全文获取类型
收费全文 | 83840篇 |
免费 | 4875篇 |
国内免费 | 9篇 |
专业分类
88724篇 |
出版年
2023年 | 471篇 |
2021年 | 1050篇 |
2020年 | 916篇 |
2019年 | 979篇 |
2018年 | 2259篇 |
2017年 | 1957篇 |
2016年 | 2681篇 |
2015年 | 3538篇 |
2014年 | 3656篇 |
2013年 | 4806篇 |
2012年 | 5639篇 |
2011年 | 4990篇 |
2010年 | 3255篇 |
2009年 | 2474篇 |
2008年 | 3982篇 |
2007年 | 3763篇 |
2006年 | 3743篇 |
2005年 | 3126篇 |
2004年 | 3132篇 |
2003年 | 2778篇 |
2002年 | 2558篇 |
2001年 | 2085篇 |
2000年 | 1957篇 |
1999年 | 1514篇 |
1998年 | 695篇 |
1997年 | 511篇 |
1996年 | 551篇 |
1995年 | 486篇 |
1992年 | 948篇 |
1991年 | 848篇 |
1990年 | 836篇 |
1989年 | 908篇 |
1988年 | 743篇 |
1987年 | 778篇 |
1986年 | 699篇 |
1985年 | 761篇 |
1984年 | 637篇 |
1983年 | 554篇 |
1979年 | 675篇 |
1978年 | 491篇 |
1977年 | 494篇 |
1975年 | 591篇 |
1974年 | 631篇 |
1973年 | 601篇 |
1972年 | 553篇 |
1971年 | 501篇 |
1970年 | 540篇 |
1969年 | 616篇 |
1968年 | 575篇 |
1967年 | 487篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
943.
944.
Carlos Landa-Solís Julio Granados-Montiel Anell Olivos-Meza Carmina Ortega-Sánchez Mónica Cruz-Lemini Cecilia Hernández-Flores María Eugenia Chang-González Ricardo Gómez García Brenda Olivos-Díaz María Cristina Velasquillo-Martínez Carlos Pineda Clemente Ibarra 《Cell and tissue banking》2016,17(1):137-145
Mobilized peripheral blood (MPB) bone marrow cells possess the potential to differentiate into a variety of mesenchymal tissue types and offer a source of easy access for obtaining stem cells for the development of experimental models with applications in tissue engineering. In the present work, we aimed to isolate by magnetic activated cell sorting CD90+ cells from MPB by means of the administration of Granulocyte-Colony Stimulating Factor and to evaluate cell proliferation capacity, after thawing of the in vitro culture of this population of mesenchymal stem cells (MSCs) in sheep. We obtained a median of 8.2 ± 0.6 million of CD90+ cells from the 20-mL MPB sample. After thawing, at day 15 under in vitro culture, the mean CD90+ cells determined by flow cytometry was 92.92 ± 1.29 % and cell duplication time determined by crystal violet staining was 47.59 h. This study describes for the first time the isolation, characterization, and post-in vitro culture thawing of CD90+ MSCs from mobilized peripheral blood in sheep. This population can be considered as a source of MSCs for experimental models in tissue engineering research. 相似文献
945.
Emma del Carmen Macías-Cortés Lidia Llanes-González Leopoldo Aguilar-Faisal Juan Asbun-Bojalil 《PloS one》2015,10(3)
Background
Perimenopausal period refers to the interval when women''s menstrual cycles become irregular and is characterized by an increased risk of depression. Use of homeopathy to treat depression is widespread but there is a lack of clinical trials about its efficacy in depression in peri- and postmenopausal women. The aim of this study was to assess efficacy and safety of individualized homeopathic treatment versus placebo and fluoxetine versus placebo in peri- and postmenopausal women with moderate to severe depression.Methods/Design
A randomized, placebo-controlled, double-blind, double-dummy, superiority, three-arm trial with a 6 week follow-up study was conducted. The study was performed in a public research hospital in Mexico City in the outpatient service of homeopathy. One hundred thirty-three peri- and postmenopausal women diagnosed with major depression according to DSM-IV (moderate to severe intensity) were included. The outcomes were: change in the mean total score among groups on the 17-item Hamilton Rating Scale for Depression, Beck Depression Inventory and Greene Scale, after 6 weeks of treatment, response and remission rates, and safety. Efficacy data were analyzed in the intention-to-treat population (ANOVA with Bonferroni post-hoc test).Results
After a 6-week treatment, homeopathic group was more effective than placebo by 5 points in Hamilton Scale. Response rate was 54.5% and remission rate, 15.9%. There was a significant difference among groups in response rate definition only, but not in remission rate. Fluoxetine-placebo difference was 3.2 points. No differences were observed among groups in the Beck Depression Inventory. Homeopathic group was superior to placebo in Greene Climacteric Scale (8.6 points). Fluoxetine was not different from placebo in Greene Climacteric Scale.Conclusion
Homeopathy and fluoxetine are effective and safe antidepressants for climacteric women. Homeopathy and fluoxetine were significantly different from placebo in response definition only. Homeopathy, but not fluoxetine, improves menopausal symptoms scored by Greene Climacteric Scale.Trial Registration
ClinicalTrials.gov NCT01635218Protocol Publication
http://www.trialsjournal.com/content/14/1/105. 相似文献946.
