全文获取类型
收费全文 | 14735篇 |
免费 | 1340篇 |
国内免费 | 1612篇 |
专业分类
17687篇 |
出版年
2024年 | 62篇 |
2023年 | 248篇 |
2022年 | 546篇 |
2021年 | 895篇 |
2020年 | 634篇 |
2019年 | 728篇 |
2018年 | 695篇 |
2017年 | 495篇 |
2016年 | 668篇 |
2015年 | 978篇 |
2014年 | 1103篇 |
2013年 | 1238篇 |
2012年 | 1347篇 |
2011年 | 1275篇 |
2010年 | 752篇 |
2009年 | 703篇 |
2008年 | 765篇 |
2007年 | 647篇 |
2006年 | 638篇 |
2005年 | 408篇 |
2004年 | 408篇 |
2003年 | 382篇 |
2002年 | 326篇 |
2001年 | 241篇 |
2000年 | 196篇 |
1999年 | 195篇 |
1998年 | 162篇 |
1997年 | 116篇 |
1996年 | 106篇 |
1995年 | 95篇 |
1994年 | 73篇 |
1993年 | 64篇 |
1992年 | 84篇 |
1991年 | 58篇 |
1990年 | 52篇 |
1989年 | 50篇 |
1988年 | 41篇 |
1987年 | 28篇 |
1986年 | 22篇 |
1985年 | 28篇 |
1984年 | 19篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1975年 | 11篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
Chunmei Liu Jing Wang Sirui Zhou Binbin Wang Xu Ma 《Reproductive biology and endocrinology : RB&E》2010,8(1):1-4
Objectives
TNF-alpha is a critical cytokine produced by Th1 cells while altered T helper 1 (Th1)-Th2 balance is found crucial for a successful pregnancy.Study Design
A cohort of 132 Southern Chinese Han RSA patients and 152 controls constituted the subjects of this study. Two functional polymorphisms -308 and -238 of TNF-alpha were studied by association analysis.Results
lack of association was found in TNF-alpha -308 SNP yet a significant difference was discovered in -238 polymorphism.Conclusion
This study suggested that TNF-alpha may be a risk factor in Chinese RSA patients. However the ethnic differences may also contribute to the results. 相似文献994.
Imatinib mesylate, currently marketed by Novartis as Gleevec in the U.S., has emerged as the leading compound to treat the chronic phase of chronic myeloid leukemia (CML), through its inhibition of Bcr-Abl tyrosine kinases, and other cancers. However, resistance to imatinib develops frequently, particularly in late-stage disease. To identify new cellular pathways affected by imatinib treatment, we applied mass spectrometry together with stable isotope labeling by amino acids in cell culture (SILAC) for the comparative study of protein expression in K562 cells that were untreated or treated with a clinically relevant concentration of imatinib. Our results revealed that, among the 1344 quantified proteins, 73 had significantly altered levels of expression induced by imatinib and could be quantified in both forward and reverse SILAC labeling experiments. These included the down-regulation of thymidylate synthase, S-adenosylmethionine synthetase, and glycerol-3-phosphate dehydrogenase as well as the up-regulation of poly(ADP-ribose) polymerase 1, hemoglobins, and enzymes involved in heme biosynthesis. We also found, by assessing alteration in the acetylation level in histone H4 upon imatinib treatment, that the imatinib-induced hemoglobinization and erythroid differentiation in K562 cells are associated with global histone H4 hyperacetylation. Overall, these results provided potential biomarkers for monitoring the therapeutic intervention of CML using imatinib and offered important new knowledge for gaining insight into the molecular mechanisms of action of imatinib. 相似文献
995.
Metabolomic analysis was carried out to investigate the metabolic differences of diploid (α/a) and homogenous haploid (α,a) yeasts, and further assess their response to ethanol stress. The dynamic metabolic variations of diploid and haploid caused by 3 and 7% (v/v) ethanol stress were evaluated by gas chromatography coupled to time-of-flight mass spectrometry combined with statistical analysis. Metabolite profiles originating from three strains in presence/absence of ethanol stress were distinctive and could be distinguished by principal components analysis. Results showed that the divergence among the strains with ethanol stress was smaller than without it. Furthermore, the levels of most glycolytic intermediates and amino acids in haploid were lower than these in diploid with/without ethanol stress, which was considered as species-specific behaviors. The increases of protective metabolites including polyols, amino acids, precursors of phospholipids, and unsaturated fatty acids under ethanol stress in three strains revealed the ethanol stress-specific responses. Higher fold change in most of these protectants in haploid indicated that haploid was more susceptible to ethanol stress than diploid. These findings provided underlying basis for better understanding diploid and haploid yeasts, and further breeding tolerant strains for efficient ethanol fermentation. 相似文献
996.
997.
油菜秸秆还田对水稻根系、分蘖和产量的影响 总被引:7,自引:0,他引:7
采用田间试验与栽培模拟试验相结合的方法,分析了油菜秸秆还田对水稻根系、分蘖和产量的影响.结果表明: 水稻移栽后0~36 d,与秸秆不还田处理相比,油菜秸秆还田处理下水稻分蘖减少1~2个,根系单株伤流量降低1.0~8.6 mg,根系谷氨酰胺合成酶(GS)、谷丙转氨酶(GPT)和谷草转氨酶(GOT) 活性分别降低0.10~6.11、0.06~0.31和0.52~0.84 μmol·g-1·h-1. 水稻移栽后56 d,与秸秆不还田处理相比,油菜秸秆翻埋还田处理下水稻根系单株伤流量增加3.4~11.7 mg,根系GS、GPT和GOT活性分别增加0.34~0.78、0.13~0.45和0.18~0.20 μmol·g-1·h-1;油菜秸秆覆盖还田处理下水稻根系单株伤流量降低19~25 mg,根系GS、GPT和GOT活性分别增加0.16~0.34、0.08~0.21和0.06~0.32 μmol·g-1·h-1.油菜秸秆还田处理中,全量还田处理下的水稻产量最高,其中,与全量覆盖还田相比,全量翻埋还田处理下的水稻产量增加0.13~0.48 t·hm-2.可见,油菜秸秆还田会导致水稻生长前期根系活力下降、氮代谢酶活性降低,从而使水稻根系生长缓慢、返青延迟,但在中后期,随着根系活力和氮代谢酶活性的增强,秸秆还田会促进水稻根系生长;油菜秸秆还田对水稻产量的影响是多因素综合作用的结果,全量翻埋还田更适宜于四川油稻两熟轮作系统. 相似文献
998.
999.
1000.
The concentrations of nine mineral elements were determined by atomic absorption spectroscopy in Gentiana rigescens from three zones (middle, southeast, and northwest zones) of Yunnan province in China. The average concentrations of mineral elements were found in the order K>Ca>Mg>Fe>Na>Zn>Cu>Cr>Se. Samples collected from the middle zone of Yunnan were enriched in Na (242.24 ± 50.80 mg/kg) and Mg (959.78 ± 54.60 mg/kg). However, materials from the southeast zone were particularly enriched in Ca (3,448.70 ± 749.82 mg/kg), but depleted in Se. Whereas those from the northwest zone were plentiful of K (2,746.89 ± 84.84 mg/kg), Fe (923.06 ± 127.52 mg/kg), Zn (261.38 ± 53.05 mg/kg), Cu (110.08 ± 46.23 mg/kg), and Se (53.99 ± 22.38 mg/kg). 相似文献