全文获取类型
收费全文 | 10234篇 |
免费 | 509篇 |
国内免费 | 210篇 |
专业分类
化学 | 6492篇 |
晶体学 | 94篇 |
力学 | 472篇 |
综合类 | 25篇 |
数学 | 1543篇 |
物理学 | 2327篇 |
出版年
2023年 | 91篇 |
2022年 | 206篇 |
2021年 | 239篇 |
2020年 | 263篇 |
2019年 | 253篇 |
2018年 | 220篇 |
2017年 | 186篇 |
2016年 | 322篇 |
2015年 | 321篇 |
2014年 | 378篇 |
2013年 | 654篇 |
2012年 | 709篇 |
2011年 | 767篇 |
2010年 | 483篇 |
2009年 | 422篇 |
2008年 | 563篇 |
2007年 | 500篇 |
2006年 | 483篇 |
2005年 | 413篇 |
2004年 | 350篇 |
2003年 | 343篇 |
2002年 | 322篇 |
2001年 | 201篇 |
2000年 | 181篇 |
1999年 | 145篇 |
1998年 | 84篇 |
1997年 | 94篇 |
1996年 | 103篇 |
1995年 | 73篇 |
1994年 | 110篇 |
1993年 | 81篇 |
1992年 | 92篇 |
1991年 | 69篇 |
1990年 | 62篇 |
1989年 | 54篇 |
1988年 | 49篇 |
1987年 | 46篇 |
1986年 | 50篇 |
1985年 | 74篇 |
1984年 | 68篇 |
1983年 | 46篇 |
1982年 | 71篇 |
1981年 | 62篇 |
1980年 | 63篇 |
1979年 | 58篇 |
1978年 | 62篇 |
1977年 | 57篇 |
1976年 | 53篇 |
1975年 | 40篇 |
1973年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Flowing and static gas-phase samples of HNO3 in O2 and N2 were analyzed by long-path ultraviolet/visible (UV/VIS) spectroscopy to reveal the presence of both NO2 and NO3, the concentrations of which were calculated using differential absorption cross sections. NO2 is produced predominantly by the heterogeneous decomposition of HNO3, whereas NO3 is generated in the gas phase by the thermal decomposition of N2O5, a product of the self-disproportionation of liquid HNO3. © 1993 John Wiley & Sons, Inc. 相似文献
2.
We investigate the dependence of the relaxation time of the current flowing in a nematic cell submitted to an external dc voltage on the physical properties of the substrate. We show that previously presented analyses of the same problem are not very useful for practical applications. We compare our theoretical predictions with experimental data, and show that the agreement is rather good. The influence of the adsorption-desorption phenomenon on the relaxation time is also discussed. 相似文献
3.
Philippe Quevauviller Rob Ritsema Roberto Morabito Wilfried M. R. Dirkx Salvatore Chiavarini Jos M. Bayona Olivier F. X. Donard 《应用有机金属化学》1994,8(6):541-549
Biogeochemical pathways of tin species in the environment are still controversial, e.g. with regard to methylation and transmethylation phenomena, owing to the fact that the identification of methylated tin-compounds is often difficult. The previous tentative identification of a mixed methylbutyltin compound in sediment and biological samples by GC/AAS after hydride generation gave an illustration of this problem. This compound was previously identified in sediments by other authors and also suspected to occur in a contaminated sediment sample from the Boyardville Marina, France. The retention time obtained by GC/AAS corresponded to the actual retention time of a mixed methylbutyltin calibrant. However, additional checks demonstrated that the compound detected was actually monophenyltin. This evidence was produced by a thorough analysis of a selected sediment sample by alternative techniques such as GC/AAS and GC/AES after pentylation, GC/FPD and GC/MS. The results presented highlight the need for a full identification of compounds to avoid mis-interpretation. 相似文献
4.
A time‐marching formulation is derived from the space–time integrated least squares (STILS) method for solving a pure hyperbolic convection equation and is numerically compared to various known methods. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
5.
本文运用信息保存法对低速二维的流动现象进行模拟,考察了低速条件下的有限平板绕流以及微槽道气体流动问题。研究表明:在对低速流动的模拟过程中,运用IP法在能够获得较好的结果的同时,具有比DSMC方法更高的计算效率。 相似文献
6.
The frequency or dispersion relation for the least‐squares mixed formulation of the shallow‐water equations is analysed. We consider the use of different approximation spaces corresponding to co‐located and staggered meshes, respectively. The study includes the effect of Coriolis, and the dispersion properties are compared analytically and graphically with those of the mixed Galerkin formulation. Numerical solutions of a test problem to simulate slow Rossby modes illustrate the theoretical results. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
The reactions of IO radicals with CH3SCH3, CH3SH, C2H4, and C3H6 have been studied using the discharge flow method with direct detection of IO radicals by mass spectrometry. The absolute rate constants obtained at 298 K are the following: IO + CH3SCH3 → products (1): k1 = (1.5 ± 0.2) × 10?14; IO + CH3SH → products (2): k2 = (6.6 ± 1.3) × 10?16; IO + C2H4 →products (3): k3 < 2 × 10?16; IO + C3H6 → products (4): k4 < 2 × 10?16 (units are cm3 molecule?1 s?1). CH3S(O)CH3 and HOI were found as products of reactions (1) and (2), respectively. The present lower value of k1 compared to our previous determination is discussed. 相似文献
8.
9.
The thiochlorides Mo6Cl10Y (Y = S, Se, Te) have been prepared; they are isostructural with Nb6I11, space group Pccn, and have four formula units per unit cell. The X-ray structure of Mo6Cl10Se has been determined from three-dimensional single-crystal counter data and refined to a final R value of 0.053 for 3350 independent reflections. The most important result concerning this structure is a statistical distribution of the Se atom on the unit (Mo6X′8) with : so the compound Mo6Cl10Se must be formulated . The diamagnetic and dielectric behavior of these new thiochlorides is discussed. 相似文献
10.