全文获取类型
收费全文 | 134511篇 |
免费 | 7604篇 |
国内免费 | 14858篇 |
专业分类
化学 | 71400篇 |
晶体学 | 1157篇 |
力学 | 2807篇 |
综合类 | 984篇 |
数学 | 13003篇 |
物理学 | 21834篇 |
综合类 | 45788篇 |
出版年
2024年 | 232篇 |
2023年 | 992篇 |
2022年 | 2439篇 |
2021年 | 2549篇 |
2020年 | 2870篇 |
2019年 | 2787篇 |
2018年 | 2503篇 |
2017年 | 3576篇 |
2016年 | 3819篇 |
2015年 | 3858篇 |
2014年 | 4998篇 |
2013年 | 8098篇 |
2012年 | 8599篇 |
2011年 | 7619篇 |
2010年 | 6184篇 |
2009年 | 7814篇 |
2008年 | 8303篇 |
2007年 | 9825篇 |
2006年 | 9093篇 |
2005年 | 7971篇 |
2004年 | 7267篇 |
2003年 | 6032篇 |
2002年 | 6786篇 |
2001年 | 4433篇 |
2000年 | 3989篇 |
1999年 | 3642篇 |
1998年 | 2951篇 |
1997年 | 2501篇 |
1996年 | 2143篇 |
1995年 | 1979篇 |
1994年 | 1790篇 |
1993年 | 1524篇 |
1992年 | 1407篇 |
1991年 | 1069篇 |
1990年 | 888篇 |
1989年 | 853篇 |
1988年 | 648篇 |
1987年 | 484篇 |
1986年 | 373篇 |
1985年 | 255篇 |
1984年 | 252篇 |
1983年 | 142篇 |
1982年 | 218篇 |
1981年 | 174篇 |
1980年 | 196篇 |
1979年 | 185篇 |
1978年 | 170篇 |
1977年 | 124篇 |
1976年 | 108篇 |
1973年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Protonation constant of an unsymmetrical Schiff base, salicylidene(N-benzoyl)glycyl hydrazone (SalBzGH), and formation constants
of its complexes have been determined potentiometrically at different temperatures in aqueous dioxane medium. Complexes of
SalBzGH with VO(IV), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) have been prepared. Elemental analyses, pH-metric,
molar conductance, magnetic susceptibility, electronic, IR, ESR, XRD (powder) and NMR studies have been carried out to study
the coordination behaviour of SalBzGH toward these metal ions. pH-metric and 1H NMR studies show the presence of two dissociable
protons in the ligand. IR and NMR spectra suggest the tridentate nature of the ligand, coordinating as a uninegative species
in the Mn(II) complex and as a dinegative species in all the other complexes. Presence of two different conformers of the
ligand at room temperature and stabilization of a single conformer upon complex formation have been established from1H NMR spectra of the metal-free ligand, Zn(II) and Hg(II) complexes recorded at 296 K. Electronic and ESR spectra indicate
highly distorted tetragonal geometry for VO(IV) and Cu(II) complexes. XRD powder patterns of the Zn(II) complexes are indexed
for an orthorhombic crystal system. 相似文献
992.
Xiu‐Li Wang Ke‐Ke Yang Yu‐Zhong Wang Zhi‐Xuan Zhou Yong‐Dong Jin 《Journal of polymer science. Part A, Polymer chemistry》2004,42(14):3417-3422
A new biodegradable starch graft copolymer, starch‐g‐poly(1,4‐dioxan‐2‐one), was synthesized through the ring‐opening graft polymerization of 1,4‐dioxan‐2‐one onto a starch backbone. The grafting reactions were conducted with various 1,4‐dioxan‐2‐one/starch feed ratios to obtain starch‐g‐poly(1,4‐dioxan‐2‐one) copolymers with various poly(1,4‐dioxan‐2‐one) graft structures. The microstructure of starch‐g‐poly(1,4‐dioxan‐2‐one) was characterized in detail with one‐ and two‐dimensional NMR spectroscopy. The effect of the feed composition on the resulting microstructure of starch‐g‐poly(1,4‐dioxan‐2‐one) was investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3417–3422, 2004 相似文献
993.
