全文获取类型
收费全文 | 251620篇 |
免费 | 17828篇 |
国内免费 | 9617篇 |
专业分类
化学 | 146512篇 |
晶体学 | 3056篇 |
力学 | 13056篇 |
综合类 | 522篇 |
数学 | 26483篇 |
物理学 | 89436篇 |
出版年
2023年 | 2326篇 |
2022年 | 4150篇 |
2021年 | 4617篇 |
2020年 | 5074篇 |
2019年 | 4718篇 |
2018年 | 4776篇 |
2017年 | 4392篇 |
2016年 | 7175篇 |
2015年 | 5995篇 |
2014年 | 7917篇 |
2013年 | 13447篇 |
2012年 | 13488篇 |
2011年 | 15119篇 |
2010年 | 10182篇 |
2009年 | 10005篇 |
2008年 | 11922篇 |
2007年 | 11278篇 |
2006年 | 10681篇 |
2005年 | 9205篇 |
2004年 | 7675篇 |
2003年 | 6443篇 |
2002年 | 6267篇 |
2001年 | 6657篇 |
2000年 | 5293篇 |
1999年 | 4722篇 |
1998年 | 4037篇 |
1997年 | 3981篇 |
1996年 | 3727篇 |
1995年 | 3363篇 |
1994年 | 3187篇 |
1993年 | 2828篇 |
1992年 | 2963篇 |
1991年 | 3006篇 |
1990年 | 2657篇 |
1989年 | 2507篇 |
1988年 | 2290篇 |
1987年 | 2126篇 |
1986年 | 2070篇 |
1985年 | 2516篇 |
1984年 | 2512篇 |
1983年 | 2044篇 |
1982年 | 2195篇 |
1981年 | 2040篇 |
1979年 | 2057篇 |
1978年 | 2213篇 |
1977年 | 2083篇 |
1976年 | 2133篇 |
1975年 | 2038篇 |
1974年 | 2091篇 |
1973年 | 2072篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
141.
F. Seiffert R. Schwengner G. Winter L. Funke W. Lieberz R. Reinhardt K. P. Schmittgen D. Weil R. Wrzal K. O. Zell P. von Brentano 《Zeitschrift für Physik A Hadrons and Nuclei》1991,340(2):141-153
Excited states of73Se have been investigated up to spin, 21/2 using techniques of in-beamγ-ray spectroscopy in connection with the70Ge(α, n) reaction. Mean lifetimes of 12 levels have been determined applying Doppler-shift andγ-RF-methods. Five different bands have been identified that reflect a variety of different excitation modes. The decoupled 9/2+ band is likely to correspond to an oblate deformation while the 5/2+ band is interpreted as a strongly coupled prolate band built on the Nilsson configuration [422] 5/2+. The 3/2? band is a strongly coupled band built on the [301] 3/2} configuration.Nuclear reactions:70Ge(α,n),E=14, 16, 18, 19, 20MeV; measuredE γ,I γ,σ(E γ,θ),γγ-coin, linear polarization, DSA,γ(t).75Se deduced levels,I, π, τ, δ(E2/M1), B(σλ). Enriched targets, Ge detectors. 相似文献
142.
The determination of doxazosin by high-performance liquid chromatography with fluorescence detection is described. Propanolol was used as the internal standard. Plasma samples were treated with methanol to precipitate the proteins. Doxazosin was isolated with C18 reversed-phase extraction columns. The determination limit is 1 ng/ml of plasma, while the extraction columns can be reused frequently. The method is applied to clinical trial samples. 相似文献
143.
144.
Electron energy distribution functions (eedf) in CO2 laser discharge (He—CO2—N2—CO mixture) have been calculated by solving the Boltzmann equation in the presence of given concentrations of excited (vibrational and electronic) states. The results show a well structured eedf as a result of second kind collisions coming from metastable electronic states of N2 and He as well as a strong dependence of rate coefficients for CO2 dissociation and for the ionization of the different species. 相似文献
145.
