全文获取类型
收费全文 | 8798篇 |
免费 | 987篇 |
国内免费 | 595篇 |
专业分类
化学 | 6367篇 |
晶体学 | 30篇 |
力学 | 228篇 |
综合类 | 117篇 |
数学 | 307篇 |
物理学 | 3331篇 |
出版年
2024年 | 14篇 |
2023年 | 122篇 |
2022年 | 250篇 |
2021年 | 392篇 |
2020年 | 367篇 |
2019年 | 303篇 |
2018年 | 226篇 |
2017年 | 399篇 |
2016年 | 438篇 |
2015年 | 443篇 |
2014年 | 597篇 |
2013年 | 581篇 |
2012年 | 638篇 |
2011年 | 518篇 |
2010年 | 467篇 |
2009年 | 554篇 |
2008年 | 503篇 |
2007年 | 508篇 |
2006年 | 437篇 |
2005年 | 457篇 |
2004年 | 395篇 |
2003年 | 245篇 |
2002年 | 186篇 |
2001年 | 130篇 |
2000年 | 127篇 |
1999年 | 117篇 |
1998年 | 100篇 |
1997年 | 106篇 |
1996年 | 82篇 |
1995年 | 104篇 |
1994年 | 61篇 |
1993年 | 65篇 |
1992年 | 58篇 |
1991年 | 36篇 |
1990年 | 54篇 |
1989年 | 46篇 |
1988年 | 51篇 |
1987年 | 41篇 |
1986年 | 29篇 |
1985年 | 28篇 |
1984年 | 18篇 |
1983年 | 17篇 |
1982年 | 31篇 |
1981年 | 14篇 |
1980年 | 5篇 |
1979年 | 11篇 |
1978年 | 3篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
21.
Benjamin Brennecke Qinghua Wang Qingyang Zhang Hai‐Yu Hu Marc Nazar 《Angewandte Chemie (International ed. in English)》2020,59(22):8512-8516
Herein we report the development of a turn‐on lanthanide luminescent probe for time‐gated detection of nitroreductases (NTRs) in live bacteria. The probe is activated through NTR‐induced formation of the sensitizing carbostyril antenna and resulting energy transfer to the lanthanide center. This novel NTR‐responsive trigger is virtually non‐fluorescent in its inactivated form and features a large signal increase upon activation. We show that the probe is capable of selectively sensing NTR in lysates as well as in live bacteria of the ESKAPE family which are clinically highly relevant multiresistant pathogens responsible for the majority of hospital infections. The results suggest that our probe could be used to develop diagnostic tools for bacterial infections. 相似文献
22.
超精密单点金刚石车削过程中需要对刀具参数进行检测。基于机器视觉原理,采用新型的机械结构设计了新型刀具在线检测系统。通过垂直放置的两组由同轴远心镜头和CMOS相机组成的光学系统来获取车刀刀尖正面及侧面的图像,再经图像处理系统来获取刀具的轮廓及位置信息,完成对刀具轮廓及位置的在线检测,实验验证可实现测量的重复性定位精度达1μm。在线检测的方式借助了超精密车床自身的高精度和运动机构,可以保证相机焦点和机床主轴之间的相对位置关系,弥补了目前刀具检测系统稳定性差和重复性精度低的不足,提高了加工的整体效率。 相似文献
23.
大视场、低成本、高性能天文望远镜是当前研究和开发的热点。基于像差平衡原理,在正入射施密特矫正板基础上推导出斜入射反射式施密特矫正板方程,针对焦距1 700 mm,成像视场角4°,波段为0.4 μm~0.9 μm,F数为4.25的光学系统,求解出施密特矫正板方程,并作为初始结构参数代入Zemax软件进一步优化。设计结果表明,在全视场范围内,该系统在奈奎斯特频率100 lp/mm处的调制传递函数MTF大于0.35,畸变小于2.5%,成像质量达到了衍射极限。优化设计后施密特矫正板与最近球面最大偏差为0.005 mm,采用特制的补偿器结合干涉仪可完成面形高精度检测。该施密特系统的设计为大视场、宽波段天文望远镜的开发提供了参考。 相似文献
24.