Matthew M. Malwitz Paul D. Butler Lionel Porcar Drew P. Angelette Gudrun Schmidt 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):3102-3112
The influence of shear on viscoelastic solutions of poly(ethylene oxide) (PEO) and clay [montmorillonite, i.e., Cloisite NA+ (CNA)] was investigated with rheology and small-angle neutron scattering (SANS). The steady-state viscosity and SANS were used to measure the shear-induced orientation and relaxation of the polymer and clay platelets. Anisotropic scattering patterns developed at much lower shear rates than in pure clay solutions. The scattering anisotropy saturated at low shear rates, and the CNA clay platelets aligned with the flow, with the surface normal parallel to the gradient direction. The cessation of shear led to partial and slow randomization of the CNA platelets, whereas extremely fast relaxation was observed for laponite (LRD) platelets. These PEO–CNA networklike solutions were compared with previously reported PEO–LRD networks, and the differences and similarities, with respect to the shear orientation, relaxation, and polymer–clay interactions, were examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3102–3112, 2004 相似文献
994.
XIE Fu-Ding Xiao-Shan LIU Feng 《理论物理通讯》2004,42(11)
Based on the rank analysis method, algorithmization idea, and symbolic computation, in this paper we have presented a method to construct the conservation laws for nonlinear evolution equations. The polynomial conservation laws for K (n 2, n) equations and mnK(m, n) equations are found by using of this approach and some new results have been obtained. 相似文献
995.
Yoshihide Yoshimoto 《Surface science》2004,556(1):52-62
A conception of a structure formation suitable for nano-technology is proposed, which is programmable and suitable for mass production-like lithography. This conception utilizes the controlled folding of chains like the scan-lines of television. Its possibility and property were studied theoretically using the modeled chains consist of beads. By adopting the interaction among the beads which can distinguish the kind of the partner by its polarity and is chiral to break the chiral symmetry of the folded state, the special chains which have the unique ground states could be designed. In these ground states, the chains are folded like the scan-lines of television. The thermodynamic properties of the suggested chains were studied by the Monte Carlo simulations and the suggested chains showed the phase-transition-like behavior which is distinct compared to both the random chains and the chain that has only the non-specific attraction. The size dependence and the effects of adding the non-specific attraction and modifying the border of the folded conformation were also studied. 相似文献
996.
997.
Synthesis and Structures of γ-Halopropyl-octa(silasesquioxanes) As a more rapid and versatile synthetic approach, we have studied the FeCl3-catalyzed hydrolytic polycondensation of suited trichlorosilanes in a biphasic system which yields e.g. the new octa(silasesquioxane) (BrCH2CH2CH2)8Si8O12. 相似文献
998.
众所周知,四阶以上辛群中指数型道路的Maslov指标可以取任意整数.本文给出了二阶辛群中指数型道路的分类及其Maslov指标的取值范围,指出了与高阶情形的不同之处. 相似文献
999.
Helge Glöckner 《manuscripta mathematica》1998,97(2):205-215
Let G be a p-adic Lie group. Then G is a locally compact, totally disconnected group, to which Willis [14] associates its scale function G : G→ℕ. We show that s can be computed on the Lie algebra level. The image of s consists of powers of p. If G is a linear algebraic group over ℚ
p
, s(x)=s(h) is determined by the semisimple part h of x∈G. For every finite extension K of ℚ
p
, the scale functions of G and H:=G(K) are related by s
H
∣
G
=s
G
[
K
:ℚ
p
]. More generally, we clarify the relations between the scale function of
a p-adic Lie group and the scale functions of its closed subgroups and Hausdorff quotients.
Received: 20 February 1997; Revised version: 18 May 1998 相似文献
1000.