全文获取类型
收费全文 | 5094篇 |
免费 | 431篇 |
国内免费 | 281篇 |
专业分类
5806篇 |
出版年
2024年 | 11篇 |
2023年 | 46篇 |
2022年 | 124篇 |
2021年 | 208篇 |
2020年 | 129篇 |
2019年 | 182篇 |
2018年 | 209篇 |
2017年 | 139篇 |
2016年 | 233篇 |
2015年 | 322篇 |
2014年 | 372篇 |
2013年 | 329篇 |
2012年 | 456篇 |
2011年 | 427篇 |
2010年 | 260篇 |
2009年 | 250篇 |
2008年 | 268篇 |
2007年 | 253篇 |
2006年 | 216篇 |
2005年 | 199篇 |
2004年 | 184篇 |
2003年 | 163篇 |
2002年 | 167篇 |
2001年 | 100篇 |
2000年 | 67篇 |
1999年 | 70篇 |
1998年 | 60篇 |
1997年 | 42篇 |
1996年 | 40篇 |
1995年 | 35篇 |
1994年 | 29篇 |
1993年 | 23篇 |
1992年 | 21篇 |
1991年 | 27篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 2篇 |
1972年 | 5篇 |
1971年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有5806条查询结果,搜索用时 15 毫秒
91.
Soil type and fertility level influence straw carbon dynamics in the agroecosystems. However, there is a limited understanding of the dynamic processes of straw-derived and soil-derived carbon and the influence of the addition of straw carbon on soil-derived organic carbon in different soils associated with different fertility levels. In this study, we applied the in-situ carborundum tube method and 13C-labeled maize straw (with and without maize straw) at two cropland (Phaeozem and Luvisol soils) experimental sites in northeast China to quantify the dynamics of maize-derived and soil-derived carbon in soils associated with high and low fertility, and to examine how the addition of maize carbon influences soil-derived organic carbon and the interactions of soil type and fertility level with maize-derived and soil-derived carbon. We found that, on average, the contributions of maize-derived carbon to total organic carbon in maize-soil systems during the experimental period were differentiated among low fertility Luvisol (from 62.82% to 42.90), high fertility Luvisol (from 53.15% to 30.00%), low fertility Phaeozem (from 58.69% to 36.29%) and high fertility Phaeozem (from 41.06% to 16.60%). Furthermore, the addition of maize carbon significantly decreased the remaining soil-derived organic carbon in low and high fertility Luvisols and low fertility Phaeozem before two months. However, the increasing differences in soil-derived organic carbon between both soils with and without maize straw after two months suggested that maize-derived carbon was incorporated into soil-derived organic carbon, thereby potentially offsetting the loss of soil-derived organic carbon. These results suggested that Phaeozem and high fertility level soils would fix more maize carbon over time and thus were more beneficial for protecting soil-derived organic carbon from maize carbon decomposition. 相似文献
92.
Lin Ding An Song Meng Dai Min Xu Wanwan Sun Baihui Xu Jichao Sun Tiange Wang Yu Xu Jieli Lu Weiqing Wang Yufang Bi Guang Ning 《Journal of lipid research》2015,56(4):920-926
Lipoprotein (a) [Lp(a)], an LDL-like particle, has been proposed as a causal risk factor for CVD among general populations. Meanwhile, both serum Lp(a) and diabetes increase the risk of CVD. However, the relationship between serum Lp(a) and T2D is poorly characterized, especially in the Asian population. Therefore, we conducted a cross-sectional study in 10,122 participants aged 40 years or older in Jiading District, Shanghai, China. Our study found that the prevalence of T2D was decreased from 20.9% to 15.0% from the lowest quartile to the highest quartile of serum Lp(a) concentrations (P for trend <0.0001). Logistic regression analyses showed that the odds ratios and 95% confidence intervals of prevalent T2D for quartiles 2–4 versus quartile 1 were 0.86 (0.73–1.01), 0.88 (0.75–1.04), and 0.76 (0.64–0.90) (P for trend = 0.0002), after adjustment for traditional confounding factors. Moreover, the risks for prevalent prediabetes, insulin resistance, and hyperinsulinemia were also decreased from the lowest to the top quartile. This inverse association between serum Lp(a) and T2D was not appreciably changed after we adjusted hypoglycemic medications or excluded the subjects with hypoglycemic and/or lipid-lowering agents and/or a history of self-reported CVD. 相似文献
93.
