全文获取类型
收费全文 | 400794篇 |
免费 | 2806篇 |
国内免费 | 815篇 |
专业分类
化学 | 192847篇 |
晶体学 | 6265篇 |
力学 | 21625篇 |
综合类 | 13篇 |
数学 | 55994篇 |
物理学 | 127671篇 |
出版年
2021年 | 2774篇 |
2020年 | 2929篇 |
2019年 | 3513篇 |
2018年 | 11687篇 |
2017年 | 12242篇 |
2016年 | 9992篇 |
2015年 | 4191篇 |
2014年 | 6257篇 |
2013年 | 13790篇 |
2012年 | 14265篇 |
2011年 | 22884篇 |
2010年 | 15431篇 |
2009年 | 15685篇 |
2008年 | 20719篇 |
2007年 | 23347篇 |
2006年 | 11266篇 |
2005年 | 15000篇 |
2004年 | 11887篇 |
2003年 | 11326篇 |
2002年 | 9624篇 |
2001年 | 10281篇 |
2000年 | 7788篇 |
1999年 | 5729篇 |
1998年 | 4520篇 |
1997年 | 4614篇 |
1996年 | 4438篇 |
1995年 | 3941篇 |
1994年 | 4028篇 |
1993年 | 3754篇 |
1992年 | 4438篇 |
1991年 | 4650篇 |
1990年 | 4387篇 |
1989年 | 4442篇 |
1988年 | 4313篇 |
1987年 | 4327篇 |
1986年 | 4044篇 |
1985年 | 5092篇 |
1984年 | 5203篇 |
1983年 | 4279篇 |
1982年 | 4241篇 |
1981年 | 4069篇 |
1980年 | 3884篇 |
1979年 | 4484篇 |
1978年 | 4558篇 |
1977年 | 4597篇 |
1976年 | 4536篇 |
1975年 | 4252篇 |
1974年 | 4202篇 |
1973年 | 4341篇 |
1972年 | 3131篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
962.
We propose a way of modifying the mathematical model of the nondestructive theoretical-experimental method of determining the residual stresses for a specific collection of technological conditions for welding two cylindrical glass shells. The method is based on the general theory of boundary-value problems for ordinary differential equations.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 33, 1991, pp. 69–73. 相似文献
963.
Jati K. Sengupta 《The Journal of the Operational Research Society》1996,47(11):1387-1397
A method is developed here for characterizing the empirical distribution of the efficient units in data envelopment analysis. Two empirical applications illustrate the various uses of the distribution approach. One involves the cost frontier which exhibits increasing returns to scale and the other involves a dynamic production frontier, where technological change causes a shift of the production frontier over time. 相似文献
964.
We propose an effective method of numerical determination of the gradient vector and the Hessian matrix of a quadratic quality
criterion in parametric optimization of continuous-discrete stochastic dynamic control systems based on the application of
adjoint equations.
Translated fromDinamicheskie Sistemy, No. 13, 1994, pp. 20–25. 相似文献
965.
G. Carelli N. Ioli A. Messina A. Moretti S. Schepis F. Strumia 《International Journal of Infrared and Millimeter Waves》1998,19(9):1191-1199
We measured the dependence of the reflectivity of InSb crystals upon temperature in the submillimeter region using monochromatic radiation from an optically pumped far infrared (FIR) laser. The measures allowed us to determine the value of the electron effective mass at low temperatures with radiations of different frequencies. Our measurements extend the results obtained recently on pure crystals with magneto-optical methods to the low temperatures region where only old measures were available. 相似文献
966.
T Akamatsu D Wang K Nakamura K Wang 《The Journal of the Acoustical Society of America》1998,104(4):2511-2516
The interclick intervals of captive dolphins are known to be longer than the two-way transit time between the dolphin and a target. In the present study, the interclick intervals of free-ranging baiji, finless porpoises, and bottlenose dolphins in the wild and in captivity were compared. The click intervals in open waters ranged up to 100-200 ms, whereas the click intervals in captivity were in the order of 4-28 ms. Echolocation of free-ranging dolphins appears to adapt to various distance in navigation or ranging, sometimes up to 140 m. Additionally, the difference of waveform characteristics of clicks between species was recognized in the frequency of maximum energy and the click duration. 相似文献
967.
DAndrea A. Tomassini N. Ferrari L. Righini M. Selci S. Bruni M. R. Simeoni G. 《Il Nuovo Cimento D》1995,17(11):1423-1427
Il Nuovo Cimento D - Normalized reflection spectra in GaInAs/GaAs quantum wells are shown for two sets of samples with different alloy concentration (x=9% and 18.5%) and well thickness ranging from... 相似文献
968.
H.-J. Sue E. I. Garcia-Meitin N. A. Orchard 《Journal of Polymer Science.Polymer Physics》1993,31(5):595-608
The fracture behavior of a core-shell rubber (CSR) modified epoxy is investigated using both fracture mechanics and microscopy tools. The CSR-modified epoxy is found to be toughened via numerous line-array cavitations of the CSR particles, followed by plastic flow of the epoxy matrix. The toughening effect via the above craze-like damage process is found to be as effective as that of the well-known widespread rubber cavitation/matrix shear yielding mechanisms. The conditions for triggering the craze-like damage appear to be both stress state and rubber concentration dependent. The type of rubber tougheners utilized also plays a critical role in triggering this rather unusual craze-like damage in epoxy systems. © 1993 John Wiley & Sons, Inc. 相似文献
969.
970.
Chemical kinetics of benzonitrile nitration with mixed acid is investigated in the temperature range 283–299 K. Pseudo-first-order rate constants are evaluated by means of rate experiments on homogeneous reacting mixtures having large stoichiometric excesses of nitric acid. The second-order kinetic constants for nitronium ion attack to the aromatic substrate are derived on the basis of the assessed nitration mechanism. An activation energy of 604 ± 37 kJ mol?1 is calculated for this reaction step. © 1993 John Wiley & Sons, Inc. 相似文献