全文获取类型
收费全文 | 1833篇 |
免费 | 138篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 32篇 |
2021年 | 66篇 |
2020年 | 45篇 |
2019年 | 64篇 |
2018年 | 75篇 |
2017年 | 75篇 |
2016年 | 99篇 |
2015年 | 103篇 |
2014年 | 118篇 |
2013年 | 138篇 |
2012年 | 138篇 |
2011年 | 129篇 |
2010年 | 89篇 |
2009年 | 64篇 |
2008年 | 106篇 |
2007年 | 99篇 |
2006年 | 77篇 |
2005年 | 57篇 |
2004年 | 52篇 |
2003年 | 41篇 |
2002年 | 40篇 |
2001年 | 32篇 |
2000年 | 19篇 |
1999年 | 24篇 |
1998年 | 8篇 |
1997年 | 14篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 6篇 |
1982年 | 9篇 |
1980年 | 5篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1970年 | 4篇 |
1968年 | 8篇 |
1967年 | 2篇 |
1965年 | 4篇 |
1964年 | 2篇 |
排序方式: 共有1971条查询结果,搜索用时 15 毫秒
191.
Baccharis dichotoma, a new dwarf shrubby species, with small leaves and few heads, of high-altitude grasslands from southeastern Brazil, is described,
illustrated, and assigned to subgenus Baccharis. 相似文献
192.
Centeno MS Guerreiro CI Dias FM Morland C Tailford LE Goyal A Prates JA Ferreira LM Caldeira RM Mongodin EF Nelson KE Gilbert HJ Fontes CM 《FEMS microbiology letters》2006,261(1):123-132
Galactomannan hydrolysis results from the concerted action of microbial endo-mannanases, manosidases and alpha-galactosidases and is a mechanism of intrinsic biological importance. Here we report the identification of a gene cluster in the aerobic soil bacterium Cellvibrio mixtus encoding enzymes involved in the degradation of this polymeric substrate. The family 27 alpha-galactosidase, termed CmAga27A, preferentially hydrolyse galactose containing polysaccharides. In addition, we have characterized an enzyme with epimerase activity, which might be responsible for the conversion of mannose into glucose. The role of the identified enzymes in the hydrolysis of galactomannan by aerobic bacteria is discussed. 相似文献
193.
Fischer FM Borges FN Rotenberg L Latorre Mdo R Soares NS Rosa PL Teixeira LR Nagai R Steluti J Landsbergis P 《Chronobiology international》2006,23(6):1165-1179
This paper aims at identifying variables associated with inadequate work ability among nursing personnel at a public hospital, considering factors related to socio-demographic, lifestyles, working conditions, and health outcomes. A cross-sectional study was conducted in a university hospital in S?o Paulo, Brazil, as part of a larger research study on tolerance to 12 h night work. Nursing staff included registered nurses, nurse technicians, and nurse aides; in total, there were 996 healthcare workers (878 female; 118 male) at the time of the study. Some 696 workers (69.9%) of the population agreed to participate. Data collection (October 2004-July 2005) was based on a comprehensive questionnaire about living and working conditions (including incivility at work, work demands, work control, and support), mental and physical health symptoms (fatigue and sleep problems), and work ability. This report presents analyses of the adapted Brazilian version of the Work Ability Index (WAI) and associated variables. The study population worked one of the following shift schedules at this hospital: 12 h nights followed by 36 h off or 9 h or 6 h day (morning or afternoon) shifts. The mean age of the respondents was 34.9 (S.D.+/-10.4) years of age; 31.5% of the participants held two jobs. Statistical analyses using a hierarchical multiple logistic regression model were performed to evaluate the factors associated with inadequate (moderate and low scores) of the WAI. The significantly associated factors were socio-demographic (income responsibility, sole breadwinner, raising kids, age group), working conditions (thermal discomfort, organization of the workplace, and verbal abuse), and health outcomes (high body mass index, obesity, sleep problems, and fatigue). In spite of limitations of the study design, results indicate that the nursing profession is associated with stressful working conditions, contributing to inadequate WAI. This is in addition to bad living conditions and precarious work. Intervention measures, either at the workplace or at individual levels, are necessary to prevent a decrease in work ability, even in this quite young working population. 相似文献
194.
