全文获取类型
收费全文 | 1537篇 |
免费 | 90篇 |
专业分类
1627篇 |
出版年
2023年 | 4篇 |
2022年 | 10篇 |
2021年 | 27篇 |
2020年 | 12篇 |
2019年 | 26篇 |
2018年 | 37篇 |
2017年 | 29篇 |
2016年 | 31篇 |
2015年 | 58篇 |
2014年 | 78篇 |
2013年 | 80篇 |
2012年 | 130篇 |
2011年 | 120篇 |
2010年 | 61篇 |
2009年 | 57篇 |
2008年 | 128篇 |
2007年 | 101篇 |
2006年 | 96篇 |
2005年 | 90篇 |
2004年 | 84篇 |
2003年 | 103篇 |
2002年 | 81篇 |
2001年 | 14篇 |
2000年 | 19篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1971年 | 3篇 |
1969年 | 2篇 |
1960年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1627条查询结果,搜索用时 15 毫秒
61.
Effects of electromagnetic field emitted by cellular phones on the EEG during an auditory memory task: a double blind replication study 总被引:5,自引:0,他引:5
Krause CM Haarala C Sillanmäki L Koivisto M Alanko K Revonsuo A Laine M Hämäläinen H 《Bioelectromagnetics》2004,25(1):33-40
The effects of electromagnetic fields (EMF) emitted by cellular phones on the event related desynchronization/synchronization (ERD/ERS) of the 4-6, 6-8, 8-10, and 10-12 Hz electroencephalogram (EEG) frequency bands were studied in 24 normal subjects performing an auditory memory task. This study was a systematic replication of our previous work. In the present double blind study, all subjects performed the memory task both with and without exposure to a digital 902 MHz field in a counterbalanced order. We were not able to replicate the findings from our earlier study. All eight of the significant changes in our earlier study were not significant in the present double blind replication. Also, the effect of EMF on the number of incorrect answers in the memory task was inconsistent. We previously reported no significant effect of EMF exposure on the number of incorrect answers in the memory task, but a significant increase in errors was observed in the present study. We conclude that EMF effects on the EEG and on the performance on memory tasks may be variable and not easily replicable for unknown reasons. 相似文献
62.
Fukue Y Sato T Teranishi H Hanada R Takahashi T Nakashima Y Kojima M 《FEBS letters》2006,580(14):3485-3488
Neuromedin U (NMU), an anorexigenic peptide, was originally isolated from porcine spinal cord in 1985. As NMU is abundant in the anterior pituitary gland, we investigated the effects of NMU on gonadotropin secretion. Both NMU and its receptors, NMUR1 and NMUR2, were expressed in the pituitary gland. NMU suppressed LH and FSH releases from rat anterior pituitary cells. Moreover, NMU-deficient mice exhibit an early onset of vaginal opening. The LHbeta/FSHbeta ratio, which is an index of puberty onset, is high in young NMU-deficient mice. These results indicate that NMU suppresses gonadotropin secretion and regulates the onset of puberty. 相似文献
63.
Asakawa K Toya M Sato M Kanai M Kume K Goshima T Garcia MA Hirata D Toda T 《EMBO reports》2005,6(12):1194-1200
Bipolar microtubule attachment is central to genome stability. Here, we investigate the mitotic role of the fission yeast EB1 homologue Mal3. Mal3 shows dynamic inward movement along the spindle, initial emergence at the spindle pole body (SPB) and translocation towards the equatorial plane, followed by sudden disappearance. Deletion of Mal3 results in early mitotic delay, which is dependent on the Bub1, but not the Mad2, spindle checkpoint. Consistently, Bub1, but not Mad2, shows prolonged kinetochore localization. Double mutants between mal3 and a subset of checkpoint mutants, including bub1, bub3, mad3 and mph1, but not mad1 or mad2, show massive chromosome mis-segregation defects. In mal3bub1 mutants, both sister centromeres tend to remain in close proximity to one of the separating SPBs. Further analysis indicates that mis-segregated centromeres are exclusively associated with the mother SPB. Mal3, therefore, has a role in preventing monopolar attachment in cooperation with the Bub1/Bub3/Mad3/Mph1-dependent checkpoint. 相似文献
64.
Spatial variations of bacterio- and phytoplankton were studied in order to compare their relationship in open-sea and coastal
areas. Sampling was done quasi-synoptically south of the Antarctic Convergence in the Lazarev Sea and in the eastern part
of the Weddell Sea during austral mid-summer. Thymidine incorporation rate was on average 1.10 nmol/m3 per hour in the open sea and 4.04 nmol/m3 per hour in the coastal area, bacterial abundance was 4.44 × 1011 and 6.11 × 1011 cells/m3 and chlorophyll a (chl a) was 0.43 and 2.42 mg/m3, respectively. Thymidine incorporation rate and chl a correlated positively in both the open-sea and coastal samples. In the coastal area bacterial numbers also correlated positively
with chl a. The scale of spatial resolution was not important for detecting empirical relationships between phytoplankton and bacterioplankton
parameters. In the coastal area, the low bacterial biomass in relation to chl a concentration compared to other oceans, indicates that generalised relationships between these parameters are not valid in
Antarctic coastal waters. Grazing could not explain the discrepancy. The results suggest a strong coupling between phytoplankton
and bacterioplankton. In addition, the results suggest that the bacterial assemblage in the coastal area was psychrophilic
and well adapted to the prevailing low temperatures.
