全文获取类型
收费全文 | 103284篇 |
免费 | 17174篇 |
国内免费 | 11825篇 |
专业分类
化学 | 72428篇 |
晶体学 | 1135篇 |
力学 | 5876篇 |
综合类 | 669篇 |
数学 | 12617篇 |
物理学 | 39558篇 |
出版年
2024年 | 351篇 |
2023年 | 2067篇 |
2022年 | 3667篇 |
2021年 | 3768篇 |
2020年 | 4175篇 |
2019年 | 3957篇 |
2018年 | 3713篇 |
2017年 | 3333篇 |
2016年 | 5013篇 |
2015年 | 4923篇 |
2014年 | 6049篇 |
2013年 | 7775篇 |
2012年 | 9276篇 |
2011年 | 9473篇 |
2010年 | 6621篇 |
2009年 | 6353篇 |
2008年 | 6676篇 |
2007年 | 5965篇 |
2006年 | 5578篇 |
2005年 | 4661篇 |
2004年 | 3647篇 |
2003年 | 2929篇 |
2002年 | 2661篇 |
2001年 | 2229篇 |
2000年 | 1945篇 |
1999年 | 2051篇 |
1998年 | 1735篇 |
1997年 | 1559篇 |
1996年 | 1555篇 |
1995年 | 1366篇 |
1994年 | 1239篇 |
1993年 | 1003篇 |
1992年 | 901篇 |
1991年 | 776篇 |
1990年 | 652篇 |
1989年 | 503篇 |
1988年 | 378篇 |
1987年 | 338篇 |
1986年 | 335篇 |
1985年 | 262篇 |
1984年 | 188篇 |
1983年 | 153篇 |
1982年 | 125篇 |
1981年 | 78篇 |
1980年 | 59篇 |
1979年 | 26篇 |
1978年 | 22篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1957年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Based on the complexation between proteins and Cu(II) coupled with the time-resolved chemiluminescence (CL) technique, a highly sensitive and quantitative assay for measuring proteins in solution is described. The complexes of proteins with Cu(II) have a strongly catalytic effect on the luminol-H2O2 CL reaction. Because the CL emission produced by the complexes is much more long-lived than that by Cu(II), the CL signals originating from proteins can be easily identified and measured with a time-resolved technique. On this basis, bovine albumin fraction V (BAF V) can be quantitatively determined in the range of 0.01 - 5.0 microg/ml with a detection limit of 5.8 ng/ml. The results show that the proposed assay exhibits a small variation in the response values for the same amount of different proteins, as compared to the Lowry as well as Bradford assays. The CL assay has also been studied for the detection of immobilized proteins. 相似文献
172.
A Nafion-modified glassy carbon electrode incorporated with tobramycin for the voltammetric stripping determination of Cu2+ has been explored. The electrode was fabricated by tobramycin containing Nafion on the glassy carbon electrode surface. The modified electrode exhibited a significantly increased sensitivity and selectivity for Cu2+ compared with a bare glassy carbon electrode and the Nafion modified electrode. Cu2+ was accumulated in HAc-NaAc buffer (pH 4.6) at a potential of -0.6 V (vs. SCE) for 300 s and then determined by differential pulse anodic stripping voltammetry. The effects of various parameters, such as the mass of Nafion, the concentration of tobramycin, the pH of the medium, the accumulation potential, the accumulation time and the scan rate, were investigated. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 1.0 x 10(-9) to 5.0 x 10(-7) mol l(-1) with a correlation coefficient of 0.9971. The relative standard deviations for eight successive determinations were 4.3 and 2.9% for 1.0 x 10(-8) and 2.0 x 10(-7) mol l(-1) Cu2+, respectively. The detection limit (three times signal to noise) was 5.0 x 10(-10) mol l(-1). A study of interfering substances was also performed, and the method was applied to the direct determination of copper in water samples, and also in analytical reagent-grade salts with satisfactory results. 相似文献
173.