Swarça AC Fenocchio AS Cestari MM Bertollo LA Dias AL 《Cytogenetic and genome research》2006,112(3-4):325-328
The chromosomes and banding patterns of Steindachneridion sp., a large catfish (Pimelodidae), endemic to the Igua?u River, Brazil, were analyzed using conventional (C-, G-banding) and restriction enzyme banding methods. The same diploid number (2n = 56) as in other members of the genus and the family was found but the karyotype displayed an XX/XY sex chromosome system. The X chromosome was the smallest submetacentric, while the Y was the largest chromosome in the karyotype. Meiotic analysis showed 27 autosomal bivalents plus one heteromorphic XY bivalent during spermatogenesis. Sex chromosomes had no particular pattern after C-banding but G- and restriction enzyme bandings showed specific banding characteristics. The present finding represents the first report of a well-differentiated and uncommon sex chromosome system in the catfish family Pimelodidae. 相似文献
195.
Alvisi G Ripalti A Ngankeu A Giannandrea M Caraffi SG Dias MM Jans DA 《Traffic (Copenhagen, Denmark)》2006,7(10):1322-1332
The catalytic subunit of human cytomegalovirus (HCMV) DNA polymerase pUL54 is a 1242-amino-acid protein, whose function, stimulated by the processivity factor, phosphoprotein UL44 (ppUL44), is essential for viral replication. The C-terminal residues (amino acids 1220-1242) of pUL54 have been reported to be sufficient for ppUL44 binding in vitro. Although believed to be important for functioning in the nuclei of infected cells, no data are available on either the interaction of pUL54 with ppUL44 in living mammalian cells or the mechanism of pUL54 nuclear transport and its relationship with that of ppUL44. The present study examines for the first time the nuclear import pathway of pUL54 and its interaction with ppUL44 using dual color, quantitative confocal laser scanning microscopy on live transfected cells and quantitative gel mobility shift assays. We showed that of two nuclear localization signals (NLSs) located at amino acids 1153-1159 (NLSA) and 1222-1227 (NLSB), NLSA is sufficient to confer nuclear localization on green fluorescent protein (GFP) by mediating interaction with importin alpha/beta. We also showed that pUL54 residues 1213-1242 are sufficient to confer ppUL44 binding abilities on GFP and that pUL54 and ppUL44 can be transported to the nucleus as a complex. Our work thus identified distinct sites within the HCMV DNA polymerase, which represent potential therapeutic targets and establishes the molecular basis of UL54 nuclear import. 相似文献
196.
d'Avila-Levy CM Santos LO Marinho FA Dias FA Lopes AH Santos AL Branquinha MH 《Current microbiology》2006,52(6):439-444
In this study, we demonstrated that metallopeptidase inhibitors (EDTA, EGTA, and 1,10-phenanthroline) were able to arrest
Phytomonas serpens growth in distinct patterns. This parasite released exclusively metallopeptidases to the extracellular environment, whereas
in cellular extracts only cysteine peptidases were detected. In addition, an extracellular polypeptide of 60 kDa reacted in
Western blotting probed with polyclonal antibody raised against gp63 of Leishmania amazonensis. In the cellular parasite extract, this antibody recognized bands migrating at 63 and 52 kDa, which partitioned on both aqueous
and membrane-rich fractions. Flow cytometry and fluorescence microscopy analyses showed that the gp63-like molecules have
a surface location. Moreover, phospholipase C (PLC)-treated parasites reduced the number of gp63-positive cells. The anti-cross-reacting
determinant (CRD) and anti-gp63 antibodies recognized the 60-kDa band in the supernatant from PLC-treated cells, suggesting
that this protein is glycosylphosphatidylinositol-anchored to the plasma membrane. This is the first report on the presence
of gp63-like molecules in members of the Phytomonas genus. The pretreatment of the parasites with anti-gp63 antibody significantly diminished their adhesion index to explanted
salivary glands of the phytophagous insect Oncopeltus fasciatus, suggesting a potential involvement of the gp63-like molecules in the adhesive process of this plant trypanosomatid. 相似文献
197.
