全文获取类型
收费全文 | 14472篇 |
免费 | 1806篇 |
国内免费 | 678篇 |
专业分类
电工技术 | 455篇 |
综合类 | 1250篇 |
化学工业 | 2566篇 |
金属工艺 | 382篇 |
机械仪表 | 1348篇 |
建筑科学 | 842篇 |
矿业工程 | 669篇 |
能源动力 | 569篇 |
轻工业 | 1451篇 |
水利工程 | 366篇 |
石油天然气 | 429篇 |
武器工业 | 96篇 |
无线电 | 1658篇 |
一般工业技术 | 2685篇 |
冶金工业 | 1139篇 |
原子能技术 | 382篇 |
自动化技术 | 669篇 |
出版年
2024年 | 10篇 |
2023年 | 191篇 |
2022年 | 303篇 |
2021年 | 509篇 |
2020年 | 526篇 |
2019年 | 466篇 |
2018年 | 430篇 |
2017年 | 506篇 |
2016年 | 590篇 |
2015年 | 569篇 |
2014年 | 848篇 |
2013年 | 896篇 |
2012年 | 1124篇 |
2011年 | 1161篇 |
2010年 | 849篇 |
2009年 | 899篇 |
2008年 | 799篇 |
2007年 | 938篇 |
2006年 | 885篇 |
2005年 | 696篇 |
2004年 | 558篇 |
2003年 | 532篇 |
2002年 | 429篇 |
2001年 | 360篇 |
2000年 | 293篇 |
1999年 | 222篇 |
1998年 | 232篇 |
1997年 | 170篇 |
1996年 | 164篇 |
1995年 | 140篇 |
1994年 | 118篇 |
1993年 | 82篇 |
1992年 | 98篇 |
1991年 | 60篇 |
1990年 | 61篇 |
1989年 | 40篇 |
1988年 | 30篇 |
1987年 | 35篇 |
1986年 | 20篇 |
1985年 | 18篇 |
1984年 | 23篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1976年 | 4篇 |
1966年 | 2篇 |
1965年 | 3篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
1.
Yin-Feng Wang Meng Li Jin-Ming Teng He-Ye Zhou Chuan-Feng Chen 《Advanced functional materials》2021,31(49):2106418
Recently, circularly polarized organic light-emitting diodes (CP-OLEDs) fabricated with thermally activated delayed fluorescence (TADF) emitters are developed rapidly. However, most devices are fabricated by vacuum deposition technology, and developing efficient solution-processed CP-OLEDs, especially nondoped devices, is still a challenge. Herein, a pair of triptycene-based enantiomers, (S,S)-/(R,R)-TpAc-TRZ, are synthesized. The novel chiral triptycene scaffold of enantiomers avoids their intermolecular π–π stacking, which is conducive to their aggregation-induced emission characteristics and high photoluminescence quantum yield of 85% in the solid state. Moreover, the triptycene-based enantiomers exhibit efficient TADF activities with a small singlet-triplet energy gap (ΔEST) of 0.03 eV and delayed fluorescence lifetime of 1.1 µs, as well as intense circularly polarized luminescence with dissymmetry factors (|gPL|) of about 1.9 × 10−3. The solution-processed nondoped CP-OLEDs based on (S,S)-/(R,R)-TpAc-TRZ not only display obvious circularly polarized electroluminescence signals with gEL values of +1.5 × 10−3 and −2.0 × 10−3, respectively, but also achieve high efficiencies with external quantum, current, and power efficiency up to 25.5%, 88.6 cd A−1, and 95.9 lm W−1, respectively. 相似文献
2.
构建下转换荧光-适配体免疫层析试纸条用于食品中黄曲霉毒素B1(aflatoxin B1,AFB1)的快速高效检测。体系中AFB1存在会减弱下转换荧光-适配体纳米颗粒层析至T线时与AFB1半抗原的结合能力,从而导致下转换荧光信号衰减,进而实现对AFB1的高效检测。该方法在AFB1质量浓度1~40 ng/mL范围内与荧光信号呈良好的线性关系,线性相关系数为0.994,检测限为0.287 ng/mL。该方法利用稀土掺杂荧光纳米颗粒的长寿命发光及近红外荧光特性,有效降低了生物背景荧光干扰并提高了检测体系的特异性。该方法在AFB1的快速高灵敏检测中具有良好的应用前景。 相似文献
3.
随着科学技术的快速发展,荧光显微镜成像在生物医学领域的应用越来越广泛。常见的荧光显微镜大致可分为普通荧光显微镜、激光扫描共聚焦显微镜、超分辨率显微镜和多光子激光扫描显微镜。本文详述了几种常见显微镜的原理、特性及其在生物医学中的应用。 相似文献
4.
5.
为研究身管烧蚀磨损对弹体发射强度的影响规律,建立了烧蚀磨损身管与弹丸的弹炮耦合有限元模型和内弹道数学模型。采用内弹道方程与弹炮耦合有限元模型双向求解算法对内弹道方程进行求解,试验与算例的对比结果验证了模型的正确性。以弹丸挤进时刻、最大膛压时刻、弹体与身管碰撞时刻的临界状态应力为表征量,分析了弹体发射强度随身管烧蚀磨损量的变化规律。结果表明,严重磨损工况相对于正常身管工况,前2个临界状态应力值分别降低了19.4%、12.5%,第3个临界状态应力增大了149.2%。由此可知,随着烧蚀磨损量增大,弹丸挤进时刻、最大膛压时刻的临界状态应力对发射强度影响度在降低,而弹丸与身管碰撞临界状态应力成为影响弹体结构发射强度的主要因素。 相似文献
6.
