全文获取类型
收费全文 | 36406篇 |
免费 | 3090篇 |
国内免费 | 3196篇 |
专业分类
42692篇 |
出版年
2024年 | 108篇 |
2023年 | 533篇 |
2022年 | 1167篇 |
2021年 | 1920篇 |
2020年 | 1294篇 |
2019年 | 1560篇 |
2018年 | 1474篇 |
2017年 | 1117篇 |
2016年 | 1533篇 |
2015年 | 2261篇 |
2014年 | 2693篇 |
2013年 | 2785篇 |
2012年 | 3382篇 |
2011年 | 2943篇 |
2010年 | 1803篇 |
2009年 | 1538篇 |
2008年 | 1979篇 |
2007年 | 1666篇 |
2006年 | 1446篇 |
2005年 | 1215篇 |
2004年 | 1056篇 |
2003年 | 895篇 |
2002年 | 827篇 |
2001年 | 673篇 |
2000年 | 542篇 |
1999年 | 578篇 |
1998年 | 360篇 |
1997年 | 314篇 |
1996年 | 353篇 |
1995年 | 277篇 |
1994年 | 330篇 |
1993年 | 209篇 |
1992年 | 288篇 |
1991年 | 252篇 |
1990年 | 223篇 |
1989年 | 144篇 |
1988年 | 125篇 |
1987年 | 97篇 |
1986年 | 80篇 |
1985年 | 94篇 |
1984年 | 68篇 |
1983年 | 65篇 |
1982年 | 53篇 |
1981年 | 32篇 |
1980年 | 30篇 |
1979年 | 39篇 |
1978年 | 25篇 |
1977年 | 26篇 |
1975年 | 28篇 |
1973年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Mutations in the conserved C-terminal sequence in thyroid hormone receptor dissociate hormone-dependent activation from interference with AP-1 activity. 总被引:4,自引:2,他引:2 下载免费PDF全文
13.
14.
Lexical gap in cQA search, resulted by the variability of languages, has been recognized as an important and widespread phenomenon. To address the problem, this paper presents a question reformulation scheme to enhance the question retrieval model by fully exploring the intelligence of paraphrase in phrase-level. It compensates for the existing paraphrasing research in a suitable granularity, which either falls into fine-grained lexical-level or coarse-grained sentence-level. Given a question in natural language, our scheme first detects the involved key-phrases by jointly integrating the corpus-dependent knowledge and question-aware cues. Next, it automatically extracts the paraphrases for each identified key-phrase utilizing multiple online translation engines, and then selects the most relevant reformulations from a large group of question rewrites, which is formed by full permutation and combination of the generated paraphrases. Extensive evaluations on a real world data set demonstrate that our model is able to characterize the complex questions and achieves promising performance as compared to the state-of-the-art methods. 相似文献
15.
16.
Xiuling Li Songbai Yang Zhonglin Tang Kui Li Max F. Rothschild Bang Liu Bin Fan 《Animal genetics》2014,45(3):329-339
Due to the direction, intensity, duration and consistency of genetic selection, especially recent artificial selection, the production performance of domestic pigs has been greatly changed. Therefore, we reasoned that there must be footprints or selection signatures that had been left during domestication. In this study, with porcine 60K BeadChip genotyping data from both commercial Large White and local Chinese Tongcheng pigs, we calculated the extended haplotype homozygosity values of the two breeds using the long‐range haplotype method to detect selection signatures. We found 34 candidate regions, including 61 known genes, from Large White pigs and 25 regions comprising 57 known genes from Tongcheng pigs. Many selection signatures were found on SSC1, SSC4, SSC7 and SSC14 regions in both populations. According to quantitative trait loci and network pathway analyses, most of the regions and genes were linked to growth, reproduction and immune responses. In addition, the average genetic differentiation coefficient FST was 0.254, which means that there had already been a significant differentiation between the breeds. The findings from this study can contribute to further research on molecular mechanisms of pig evolution and domestication and also provide valuable references for improvement of their breeding and cultivation. 相似文献
17.
Yuhui He Makusu Tsutsui Ralph H. Scheicher Chun Fan Masateru Taniguchi Tomoji Kawai 《Biophysical journal》2013
Experiments using nanopores demonstrated that a salt gradient enhances the capture rate of DNA and reduces its translocation speed. These two effects can help to enable electrical DNA sequencing with nanopores. Here, we provide a quantitative theoretical evaluation that shows the positive net charges, which accumulate around the pore entrance due to the salt gradient, are responsible for the two observed effects: they reinforce the electric capture field, resulting in promoted molecule capture rate; and they induce cationic electroosmotic flow through the nanopore, thus significantly retarding the motion of the anionic DNA through the nanopore. Our multiphysical simulation results show that, during the polymer trapping stage, the former effect plays the major role, thus resulting in promoted DNA capture rate, while during the nanopore-penetrating stage the latter effect dominates and consequently reduces the DNA translocation speed significantly. Quantitative agreement with experimental results has been reached by further taking nanopore wall surface charges into account. 相似文献
18.
19.
20.
A comparative analysis of photosynthetic characteristics of hulless barley at two altitudes on the Tibetan Plateau 总被引:1,自引:0,他引:1
To determine the photosynthetic characteristics of C3 plants and their sensitivity to CO2 at different altitudes on the Tibetan Plateau, hulless barley (Hordeum vulgare L. ssp. vulgare) was grown at altitudes of 4,333 m and 3,688 m. Using gas-exchange measurements, photosynthetic parameters were simulated,
including the maximum net photosynthesis (P
max) and the apparent quantum efficiency (α). Plants growing at higher altitude had higher net photosynthetic rates (P
N), photosynthesis parameters (P
max and α) and sensitivities to CO2 enhancement than plants growing at lower altitude on the Tibetan Plateau. The enhancements of P
N, P
max, and α for plants growing at higher altitude, corresponding with 10 μmol(CO2) mol−1 increments, were approximately 0.20∼0.45%, 0.05∼0.20% and 0.12∼0.36% greater, respectively, than for plants growing at lower
altitude, respectively, where CO2 levels rose from 10 to 170 μmol(CO2) mol−1. Therefore, on the Tibetan Plateau, the changes in the photosynthetic capacities and the photosynthetic sensitivities to
CO2 observed in the C3 plants grown above 3,688 m are likely to increase with altitude despite the decreasing CO2 partial pressure. 相似文献