全文获取类型
收费全文 | 7517篇 |
免费 | 1018篇 |
国内免费 | 1080篇 |
出版年
2024年 | 10篇 |
2023年 | 192篇 |
2022年 | 161篇 |
2021年 | 278篇 |
2020年 | 391篇 |
2019年 | 406篇 |
2018年 | 409篇 |
2017年 | 389篇 |
2016年 | 367篇 |
2015年 | 370篇 |
2014年 | 445篇 |
2013年 | 724篇 |
2012年 | 371篇 |
2011年 | 354篇 |
2010年 | 324篇 |
2009年 | 377篇 |
2008年 | 390篇 |
2007年 | 389篇 |
2006年 | 364篇 |
2005年 | 329篇 |
2004年 | 273篇 |
2003年 | 217篇 |
2002年 | 228篇 |
2001年 | 220篇 |
2000年 | 177篇 |
1999年 | 171篇 |
1998年 | 128篇 |
1997年 | 126篇 |
1996年 | 99篇 |
1995年 | 96篇 |
1994年 | 105篇 |
1993年 | 96篇 |
1992年 | 81篇 |
1991年 | 72篇 |
1990年 | 63篇 |
1989年 | 53篇 |
1988年 | 38篇 |
1987年 | 38篇 |
1986年 | 35篇 |
1985年 | 28篇 |
1984年 | 55篇 |
1983年 | 20篇 |
1982年 | 36篇 |
1981年 | 24篇 |
1980年 | 25篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1973年 | 7篇 |
排序方式: 共有9615条查询结果,搜索用时 15 毫秒
51.
Clinal variation was observed at the aspartate aminotransferase-2 (AAT-2) locus in the marine fish Cynoscion nebulosus (Cuvier) inhabiting the bays and estuaries of the Texas and northern Mexico Gulf coasts. Frequency of the AAT-2(80) allele increased from 0.9% at Sabine Lake, Texas to 17.1% at Rio Soto La Marina, Mexico. A statistically significant correlation existed in the frequency of this allele with degrees north latitude and west longitude. This information, if properly incorporated into a comprehensive enhancement programme, could facilitate supplemental stocking success. 相似文献
52.
53.
Marine ecosystems are complex adaptive systems with physical and biological processes operating on multiple spatial and temporal scales. Here, we present an operational regional indicator for California's continental shelf system and investigate its skill in predicting a variety of biological responses across trophic levels. This updated Multivariate Ocean Climate Indicator (MOCI) version 2 includes data that are readily available from the Internet so the indicator can be automatically updated and shared regularly. MOCIv.2 is a simplified version of MOCIv.1, but it captures ocean-climate variability similarly. MOCIv.2 illustrates all major ENSO events that occurred over the past 25 years as well as the phasing and magnitude of the most recent North Pacific marine heat wave, dubbed ‘The Blob’. It also shows differences in the magnitude and timing of ocean-climate variability in different regions off California. MOCIv.2 has skill in nowcasting marine ecosystem dynamics, from zooplankton to top predators, and therefore may be useful in establishing bio-physical relationships important to ecosystem-based fisheries and wildlife management in California. 相似文献
54.
55.
Distribution of microaerophilic bacteria through the oxic-anoxic transition zone of lagoon sediments
In marine sediments, where soluble gases diffuse only very slightly, many organisms struggle for molecular oxygen. Microaerophilic bacteria, able to grow at reduced pO2 between 0.2 and 12%, have an advantage. Distribution of aerobes, microaerophiles and anaerobes was compared with the oxygen gradient in seawater and sediment samples collected in a northern Mediterranean lagoon. In the near bottom seawater and in the 0–10 mm upperlayer of sediment, the microaerophilic counts were less than 1% of aerobe densities. In the 10–15 mm zone, these two groups were equivalent in density (1 × 105 cells ml–1). As expected, the microaerophiles took advantage of their low oxygen tension requirements in the subsurface sediments, between the well aerated zone (0–5 mm depth) and the low redox potential zone. Then, beyond a depth of 20 mm, the anaerobes prevailed in this sandy clay. 相似文献
56.
