全文获取类型
收费全文 | 10697篇 |
免费 | 731篇 |
国内免费 | 1篇 |
专业分类
11429篇 |
出版年
2024年 | 15篇 |
2023年 | 93篇 |
2022年 | 217篇 |
2021年 | 349篇 |
2020年 | 308篇 |
2019年 | 321篇 |
2018年 | 425篇 |
2017年 | 330篇 |
2016年 | 485篇 |
2015年 | 642篇 |
2014年 | 688篇 |
2013年 | 814篇 |
2012年 | 979篇 |
2011年 | 834篇 |
2010年 | 492篇 |
2009年 | 473篇 |
2008年 | 530篇 |
2007年 | 527篇 |
2006年 | 442篇 |
2005年 | 381篇 |
2004年 | 335篇 |
2003年 | 296篇 |
2002年 | 272篇 |
2001年 | 166篇 |
2000年 | 147篇 |
1999年 | 130篇 |
1998年 | 48篇 |
1997年 | 42篇 |
1996年 | 28篇 |
1995年 | 35篇 |
1994年 | 26篇 |
1993年 | 24篇 |
1992年 | 48篇 |
1991年 | 50篇 |
1990年 | 37篇 |
1989年 | 36篇 |
1988年 | 31篇 |
1987年 | 29篇 |
1986年 | 27篇 |
1985年 | 27篇 |
1984年 | 30篇 |
1983年 | 21篇 |
1982年 | 23篇 |
1981年 | 11篇 |
1980年 | 25篇 |
1979年 | 17篇 |
1978年 | 23篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1974年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
de Lira FA Farias Mde S de Figueiredo AF Gil Fdos S dos Santos MA Malheiros BV Ferreira JE Pinheiro JC Treu-Filho O Kondo RT 《Journal of molecular modeling》2011,17(7):1621-1624
In a previous article, we used Hartree-Fock (HF) theory to study the piezoelectricity in BaTiO3. In this paper, we applied the Douglas-Kroll-Hess second order scalar relativistic method to investigate the possible piezoelectric
properties in the perovskite YFeO3 structure, which has not yet been studied experimentally. The 30s20p13d and 31s21p17d Gaussian basis sets for the Fe (5D) and Y (2D) atoms, respectively, were built with the Generator Coordinate HF method. After contraction to [13s7p5d] and [13s8p7d],
in combination with the 20s14p/6s4p basis set for the O (3P) atom from literature, they had their quality evaluated using calculations of the total and the orbital energies for the
2FeO+1 and 1YO+1 fragments. The dipole moment, the total energy, and the total atomic charges in YFeO3 in Cs space group were calculated. The results and the analysis lead us to believe that the perovskite YFeO3 does not present piezoelectric properties. 相似文献
992.
Caleja C de Toro M Gon?alves A Themudo P Vieira-Pinto M Monteiro D Rodrigues J Sáenz Y Carvalho C Igrejas G Torres C Poeta P 《International microbiology》2011,14(1):19-24
The antibiotic resistance phenotype and genotype and the integron type were characterized in 58 Salmonella enterica isolates recovered from Bísaro pigs and wild boars (20 S. Typhimurium, 17 S. Rissen, 14 S. Enteritidis and 7 S. Havana). Most S. Typhimurium isolates (15/20 of Bísaro pigs and wild boars) showed ampicillin, chloramphenicol, streptomycin, tetracycline, sulfonamide, and amoxicillin-clavulanic acid resistances. Of the 17 S. Rissen isolates of both origins, 13 were resistant to ampicillin, tetracycline and trimethoprim-sulfamethoxazole. Among the S. Enteritidis isolates of Bísaro pigs, eight were nalidixic acid-resistant and three were sulfonamide-resistant. The tet(A) or tet(G) genes were detected in most tetracycline-resistant isolates. The intI1 gene was identified in 72.5% of S. enterica isolates in which the conserved region 3' of class 1 integrons (qacEΔ1+sul1) was also amplified, whereas none had the intI2 gene. The dfrA12+orfF+aadA2 gene cassette arrangement was found in the variable region of class 1 integrons in 14 S. Rissen isolates. Fifteen S. Typhimurium isolates had two integrons with variable regions of 1000 and 1200 bp that harbored the aadA2 and blaPSE-1 gene cassettes, respectively. In these isolates the floR and tet(G) genes were also amplified, indicative of the genomic island 1 (SGI1). Salmonella Typhimurium and S. Rissen of animal origin frequently show a multi-antimicrobial resistant phenotype, which may have implications in public health. 相似文献
993.