7.
Jos L. Neira Ana Cmara-Artigas Jos Gins Hernndez-Cifre María Grazia Ortore 《International journal of molecular sciences》2021,22(6)
The histidine phosphocarrier protein (HPr) kinase/phosphorylase (HPrK/P) modulates the phosphorylation state of the HPr protein, and it is involved in the use of carbon sources by Gram-positive bacteria. Its X-ray structure, as concluded from crystals of proteins from several species, is a hexamer; however, there are no studies about its conformational stability, and how its structure is modified by the pH. We have embarked on the conformational characterization of HPrK/P of Bacillus subtilis (bsHPrK/P) in solution by using several spectroscopic (namely, fluorescence and circular dichroism (CD)) and biophysical techniques (namely, small-angle X-ray-scattering (SAXS) and dynamic light-scattering (DLS)). bsHPrK/P was mainly a hexamer in solution at pH 7.0, in the presence of phosphate. The protein had a high conformational stability, with an apparent thermal denaturation midpoint of ~70 °C, at pH 7.0, as monitored by fluorescence and CD. The protein was very pH-sensitive, precipitated between pH 3.5 and 6.5; below pH 3.5, it had a molten-globule-like conformation; and it acquired a native-like structure in a narrow pH range (between pH 7.0 and 8.0). Guanidinium hydrochloride (GdmCl) denaturation occurred through an oligomeric intermediate. On the other hand, urea denaturation occurred as a single transition, in the range of concentrations between 1.8 and 18 µM, as detected by far-UV CD and fluorescence. 相似文献
8.
Gheorghita Menghiu Vasile Ostafe Radivoje Prodanovi Rainer Fischer Raluca Ostafe 《International journal of molecular sciences》2021,22(6)
Chitinases catalyze the degradation of chitin, a polymer of N-acetylglucosamine found in crustacean shells, insect cuticles, and fungal cell walls. There is great interest in the development of improved chitinases to address the environmental burden of chitin waste from the food processing industry as well as the potential medical, agricultural, and industrial uses of partially deacetylated chitin (chitosan) and its products (chito-oligosaccharides). The depolymerization of chitin can be achieved using chemical and physical treatments, but an enzymatic process would be more environmentally friendly and more sustainable. However, chitinases are slow-acting enzymes, limiting their biotechnological exploitation, although this can be overcome by molecular evolution approaches to enhance the features required for specific applications. The two main goals of this study were the development of a high-throughput screening system for chitinase activity (which could be extrapolated to other hydrolytic enzymes), and the deployment of this new method to select improved chitinase variants. We therefore cloned and expressed the Bacillus licheniformis DSM8785 chitinase A (chiA) gene in Escherichia coli BL21 (DE3) cells and generated a mutant library by error-prone PCR. We then developed a screening method based on fluorescence-activated cell sorting (FACS) using the model substrate 4-methylumbelliferyl β-d-N,N′,N″-triacetyl chitotrioside to identify improved enzymes. We prevented cross-talk between emulsion compartments caused by the hydrophobicity of 4-methylumbelliferone, the fluorescent product of the enzymatic reaction, by incorporating cyclodextrins into the aqueous phases. We also addressed the toxicity of long-term chiA expression in E. coli by limiting the reaction time. We identified 12 mutants containing 2–8 mutations per gene resulting in up to twofold higher activity than wild-type ChiA. 相似文献
9.
中性束注入加热为全超导非圆截面托卡马克(EAST)主要辅助加热方式之一。伴随着中性束注入加热,等离子体中子出射强度可达到1014 n/s。由于中性束注入窗口具有较大的开口尺寸,窗口泄露的大量中子可能影响系统的安全稳定运行。本文基于EAST 中性束二维模型和蒙特卡洛程序MCNP与材料活化程序FISPACT, 研究EAST 两条中性束夹角112.5°时,中性束关键部件材料SS304和铜活化情况,并研究材料活化所导致的停机剂量率,最后利用高纯锗能谱仪测量活化核素的γ能谱。研究表明,理论模拟与实验测量结果吻合较好。中长寿命核素51Cr、58Co、54Mn等为SS304主要活化核素。EAST停止运行5 min后,停机剂量率已经降低到国际热核聚变实验堆计划(ITER)设计的剂量率限值10-5 Sv/h。本研究可为研究聚变堆中性束注入窗口的材料活化和停机维护方案设计提供指导。 相似文献
10.
以海洋微拟球藻Nannochloropsis oceanica为受试对象,采用尼罗红染色荧光定量胞内油脂含量。采用单因素实验考察了激发波长、发射波长、二甲基亚砜体积分数、染色时间、尼罗红质量浓度对微藻胞内油脂荧光强度的影响,在此基础上,采用响应面实验进行染色荧光定量条件优化。结果表明,优化的微拟球藻胞内油脂尼罗红染色荧光定量最佳条件为二甲基亚砜体积分数25.6%、染色时间16 min、尼罗红质量浓度0.11 μg/mL、激发波长430 nm、发射波长685 nm。在最佳条件下,尼罗红染色微拟球藻胞内油脂荧光强度与油脂含量显著正相关(R2=0999 9),说明通过尼罗红染色荧光法可快速表征微拟球藻胞内油脂含量。研究结果为后续微拟球藻资源高值化应用及高产油脂海洋微藻快速筛选和动态追踪微藻产油过程提供了依据。 相似文献