《Physics letters. A》2020,384(32):126832
We propose a novel method for detection of the faint machinery vibration at the nanometer resolution based on the spin magnetic resonant effect. A suspension magnet acts as a vibration sensor to transfer the vibration signals as the magnetic field fluctuation to excite the spin magnetic resonance. Due to the high sensitivity of the magnetic field of the nitrogen-vacancy center in diamond, the theoretical detection limit of mechanical vibration is as high as 5.7 nm, and the actual measurement resolution reached 12.8 nm, and proved the potential for further improvement to ∼pm resolution. The feasibility of this method is verified by dynamic tests. This method provides a novel approach for the detection of micro-mechanical vibrations. 相似文献
25.
为实现激光束对空域的有效扫描和探测,研究了栅形扫描、李萨茹形扫描、螺旋形扫描和六边形扫描四种常见的激光雷达扫描方式,推导了相应的扫描方程,讨论了参数的物理意义及调整方法;重点研究了栅形扫描和六边形扫描方式下光斑的分布情况,通过仿真分析了两种扫描方式下光束的漏扫率和重叠率,结果表明,在相同扫描条件下六边形扫描方式的漏扫区域最少。展示了基于上述研究内容的扫描控制系统实物图及扫描图案。分析总结了四种扫描方式的特点,给出了每种扫描方式的适用情况及使用建议。 相似文献
26.
黑色签字笔字迹种类与书写时间的鉴定一直是国内外法庭科学研究领域的热点问题。基于拉曼光谱法的分辨率高、稳定性好、效率高以及无损检测等优点,对收集的16种品牌或牌号的黑色签字笔字迹样本进行测试。完成同一品牌或牌号同一时间在不同存储条件(暗室和光照)与不同纸张本底(复印纸和笔记本)字迹样本的制备。将样本字迹剪裁,双面胶固定在载玻片上,放入储存箱内避光保存,间隔一段时间对样品进行测试,测试工作共持续1年,形成图谱数据库。在考察实验条件如测量点、激光功率及共焦类型等因素影响的基础上,筛选出最佳条件。在此条件基础上,检测黑色签字笔在不同书写时间、储存环境、纸张本底等条件下的字迹样本。实验结果表明:(1)存储条件(暗室和光照)、纸张本底(复印纸和笔记本)等不同条件下,同种黑色签字笔字迹的拉曼位移相同,重复性好,受水和纸张等本底的干扰较小。(2)根据拉曼位移的差异可将16种黑色签字笔分成5类。(3)以2#样本为例, 1 140 cm^-1处拉曼光谱特征峰,归属为酯类化合物的C-O伸缩振动ν(CO)。酯类化合物的含量随着时间延长而不断减少,因此随着书写时间越久远,特征峰的相对强度越大(8→1)。通过拟合后计算出相对面积数值I,样本书写时间越早,I值越大,反之I值越小。研究结果可用于快速、准确、无损判定黑色签字笔字迹的种类和推断其相对书写时间。 相似文献
27.
Yanxia Xu Yanbing Lv Ruili Wu Huaibin Shen Huawei Yang Han Zhang Jinjie Li Lin Song Li 《Particle & Particle Systems Characterization》2020,37(3):1900441
Indium phosphide (InP) quantum dots (QDs) are ideal substitutes for widely used cadmium-based QDs and have great application prospects in biological fields due to their environmentally benign properties and human safety. However, the synthesis of InP core/shell QDs with biocompatibility, high quantum yield (QY), uniform particle size, and high stability is still a challenging subject. Herein, high quality (QY up to 72%) thick shell InP/GaP/ZnS core/shell QDs (12.8 ± 1.4 nm) are synthesized using multiple injections of shell precursor and extension of shell growth time, with GaP serving as the intermediate layer and 1-octanethiol acting as the new S source. The thick shell InP/GaP/ZnS core/shell QDs still keep high QY and photostability after transfer into water. InP/GaP/ZnS core/shell QDs as fluorescence labels to establish QD-based fluorescence-linked immunosorbent assay (QD-FLISA) for quantitative detection of C-reactive protein (CRP), and a calibration curve is established between fluorescence intensity and CRP concentrations (range: 1–800 ng mL−1, correlation coefficient: R2 = 0.9992). The limit of detection is 2.9 ng mL−1, which increases twofold compared to previously reported cadmium-free QD-based immunoassays. Thus, InP/GaP/ZnS core/shell QDs as a great promise fluorescence labeling material, provide a new route for cadmium-free sensitive and specific immunoassays in biomedical fields. 相似文献
28.