Barbosa LF de Souza MR Caritá RA Caputo F Denadai BS Greco CC 《Journal of strength and conditioning research / National Strength & Conditioning Association》2011,25(12):3385-3390
Barbosa, LF, de Souza, MR, Corrêa Caritá, RA, Caputo, F, Denadai, BS, and Greco, CC. Maximal lactate steady-state independent of recovery period during intermittent protocol. J Strength Cond Res 25(12): 3385-3390, 2011-The purpose of this study was to analyze the effect of the measurement time for blood lactate concentration ([La]) determination on [La] (maximal lactate steady state [MLSS]) and workload (MLSS during intermittent protocols [MLSSwi]) at maximal lactate steady state determined using intermittent protocols. Nineteen trained male cyclists were divided into 2 groups, for the determination of MLSSwi using passive (VO(2)max = 58.1 ± 3.5 ml·kg·min; N = 9) or active recovery (VO(2)max = 60.3 ± 9.0 ml·kg·min; N = 10). They performed the following tests, in different days, on a cycle ergometer: (a) Incremental test until exhaustion to determine (VO(2)max and (b) 30-minute intermittent constant-workload tests (7 × 4 and 1 × 2 minutes, with 2-minute recovery) to determine MLSSwi and MLSS. Each group performed the intermittent tests with passive or active recovery. The MLSSwi was defined as the highest workload at which [La] increased by no more than 1 mmol·L between minutes 10 and 30 (T1) or minutes 14 and 44 (T2) of the protocol. The MLSS (Passive-T1: 5.89 ± 1.41 vs. T2: 5.61 ± 1.78 mmol·L) and MLSSwi (Passive-T1: 294.5 ± 31.8 vs. T2: 294.7 ± 32.2 W; Active-T1: 304.6 ± 23.0 vs. T2: 300.5 ± 23.9 W) were similar for both criteria. However, MLSS was lower in T2 (4.91 ± 1.91 mmol·L) when compared with in T1 (5.62 ± 1.83 mmol·L) using active recovery. We can conclude that the MLSSwi (passive and active conditions) was unchanged whether recovery periods were considered (T1) or not (T2) for the interpretation of [La] kinetics. In contrast, MLSS was lowered when considering the active recovery periods (T2). Thus, shorter intermittent protocols (i.e., T1) to determine MLSSwi may optimize time of the aerobic capacity evaluation of well-trained cyclists. 相似文献
994.
Lieberman RL Culver JA Entzminger KC Pai JC Maynard JA 《Methods (San Diego, Calif.)》2011,55(4):293-302
From G protein-coupled receptors to ion channels, membrane proteins represent over half of known drug targets. Yet, structure-based drug discovery is hampered by the dearth of available three-dimensional models for this large category of proteins. Other than efforts to improve membrane protein expression and stability, current strategies to improve the ability of membrane proteins to crystallize involve examining many orthologs and DNA constructs, testing the effects of different detergents for purification and crystallization, creating a lipidic environment during crystallization, and cocrystallizing with covalent or non-covalent soluble protein chaperones with an intrinsic high propensity to crystallize. In this review, we focus on this last category, highlighting successes of crystallization chaperones in membrane protein structure determination and recent developments in crystal chaperone engineering, including molecular display to enhance chaperone crystallizability, and end with a novel generic approach in development to target any membrane protein of interest. 相似文献
995.
996.
