全文获取类型
收费全文 | 428071篇 |
免费 | 8051篇 |
国内免费 | 5238篇 |
专业分类
化学 | 213088篇 |
晶体学 | 6337篇 |
力学 | 23182篇 |
综合类 | 331篇 |
数学 | 62008篇 |
物理学 | 136414篇 |
出版年
2021年 | 3517篇 |
2020年 | 4102篇 |
2019年 | 4453篇 |
2018年 | 12696篇 |
2017年 | 13155篇 |
2016年 | 10789篇 |
2015年 | 5481篇 |
2014年 | 7412篇 |
2013年 | 15123篇 |
2012年 | 16122篇 |
2011年 | 24735篇 |
2010年 | 16584篇 |
2009年 | 16449篇 |
2008年 | 21820篇 |
2007年 | 24606篇 |
2006年 | 12219篇 |
2005年 | 15944篇 |
2004年 | 12479篇 |
2003年 | 11781篇 |
2002年 | 10209篇 |
2001年 | 9514篇 |
2000年 | 7607篇 |
1999年 | 5760篇 |
1998年 | 5191篇 |
1997年 | 4962篇 |
1996年 | 4864篇 |
1995年 | 4355篇 |
1994年 | 4540篇 |
1993年 | 4189篇 |
1992年 | 4585篇 |
1991年 | 4633篇 |
1990年 | 4573篇 |
1989年 | 4345篇 |
1988年 | 4370篇 |
1987年 | 4223篇 |
1986年 | 4040篇 |
1985年 | 5149篇 |
1984年 | 5412篇 |
1983年 | 4561篇 |
1982年 | 4676篇 |
1981年 | 4551篇 |
1980年 | 4454篇 |
1979年 | 4566篇 |
1978年 | 4885篇 |
1977年 | 4741篇 |
1976年 | 4891篇 |
1975年 | 4480篇 |
1974年 | 4565篇 |
1973年 | 4749篇 |
1972年 | 3457篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
Chandrachood Pranav S. Jadhav Amol R. Garud Dinesh R. Deshpande Nirmala R. Puranik Vedavati G. Kashalkar Rajashree V. 《Research on Chemical Intermediates》2020,46(12):5219-5230
Research on Chemical Intermediates - A series of quinoxaline derivatives were efficiently synthesized by convenient and simple procedure in excellent yields using 1 wt.% of titanium silicate (TS-1)... 相似文献
142.
143.
Galkina E. G. Zaspel C. E. Ivanov B. A. Kulagin N. E. Lerman L. M. 《JETP Letters》2019,110(7):481-486
JETP Letters - The motion of domain walls in GdFeCo-type ferrimagnets near the point of compensation of sublattice spins s1 and s2, when the effects of the exchange increase in the limiting wall... 相似文献
144.
145.
Yeong‐Tarng Shieh Pei‐Yu Tai Chih‐Chia Cheng 《Journal of polymer science. Part A, Polymer chemistry》2019,57(21):2149-2156
Poly(methyl methacrylate) (PMMA) nanoparticles with a sensitive CO2‐responsive hydrophilic/hydrophobic surface that confers controlled dispersion and aggregation in water were prepared by emulsion polymerization at 50 °C under CO2 bubbling using amphiphilic diblock copolymers of 2‐dimethylaminoethyl methacrylate (DMAEMA) and N‐isopropyl acrylamide (NIPAAm) as an emulsifier. The amphiphilicity of the hydrophobic–hydrophilic diblock copolymer at 50 °C was triggered by CO2 bubbling in water and enabled the copolymer to serve as an emulsifier. The resulting PMMA nanoparticles were spherical, approximately 100 nm in diameter and exhibited sensitive CO2/N2‐responsive dispersion/aggregation in water. Using copolymers with a longer PNIPAAm block length as an emulsifier resulted in smaller particles. A higher concentration of copolymer emulsifier led to particles with a stickier surface. Given its simple preparation and reversible CO2‐triggered amphiphilic behavior, this newly developed block copolymer emulsifier offers a highly efficient route toward the fabrication of sensitive CO2‐stimuli responsive polymeric nanoparticle dispersions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2149–2156 相似文献
146.
