全文获取类型
收费全文 | 19706篇 |
免费 | 2068篇 |
国内免费 | 1886篇 |
专业分类
化学 | 3749篇 |
晶体学 | 226篇 |
力学 | 2557篇 |
综合类 | 374篇 |
数学 | 13220篇 |
物理学 | 3534篇 |
出版年
2024年 | 46篇 |
2023年 | 190篇 |
2022年 | 242篇 |
2021年 | 321篇 |
2020年 | 488篇 |
2019年 | 454篇 |
2018年 | 469篇 |
2017年 | 551篇 |
2016年 | 613篇 |
2015年 | 433篇 |
2014年 | 797篇 |
2013年 | 1415篇 |
2012年 | 985篇 |
2011年 | 1167篇 |
2010年 | 1122篇 |
2009年 | 1225篇 |
2008年 | 1333篇 |
2007年 | 1394篇 |
2006年 | 1203篇 |
2005年 | 1104篇 |
2004年 | 1000篇 |
2003年 | 989篇 |
2002年 | 869篇 |
2001年 | 665篇 |
2000年 | 669篇 |
1999年 | 567篇 |
1998年 | 502篇 |
1997年 | 429篇 |
1996年 | 354篇 |
1995年 | 341篇 |
1994年 | 255篇 |
1993年 | 201篇 |
1992年 | 188篇 |
1991年 | 144篇 |
1990年 | 137篇 |
1989年 | 93篇 |
1988年 | 86篇 |
1987年 | 69篇 |
1986年 | 77篇 |
1985年 | 72篇 |
1984年 | 64篇 |
1983年 | 32篇 |
1982年 | 69篇 |
1981年 | 48篇 |
1980年 | 38篇 |
1979年 | 32篇 |
1978年 | 27篇 |
1977年 | 22篇 |
1976年 | 14篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
The interaction between poly(methymethacrylate) (PMMA) and poly(vinyl chloride) (PVC) has been studied indilute urea solutions of dimethylformamide (DMF) at 28℃ using a dilute solution viscometry method. The results show thatthe polymer mixtures are compatible in DMF solution in the absence of urea. The influence of urea addition on the degree ofcompatibility of the polymer mixtures has been studied in terms of the compatibility parameters (△b_m and △[η]_m). It wasfound that the compatibility of the polymer mixtures is decreased with increasing urea addition, passing through a minimumat 0.5 M urea. 相似文献
203.
盐类和温度对非离子型表面活性剂溶液粘度的影响 总被引:1,自引:1,他引:1
研究在各种盐类存在下,温度对非离子表面活性剂(OP类)溶液粘度的影响,发现相对粘度的对数值与1/T呈线性关系,从直线的斜率可得活化自由能ΔG′。由热力学关系式可计算粘性流体的活化焓ΔII′和活化熵ΔS′。用所得热力学函数对胶束型态的转化进行了讨论。 相似文献
204.
Brunsveld L Watzke A Durek T Alexandrov K Goody RS Waldmann H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(9):2756-2772
Prenylated proteins with non-native functionalities are generally very difficult to obtain by recombinant or enzymatic means. The semisynthesis of preparative amounts of prenylated Rab guanosine triphosphatases (GTPases) from recombinant proteins and synthetic prenylated peptides depends largely on the availability of functionalised prenylated peptides corresponding to the proteins' native structure or modifications thereof. Here, we describe and compare solution-phase and solid-phase strategies for the generation of peptides corresponding to the prenylated C terminus of Rab7 GTPase. The solid-phase with utilisation of a hydrazide linker emerges as the more favourable approach. It allows a fast and practical synthesis of pure peptides and gives a high degree of flexibility in their modification. To facilitate the analysis of semisynthetic proteins, the synthesised peptides were equipped with a fluorescent group. Using the described approach, we introduced fluorophores at several different positions of the Rab7 C terminus. The position of the incorporated fluorescent groups in the peptides did not influence the protein-ligation reaction, as the generated peptides could be ligated onto thioester-tagged Rab7. However, it was found that the positioning of the fluorescent group had an influence on the functionality of the Rab7 proteins; analysis of the interaction of the semisynthetic Rab7 proteins with REP (Rab escort protein) and GDI (guanosine diphosphate dissociation inhibitor) molecules revealed that modification of the peptide side chains or of the C-terminal isoprenoid did not significantly interfere with complex formation. However, functionalisation of the C terminus was found to have an adverse effect on complex formation and stability, possibly reflecting low structural flexibility of the Rab GDI/REP molecules in the vicinity of the lipid-binding site. 相似文献
205.
