全文获取类型
收费全文 | 179966篇 |
免费 | 6959篇 |
国内免费 | 7030篇 |
专业分类
193955篇 |
出版年
2024年 | 201篇 |
2023年 | 1254篇 |
2022年 | 2942篇 |
2021年 | 4868篇 |
2020年 | 3193篇 |
2019年 | 4016篇 |
2018年 | 14746篇 |
2017年 | 12614篇 |
2016年 | 10834篇 |
2015年 | 6379篇 |
2014年 | 7147篇 |
2013年 | 7519篇 |
2012年 | 12380篇 |
2011年 | 19712篇 |
2010年 | 15844篇 |
2009年 | 11968篇 |
2008年 | 14124篇 |
2007年 | 15078篇 |
2006年 | 3774篇 |
2005年 | 3306篇 |
2004年 | 3255篇 |
2003年 | 3102篇 |
2002年 | 2462篇 |
2001年 | 1721篇 |
2000年 | 1499篇 |
1999年 | 1430篇 |
1998年 | 826篇 |
1997年 | 913篇 |
1996年 | 822篇 |
1995年 | 775篇 |
1994年 | 679篇 |
1993年 | 599篇 |
1992年 | 700篇 |
1991年 | 572篇 |
1990年 | 462篇 |
1989年 | 338篇 |
1988年 | 295篇 |
1987年 | 232篇 |
1986年 | 185篇 |
1985年 | 210篇 |
1984年 | 131篇 |
1983年 | 135篇 |
1982年 | 56篇 |
1981年 | 23篇 |
1980年 | 21篇 |
1979年 | 18篇 |
1972年 | 246篇 |
1971年 | 274篇 |
1965年 | 13篇 |
1962年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Alireza Sharif Hamed Haddad Kashani Elahe Nasri Zahra Soleimani Mohammad Reza Sharif 《Probiotics and antimicrobial proteins》2017,9(4):380-385
Diarrhea is considered as an important cause of morbidity and mortality, even though one of the main reasons of death following diarrhea is initiated by dysentery. In recent years, the consumption of probiotics has been proposed for the treatment of infectious diarrhea. Despite most of the studies on probiotics have focused on acute watery diarrhea, few studies in the field of dysentery have found beneficial effects of probiotics. This study is a randomized double-blind clinical trial. The patients were randomly placed into control and case groups. In the intervention group, the patients received probiotics in the form of Kidilact® sachet, which contained high amounts of 7-strain friendly bacteria strains of Lactobacillus casei, Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactobacillus bulgaricus, Bifidobacterium infantis, Bifidobacterium breve, and Streptococcus thermophiles. On the other hand, the patients in the control group received placebo sachets on a daily basis for 5 days. It is notable that the treatment protocol of acute dysentery was done on both groups. The results of this study showed significant differences in the duration of blood in diarrhea between probiotic consumers (2.62 days) and the control group (3.16 days) (P value = 0.05). Additionally, significant differences in the average length of hospitalization in probiotic consumers (3.16 days) and control (3.66 days), (P value = 0.02) could be claimed that the consumption of probiotics is effective in reducing the duration of dysentery and diarrhea. The results of this study suggest that the use of probiotics can be effective in reducing the duration of blood in diarrhea. This study was also recorded in the Iran center of clinical trials registration database (IRCT2014060617985N1). 相似文献
992.
Wenchao Liu Panyu Hua Junpeng Zhang Stephen J. Rossiter Shuyi Zhang 《Conservation Genetics》2008,9(5):1341-1343
We developed nine microsatellite loci using an enriched library method from the genomic DNA of Pratt’s leaf-nosed bat (Hipposideros pratti). These loci were tested on 96 individuals sampled from Sichuan Province, China. The number of alleles per locus varied from
4 to 14. The expected and observed heterozygosity values ranged from 0.513 to 0.886 and from 0.375 to 0.966, respectively.
Three microsatellite loci departed significantly from Hardy–Weinberg equilibrium (HWE). No linkage disequilibrium was found.
These microsatellite loci will be used in studies of conservation genetics in this species. 相似文献
993.
To investigate the effects of Procambarus clarkii on macroinvertebrate diversity, we conducted a mesocosm experiment simulating small pools in rice field pads after the rice
season. We hypothesized that crayfish predation would negatively impact macroinvertebrate diversity, and the magnitude of
this impact should vary with the size of P. clarkii. We conducted a short-term mesocosm experiment to determine macroinvertebrate diversity in the presence of three size classes
and in the absence of crayfish, as well as the diet composition of crayfish from the three size classes. At the end of the
experiments, the diet of crayfish was composed of the most available taxa (Culicidae, Chironomus, Tanytarsini and Orthocladinae). These results also show evidence that, in confined areas, crayfish are important predators
of major rice pests such as rice Chironominae larvae. Macroinvertebrate diversity was negatively affected by crayfish presence,
but the effect was inversely proportional to crayfish size. The highest diversity index was obtained in the absence of P. clarkii, and juvenile crayfish significantly reduced macroinvertebrate diversity. Thus, the impact of P. clarkii on aquatic macroinvertebrates is size dependent and may be relevant in small pools formed in rice field pads from early autumn
to late winter. Overall, our findings suggest that the negative effects of P. clarkii on macroinvertebrate diversity may be particularly strong in local natural assemblages confined to puddles of water or small
ponds in wetland areas. 相似文献
994.
