全文获取类型
收费全文 | 551261篇 |
免费 | 4880篇 |
国内免费 | 1554篇 |
专业分类
化学 | 276771篇 |
晶体学 | 6837篇 |
力学 | 27262篇 |
综合类 | 29篇 |
数学 | 76708篇 |
物理学 | 170088篇 |
出版年
2021年 | 5047篇 |
2020年 | 5528篇 |
2019年 | 6267篇 |
2018年 | 9561篇 |
2017年 | 9915篇 |
2016年 | 12334篇 |
2015年 | 6724篇 |
2014年 | 10921篇 |
2013年 | 24152篇 |
2012年 | 21192篇 |
2011年 | 23944篇 |
2010年 | 17835篇 |
2009年 | 17506篇 |
2008年 | 21229篇 |
2007年 | 21103篇 |
2006年 | 19194篇 |
2005年 | 20670篇 |
2004年 | 19054篇 |
2003年 | 16063篇 |
2002年 | 14302篇 |
2001年 | 14917篇 |
2000年 | 11426篇 |
1999年 | 8869篇 |
1998年 | 7695篇 |
1997年 | 7535篇 |
1996年 | 6980篇 |
1995年 | 6306篇 |
1994年 | 6310篇 |
1993年 | 6036篇 |
1992年 | 6507篇 |
1991年 | 6980篇 |
1990年 | 6545篇 |
1989年 | 6419篇 |
1988年 | 6253篇 |
1987年 | 6068篇 |
1986年 | 5779篇 |
1985年 | 7329篇 |
1984年 | 7701篇 |
1983年 | 6468篇 |
1982年 | 6751篇 |
1981年 | 6242篇 |
1980年 | 5908篇 |
1979年 | 6450篇 |
1978年 | 6681篇 |
1977年 | 6606篇 |
1976年 | 6594篇 |
1975年 | 6273篇 |
1974年 | 6098篇 |
1973年 | 6429篇 |
1972年 | 4702篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
71.
Abiola O. Ajayeoba Adewoye A. Olanipekun Wasiu A. Raheem Oluwaseun O. Ojo Ayowumi R. Soji–Adekunle 《声与振动》2021,55(1):69-85
Economic wood processing employs the use of industrial machines for cutting, shaping, milling, and sawing timber, thereby leading to the generation of high levels of noise. Published data from empirical studies have categorized noise as an environmental hazard of global significance. Furthermore, noise exposure limits for different industries and all the industrial machines available has not been formally established as it presently exists in developed nations around the world. Therefore, this study assessed the daily exposure of sawmills workers to noise in Southwestern Nigeria. Reconnaissance surveys were first carried out in Osun, Oyo, Ondo, Ekiti, Lagos, and Ogun States to select sawmills that were fully operational and fit for the study. Two fully functional sawmills in two cities of each State were eventually selected for data collection, making a total of 24 sawmills, while the Circular Machines (CM), Planer Machines (PM), and Band-saw Machines (BM) were the machines in each sawmill considered. Two machines each of CM, PM, and BM were considered in each sawmill, making a total of forty-eight (48) machines each of CM, PM, and BM. Sound data were collected between 7 am and 7 pm each day for six days (between Monday and Saturday) using Extech 407732 sound level meter and all stabilized measurements were taken three times at different intervals. The data collected were in three different periods: Machine No-work Period (NPm), Machine Idle Period (IPm), and Machine Working Period (WPm). A two–way Analysis of Variance (ANOVA) was carried out at P < 0.05 to determine whether there is a significant difference in the sound level average before and after the break, for both the idle and working periods of the three machines considered. This was also done to determine whether there is a significant difference between the sound level average of the results collected during idle and working periods of the three machines. Noise Pollution Levels (Lnp) ranged from 83.20 dB (PM) to 107.65 (BM) and 93.42 (CM and PM) – 116.00 (BM) respectively, while IPm also gave the least noise pollution level of 95.79 dB and WPm gave the highest level of 102.88 dB. The results revealed that all the machines’ Lnp values in the working period are more than the 90 dB acceptable limit the recommendation value of 90 dB while 89.6% of CMs, 75% of PMs, and 89.6% of BM had their Lnp above 90 dB in the idle period respectively. The minimum and the maximum noise dose levels for IPm, WPm and overall are 0.09 (BM) and 2.37 (CM), 0.50 (CM), and 4.77 (PM) and 0.69 (BM) and 6.64 (PM) respectively. The study found out that the fundamental contributing factors to the high noise levels in sawmills are poor machine maintenance, use of old and obsolete machines, poor housekeeping strategy, limited space, workers’ negligence, lack of PPE, and lack of occupational safety training. The study recommends that proper workplace practices such as use of personal protective equipment, new and modern machines, training, and occupational safety programmes be implemented in the considered sawmills. 相似文献
72.
73.
Nonlinear Dynamics - In this paper, we analyze the effect which the choice of a friction model has on tippe top inversion in the case where the resulting action of all dissipative forces is... 相似文献
74.
Safaei Bezgabadi A. Zarandi M. Borhani Bolorizadeh M. A. 《Optical and Quantum Electronics》2021,53(3):1-20
Optical and Quantum Electronics - Classification of hyperspectral image (HSI) is widely used for the study of remotely sensed images. Convolutional Neural Networks (CNNs) are one of the most... 相似文献
75.
Zmushko V. V. Razin A. N. Sinelnikova A. A. 《Journal of Applied Mechanics and Technical Physics》2022,63(3):400-407
Journal of Applied Mechanics and Technical Physics - Turbulent mixing at interfaces of three-layer gas systems after shock-wave passage has been studied. The influence of the initial roughness of... 相似文献
76.
Radiophysics and Quantum Electronics - We find self-consistent stationary distributions of the electric field and plasma density in the process of ionization self-channeling of quasielectrostatic... 相似文献
77.
Physics of Atomic Nuclei - We have investigated the robustness of the spin-navigator based method for manipulating the beam polarization to bend magnet installation errors. Toward that end,... 相似文献
78.
Chueshova A. G. Pavlova L. A. Peshcherova S. M. Nepomnyashchikh A. I. 《Crystallography Reports》2021,66(7):1206-1215
Crystallography Reports - The orientation of grains and the special boundaries formed by them in multicrystalline silicon has been studied by electron backscattered diffraction. It is found that... 相似文献
79.
Crystallography Reports - Some questions related to the establishment, development, and prospects of physical studies using inelastic thermal-neutron scattering are briefly reviewed. The directions... 相似文献
80.
Avrutskiy V. I. Ishkhanyan A. M. Krainov V. P. 《Theoretical and Mathematical Physics》2021,208(3):1201-1206
Theoretical and Mathematical Physics - The fractional derivative method is used to take wave dispersion into account in the wave equation when describing the propagation of gravitational soliton... 相似文献