Infectious bursal disease virus (IBDV), a member of the Birnaviridae family, is a major avian pathogen responsible for an immunosuppressive disease affecting juvenile chickens. The IBDV genome is formed by two dsRNA segments. The largest one harbors two partially overlapping open reading frames encoding a non-structural polypeptide, known as VP5, and a large polyprotein, respectively. VP5 is non-essential for virus replication. However, it plays a major role in IBDV pathogenesis. VP5 accumulates at the plasma membrane (PM) of IBDV-infected cells. We have analyzed the mechanism underlying the VP5 PM targeting. Updated topological prediction algorithm servers fail to identify a transmembrane domain within the VP5 sequence. However, the VP5 polycationic C-terminal region, harboring three closely spaced patches formed by two or three consecutive basic amino acid residues (lysine or arginine), might account for its PM tropism. We have found that mutations, either C-terminal VP5 deletions or replacement of basic amino acids by alanine residues, that reduce the electropositive charge of the VP5 C-terminus abolish PM targeting. Lipid overlay assays performed with an affinity-purified Flag-tagged VP5 (FVP5) protein version show that this polypeptide binds several phosphoinositides (PIP), exhibiting a clear preference for monophosphate species. Experiments performed with FVP5 mutant proteins lacking the polycationic domain demonstrate that this region is essential for PIP binding. Data gathered with IBDV mutants expressing C-terminal deleted VP5 polypeptides generated by reverse genetics demonstrate that the VP5-PIP binding domain is required both for its PM targeting in infected cells, and for efficient virus dissemination. Data presented here lead us to hypothesize that IBDV might use a non-lytic VP5-dependent cell-to-cell spreading mechanism. 相似文献
947.
José Miguel Gasulla Fernando Escaso Iván Narváez Francisco Ortega José Luis Sanz 《PloS one》2015,10(12)
A new styracosternan ornithopod genus and species is here described based on a partial postcranial skeleton and an associated dentary tooth of a single specimen from the Arcillas de Morella Formation (Early Cretaceous, late Barremian) at the Morella locality, (Castellón, Spain). Morelladon beltrani gen. et sp. nov. is diagnosed by eight autapomorphic features. The set of autapomorphies includes: very elongated and vertical neural spines of the dorsal vertebrae, midline keel on ventral surface of the second to fourth sacral vertebrae restricted to the anterior half of the centrum, a posterodorsally inclined medial ridge on the postacetabular process of the ilium that meets its dorsal margin and distal end of the straight ischial shaft laterally expanded, among others. Phylogenetic analyses reveal that the new Iberian form is more closely related to its synchronic and sympatric contemporary European taxa Iguanodon bernissartensis and Mantellisaurus atherfieldensis, known from Western Europe, than to other Early Cretaceous Iberian styracosternans (Delapparentia turolensis and Proa valdearinnoensis). The recognition of Morelladon beltrani gen. et sp. nov. indicates that the Iberian Peninsula was home to a highly diverse medium to large bodied styracosternan assemblage during the Early Cretaceous. 相似文献
948.
949.
The genus Impatiens (Balsaminaceae) includes three widespread species in the Czech Republic, central Europe: the native I. noli-tangere, and two invasive species, I. parviflora and I. glandulifera, differing in the dynamics of invasion. They all occur in similar habitats and share basic life-history characteristics, which make them a suitable model for studying species traits associated with invasiveness. In this study we investigated differences in habitat requirements of these Impatiens species, their coexistence and short-term population dynamics in the field. We established 84 1 × 1 m permanent plots in five localities where all three species co-occurred. In each plot vascular plant species were determined, their cover estimated and all individuals of Impatiens species counted. Site characteristics including tree canopy cover, soil moisture, nitrogen and carbon content, and slope were measured directly. Nutrients, light, humidity and soil reaction were estimated using Ellenberg indicator values. The presence of I. noli-tangere was strongly correlated with high soil moisture, that of I. parviflora with high tree canopy cover and low soil moisture. Impatiens glandulifera exhibited a unimodal response to tree canopy cover, avoiding both very shaded and fully open sites. The current-year abundances of all species were negatively related to those of congeneric species. These results suggest that the coexistence of Impatiens species in the same habitat is due to microsite differentiation. Further spread of I. glandulifera to new habitats, and reduction of the native I. noli-tangere niche, can be expected in areas where the latter species co-occurs with competitively strong invasive congeners. 相似文献
950.
Miguel Arredondo María José Mendiburo Sebastián Flores Steven T. Singleton Michael D. Garrick 《Biometals》2014,27(1):115-123
Divalent Metal Transporter 1 (DMT1) is an apical Fe transporter in the duodenum and is involved in endosomal Fe export. Four protein isoforms have been described for DMT1, two from mRNA with an iron responsive element (IRE) and two from mRNA without it. The sets of two begin in exon 1A or 2. We have characterized copper transport using mouse 2/?IRE DMT1 during regulated ectopic expression. HEK293 cells carrying a TetR:Hyg element were stably transfected with pDEST31 containing a 2/?IRE construct. 64Cu1+ incorporation in doxycycline treated cells exhibited 18.6 and 30.0-fold increases in Cu content, respectively when were exposed to 10 and 100 μM of extracellular Cu. Cu content was ~4-fold above that of parent cells or cells carrying just the vector. 64Cu uptake in transfected cells pre-incubated with 5 μM of Cu-His revealed a Vmax and Km of 11.98 ± 0.52 pmol mg protein?1 min?1 and 2.03 ± 0.03 μM, respectively. Doxycycline-stimulated Cu uptake was linear with time. The rates of apical Cu uptake decreased and transepithelial transport increased when intracellular Cu increased. The optimal pH for Cu transport was 6.5; uptake of Cu was temperature dependent. Silver does not inhibit Cu uptake in cells carrying the vector. In conclusion, Cu uptake in HEK293 cells that over-expressed the 2/?IRE isoform of DMT1 transporter supports our earlier contention that DMT1 transports Cu as Cu1+. 相似文献