全文获取类型
收费全文 | 4551篇 |
免费 | 363篇 |
国内免费 | 98篇 |
专业分类
5012篇 |
出版年
2024年 | 5篇 |
2023年 | 85篇 |
2022年 | 120篇 |
2021年 | 86篇 |
2020年 | 109篇 |
2019年 | 158篇 |
2018年 | 197篇 |
2017年 | 159篇 |
2016年 | 163篇 |
2015年 | 200篇 |
2014年 | 399篇 |
2013年 | 440篇 |
2012年 | 313篇 |
2011年 | 445篇 |
2010年 | 420篇 |
2009年 | 301篇 |
2008年 | 224篇 |
2007年 | 214篇 |
2006年 | 229篇 |
2005年 | 213篇 |
2004年 | 111篇 |
2003年 | 81篇 |
2002年 | 52篇 |
2001年 | 36篇 |
2000年 | 24篇 |
1999年 | 32篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 9篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 33篇 |
1984年 | 23篇 |
1983年 | 6篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 10篇 |
1973年 | 7篇 |
排序方式: 共有5012条查询结果,搜索用时 15 毫秒
51.
Many attempts on optimization of sorghum [Sorghum bicolor (L.)
Moench] tissue culture induction media have been made, but the culture system
remains with some bottlenecks compared to that of other crops. This study aimed
at assessing the suitability of various induction media to produce embryogenic
callus (yellow and friable) with high induction rates and reduced phenolic
exudation. The six culture medium modifications: 3 based on Murashige and
Skoog (MS) medium and one each based on Chu N6, Gamborg B5 and 190-2
media respectively were applied in the culture of mature embryos from 10
sorghum genotypes. Although there was a genotype influence on the attainment
of a yellow callus, friability of the callus was determined to be dependent on the
culture medium and not the genotype. Half strength MS medium with 0.2 mg/l
2,4-D with 2.8 g/l Gelrite® as the gelling agent modified with 1.0 g/l KH2PO4,
1.0 g/l L-proline, 1.0 g/l L-asparagine and 0.16 mg/l CuSO4·5H2O (type E) was
found to be the most effective resulting in about 60% yellow coloured callus
induction with 25% friability. Addition of CuSO4·5H2O, KH2PO4, L-proline and
L-asparagine significantly reduced the phenolic production. Half strength MS
medium was observed to contribute to quality callus production when compared
to full strength MS media modified with the compounds. The half strength MS
medium was also observed to suppress phenolic production. Medium 190-2
produced the highest regeneration frequency (40%) among the 3-regeneration
media tested. The results provide information on a suitable sorghum callus
induction medium necessary for embryogenesis. 相似文献
52.
Cha IS Kwon J Park SH Nho SW Jang HB Park SB del Castillo CS Hikima J Aoki T Jung TS 《Journal of Proteomics》2012,75(17):5166-5175
The proteomic response to bacterial infection in a teleost fish (Paralichthys olivaceus) infected with Streptococcus parauberis was analyzed using label-free protein quantitation coupled with LC-MS(E) tandem mass spectrometry. A total of 82 proteins from whole kidney, a major lymphoid organ in this fish, were found to be differentially expressed between healthy and diseased fish analyzed 6, 24, 72 and 120 h post-infection. Among the differentially expressed proteins, those involved in mediating immune responses (e.g., heat shock proteins, cathepsins, goose-type lysozyme and complement components) were most significantly up-regulated by infection. In addition, cell division cycle 48 (CDC48) and calreticulin, which are associated with cellular recovery and glycoprotein synthesis, were up-regulated in the universal protein group, whereas the other proteins in that group were down-regulated. There was continuous activation of expression of immune-associated proteins during infection, but there was also loss of expression of proteins not involved in immune function. We expect that our findings regarding immune response at the protein level would offer new insight into the systemic response to bacterial infection of a major immune organ in teleost fish. 相似文献
53.
大花栀子植物挥发物成分测定及其日变化分析 总被引:1,自引:0,他引:1
为探究大花栀子植物挥发物成分组成及其一天内早、中、晚的差异,采用热脱附气质联用技术对其进行香气成分的分析。结果表明:全天从其花朵中共鉴定出62种成分,主要为萜烯类、酯类、醇类物质,且不同时间其成分差异显著,如早、中、晚3个时间段,β-蒎烯相对含量分别为1.93%、1.69%、8.81%,顺式-β-罗勒烯分别为28.22%、4.35%、16.47%。3-蒈烯(3.45%)、异丁子香酚(0.21%)等只在早上检出;月桂烯(0.38%)、伞花烃(2.46%)等只在晚上检出;芳樟醇、金合欢烯等在早上和午间两个时间段相对含量较高,而在晚上却未检测出。从植物VOCs角度结合其日变化动态,为大花栀子园林配置及其综合开发利用提供理论依据。 相似文献
54.