基于4种生态位模型的金钱松潜在适生区预测 总被引:2,自引:0,他引:2
金钱松(Pseudolarix amabilis)是我国特有孑遗植物,为国家II级保护植物。基于4种生态位模型(GARP、Bioclim、Domain和Maxent)预测金钱松潜在适生区,采用受试者工作特征曲线(Receiver Operating Characteristic,ROC)和Kappa统计量检验模型的预测效果。预测结果表明金钱松在浙江西北部、安徽南部、湖北南部、湖南北部以及江西北部表现为高度适生,并以这些地带为中心向外延伸至北纬24.43°-33.35°和东经106.41°-123.42°之间,4种模型预测结果的受试者工作特征曲线下面积(Area under recriver operating characteristic curve,AUC)平均值均大于0.9,Kappa平均值亦大于0.75,精度较高。通过"刀切法"分析得出年均温是预测金钱松潜在适生区的关键影响因子,可能为当前金钱松分布格局形成的决定因素。模拟金钱松在末次盛冰期和2070年气候条件下的分布,结果表明其分布格局随气候变化由"南扩北缩"变为"南缩北扩",未来分布面积将大幅减小,气候变化是导致其"南缩北扩"的主要驱动因子。建议在当前金钱松高适分布区域内(江西铜鼓县、湖南张家界和衡阳)建立自然保护区或种子园,并在未来气候条件下高适分布区域内(如安徽北部、河南南部、湖北东南部等地)通过人工引种辅助金钱松的北向迁移。 相似文献
57.
《Bioscience, biotechnology, and biochemistry》2013,77(4):567-571
Casein was conjugated with dextran and galactomannan in a controlled dry state at a relative humidity of 79% and at 60°C for 24 hr. The covalent attachment of polysaccharides to casein was confirmed by SDS-PAGE and HPLC. The emulsifying activity of the casein-dextran and casein-galactomannan conjugates was 1.5 times higher than that of casein. The emulsion stability of the casein-dextran and casein-galactomannan conjugates was 10 times higher than that of casein. The improvement in these emulsifying properties reached a steady state when the conjugation of casein with polysaccharide was done for 24 hr in a controlled dry state, suggesting the rapid formation of conjugates through a Maillard reaction in the case of casein. Compared to commercial emulsifiers, the casein-polysaccharide conjugates showed better emulsifying properties in acidic and high-salt concentration systems. 相似文献
58.
《Journal of receptor and signal transduction research》2013,33(4):202-208
The evidence for the existence of receptor heteromers opens up a new field for a better understanding of neural transmission. Based on our theory, we have discovered main triplets of amino acid residues in cell-adhesion receptors of marine sponges, which appear also as homologies in several dopamine D2 receptor heteromers of human brain. The obtained results probably mean a general molecular mechanism for receptor–receptor interactions in heteromers originated from the lowest animals (marine sponges). 相似文献
59.
60.
María A. Ruvira Teresa LucenaMaría J. Pujalte David R. ArahalM. Carmen Macián 《Systematic and applied microbiology》2013
A facultatively anaerobe, moderately halophilic, Gram-negative, filamentous, non motile and unpigmented bacterium, designated M30T, was isolated from coastal Mediterranean Sea water in Valencia, Spain. Phylogenetic analysis based on 16S rRNA sequences placed this strain in the phylum “Bacteroidetes” with Marinifilum fragile JC2469T as its closest relative with 97% sequence similarity. Average nucleotide identity (ANI) values between both strains were far below the 95% threshold value for species delineation (about 89% using BLAST and about 90% using MUMmer). A comprehensive polyphasic study, including morphological, biochemical, physiological, chemotaxonomic and phylogenetic data, confirmed the independent species status of strain M30T within the genus Marinifilum, for which the name Marinifilum flexuosum sp. nov. is proposed. The type strain of Marinifilum flexuosum is M30T (=CECT 7448T = DSM 21950T). 相似文献