全文获取类型
收费全文 | 8834篇 |
免费 | 201篇 |
国内免费 | 1篇 |
出版年
2021年 | 53篇 |
2020年 | 52篇 |
2019年 | 58篇 |
2018年 | 105篇 |
2017年 | 79篇 |
2016年 | 145篇 |
2015年 | 162篇 |
2014年 | 190篇 |
2013年 | 328篇 |
2012年 | 480篇 |
2011年 | 1065篇 |
2010年 | 513篇 |
2009年 | 529篇 |
2008年 | 235篇 |
2007年 | 261篇 |
2006年 | 257篇 |
2005年 | 231篇 |
2004年 | 188篇 |
2003年 | 229篇 |
2002年 | 184篇 |
2001年 | 137篇 |
2000年 | 127篇 |
1999年 | 109篇 |
1998年 | 53篇 |
1992年 | 131篇 |
1991年 | 147篇 |
1990年 | 102篇 |
1989年 | 125篇 |
1988年 | 134篇 |
1987年 | 137篇 |
1986年 | 137篇 |
1985年 | 143篇 |
1984年 | 117篇 |
1983年 | 95篇 |
1982年 | 50篇 |
1979年 | 115篇 |
1978年 | 79篇 |
1977年 | 78篇 |
1976年 | 73篇 |
1975年 | 100篇 |
1974年 | 150篇 |
1973年 | 124篇 |
1972年 | 132篇 |
1971年 | 121篇 |
1970年 | 139篇 |
1969年 | 140篇 |
1968年 | 110篇 |
1967年 | 117篇 |
1966年 | 90篇 |
1965年 | 77篇 |
排序方式: 共有9036条查询结果,搜索用时 953 毫秒
951.
The mammalian olfactory cortex is a complex structure located along the rostro-caudal extension of the ventrolateral prosencephalon, which is divided into several anatomically and functionally distinct areas: the anterior olfactory nucleus, piriform cortex, olfactory tubercle, amygdaloid olfactory nuclei, and the more caudal entorhinal cortex. Multiple forebrain progenitor domains contribute to the cellular diversity of the olfactory cortex, which is invaded simultaneously by cells originating in distinct germinal areas in the dorsal and ventral forebrain. Using a combination of dye labeling techniques, we identified two novel areas that contribute cells to the developing olfactory cortices, the septum and the ventral pallium, from which cells migrate along a radial and then a tangential path. We characterized these cell populations by comparing their expression of calretinin, calbindin, reelin and Tbr1 with that of other olfactory cell populations. 相似文献
952.
Soybean meal (SBM) is an important protein source in animal feed. However, the levels of SBM inclusion are restricted in some animal species by the presence of antinutritional factors (ANFs), including non-starch polysaccharides (NSPs) and α-galactosides (GOSs). The aim of this study was to reduce the soybean meal NSPs and GOSs by solid-state fermentation (SSF) using a combination of cellulolytic bacteria isolated from different environments (termites, earthworms, corn silage and bovine ruminal content). To analyse the key enzymatic activities, the isolates were grown in minimal media containing NSPs extracted from SBM. The selected bacterial strains belonged to the genera Streptomyces, Cohnella and Cellulosimicrobium. SSF resulted in a reduction of nearly 24% in the total NSPs, 83% of stachyose and 69% of raffinose and an increase in the protein content. These results suggest that cellulolytic bacteria-based SSF processing facilitates SBM nutritional improvement. In addition, the use of fermented SBM in animal diets can be recommended. 相似文献
953.
