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   2045篇
  免费   684篇
  国内免费   112篇
化学   351篇
晶体学   5篇
力学   299篇
综合类   37篇
数学   279篇
物理学   1870篇
  2024年   4篇
  2023年   28篇
  2022年   73篇
  2021年   71篇
  2020年   73篇
  2019年   44篇
  2018年   56篇
  2017年   119篇
  2016年   118篇
  2015年   129篇
  2014年   199篇
  2013年   147篇
  2012年   171篇
  2011年   156篇
  2010年   139篇
  2009年   140篇
  2008年   149篇
  2007年   162篇
  2006年   124篇
  2005年   104篇
  2004年   93篇
  2003年   74篇
  2002年   63篇
  2001年   70篇
  2000年   49篇
  1999年   49篇
  1998年   47篇
  1997年   38篇
  1996年   19篇
  1995年   22篇
  1994年   15篇
  1993年   18篇
  1992年   19篇
  1991年   6篇
  1990年   7篇
  1989年   8篇
  1988年   6篇
  1987年   3篇
  1986年   4篇
  1985年   8篇
  1984年   2篇
  1983年   1篇
  1982年   4篇
  1981年   3篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1957年   2篇
排序方式: 共有2841条查询结果,搜索用时 15 毫秒
71.
Platinum–acridine hybrid agents show low‐nanomolar potency in chemoresistant non‐small cell lung cancer (NSCLC), but high systemic toxicity in vivo. To reduce the promiscuous genotoxicity of these agents and improve their pharmacological properties, a modular build–click–screen approach was used to evaluate a small library of twenty hybrid agents containing truncated and extended chromophores of varying basicities. Selected derivatives were resynthesized and tested in five NSCLC cell lines representing large cell, squamous cell, and adenocarcinomas. 7‐Aminobenz[c]acridine was identified as a promising scaffold in a hybrid agent ( P1–B1 ) that maintained submicromolar activity in several of the DNA‐repair proficient and p53‐mutant cancer models, while showing improved tolerability in mice by 32‐fold compared to the parent platinum–acridine ( P1–A1 ). The distribution and DNA/RNA adduct levels produced by the acridine‐ and benz[c]acridine‐based analogues in NCI‐H460 cells (confocal microscopy, ICP‐MS), and their ability to bind G‐quadruplex forming DNA sequences (CD spectroscopy, HR‐ESMS) were studied. P1–B1 emerges as a less genotoxic, more tolerable, and potentially more target‐selective hybrid agent than P1–A1 .  相似文献   
72.
Herein, we report an efficient approach for exploring the novel anticancer mechanism of (?)‐ainsliatrimer A, a structurally complex and unique trimeric sesquiterpenoid, through a combined strategy of diverted total synthesis (DTS) and bioorthogonal ligation (TQ ligation), which allowed us to visualize the subcellular localization of this natural product in live cells. Further biochemical studies facilitated by pretarget imaging revealed that PPARγ, a nucleus receptor, was a functional cellular target of ainsliatrimer A. We also confirmed that the anticancer activity of ainsliatrimer A was caused by the activation of PPARγ.  相似文献   
73.
The in situ tracking of the pyrolysis of a binary molecular cluster [Zn73-CH3O)6(L)6][ZnLCl2]2 is presented with one brucite disk and two mononuclear fragments (L=mmimp: 2-methoxy-6-((methylimino)-methyl)phenolate) to porous carbon using TG-MS from 30 to 900 °C. Following up the spilled gas product during the decomposed reaction of zinc cluster along the temperature rising, and in conjunction with XRD, SEM, BET and other materials characterization, where three key steps were observed: 1) cleavage of the bulky external ligand; 2) reduction of ZnO and 3) volatilization of Zn. The real-time-dependent phase-sequential evolution of the remaining products and the processing of pore forming template transformation are proposed simultaneously. The porous carbon structure featuring a uniform nano-sized pore distribution synthesized at 900 °C with the highest surface area of 1644 m2 g−1 and pore volume of 0.926 cm3 g−1 exhibits the best known capacitance of 662 F g−1 at 0.5 A g−1.  相似文献   
74.
The statin drug Simvastatin is a HMG-CoA reductase inhibitor that has been widely used to lower blood lipid. However, the drug is clinically observed to reposition a significant suppressing potency on glioblastoma (GBM) by unexpectedly targeting diverse kinase pathways involved in GBM tumorigensis. Here, an inverse screening strategy is described to discover potential kinase targets of Simvastatin. Various human protein kinases implicated in GBM are enriched to define a druggable kinome; the binding behavior of Simvastatin to the kinome is profiled systematically via an integrative computational approach, from which most kinases have only low or moderate binding potency to Simvastatin, while only few are identified as promising kinase hits. It is revealed that Simvastatin can potentially interact with certain known targets or key regulators of GBM such as ErbB, c-Src and FGFR signaling pathways, but exhibit low affinity to the well-established GBM target of PI3K/Akt/mTOR pathway. Further assays determine that Simvastatin can inhibit kinase hits EGFR, MET, SRC and HER2 at nanomolar level, which are comparable with those of cognate kinase inhibitors. Structural analyses reveal that the sophisticated T790 M gatekeeper mutation can considerably reduce Simvastatin sensitivity to EGFR by inducing the ligand change between different binding modes.  相似文献   
75.
