首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5441篇
  免费   618篇
  国内免费   628篇
  2024年   17篇
  2023年   49篇
  2022年   141篇
  2021年   271篇
  2020年   229篇
  2019年   274篇
  2018年   251篇
  2017年   201篇
  2016年   254篇
  2015年   351篇
  2014年   384篇
  2013年   418篇
  2012年   522篇
  2011年   462篇
  2010年   306篇
  2009年   277篇
  2008年   282篇
  2007年   291篇
  2006年   245篇
  2005年   209篇
  2004年   199篇
  2003年   219篇
  2002年   157篇
  2001年   130篇
  2000年   93篇
  1999年   79篇
  1998年   85篇
  1997年   42篇
  1996年   38篇
  1995年   19篇
  1994年   16篇
  1993年   14篇
  1992年   30篇
  1991年   18篇
  1990年   28篇
  1989年   22篇
  1988年   8篇
  1987年   9篇
  1986年   4篇
  1985年   3篇
  1984年   6篇
  1983年   4篇
  1982年   3篇
  1981年   4篇
  1980年   2篇
  1979年   2篇
  1976年   2篇
  1973年   2篇
  1972年   5篇
  1958年   2篇
排序方式: 共有6687条查询结果,搜索用时 359 毫秒
91.
Liu  Tengfei  Sun  Liang  Meng  Qiucheng  Yu  Jianghui  Weng  Lushui  Li  Jinjiang  Deng  Lihua  Zhu  Qihong  Gu  Xingyou  Chen  Caiyan  Teng  Sheng  Xiao  Guoying 《Plant and Soil》2021,463(1-2):39-53
Plant and Soil - Rice accumulates higher levels of cadmium (Cd) in grain than other cereals, and hybrid rice varieties cover around half of the total rice area in China. Therefore, understanding...  相似文献   
92.
The relationship between rs3746444 T>C single-nucleotide polymorphism (SNP) in microRNA (mir)-499 and risk of gastric cancer (GC) has been widely investigated. However, the association was still unconfirmed. Here, we first recruited 490 GC patients and 1476 controls, and conducted a case-control study. And we did not find any association between rs3746444 T>C SNP polymorphism and risk of GC. Subsequently, we conducted a meta-analysis to explore the association of mir-499 rs3746444 polymorphism with GC development. Two authors searched the PubMed and EMBASE databases up to October 15, 2019 independently. Finally, nine literatures involving 12 independent studies were included. In total, 3954 GC cases and 9745 controls were recruited for meta-analysis. The results suggested that allele model, homozygote model and recessive model could increase the risk of overall GC (P = 0.002, 0.009 and 0.013, respectively). When we excluded the studies violated HWE, this association was also found in allele model (P = 0.020) and dominant model (P= 0.044). In subgroup analyses, we identified that rs3746444 SNP in mir-499 increased the risk of GC in Asians and gastric cardiac adenocarcinoma (GCA) subgroups. No significant bias of selection was found (all P>0.1). Test of sensitivity analysis indicated that our findings were stable. Additionally, we found that the power value was 0.891 in the allele model, suggesting the reliability of our findings. In summary, our analysis confirmed the association between rs3746444 and the risk of GC, especially in Asians and in patients with GCA.  相似文献   
93.
Sheng  Yumeng  Cao  Manlin  Liu  Yiwen  He  Yiqing  Zhang  Guoliang  Du  Yan  Gao  Feng  Yang  Cuixia 《Molecular and cellular biochemistry》2021,476(9):3383-3391
Molecular and Cellular Biochemistry - Although luminal breast cancer cells are typically highly cohesive epithelial cells and have low invasive ability, many eventually develop metastasis. Until...  相似文献   
94.
Jiang  Lei  Zhou  Guo-Wei  Zhang  Yu-Yang  Lei  Xin-Ming  Yuan  Tao  Guo  Ming-Lan  Yuan  Xiang-Cheng  Lian  Jian-Sheng  Liu  Sheng  Huang  Hui 《Coral reefs (Online)》2021,40(5):1563-1576
Coral Reefs - Symbiosis establishment is a milestone in the life cycles of most broadcast-spawning corals; however, it remains largely unknown how initial symbiont infection is affected by ocean...  相似文献   
95.
World Journal of Microbiology and Biotechnology - Chickpea (Cicer arietinum L., Fabaceae) is the second most important legume after common bean (Phaseolus vulgaris L., Fabaceae) and third in...  相似文献   
96.
97.
Liu  Jin Yue  Sheng  Ze Wen  Hu  Yu Qi  Liu  Qi  Qiang  Sheng  Song  Xiao Ling  Liu  Biao 《Transgenic research》2021,30(1):105-119
Transgenic Research - The releasing of transgenic soybeans (Glycine max (L.) Merr.) into farming systems raises concerns that transgenes might escape from the soybeans via pollen into...  相似文献   
98.
中国兽类(即哺乳动物)种类繁多,对维持生态平衡发挥着重要的作用。自John R.Reeves于1829—1834年在我国广东开展兽类调查以来,近200年我国兽类分类及系统学研究取得了令世人瞩目的进步和发展。目前中国已知的兽类物种数已达686种,约占全世界兽类种数的10%,是世界上兽类物种多样性最丰富的国家之一。随着我国对生态环境保护的重视,生态环境日益改善,但全球气候变化、生境破碎化、人类活动增加及人兽共患重大疫情涌现等问题仍十分突出,兽类多样性调查及分类学研究的必要性越发明显。同时,兽类分类学这门古老而传统的学科也在不断引入各种新方法与技术,如整合分类学、标本数字化、模式标本测序、便携式测序技术及基于深度学习技术的物种识别鉴定等,分类学研究的成果及应用在近年得到了飞速发展。动物分类学作为传统的基础学科,是遗传学、生理学、生态学、医学、药学等现代生物学的基石。然而,由于学科特征和差异等原因,该学科近年来没有得到足够的重视,导致出现了学科萎缩和分类学人才后继无人的危机。因此,从国家层面对分类学、形态学等基础学科的人才培养、课题设置和资金投入等,予以特殊的政策支持,十分必要,也亟待解决。  相似文献   
99.
Large sample theory of semiparametric models based on maximum likelihood estimation (MLE) with shape constraint on the nonparametric component is well studied. Relatively less attention has been paid to the computational aspect of semiparametric MLE. The computation of semiparametric MLE based on existing approaches such as the expectation‐maximization (EM) algorithm can be computationally prohibitive when the missing rate is high. In this paper, we propose a computational framework for semiparametric MLE based on an inexact block coordinate ascent (BCA) algorithm. We show theoretically that the proposed algorithm converges. This computational framework can be applied to a wide range of data with different structures, such as panel count data, interval‐censored data, and degradation data, among others. Simulation studies demonstrate favorable performance compared with existing algorithms in terms of accuracy and speed. Two data sets are used to illustrate the proposed computational method. We further implement the proposed computational method in R package BCA1SG , available at CRAN.  相似文献   
100.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号