全文获取类型
收费全文 | 37101篇 |
免费 | 1472篇 |
国内免费 | 1008篇 |
专业分类
化学 | 16110篇 |
晶体学 | 346篇 |
力学 | 1935篇 |
综合类 | 56篇 |
数学 | 9989篇 |
物理学 | 11145篇 |
出版年
2023年 | 175篇 |
2022年 | 277篇 |
2021年 | 299篇 |
2020年 | 406篇 |
2019年 | 339篇 |
2018年 | 1466篇 |
2017年 | 1706篇 |
2016年 | 1122篇 |
2015年 | 970篇 |
2014年 | 936篇 |
2013年 | 1232篇 |
2012年 | 3894篇 |
2011年 | 3052篇 |
2010年 | 2321篇 |
2009年 | 2031篇 |
2008年 | 1088篇 |
2007年 | 1019篇 |
2006年 | 1057篇 |
2005年 | 4742篇 |
2004年 | 4167篇 |
2003年 | 2503篇 |
2002年 | 644篇 |
2001年 | 420篇 |
2000年 | 243篇 |
1999年 | 351篇 |
1998年 | 270篇 |
1997年 | 197篇 |
1996年 | 177篇 |
1995年 | 153篇 |
1994年 | 137篇 |
1993年 | 102篇 |
1992年 | 248篇 |
1991年 | 233篇 |
1990年 | 180篇 |
1989年 | 146篇 |
1988年 | 139篇 |
1987年 | 92篇 |
1986年 | 69篇 |
1985年 | 56篇 |
1984年 | 48篇 |
1983年 | 47篇 |
1976年 | 89篇 |
1975年 | 46篇 |
1974年 | 45篇 |
1973年 | 56篇 |
1972年 | 45篇 |
1970年 | 39篇 |
1969年 | 41篇 |
1968年 | 39篇 |
1966年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
991.
992.
CP violation in partial-decay-rate asymmetries are examined for some two-body baryonic decays of \(B_d^0 - \bar B_d^0 \) system. We discuss two feasible experimental circumstances: the symmetrice + e ? collisions (i) on theZ 0 resonance to produce incoherent \(B_d^0 \bar B_d^0 \) states, and (ii) just above the ?(4S) resonance to produceC=even \(B_d^0 \bar B_d^0 \) states. Using the quark-diagram scheme, we estimate the branching ratios of those decays, and the numbers ofb \(\bar b\) pairs needed for testing theCP-violating effects for 3σ signature. We find that the promising channels may beB d 0 , \(\bar B_d^0 \to p\bar p\) , \(\Delta ^ + \bar \Delta ^ - \) , \(p\bar \Delta ^ - \) , \(\Delta ^ + \bar p\) , \(n\bar n\) , \(\Delta ^0 \bar \Delta ^0 \) , \(n\bar \Delta ^0 \) , \(\Delta ^0 \bar n\) , \(\Sigma _c^ + \bar \Sigma _c^ - \) , \(\Lambda _c^ + \bar \Lambda _c^ - \) , \(\Sigma _c^ + \bar \Lambda _c^ - \) , \(\Lambda _c^ + \bar \Sigma _c^ - \) , \(\Sigma _c^0 \bar \Sigma _c^0 \) , \(\Xi _c^0 \bar \Xi _c^0 \) , which should be interesting for experimental observation. 相似文献
993.
994.
T. ?kesson S. Almehed A. L. S. Angelis H. Atherton P. Aubry H. W. Bartels G. Beaudoin J. M. Beaulieu H. Beker O. Benary et al. 《Zeitschrift fur Physik C Particles and Fields》1991,49(3):355-366
Diffractive dissociation of nuclei (Be, Al, W) in collisions with 450 GeV/c protons,pApX, has been measured with the HELIOS spectrometer at the CERN Super Proton synchrotron. The dependence of the single-diffraction cross-section on the nuclear massA can be parametrized as SD mb×A
0.35±0.02, showing the peripheral nature of the process. The differential cross-section dSD=(3.8±0.3)mb ×A
0.35±0.02, is exponential with the slope parameter, increasing from 6.2±0.4 (GeV/c)–2 for beryllium to 7.9±0.5 (GeV/c)–2 for tungsten. The slope parameter also increases with increasing massM
X
of the diffractively produced state. The rapidity, multiplicity, and transverse-momentum distributions of the particles of the diffractively produced stateX show a longitudinal phase-space population and are remarkably insensitive to the nuclear mass. This, together with theA
1/3 dependence of SD, suggests that the dominant process of nuclear diffractive excitation is the dissociation of single nucleons.Deceased 相似文献
995.