《Saudi Journal of Biological Sciences》2021,28(10):5609-5616
The hydroalcoholic extract (MIT) of Micromeria imbricata (Forssk.) growing in Saudi Arabia in addition to the chloroform (MIC) and n-butanol (MIB) fractions were investigated for the first time using UPLC-ESI-MS/MS. The analysis revealed the tentative identification of fifty-eight compounds including three organic acids, twenty-five phenolic compounds, three coumarins, two anthocyanins, twenty-one flavonoids, three terpenes, and one miscellaneous. Moreover, the therapeutic potential of M. imbricata (MIT) and its fractions (MIC and MIB) were determined by in vitro evaluation of their cytotoxic, antioxidant, and anti-obesity characteristics. The MIT extract showed the highest phenolic (125.23 ± 0.87 mg gallic acid equivalent/100 gm extract) and flavonoid (112.24 ± 2.45 mg quercetin equivalent/100 gm extract) contents followed by n-butanol and chloroform fractions. The MIT extract revealed a potent cytotoxic activity against HepG-2 (Hepatocellular carcinoma) and MCF-7 (Breast carcinoma) with IC50 28.5 ± 2.0 and 35.2 ± 1.2 µg/mL, respectively. Additionally, the tested hydroalcoholic extract exhibited a significant DPPH scavenging activity with SC50 28.4 ± 1.2 µg/mL and a remarkable lipase inhibitory activity with IC50 54.2 ± 1.2 µg/mL. In conclusion, the current study presents the first insights into the phytochemical constituents and pharmacological properties of M. imbricata extract and its chloroform and n-butanol fractions. The results revealed that M. imbricata hydroalcoholic extract might be a prolific source of bioactive constituents with potent antioxidant, cytotoxic and anti-obesity potential. It might be a natural alternative therapy and nutritional strategy for obesity treatment. 相似文献
55.
Systems pathology analysis identifies neurodegenerative nature of age‐related vitreoretinal interface diseases 下载免费PDF全文
Aging is a phenomenon that is associated with profound medical implications. Idiopathic epiretinal membrane (iEMR) and macular hole (MH) are the major vision‐threatening vitreoretinal diseases affecting millions of aging people globally, making these conditions an important public health issue. iERM is characterized by fibrous tissue developing on the surface of the macula, which leads to biomechanical and biochemical macular damage. MH is a small breakage in the macula and is associated with many ocular conditions. Although several individual factors and pathways are suggested, a systems pathology level understanding of the molecular mechanisms underlying these disorders is lacking. Therefore, we performed mass spectrometry‐based label‐free quantitative proteomics analysis of the vitreous proteomes from patients with iERM and MH to identify the key proteins, as well as the multiple interconnected biochemical pathways, contributing to the development of these diseases. We identified a total of 1,014 unique proteins, many of which are linked to inflammation and the complement cascade, revealing the inflammation processes in retinal diseases. Additionally, we detected a profound difference in the proteomes of iEMR and MH compared to those of diabetic retinopathy with macular edema and rhegmatogenous retinal detachment. A large number of neuronal proteins were present at higher levels in the iERM and MH vitreous, including neuronal adhesion molecules, nervous system development proteins, and signaling molecules, pointing toward the important role of neurodegenerative component in the pathogenesis of age‐related vitreoretinal diseases. Despite them having marked similarities, several unique vitreous proteins were identified in both iERM and MH, from which candidate targets for new diagnostic and therapeutic approaches can be provided. 相似文献
56.
Yavuz Bülent Köse Gökalp İşcan Fatih Göger Gülşen Akalın Betül Demirci Kemal Hüsnü Can Başer 《化学与生物多样性》2016,13(10):1369-1379
The genus Centaurea L. is one of the largest and important genera of Asteraceae family. Centaurea species have been widely used as herbal remedies in folk medicine for their antidandruff, antidiarrheic, antirheumatic, anti‐inflammatory, choleretic, diuretic, digestive, stomachic, astringent, antipyretic, cytotoxic, and antibacterial properties. Centaurea baseri Kose & Alan is a recently described local endemic species in Turkey and this is the first study on the chemical composition and bioactivity of its hydrodistilled essential oil and the crude extract. According to chromatospectral analysis, hexadecanoic acid (42.3%), nonacosane (8.2%), and heptacosane (8.0%) were the main compounds of the essential oil, while 16 compounds were determined in the MeOH extract using LC/MS. Furthermore, antimicrobial, antioxidant, and cytotoxic effects of the essential oil and the extract were evaluated in comparison with the standard agents. The extract showed strong antifungal effect against Candida utilis at the concentration of 60 μg/ml (MIC) where the EO showed growth inhibition at the concentration of 47.00 μg/ml (MIC) against pathogen Bacillus cereus. Both the essential oil and the extract did not show any selective antioxidant properties. The extract showed remarkably selective cytotoxic properties against MCF‐7, PANC‐1, A549, and C6 glioma cells. 相似文献
57.
