全文获取类型
收费全文 | 3086篇 |
免费 | 399篇 |
国内免费 | 220篇 |
专业分类
化学 | 2098篇 |
晶体学 | 43篇 |
力学 | 109篇 |
综合类 | 8篇 |
数学 | 418篇 |
物理学 | 1029篇 |
出版年
2024年 | 6篇 |
2023年 | 40篇 |
2022年 | 69篇 |
2021年 | 92篇 |
2020年 | 111篇 |
2019年 | 103篇 |
2018年 | 92篇 |
2017年 | 84篇 |
2016年 | 128篇 |
2015年 | 160篇 |
2014年 | 145篇 |
2013年 | 260篇 |
2012年 | 273篇 |
2011年 | 277篇 |
2010年 | 166篇 |
2009年 | 152篇 |
2008年 | 200篇 |
2007年 | 192篇 |
2006年 | 141篇 |
2005年 | 142篇 |
2004年 | 97篇 |
2003年 | 114篇 |
2002年 | 76篇 |
2001年 | 76篇 |
2000年 | 58篇 |
1999年 | 49篇 |
1998年 | 46篇 |
1997年 | 36篇 |
1996年 | 46篇 |
1995年 | 30篇 |
1994年 | 36篇 |
1993年 | 36篇 |
1992年 | 24篇 |
1991年 | 24篇 |
1990年 | 10篇 |
1989年 | 27篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 20篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1940年 | 1篇 |
1938年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有3705条查询结果,搜索用时 15 毫秒
971.
972.
In this Letter, different kinds of solutions including breather-type soliton and two-soliton solutions, are obtained for the modified Korteweg-de Vries (M-KdV) equation by using bilinear form, the extended homoclinic test approach and dependent variable transformations. Moreover,we point out that the author did not obtain so-called periodic two-soliton solutions in W. Long (in press) [1]. 相似文献
973.
Marco A. Fontelos Ana I. Muñoz Emanuele Schiavi 《Nonlinear Analysis: Real World Applications》2010,11(4):2350-2365
In this paper we address one of the problems that has attracted much interest in the glaciological scientific community which is the grounding line dynamics. The grounding line is the line where transition between ice attached to the solid ground and ice floating over the sea takes place. We analyze a mathematical model describing the ice flow near the grounding line where the ice is considered a non-Newtonian fluid. This generalizes the results obtained in [M.A. Fontelos, A.I. Muñoz, A free boundary problem in glaciology: The motion of grounding lines, Interfaces Free Bound. (9) (2007) 67–93] for the Newtonian case and allows us to consider a more realistic rheological model. We prove the existence and uniqueness (in a class to be defined) of weak solutions with moving grounding lines and zero contact angle and also determine the shape and asymptotic properties of the free boundary. Finally some finite element numerical simulations will illustrate the local and global behavior of the problem solutions. 相似文献
974.
The loop space associated to a Riemannian manifold admits a quasisymplectic structure (that is, a closed 2-form which is non-degenerate
up to a finite-dimensional kernel). We show how to construct a compatible almost-complex structure. Finally conditions to
have contact structures on loop spaces are studied. 相似文献
975.
西部地区高技术产业自主创新能力组合评价研究 总被引:3,自引:0,他引:3
为了提高综合评价的全面性、科学性和合理性,分别运用模糊综合评价法和灰色关联投影法对西部7省(区)1市高技术产业自主创新能力进行评价,在此基础上,利用模糊Borda法对两种单一方法的评价结果进行组合,得出组合评价结果.与单一方法相比,组合评价结果具有较高的可信度,可作为全面提升西部地区高技术产业自主创新能力的决策依据. 相似文献
976.
Global asymptotic stability of a generalized SIRS epidemic model with transfer from infectious to susceptible 下载免费PDF全文
In this paper, we propose a generalized SIRS epidemic model with varying total population size caused by the death rate due to the disease and transfer from infectious to susceptible, where the incidence rate employed includs a wide range of monotonic and concave incidence rates. Applying the geometric approach developed by Smith, Li and Muldowey, we prove that the endemic equilibrium is globally asymptotically stable provided that the rate of loss of immuity $\delta$ is in a critical interval $[\eta,\bar\delta)$ when the basic reproduction number $R_0$ is greater than unity. 相似文献
977.