Received: 18 October 1996 / Accepted: 8 December 1996 相似文献
65.
Roseli Santos de Freitas Camila Mika Kamikawa Adriana Pardini Vicentini 《Revista iberoamericana de micología》2018,35(1):27-31
Background
Current methods for the production of Histoplasma capsulatum antigens are problematic in terms of standardization, specificity, stability, repeatability and reproducibility.Aims
In this study, we sought to optimize the methodology for producing H. capsulatum antigens, and to evaluate its applicability.Methods
Antigenic preparations obtained from 12 H. capsulatum isolates were evaluated by double immunodiffusion and immunoblotting assays against homologous and heterologous sera.Results
The evaluated and optimized protocol allowed a more stable production, as well as repeatable, reproducible, with shorter culture time and less costly. By double immunodiffusion and immunoblotting assays, the best pattern of reactivity was observed for antigens obtained with 33 days of culture from the isolates 200 and 406 against the M antigen and for the isolate 200 with 15 days against H antigen. The SDS-PAGE presented antigenic components of molecular masses between 17 and 119 kDa. The immunoblotting sensitivity was 95.5% and 100% with histoplasmosis sera from ill patients and sera from H. capsulatum infected but otherwise healthy patients, respectively, to the antigen derived from isolates 200 and 406.Conclusions
We suggest the employment of the antigen from isolate 200, with 15 or 30 days of culture, in the double immunodiffusion and immunoblotting assays due to its good ability to discriminate both sera from patients with histoplasmosis illness and histoplasmosis infection, in addition to its high specificity against heterologous sera. 相似文献66.
Akira Nakatsuma Mugiho Kaneda Hiromi Kodama Mika Morikawa Satoshi Watabe Kazunari Nakaishi Masakane Yamashita Teruki Yoshimura Toshiaki Miura Masaki Ninomiya Etsuro Ito 《PloS one》2015,10(6)
To reduce the window period between HIV-1 infection and the ability to diagnose it, a fourth-generation immunoassay including the detection of HIV-1 p24 antigen has been developed. However, because the commercially available systems for this assay use special, high-cost instruments to measure, for example, chemiluminescence, it is performed only by diagnostics companies and hub hospitals. To overcome this limitation, we applied an ultrasensitive ELISA coupled with a thio-NAD cycling, which is based on a usual enzyme immunoassay without special instruments, to detect HIV-1 p24. The p24 detection limit by our ultrasensitive ELISA was 0.0065 IU/assay (i.e., ca. 10-18 moles/assay). Because HIV-1 p24 antigen is thought to be present in the virion in much greater numbers than viral RNA copies, the value of 10-18 moles of the p24/assay corresponds to ca. 103 copies of the HIV-1 RNA/assay. That is, our ultrasensitive ELISA is chasing the detection limit (102 copies/assay) obtained by PCR-based nucleic acid testing (NAT) with a margin of only one different order. Further, the detection limit by our ultrasensitive ELISA is less than that mandated for a CE-marked HIV antigen/antibody assay. An additional recovery test using blood supported the reliability of our ultrasensitive ELISA. 相似文献
67.
Collier N Doan S Kawazoe A Goodwin RM Conway M Tateno Y Ngo QH Dien D Kawtrakul A Takeuchi K Shigematsu M Taniguchi K 《Bioinformatics (Oxford, England)》2008,24(24):2940-2941
SUMMARY: BioCaster is an ontology-based text mining system for detecting and tracking the distribution of infectious disease outbreaks from linguistic signals on the Web. The system continuously analyzes documents reported from over 1700 RSS feeds, classifies them for topical relevance and plots them onto a Google map using geocoded information. The background knowledge for bridging the gap between Layman's terms and formal-coding systems is contained in the freely available BioCaster ontology which includes information in eight languages focused on the epidemiological role of pathogens as well as geographical locations with their latitudes/longitudes. The system consists of four main stages: topic classification, named entity recognition (NER), disease/location detection and event recognition. Higher order event analysis is used to detect more precisely specified warning signals that can then be notified to registered users via email alerts. Evaluation of the system for topic recognition and entity identification is conducted on a gold standard corpus of annotated news articles. AVAILABILITY: The BioCaster map and ontology are freely available via a web portal at http://www.biocaster.org. 相似文献
68.
