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   39773篇
  免费   3101篇
  国内免费   3025篇
  2024年   60篇
  2023年   468篇
  2022年   802篇
  2021年   2204篇
  2020年   1423篇
  2019年   1782篇
  2018年   1789篇
  2017年   1224篇
  2016年   1706篇
  2015年   2502篇
  2014年   2940篇
  2013年   3189篇
  2012年   3701篇
  2011年   3265篇
  2010年   2074篇
  2009年   1677篇
  2008年   2032篇
  2007年   1799篇
  2006年   1660篇
  2005年   1335篇
  2004年   1088篇
  2003年   944篇
  2002年   778篇
  2001年   668篇
  2000年   598篇
  1999年   641篇
  1998年   362篇
  1997年   374篇
  1996年   349篇
  1995年   322篇
  1994年   333篇
  1993年   264篇
  1992年   316篇
  1991年   242篇
  1990年   213篇
  1989年   190篇
  1988年   127篇
  1987年   102篇
  1986年   93篇
  1985年   86篇
  1984年   59篇
  1983年   53篇
  1982年   34篇
  1981年   9篇
  1980年   9篇
  1979年   11篇
  1976年   1篇
  1965年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
生物入侵是继栖息地破坏之后,全球生物多样性丧失的第二大驱动因素。近年来,原产于南美洲地区的斑纹小贻贝(Mytella strigata)在印度-西太平洋海区被陆续报道,而我国台湾、广东、海南、福建、广西等省份同样发现斑纹小贻贝,且其已经建立可自我维持的种群。但是,作为一种新型入侵生物,斑纹小贻贝尚未引起国内海洋管理部门和科研人员足够重视,亟待查明其在我国沿海的分布现状、扩散趋势和生态影响等,为斑纹小贻贝的检测、监测、防控和管理提供科学依据。综述了斑纹小贻贝的基础生物学特征和全球生物入侵现状,发现国内的斑纹小贻贝源于南美洲加勒比海地区,于2014年左右通过船舶压舱水或船体生物污损的形式侵入我国南方沿海并迅速扩散。此外,斑纹小贻贝在我国的生物入侵处于"引进-传播"阶段,即将大规模扩繁,因此亟需开展应急清除行动。  相似文献   
42.
43.
H. Bai  Y. Sun  N. Liu  Y. Liu  F. Xue  Y. Li  S. Xu  A. Ni  J. Ye  Y. Chen  J. Chen 《Animal genetics》2018,49(3):226-236
Beak deformity (crossed beaks) is found in several indigenous chicken breeds including Beijing‐You studied here. Birds with deformed beaks have reduced feed intake and poor production performance. Recently, copy number variation (CNV) has been examined in many species and is recognized as a source of genetic variation, especially for disease phenotypes. In this study, to unravel the genetic mechanisms underlying beak deformity, we performed genome‐wide CNV detection using Affymetrix chicken high‐density 600K data on 48 deformed‐beak and 48 normal birds using penncnv . As a result, two and eight CNV regions (CNVRs) covering 0.32 and 2.45 Mb respectively on autosomes were identified in deformed‐beak and normal birds respectively. Further RT‐qPCR studies validated nine of the 10 CNVRs. The ratios of six CNVRs were significantly different between deformed‐beak and normal birds (< 0.01). Within these six regions, three and 21 known genes were identified in deformed‐beak and normal birds respectively. Bioinformatics analysis showed that these genes were enriched in six GO terms and one KEGG pathway. Five candidate genes in the CNVRs were further validated using RT‐qPCR. The expression of LRIG2 (leucine rich repeats and immunoglobulin like domains 2) was lower in birds with deformed beaks (< 0.01). Therefore, the LRIG2 gene could be considered a key factor in view of its known functions and its potential roles in beak deformity. Overall, our results will be helpful for future investigations of the genomic structural variations underlying beak deformity in chickens.  相似文献   
44.
