全文获取类型
收费全文 | 10750篇 |
免费 | 784篇 |
国内免费 | 749篇 |
出版年
2024年 | 9篇 |
2023年 | 128篇 |
2022年 | 371篇 |
2021年 | 659篇 |
2020年 | 382篇 |
2019年 | 474篇 |
2018年 | 415篇 |
2017年 | 309篇 |
2016年 | 457篇 |
2015年 | 715篇 |
2014年 | 824篇 |
2013年 | 805篇 |
2012年 | 1025篇 |
2011年 | 816篇 |
2010年 | 495篇 |
2009年 | 468篇 |
2008年 | 506篇 |
2007年 | 477篇 |
2006年 | 388篇 |
2005年 | 366篇 |
2004年 | 285篇 |
2003年 | 256篇 |
2002年 | 188篇 |
2001年 | 207篇 |
2000年 | 150篇 |
1999年 | 163篇 |
1998年 | 96篇 |
1997年 | 109篇 |
1996年 | 110篇 |
1995年 | 100篇 |
1994年 | 106篇 |
1993年 | 65篇 |
1992年 | 64篇 |
1991年 | 84篇 |
1990年 | 53篇 |
1989年 | 43篇 |
1988年 | 25篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 23篇 |
1984年 | 14篇 |
1983年 | 17篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Serum and Urine Metabolite Profiling Reveals Potential Biomarkers of Human Hepatocellular Carcinoma*
992.
The presence of callose in sieve plates has been known for a long time, but how this polysaccharide plug is synthesized has remained unsolved. Two independent laboratories have recently reported the identification of callose synthase 7 (CalS7), also known as glucan synthase-like 7 (GSL7), as the enzyme responsible for callose deposition in sieve plates. Mutant plants defective in this enzyme failed to synthesize callose in developing sieve plates during phloem formation and were unable to accumulate callose in sieve pores in response to stress treatments. The mutant plants developed less open pores per sieve plate and the pores were smaller in diameter. As a result, phloem conductivity was reduced significantly and the mutant plants were shorter and set fewer seeds.Key words: Arabidopsis thaliana, callose, callose synthase, glucan synthase-like, phloem, plasmodesmata, sieve plate 相似文献
993.
Yangbo Xie Huanyang Chen Yadong Xu Lin Zhu Hongru Ma Jian-Wen Dong 《Plasmonics (Norwell, Mass.)》2011,6(3):477-481
In this paper, we use the parameter retrieval method together with an analytical effective medium approach to design a well-performed
invisible cloak, which is based on an empirical revised version of the reduced cloak. The designed cloak can be implemented
by silver nanowires with elliptical cross sections embedded in a polymethyl methacrylate host. This cloak is numerically proved
to be robust for both the inner hidden object as well as incoming detecting waves and is much simpler, thus easier to manufacture
when compared with the earlier one proposed by Cai et al. (Nat Photon 1: 224, 2007). 相似文献
994.
Xie K Jia L Yao Y Xu D Chen S Xie X Pei Y Bao W Dai G Wang J Liu Z 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2011,879(23):2351-2354
A specific, sensitive and widely applicable reversed-phase high-performance liquid chromatography with fluorescence detection (RP-HPLC-FLD) method was developed for the simultaneous determination of thiamphenicol (TAP), florfenicol (FF) and florfenicol amine (FFA) in eggs. Samples were extracted with ethyl acetate-acetonitrile-ammonium hydroxide (49:49:2, v/v), defatted with hexane, followed by RP-HPLC-FLD determination. Liquid chromatography was performed on a 5 μm LiChrospher C(18) column using a mobile phase composed of acetonitrile (A), 0.01 M sodium dihydrogen phosphate containing 0.005 M sodium dodecyl sulfate and 0.1% triethylamine, adjusted to pH 4.8 by 85% phosphoric acid (B) (A:B, 35:65 v/v), at a flow rate of 1.0 mL/min. The fluorescence detector of HPLC was set at 224 nm for excitation wavelength and 290 nm for emission wavelength. Limits of detection (LODs) were 1.5 μg/kg for TAP and FF, 0.5 μg/kg for FFA in eggs; limits of quantitation (LOQs) were 5 μg/kg for TAP and FF, 2 μg/kg for FFA in eggs. Linear calibration curves were obtained over concentration ranges of 0.025-5.0 μg/mL for TAP with determination coefficients of 0.9997, 0.01-10.0 μg/mL for FF with determination coefficients of 0.9997 and 0.0025-2.50 μg/mL for FFA with determination coefficients of 0.9998, respectively. The recovery values ranged from 86.4% to 93.8% for TAP, 87.4% to 92.3% for FF and from 89.0% to 95.2% for FFA. The corresponding intra-day and inter-day variation (relative standard deviation, R.S.D.) found to be less than 6.7% and 10.8%, respectively. 相似文献
995.
