全文获取类型
收费全文 | 3457篇 |
免费 | 240篇 |
国内免费 | 249篇 |
专业分类
3946篇 |
出版年
2024年 | 7篇 |
2023年 | 42篇 |
2022年 | 108篇 |
2021年 | 194篇 |
2020年 | 128篇 |
2019年 | 155篇 |
2018年 | 164篇 |
2017年 | 102篇 |
2016年 | 132篇 |
2015年 | 189篇 |
2014年 | 257篇 |
2013年 | 255篇 |
2012年 | 333篇 |
2011年 | 286篇 |
2010年 | 164篇 |
2009年 | 142篇 |
2008年 | 179篇 |
2007年 | 127篇 |
2006年 | 121篇 |
2005年 | 99篇 |
2004年 | 78篇 |
2003年 | 92篇 |
2002年 | 77篇 |
2001年 | 40篇 |
2000年 | 56篇 |
1999年 | 60篇 |
1998年 | 34篇 |
1997年 | 30篇 |
1996年 | 23篇 |
1995年 | 30篇 |
1994年 | 26篇 |
1993年 | 22篇 |
1992年 | 32篇 |
1991年 | 24篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1969年 | 3篇 |
1966年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有3946条查询结果,搜索用时 15 毫秒
121.
Background
Many studies have reported the associations of polymorphic CAG repeats in androgen receptor (AR) gene with PCOS risk, but with inconsistent results. So, the aim of present meta-analysis was to clarify such inconsistence, so as to provide more conclusive results.Methods
PubMed was searched for the eligible reports published until February 2012 without language limitation. The studies reporting the relationship between CAG repeat length and PCOS were selected for the meta-analysis according to the inclusion criteria. Two reviewers independently extracted the data and evaluated the study quality.Principal findings
As for the relationship between CAG repeat length and PCOS risk, the pooled results showed that the biallelic mean was not significantly different between PCOS and controls (SMD − 0.03, 95% CI − 0.16–0.10, P = 0.603), and that the ORs of PCOS were not demonstrated for the individuals with the biallelic mean less than median (OR 0.96, 95% CI 0.68–1.35, P = 0.794), with the short CAG allele (OR 0.94, 95% CI 0.80–1.10, P = 0.424), or with the X-weighted biallelic mean (OR 0.81, 95% CI 0.46–1.41, P = 0.447). Further, as for the relationship between CAG repeat length and T levels in PCOS patients, the biallelic mean was not significantly different between PCOS patients with high T and those with low T (SMD 0.79, 95% CI − 0.12–1.70, P = 0.088), while the summary correlation r indicated that the CAG biallelic mean appeared to be positively associated with T levels in PCOS (r 0.20, 95% CI 0.11–0.30, p = 0.000).Conclusions
This meta-analysis demonstrates no evident association between the CAG length variations in AR gene and PCOS risk, while the CAG length appears to be positively associated with T levels in PCOS patients. 相似文献122.
In this paper, the melting of ice 1h is studied using molecular dynamics (MD). Common potential functions employed in the MD simulations include SPC/E, TIP4P, TIP5P, TIP4/ice and TIP5P/E. We first conducted melting of ice bulks and then studied the melting speed of the ice/water interface during ice melting. It is found that various potentials result in similar ice-melting phenomena. The result is compared with the analytical solution for phase change problem. We also studied size effects and temperature gradient effects on ice melting. 相似文献
123.
124.
Aims
Our aims were to identify the primary factors involved in soil respiration (Rs) variability and the role that spectral vegetation indices played in Rs estimation in irrigated and rainfed agroecosystems during the growing season.Methods
We employed three vegetation indices [i.e., normalized difference vegetation index (NDVI), green edge chlorophyll index (CIgreen edge) and enhanced vegetation index (EVI)] derived from the Moderate-resolution Imaging Spectroradiometer (MODIS) surface reflectance product as approximations of crop gross primary production (GPP) for Rs estimation. Different statistical models were used to analyze the dependencies of Rs on soil temperature, soil water content and plant photosynthesis, and accuracy of these models were compared in the irrigated and rainfed agroecosystems.Results
The results demonstrated that a model based only on abiotic factors (e.g., soil temperature and soil water content) failed to describe part of the growing-season variability in Rs. Residual analysis indicated that Rs was influenced by a short-term gross primary production (GPP) and a longer-term (≥3 days) accumulated GPP in the irrigated and rainfed agroecosystems. Therefore, photosynthesis dependency of Rs should be included in the Rs model to describe the growing-season dynamics of Rs. Among the three VIs, CIgreen edge showed generally better correlations with GPP at different cumulative times and canopy green leaf area index than EVI and NDVI. Adding the CIgreen edge into the model considering only soil temperature and soil water content significantly improved the simulation accuracy of Rs.Conclusions
Our results suggest that spectral vegetation index from remote sensing could be used to estimate Rs, which will be helpful for the development of a future Rs model over a large spatial scale. 相似文献125.
