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   14929篇
  免费   1305篇
  国内免费   924篇
  17158篇
  2024年   57篇
  2023年   297篇
  2022年   437篇
  2021年   499篇
  2020年   480篇
  2019年   712篇
  2018年   706篇
  2017年   434篇
  2016年   496篇
  2015年   531篇
  2014年   839篇
  2013年   1226篇
  2012年   570篇
  2011年   793篇
  2010年   626篇
  2009年   648篇
  2008年   696篇
  2007年   771篇
  2006年   622篇
  2005年   565篇
  2004年   478篇
  2003年   396篇
  2002年   421篇
  2001年   399篇
  2000年   288篇
  1999年   233篇
  1998年   259篇
  1997年   259篇
  1996年   231篇
  1995年   197篇
  1994年   171篇
  1993年   150篇
  1992年   146篇
  1991年   137篇
  1990年   134篇
  1989年   116篇
  1988年   88篇
  1987年   95篇
  1986年   76篇
  1985年   126篇
  1984年   136篇
  1983年   110篇
  1982年   131篇
  1981年   95篇
  1980年   49篇
  1979年   65篇
  1978年   49篇
  1977年   48篇
  1976年   32篇
  1973年   12篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Membranes of adjacent cells form intercellular junctional complexes to mechanically anchor neighbour cells (anchoring junctions), to seal the paracellular space and to prevent diffusion of integral proteins within the plasma membrane (tight junctions) and to allow cell-to-cell diffusion of small ions and molecules (gap junctions). These different types of specialised plasma membrane microdomains, sharing common adaptor molecules, particularly zonula occludens proteins, frequently present intermingled relationships where the different proteins co-assemble into macromolecular complexes and their expressions are co-ordinately regulated. Proteins forming gap junction channels (connexins, particularly) and proteins fulfilling cell attachment or forming tight junction strands mutually influence expression and functions of one another.  相似文献   
92.
93.
摘要 目的:探讨血清鸢尾素(Irisin)、氧化三甲胺(TMAO)、巨噬细胞迁移抑制因子(MIF)与慢性心力衰竭(CHF)合并心房颤动(AF)患者预后的关系及其预测价值。方法:选取2020年1月~2023年1月甘肃省人民医院收治的CHF合并AF患者175例纳入合并AF组,根据预后情况分为预后不良组和预后良好组。另选取同期收治未合并AF的CHF患者100例纳入未合并AF组。通过酶联免疫吸附法检测血清Irisin、TMAO、MIF水平。采用多因素Logistic回归分析CHF合并AF患者预后的影响因素,受试者工作特征(ROC)曲线分析血清Irisin、TMAO、MIF对CHF合并AF患者预后不良的预测价值。结果:与未合并AF组比较,合并AF组血清Irisin水平降低,血清TMAO、MIF水平升高(P<0.05)。与预后良好组比较,预后不良组血清Irisin水平降低,血清TMAO、MIF水平升高(P<0.05)。随访6个月,175例CHF合并AF患者预后不良发生率为26.29%。多因素Logistic回归分析显示,纽约心脏病协会(NYHA)心功能分级Ⅲ~Ⅳ级和N末端前体B型钠尿肽(NT-proBNP)、TMAO、MIF升高为CHF合并AF患者预后不良的独立危险因素,Irisin升高为独立保护因素(P<0.05)。ROC曲线分析显示,血清Irisin、TMAO、MIF联合预测CHF合并AF患者预后不良的曲线下面积(AUC)为0.919,大于血清Irisin、TMAO、MIF单独预测的0.787、0.780、0.777。结论:CHF合并AF患者血清Irisin水平降低,TMAO、MIF水平升高,且与预后不良密切相关。血清Irisin、TMAO、MIF水平联合检测对CHF合并AF患者预后不良具有较高的预测价值。  相似文献   
94.
Risks and benefit evaluation for controlled human infection studies, where healthy volunteers are deliberately exposed to infectious agents to evaluate vaccine efficacy, should be explicit, systematic, thorough, and non-arbitrary. Decision analysis promotes these qualities using four steps: (1) determining explicit criteria and measures for evaluation, (2) identifying alternatives to the study, (3) defining the models used to estimate the measures for each alternative, and (4) running the models to produce the estimates and compare the alternatives. In this paper, we describe how decision analysis might be applied by funders and regulators, as well as by others contemplating the use of novel controlled human infection studies for vaccine development and evaluation.  相似文献   
95.
用固相化甲肝抗原,对所构建的噬菌体抗体库进行了3轮淘筛。第3轮淘筛后洗脱下来的噬菌体,较第l轮增加了近100倍。含有抗体重链基因和轻链基因的重组克隆.也由淘筛前的25%增至100%。说明甲肝抗原对抗体库的淘筛,富集了表面呈现甲肝人单抗的噬菌体。经夹心ELISA法筛选到抗甲肝病毒噬菌体抗体,并以竞争抑制实验进一步证实了这些抗体的特异性。  相似文献   
96.
