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   63064篇
  免费   17907篇
  国内免费   3035篇
  2024年   101篇
  2023年   599篇
  2022年   1432篇
  2021年   2520篇
  2020年   3477篇
  2019年   5452篇
  2018年   5360篇
  2017年   5177篇
  2016年   5725篇
  2015年   6279篇
  2014年   6442篇
  2013年   7103篇
  2012年   5123篇
  2011年   4491篇
  2010年   4759篇
  2009年   3397篇
  2008年   2575篇
  2007年   1947篇
  2006年   1668篇
  2005年   1388篇
  2004年   1226篇
  2003年   1158篇
  2002年   951篇
  2001年   906篇
  2000年   774篇
  1999年   668篇
  1998年   357篇
  1997年   327篇
  1996年   344篇
  1995年   315篇
  1994年   288篇
  1993年   198篇
  1992年   268篇
  1991年   223篇
  1990年   172篇
  1989年   130篇
  1988年   116篇
  1987年   99篇
  1986年   59篇
  1985年   72篇
  1984年   44篇
  1983年   58篇
  1982年   36篇
  1981年   37篇
  1980年   18篇
  1979年   14篇
  1978年   13篇
  1977年   15篇
  1976年   18篇
  1974年   15篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
931.
Prenatal and neonatal exposure to estrogenic compounds, such as ethinylestradiol (EE), promotes a variety of developmental disorders, including malformations and alterations in the morphology of glands, such as the prostate gland. Therefore, the aim of this study was to evaluate the morphological effects of neonatal exposure to EE on prostatic tissue and on the identification and quantification of gerbil gland macrophages in adult and senile Mongolian gerbils. The animals were exposed to EE (10 μg/kg/day) and to the vehicle, mineral oil (100 μL) (control group) during the first 10 days of postnatal life (lactation period). Adult gerbils were euthanized at 120 days and senile gerbils at 12 months of age. Our findings permitted verification of the presence of areas with proliferative foci in the prostate glandular portions in the adult and senile animals exposed to EE. There was also an increase in macrophages in the prostate tissue of adult and senile gerbils; these cell types alter the stromal microenvironment and possibly modify the interactions between the epithelium and stroma. Neonatal exposure to EE changes the pattern of prostatic development, leading to alterations in the arrangement of cells, including macrophages, and may be related to the onset of proliferative disorders in the prostate of adult gerbils and during aging.  相似文献   
932.
933.
Reactive oxygen species (ROS) act as signaling molecules to regulate various cell functions. Numerous studies have demonstrated ROS to be essential for the differentiation of adipocytes. Peroxiredoxins (Prxs) are a ubiquitous family of antioxidant enzymes in mammalian cells. Prx2 is present in the cytoplasm and cell membranes and demonstrates ROS scavenging activity. We focused on Prx2 involvement in regulating adipogenesis and lipid accumulation and demonstrated that Prx2 expression was upregulated during adipocyte differentiation. In addition, the silencing of Prx2 (shPrx2) inhibited adipogenesis by modulating adipogenic gene expression, and cell death was enhanced via increased ROS production in shPrx2‐3T3‐L1 cells. These results demonstrate that shPrx2 triggers adipocyte cell death and weakens adipocyte function via ROS production. Taken together, our data suggest the participation of Prx2 in adipocyte function and differentiation. Our results also imply that the downregulation of Prx2 activity could help prevent obesity. Overall, findings support the development of ROS‐based therapeutic solutions for the treatment of obesity and obesity‐related metabolic disorders.  相似文献   
934.
Small‐cell lung cancer (SCLC) accounts for approximately 15% of lung cancer cases; however, it is characterized by easy relapse and low survival rate, leading to one of the most intractable diseases in clinical practice. Despite decades of basic and clinical research, little progress has been made in the management of SCLC. The current standard first‐line regimens of SCLC still remain to be cisplatin or carboplatin combined with etoposide, and the adverse events of chemotherapy are by no means negligible. Besides, the immunotherapy on SCLC is still in an early stage and novel studies are urgently needed. In this review, we describe SCLC development and current therapy, aiming at providing useful advices on basic research and clinical strategy.  相似文献   
935.
