全文获取类型
收费全文 | 1218篇 |
免费 | 100篇 |
国内免费 | 75篇 |
出版年
2023年 | 13篇 |
2022年 | 24篇 |
2021年 | 57篇 |
2020年 | 31篇 |
2019年 | 50篇 |
2018年 | 55篇 |
2017年 | 28篇 |
2016年 | 45篇 |
2015年 | 69篇 |
2014年 | 92篇 |
2013年 | 93篇 |
2012年 | 81篇 |
2011年 | 96篇 |
2010年 | 63篇 |
2009年 | 71篇 |
2008年 | 67篇 |
2007年 | 46篇 |
2006年 | 60篇 |
2005年 | 47篇 |
2004年 | 29篇 |
2003年 | 35篇 |
2002年 | 37篇 |
2001年 | 25篇 |
2000年 | 23篇 |
1999年 | 26篇 |
1998年 | 11篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1977年 | 2篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1964年 | 2篇 |
1960年 | 1篇 |
排序方式: 共有1393条查询结果,搜索用时 15 毫秒
1.
Biological soil crusts (BSCs, or biocrusts) have important positive ecological functions such as erosion control and soil fertility improvement, and they may also have negative effects on soil moisture in some cases. Simultaneous discussions of the two-sided impacts of BSCs are key to the rational use of this resource. This study focused on the contribution of BSCs while combining with specific types of vegetation to erosion reduction and their effects on soil moisture, and it addressed the feasibility of removal or raking disturbance. Twelve plots measuring 4 m × 2 m and six treatments (two plots for each) were established on a 15° slope in a small watershed in the Loess Plateau using BSCs, bare land (as a control, BL), Stipa bungeana Trin. (STBU), Caragana korshinskii Kom. (CAKO), STBU planted with BSCs (STBU+BSCs) and CAKO planted with BSCs (CAKO+BSCs). The runoff, soil loss and soil moisture to a depth of 3 m were measured throughout the rainy season (from June to September) of 2010. The results showed that BSCs significantly reduced runoff by 37.3% and soil loss by 81.0% and increased infiltration by 12.4% in comparison with BL. However, when combined with STBU or CAKO, BSCs only made negligible contributions to erosion control (a runoff reduction of 7.4% and 5.7% and a soil loss reduction of 0.7% and 0.3%). Generally, the soil moisture of the vegetation plots was lower in the upper layer than that of the BL plots, although when accompanied with a higher amount of infiltration, this soil moisture consumption phenomenon was much clearer when combining vegetation with BSCs. Because of the trivial contributions from BSCs to erosion control and the remaining exacerbated consumption of soil water, moderate disturbance by BSCs should be considered in plots with adequate vegetation cover to improve soil moisture levels without a significant erosion increase, which was implied to be necessary and feasible. 相似文献
2.
Cvek Jakub Vondráček Vladimir Dvořák Jan Argalacsová Sona Navrátil Matej Buřil Jan 《Reports of Practical Oncology and Radiotherapy》2012,17(2):79-84
AimTo evaluate the outcome of prostate cancer patients with initial PSA value >40 ng/ml.BackgroundThe outcome of prostate cancer patients with very high initial PSA value is not known and patients are frequently treated with palliative intent. We analyzed the outcome of radical combined hormonal treatment and radiotherapy in prostate cancer patients with initial PSA value >40 ng/ml.MethodsBetween January 2003 and December 2007 we treated, with curative intent, 56 patients with non-metastatic prostate cancer and initial PSA value >40 ng/ml. The treatment consisted of two months of neoadjuvant hormonal treatment (LHRH analog), radical radiotherapy (68–78 Gy, conformal technique) and an optional two-year adjuvant hormonal treatment.ResultsThe median time of follow up was 61 months. 5-Year overall survival was 90%. 5-Year biochemical disease free survival was 62%. T stage, Gleason score, PSA value, and radiotherapy dose did not significantly influence the outcome. Late genitourinal and gastrointestinal toxicity was acceptable.ConclusionRadical treatment in combination with hormonal treatment and radiotherapy can be recommended for this subgroup of prostate cancer patients with good performance status and life expectancy. 相似文献
3.