Xie C Yang S Zhong D Dai X Chen X 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2011,879(28):3071-3075
Dronedarone is a derivative of amiodarone--a popular antiarrhythmic drug. It was developed to overcome the limiting iodine-associated toxicities of amiodarone. Debutyldronedarone is a major circulating active metabolite of dronedarone in humans. To investigate the pharmacokinetics of dronedarone, a rapid, simple, and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to simultaneously determine dronedarone and debutyldronedarone in human plasma using amiodarone as internal standard (IS). Acetonitrile with IS was used to precipitate proteins from a 50-μL aliquot of plasma. Effective chromatographic separation was performed on a CAPCELL PAK C(18) MG (100 mm × 4.6 mm, 5 μm) column with gradient elution (5 mmol/L ammonium acetate-acetonitrile, with each phase containing 0.2% acetic acid) at a flow rate of 0.7 mL/min. Complete separation was achieved within 5.5 min. Detection was carried out on an tandem mass spectrometer in multiple reaction monitoring mode using a positive atmospheric pressure chemical ionization interface. A lower limit of quantification of 0.200 ng/mL was achieved for both dronedarone and debutyldronedarone, with acceptable precision and accuracy. The linear range of the method was from 0.200 to 200 ng/mL for each analyte. Intra- and inter-day precisions were lower than 7.2% in relation to relative standard deviation, while accuracy was within ±5.1% in terms of relative error for analytes. Our findings demonstrate the successful application of the validated LC-MS/MS method to a pharmacokinetic study after a single oral administration of 400mg dronedarone to six healthy volunteers. 相似文献
996.
Identification of genes regulating fat accumulation is important for basic and medical research; genetic screening for those genes in Caenorhabditis elegans, a widely used model organism, requires in vivo quantification of lipids. We demonstrated RNA interference screening based on quantitative imaging of lipids with label-free stimulated Raman scattering (SRS) microscopy, which overcomes major limitations of coherent anti-Stokes Raman scattering microscopy. Our screening yielded eight new genetic regulators of fat storage. 相似文献
997.
998.
Junyong Zhang Yonghui Deng Dong Gu Shutao Wang Lan She Renchao Che Zhong‐Sheng Wang Bo Tu Songhai Xie Dongyuan Zhao 《Liver Transplantation》2011,1(2):241-248
A novel ligand‐assisted assembly approach is demonstrated for the synthesis of thermally stable and large‐pore ordered mesoporous titanium dioxide with a highly crystalline framework by using diblock copolymer poly(ethylene oxide)‐b‐polystyrene (PEO‐b‐PS) as a template and titanium isopropoxide (TIPO) as a precursor. Small‐angle X‐ray scattering, X‐ray diffraction (XRD), transmission electron microscopy (TEM), high‐resolution scanning electron microscopy, and N2‐sorption measurements indicate that the obtained TiO2 materials possess an ordered primary cubic mesostructure with large, uniform pore diameters of about 16.0 nm, and high Brunauer–Emmett–Teller surface areas of ~112 m2 g?1, as well as high thermal stability (~700 °C). High resolution TEM and wide‐angle XRD measurements clearly illustrate the high crystallinity of the mesoporous titania with an anatase structure in the pore walls. It is worth mentioning that, in this process, in addition to tetrahydrofuran as a solvent, acetylacetone was employed as a coordination agent to avoid rapid hydrolysis of the titanium precursor. Additionally, stepped evaporation and heating processes were adopted to control the condensation rate and facilitate the assembly of the ordered mesostructure, and ensure the formation of fully polycrystalline anatase titania frameworks without collapse of the mesostructure. By employing the obtained mesoporous and crystallized TiO2 as the photoanode in a dye‐sensitized solar cell, a high power‐conversion efficiency (5.45%) can be achieved in combination with the N719 dye, which shows that this mesoprous titania is a great potential candidate as a catalyst support for photonic‐conversion applications. 相似文献
999.