This work aimed to investigate miR‐93‐5p expression in tumor tissue and its in vitro effects in colorectal cancer (CRC) by targeting programmed death ligand‐1 (PD‐L1). MiR‐93‐5p and PD‐L1 expression was detected in CRC and adjacent normal tissues by quantitative real‐time polymerase chain reaction and immunohistochemistry. The correlation between miR‐93‐5p and PD‐L1 was validated by a dual‐luciferase reporter assay. HCT116 and SW480 cells were divided into blank, miR‐NC, miR‐93‐5p mimics, miR‐93‐5p inhibitor, PD‐L1 small interfering RNA (siRNA) and miR‐93‐5p inhibitor + PD‐L1 siRNA groups, and wound‐healing and transwell assays were performed to detect cell migration and invasion, respectively. Protein expression was measured by western blotting. The secretion of cytokines was detected in the CRC cell/T coculture models. MiR‐93‐5p was downregulated in CRC tissues with upregulated PD‐L1. In PD‐L1‐negative patients, miR‐93‐5p expression was increased compared with that in PD‐L1‐positive patients. MiR‐93‐5p and PD‐L1 expression levels were associated with the tumor differentiation, lymphatic metastasis, TNM, Duke's stage, and prognosis of CRC. PD‐L1 siRNA weakened the migration and invasion abilities via decreased expression of matrix metalloproteinase‐1 (MMP‐1), ‐2, and ‐9, and these effects were abolished by the miR‐93‐5p inhibitor. Additionally, anti‐PD‐L1 upregulated the expressions of interleukin‐2 (IL‐2), tumor necrosis factor‐α (TNF‐α), and interferon γ (IFN‐γ) in the coculture of T cells with CRC cells, but downregulated the expressions of IL‐1β, IL‐10, and TGF‐β. However, these changes were partially reversed by miR‐93‐5p inhibition. miR‐93‐5p is expected to be a novel target for CRC treatment since it decreases the migration and invasion, as well as the immune evasion, of CRC cells via targeting PD‐L1.  相似文献   
936.
937.
938.
We report the morphology and morphogenesis of Urosoma caudata (Ehrenberg, 1833) Berger, 1999 based on in vivo observation and protargol impregnation and provide an improved diagnosis of Ucaudata based on previous and current work. Urosoma caudata differs from its congeners mainly by the combination of the following features: tail‐like posterior end, colorless cortical granules, and two macronuclear nodules. Urosoma caudata shares most of the ontogenetic features with its congeners: the oral primordium of the opisthe develops apokinetally, and the frontal‐ventral‐transverse cirral anlagen develop in five streaks. However, a unique morphogenetic characteristic is recognizable: the anlagen of three dorsal kineties occur de novo to the left of the parental structures differing from their intrakinetal origin in other Urosoma species. The first record of the 18S rRNA gene sequence for the species is also provided. Phylogenetic analyses based on 18S rRNA gene sequence data suggest that the genus Urosoma is a nonmonophyletic group.  相似文献   
939.
Presently, echinocandins have been recommended as the first‐line drugs for the treatment of invasive candidiasis. However, low oral bioavailability and solubility limit their application. To improve this situation, this study chose amino acid and fatty acid as raw materials to modify the nucleus of echinocandin B. Six N‐acylated analogs were screened from the derivatives that possessed potent antifungal activity and good water solubility. Based on antifungal susceptibility and hemolytic toxicity, compound 5 as the candidate had good antifungal activity and no hemolytic effect. Moreover, compared with anidulafungin, compound 5 showed a comparable fungicidal effect, much higher solubility, and lower toxicity. In conclusion, compound 5 has the potential for further research and development on account of reserved antifungal activity, high solubility, and low toxicity.  相似文献   
940.
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