This paper mainly deals with the design and synthesis of a novel styrene-butadieneblock copolymer. When this copolymer is used in the tread portion of tyres, it can improvewet skid resistance and reduce rolling resistance without sacrificing its general physical-mechanical properties. The visco-elastic curve of tire tread using the novel copolymer asits rubber portion was showed. Reactivity ratios for two monomers in the polymerizingsystem were calculated. The diagrams of differelitial, integral and finite difference calculithroughout the whole molecular chain were presented. The influence of the micro- andmacro-structure of the copolymer chain on wet skid resistance and rolling resistance wasdiscussed 相似文献
206.
207.
208.
K. Osaki T. Inoue T. Uematsu Y. Yamashita 《Journal of Polymer Science.Polymer Physics》2002,40(10):1038-1045
Linear viscoelasticity behavior is described with the sum of two terms for polystyrene solutions in tricresyl phosphate around the coil overlapping concentration (K. Osaki, T. Inoue, & T. Uematsu, J Polym Sci Part B: Polym Phys 2001, 39, 211). One is a Rouse–Zimm (RZ) term represented by the Zimm theory with arbitrarily chosen values of the hydrodynamic interaction parameter and the longest relaxation time (τRZ). The other (the L term) consists of a relaxation mode with a single relaxation time (τL > τRZ) and a high‐frequency limiting modulus proportional to the square of the concentration. In this study, we describe the viscosity (η) and first normal stress coefficient (Ψ1) in steady shear with simple formulas. The stress due to the L term is assumed to be given by a Kaye, Bernstein, Kearsley, and Zapas (K‐BKZ) equation with the damping function h(γ) = (1 + 0.2γ2)?1/2, where γ is the magnitude of shear. Contributions to η and Ψ1 from the RZ term are derived from the RZ model, in which the relaxation time in steady flow is given by τst = τ + (τRZ ? τ)/(1 + 0.35τRZ γ˙) instead of τRZ. Here, γ˙ is the rate of shear, and τ is the τRZ value at the infinite dilution limit. η and Ψ1 at various concentrations for two polystyrene samples (with molecular weights of 2890 and 8420 kg mol?1) are well described with parameters derived from dynamic viscoelasticity. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1038–1045, 2002 相似文献
209.
The stability of hexacyanoferrate(II)-amine(methylamine, ethylenediamine, diethylenetriamine and tetraethylenepentamine) was determined potentiometrically. Species Fe(CN)6(A)H
j
(j–4)
(A=amine) are formed in all the systems investigated, with j=1...n+2 (n=number of aminogroups). Some other complexes Fe(CN)6(A)iHj (with i>1) were also found. The stability of these complexes is fairly high: the full protonated amine species, show for the reaction Fe(CN)6
4- + HnAn+ = Fe(CN)6(A)Hn
(n-4) an equilibrium constant given by logK=0.686+2.10n. Factors affecting the stability are discussed in comparison with similar systems, together with the importance of interferences. 相似文献
210.
《Electroanalysis》2004,16(8):650-655
An analytical solution is developed for heterogeneous ECE processes occurring at channel electrode surface for both laminar and turbulent flow. The solution explicitly links the behavior of ECE processes and the parameters. A simple expression of the effective number of electrons transferred, covering all the reaction rate constants and different diffusion coefficients of the reactant A and the intermediate product B, is obtained. Excellent agreement with previous numerical and analytical results is shown . Parametric studies illustrate the effects of diffusion coefficients, hydrodynamic factors and reaction rate constants on the effective number of electrons transferred and the currents. 相似文献