全文获取类型
收费全文 | 9899篇 |
免费 | 861篇 |
国内免费 | 3篇 |
出版年
2023年 | 62篇 |
2022年 | 78篇 |
2021年 | 252篇 |
2020年 | 189篇 |
2019年 | 274篇 |
2018年 | 296篇 |
2017年 | 278篇 |
2016年 | 362篇 |
2015年 | 537篇 |
2014年 | 531篇 |
2013年 | 679篇 |
2012年 | 752篇 |
2011年 | 767篇 |
2010年 | 489篇 |
2009年 | 401篇 |
2008年 | 549篇 |
2007年 | 514篇 |
2006年 | 456篇 |
2005年 | 436篇 |
2004年 | 373篇 |
2003年 | 362篇 |
2002年 | 320篇 |
2001年 | 165篇 |
2000年 | 144篇 |
1999年 | 132篇 |
1998年 | 84篇 |
1997年 | 76篇 |
1996年 | 73篇 |
1995年 | 68篇 |
1994年 | 56篇 |
1993年 | 55篇 |
1992年 | 97篇 |
1991年 | 77篇 |
1990年 | 83篇 |
1989年 | 55篇 |
1988年 | 65篇 |
1987年 | 53篇 |
1986年 | 37篇 |
1985年 | 47篇 |
1984年 | 36篇 |
1983年 | 49篇 |
1982年 | 46篇 |
1981年 | 41篇 |
1980年 | 28篇 |
1979年 | 32篇 |
1978年 | 17篇 |
1977年 | 29篇 |
1976年 | 27篇 |
1975年 | 22篇 |
1974年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Nadine Correia Santos Patrício Soares Costa Liliana Amorim Pedro Silva Moreira Pedro Cunha Jorge Cotter Nuno Sousa 《PloS one》2015,10(4)
Here we focus on factor analysis from a best practices point of view, by investigating the factor structure of neuropsychological tests and using the results obtained to illustrate on choosing a reasonable solution. The sample (n=1051 individuals) was randomly divided into two groups: one for exploratory factor analysis (EFA) and principal component analysis (PCA), to investigate the number of factors underlying the neurocognitive variables; the second to test the “best fit” model via confirmatory factor analysis (CFA). For the exploratory step, three extraction (maximum likelihood, principal axis factoring and principal components) and two rotation (orthogonal and oblique) methods were used. The analysis methodology allowed exploring how different cognitive/psychological tests correlated/discriminated between dimensions, indicating that to capture latent structures in similar sample sizes and measures, with approximately normal data distribution, reflective models with oblimin rotation might prove the most adequate. 相似文献
2.
The major function of lactic starter cultures in cheese making is to produce lactic and other organic acids from the carbohydrates present in milk. The activity of six starter cultures consisting of two Lactococcus lactis ssp. lactis , two Lactococcus lactis ssp. lactis biovar. diacetylactis and two Leuconostoc strains, was tested by monitoring the evolution of the organic acid composition of milk by a modified HPLC method. In addition, their performance as cheese starters was also tested. The HPLC method developed proved to be a precise tool to monitor the organic acid content. Thus, it can be used to follow the fermentation ability of starter cultures, providing information about the type of fermentation. The use of any of the six starters assayed is suggested for manufacturing Afuega'l Pitu cheese. 相似文献
3.
The intensity of sperm competition is often measured using the gonadosomatic index (testes/body weight). But sperm competition could be mediated more by size of the epididymis than by size of the testicles, and little information is available on the relationship between testicular and epididymal size. We found that both organs were positively correlated in size among male rhesus macaques. Body weight accounted for over 70% of the variance in testicle size and volumetric estimates of testicle size accurately reflected testicle weight. We conclude that methods for ascertaining testicle size are accurate, but the covariation in size between testicles and epididymis will hamper understanding of the physiological mechanisms involved in sperm competition in primates. © 1993 Wiley-Liss, Inc. 相似文献
4.
5.
6.
Sonia Tarazona Pedro Furió-Tarí David Turrà Antonio Di Pietro María José Nueda Alberto Ferrer Ana Conesa 《Nucleic acids research》2015,43(21):e140
As the use of RNA-seq has popularized, there is an increasing consciousness of the importance of experimental design, bias removal, accurate quantification and control of false positives for proper data analysis. We introduce the NOISeq R-package for quality control and analysis of count data. We show how the available diagnostic tools can be used to monitor quality issues, make pre-processing decisions and improve analysis. We demonstrate that the non-parametric NOISeqBIO efficiently controls false discoveries in experiments with biological replication and outperforms state-of-the-art methods. NOISeq is a comprehensive resource that meets current needs for robust data-aware analysis of RNA-seq differential expression. 相似文献
7.
Dora E. Vega-Salas Julio A. San Martino Pedro J.I. Salas Alberto Baldi 《Differentiation; research in biological diversity》1993,54(3):131-141
Abstract. We have previously shown that an integral plasma membrane glycoprotein (AP2) is highly polarized to the apical domain in confluent Madin-Darby canine kidney (MDCK) epithelial cells. However, when the monolayers are prevented from forming intercellular contacts, approximately 60% of the AP2 cellular content is stored in the intracellular vacuolar apical compartment (VAC). In the current work we found that AP2 was present in the non-tumorigenic human mammary epithelial cell line MCF-10A. in the breast carcinoma cell lines MCF-7 and T47D, and in breast ductal carcinomas in vivo. By radioimmunoassay, an intracellular Compartment of AP2 was identified in the mammary cell lines in culture. In MCF-10A, this compartment behaved as in MDCK cells; namely it was observed only when the cells cannot form cell-cell contacts. However, in the carcinoma cell lines MCF-7 and T47D, a significant AP2 intracellular compartment was observed also under conditions permissive for the formation of intercellular contacts. These results were confirmed by immunofluorescence and immunoelectron microscopy experiments that showed VACs in MCF-7 and T47D, even in cells with extensive intercellular contacts. In MCF-7 cells, the addition of serum caused a partial decrease of the AP2 intracellular compartment. The exocytosis of VACs occurred towards the center of multi-cellular groups, forming intercellular lumens, similar to those transiently observed in MDCK cells and to structures described by others during embryo development. Altogether, these results suggest that VAC exocytosis is controlled by cell-cell contact signalling, which may be defective in carcinoma cells. 相似文献
8.
9.
10.
Escherichia coli strains harbouring pbpAts mutations are particularly sensitive to functional alterations of penicillin-binding protein 2 (PBP 2) at the initiation of growth. Shift-up to 42 degrees C results in the inability of cells to reach a steady rate of growth and division. Furthermore, a very high proportion of cells generate minicell-like structures which are pinched-off through a process requiring the activity of penicillin-binding protein 3 (PBP 3). 相似文献