Tsunehito Higashi Yosuke Mai Yoichi Noya Takahiro Horinouchi Koji Terada Akimasa Hoshi Prabha Nepal Takuya Harada Mika Horiguchi Chizuru Hatate Yuji Kuge Soichi Miwa 《PloS one》2014,9(9)
Cigarette smoke consists of tar and gas phase: the latter is toxicologically important because it can pass through lung alveolar epithelium to enter the circulation. Here we attempt to establish a standard method for preparation of gas phase extract of cigarette smoke (CSE). CSE was prepared by continuously sucking cigarette smoke through a Cambridge filter to remove tar, followed by bubbling it into phosphate-buffered saline (PBS). An increase in dry weight of the filter was defined as tar weight. Characteristically, concentrations of CSEs were represented as virtual tar concentrations, assuming that tar on the filter was dissolved in PBS. CSEs prepared from smaller numbers of cigarettes (original tar concentrations ≤15 mg/ml) showed similar concentration-response curves for cytotoxicity versus virtual tar concentrations, but with CSEs from larger numbers (tar ≥20 mg/ml), the curves were shifted rightward. Accordingly, the cytotoxic activity was detected in PBS of the second reservoir downstream of the first one with larger numbers of cigarettes. CSEs prepared from various cigarette brands showed comparable concentration-response curves for cytotoxicity. Two types of CSEs prepared by continuous and puff smoking protocols were similar regarding concentration-response curves for cytotoxicity, pharmacology of their cytotoxicity, and concentrations of cytotoxic compounds. These data show that concentrations of CSEs expressed by virtual tar concentrations can be a reference value to normalize their cytotoxicity, irrespective of numbers of combusted cigarettes, cigarette brands and smoking protocols, if original tar concentrations are ≤15 mg/ml. 相似文献
69.
Murata Y Homma T Kitagawa E Momose Y Sato MS Odani M Shimizu H Hasegawa-Mizusawa M Matsumoto R Mizukami S Fujita K Parveen M Komatsu Y Iwahashi H 《Extremophiles : life under extreme conditions》2006,10(2):117-128
Adaptation to temperature fluctuation is essential for the survival of all living organisms. Although extensive research has been done on heat and cold shock responses, there have been no reports on global responses to cold shock below 10°C or near-freezing. We examined the genome-wide expression in Saccharomyces cerevisiae, following exposure to 4°C. Hierarchical cluster analysis showed that the gene expression profile following 4°C exposure from 6 to 48 h was different from that at continuous 4°C culture. Under 4°C exposure, the genes involved in trehalose and glycogen synthesis were induced, suggesting that biosynthesis and accumulation of those reserve carbohydrates might be necessary for cold tolerance and energy preservation. The observed increased expression of phospholipids, mannoproteins, and cold shock proteins (e.g., TIP1) is consistent with membrane maintenance and increased permeability of the cell wall at 4°C. The induction of heat shock proteins and glutathione at 4°C may be required for revitalization of enzyme activity, and for detoxification of active oxygen species, respectively. The genes with these functions may provide the ability of cold tolerance and adaptation to yeast cells. 相似文献
70.
Growth factor combination for chondrogenic induction from human mesenchymal stem cell 总被引:36,自引:0,他引:36
Indrawattana N Chen G Tadokoro M Shann LH Ohgushi H Tateishi T Tanaka J Bunyaratvej A 《Biochemical and biophysical research communications》2004,320(3):914-919
During the last decade, many strategies for cartilage engineering have been emerging. Stem cell induction is one of the possible approaches for cartilage engineering. The mesenchymal stem cells (MSCs) with their pluripotency and availability have been demonstrated to be an attractive cell source. It needs the stimulation with cell growth factors to make the multipluripotent MSCs differentiate into chondrogenic lineage. We have shown particular patterns of in vitro chondrogenesis induction on human bone marrow MSCs (hBMSCs) by cycling the growth factors. The pellet cultures of hBMSCs were prepared for chondrogenic induction. Growth factors: TGF-beta3, BMP-6, and IGF-1 were used in combination for cell induction. Gene expression, histology, immunohistology, and real-time PCR methods were measured on days 21 after cell induction. As shown by histology and immunohistology, the induced cells have shown the feature of chondrocytes in their morphology and extracellular matrix in both inducing patterns of combination and cycling induction. Moreover, the real-time PCR assay has shown the expression of gene markers of chondrogenesis, collagen type II and aggrecan. This study has demonstrated that cartilage tissue can be created from bone marrow mesenchymal stem cells. Interestingly, the combined growth factors TGF-beta3 and BMP-6 or TGF-beta3 and IGF-1 were more effective for chondrogenesis induction as shown by the real-time PCR assay. The combination of these growth factors may be the important key for in vitro chondrogenesis induction. 相似文献