Abstract

Novel Mannich base derivatives of glabridin were synthesized and their antiproliferative activity were performed along with our previously reported glabridin-chalcone hybrids molecules (GCHMs) against various human cell lines MDA-MB-231 (breast adenocarcinoma), HEK-293 (embryonic kidney cell line), K562 (leukemia), MCF-7 (breast adenocarcinoma), HeLa (cervix adenocarcinoma), HepG2 (hepatocellular carcinoma) and WRL-68 (hepatic carcinoma). The result showed that the glabridin significantly reduced cell proliferation with IC50 ranges from 3.67 to 58.30?µM against all the tested cell lines. The remarkable reduction in antiproliferative activity 2’,4’-dimethoxyglabridin and GCHMs compounds with phenolic OH groups protected by methoxy (OCH3) groups suggested that the free OH groups are essential factor for the antiproliferative activity of glabridin and its derivatives. The Mannich base derivatives of glabridin showed moderate activity IC50 (2.20–>95.78?µM). Furthermore, in silico target identification analysis revealed that AKT1, DECR1 and NOS1 are the potential targets for glabridin and their derivatives.  相似文献   
76.
Particle-laden flows are calculated for a classical laminar backward- facing step problem. The particle tracks are calculated using a recently developed exponential Lagrangian tracking scheme. The behaviour of the particle-laden flow is considered for various inlet for Reynolds number, Stokes numbers and void fractions. Doping the flow with low-Stokes-number particles has the effect of increasing the inlet inertia of the flow and this increases the strength of the recirculation behind the step. High-Stokes- number particles are dominated by gravitational effects which affect the flow accordingly. Differences between the single-phase flow and the particle-laden flows are therefore dependent on the Stokes number and increase linearly with void fraction.  相似文献   
77.
灰度人脸识别形态学相关的一般理论研究   总被引:5,自引:4,他引:1  
余杨  张旭苹 《光子学报》2006,35(2):299-303
提出一般形态学相关概念,并提出一种小型联合变换相关器的硬件设计以实现一般形态学相关.提出两种改进的一般形态学相关算法,灰度图像按某种分解方法分解成一系列二值图像片.在第一种算法中,每片二值联合图像片的边缘被检测,其功率谱求和.在第二种算法中,一种情况是每片的联合变换功率谱被二值化或细化再求和;另一种情况是这些片的联合变换功率谱的总和被二值化或细化.计算机模拟结果表明,改进后的算法能改善高相似度灰度人脸图像识别的鉴别率.  相似文献   
78.
中高分辨力遥感图像中飞机目标自动识别算法研究   总被引:2,自引:0,他引:2  
提出了一种中高分辨力的航空航天遥感图像中飞机目标快速自动识别的新算法。在分割和分类过程中充分利用飞机目标的先验知识,提出了一种改进区域分割方法,并应用树分类器对飞机目标进行自动识别。所提出的改进区域分割方法较好地实现了区域分割中阈值的准确自动选取,克服了复杂背景图像中小目标的全局阈值自动分割的失效问题。采用二叉树分类器,通过提取简单的目标几何特征,分层进行种类识别,提高了识别速度,降低了漏检率和虚警率。运用该方法进行了实验。结果表明,识别率达到了100%。  相似文献   
79.
基于DIGNET网络的数据融合方法   总被引:2,自引:0,他引:2  
针对数据融合和目标识别的特点,提出了基于DIGNET自组织聚类人工神经网络的数据融合方法。考虑到多传感器系统测量多个参量的特点,用并行的子网络结构代替中间隐层,实现了基于决策层的信息融合目标识别。利用仿真数据对基于DIGNET的数据融合方法进行了实验研究。实验结果表明,该方法具有数据正确分类率高和抗噪能力强等优点,有效地实现了融合识别。将该方法应用于前视红外和可见光双传感器目标跟踪系统的数据融合识别是可行的。  相似文献   
80.
基于红外/毫米波双模融合的目标识别方法   总被引:2,自引:1,他引:1  
在数据融合的基础上,以红外/毫米波双模传感器的智能融合结构为模型,将模糊神经网络与D-S证据理论相结合,提出了一种新的目标识别方法.该算法根据红外/毫米波传感器的性能及工作范围,构造模糊变量作为神经网络的输入,根据神经网络的不同输出判别目标的真伪,并利用D-S证据理论进行目标身份识别.仿真结果证明了该算法的可行性.  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