QiuHong Wang Abdusalam Abdukerim Wei Chen Xun Chen YunHua Chen XiangYi Cui YingJie Fan DeQing Fang ChangBo Fu LiSheng Geng Karl Giboni Franco Giuliani LinHui Gu XuYuan Guo Ke Han ChangDa He Di Huang Yan Huang YanLin Huang Zhou Huang Peng Ji XiangDong Ji YongLin Ju YiHui Lai Kun Liang HuaXuan Liu JiangLai Liu WenBo Ma YuGang Ma YaJun Mao Yue Meng Parinya Namwongsa KaiXiang Ni JinHua Ning XuYang Ning XiangXiang Ren ChangSong Shang Lin Si AnDi Tan AnQing Wang HongWei Wang Meng Wang SiGuang Wang XiuLi Wang Zhou Wang MengMeng Wu ShiYong Wu JingKai Xia MengJiao Xiao PengWei Xie BinBin Yan JiJun Yang Yong Yang ChunXu Yu Jumin Yuan Dan Zhang HongGuang Zhang Tao Zhang Li Zhao QiBin Zheng JiFang Zhou Ning Zhou XiaoPeng Zhou 《中国科学:物理学 力学 天文学(英文版)》2020,(3):54-63
In dark matter direct detection experiments,neutron is a serious source of background,which can mimic the dark matter-nucleus scattering signals.In this paper,we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach.Instead of fully relying on the Monte Carlo simulation,the overall neutron background is determined from the neutron-induced high energy signals in the data.In addition,the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator,where the correlated emission of neutron(s)andγ(s)in the(α,n)reactions and spontaneous fissions is taken into consideration.With this method,the neutron backgrounds in the Run 9(26-ton-day)and Run 10(28-ton-day)data sets of PandaX-II are estimated to be(0.66±0.24)and(0.47±0.25)events,respectively. 相似文献
29.
M. Araceli Snchez-Snchez Cristina Conde Beatriz Gmez-Aylln David Ortega-DelCampo Aristeidis Tsitiridis Daniel Palacios-Alonso Enrique Cabello 《Entropy (Basel, Switzerland)》2020,22(11)
Automated border control systems are the first critical infrastructure point when crossing a border country. Crossing border lines for unauthorized passengers is a high security risk to any country. This paper presents a multispectral analysis of presentation attack detection for facial biometrics using the learned features from a convolutional neural network. Three sensors are considered to design and develop a new database that is composed of visible (VIS), near-infrared (NIR), and thermal images. Most studies are based on laboratory or ideal conditions-controlled environments. However, in a real scenario, a subject’s situation is completely modified due to diverse physiological conditions, such as stress, temperature changes, sweating, and increased blood pressure. For this reason, the added value of this study is that this database was acquired in situ. The attacks considered were printed, masked, and displayed images. In addition, five classifiers were used to detect the presentation attack. Note that thermal sensors provide better performance than other solutions. The results present better outputs when all sensors are used together, regardless of whether classifier or feature-level fusion is considered. Finally, classifiers such as KNN or SVM show high performance and low computational level. 相似文献
30.
《中国化学快报》2020,31(8):2099-2102
In this work, the two-dimensional MoS2 film was prepared by sulfuring the molybdenum atomic layer on SiO2/Si substrate. The reaction temperature, heating rate, holding time and carrier gas flow rate were investigated comprehensively. The quality of MoS2 film was characterized by optical microscopy, atomic force microscopy, Raman and photoluminescence spectroscopy. The characterization results showed that the optimum synthesis parameters were heating rate of 25 °C/min, reaction temperature of 750 °C, holding time of 30 min and carrier gas velocity of 100 sccm. The MoS2 gas sensor was fabricated and its gas sensing performance was tested. The test results indicated that the sensor had a good response to both reducing gas (NH3) and oxidizing gas (NO2) at room temperature. The sensitivity to 100 ppm of NO2 was 31.3%, and the response/recovery times were 4 s and 5 s, respectively. In addition, the limit of detection could be as low as 1 ppm. This work helps us to develop low power and integrable room temperature NO2 sensors. 相似文献