M. I. Cervera C. Medina T. Portolés E. Pitarch J. Beltrán E. Serrahima L. Pineda G. Muñoz F. Centrich F. Hernández 《Analytical and bioanalytical chemistry》2010,397(7):2873-2891
A multi-residue method has been developed and validated for the simultaneous quantification and confirmation of around 130
multiclass pesticides in orange, nectarine and spinach samples by GC-MS/MS with a triple quadrupole analyzer. Compounds have
been selected from different chemical families including insecticides, herbicides, fungicides and acaricides. Three isotopically
labeled standards have been used as surrogates in order to improve accurate quantitation. Samples were extracted by using
accelerated solvent extraction (ASE) with ethyl acetate. In the case of spinach, an additional clean-up step by gel permeation
chromatography was applied. Determination was performed by GC-MS/MS in electron ionization mode acquiring two MS/MS transitions
for each analyte. The intensity ratio between quantitation transition (Q) and identification transition (q) was used as confirmatory parameter (Q/q ratio). Accuracy and precision were evaluated by means of recovery experiments in orange, nectarine, and spinach samples
spiked at two concentration levels (0.01 and 0.05 mg/kg). Recoveries were, in most cases, between 70% and 120% and RSD were
below 20%. The limits of quantification objective for which the method was satisfactorily validated in the three samples matrices
were for most pesticides 0.01 mg/kg. Matrix effects over the GC-MS/MS determination were tested by comparison of reference
standards in pure solvent with matrix-matched standards of each matrix. Data obtained showed enhancement of signal for the
majority of analytes in the three matrices investigated. Consequently, in order to reduce the systematic error due to this
effect, quantification was performed using matrix-matched standard calibration curves. The matrix effect study was extended
to other food matrices such as raisin, paprika, cabbage, pear, rice, legume, and gherkin, showing in all cases a similar signal
enhancement effect. 相似文献
978.
Zhou J Wu J Liu X Qu F Xiao M Zhang Y Charles L Zhang CC Peng L 《Organic & biomolecular chemistry》2006,4(3):581-585
Tri(ethylene glycol) derived, low molecular-weight dendrons with various amine end groups were synthesized and characterized for their properties of binding and self-assembling with RNA using the Candida ribozyme as a model RNA molecule. These dendritic compounds form stable complexes and well-defined nanoscale particles with RNA molecules via electrostatic interactions and self-assembly process, while leaving the other terminal of the tri(ethylene glycol) chain accessible for targeting. This suggests that dendrimers of this type hold great promise for specific RNA targeting and RNA delivery. 相似文献
979.
Muñoz A Alonso JA Martínez-Lope MJ Falcón H García-Hernández M Morán E 《Dalton transactions (Cambridge, England : 2003)》2006,(41):4936-4943
We describe the preparation of SeMO(3) (M = Ni, Mn) under high pressure conditions (3.5 GPa), starting from reactive H(2)SeO(3) and MO mixtures, contained in sealed gold capsules under the reaction conditions 850 degrees C for 1 h. The polycrystalline samples have been studied by neutron powder diffraction (NPD) data and magnetization measurements. SeMO(3) (M = Ni, Mn) are orthorhombically distorted perovskites (space group Pnma). Below T(N) approximately 104 K (M = Ni) and T(N) approximately 53.5 K (M = Mn) these oxides experience an antiferromagnetic ordering, as demonstrated by susceptibility and NPD measurements. The magnetic reflections observed in the neutron patterns can be indexed with a propagation vector k = 0. Both compounds present the same magnetic structure, which is given by the basis vector (0, 0, A(z)). It can be described as antiferromagnetic (010) layers of magnetic moments lying along the c direction, which are antiferromagnetically coupled along the b direction. For the Ni(2+) ions, the ordered magnetic moment at T = 2.3 K is 2.11(3) micro(B), whereas for Mn(2+) at T = 2.6 K, |m| = 4.64(2) micro(B), consistent with the electronic configurations te (Ni(2+)) and te (Mn(2+)). 相似文献
980.