自由电子激光光导的数值模拟与分析 总被引:1,自引:0,他引:1
从一维自由电子激光理论出发,唯象地考虑衍射效应,计算和分析了光导效应的特点和规律;针对曙光一号装置的自由电子激光参数,利用二维理论对光场剖面、填充因子、光场半径等进行了数值模拟;根据计算结果分析和讨论了影响光导的因素和实验条件。 相似文献
996.
R. ?obiński J. A. C. Broekaert P. Tsch?pel G. T?lg 《Fresenius' Journal of Analytical Chemistry》1992,342(7):569-580
Four independent procedures including one using slurry nebulization ICP-AES were developed for the trace analysis of ZrO2 powders. They were evaluated with respect to detection limits, blank values, interferences, accuracy and precision. For the procedures I–III ZrO2 powder was decomposed by fusion with a 10-fold excess of NH4HSO4 and subsequent dissolution of the melt in either water or, after evaporation of NH4HSO4, in diluted HNO3. In procedure I the solution was directly analyzed by ICP-AES, which was optimized with the aid of a simplex algorithm. In procedure II Zr was separated by extraction from 6 mol/l HNO3 with a 0.5 mol/l solution of 2-thenoyltrifluoroacetone (TTA) in xylene. More than 99.5% of the Zr was removed and more than 95% of the trace elements retained. In procedure III the matrix was separated by its precipitation as ZrOCl2·8 H2O from a (1:4) HCl-acetone medium. More than 98% of Zr were removed and more than 90% of the trace elements were retained. In procedure IV the ZrO2 powder was dispersed by ultrasonic treatment in water acidified with HCl (pH 2) and the slurry was directly analyzed by ICP-AES using a Babington nebulizer. The optimization and the analytical features of this procedure will be described in a subsequent paper. In all procedures the calibration was performed by standard addition and matrix matching was not necessary. The detection limits varied from 0.3 g/g (Ca) to 10 g/g (Al). The standard deviations obtained were 1–10% depending on the element and its concentration in the sample. The results of the procedures for 6 commercially available fine ZrO2 powders were found to agree for Al, Ca, Fe, Mg, Na, Ti and Y. A good agreement between the results of the procedures using matrix separation was also observed for Cu, Mn, V, but the concentrations of these elements found by methods without matrix separation were considerably higher. Except for Ca and Mg the blank values encountered were below the detection limits.On leave from Department of Analytical Chemistry, Technical University, PL-00-664 Warsaw, Poland 相似文献
997.
998.
The electrochemical reduction of fenofibrate at a hanging mercury drop electrode (HMDE) was investigated by cyclic voltammetry, square-wave voltammetry, and chronoamperometry. Different buffer solutions were used over a wide pH range (3.0–10.0). The best definition of the analytical signals was found in borate buffer (pH 9.0)–tetrabutylammonium iodide mixture containing 12.5% (v/v) methanol at –1.2 V (versus Ag/AgCl). According to cyclic voltammetric studies, the reduction was irreversible and diffusion controlled. The diffusion coefficient was 2.38×10–6 cm2 s–1 as determined by chronoamperometry. Under optimized conditions of square-wave voltammetry, a linear relationship was obtained between 0.146–4.96 g mL–1 of fenofibrate with a limit of detection of 0.025 g mL–1. Validation parameters such as sensitivity, accuracy, precision, and recovery were evaluated. The proposed method was applied to the determination of fenofibrate in pharmaceutical formulations. The results were compared with those obtained by a published high-performance liquid chromatography method. No difference was found statistically. 相似文献
999.
稀土离子(Ⅲ)与牛血清白蛋白作用的紫外光谱 总被引:18,自引:1,他引:18
用紫外光谱研究了稀土离子(Ⅲ)与牛血清白蛋白(BSA)的作用.14种稀土离子均使BSA~280um特征吸收峰强增加,诱导BSA构象发生改变.紫外差谱结果表明,只有氧原子参加与稀土配位.BSA与稀土配位基团为亲水外壳的氨基酸波基和肽键上的C=O基团. 相似文献
1000.
J. Dušek 《Czechoslovak Journal of Physics》1982,32(11):1195-1220
The operatorsT
C,l
E+i0)[–G
0(E+i0)]1–i
andT
C,l(E+i)G
0[–iG
0(E+i)]i acting on spaces of Hölder continuous, differentiable and analytic functions are investigated. The results of their action are expressed in terms of explicit singular factors and terms and Hölder (differentiable, analytic) functions. The most singular part of these operators is shown to be determined by a simple functional. 相似文献