Emmanuel Grellety Susan Shepherd Thomas Roederer Mahamane L. Manzo St��phane Doyon Eric-Alain Ategbo Rebecca F. Grais 《PloS one》2012,7(9)
Background
Previous studies have shown the benefits of ready-to-use supplementary food (RUSF) distribution in reducing the incidence and prevalence of severe acute malnutrition.Methods and Findings
To compare the incidence of wasting, stunting and mortality between children aged 6 to 23 mo participating and not participating in distributions of RUSF, we implemented two exhaustive prospective cohorts including all children 60 cm to 80 cm, resident in villages of two districts of Maradi region in Niger (n = 2238). Villages (20) were selected to be representative of the population. All registered children were eligible for the monthly distributions between July and October 2010. Age, sex, height, weight, and Mid-Upper Arm Circumference (MUAC) were measured at baseline and two weeks after each distribution; the amount and type of distribution and the amount shared and remaining were also assessed. We compared the incidence of wasting, stunting, and mortality among children participating in the distribution (intervention) of RUSF versus children not participating in the distribution (comparison). The absolute rate of wasting was 4.71 events per child-year (503 events/106.59 child-year) in the intervention group and 4.98 events per child-year (322 events/64.54 child-year) in the comparison group. The intervention group had a small but higher weight-for-length Z-score gain (−0.2z vs. −0.3z) and less loss of MUAC than the comparison group (−2.8 vs. −4.0 mm). There was no difference in length gain (2.7 vs. 2.8 cm). Mortality was lower for children whose households received the intervention than those who did not (adjusted HR 0.55, 95% CI: 0.32–0.98).Conclusions
Short-term distribution with RUSF for children 6 to 23 months improve the nutritional status of children at risk for malnutrition. Fewer children who participated in the RUSF distribution died than those who did not. 相似文献954.
955.
956.
957.
Background
Retrospective single center natural history studies have shown that times to reach disability milestones and ages at which they are reached are similar in primary (PPMS) and secondary (SPMS) progressive multiple sclerosis suggesting that they may be phenotypic variations of the same disease.Objective
Here we compared longitudinal disease activity in SPMS and PPMS in the context of international multicenter clinical trials.Methods
We analyzed all objective outcome measures that were systematically collected over 2 years for all subjects randomized to placebo arms in one SPMS and one PPMS clinical trial over the last decade. Conventional and exploratory definitions of clinical disease activity were used. Disease activity was analyzed in 3 different categories intermittent activity, progression, and improvement. Conventional MRI measures and one patient reported outcome measure of quality of life were included when available for comparison. Heat maps were drawn for all results followed by hierarchical clustering.Results
There were 101 outcome variables from 206 SPMS subjects and 79 outcome variables from 135 PPMS subjects. The comparison revealed that SPMS and PPMS subjects exhibited similar disease activity over 2 years in all but two of the variables in common worsening in the EDSS sensory system was more common in PPMS while worsening on the 9 hole PEG was more common in SPMS. Intermittent activity was the most common pattern of disease activity in SPMS and PPMS. Clinical worsening and improvement occurred at similar frequency in both.Conclusion
Longitudinal disease activity was nearly identical in SPMS and PPMS subjects in the context of the two multicenter international clinical trials we examined. 相似文献958.
959.
Xinhui Wang Marinus J. C. Eijkemans Jacco Wallinga Giske Biesbroek Krzysztof Trzciński Elisabeth A. M. Sanders Debby Bogaert 《PloS one》2012,7(11)
To understand the role of human microbiota in health and disease, we need to study effects of environmental and other epidemiological variables on the composition of microbial communities. The composition of a microbial community may depend on multiple factors simultaneously. Therefore we need multivariate methods for detecting, analyzing and visualizing the interactions between environmental variables and microbial communities. We provide two different approaches for multivariate analysis of these complex combined datasets: (i) We select variables that correlate with overall microbiota composition and microbiota members that correlate with the metadata using canonical correlation analysis, determine independency of the observed correlations in a multivariate regression analysis, and visualize the effect size and direction of the observed correlations using heatmaps; (ii) We select variables and microbiota members using univariate or bivariate regression analysis, followed by multivariate regression analysis, and visualize the effect size and direction of the observed correlations using heatmaps. We illustrate the results of both approaches using a dataset containing respiratory microbiota composition and accompanying metadata. The two different approaches provide slightly different results; with approach (i) using canonical correlation analysis to select determinants and microbiota members detecting fewer and stronger correlations only and approach (ii) using univariate or bivariate analyses to select determinants and microbiota members detecting a similar but broader pattern of correlations. The proposed approaches both detect and visualize independent correlations between multiple environmental variables and members of the microbial community. Depending on the size of the datasets and the hypothesis tested one can select the method of preference. 相似文献
960.