全文获取类型
收费全文 | 4921篇 |
免费 | 140篇 |
国内免费 | 30篇 |
专业分类
化学 | 3428篇 |
晶体学 | 52篇 |
力学 | 143篇 |
数学 | 613篇 |
物理学 | 855篇 |
出版年
2022年 | 25篇 |
2021年 | 47篇 |
2020年 | 53篇 |
2019年 | 61篇 |
2018年 | 38篇 |
2017年 | 44篇 |
2016年 | 116篇 |
2015年 | 78篇 |
2014年 | 107篇 |
2013年 | 216篇 |
2012年 | 275篇 |
2011年 | 330篇 |
2010年 | 181篇 |
2009年 | 152篇 |
2008年 | 262篇 |
2007年 | 292篇 |
2006年 | 306篇 |
2005年 | 262篇 |
2004年 | 233篇 |
2003年 | 228篇 |
2002年 | 203篇 |
2001年 | 61篇 |
2000年 | 62篇 |
1999年 | 37篇 |
1998年 | 55篇 |
1997年 | 53篇 |
1996年 | 83篇 |
1995年 | 43篇 |
1994年 | 46篇 |
1993年 | 44篇 |
1992年 | 26篇 |
1991年 | 42篇 |
1990年 | 47篇 |
1989年 | 35篇 |
1988年 | 44篇 |
1987年 | 29篇 |
1986年 | 29篇 |
1985年 | 64篇 |
1984年 | 61篇 |
1983年 | 41篇 |
1982年 | 63篇 |
1981年 | 64篇 |
1980年 | 56篇 |
1979年 | 55篇 |
1978年 | 52篇 |
1977年 | 50篇 |
1976年 | 39篇 |
1975年 | 41篇 |
1974年 | 40篇 |
1973年 | 36篇 |
排序方式: 共有5091条查询结果,搜索用时 125 毫秒
21.
22.
A new flow electrical conductance instrument was constructed and tested on dilute NaCl solutions up to 458 K, and on more
concentrated solutions (maximum 0.436 mol⋅kg−1) at 373 K. The results of the new instrument agreed with those of previous authors within the estimated experimental errors.
The model of Bernard et al. (J. Phys. Chem. 96, 3833–3840 (1992), MSA) was found to represent the high-temperature results without introducing an ion-pairing equilibrium constant. The Fuoss–Hsia
conductance equation as given by Fernandez-Prini was found to represent the dilute concentrations with Λ° (NaCl) as the only adjustable parameter. It was found that Λ° (NaCl) could be expressed as a function of solvent viscosity and density by using three parameters found by regression of
literature results between 278.15 and 523 K. This equation along with the FHFP theory permits the equivalent conductivity
of dilute sodium chloride solutions to be calculated within the accuracy of the existing experimental measurements. 相似文献
23.
Ying‐Hung So Pamela Foster Jang‐Hi Im Philip Garrou Jack Hetzner Edmund Stark Kayla Baranek 《Journal of polymer science. Part A, Polymer chemistry》2006,44(5):1591-1599
Divinylsiloxane‐bisbenzocyclobutene (DVS‐bisBCB) polymer has very low dielectric constant and dissipation factor, good thermal stability, and high chemical resistance. The fracture toughness of the thermoset polymer is moderate due to its high crosslink density. A thermoplastic elastomer, polystyrene–polybutadiene–polystyrene triblock copolymer, was incorporated into the matrix to enhance its toughness. The cured thermoset matrix showed different morphology when the elastomer was added to the B‐staged prepolymer or when the elastomer was B‐staged with the DVS‐bisBCB monomer. Small and uniformly distributed elastomer domains were detected by transmission electron micrographs (TEM) in the former case, but TEM did not detect a separate domain in the latter case. A high percentage of the polystyrene–polybutadiene–polystyrene triblock copolymer could be incorporated into the DVS‐bisBCB thermoset matrix by B‐staging the triblock copolymer with the BCB monomer. The elastomer increased the fracture toughness of DVS‐bisBCB polymer as indicated by enhanced elongation at break and increased K1c values obtained by the modified edge‐lift‐off test. Elastomer modified DVS‐bisBCB maintained excellent electrical properties, high Tg and good thermal stability, but showed higher coefficient of linear thermal expansion values. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1591–1599, 2006 相似文献
24.
Philip E. Gibbs 《International Journal of Theoretical Physics》1996,35(6):1037-1062
To accommodate topology change, the symmetry of space-time must be extended from the diffeomorphism group of a manifold to the symmetric group acting on the discrete set of space-time events. This is the principle ofevent-symmetric space-time. I investigate a number of physical toy models with this symmetry to gain some insight into the likely nature of event-symmetric space-time. In the more advanced models the symmetric group is embedded into larger structures such as matrix groups which provide scope to unify space-time symmetry with the internal gauge symmetries of particle physics. I also suggest that the symmetric group of space-time could be related to the symmetric group acting to exchange identical particles, implying a unification of space-time and matter. I end with a definition of a new type of loop symmetry which is important in event-symmetric superstring theory. 相似文献
25.
26.
Summary Bhattacharya, Chernoff and Yang (1983) proposed a nonparametric estimate for the slope of a regression lineY =
o
X + V subjected to the truncationYy
0. The estimate corresponds to the zero-crossing of a random functionS
n
(). In this paper an estimate for the asymptotic variance of the estimate of the slope is proposed and the rate of convergence is given. The proofs rest heavily on the local behavior ofS
n
() in the neighborhood of the true value o. 相似文献
27.
28.
Sinclair JL 《Journal of AOAC International》2000,83(5):1108-1114
The occurrence of Cryptosporidium parvum or other pathogenic Cryptosporidium species in water must be known in order to assess risk and determine the treatment needed to reduce Cryptosporidium oocysts to acceptable levels in finished drinking water. Because Cryptosporidium oocyst occurrence may be sparse, methods must concentrate a large volume of water and correctly identify oocysts in the concentrate. The U.S. Environmental Protection Agency Information Collection Rule (ICR) protozoan method gives low and variable recoveries of Cryptosporidium oocysts, making risk assessment difficult. Therefore, a method giving better oocyst recovery and more consistent results was needed. Method 1622 was developed with existing materials and procedures, and improvements were made in filtration, cleanup, and detection. Absolute porosity filters were used, with cleanup by immunomagnetic separation and detection by direct fluorescent antibody stain with 4',6-diamidino-2-phenylindole (DAPI) staining for additional cell structures. Both the level and consistency of oocyst recovery were improved compared to recovery with the ICR method. 相似文献
29.
John A Philip D Morgan KR Devanarayanan S 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(14):2715-2723
The FT IR and FT Raman spectra of Co(en)3Al3P4O16.3H2O (compound I) and [NH4]3[Co(NH3)6]3[Al2 (PO4)4]2.2H2O (compound II) are recorded and analysed based on the vibrations of Co(en)(3)3+, Co(NH3)(6)3+, NH4, Al-O-P, PO3, PO2 and H2O. The observed splitting of bands indicate that the site symmetry and correlation field effects are appreciable in both the compounds. In compound I, the overtone of CH2 deformation Fermi resonates with its symmetric stretching vibration. The NH4 ion in compound II is not free to rotate in the crystalline lattice. Hydrogen bonding of different groups is also discussed. 相似文献