Gregory A Babbitt 《BMC developmental biology》2008,8(1):19
Background
The accuracy by which phenotype can be reproduced by genotype potentially is important in determining the stability, environmental sensitivity, and evolvability of morphology and other phenotypic traits. Because two sides of an individual represent independent development of the phenotype under identical genetic and environmental conditions, average body asymmetry (or "fluctuating asymmetry") can estimate the developmental instability of the population. The component of developmental instability not explained by intrapopulational differences in gene or environment (or their interaction) can be further defined as internal developmental noise. Surprisingly, developmental noise remains largely unexplored despite its potential influence on our interpretations of developmental stability, canalization, and evolvability. Proponents of fluctuating asymmetry as a bioindicator of environmental or genetic stress, often make the assumption that developmental noise is minimal and, therefore, that phenotype can respond sensitively to the environment. However, biologists still have not measured whether developmental noise actually comprises a significant fraction of the overall environmental response of fluctuating asymmetry observed within a population. 相似文献995.
Background
Many studies of biochemical networks have analyzed network topology. Such work has suggested that specific types of network wiring may increase network robustness and therefore confer a selective advantage. However, knowledge of network topology does not allow one to predict network dynamical behavior – for example, whether deleting a protein from a signaling network would maintain the network's dynamical behavior, or induce oscillations or chaos. 相似文献996.
Liu Q He X Liu Y Du B Wang X Zhang W Jia P Dong J Ma J Wang X Li S Zhang H 《Biochemical and biophysical research communications》2008,377(3):775-779
Oxidative damage is an important mechanism in X-ray-induced cell death. Radiolysis of water molecules is a source of reactive oxygen species (ROS) that contribute to X-ray-induced cell death. In this study, we showed by ROS detection and a cell survival assay that NADPH oxidase has a very important role in X-ray-induced cell death. Under X-ray irradiation, the upregulation of the expression of NADPH oxidase membrane subunit gp91phox was dose-dependent. Meanwhile, the cytoplasmic subunit p47phox was translocated to the cell membrane and localized with p22phox and gp91phox to form reactive NADPH oxidase. Our data suggest, for the first time, that NADPH oxidase-mediated generation of ROS is an important contributor to X-ray-induced cell death. This suggests a new target for combined gene transfer and radiotherapy. 相似文献
997.
Rutherford NJ Zhang YJ Baker M Gass JM Finch NA Xu YF Stewart H Kelley BJ Kuntz K Crook RJ Sreedharan J Vance C Sorenson E Lippa C Bigio EH Geschwind DH Knopman DS Mitsumoto H Petersen RC Cashman NR Hutton M Shaw CE Boylan KB Boeve B Graff-Radford NR Wszolek ZK Caselli RJ Dickson DW Mackenzie IR Petrucelli L Rademakers R 《PLoS genetics》2008,4(9):e1000193
The TAR DNA-binding protein 43 (TDP-43) has been identified as the major disease protein in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin inclusions (FTLD-U), defining a novel class of neurodegenerative conditions: the TDP-43 proteinopathies. The first pathogenic mutations in the gene encoding TDP-43 (TARDBP) were recently reported in familial and sporadic ALS patients, supporting a direct role for TDP-43 in neurodegeneration. In this study, we report the identification and functional analyses of two novel and one known mutation in TARDBP that we identified as a result of extensive mutation analyses in a cohort of 296 patients with variable neurodegenerative diseases associated with TDP-43 histopathology. Three different heterozygous missense mutations in exon 6 of TARDBP (p.M337V, p.N345K, and p.I383V) were identified in the analysis of 92 familial ALS patients (3.3%), while no mutations were detected in 24 patients with sporadic ALS or 180 patients with other TDP-43-positive neurodegenerative diseases. The presence of p.M337V, p.N345K, and p.I383V was excluded in 825 controls and 652 additional sporadic ALS patients. All three mutations affect highly conserved amino acid residues in the C-terminal part of TDP-43 known to be involved in protein-protein interactions. Biochemical analysis of TDP-43 in ALS patient cell lines revealed a substantial increase in caspase cleaved fragments, including the approximately 25 kDa fragment, compared to control cell lines. Our findings support TARDBP mutations as a cause of ALS. Based on the specific C-terminal location of the mutations and the accumulation of a smaller C-terminal fragment, we speculate that TARDBP mutations may cause a toxic gain of function through novel protein interactions or intracellular accumulation of TDP-43 fragments leading to apoptosis. 相似文献
998.
