全文获取类型
收费全文 | 13887篇 |
免费 | 1734篇 |
国内免费 | 704篇 |
专业分类
16325篇 |
出版年
2025年 | 95篇 |
2024年 | 377篇 |
2023年 | 487篇 |
2022年 | 670篇 |
2021年 | 828篇 |
2020年 | 873篇 |
2019年 | 1014篇 |
2018年 | 807篇 |
2017年 | 658篇 |
2016年 | 597篇 |
2015年 | 710篇 |
2014年 | 1245篇 |
2013年 | 1176篇 |
2012年 | 743篇 |
2011年 | 636篇 |
2010年 | 471篇 |
2009年 | 605篇 |
2008年 | 535篇 |
2007年 | 513篇 |
2006年 | 484篇 |
2005年 | 391篇 |
2004年 | 317篇 |
2003年 | 327篇 |
2002年 | 233篇 |
2001年 | 217篇 |
2000年 | 169篇 |
1999年 | 150篇 |
1998年 | 125篇 |
1997年 | 105篇 |
1996年 | 93篇 |
1995年 | 83篇 |
1994年 | 70篇 |
1993年 | 56篇 |
1992年 | 60篇 |
1991年 | 45篇 |
1990年 | 51篇 |
1989年 | 46篇 |
1988年 | 29篇 |
1987年 | 32篇 |
1986年 | 15篇 |
1985年 | 35篇 |
1984年 | 38篇 |
1983年 | 24篇 |
1982年 | 30篇 |
1981年 | 18篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 4篇 |
1974年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
SNUFER is a software for the automatic localization and generation of tables used for the presentation of single nucleotide polymorphisms (SNPs). After input of a fasta file containing the sequences to be analyzed, a multiple sequence alignment is generated using ClustalW ran inside SNUFER. The ClustalW output file is then used to generate a table which displays the SNPs detected in the aligned sequences and their degree of similarity. This table can be exported to Microsoft Word, Microsoft Excel or as a single text file, permitting further editing for publication. The software was written using Delphi 7 for programming and FireBird 2.0 for sequence database management. It is freely available for noncommercial use and can be downloaded from http://www.heranza.com.br/bioinformatica2.htm. 相似文献
73.
In order to obtain direct information of stimulus dynamics perceived by a male moth under field conditions a portable device was constructed which enables continuous recording of responses from individual pheromone receptors. The device is suitable for tip recording by means of micro-knives as well as for recording with tungsten electrodes making it applicable for a wide range of insects. A micro thermistor air velocity sensor is placed within 2 mm from the preparation to record the momentary air flow. The signal conditioning electronic circuits are battery powered, and the signals can be stored on a portable tape recorder. Field recordings were made from individual male antennal pheromone receptors ofAegeria myopaeformis andAdoxophyes orana. In all recordings the instantaneous firing frequency of the receptor cells was strongly modulated by the air velocity. Analysis of the data may provide information about the average pheromone concentration and the fine structure of pheromone plumes under various conditions. 相似文献
74.
Atomic force microscopy was used to image single-stranded DNA (ssDNA) adsorbed on mica modified by Mg(2+), by 3-aminopropyltriethoxysilane or on modified highly oriented pyrolytic graphite (HOPG). ssDNA molecules on mica have compact structures with lumps, loops and super twisting, while on modified HOPG graphite ssDNA molecules adopt a conformation without secondary structures. We have shown that the immobilization of ssDNA under standard conditions on modified HOPG eliminates intramolecular base-pairing, thus this method could be important for studying certain processes involving ssDNA in more details. 相似文献
75.
We examined, using a Western blot technique, the contents and compositions of a specific neuronal protein, NCAM, and of an
astrocyte marker, GFAP, in the hippocampus and cortex of rats with streptozotocin (STZ)-induced diabetes and compared these
indices with those in control (intact) animals and STZ-diabetic rats treated with melatonin. Behavioral cognitive indices
manifested in the passive avoidance test (PAT) and Morris water maze (MWM) learning performance were also estimated in the
above groups of animals. As was found, STZ-diabetic rats demonstrated clear cognitive deficits according to the values of
the retention latency in the PAT and time of reaching the escape platform in the MWM performance. In these animals, the GFAP
content was elevated, and the amount of degraded products of this protein increased, as compared with the control. Simultaneously,
considerable down-regulation of the NCAM expression and modifications of NCAM isoform composition were found in diabetic animals.
In addition, significantly increased levels of lipid peroxidation (according to the amounts of malondialdehyde + 4-hydroxyalkenals)
were measured in the cortex and hippocampus of rats with stable diabetic hyperglycemia. All the above-mentioned shifts were
significantly smoothed or even nearly completely compensated in the case of treatment of STZ-diabetic rats with melatonin
(10 mg/kg per day). The role of diabetes-related changes in the amount and composition of specific neural and glial proteins
in the development of cognitive deficits, the involvement of oxidative stress in the mechanisms of the respective shifts,
and possible mechanisms of the neuroprotective effect of melatonin with respect to diabetes-related pathological biochemical
and behavioral shifts are discussed.
Neirofiziologiya/Neurophysiology, Vol. 40, No. 2, pp. 105–111, March–April, 2008. 相似文献
76.