Zhong‐Fei Ni Zhi‐Wei Ma Ao‐Ji Xie Xiang‐Shu Cheng Qun Wang Jian‐Zhi Wang Gong‐Ping Liu 《Journal of neurochemistry》2013,124(3):388-396
Hyperhomocysteinemia (Hhcy) may induce memory deficits with β‐amyloid (Aβ) accumulation and tau hyperphosphorylation. Simultaneous supplement of folate and vitamin B12 partially restored the plasma homocysteine level and attenuated tau hyperphosphorylation, Aβ accumulation and memory impairments induced by Hhcy. However, folate and vitamin B12 treatment have no effects on Hhcy which has the methylenetetrahydrofolate reductase genotype mutation. In this study, we investigated the effects of simultaneous supplement of betaine on Alzheimer‐like pathological changes and memory deficits in hyperhomocysteinemic rats after a 2‐week induction by vena caudalis injection of homocysteine (Hcy). We found that supplementation of betaine could ameliorate the Hcy‐induced memory deficits, enhance long‐term potentiation (LTP) and increase dendritic branches numbers and the density of the dendritic spines, with up‐regulation of NR1, NR2A, synaptotagmin, synaptophysin, and phosphorylated synapsin I protein levels. Supplementation of betaine also attenuated the Hcy‐induced tau hyperphosphorylation at multiple AD‐related sites through activation protein phosphatase‐2A (PP2A) with decreased inhibitory demethylated PP2AC at Leu309 and phosphorylated PP2AC at Tyr307. In addition, supplementation of betaine also decreased Aβ production with decreased presenilin‐1 protein levels. Our data suggest that betaine could be a promising candidate for arresting Hcy‐induced AD‐like pathological changes and memory deficits. 相似文献
126.
Yubo Chen Lu Qi Xiaoyu Zhang Jixiang Huang Jibian Wang Hongcheng Chen Xiyuan Ni Fei Xu Yanjun Dong Haiming Xu Jianyi Zhao 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2013,126(10):2499-2509
Increasing seed oil content has become one of the most important breeding criteria in rapeseed (Brassica napus). However, oil content is a complex quantitative trait. QTL mapping in a double haploid population (SG population) emerging from a cross between a German (Sollux) and Chinese (Gaoyou) cultivars revealed one QTL for oil content on linkage group A1 (OilA1), which was mapped to a 17 cM genetic interval. To further validate and characterize the OilA1, we constructed a high-resolution map using B. rapa sequence resources and developed a set of near-isogenic lines (NILs) by employing a DH line SG-DH267 as donor and Chinese parent Gaoyou as recurrent background. The results showed highly conserved synteny order between B. rapa and B. napus within the linkage group A1 and revealed a possible centromere region between two markers ZAASA1-38 and NTP3 (2.5 cM). OilA1 was firstly validated by 250 BC5F2 plants and was confirmed in a 10.6 cM interval between the markers ZAASA1-47 and ZAASA1-77. Further substitution mapping was conducted by using two generations of QTL-NILs, 283 lines from eight BC5F3:4 families and 428 plants from six BC5F4 sub-NILs and thus narrowed the OilA1 interval to 6.9 cM and 4.3 cM (1.4 Mb), respectively. Field investigations with two replications using homozygous BC5F3:4 sister sub-NILs indicated that NILs, which carry a Sollux chromosome segment across the target region showed significant higher oil content (1.26 %, p < 0.001) than their sister NILs containing Gaoyou chromosome. The OilA1 locus is of particular interest for breeding purpose in China because 80 % of Chinese cultivars do not carry this desirable allele. 相似文献
127.
128.
129.
130.