This paper studies a Non-convex State-dependent Linear Quadratic Regulator (NSLQR) problem, in which the control penalty weighting matrix in the performance index is state-dependent. A necessary and sufficient condition for the optimal solution is established with a rigorous proof by Euler-Lagrange Equation. It is found that the optimal solution of the NSLQR problem can be obtained by solving a Pseudo-Differential-Riccati-Equation (PDRE) simultaneously with the closed-loop system equation. A Comparison Theorem for the PDRE is given to facilitate solution methods for the PDRE. A linear time-variant system is employed as an example in simulation to verify the proposed optimal solution. As a non-trivial application, a goal pursuit process in psychology is modeled as a NSLQR problem and two typical goal pursuit behaviors found in human and animals are reproduced using different control weighting . It is found that these two behaviors save control energy and cause less stress over Conventional Control Behavior typified by the LQR control with a constant control weighting , in situations where only the goal discrepancy at the terminal time is of concern, such as in Marathon races and target hitting missions.  相似文献   
45.
Graft-versus-host disease (GVHD) induced by host antigen-presenting cells (APCs) and donor-derived T cells remains the major limitation of allogeneic bone marrow transplantation (allo-BMT). Notch signaling pathway is a highly conserved cell-cell communication that is important in T cell development. Recently, Notch signaling pathway is reported to be involved in regulating GVHD. To investigate the role of Notch inhibition in modulating GVHD, we established MHC-mismatched murine allo-BMT model. We found that inhibition of Notch signaling pathway by γ-secretase inhibitor in vivo could reduce aGVHD, which was shown by the onset time of aGVHD, body weight, clinical aGVHD scores, pathology aGVHD scores, and survival. Inhibition of Notch signaling pathway by DAPT ex vivo only reduced pathology aGVHD scores in the liver and intestine and had no impact on the onset time and clinical aGVHD scores. We investigated the possible mechanism by analyzing the phenotype of host APCs and donor-derived T cells. Notch signaling pathway had a broad effect on both host APCs and donor-derived T cells. The expressions of CD11c, CD40, and CD86 as the markers of activated dendritic cells (DCs) were decreased. The proliferative response of CD8+ T cell decreased, while CD4+ Notch-deprived T cells had preserved expansion with increased expressions of CD25 and Foxp3 as markers of regulatory T cells (Tregs). In conclusion, Notch inhibition may minimize aGVHD by decreasing proliferation and activation of DCs and CD8+ T cells while preserving Tregs expansion.  相似文献   
46.
47.
Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related death worldwide with limited therapeutic options. Comprehensive investigation of protein posttranslational modifications in HCC is still limited. Lysine acetylation is one of the most common types of posttranslational modification involved in many cellular processes and plays crucial roles in the regulation of cancer. In this study, we analyzed the proteome and K-acetylome in eight pairs of HCC tumors and normal adjacent tissues using a timsTOF Pro instrument. As a result, we identified 9219 K-acetylation sites in 2625 proteins, of which 1003 sites exhibited differential acetylation levels between tumors and normal adjacent tissues. Interestingly, many novel tumor-specific K-acetylation sites were characterized, for example, filamin A (K865), filamin B (K697), and cofilin (K19), suggesting altered activities of these cytoskeleton-modulating molecules, which may contribute to tumor metastasis. In addition, we observed an overall suppression of protein K-acetylation in HCC tumors, especially for enzymes from various metabolic pathways, for example, glycolysis, tricarboxylic acid cycle, and fatty acid metabolism. Moreover, the expression of deacetylase sirtuin 2 (SIRT2) was upregulated in HCC tumors, and its role of deacetylation in HCC cells was further explored by examining the impact of SIRT2 overexpression on the proteome and K-acetylome in Huh7 HCC cells. SIRT2 overexpression reduced K-acetylation of proteins involved in a wide range of cellular processes, including energy metabolism. Furthermore, cellular assays showed that overexpression of SIRT2 in HCC cells inhibited both glycolysis and oxidative phosphorylation. Taken together, our findings provide valuable information to better understand the roles of K-acetylation in HCC and to treat this disease by correcting the aberrant acetylation patterns.  相似文献   
48.
49.
50.
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