Sotero-Caio CG de Souza MJ Cabral-de-Mello DC Brasileiro-Vidal AC Guerra M 《Cytogenetic and genome research》2011,135(2):111-117
Phosphorylation of serine 10 in histone H3 (H3S10ph) has been extensively analyzed and appears to be a conserved chromatin change associated with chromosome condensation in different eukaryotic organisms. In this work, we report the distribution of H3S10ph during meiosis in monocentric and holokinetic chromosomes of 6 insect species and in mitotic chromosomes of 7 mammalian species, aiming to investigate the labeling patterns in phylogenetically distant groups. The results indicated a very similar phosphorylation timing and distribution pattern among insects. The sex chromosomes of insects analyzed were always undercondensed and hypophosphorylated. Similarly, the micro chromosomes of the bug Pachylis aff pharaonis were also undercondensed and hypophosphorylated. Holokinetic chromosomes of bugs and monocentric chromosomes of grasshoppers and beetles displayed identical phosphorylation pattern in spite of the difference in the centromere type. Among mammals, a uniform chromosome phosphorylation was observed in marsupials, whereas bat chromosomes displayed a longitudinal banding pattern. These data indicate that, in general, the intensity of H3S10 phosphorylation in animal chromosomes is variable among the distinct chromosome types and associated with the degree of chromatin condensation at metaphase, but it may vary between different groups of animals. 相似文献
997.
Jorge C. Pereira Raquel Chaves Alexandra Leitão Domitilia Matias Henrique Guedes-Pinto 《Helgoland Marine Research》2011,65(3):361-367
The clam Ruditapes decussatus is commercially important in the south of Portugal. The random amplified polymorphic DNA (RAPD) technique was applied to
assess the genetic diversity and population structure of two Portuguese populations occurring in the Ria Formosa (Faro) and
the Ria de Alvor, respectively. Twenty-five individuals of each population were investigated by RAPD profiles. Genetic diversity
within populations, measured by the percentage of polymorphic loci (%P), varied between 68.57% (Alvor) and 73.88% (Faro). Shannon’s information index (H) and Nei’s gene diversity (h) were 0.281 and 0.176, respectively, for the Alvor population and 0.356 and 0.234 for the Faro population. Overall, genetic
variation within R. decussatus populations was high. The total genetic diversity (H
T) was explained by a low variation between populations (G
ST = 0.145), which is consistent with high gene flow (N
m = 2.9). The analysis of molecular variance (AMOVA) showed that 65% of variability is within populations and 35% between populations
(ΦPT = 0.345; P ≥ 0.001). The value of Nei’s genetic distance was 0.0881, showing a low degree of population genetic distance, despite the
different geographic origin. This is the first study on the population genetics of R. decussatus by RAPD technique. The results may be useful for restocking programs and aquaculture. 相似文献
998.
Pterodon pubescens cavities are constituted by lumen and uniseriated epithelium surrounded by multiseriate parenchyma sheath. We studied the development of secretory cavities, including the role of parenchyma sheath, using light and transmission electron microscopy. A Tunel assay was performed to verify whether programmed cell death (PCD) occurs during the process. The lumen is formed by schizogeny and lysigeny occur in later developmental stages of the secretory cavities. Ultrastructurally, epithelial cells in later developmental stages become dark and with sinuous walls; the protoplast becomes retracted and the cytoplasm shows low organelle definition. Degenerated cells are released toward the lumen. Our results showed that PCD occurs during later developmental stages of cavities and plays a critical role in functioning of these glands. New cells originated from the parenchyma sheath differentiate into secretory cells and replace those degenerated ones. This fact associated to PCD guarantees epithelium renovation during the secretory cycle and the maintenance of secretory activity of cavities. 相似文献
999.
Tuberculosis, the disease caused by Mycobacterium tuberculosis, remains a relevant public health issue. This is due mostly to the coepidemiology with HIV/AIDS, the appearance of multidrug-resistant strains globally, and failure of BCG (bacillus Calmette-Guerin) vaccination to confer complete protection. This bacterium was one of the first to have its genome sequenced, yet over a decade after the release of the genomic information, the characterization of its phylogenetic tree and of different strain variants inside this species revealed that much is still needed to be done for a full understanding of the M. tuberculosis genome and proteome. Current methods using LC-MS/MS and hybrid high-resolution mass spectrometers can identify 2400-2800 proteins of the 4000 predicted genes in M. tuberculosis. In this article, we review relevant details of this bacterium's pathology and immunology, describing articles where proteomics helped the community to tackle some of the organism biology, from understanding strain diversity, cellular structure composition, immunogenicity, and host-pathogen interactions. Finally, we will discuss the challenges yet to be fulfilled in order to better characterize M. tuberculosis by proteomics. 相似文献
1000.