146.
T Christensen E B Jensen F Junker H Dalb?ge F Abildgaard J J Led 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1992,46(1):97-99
Biosynthetic human growth hormone specifically 13C-labelled in the carbonyl positions of all 26 leucine residues has been obtained by recombinant DNA techniques using 13C-labelled leucine and an E. coli strain that requires leucine. It is shown that, on the whole, the labelling is specific with no significant mislabelling as would have been the case had the 13C-labelled leucine been metabolized. 相似文献
147.
Main chain liquid crystal polymers are modelled as either worms or jointed rods. In reality they are composed of mesogenic units (rods) linked by spacers with varying degrees of flexibility. We present a molecular model to describe non-homogeneous nematic polymers. The model takes account of molecular parameters, such as the lengths of the mesogenic group and the spacer units, and the interactions between them. The spacers are found to have an order differing from the mesogenic units. If the spacer is not very long and thus in effect is inflexible, one end of the spacer can retain to some extent the orientation of the other end, allowing orientational correlation between spacers mediated by the intermediate mesogenic unit. This is important in giving the chain a global rod-like behaviour as the nematic field becomes strong or the temperature low. The nematic order of the two components (mesogens and spacers), the nematic-isotropic transition as well as the latent entropy are examined. Furthermore, the anisotropic conformations of the polymers are investigated, which show either rod-like or random walk behaviour. Comparison of our results with experiment is found to be satisfactory. 相似文献
148.
Li Changjun; Li Zheng; Evans David J.; Zhang Tie 《IMA Journal of Numerical Analysis》2003,23(4):581-592
Golub et al. (2001, BIT, 41, 7185) gave a generalizedsuccessive over-relaxation method for the augmented systems.In this paper, the connection between the SOR-like method andthe preconditioned conjugate gradient (PCG) method for the augmentedsystems is investigated. It is shown that the PCG method isat least as accurate (fast) as the SOR-like method. Numericalexamples demonstrate that the PCG method is much faster thanthe SOR-like method. 相似文献
149.
Wilfried B. Kr tzig Jian-Wu Zhang 《Journal of Computational and Applied Mathematics》1994,50(1-3):361-373
A simple and accurate four-node quadrilateral finite element based on the Mindlin plate theory and Kirchhoff constraints is presented for general thin plate bending applications. The derivation of the element stiffness properties is straightforward, starting with a specified eight-node interpolation; usual discrete Kirchhoff (DK) constraints are employed to constrain out the four midside nodes of the element. The present resulting DK element passes patch tests with elements of arbitrary and even highly distorted mesh types. Numerical studies of the element convergence behaviours are undertaken for various plate bending problems so far investigated. It is indicated from comparative examples that fairly good convergence characteristics have been achieved. 相似文献
150.
Methotrexate (MTX) has been convalently attached to an IgG-type monoclonal antibody (791T/36) directed to tumour-associated antigen gp72. Conjugates were synthesized by the active ester method using MTX N-succinimidyl ester at various pH values (7.5-10.5). Following purification by gel filtration, high performance liquid chromatography was used to assess the free drug or its derivatives in samples of MTX-791T/36 conjugates previously treated (or not) with hydroxylamine. Quantitative analysis, performed on a reversed phase column (pore size 300 A) with isocratic acetonitrile-sodium acetate buffer (pH 4.8) as mobile phase, indicated no detectable amount of free methotrexate in hydroxylamine-treated conjugates even six months after their preparation. Similar observations were made with conjugates, whose synthesis were performed at pH greater than or equal to 10. In contrast, the presence of increasing amounts of drug/metabolite could be demonstrated in samples produced at lower pH values. Based on these findings, the pH-dependent kinetics of MTX release has been determined and used to design conditions under which stable MTX-791T/36 conjugates could be prepared without hydroxylamine reaction. 相似文献