K.M.J. Rocha R.G. Leitão E.G. Oliveira-Barros M.A. Oliveira C.G.L. Canellas M.J. Anjos L.E. Nasciutti R.T. Lopes 《X射线光谱测定》2019,48(5):476-481
Prostate cancer is a highly prevalent disease and ranks second among malignant neoplasms that affect men around the world, behind lung cancer alone. Trace elements are very important and are involved in many cellular processes. The X-ray microfluorescence technique is an advanced tool of high spatial resolution, sensitivity, multielemental analysis, and nondestructiveness for trace element study. This study aimed to investigate the elemental distribution in spheroids obtained through the following human prostate cell lines using synchrotron X-ray microfluorescence: tumor cell line androgen independent (DU145), tumor cell line androgen dependent (LNCaP), and normal cell line (RWPE-1). The measurements were performed with a standard geometry of 45° of incidence, excited by a white beam using a pixel of 25 μm and an acquisition time of 300 ms/pixel at the X-ray fluorescence beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). The synchrotron X-ray microfluorescence results showed differences between groups in all elements analyzed and suggested that further studies should be performed to understand the relationship of these trace elements with the progression and development of the disease. 相似文献
147.
JETP Letters - At the resonant passage of a plane elastic shear wave through an acoustically continuous heterostructure consisting of magnetic and nonmagnetic layers in a symmetric nonmagnetic... 相似文献
148.
静止轨道卫星差分吸收光谱仪采用摆扫成像方式对大气进行探测,针对其工作时CCD成像系统信噪比大于1 000、高速探测模式下探测周期小于10min、高分辨率模式下探测周期小于1h的要求,进行CCD成像系统设计.选取CCD47-20作为探测器,设计成像电路实现光谱图像信号的采集和上传.分析了帧叠加和像元合并对时间、空间分辨率的影响.结合帧转移CCD的特点设计了每个位置最后一帧读出时摆镜转动的成像方式,并合理设置了帧叠加数和像元合并数,达到优化成像周期的目的.1s曝光时间条件下,该CCD成像系统的高速、高分辨率模式探测周期分别为515s和3 315s,图像信噪比均大于1 000,污染物观测实验中未出现失帧或重复的现象.该CCD成像系统方案满足静止轨道星载差分吸收光谱仪的探测需求,为静止轨道环境监测仪器设计提供参考. 相似文献
149.
Kaplunov I. A. Kolesnikov A. I. Kropotov G. I. Rogalin V. E. 《Optics and Spectroscopy》2019,126(3):191-194
Optics and Spectroscopy - The transmission of intrinsic, antimony-doped, and gallium-doped Ge single crystals in the THz spectral range have been experimentally investigated. It is shown that the... 相似文献
150.
Yingchun Wu Haipeng Li Xuecheng Wu Gérard Gréhan Lutz Mädler Cyril Crua 《Proceedings of the Combustion Institute》2019,37(3):3211-3218
Droplet evaporation characterization, although of great significance, is still challenging. The recently developed phase rainbow refractometry (PRR) is proposed as an approach to measuring the droplet temperature, size as well as evaporation rate simultaneously, and is applied to a single flowing n-heptane droplet produced by a droplet-on-demand generator. The changes of droplet temperature and evaporation rate after a transient spark heating are reflected in the time-resolved PRR image. Results show that droplet evaporation rate increases with temperature, from ?1.28 m2/s at atmospheric 293 K to a range of (?1.5, ?8) m2/s when heated to (294, 315) K, agreeing well with the Maxwell and Stefan–Fuchs model predictions. Uncertainty analysis suggests that the main source is the indeterminate gradient inside droplet, resulting in an underestimation of droplet temperature and evaporation rate. With the demonstration on simultaneous measurements of droplet refractive index as well as droplet transient and local evaporation rate in this work, PRR is a promising tool to investigate single droplet evaporation in real engine conditions. 相似文献