全文获取类型
收费全文 | 129090篇 |
免费 | 8842篇 |
国内免费 | 6073篇 |
专业分类
化学 | 60505篇 |
晶体学 | 1405篇 |
力学 | 9621篇 |
综合类 | 348篇 |
数学 | 37501篇 |
物理学 | 34625篇 |
出版年
2024年 | 183篇 |
2023年 | 1136篇 |
2022年 | 2119篇 |
2021年 | 2237篇 |
2020年 | 2316篇 |
2019年 | 2170篇 |
2018年 | 11848篇 |
2017年 | 11628篇 |
2016年 | 8454篇 |
2015年 | 3471篇 |
2014年 | 3407篇 |
2013年 | 4293篇 |
2012年 | 8515篇 |
2011年 | 15004篇 |
2010年 | 8785篇 |
2009年 | 8970篇 |
2008年 | 9755篇 |
2007年 | 11501篇 |
2006年 | 2875篇 |
2005年 | 3545篇 |
2004年 | 3232篇 |
2003年 | 3322篇 |
2002年 | 2272篇 |
2001年 | 1261篇 |
2000年 | 1191篇 |
1999年 | 1205篇 |
1998年 | 1057篇 |
1997年 | 958篇 |
1996年 | 997篇 |
1995年 | 847篇 |
1994年 | 689篇 |
1993年 | 614篇 |
1992年 | 483篇 |
1991年 | 456篇 |
1990年 | 381篇 |
1989年 | 298篇 |
1988年 | 238篇 |
1987年 | 223篇 |
1986年 | 217篇 |
1985年 | 186篇 |
1984年 | 129篇 |
1983年 | 129篇 |
1982年 | 96篇 |
1981年 | 77篇 |
1980年 | 75篇 |
1979年 | 62篇 |
1978年 | 42篇 |
1973年 | 41篇 |
1914年 | 45篇 |
1909年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
By constructing close-one-cochain density Ω^12n in the gauge group space we get the Wess-Zumino-Witten (WZW) effective Lagrangian on high-dimensional noncommutative space.Especially consistent anomalies derived from this WZW effective action in noncommutative four-dimensional space coincide with those obtained by L.Bonora etc.(het-th/0002210). 相似文献
102.
The most promising next generation Image Velocimtry (IV) is the high-speed Dynamic PIV. It requires the development of innovative
high-speed video camera sensors. We started by specifying the required performance of these new sensors, for measurements
in air and water flows. These criteria founded on the most recent developments in PIV algorithms and incorporate results from
a large questionnaire survey of users of high-speed video cameras in Japan. The results suggest that the followings are required:
(1) frame rate of 1,000,000 fps, (2) pixel count of 1,000,000 pixels, (3) frame storage capacity of 100–200 frames for tracing
a single event and 10,000 frames for turbulent measurements, (4) gray levels of 4–8 bits for PTV; 12 bits for observation.
Finally, we reviewed the state of the art of high-speed video-image sensors. Currently the standard parallel-readout sensors
can operate at 1 Kfps with a pixel count of approximately 1 Kpixels. The In-situ Storage Image Sensor (ISIS) developed by
the authors has recently achieved frame rates of 1 Mfps. 相似文献
103.
104.
R Ehrhardt 《The Journal of the Operational Research Society》1997,48(10):1013-1021
We consider a firm that manages its internal manufacturing operations according to a just-in-time (JIT) system but maintains an inventory of finished goods as a buffer against random demands from external customers. We formulate a model in which finished goods are replenished by a small fixed quantity each time period. In the interest of schedule stability, the size of the replenishment quantity must remain fixed for a predetermined interval of time periods. We analyse the single-interval problem in depth, showing how to compute a cost-minimising value of the replenishment quantity for a given interval length, and characterising the optimal cost, inventory levels and service as functions of the interval length and initial inventory. The model displays significant cost and service penalties for schedule stability. A dynamic version of the problem is also formulated, and shown to be convex in nature with relatively easily computed optima. 相似文献
105.
本文以fp 同伦方法为工具,借助于一些适当的变换,研究有序的(B)空间中的集值映象方程的多正解问题;在文中的有关工作中,还使用了集值映象的拟导数的某些性质. 相似文献
106.
Christian Prins 《The Journal of the Operational Research Society》1994,45(6):611-623
Satellite communications, like batches of work in a job shop, need to be scheduled in order to use their resources as efficiently as possible. The most common satellite communications system in use today is known as Time Division Multiple Access (TDMA), in which data from earth stations is buffered before being transmitted to the appropriate receiver on a satellite. Cycles of transmission are fixed for all stations. Since the same satellite will be used for routeing data in several different ways, a schedule must be devised to use the receivers, repeaters and transmitters on board to minimize the time needed for completion of a batch of work. This paper is a survey of current scheduling algorithms used for optimizing satellite communications resources. Apart from telecommunications, the methods presented here could be applied to more general scheduling problems with renewable resources but without precedence constraints. 相似文献
107.
108.
109.
In theory, both polarity and steric hindrance are basic factors which affect molecular interactions. To investigate the optical properties and steric structures of chiral compounds having different chiral moieties which affect the wavelength of light reflection in liquid crystal (LC) cells, a series of novel chiral compounds and azobenzene derivatives were synthesized. The liquid crystalline phases of the compounds were identified using small angle X-ray diffraction, differential scanning calorimetry and polarizing optical microscopy. Cholesteric LC cells with various synthesized chiral dopants which selectively reflect visible light were first prepared, the photochemical switching behaviour of colours was then investigated, with special reference to the change in transmittance in cholesteric LC cells containing an azobenzene derivative as a photoisomerizable guest molecule. Reversible isomerization of azobenzene molecules occurred in the cholesteric systems, resulting in a depression of TChI and a shift of the selectively reflected wavelength. We discuss the photochemically driven change in the helical pitch of the cholesteric LCs with respect to structural effects involving the chiral moieties. Molecular interactions caused by the added dopants, reliability and stability of the photoisomerization, and UV irradiation effects on the cholesteric LC cells were also investigated. A real image was recorded through a mask on a cholesteric LC cell fabricated in this investigation. 相似文献
110.
Vasily L. Morgunov 《Pramana》2007,69(6):1097-1100
A new calorimeter energy calibration method was developed for the proposed ILC detectors. The method uses the center-of-mass
energy of the accelerator as the reference. It has been shown that using the energy conservation law it is possible to make
ECAL and HCAL cross calibration to reach a good energy resolution for the simple calorimeter energy sum.
相似文献