全文获取类型
收费全文 | 111849篇 |
免费 | 6117篇 |
国内免费 | 3913篇 |
专业分类
化学 | 48318篇 |
晶体学 | 1121篇 |
力学 | 8756篇 |
综合类 | 201篇 |
数学 | 35586篇 |
物理学 | 27897篇 |
出版年
2024年 | 113篇 |
2023年 | 707篇 |
2022年 | 1211篇 |
2021年 | 1336篇 |
2020年 | 1339篇 |
2019年 | 1379篇 |
2018年 | 11370篇 |
2017年 | 11087篇 |
2016年 | 7577篇 |
2015年 | 2410篇 |
2014年 | 2273篇 |
2013年 | 2828篇 |
2012年 | 6885篇 |
2011年 | 13492篇 |
2010年 | 7689篇 |
2009年 | 7893篇 |
2008年 | 8670篇 |
2007年 | 10574篇 |
2006年 | 2132篇 |
2005年 | 2821篇 |
2004年 | 2667篇 |
2003年 | 2873篇 |
2002年 | 1953篇 |
2001年 | 1020篇 |
2000年 | 896篇 |
1999年 | 889篇 |
1998年 | 742篇 |
1997年 | 696篇 |
1996年 | 766篇 |
1995年 | 587篇 |
1994年 | 483篇 |
1993年 | 460篇 |
1992年 | 360篇 |
1991年 | 393篇 |
1990年 | 303篇 |
1989年 | 274篇 |
1988年 | 224篇 |
1987年 | 198篇 |
1986年 | 202篇 |
1985年 | 159篇 |
1984年 | 152篇 |
1983年 | 109篇 |
1982年 | 105篇 |
1981年 | 92篇 |
1980年 | 101篇 |
1979年 | 73篇 |
1978年 | 71篇 |
1977年 | 55篇 |
1976年 | 55篇 |
1973年 | 66篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
1.
Gang Wang Xiulin Zhu Zhenping Cheng Jian Zhu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2912-2921
A series of (di)picolinic acids and their derivates are investigated as novel complexing tridentate or bidentate ligands in the iron‐mediated reverse atom transfer radical polymerization of methyl methacrylate in N,N‐dimethylformamide at 100 °C with 2,2′‐azobisisobutyrontrile as an initiator. The polymerization rates and polydispersity indices (1.32–1.8) of the resulting polymers are dependent on the structures of the ligands employed. Different iron complexes may be involved in iron‐mediated reverse atom transfer radical polymerization, depending on the type of acid used. 1H NMR spectroscopy has been used to study the structure of the resulting polymers. Chain‐extension reactions have been performed to further confirm the living nature of this catalytic system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2912–2921, 2006 相似文献
2.
3.
4.
5.
Christiane Albrecht 《Analytical and bioanalytical chemistry》2008,390(5):1223-1224
6.
7.
Chengzhi Qi Mingyang Wang Qihu Qian Jianjie Chen 《Moscow University Mechanics Bulletin》2008,63(5):113-121
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed. 相似文献
8.
Howard Robinson 《Acta Analytica》2005,20(3):7-10
Nicholas Nathan tries to resist the current version of the causal argument for sense-data in two ways. First he suggests that,
on what he considers to be the correct re-construction of the argument, it equivocates on the sense of proximate cause. Second
he defends a form of disjunctivism, by claiming that there might be an extra mechanism involved in producing veridical hallucination,
that is not present in perception. I argue that Nathan’s reconstruction of the argument is not the appropriate one, and that,
properly interpreted, the argument does not equivocate on proximate cause. Furthermore, I claim that his postulation of a
modified mechanism for hallucinations is implausibly ad hoc. 相似文献
9.
Zhaoqiang Lu Lin Cheng Jun Li Kai Zhang Song Yi Jingui Qin 《Journal of polymer science. Part A, Polymer chemistry》2004,42(4):925-932
The synthesis and structural characterization of a series of novel, fluorinated poly(phthalazinone ether)s containing perfluorophenylene moieties are described. The monomers, 4‐(4′‐hydroxyaryl)phthalazin‐1(2H)‐ones ( 2a – 2d ), were conveniently and efficiently synthesized from phenols and phthalic anhydride in two steps via 2‐(4′‐hydroxybenzoyl)benzoic acids, which were first obtained by the Friedel–Crafts reaction in good yields and with high stereoselectivity and were then converted into 2a – 2d by fusion with hydrazine. All the polymers were prepared by nucleophilic aromatic substitution (SNAr) polycondensation between the compounds perfluorobiphenyl and 4‐(4′‐hydroxyaryl)phthalazin‐1(2H)‐ones ( 2a ‐ 2d ). The resulting fluorinated polymers were readily soluble in common organic solvents (e.g., CHCl3, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, N‐methylpyrrolidone, etc.) at room temperature. Their weight‐average molecular weights and the polydispersities ranged from (7.96–18.25) × 103 to 1.31–2.71, respectively. Their glass‐transition temperatures varied from 213 to 263 °C. They were all stable up to 390 °C both in air and in argon. The 5% weight‐loss temperatures of these polymers in air and argon ranged from 393–487 to 437–509 °C, respectively. Wide‐angle X‐ray diffraction studies indicated they were all amorphous and could be attributed to the presence of kink nonplanar moiety, phenyl phthalazinone along the polymer backbone. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 925–932, 2004 相似文献
10.
Hongchao Li Yufeng Hu Yanguang Zhang Dongge Ma Lixiang Wang Xiabin Jing Fosong Wang 《Journal of polymer science. Part A, Polymer chemistry》2004,42(16):3947-3953
A conjugated poly(p‐CN‐phenylenevinylene) (PCNPV) containing both electron‐donating triphenylamine units and electron‐withdrawing cyano groups was prepared via Knoevenagel condensation in a good yield. Gel permeation chromatography suggested that the soluble polymer had a very high weight‐average molecular weight of 309,000. A bright and saturated red emission was observed under UV excitation in solution and film. Cyclic voltammetry showed that the polymer presented quasi‐reversible oxidation with a relatively low potential because of the triphenylamine unit. A single‐layer indium tin oxide/PCNPV/Mg–Ag device emitted a bright red light (633 nm). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3947–3953, 2004 相似文献