Molecular dynamics simulations employing a molecular mechanics (MM) force field and hybrid quantum mechanics (QM) and MM (QM/MM) have been carried out to investigate the product specificity and mechanism of the histone H4 lysine 20 (H4-K20) methylation by human histone lysine methyltransferase SET8. At neutral pH, the target lysine is available to only the enzyme in the protonated state. The first step in the methylation reaction must be deprotonation of the lysine target which is followed by the (+)AdoMet methylation of the neutral lysine [Enz.Lys-CH(2)-NH(3)(+).(+)AdoMet --> H(+) + Enz.Lys-CH(2)-NH(2).(+)AdoMet -->--> Enz.Lys-CH(2)-N(Me)H(2)(+).AdoHcy]. The electrostatic interactions between two positive charges on (+)AdoMet and Lys20-NH(3)(+) decrease the pK(a) of Lys20-NH(3)(+). Upon formation of Enz.Lys-NH(3)(+).(+)AdoMet, a water channel by which the proton escapes to the outer solvent phase is formed. The formation of a water channel for the escape of a proton from Lys20-N(Me)H(2)(+) in Enz.Lys20-N(Me)H(2)(+).(+)AdoMet is not formed because the methyl substituent blocks the starting of the water channel. Thus, a second methylation does not take place. The dependence of the occurrence of methyl transfer on the formation of a water channel in SET8 is in accord with our previous reports on product specificity by histone lysine monomethyltransferase SET7/9, large subunit lysine dimethyltransferase (LSMT), and viral histone lysine trimethyltransferase (vSET). The average value of the experimental DeltaG(E)() for the six lysine methyl transfer reactions catalyzed by vSET, LSMT, and SET7/9 with p53 as a substrate is 22.1 +/- 1.0 kcal/mol, and the computed average (DeltaG(C)()) is 22.2 +/- 0.8 kcal/mol. In this study, the computed free energy barrier of the methyl transfer reaction [Lys20-NH(2) + (+)AdoMet --> Lys20-N(Me)H(2)(+) + AdoHcy] catalyzed by SET8 is 20.8 kcal/mol. This is in agreement with the value of 20.6 kcal/mol calculated from the experimental rate constant (0.43 +/- 0.02 min(-1)). Our bond-order computations establish that the H4-K20 monomethylation in SET8 is a concerted linear S(N)2 displacement reaction. 相似文献
999.
Xiaomeng Yang Shuya Li Xingquan Zhao Liping Liu Yong Jiang Zixiao Li Yilong Wang Yongjun Wang 《BMC neurology》2017,17(1):207
Background
Atrial fibrillation (AF) is reported to be a less frequent cause of ischemic stroke in China than in Europe and North America, but it is not clear whether this is due to underestimation. Our aim was to define the true frequency of AF-associated stroke, to determine the yield of 6-day Holter ECG to detect AF in Chinese stroke patients, and to elucidate predictors of newly detected AF.Methods
Patients with acute ischemic stroke or transient ischemic attack (TIA) were enrolled in a prospective, multicenter cohort study of 6-day Holter monitoring within 7 days after stroke onset at 20 sites in China between 2013 and 2015. Independent predictors of newly-detected AF were determined by multivariate analysis.Results
Among 1511 patients with ischemic stroke and TIA (mean age 63 years, 33.1% women), 305 (20.2%) had either previously known (196, 13.0%) or AF newly-detected by electrocardiography (53, 3.5%) or by 6-day Holter monitoring (56/1262, 4.4%). A history of heart failure (OR?=?4.70, 95%CI, 1.64–13.5), advanced age (OR?=?1.06, 95%CI, 1.04–1.09), NIHSS at admission (OR?=?1.06, 95%CI, 1.02–1.10), blood high density lipoprotein (HDL) (OR?=?1.52, 95%CI, 1.09–2.13), together with blood triglycerides (OR?=?0.64, 95%CI, 0.45–0.91) were independently associated with newly-detected AF.Conclusions
Contrary to previous reports, AF-associated stroke is frequent (20%) in China if systemically sought. Prolonged noninvasive cardiac rhythm monitoring importantly increases AF detection in patients with recent ischemic stroke and TIA in China. Advanced age, history of heart failure, and higher admission NIHSS and higher level of HDL were independent indicators of newly-detected AF.Trial registration
NCT02156765 (June 5, 2014).1000.
Focal adhesion kinase (FAK) functions as a key enzyme in the integrin-mediated adhesion-signalling pathway. Here, we aimed to investigate the effects of FAK on adhesion of human dental pulp (HDP) cells. We transfected lentiviral vectors to silence or overexpress FAK in HDP cells ex vivo. Early cell adhesion, cell survival and focal contacts (FCs)-related proteins (FAK and paxillin) were examined. By using immunofluorescence, the formation of FCs and cytoskeleton was detected, respectively. We found that both adhesion and survival of HDP cells were suppressed by FAK inhibition. However, FAK overexpression slightly inhibited cell adhesion and exhibited no change in cell survival compared with the control. A thick rim of cytoskeleton accumulated and smaller dot-shaped FCs appeared in FAK knockdown cells. Phosphorylation of paxillin (p-paxillin) was inhibited in FAK knockdown cells, verifying that the adhesion was inhibited. Less cytoskeleton and elongated FCs were observed in FAK-overexpressed cells. However, p-paxillin had no significant difference compared with the control. In conclusion, the data suggest that FAK maintains cell adhesion, survival and cytoskeleton formation, but excessive FAK has no positive effects on these aspects. 相似文献