy number variation in Cavendish bananas using the cultivar ‘Williams’. Putative mutations were recovered in 70% of lines treated with 20 Gy and 60% of the lines treated with 40 Gy. While deletion events predominate, insertions were identified in 20 Gy‐treated material. Based on these results, we believe this approach can be scaled up to support large breeding projects. 相似文献
995.
Sophie Calderari Massimiliano Ria Christelle Gérard Tatiane C. Nogueira Olatz Villate Stephan C. Collins Helen Neil Nicolas Gervasi Christophe Hue Nicolas Suarez-Zamorano Cécilia Prado Miriam Cnop Marie-Thérèse Bihoreau Pamela J. Kaisaki Jean-Baptiste Cazier Cécile Julier Mark Lathrop Michel Werner Dominique Gauguier 《Genomics》2018,110(2):98-111
The GLIS family zinc finger 3 isoform (GLIS3) is a risk gene for Type 1 and Type 2 diabetes, glaucoma and Alzheimer's disease endophenotype. We identified GLIS3 binding sites in insulin secreting cells (INS1) (FDR q < 0.05; enrichment range 1.40–9.11 fold) sharing the motif wrGTTCCCArTAGs, which were enriched in genes involved in neuronal function and autophagy and in risk genes for metabolic and neuro-behavioural diseases. We confirmed experimentally Glis3-mediated regulation of the expression of genes involved in autophagy and neuron function in INS1 and neuronal PC12 cells. Naturally-occurring coding polymorphisms in Glis3 in the Goto-Kakizaki rat model of type 2 diabetes were associated with increased insulin production in vitro and in vivo, suggestive alteration of autophagy in PC12 and INS1 and abnormal neurogenesis in hippocampus neurons. Our results support biological pleiotropy of GLIS3 in pathologies affecting β-cells and neurons and underline the existence of trans?nosology pathways in diabetes and its co-morbidities. 相似文献
996.
Karen L. Thorpe Patricia Gorman Claire Thomas Denise Sheer John Trowsdale Stephan Beck 《Gene》1997,200(1-2):177-183
We have mapped the human ORFX gene to chromosome 9q34 and determined its complete gene structure. Comparison with RING3, the human MHC-linked homologue on 6p21.3, shows the two gene structures to be highly conserved but with an approximate threefold expansion in the ORFX introns. RING3 and ORFX are found to be ubiquitously expressed in human adult and foetal tissues. Evidence suggests that the two genes may have arisen from an ancient duplication in a common ancestral chromosome. 相似文献
997.
Ecosystem-level experiments on the effects of atmospheric CO2 enrichment and N deposition on forest trees are urgently needed. Here we present data for nine model ecosystems of spruce
(Picea abies) on natural nutrient-poor montane forest soil (0.7 m2 of ground and 350 kg weight). Each system was composed of six 7-year-old (at harvest) trees each representing a different
genotype, and a herbaceous understory layer (three species). The model ecosystems were exposed to three different CO2 concentrations (280, 420, 560 μl l−1) and three different rates of wet N deposition (0, 30, 90 kg ha−1 year−1) in a simulated annual course of Swiss montane climate for 3 years. The total ecosystem biomass was not affected by CO2 concentration, but increased with increasing N deposition. However, biomass allocation to roots increased with increasing
CO2 leading to significantly lower leaf mass ratios (LMRs) and leaf area ratios (LARs) in trees grown at elevated CO2. In contrast to CO2 enrichment, N deposition increased biomass allocation to the aboveground plant parts, and thus LMR and LAR were higher with
increasing N deposition. We observed no CO2 × N interactions on growth, biomass production, or allocation, and there were also no genotype × treatment interactions.
The final leaf area index (LAI) of the spruce canopies was 19% smaller at 420 and 27% smaller at 560 than that measured at
280 μl CO2 l−1, but was not significantly altered by increasing N deposition. Lower LAIs at elevated CO2 largely resulted from shorter branches (less needles per individual tree) and partially from increased needle litterfall.
Independently of N deposition, total aboveground N content in the spruce communities declined with increasing CO2 (−18% at 420 and −31% at 560 compared to 280 μl CO2 l−1). N deposition had the opposite effect on total above ground N content (+18% at 30 and +52% at 90 compared to 0 kg N ha−1 year−1). Our results suggest that under competitive conditions on natural forest soil, atmospheric CO2 enrichment may not lead to higher ecosystem biomass production, but N deposition is likely to do so. The reduction in LAI
under elevated CO2 suggests allometric down-regulation of photosynthetic carbon uptake at the canopy level. The strong decline in the tree nitrogen
mass per unit ground area in response to elevated CO2 may indicate CO2-induced reductions of soil N availability.
Received: 11 May 1997 / Accepted: 4 August 1997 相似文献
998.
Huy Riem Ha Ferenc Follath Yvonne Bloemhard Stephan Krähenbühl 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1997,694(2):248
We developed and characterized a high-performance liquid chromatography (HPLC) assay for the determination of saquinavir, an HIV protease inhibitor, in human plasma samples. Extraction of plasma samples with diethyl ether resulted in quantitative recovery of both saquinavir and its stereoisomer Ro 31-8533 which was used as an internal standard. The assay was performed isocratically using 5 mM H2SO4 (pH 3.5) and acetonitrile (75.5:24.5, v/v) containing 10 mM tetrabutylammonium hydrogen sulfate (TBA) as a mobile phase, a Nucleosil 3C8 column kept at 45°C and UV detection at 240 nm. Using this method, saquinavir and Ro 31-8533 can be separated from endogenous substances, and in the concentration range of 5–110 ng/ml the relative standard deviations for the determination of saquinavir were below 5%. The detection limit of saquinavir in human plasma was 1 ng/ml. The usefulness of the method was demonstrated by quantification of saquinavir in plasma of human subjects treated with 600 mg of saquinavir per os or 12 mg intravenously. 相似文献
999.
1000.
W Mustafa A Mustafa N Elbakri H Link A Adem 《Journal of receptor and signal transduction research》2001,21(1):47-54
The nonobese diabetic mouse (NOD) develops destruction and functional impairment of salivary and lachrymal glands, experimental autoimmune sialadenitis (EAS), resembling and representing a model for Sjogren's syndrome (SS). To investigate the mechanisms of tissue destruction in EAS, we analyzed a cell survival promoter insulin-like growth factor-1 receptor (IGF-1R) in the submandibular glands of NOD mice with this disease. We also evaluated the expression of a downstream effector of IGF-1R, BAD. Receptor-binding autoradiography revealed that the IGF-1R levels in submandibular glands from young NOD mice were lower than those in adult NOD mice. Immunofluorescence staining demonstrated that BAD expression in the epithelial cells of the submandibular gland was consistently enhanced throughout the course of EAS in NOD mice. These findings suggest that a reduction in the levels of IGF-1R induces a defective glandular homeostasis in the submandibular gland epithelial cells and triggers EAS. 相似文献