Jacklyn N. Hellwege Nicholette D. Palmer W. Mark Brown Julie T. Ziegler S. Sandy An Xiuqing Guo Y.-D. Ida Chen Kent Taylor Gregory A. Hawkins Maggie C. Y. Ng Elizabeth K. Speliotes Carlos Lorenzo Jill M. Norris Jerome I. Rotter Lynne E. Wagenknecht Carl D. Langefeld Donald W. Bowden 《Human genetics》2015,134(2):215-215
94.
Nanoflake‐Assembled Hierarchical Na3V2(PO4)3/C Microflowers: Superior Li Storage Performance and Insertion/Extraction Mechanism 下载免费PDF全文
Qinyou An Fangyu Xiong Qiulong Wei Jinzhi Sheng Liang He Dongling Ma Yan Yao Liqiang Mai 《Liver Transplantation》2015,5(10)
Na3V2(PO4)3 (NVP) has excellent electrochemical stability and fast ion diffusion coefficient due to the 3D Na+ ion superionic conductor framework, which make it an attractive cathode material for lithium ion batteries (LIBs). However, the electrochemical performance of NVP needs to be further improved for applications in electric vehicles and hybrid electric vehicles. Here, nanoflake‐assembled hierarchical NVP/C microflowers are synthesized using a facile method. The structure of as‐synthesized materials enhances the electrochemical performance by improving the electron conductivity, increasing electrode–electrolyte contact area, and shortening the diffusion distance. The as‐synthesized material exhibits a high capacity (230 mAh g?1), excellent cycling stability (83.6% of the initial capacity is retained after 5000 cycles), and remarkable rate performance (91 C) in hybrid LIBs. Meanwhile, the hybrid LIBs with the structure of NVP || 1 m LiPF6/EC (ethylene carbonate) + DMC (dimethyl carbonate) || NVP and Li4Ti5O12 || 1 m LiPF6/EC + DMC || NVP are assembled and display capacities of 79 and 73 mAh g?1, respectively. The insertion/extraction mechanism of NVP is systematically investigated, based on in situ X‐ray diffraction. The superior electrochemical performance, the design of hybrid LIBs, and the insertion/extraction mechanism investigation will have profound implications for developing safe and stable, high‐energy, and high‐power LIBs. 相似文献
95.
Ning An Xiaoyu Shi Yueming Zhang Ning Lv Lin Feng Xuebing Di Naijun Han Guiqi Wang Shujun Cheng Kaitai Zhang 《PloS one》2015,10(9)
Immune response-related genes play a major role in colorectal carcinogenesis by mediating inflammation or immune-surveillance evasion. Although remarkable progress has been made to investigate the underlying mechanism, the understanding of the complicated carcinogenesis process was enormously hindered by large-scale tumor heterogeneity. Development and carcinogenesis share striking similarities in their cellular behavior and underlying molecular mechanisms. The association between embryonic development and carcinogenesis makes embryonic development a viable reference model for studying cancer thereby circumventing the potentially misleading complexity of tumor heterogeneity. Here we proposed that the immune genes, responsible for intra-immune cooperativity disorientation (defined in this study as disruption of developmental expression correlation patterns during carcinogenesis), probably contain untapped prognostic resource of colorectal cancer. In this study, we determined the mRNA expression profile of 137 human biopsy samples, including samples from different stages of human colonic development, colorectal precancerous progression and colorectal cancer samples, among which 60 were also used to generate miRNA expression profile. We originally established Spearman correlation transition model to quantify the cooperativity disorientation associated with the transition from normal to precancerous to cancer tissue, in conjunction with miRNA-mRNA regulatory network and machine learning algorithm to identify genes with prognostic value. Finally, a 12-gene signature was extracted, whose prognostic value was evaluated using Kaplan–Meier survival analysis in five independent datasets. Using the log-rank test, the 12-gene signature was closely related to overall survival in four datasets (GSE17536, n = 177, p = 0.0054; GSE17537, n = 55, p = 0.0039; GSE39582, n = 562, p = 0.13; GSE39084, n = 70, p = 0.11), and significantly associated with disease-free survival in four datasets (GSE17536, n = 177, p = 0.0018; GSE17537, n = 55, p = 0.016; GSE39582, n = 557, p = 4.4e-05; GSE14333, n = 226, p = 0.032). Cox regression analysis confirmed that the 12-gene signature was an independent factor in predicting colorectal cancer patient’s overall survival (hazard ratio: 1.759; 95% confidence interval: 1.126–2.746; p = 0.013], as well as disease-free survival (hazard ratio: 2.116; 95% confidence interval: 1.324–3.380; p = 0.002). 相似文献
96.