Xiao-Long Lin Yan-Min Zhao Li-Ping Yan Wen-Bin Liu Wen-Jun Bu Xin-Hua Wang Chen-Guang Zheng 《Zoologica scripta》2022,51(1):119-132
Evolutionary analysis of Prodiamesinae has long been impeded by lack of information, and its phylogenetic relationship with Orthocladiinae remains questionable. Here, ten complete mitochondrial genomes (mitogenomes) of Orthocladiinae sensu lato were newly sequenced, including three Prodiamesinae species and seven Orthocladiinae species. Coupled with published mitogenomes, a total of 12 mitogenomes of Orthocladiinae sensu lato were selected for a comparative mitogenomic analysis and phylogenetic reconstruction. Mitogenomes of Orthocladiinae sensu lato are conserved in structure, and all genes arrange the same gene order as the ancestral insect mitogenome. Nucleotide composition is highly biased, and the control region displayed the highest A + T content. All protein-coding genes are under purifying selection, and the ATP8 evolves at the fastest rate. In addition, the mitogenomes of Orthocladiinae sensu lato are highly conserved, and they are practically useful for phylogenetic inference, suggesting a re-classification of Orthocladiinae by sinking Prodiamesinae as a subgroup of Orthocladiinae. 相似文献
4.
Kimberly R. Holloway Vidya C. Sinha Michael J. Toneff Wen Bu Susan G. Hilsenbeck Yi Li 《PloS one》2015,10(1)
While most breast cancers are thought to arise from the luminal layer of the breast tissue, it remains unclear which specific cells in the luminal layer are the cells of origin of breast cancer. We have previously reported that WAP-positive luminal epithelial cells are at increased susceptibility to tumor initiation by ErbB2 compared to the bulk population, while the mammary cells with canonical Wnt signaling activity fail to evolve into tumors upon ErbB2 activation. Here, we used retrovirus to introduce ErbB2 into the Krt6a-positive mammary progenitor subset of the luminal epithelium and, for comparison, into the mammary luminal epithelium indiscriminately. Tumors developed from both groups of cells with a similar latency. These data indicate that the Krt6a-positive subset of mammary epithelial cells can be induced to form cancer by ErbB2 but it is not more susceptible to tumorigenesis initiated by ErbB2 than the bulk population of the luminal epithelium. 相似文献
5.
6.
7.
Four new hetisine‐type C20‐diterpenoid alkaloids, named as coreanines A–D ( 1 – 4 ), were isolated from the roots of Aconitum coreanum, together with thirteen known alkaloids ( 5 – 17 ). Their structures were elucidated by extensive spectroscopic methods including IR, HR‐ESI‐MS and NMR techniques. All the isolated compounds were screened for the acetylcholinesterase (AChE) inhibitory effects, and none of them showed considerable inhibitory activity. 相似文献
8.
9.
10.
吉林省中西部平原区土壤线虫群落生态特征 总被引:9,自引:0,他引:9
于 2 0 0 3年 7月和 9月 ,在吉林省中西部平原区进行土壤线虫取样 ,10个采样区 2 8个调查样地 2次共捕获线虫 10 2 2 0只 ,个体密度平均 182 5 0只 /m2 ,分别隶属于线形动物门 2纲 7目 2 0科 32属。真滑刃属、短体属和垫刃属为优势类群 ,是吉林省中西部平原区土壤线虫群落最重要的类群 ,稀有类群个体数量尽管很少 ,但分布的范围并不狭小 ,线虫各类群空间分布的广狭与个体数量的多寡在吉林省中西部平原区并末呈现出明显的一致性。土壤线虫群落垂直分布 ,受人类活动扰动的生境土壤线虫类群数和个体密度表聚性较差 ,土壤线虫向土壤下层移动明显 ;水平分布 ,天然林和受人类活动扰动生境土壤线虫类群数和个体密度差异显著 ;农田土地利用方式对土壤线虫群落特征影响总体是负面的 ,而居民点园地可能增加土壤线虫的类群数和生物多样性。 PPI/MI值对于不同人类活动对土壤生态环境的变化反映更敏感 相似文献