全文获取类型
收费全文 | 14691篇 |
免费 | 1088篇 |
国内免费 | 34篇 |
专业分类
15813篇 |
出版年
2023年 | 103篇 |
2022年 | 189篇 |
2021年 | 334篇 |
2020年 | 253篇 |
2019年 | 355篇 |
2018年 | 454篇 |
2017年 | 380篇 |
2016年 | 533篇 |
2015年 | 675篇 |
2014年 | 733篇 |
2013年 | 1017篇 |
2012年 | 1283篇 |
2011年 | 1670篇 |
2010年 | 920篇 |
2009年 | 903篇 |
2008年 | 694篇 |
2007年 | 631篇 |
2006年 | 588篇 |
2005年 | 469篇 |
2004年 | 503篇 |
2003年 | 445篇 |
2002年 | 421篇 |
2001年 | 279篇 |
2000年 | 295篇 |
1999年 | 211篇 |
1998年 | 129篇 |
1997年 | 110篇 |
1996年 | 87篇 |
1995年 | 66篇 |
1994年 | 69篇 |
1993年 | 57篇 |
1992年 | 117篇 |
1991年 | 85篇 |
1990年 | 92篇 |
1989年 | 60篇 |
1988年 | 62篇 |
1987年 | 71篇 |
1986年 | 58篇 |
1985年 | 60篇 |
1984年 | 37篇 |
1983年 | 35篇 |
1982年 | 30篇 |
1980年 | 22篇 |
1975年 | 21篇 |
1974年 | 14篇 |
1973年 | 15篇 |
1972年 | 15篇 |
1971年 | 16篇 |
1970年 | 15篇 |
1969年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Suzanne Camus Sergio Menéndez Kenneth Fernandes Nelly Kua Geng Liu Dimitris P. Xirodimas David P. Lane Jean-Christophe Bourdon 《Cell cycle (Georgetown, Tex.)》2012,11(8):1646-1655
The discovery that the single p53 gene encodes several different p53 protein isoforms has initiated a flurry of research into the function and regulation of these novel p53 proteins. Full-length p53 protein level is primarily regulated by the E3-ligase Mdm2, which promotes p53 ubiquitination and degradation. Here, we report that all of the novel p53 isoforms are ubiquitinated and degraded to varying degrees in an Mdm2-dependent and -independent manner, and that high-risk human papillomavirus can degrade some but not all of the novel isoforms, demonstrating that full-length p53 and the p53 isoforms are differentially regulated. In addition, we provide the first evidence that Mdm2 promotes the NEDDylation of p53β. Altogether, our data indicates that Mdm2 can distinguish between the p53 isoforms and modify them differently. 相似文献
2.
We perform first principles total energy calculations to investigate the atomic structures of the adsorption of phenol (C6H5OH) on hexagonal boron nitride (BN) sheets. Calculations are done within the density functional theory as implemented in the
DMOL code. Electron-ion interactions are modeled according to the local-spin-density-approximation (LSDA) method with the
Perdew-Wang parametrization. Our studies take into account the hexagonal h-BN sheets and the modified by defects d-BN sheets.
The d-BN sheets are composed of one hexagon, three pentagons and three heptagons. Five different atomic structures are investigated:
parallel to the sheet, perpendicular to the sheet at the B site, perpendicular to the sheet at the N site, perpendicular to
the central hexagon and perpendicular to the B-N bond (bridge site). To determine the structural stability we apply the criteria
of minimum energy and vibration frequency. After the structural relaxation phenol molecules adsorb on both h-BN and d-BN sheets.
Results of the binding energies indicate that phenol is chemisorbed. The polarity of the system increases as a consequence
of the defects presence which induces transformation from an ionic to covalent bonding. The elastic properties on the BN structure
present similar behavior to those reported in the literature for graphene. 相似文献
3.
E. Molina Grima J. A. Sánchez Pérez F. García Camacho F. G. Acién Fernández J. M. Fernández Sevilla F. Valdés Sanz 《Biotechnology letters》1994,16(10):1035-1040
Summary Eicosapentaenoic acid (EPA) volumetric productivity from an outdoor chemostat culture ofPhaeodactylum tricornutum UTEX 640 in a 50-l tubular photobioreactor varies with dilution rate, reaching a maximum of 47.8 mg l–1 d–1 at D=0.36 d–1. Continuous culture at high dilution rates' is proposed as the most adequate operating mode to maximize polyunsaturated fatty acid production. 相似文献
4.
5.
C López-Otin A O Grubb E Méndez 《Biochemical and biophysical research communications》1983,117(1):202-209
An apparently novel human plasma and urinary protein of low molecular weight was isolated from several highly purified preparations of protein HC by gel chromatography and high voltage electrophoresis with a yield of about 8 mg/g. The protein has a molecular weight of about 20,000, neutral electrophoretic mobility at pH 6.5 and a high content of half-cystine. It is associated with a yellow-brown chromophore like protein HC and could be demonstrated in all investigated preparations of isolated human, rabbit and guinea-pig protein HC and alpha 1-microglobulin. 相似文献
6.