Xiang-Lan Sun Sarah J. Lessard Ding An Ho-Jin Koh Hiroyasu Esumi Michael F. Hirshman Laurie J. Goodyear 《Journal of cellular biochemistry》2019,120(1):685-696
The signaling mechanisms mediating myocardial glucose transport are not fully understood. Sucrose nonfermenting AMP-activated protein kinase (AMPK)-related kinase (SNARK) is an AMPK-related protein kinase that is expressed in the heart and has been implicated in contraction-stimulated glucose transport in mouse skeletal muscle. We first determined if SNARK is phosphorylated on Thr208, a site critical for SNARK activity. Mice were treated with exercise, ischemia, submaximal insulin, or maximal insulin. Treadmill exercise slightly, but significantly increased SNARK Thr208 phosphorylation. Ischemia also increased SNARK Thr208 phosphorylation, but there was no effect of submaximal or maximal insulin. HL1 cardiomyocytes were used to overexpress wild-type (WT) SNARK and to knockdown endogenous SNARK. Overexpression of WT SNARK had no effect on ischemia-stimulated glucose transport; however, SNARK knockdown significantly decreased ischemia-stimulated glucose transport. SNARK overexpression or knockdown did not alter insulin-stimulated glucose transport or glycogen concentrations. To study SNARK function in vivo, SNARK heterozygous knockout mice (SNARK+/−) and WT littermates performed treadmill exercise. Exercise-stimulated glucose transport was decreased by ~50% in hearts from SNARK+/− mice. In summary, exercise and ischemia increase SNARK Thr208 phosphorylation in the heart and SNARK regulates exercise-stimulated and ischemia-stimulated glucose transport. SNARK is a novel mediator of insulin-independent glucose transport in the heart. 相似文献
97.
Well-spread meiotic pachytene bivalents were obtained by using the prolonged hypotonic treatment combined with high chloroform Carnory's fixative solution from cells of the testes of domestic pigs. Comparison in the division index and length of pachytene bivalents with metaphase chromosomes showed that those of the former are 5 times higher and 3.42(1.87-5.98) times longer than those of the latter. Comparative studies on chromomere maps of bivalents and mitotic chromosomal G-bands were conducted by using the chromosome 12 as a example. Sex vesicle and various shapes of synaptic sex chromosomes have been observed. Two-color PRimed IN Situ (PRINS) labeling has been conducted successfully on pachytene bivalents of pigs. 相似文献
98.
