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11.
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
12.
Dong Il Han Hoe Jin Hah Hong-Woo Park Sang Man Koo 《Journal of Sol-Gel Science and Technology》2004,32(1-3):47-51
Composite silica particles were synthesized by a two-step (acid-base) process in an aqueous solution with a mixture of organoalkoxysilane monomers. The two-step process separates the hydrolysis and condensation procedures to easily control condensation rate. In this study, the silane monomers used were phenyltrimethoxysilane (PTMS), vinyltrimethoxysilane (VTMS), methyltrimethoxysilane (MTMS), and tetraethyl-orthosilicate (TEOS). The physical properties of the resultant composite particles were investigated with the change in the molar ratio of monomers. The size of the particles increased with increasing the molar ratio of RaSi(OR)3/RbSi(OR)3 or RaSi(OR)3/TEOS (Ra: phenyl; Rb: vinyl, methyl). 相似文献
13.
Sang‐Uk Kim Choonkeun Lee Saimani Sundar Wonbong Jang Seung‐Jin Yang Haksoo Han 《Journal of Polymer Science.Polymer Physics》2004,42(23):4303-4312
A series of polyimides were synthesized from 2,2‐Bis(3,4‐dicarboxyphenyl)hexafluoropropane, 2,2‐bis(3‐amino‐4‐hydroxyphenyl)‐hexafluoropropane, and 4,4′‐oxydianiline by chemical imidization. The effects of the diamine ratios on the properties of the films were evaluated through the study of their thermal, electrical, and morphological properties. All the polymers exhibited better solubility in most of the organic solvents and hence were easily processable. Polyimides with more 2,2‐bis(3‐amino‐4‐hydroxyphenyl)‐hexafluoropropane exhibited better solubility and a low refractive index, which is highly desired for microelectronic applications. The dielectric constant and birefringence were strongly dependent on the fluorine content. With an increase in the fluorine substitution, both the dielectric constant and birefringence decreased. All the polymers exhibited high thermal stability (>400 °C). The absence of crystalline melting in differential scanning calorimetry and broad wide‐angle X‐ray diffraction patterns revealed the amorphous nature of the polymers, which was due to the presence of bulky CF3 groups and hinged ether linkages of the diamine component. The residual stress values decreased with an increase in the 4,4′‐oxydianiline content, and the results were in agreement with the dielectric constant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4303–4312, 2004 相似文献
14.
Zhong Hong YAN Chun Hao YANG Xi Han WU Yu Yuan XIEDivision of Chemistry Shanghai Second Medical University Shanghai Sate Key Laboratory of Drug Research Shanghai Institute of Materia Medica Shanghai Institutesfor Biological Sciences Shanghai 《中国化学快报》2004,(4)
The first and facile synthesis of (±)syringaresinol was described. 相似文献
15.
本文通过研究匹配问题的实例空间,匈牙利算法和解空间三者之间的关系,指出S实例空间的数目与问题复杂度之间的关系既不是充分也不是必要的,而如何对问题的解空间进行合理的分解才能是问题的关键。 相似文献
16.
时滞种群模型的正周期解对所有正解的吸引性 总被引:5,自引:0,他引:5
李永昆 《高校应用数学学报(A辑)》1997,(3)
建立了对数种群模型N′(t)=N(t){r(t)-a1(t)ln[N(t)]-a2(t)ln[N(t-τ(t))]}的周期正解的存在性,并得到了正周期解对所有正解的吸引性. 相似文献
17.
L.-Q. Han S.-Y. Zhao Y.-D. Zhou P.-L. Zhang 《Applied physics. B, Lasers and optics》1997,65(3):399-402
Received: 18 June 1996/Revised version: 3 January 1997 相似文献
18.
Benjamin S. Hsiao Rong-Ming Ho Stephen Z. D. Cheng 《Journal of Polymer Science.Polymer Physics》1995,33(17):2439-2447
Unique crystallization and melting behavior in poly(aryl ether ketone ketone) containing alternated terephthalic and isophthalic moieties were studied by time-resolved synchrotron x-ray methods. Recently, this material has been shown to exhibit three polymorphs (forms I, II, and III). In this work, we further investigated their distinctive thermal properties and found that form I is the dominating and the most thermally stable phase while form II is favored by fast nucleation conditions and is the least stable phase. On the other hand, form III represents a minor intermediate phase that usually coexists with form I and can be transferred from form II and to form I. Structural and morphological changes in form I have been followed by simultaneous wide-angle x-ray diffraction (WAXD)/small-angle x-ray scattering (SAXS) measurements during cold- or melt-crystallization and subsequent melting. In all cases, a larger dimensional change was found in the crystallographic a-axis than the b-axis during heating and cooling. This may be due to the greater lateral stress variation with respect to temperature along the a direction of the primary lamellae which is induced by either the formation of secondary lamellae or the preferential chain-folding direction in poly(aryl ether ketone ketone)s. During the phase transitions of form II ← III in the cold-crystallized specimen and form III ← I in the melt-crystallized samples, lamellar variables (long period, lamellar thickness, and invariant) obtained from SAXS remain almost constant. This indicates that the density distribution in the long spacing is independent of the melting in form II or III. For melt-crystallization, the corresponding changes in unit-cell dimensions and lamellar morphology during the annealing-induced low endotherm are most consistent with the argument that these changes are due to the melting of thin lamellar population. © 1995 John Wiley & Sons, Inc. 相似文献
19.
We established that acetylacetone and acetone photolytically sensitize norbornene to undergo an efficient radical addition
of solvent (ranging from hexane, cyclic ethers, haloalkanes, acetone, alcohols and acetonitrile) across the double bond. In
view of its synthetic applicability, sensitized photoreactions of norbornene were reviewed and their mechanisms were compared.
Photolysis of acetylacetone in the presence of norbornene in hexane induced i) acetylacetone to cycloadd to norbornene giving
the expected 1,5-diketone, and ii) sensitization by triplet excited acetylacetone to generate reactive norbornene, which underwent
dimerization as well as the addition of a solvent molecule by radical chain processes. In other solvents, the radical chain
addition of solvent dominated the photoreaction, and superseded the cycloaddition, to give excellent to good yields of adducts
to norbornene. While the excited species of acetylacetone for the sensitization was deduced to be its spectroscopic triplet
excited state, that for the cycloaddition should involve a different one which may be a twisted triplet acetylacetone; sensitization
experiments showed that the cycloaddition did not occur from the spectroscopic triplet state. Triplet excited acetone sensitized
norbornene to undergo the same solvent addition more efficiently and cleanly than acetylacetone did. In view of various conflicts
existing in the proposed energy transfer mechanism, the sensitized norbornene reactions were rationalized with electron transfer
and a cation radical chain mechanism. 相似文献
20.