Taek‐Joong Kim Baoan Li May‐Britt Hgg 《Journal of Polymer Science.Polymer Physics》2004,42(23):4326-4336
Fixed‐site–carrier membranes were prepared for the facilitated transport of CO2 by casting polyvinylamine (PVAm) on various supports, such as poly(ether sulfone) (PES), polyacrylonitrile (PAN), cellulose acetate (CA), and polysulfone (PSO). The cast PVAm on the support was crosslinked by various methods with glutaraldehyde, hydrochloric acid, sulfuric acid, and ammonium fluoride. Among the membranes tested, the PVAm cast on polysulfone and crosslinked by ammonium fluoride showed the highest selectivity of CO2 over CH4 (>1000). The permeance of CO2 was then measured to be 0.014 m3 (STP)/(m2 bar h) for a 20 μm thick membrane. The effect of the molecular weight of PVAm and feed pressure on the permeance was also investigated. The selectivity increased remarkably with increasing molecular weight and decreased slightly with increased pressure in the range of 1 to 4 bar. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4326–4336, 2004 相似文献
174.
According to a multiphase mixture theory, we have mathematically developed a multiphysical model with chemoelectromechanical coupling considerations, termed the multieffect‐coupling electric‐stimulus (MECe) model, to simulate the responsive behavior of electric‐sensitive hydrogels immersed in a bath solution under an externally applied electric field. For solutions of the MECe model consisting of coupled nonlinear partial differential governing equations, a meshless Hermite–Cloud method with a hierarchical iteration technique has been used for a one‐dimensional steady‐state analysis of a hydrogel strip. The computed results are compared with the experimental data, and there is very good agreement. Simulations within the domains of both hydrogels and surrounding solutions also present distributions of the ionic concentrations and electric potential as well as the hydrogel displacement. The effects of various physical parameters on the response behavior of electric‐stimulus responsive hydrogels are discussed in detail. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1514–1531, 2004 相似文献
175.
Polypropylene (PP) was modified with elastomer or CaCO3 particles of two different sizes (1 μm and 50 nm) in various volume fractions. The dispersion morphology and mechanical properties of the two systems were investigated as functions of the particle size and volume fraction of the modifier. The brittle‐to‐tough transition occurred when the matrix ligament thickness was less than the critical ligament thickness, which was about 0.1 μm for the PP used here, being independent of the type of modifier. At the same matrix ligament thickness, the improvement of the toughness was obviously higher with the elastomer rather than with CaCO3, but adding CaCO3 increased the modulus of PP. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1656–1662, 2004 相似文献
176.
A hybrid cluster complex, formed by chelating a chromogenic ligand to a [2Fe-2S] cluster, sensitively exhibited differential colorimetric responses towards Hg2+, Cd2+, Cr3+, Pb2, Sn2+, Cu2+, Zn2+, Fe3+ and Co2+ in water at physiological pH. Speciation of some of these metal elements, such as Cr(III) and Sn(IV), was also studied by UV/Vis absorption. 相似文献
177.
Raymond Mackay Jie Zhang Qi Wu Yuzhuo Li 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):343-348
The longitudinal relaxation times (T1) of water in concentrated silica and alumina slurries were measured as a function of solids content. It was shown that the results could be fit very well with a two-phase fast-exchange model between free and surface-bound water. As expected, values of T1 for bound water were in the order of 20–2000 times lower than that for free water, indicating a higher effective viscosity of the surface-bound water. The strength of the interaction depended on the particular surface, and all of the aluminas examined interacted more strongly with water than the two silicas studied, which themselves differed considerably. The chemical mechanical polishing (CMP) removal rate of tantalum by silica slurries was shown to be directly correlated with the interaction parameters, derived from the NMR relation times rather than with total surface hydroxyl group concentration. 相似文献
178.
179.
180.
Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products. 相似文献