《MABS-AUSTIN》2013,5(6):1036-1044
Cysteine-conjugated antibody-drug conjugates (ADCs) are manufactured using controlled partial reduction and conjugation chemistry with drug payloads that typically occur in intervals of 0, 2, 4, 6, and 8. Control of heterogeneity is of particular importance to the quality of ADC product because drug loading and distribution can affect the safety and efficacy of the ADC. Liquid chromatography ultra-violet (LC-UV)-based methods can be used to acquire the drug distribution profiles of cysteine-conjugated ADCs when analyzed using hydrophobic interaction chromatography (HIC). However, alternative analysis techniques are often required for structural identification when conjugated drugs do not possess discrete ultra-violet absorbance properties for precise assessment of the drug-to-antibody ratio (DAR). In this study, multidimensional chromatography was used as an efficient method for combining non-compatible techniques, such as HIC, with analysis by mass spectrometry (LC/LC/QTOF-MS) for rapid on-line structural elucidation of species observed in HIC distribution profiles of cysteine-conjugated ADCs. The methodology was tested using an IgG1 mAb modified by cysteine conjugation with a non-toxic drug mimic. Structural elucidation of peaks observed in the HIC analysis (1st dimension) were successfully identified based on their unique sub-unit masses via mass spectrometry techniques once dissociation occurred under denaturing reversed phase conditions (2nd dimension). Upon identification, the DAR values were determined to be 2.83, 4.44, and 5.97 for 3 drug load levels (low-, medium-, and high-loaded ADC batches), respectively, based on relative abundance from the LC-UV data. This work demonstrates that multidimensional chromatography coupled with MS, provides an efficient approach for on-line biotherapeutic characterization to ensure ADC product quality. 相似文献
58.
《Free radical research》2013,47(10):1291-1295
AbstractBackground. Measurement of urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) has recently become more popular as a means of assessing oxidative stress in the human body. The aim of this study is to compare the levels of urine 8-OHdG in patients with type 2 diabetes with and without nephropathy and to evaluate its role as a biochemical marker for distinguishing these patients from healthy and patients without complications. Methods. For this purpose, 52 patients with type 2 diabetes mellitus (32 with nephropathy (DMN), 20 without nephropathy (DM)) and 20 healthy control subjects (C) were included in this study. The urine concentrations of 8-OHdG were measured by modified LC-MS/MS method and compared with the first morning voiding urine albumin/creatinine ratio (UACR) and HbA1c values of the same patients. Results. The concentrations of urine 8-OHdG in DMN and DM patients were higher than those of the control subjects (3.47?±?0.94, 2.92?±?1.73, 2.1?±?0.93 nmol/mol creatinine, respectively). But there was no statistical difference between DMN and DM (p =?0.115). There is significant correlation between urinary 8-OHdG and UACR (r =?0.501, p <?0.001). According to ROC analysis, the AUC value of HbA1c was higher than the value of the AUC of 8-OHdG (0.882 and 0.771, respectively). Conclusions. This study shows that the urine 8-OHdG levels increase in diabetic patients. However, urinary 8-OHdG is not a useful clinical marker, compared with UACR, to predict the development of diabetic nephropathy in diabetic patients. 相似文献
59.
Most methods of analyzing intracellular metabolites require extraction of metabolites from the cells. A concern in these methods is underestimation of metabolite levels due to incomplete extraction. In comparing extraction methods, then, it would seem that the best method for extracting a particular metabolite is the one that gives the largest yield. In extracting Escherichia coli with different methanol:water mixtures, we observed that >or=50% water gave an increased yield of nucleosides and bases compared with 相似文献
60.
The citrus fruit proteome: insights into citrus fruit metabolism 总被引:1,自引:0,他引:1
Fruit development and ripening are key processes in the production of the phytonutrients that are essential for a balanced diet and for disease prevention. The pathways involved in these processes are unique to plants and vary between species. Climacteric fruit ripening, especially in tomato, has been extensively studied; yet, ripening of non-climacteric fruit is poorly understood. Although the different species share common pathways; developmental programs, physiological, anatomical, biochemical composition and structural differences must contribute to the operation of unique pathways, genes and proteins. Citrus has a non-climacteric fruit ripening behavior and has a unique anatomical fruit structure. For the last few years a citrus genome-wide ESTs project has been initiated and consists of 222,911 clones corresponding to 19,854 contigs and 37,138 singletons. Taking advantage of the citrus database we analyzed the citrus proteome. Using LC-MS/MS we analyzed soluble and enriched membrane fractions of mature citrus fruit to identify the proteome of fruit juice cells. We have identified ca. 1,400 proteins from these fractions by searching NCBI-nr (green plants) and citrus ESTs databases, classified these proteins according to their putative function and assigned function according to known biosynthetic pathways. 相似文献