Thea Kristiansen Jens‐Christian Svenning Wolf L. Eiserhardt Dennis Pedersen Hans Brix Søren Munch Kristiansen Maria Knadel César Grández Henrik Balslev 《Journal of Biogeography》2012,39(7):1318-1332
Aim It is a central issue in ecology and biogeography to understand what governs community assembly and the maintenance of biodiversity in tropical rain forest ecosystems. A key question is the relative importance of environmental species sorting (niche assembly) and dispersal limitation (dispersal assembly), which we investigate using a large dataset from diverse palm communities. Location Lowland rain forest, western Amazon River Basin, Peru. Methods We inventoried palm communities, registering all palm individuals and recording environmental conditions in 149 transects of 5 m × 500 m. We used ordination, Mantel tests and indicator species analysis (ISA) to assess compositional patterns, species responses to geographical location and environmental factors. Mantel tests were used to assess the relative importance of geographical distance (as a proxy for dispersal limitation) and environmental differences as possible drivers of dissimilarity in palm species composition. We repeated the Mantel tests for subsets of species that differ in traits of likely importance for habitat specialization and dispersal (height and range size). Results We found a strong relationship between compositional dissimilarity and environmental distance and a weaker but also significant relationship between compositional dissimilarity and geographical distance. Consistent with expectations, relationships with environmental and geographical distance were stronger for understorey species than for canopy species. Geographical distance had a higher correlation with compositional dissimilarity for small‐ranged species compared with large‐ranged species, whereas the opposite was true for environmental distance. The main environmental correlates were inundation and soil nutrient levels. Main conclusions The assembly of palm communities in the western Amazon appears to be driven primarily by species sorting according to hydrology and soil, but with dispersal limitation also playing an important role. The importance of environmental characteristics and geographical distance varies depending on plant height and geographical range size in agreement with functional predictions, increasing our confidence in the inferred assembly mechanisms. 相似文献
7.
Francisco Gutirrez‐Corchero M. Victoria Arruga Lourdes Sanz Cristina García M. Angeles Hernndez Francisco Campos 《Molecular ecology resources》2002,2(1):75-77
FTA® cards were used for long‐term storage of avian blood samples. Blood DNA was extracted by a simple method and used in PCR for sex identification of adult and nestling Great Grey Shrikes Lanius excubitor. 相似文献
8.
Sandra L. Almeyda Zambrano Eben N. Broadbent Sam Shanee Noga Shanee Anneke Deluycker Michael Steinberg Scott A. Ford Alma Hernndez Jaramillo Robin Fernandez‐Hilario Carolina Lagos Castillo Angelica M. Almeyda Zambrano 《American journal of primatology》2019,81(8)
Habitat loss is one of the main threats to wildlife. Therefore, knowledge of habitat use and preference is essential for the design of conservation strategies and identification of priority sites for the protection of endangered species. The yellow‐tailed woolly monkey (Lagothrix flavicauda Humboldt, 1812), categorized as Critically Endangered on the IUCN Red List, is endemic to montane forests in northern Peru where its habitat is greatly threatened. We assessed how habitat use and preference in L. flavicauda are linked to forest structure and composition. The study took place near La Esperanza, in the Amazonas region, Peru. Our objective was to identify characteristics of habitat most utilized by L. flavicauda to provide information that will be useful for the selection of priority sites for conservation measures. Using presence records collected from May 2013 to February 2014 for one group of L. flavicauda, we classified the study site into three different use zones: low‐use, medium‐use, and high‐use. We assessed forest structure and composition for all use zones using 0.1 ha Gentry vegetation transects. Results show high levels of variation in plant species composition across the three use zones. Plants used as food resources had considerably greater density, dominance, and ecological importance in high‐use zones. High‐use zones presented similar structure to medium‐ and low‐use zones; thus it remains difficult to assess the influence of forest structure on habitat preference. We recommend focusing conservation efforts on areas with a similar floristic composition to the high‐use zones recorded in this study and suggest utilizing key alimentation species for reforestation efforts. 相似文献
9.
A González-Fernández J Sans P Aller C de la Torre 《Cell biology international reports》1985,9(3):237-243
Bromosubstitution for most of the S period in synchronous populations of Allium cepa L. meristematic cells resulted in a delay in the late S-G2 transition point where protein synthesis is needed for later mitotic entrance to occur. This retardation in the position of the transition point was not accompanied by the expected delay in the entrance into mitosis, suggesting that such protein synthesis is a requisite, but not a timer for prophase triggering. 相似文献
10.