全文获取类型
收费全文 | 15377篇 |
免费 | 657篇 |
国内免费 | 44篇 |
专业分类
化学 | 10441篇 |
晶体学 | 246篇 |
力学 | 492篇 |
综合类 | 1篇 |
数学 | 1157篇 |
物理学 | 3741篇 |
出版年
2024年 | 66篇 |
2023年 | 174篇 |
2022年 | 455篇 |
2021年 | 446篇 |
2020年 | 484篇 |
2019年 | 542篇 |
2018年 | 506篇 |
2017年 | 496篇 |
2016年 | 702篇 |
2015年 | 493篇 |
2014年 | 795篇 |
2013年 | 1332篇 |
2012年 | 1172篇 |
2011年 | 1203篇 |
2010年 | 794篇 |
2009年 | 624篇 |
2008年 | 764篇 |
2007年 | 756篇 |
2006年 | 605篇 |
2005年 | 522篇 |
2004年 | 399篇 |
2003年 | 329篇 |
2002年 | 268篇 |
2001年 | 158篇 |
2000年 | 139篇 |
1999年 | 102篇 |
1998年 | 74篇 |
1997年 | 101篇 |
1996年 | 96篇 |
1995年 | 80篇 |
1994年 | 77篇 |
1993年 | 102篇 |
1992年 | 101篇 |
1991年 | 80篇 |
1990年 | 70篇 |
1989年 | 73篇 |
1988年 | 51篇 |
1987年 | 46篇 |
1986年 | 44篇 |
1985年 | 65篇 |
1984年 | 65篇 |
1983年 | 58篇 |
1982年 | 51篇 |
1981年 | 38篇 |
1980年 | 48篇 |
1979年 | 63篇 |
1978年 | 50篇 |
1977年 | 54篇 |
1976年 | 41篇 |
1975年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
991.
P.?Bhargava M.?Kumar H.?Kumar P.?Pandit R.?Pandey A.?K.?NathEmail author 《Pramana》2004,62(4):923-932
We have studied about the thrust imparted to targets of different materials by pulsed TEA CO2 laser and chopped CW CO2 laser in air and its dependence on different parameters such as laser intensity and pulse duration. We estimated the impulse-coupling
coefficient and compared it with the published results. The mechanism of generation of thrust by laser incident on targets
in air is, in effect, combination of those involved in laser ablation in vacuum and laser-induced air detonation. 相似文献
992.
993.
Majeti BK Singh RS Yadav SK Bathula SR Ramakrishna S Diwan PV Madhavendra SS Chaudhuri A 《Chemistry & biology》2004,11(4):427-437
Herein, we report enhanced intravenous mouse lung transfection using novel cyclic-head-group analogs of usually open-head cationic transfection lipids. Design and synthesis of the new cyclic-head lipid N,N-di-n-tetradecyl-3,4-dihydroxy-pyrrolidinium chloride (lipid 1) and its higher alkyl-chain analogs (lipids 2-4) and relative in vitro and in vivo gene transfer efficacies of cyclic-head lipids 1-4 to their corresponding open-head analogs [lipid 5, namely N,N-di-n-tetradecyl-N,N-(2-hydroxyethyl)ammonium chloride and its higher alkyl-chain analogs, lipids 6-8] have been described. In stark contrast to comparable in vitro transfection efficacies of both the cyclic- and open-head lipids, lipids 1-4 with cyclic heads were found to be significantly more efficient (by 5- to 11-fold) in transfecting mouse lung than their corresponding open-head analogs (5-8) upon intravenous administration. The cyclic-head lipid 3 with di-stearyl hydrophobic tail was found to be the most promising for future applications. 相似文献
994.
Krishnamoorthy K Gokhale RS Contractor AQ Kumar A 《Chemical communications (Cambridge, England)》2004,(7):820-821
We report on the design and development of a novel label-free DNA sensor based on conducting poly(3,4-ethylenedioxythiophene) for the direct detection and quantification of target ssDNA. 相似文献
995.
A solution phase UV-irradiation technique has been exploited to produce an AuSe nanoalloy through fusion of preformed Au (photoproduced) and Se (chemically prepared) in a micellar (TX-100) medium. 相似文献
996.
Sur UK Marken F Coles BA Compton RG Dupont J 《Chemical communications (Cambridge, England)》2004,(24):2816-2817
Self-focusing of intense microwave radiation at the tip of a 25 microm diameter platinum disk microelectrode immersed into the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM(+)PF(6)(-)) containing 1 mM ferrocene causes dramatically (two orders of magnitude) enhanced voltammetric current signals and temperatures in excess of 600 K (at the electrode surface)--extreme conditions sufficient for condensed phase pyrolysis processes to occur. 相似文献
997.
The role of charges in determining the water solubility of polyelectrolytes, a question of considerable relevance to biology, is currently unresolved. We use computer simulations to study the purely Coulombic phase separation of flexible polyelectrolytes with monovalent counterions in an athermal solvent. In agreement with recent theories we find that the critical temperature for this transition increases with chain length, but that the critical density remains unchanged. We therefore stress that the phase behavior of polyelectrolytes is qualitatively different from uncharged polymers, where the critical density decreases towards zero for long chains. 相似文献
998.
An incremental algorithm may yield an enormous computational time saving to solve a network flow problem. It updates the solution to an instance of a problem for a unit change in the input. In this paper we have proposed an efficient incremental implementation of maximum flow problem after inserting an edge in the network G. The algorithm has the time complexity of O((n)2
m), where n is the number of affected vertices and m is the number of edges in the network. We have also discussed the incremental algorithm for deletion of an edge in the network G. 相似文献
999.
Traumatic brain injury (TBI) is one of the commonest causes of morbidity and mortality in the developed countries with posttraumatic epilepsy and functional disability being its major sequelae. The purpose of this study was to test the hypothesis whether the normal appearing adjacent gray and white matter regions on T2 and T1 weighted magnetization transfer (MT) weighted images show any abnormality on quantitative imaging in patients with TBI. A total of 51 patients with TBI and 10 normal subjects were included in this study. There were significant differences in T2 and MT ratio values of T2 weighted and T1 weighted MT normal appearing gray matter regions adjacent to focal image abnormality compared to normal gray matter regions in the normal individuals as corresponding contralateral regions of the TBI patient's group (p < 0.05). However the adjoining normal appearing white matter quantitative values did not show any significant change compared to the corresponding contralateral normal white matter values. We conclude that quantitative T2 and MT ratio values provide additional abnormality in patients with TBI that is not discernable on conventional T2 weighted and T1 weighted MT imaging especially in gray matter. This additional information may be of value in overall management of these patients with TBI. 相似文献
1000.
We solve the double exchange model in the presence of arbitrary substitutional disorder by using a self-consistently generated effective Hamiltonian for the spin degrees of freedom. The magnetic properties are studied through classical Monte Carlo while the effective exchange, D(ij), is calculated by solving the disordered fermion problem, and renormalized self-consistently with increasing temperature. We present results on the conductivity, magnetoresistance, optical response, and "real space" structure of the inhomogeneous ferromagnetic state, and compare our results with charge dynamics in disordered La1-xSrxMnO3. The large sizes, O(10(3)), accessible within our method allows a complete, controlled calculation on the disordered strongly interacting problem. 相似文献