Background: Long‐term Helicobacter pylori infection leads to chronic gastritis, peptic ulcer, and gastric malignancies. Indigenous microflora in alimentary tract maintains a colonization barrier against pathogenic microorganisms. This study is aimed to observe the gastric and duodenum microflora alteration after H. pylori infection in Mongolian Gerbils model. Materials and Methods: A total of 18 Mongolian gerbils were randomly divided into two groups: control group and H. pylori group that were given H. pylori NCTC J99 strain intragastrically. After 12 weeks, H. pylori colonization was identified by rapid urease tests and bacterial culture. Indigenous microorganisms in stomach and duodenum were analyzed by culture method. Histopathologic examination of gastric and duodenum mucosa was also performed. Results: Three of eight gerbils had positive H. pylori colonization. After H. pylori infection, Enterococcus spp. and Staphylococcus aureus showed occurrences in stomach and duodenum. Lactobacillus spp. showed a down trend in stomach. The levels and localizations of Bifidobacterium spp., Bacteroides spp., and total aerobes were also modified. Bacteroides spp. significantly increased in H. pylori positive gerbils. No Enterobacteriaceae were detected. Positive colonization gerbils showed a higher histopathologic score of gastritis and a similar score of duodenitis. Conclusions: Long‐term H. pylori colonization affected the distribution and numbers of indigenous microflora in stomach and duodenum. Successful colonization caused a more severe gastritis. Gastric microenvironment may be unfit for lactobacilli fertility after long‐term H. pylori infection, while enterococci, S. aureus, bifidobacteria, and bacteroides showed their adaptations. 相似文献
1000.
Tyrosine phosphorylation of mitochondrial pyruvate dehydrogenase kinase 1 is important for cancer metabolism 总被引:1,自引:0,他引:1
Hitosugi T Fan J Chung TW Lythgoe K Wang X Xie J Ge Q Gu TL Polakiewicz RD Roesel JL Chen GZ Boggon TJ Lonial S Fu H Khuri FR Kang S Chen J 《Molecular cell》2011,44(6):864-877
Many tumor cells rely on aerobic glycolysis instead of oxidative phosphorylation for their continued proliferation and survival. Myc and HIF-1 are believed to promote such a metabolic switch by, in part, upregulating gene expression of pyruvate dehydrogenase (PDH) kinase 1 (PDHK1), which phosphorylates and inactivates mitochondrial PDH and consequently pyruvate dehydrogenase complex (PDC). Here we report that tyrosine phosphorylation enhances PDHK1 kinase activity by promoting ATP and PDC binding. Functional PDC can form in mitochondria outside of the matrix in some cancer cells and PDHK1 is commonly tyrosine phosphorylated in human cancers by diverse oncogenic tyrosine kinases localized to different mitochondrial compartments. Expression of phosphorylation-deficient, catalytic hypomorph PDHK1 mutants in cancer cells leads to decreased cell proliferation under hypoxia and increased oxidative phosphorylation with enhanced mitochondrial utilization of pyruvate and reduced tumor growth in xenograft nude mice. Together, tyrosine phosphorylation activates PDHK1 to promote the Warburg effect and tumor growth. 相似文献