The objective was to determine the effect of 2-mercaptoethanol and cysteine on in vitro developmental competence of oocytes from lambs (4-8-week old) stimulated with eCG and pFSH. Oocytes were matured in medium (TCM199) with no supplement (Control group) or with 100muM 2-mercaptoethanol and 600muM cysteine (GSH group). Oocytes from adult sheep were also included (Adult group). The addition of 2-mercaptoethanol and cysteine did not improve nuclear maturation or microtubule configuration 12, 15, 18, or 24h after placement in maturation medium. Sperm head decondensation and male pronucleus formation were evaluated at 6, 12, and 18h after commencement of IVF; sperm decondensation appeared earlier in the GSH group (6h after the start of IVF). There were differences (P<0.05) between the Control group and the GSH and Adult groups for: fertilization rate at both 12h (55.4, 77.0, and 80.6%, respectively) and 18h (67.9, 86.9, and 88.7%); parthenogenesis rate at both 12h (25.0, 10.8, and 5.6%) and 18h (28.3, 9.8, and 4.5%); and polyspermy rate at 18h (26.4, 4.9, and 5.7%). Blastocyst rate at 7d was higher in the GSH group than the Control group (23.9% vs. 14.9%, P<0.05), but both were lower (P<0.05) than the Adult group (38.3%). The addition of 2-mercaptoethanol and cysteine improved sperm decondensation and rates of fertilization and the blastocyst development to 7d, with no effect on blastocyst rate at 9d. 相似文献
99.
Yan G Zhang G Fang X Zhang Y Li C Ling F Cooper DN Li Q Li Y van Gool AJ Du H Chen J Chen R Zhang P Huang Z Thompson JR Meng Y Bai Y Wang J Zhuo M Wang T Huang Y Wei L Li J Wang Z Hu H Yang P Le L Stenson PD Li B Liu X Ball EV An N Huang Q Zhang Y Fan W Zhang X Li Y Wang W Katze MG Su B Nielsen R Yang H Wang J Wang X Wang J 《Nature biotechnology》2011,29(11):1019-1023
The nonhuman primates most commonly used in medical research are from the genus Macaca. To better understand the genetic differences between these animal models, we present high-quality draft genome sequences from two macaque species, the cynomolgus/crab-eating macaque and the Chinese rhesus macaque. Comparison with the previously sequenced Indian rhesus macaque reveals that all three macaques maintain abundant genetic heterogeneity, including millions of single-nucleotide substitutions and many insertions, deletions and gross chromosomal rearrangements. By assessing genetic regions with reduced variability, we identify genes in each macaque species that may have experienced positive selection. Genetic divergence patterns suggest that the cynomolgus macaque genome has been shaped by introgression after hybridization with the Chinese rhesus macaque. Macaque genes display a high degree of sequence similarity with human disease gene orthologs and drug targets. However, we identify several putatively dysfunctional genetic differences between the three macaque species, which may explain functional differences between them previously observed in clinical studies. 相似文献
100.
Sebastian Fernandez-Pol Zdenek Slouka Souvik Bhattacharjee Yana Fedotova Stefan Freed Xiuli An Anthony A. Holder Estela Campanella Philip S. Low Narla Mohandas Kasturi Haldar 《Eukaryotic cell》2013,12(9):1179-1191
Eukaryotic parasites of the genus Plasmodium cause malaria by invading and developing within host erythrocytes. Here, we demonstrate that PfShelph2, a gene product of Plasmodium falciparum that belongs to the Shewanella-like phosphatase (Shelph) subfamily, selectively hydrolyzes phosphotyrosine, as shown for other previously studied Shelph family members. In the extracellular merozoite stage, PfShelph2 localizes to vesicles that appear to be distinct from those of rhoptry, dense granule, or microneme organelles. During invasion, PfShelph2 is released from these vesicles and exported to the host erythrocyte. In vitro, PfShelph2 shows tyrosine phosphatase activity against the host erythrocyte protein Band 3, which is the most abundant tyrosine-phosphorylated species of the erythrocyte. During P. falciparum invasion, Band 3 undergoes dynamic and rapid clearance from the invasion junction within 1 to 2 s of parasite attachment to the erythrocyte. Release of Pfshelph2 occurs after clearance of Band 3 from the parasite-host cell interface and when the parasite is nearly or completely enclosed in the nascent vacuole. We propose a model in which the phosphatase modifies Band 3 in time to restore its interaction with the cytoskeleton and thus reestablishes the erythrocyte cytoskeletal network at the end of the invasion process. 相似文献