Oliveira MD Martins RM Matos MA Ferreira RC Dias MA Carneiro MA Junqueira AL Teles SA 《Memórias do Instituto Oswaldo Cruz》2006,101(3):251-256
In order to evaluate the seroepidemiology and response to Butang vaccine in adolescents from low income families in Central Brazil, blood samples of 664 adolescents were tested for hepatitis B surface antigen (HBsAg), hepatitis B core antibody (anti-HBc), and hepatitis B surface antibody (anti-HBs) markers, and multiple logistical regression analysis was carried out to determine variables associated with hepatitis B virus (HBV) infection markers. further, three 20 microg Butang vaccine doses were offered to all susceptible individuals (n = 304). Among those who accepted them (n = 182), the seroresponse was evaluated in 170 individuals by quantitative anti-HBs. an overall hbv prevalence of 5.9% was found: four adolescents were HBsAg positive, 24 were anti-HBc, anti-HBs-reactive, and 11 were anti-HBc only. The analyse of risk factors showed that age 16-19 years, place of birth outside Goiás, school B and body piercing were statistically associated with HBV infection markers (p < 0.05). All 170 adolescents responded to Butang, and a geometric mean titer (gmt) of 4344 mUI/ml was obtained. these results reinforce the importance of hepatitis b vaccine in adolescents despite of the hbv regional endemicity, and suggest that three doses of 20 microg of the Butang should guarantee protective anti-hbs levels to individuals at a critical time for hepatitis b acquiring such as latter adolescence and adulthood. 相似文献
198.
Dias AL Brigagão MR Colepicolo P Siqueira AM Silva EG Paula CR 《Memórias do Instituto Oswaldo Cruz》2006,101(1):107-109
Some clear dissimilarities occur among the varieties of Cryptococcus neoformans but there are few studies about the differences among individual yeast antioxidant enzymes. The total superoxide dismutase (SOD) activities and the copper, zinc-depend SOD (Cu,ZnSOD) and manganese-dependent SOD (MnSOD) isoenzymes of five reference C. neoformans strains belonged to A, B, C, AD and D serotypes (Table I) and other nine C. neoformans isolates (Table II) were determined. There were significant differences (p < 0.01 and p < 0.05) in total SOD activity among the varietie gattii (serotype C) and the other varieties. Cu,ZnSOD showed difference (p < 0.05) between A and D serotypes. These results point out a variety and serotype-independent SOD activity in C. neoformans reference strains and the other isolates that were evaluated. 相似文献
199.
Oocytes were recovered by ovum pick up (OPU) from nine pairs of monozygotic twin German Simmental cows. The hypothesis was that there is less variability between identical twins versus among non-related individuals in the variation in the recovery of oocytes by OPU and in the efficiency of in vitro embryo production. Estrous cycles were synchronized with two doses of cloprostenol, 11 days apart. Beginning 3-4 days after synchronized estrus, OPU was done twice weekly (every 3 or 4 days; total of 11 sessions). The influence of repeated OPU on estrous cyclicity was established by estrus detection, plasma progesterone concentrations, and ovarian ultrasonography. There were no differences among days of collection for the number and quality of cumulus oocyte-complexes (COCs), and rates of cleavage and blastocyst formation. A total of 1,661 COCs, including 657 (39.6%) good-quality COCs, were recovered. From 1,457 (87.7%) cultured COCs, 827 zygotes cleaved and 314 blastocysts were produced on Day 7. The total number of COCs and the blastocyst rates varied among pairs of monozygotic twins; within pairs, only slight differences were observed. In conclusion, recovery of COCs and production of embryos had substantially less variation within pairs of monozygotic twins than among non-related cattle. 相似文献
200.
Pre-mRNAs undergo splicing to remove introns, and the spliced mRNA is exported to the cytoplasm for translation. Here we investigated the mechanism for recruitment of the conserved mRNA export machinery (TREX complex) to mRNA. We show that the human TREX complex is recruited to a region near the 5' end of mRNA, with the TREX component Aly bound closest to the 5' cap. Both TREX recruitment and mRNA export require the cap, and these roles for the cap are splicing dependent. CBP80, which is bound to the cap, associates efficiently with TREX, and Aly mediates this interaction. Together, these data indicate that the CBP80-Aly interaction results in recruitment of TREX to the 5' end of mRNA, where it functions in mRNA export. As a consequence, the mRNA would be exported in a 5' to 3' direction through the nuclear pore, as observed in early electron micrographs of giant Balbiani ring mRNPs. 相似文献