The recent cloning of the special calcium channels TRPV5 and TRPV6 (transient receptor potential vanilloid channels) has provided a molecular basis for studying previously unidentified calcium influx channels in electrically nonexcitable cells. In the present work using RT-PCR, we obtained the endogenous expression of mRNAs of genes trpv5 and trpv6 in lymphoblast leukemia Jurkat cells and in normal human T lymphocytes. Additionally, by immunoblotting, the presence of the channel-forming TRPV5 proteins has been shown both in the total lysate and in crude membrane fractions from Jurkat cells and normal T lymphocytes. The use of immunoprecipitation revealed TRPV6 proteins in Jurkat cells, whereas in normal T lymphocytes, this protein was not detected. The expression pattern and the selective Ca2+ permeation properties of TRPV5 and TRPV6 channels indicate the important role of these channels in Ca2+ homeostasis, as well as most likely in malignant transformation of blood cells.  相似文献   
97.
The factors that explain the diverse arrangement of the major arteries of tetrapods are not known. Here, I aim to illuminate some of the underpinnings of these patterns. I review the variation in the sauropsid left, right, and dorsal aortae regarding the origin of the gastrointestinal blood vessels and the relative diameters of left and right aortae where they join together to form the dorsal aorta. I focus on these features because the quality of blood that flows through these aortae can vary depending on the state of cardiac shunting and the size of the vessel can provide insight into the quantity of blood borne by the vessels. I then place the information in a phyletic, historical, and ecological context. The plesiomorphic pattern is for the gastrointestinal vessels to arise as segmental arteries from the dorsal aorta, which is formed from the confluence of left and right aortae with similar diameters. The pattern is well conserved with only two major variations. First, in several clades of reptiles (testudines, crocodilians, lizards of the genera Varanus and Hydrosaurus) a substantial portion of the gastrointestinal arteries arises from the left aorta, leaving the diameter of the left aorta smaller than the right at their confluence. I hypothesize that this vascular arrangement facilitates growth by allowing more alkaline blood to flow to the somatic (body wall) and appendicular circulations, which may promote bone deposition and inhibit resorption, whereas hypercapnic, acidic blood flows to the digestive viscera, which may provide CO2 as a substrate for the synthesis of gastric acid, bicarbonate, fatty acids, glutamine, purine rings, as well as glucose from lactate. Second, in some snakes and lizards with snake‐like body forms, such as Amphisbaenidae, the diameters of left and right aortae are asymmetrical at their confluence with the left aorta exceeding the right, but in members of the amphibian order Gymnophiona the right generally exceeds the left. This condition is associated with asymmetrical development of the lungs. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.  相似文献   
98.
99.
Background Hepatitis B virus (HBV) is a public health problem worldwide and apart from infecting humans, HBV has been found in non‐human primates. Methods We subjected 93 non‐human primates comprising 12 species to ELISA screening for the serological markers HBsAg, antiHBs and antiHBc. Subsequently, we detected HBV DNA, sequenced the whole HBV genome and performed phylogenetic analysis. Results HBV infection was detected in gibbon (4/15) and orangutan (7/53). HBV DNA isolates from two gibbons and seven orangutans were chosen for complete genome amplification. We aligned the Pre‐S/S, Pre‐C/C and entire genomes with HBV sequences and performed phylogenetic analysis. The gibbon and orangutan viruses clustered within their respective groups. Conclusions Both geographic location and host species influence which HBV variants are found in gibbons and orangutans. Hence, HBV transmission between humans and non‐human primates might be a distinct possibility and additional studies will be required to further investigate this potential risk.  相似文献   
100.
Infiltration of human immunodeficiency virus type 1 (HIV-1)-infected and uninfected monocytes/macrophages in organs and tissues is a general phenomenon observed in progression of acquired immunodeficiency syndrome (AIDS). HIV-1 protein Nef is considered as a progression factor in AIDS, and is released from HIV-1-infected cells. Here, we show that extracellular Nef increases migration of monocytes. This effect is (i) concentration-dependent, (ii) reaches the order of magnitude of that induced by formyl-methyonyl-leucyl-proline (fMLP) or CC chemokine ligand 2 (CCL2)/monocyte chemotactic protein (MCP)-1, (iii) inhibited by anti-Nef monoclonal antibodies as well as by heating, and (iv) depends on a concentration gradient of Nef. Further, Nef does not elicit monocytic THP-1 cells to express chemokines such as CCL2, macrophage inhibitory protein-1alpha (CCL3) and macrophage inhibitory protein-1beta (CCL4). These data suggest that extracellular Nef may contribute to disease progression as well as HIV-1 spreading through affecting migration of monocytes.  相似文献   
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