Michael A. Samaan Stacie I. Ringleb Sebastian Y. Bawab Eric K. Greska Joshua T. Weinhandl 《Computer methods in biomechanics and biomedical engineering》2018,21(4):344-358
The effects of ACL-reconstruction on lower extremity joint mechanics during performance of the Star Excursion Balance Test (SEBT) and Single Leg Hop (SLH) are limited. The purpose of this study was to determine if altered lower extremity mechanics occur during the SEBT and SLH after ACL-reconstruction. One female Division I collegiate athlete performed the SEBT and SLH tasks, bilaterally, both before ACL injury and 27 months after ACL-reconstruction. Maximal reach, hop distances, lower extremity joint kinematics and moments were compared between both time points. Musculoskeletal simulations were used to assess muscle force production during the SEBT and SLH at both time points. Compared to the pre-injury time point, SEBT reach distances were similar in both limbs after ACL-reconstruction except for the max anterior reach distance in the ipsilateral limb. The athlete demonstrated similar hop distances, bilaterally, after ACL-reconstruction compared to the pre-injury time point. Despite normal functional performance during the SEBT and SLH, the athlete exhibited altered lower extremity joint mechanics during both of these tasks. These results suggest that measuring the maximal reach and hop distances for these tasks, in combination with an analysis of the lower extremity joint mechanics that occur after ACL-reconstruction, may help clinicians and researchers to better understand the effects of ACL-reconstruction on the neuromuscular system during the SEBT and SLH. 相似文献
77.
David R. Abbott Robert T. Abbott Stephen D. Jenson G. Chris Fillmore Kojo S. J. Elenitoba-Johnson Megan S. Lim 《Journal of Hematopathology》2009,2(2):113-119
Overexpression of Bcl-2 protein occurs via both t(14;18)-dependent and independent mechanisms and contributes to the survival and chemoresistance of non-Hodgkin lymphomas. HA14–1 is a nonpeptidic organic small molecule, which has been shown to inhibit the interaction of Bcl-2 with Bax, thereby interfering with the antiapoptotic function of Bcl-2. In this study, we sought to determine the in vitro efficacy of HA14–1 as a therapeutic agent for non-Hodgkin lymphomas expressing Bcl-2. Assessment of cell viability demonstrated that HA14–1 induced a dose- (IC50 = 10 μM) and time-dependent growth inhibition of a cell line (SudHL-4) derived from a t(14;18)-positive, Bcl-2-positive, non-Hodgkin lymphoma. HA14–1 effectively induced apoptosis via a caspase 3-mediated pathway but did not affect either the p38 MAPK or p44/42 MAPK pathways. Western blot analyses of Bcl-2 family proteins and other cell cycle-associated proteins were performed to determine the molecular sequelae of HA14–1-induced apoptosis. The results show down-regulation of Mcl-1 but up-regulation of p27kip1, Bad, Bcl-xL, and Bcl-2 proteins, without change in Bax levels during HA14–1-mediated apoptosis. Our findings further elucidate the cellular mechanisms accompanying Bcl-2 inhibition and demonstrate the potential of Bcl-2 inhibitors as therapeutic agents for the treatment of non-Hodgkin lymphomas. 相似文献
78.
AbstractKrishna Godavari (KG) basin, located in the eastern continental margin of India, is a geological region well known for the abundance of economically important minerals. However, less is known about the microbial ecology of its subsurface sediments. The present study is the first report on the comprehensive culture-independent census of bacterial communities of deep subsurface of KG basin and their relationship with the geochemical environment. Elemental and mineralogical characterization of the sediments highlighted the presence of carbon and nitrogen deprived conditions along with the abundance of metalliferous minerals, especially rich in valuable elements like zirconium, vanadium, cesium, and rare earth elements. Diversity analysis based on Illumina MiSeq high-throughput sequencing platform revealed the predominance of Firmicutes (44.24%), Proteobacteria (34.17%), Bacteroidetes (15.18%), and Actinobacteria (3.81%) in the deep subsurface of this basin. ‘Abundant’ and ‘rare’ sub-communities analysis indicated that a large number of phyla like Acidobacteria, Armatimonadetes, Chloroflexi, and Deinococcus-Thermus were exclusively present as a rare community. Statistical analyses demonstrated that geochemical parameters, especially depth, pH, and metal content, showed significant influence on the microbial community structure. The present study should help future investigations for microbial mediated sustainable utilization of mineral-rich sediments of the region. 相似文献
79.
Losses of proteolytic peptides during extraction and/or purification procedures succeeding in-gel or in-solution digests of proteins frequently occur in the course of protein identification investigations. In order to overcome this disadvantage, the method of in-capillary digest was developed: native proteins were incubated in the presence of endoproteases in the electrospray capillary and the resulting peptides were analyzed by nanoelectrospray-mass spectrometry during the ongoing proteolysis. In-capillary digest of apomyglobin by use of trypsin in a molar ratio of 25:1 yielded complete degradation already after 15 min. The sequence coverage based on formation of molecular ions was 100% and peptide ions could be fragmented by collision-induced dissociation and sequenced. When myoglobin was incubated in the electrospray capillary with trypsin in a molar ratio of 500:1, a clear shift from molecular ions and miscleaved peptide ions to the expected final tryptic peptide ions was observed over a 2 h period. The peptide spectra obtained from tryptic in-capillary proteolysis of bovine serum albumin and apotransferrin, respectively, gave rise to sequence coverages of more than 40% for both proteins. The data obtained from the peptide maps as well as from collision-induced dissociation (CID) of selected peptides were more than sufficient for protein identification by database searches. An elephant milk protein preparation was used to demonstrate the application of in-capillary proteolysis on protein mixtures. Tryptic digest, simultaneous analysis of the proteolytic peptides by use of CID, and subsequent sequencing allowed the identification of lactoferrin, alphas1-casein, beta-casein, delta-casein, and kappa-casein by homology search. 相似文献
80.